Title of Invention	"A PROCESS FOR PRODUCING A CARBOXYLIC ACID/DIOL MIXTURE"
Abstract	The present invention relates a process for making a hydroxyalkyl ester wherein a carboxylic acid and at least one diol starting materials are esterified in an esterification zone, wherein said process includes obtaining a carboxylic acid and diol slurry without isolation of dry carboxylic acid solid, said process comprising optional steps of mixing a crude carboxylic acid powder with water to make a solution, decolorizing said carboxylic acid solution and flashing said decolorized carboxylic acid solution to form a decolorized carboxylic acid and water solution followed by adding a heated diol to the decolorized carboxylic acid and water solution in an esterification reactor zone to vaporize a portion of the water to form said carboxylic acid and diol slurry; wherein said diol is the dominant liquid and is heated to a temperature of from 150°C to 300°C and said esterification reactor zone is at a temperature of from 240°C to 280°C and a pressure of from 40 psia to 100 psia; wherein said carboxylic acid and diol subsequently reacts in said esterification zone to form a hydroxyalkyl ester.

Title of Invention

"A PROCESS FOR PRODUCING A CARBOXYLIC ACID/DIOL MIXTURE"

Abstract

The present invention relates a process for making a hydroxyalkyl ester wherein a carboxylic acid and at least one diol starting materials are esterified in an esterification zone, wherein said process includes obtaining a carboxylic acid and diol slurry without isolation of dry carboxylic acid solid, said process comprising optional steps of mixing a crude carboxylic acid powder with water to make a solution, decolorizing said carboxylic acid solution and flashing said decolorized carboxylic acid solution to form a decolorized carboxylic acid and water solution followed by adding a heated diol to the decolorized carboxylic acid and water solution in an esterification reactor zone to vaporize a portion of the water to form said carboxylic acid and diol slurry; wherein said diol is the dominant liquid and is heated to a temperature of from 150°C to 300°C and said esterification reactor zone is at a temperature of from 240°C to 280°C and a pressure of from 40 psia to 100 psia; wherein said carboxylic acid and diol subsequently reacts in said esterification zone to form a hydroxyalkyl ester.

Full Text	The present invention relates of a process for producing a carboxylic acid/diol mixture. FIELD OF INVENTION The present invention relates to a process by which a carboxylic acid/diol mixture is obtained from a decolorized carboxylic acid solution without isolation of a substantially dry carboxylic acid solid. More specifically, the present invention relates to a process by which a terephthalic acid/ethylerie glycol mixture suitable as a starting material for polyester production is. obtained from a decolorized terephthalic acid solution without isolation of a substantially dry terephthalic acid solid. BACKGROUND OF THE INVENTION Thermoplastic polyesters are step growth polymers that are useful when made to high molecular weights. The first step in a common method of producing a polyester such as polyethylene terephthalate (PET) is an esferification or ester-exchange stage where a diacid (typically terephthalic acid) reacts with an appropriate diol (typically ethylene glycol) to give a bis(h.ydroxyalkyl)ester and some linear oligomers. Water is evolved at this stage and is usually removed by fractional distillation. Pursuant to the goal of making polyethylene terephthalate and other polyesters, a great deal of patent literature is dedicated to the describing processes for preparing terephthalic acid/ethylene glycol mixtures suitable as starting material. In general, these inventions describe specific mixing schemes with a purified terephthalic acid solid and liquid ethylene glycol as starting materials. Additionally, there is substantial body of literature devoted to producing a purified terephthalic acid in the powder form that is suitable for use in producing PET. The objective of this invention is to describe a process by which a terephthalic acid/ethylene glycol mixture suitable as starting material for polyester production is obtained from a decolorized terephthalic acid solution without isolation of a substantially dry terephthalic acid solid. A number of processes for producing the purified terephthalic acid solid have been developed and are commercially available. Usually, the purified terephthalic acid solid is produced in a multi-step process .wherein a crude terephthalic acid is produced. The crude terephthalic acid does not have sufficient quality for direct use as starting material in commercial PET. Instead, the crude terephthalic acid is usually refined to purified terephthalic acid solid. Liquid phase oxidation of p-xylene produces crude terephthalic acid. The crude terephthalic acid is dissolved in water and hydrogenated for the purpose of converting 4-carboxybenzaldehyde to p-toluic acid, which is a more water-soluble derivative, and for the purpose of converting characteristically yellow compounds to colorless derivatives. Any 4»carboxybenza!dehyde and p-toluic acid in the final purified terephthalic acid product is particularly detrimental to polymerization processes as they act as a chain terminator during the condensation reaction between terephthalic acid and ethylene glycol in the production of PET. Typical purified terephthalic acid contains on a weight basis less than 25 parts per million (ppm) 4-carboxybenzaidehyde and less than. 150 ppm p-toluic acid. The crude terephthalic acid typically contains on a weight basis from 800 to 7,000 parts per million (ppm) 4-carboxybenzaldehyde and 200 to 1,500 ppm p-toluic acid as the main impurities. The crude terephthalic acid also contains lesser amounts, 20-200 ppm range, of yellow color aromatic compounds having the structures of benzil, fluorenone, and/or anthraquinone, which are characteristically yellow compounds as impurities resulting from coupling side reactions occurring during oxidation of p-xylene. It is necessary to purify the crude terephthalic acid when using it as a starting material for producing polyester fiber, which requires a purified terephthalic acid as a starting material. Such a purification process typically comprises adding water to the crude terephthalic acid to form a crude terephthalic acid solution, which is heated to dissolve the crude terephthalic acid. The crude terephthalic acid solution is then passed to a reactor zone in which the solution is contacted with hydrogen in the presence of a heterogeneous catalyst at temperatures of 200° to 375° C. This reduction step converts .the various color bodies present in the crude terephthalic acid to colorless products. The principal impurity, 4-carbpxyber4zaldehyde, is converted to p-toluic acid. Typical crude terephthalic acid contains excessive amounts of both 4-carboxybenzaldehyde and p-toluic acid on a weight basis. Therefore, to achieve less than 25 ppmw 4-carboxybenzaldehyde and less than 150 ppmw p-toluic acid in the purified terephthalic acid requires mechanisms for purifying the crude terephthalic acid and removing the contaminants. Subsequent separation and isolation of the purified terephthalic acid can be accomplished via a wide variety of separation methods including crystallization, centrifugation, filtration, extraction and combinations thereof followed by drying. These processes are described in U.S. patents 4,500,732; 5,175,355; and 5,583,254; all of which are herein incorporated by reference. It Is necessary to perform a separation step" due the nature of the crude terephthaiic acid feedstock to the hydrogenation process. A number of processes have been developed for producing a purified terephthalic acid solid from crude terephthalic acid. In general, the common features among these processes are as follows: Step (1) is decolonization of the crude terephthalic acid usually via hydrogenation treatment in an aqueous medium; Step (2) is purification/separation of the terephthalic acid from partial oxidation products usually via fractional crystallization followed by liquor exchange with contaminant-free water; and Step (3) is production of a solid purified terephthalic acid product with consistent material handling properties usually via-crystallization of terephthalic acid followed by drying of purified terephthalic acid from water. The resultant purified terephthalic acid powder along with ethylene glycol are starting materials in the production of polyesters specifically PET. Because the difficulty in handling, mixing, and dissolving terephthalic acid solids,'the purified terephthalic acid solid is usually mixed with ethylene glycol to form a paste prior to introduction into an esterification reactor system. In the present invention, a novel process has been discovered resulting in fewer steps than the currently employed processes. The primary utility of the invention is reduction of capital and operating costs associated with the isolation of a terephthalic acid powder. In the conventional approach toward producing "terephthalic acid, the post-hydrogenated aqueous solution is passed to a series of crystallizer vessels for the purpose of purifying the terephthalic acid by crystallization and for the purpose of obtaining a uniform particle size distribution necessary for good flowability of purified terephthalic powder. Further, the p-toluic acid contaminated mother liquor from the crystallization process must be removed prior to a drying step .to isolate the purified terephthalic powder. In on embodiment of the present invention, the crude terephthalic acid solution with low concentrations of p-toluic acid and 4-. carboxybenzaldehyde is hydrogenated to form a decolorized terephthalic acid solution. Starting with crude terephthalic acid with low concentrations of the p-toluic acid and 4-carboxybenzaldehyde t eliminates the need for separation of p-toluic acid-contaminated mother liquor from the terephthalic acid. Hence, the decolorized terephthalic acid solution can be directly combined with ethylene glycol in an esterification zone to produce a terephthalic acid/ethylene glycol mixture. By bypassing conventional processes for producing a purified terephthalic acid powder, the need for the equipment necessary to purify and isolate purified terephthalic powder is eliminated. Another surprising and seemingly contradictory aspect of the invention is the benefits of addition of large amounts of water to the esterification reaction starting materials. This is directly contrary to accepted esterification procedures. The esterification reaction: RCOOH + R'OH •» RCOOR1 + H20 is generally not complete". The water formed in the course of the reaction tends to react with the ester to hydrolyze it, i.e. to regenerate the original alcohol and acid. In order to drive the reaction toward the ester, the prior art teaches removal of water from the system by a variety of methods such as distillation or dehydration with a hydrophilic compound. According to .conventional esterification procedures, it is non-intuitive to add large amount of the water to the acid/alcohol starting material. SUMMARY OF THE INVENTION The present Invention relates to a process by which a carboxylic acid/diol mixture is obtained from a decolorized carboxylic acid solution without isolation of a substantially dry carboxylic acid solid. More specifically, the present invention relates to a process for the production of a terephthalic acid/ethylene glycol mixture suitable as feedstock for the production of commercial PET. The resulting process has fewer steps than currently employed processes and can be operated at lower operating cost and constructed at lower capital cost. Specifically, the present invention incorporates a direct displacement of water with ethylene glycol step following hydrogenation treatment of crude terephthalic acid. Incorporation .of the displacement step eliminates the need to isolate a purified terephthalic acid solid thereby eliminating the need for crystallization, solid-liquid separation, and solids handling equipment normally found in commercial purified terephthalic acid processes. It is an object of this invention to provide a process for producing a carboxylic acid/diol mixture without isolation of a substantially dry carboxylic acid solid. It is another object of this invention to provide a process for producing a terephthalic acid/diol mixture without isolation of a substantially dry terephthalic acid solid. It is another object of this invention to provide a process for producing a terephthalic acid/ethylene glycol mixture without isolation of a substantially dry terephthalic acid solid. It is another object of this invention to provide a process for producing a terephthalic acid/ethylene glycol mixture without isolation of a substantially dry terephthalic acid solid by vaporization of the water from a decolorized terephthalic acid solution with enthalpy supplied by ethylene glycol in a esterification reactor. It is another object of this invention to provide a process for producing a terephthalic acid/ethylene glycol mixture without isolation of a substantially dry terephthalic acid solid by removing water from a decolorized terephthalic acid solution through the use of solid liquid displacement devices such as centrifuges, filters or cyclones. In a first embodiment of this invention, a process for producing a carboxylic acid/diol mixture is provided, the process comprising adding a diol to a decolorized carboxylic acid solution in an esterification reactor zone to remove a portion of the water to form the carboxylic acid/dio! mixture; wherein said carboxylic acid and diol subsequently reacts in the esterification zone to form a hydroxyalky'ester stream. Typically, the carboxylic acid is selected from a group consisting of terephthalic acid, isophthaiic acid, naphthalene dicarboxylic acid, and mixtures thereof In another embodiment of this invention, a process for producing a carboxylic acid/diol mixture is provided, the process comprising the following steps: (a) mixing a crude carboxylic acid powder with water in a mixing zone to form a crude carboxylic acid solution; wherein the carboxylic acid is selected from a group consisting of terephthalic acid, isophthaiic acid, naphthalene dicarboxylic acid, and mixtures thereof; (b) decolorizing the crude carboxylic acid solution in a reactor zone to produce a decolorized earboxylic acid solution. (c) optionally, flashing the decolorized carboxylic acid solution in a flashing zone to remove a portion of the contaminated water from the decolorized carboxylic acid solution; and c acid solution in an esterification reactor zone to vaporize a portion of the water to form the carboxylic acid/diol mixture; wherein the carboxylic acid and diol subsequently reacts in the esterification zone to form a hydroxyalky ester stream In another embodiment of this invention, a process for producing a terephthalic acid/diol mixture is provided, the process comprising vaporizing a decolorized terephthalic acid solution with a diol in an esterification reactor zone to remove a portion of the water to form the terephthalic acid/diol mixture; wherein the terephthalic acid and diol subsequently reactsln the" esterification zone'to form a' hydroxyalky ester stream. In another embodiment of this invention, a process for producing a terephthalic acid/diol mixture is provided, the process comprising the following steps: (a) mixing a crude terephthalic acid powder with water in a mixing zone to form a crude terephthalic acid solution; (b) decolorizing the crude'terephthalic acid solution in a reactor zone to form a decolorized terephthalic acid solution. (c) optionally, flashing the decolorized terephthalic acid .solution in a flashing zone to remove a portion of water from the aqueous terephthalic solution; and (d) adding a diol to the decolorized terephthalic acid solution in an esterification reactor zone to remove a portion of water to form the terephthalic acid/diol mixture; wherein the terephthalic acid and diol subsequently reacts to from a hydroxalky ester stream. • In another embodiment of this invention, a process for producing a carboxylic acid/diol mixture is provided, the process comprising removing a portion of the p-toluic contaminated water in an terephttlalic acid aqueous slurry by adding a diol in a liquor removal zone to produce said carboxylic acid/ethylene glycol mixture. In another embodiment of this invention, a process for producing a carboxylic acid/dioi mixture is provided, the process comprising the following steps: (a) mixing a crude carboxylic acid powder with wafer in a mixing zone to form a crude carboxylic acid solution; (b) decolorizing the crude carboxylic acid in a reactor zone to produce a decolorized carboxylic acid solution. (c) crystallizing the decolorized carboxylic acid solution in a crystallization zone to form a terephthalic acid aqueous slurry; and (d) removing a portion of the contaminated water in said terephthalic acid aqueous slurry by adding a diol in a liquor removal zone to produce said carboxyiic acid/diol mixture. In another embodiment of this invention, a process for producing a terephthalic acid/ethylene glycot mixture is provided, the process comprising removing a portion of the p-toltitc contaminated water in an terephthalic acid aqueous slurry by adding a diol in a liquor removal zone to produce the terephthalic acid/diol mixture. In another embodiment of this invention, B process for producing a terephthalic acid/ethylene glycol mixture is provided, the process comprising the following steps: (a) mixing a crude terephthalic acid powder with water in a mixing zone to form a crude terephthalic acid solution; (b) decolorizing the crude terephthalic acid solution in a reactor zone to form a decolorized terephthalic acid solution; (c) crystallizing of the decolorized terephthalic acid solution in a crystallization zone to form an terephthalic acid aqueous slurry; and (d) removing a portion of p-toluic acid contaminated water in the terephthalic"acfd"aqueous slurry by adding a diol in a liquor removal zone to produce the terephthalic acid/diol mixture. These objects, and other objects, will become more apparent to others with ordinary skill in the art after reading this disclosure. Brief Description of the Drawings Figure 1 illustrates one embodiment of this invention. A process is provided utilizing carboxylic acid powder to produce a carboxylic acid/diol mixture with the carboxylic acid and diol subsequently reacting to form a hydroxyalky ester stream Figure 2 illustrates an alternative embodiment of this invention. A process is provided utilizing a terephthalic acid powder to produce a terephthalic acid/diol mixture with the terephthalic acid and diol subsequently react to form a hydroxyalky ester stream Figure 3 illustrates another alternative embodiment of this invention. A process is provided which utilizes a carboxylic acid powder to produce a carboxylic acfd/diol mixture. Figure 4 illustrates yet another alternative embodiment of this invention. A process is provided where a crude terephthalic acid powder is utilized to produce a terephthalic acid/diol mixture. DETAILED DESCRIPTION OF THE INVENTION in the first embodiment of this invention a process for producing a carboxylic acfd/diol mixture" the p'rocess comprising the adding a" diol to a decolorized carboxylic acid solution in an esterification reactor zone to remove a portion of the water to form the carboxylic acid/diol mixture; wherein the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof; wherein, said carboxylic acid and diol subsequently reacts in the esterification zone to from a hydroxyalky ester stream. The esterification reactor zone, the decolorized carboxylic acid solution and a process to produce the decolorized carboxylic acid solution is described subsequently in a second embodiment of this invention. In the second embodiment of this itwentiorv a process for producing a carboxylic acid/diol mixture is provided as shown in Figure #1. Step (1) comprises mixing a crude carboxylic acid powder in conduit 105 with water in conduit 115 in a mixing zone 110 to form a crude .carboxylic acid solution in conduit 120; Typically, the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof. The mixing of the crude carboxylic powder in conduit 105 with water in conduit 115 in the mixing zone .110 can be accomplished by any means known in the art. The mixing zone 110 can be any vessel or equipment capable of mixing the crude carboxylic acid powder. The temperature and pressure of the mixing zone 110 is that which is sufficient to properly slurry the crude carboxylic acid powder fn conduit" 105 with water in conduit 115. Typically, the crude carboxylic acid powder in conduit 105 is slurried with water in conduit 115 in mixing zone. 110 at a concentration of 15-35% by weight. Step (2) is decolorizing the crude carboxylic acid solution in conduit 120 in a reactor zone 125 to produce a decolorized carboxylic acid solution 135. The decolorizing of the crude carboxylic acid solution in conduit 120 can be accomplished by any means known in the art. Preferably, the decolorizing can be accomplished by reacting the crude carboxylic acid solution in conduit 120 with hydrogen in conduit 130 in the presence of a catalyst in a reactor zone 125 to produce a decolorized carboxylic solution. For the reactor zone 125, there are no special limitations in the form or construction thereof, subject to an arrangement that allows supply of hydrogen in conduit 130 to effect intimate contact of the crude carboxylic acid solution in conduit 120 with the catalyst in the reactor zone 125. Typically, the catalyst is usually a single Group VIII metal or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combination thereof. Most preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably on porous carbon. The reactor zone 125 comprises a hydrogenation reactor that operates at a temperature and pressure sufficient to hydrogenate the characteristically yellow compounds in the crude carboxylic acid solution in conduit 120. By hydrogenation treatment, the characteristically yellow compounds in the crude carboxylic acid solution are converted to colorless derivatives. The b* color of in the decolorized carboxylic acid solution in conduit 135 is between 0.5 to 4. Preferably the b* color of the carboxylic acid solution in conduit 135 is between 0.5 to 2.0. Most preferably the b* color in the carboxylic solution in conduit 135 is between 0.5 to 1.5. The b* is one of the three-color attributes .measured on a spectroscoplc reflectance-based instrument. The color can be measure by any device known in the art. A Hunter Ultrascan XE instrument is typically the measuring device. Positive readings signify .the degree of yellow (or absorbance of blue), while negative readings signify the degree of blue (or absqr-banoe of yellow). The fiydrogen in conduit 130 is fed at a rate sufficient to convert the characteristically yellow compounds in the crude carboxylic slurry in conduit 120 to colorless derivatives; wherein the b* color is between 0.5 to 4.0 in the decolorized carboxylic acid solution in conduit 135 . Step (3) comprises, optionally, flashing the decolorized carboxylic acid solution 135 in a flashing zone 145 to remove a portion of the water from the decolorized carboxylic acid solution in conduit 135. The flashing of the aqueous carboxylic solution 135 can be accomplished by any means know in the art. Typically, a vessel or a plurality of vessels are used to accomplish the flashing. In the flashing zone 145, water and residual hydrogen can be removed as a vapor via conduit 150. The flash vessel(s) operate at a temperature sufficient to remove a portion of -the water. Alternatively, flashing ~zbne 145 can be omitted as indicated by conduit 140. . Step (4) comprises, adding a diol in conduit 170 to the decolorized carboxylic acid solution in conduit 155. A portion of the water via conduit 165 is removed from an esterification reactor zone 160 to form said carboxyfic acid/diol mixture in the esterification reactor zone 160. The carboxylic acid and diol subsequently reacts to form a hydroxyalkyester stream 175.. The hydroxyalkyester stream 175 comprises a hydroxyalky ester compound. The diol in conduit 170 is introduced in such a manner as to displace the water as the dominant slurrying liquid. This can be accomplished by introdueing a did via-conduit 170 as a saturated liquid at a temperature which is sufficient to vaporize the water. Preferably, the diol in conduit 170 is introduced as a saturated or superheated vapor. The diol in conduit 170 is selected from the group consisting of ethylene glycot, diethylene glycol, n-butyiene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in conduit 170 isethylene glycol. Alternatively, an external heat source can be used to introduce sufficient enthalpy to vaporize the water, which exits via conduit 165. The hydroxalky ester stream exits via conduit stream 175. The esterification reactor zone 160 operates at a temperature that is sufficient to produce a hydroxyethyt from the carboxylic acid mixture. The esterification reactor zone 160 comprises an esterification reactor. The esterification can be accomplished by any means know in the art. In a'tfiird embodiment" of this invention a process for producing a terephthalic acid/diol comprises vaporizing a decolorized terephthalic acid solution with a diol in an esterification reactor zone to remove a portion of the water to form the terephthalic acid/diol mixture; wherein the terephthalic acid and diol subsequently reacts in the esterification zone to form a hydroxyalky ester stream. The esterification reactor zone, the decolorized terephthalic acid solution and a process to produce the decolorized terephthalic acid solution is described subsequently in a fourth embodiment of this invention. in the forth embodiment of this invention a process for producing aterepnthaHc aejd/diol mixture is provided as shown in Figure #2. Step (1) comprises mixing a crude terephthalic acid powder in conduit 205 with water in conduit 215 in a mixing zone 210 to form a crude terephthalic acid solution in conduit 220. The mixing of the crude terephthalic powder in conduit 205 with water in conduit 215 can be accomplished by any means known in the art. The starting feed material is the crude terephthalic acid powder in conduit 205 with some specific physical characteristics that differ from crude terephthalic add described in U.S. Patent 5,095,146 and U.S: Patent 5,175,355, herein incorporated by reference. Specifically, the total amount of p-toluic acid and 4-carboxybenzaldehyde in the crude terephthalic acid powder in conduit 205 is less than 900 ppm on a weight basis, preferably, less than 500 ppm, and most preferably, less than 250 ppm. Another characteristic of the crude terephthalic powder in conduit 205 is the color as measured by ,„ bls less fJiahT". "Preferably, the color measured by b* is between 4 and 6. The mixing zone 210 can be. any vessel or equipment capable of mixing the crude terephthalic acid powder in conduit 205 with water in conduit 215. The crude terephthalic acid powder in conduit 205 is slurried in water in conduit 215 in the mixing zone 210 to produce the crude terephthalic acid solution in conduit 220. The crude terephthalic acid and water are heated in ,a mixing zone 210 to a temperature of 230 °C or higher to dissolve the crude terephthalic acid powder in conduit 205 in the mixing zone 210 to produce the crude terephthalic acid solution in conduit 220. Preferably, the crude terephthalic slurry in the mixing zone 21t) Is hea'ted to a temperature in the range of 240 °C to 300 °C. The pressure of the mixing zone is 900 psia to 1400 psia to dissolve the crude terephthalic acid powder in conduit 205 in the mixing zone 210. Generally, the concentration of crude terephthalic acid in the crude terephthalic acid solution is 15% to 30% by weight, preferably, 20 to 30% by weight. Step (2) \s decolorizing the crude terephthalic acid solution in conduit 220 in a reactor zone 225 to form a decolorized terephthalic acjd solution in conduit 235. The decolorizing of the crude terephthalic acid solution in conduit 220 can be accomplished by any means known in the art. Preferably, the decolorizing can be accomplished by reacting the crude terephthalic acid solution in conduit 220 with hydrogen in conduit 230 in the presence of a catalyst in a "rea'ctor'zbhe 225" fo~ produce a decolorized terephthalic acid solution. For the reactor zone 225, there are no special limitations In the form or construction thereof, subject to an arrangement that allows supply of hydrogen in conduit 230 to effect intimate contact of the crude terephthalic acid solution -in conduit 220 with the catalyst in the reactor zone 225. Generally, the catalyst is usually a single Group VIII metal or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combination thereof. Most preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably on porous carbon. The reactor zone 225 comprises a hydrqgenation reactor Which operates at a temperature of 230 °C or higher. Preferably, the hydrogenation reactor operates in the range of 240°C to 300 °C. The hydrogenation reactor operates at a pressure of 900 psia to 1400 psia and at a hydrogen partial pressure of at least 100 psia. Preferably, the hydrogen partial pressure is in the range of 100 to 300 psia. By hydrogenation treatment, the characteristically yellow compounds in the crude terephthalic acid solution are converted to colorless derivatives. In addition, the reactor zone converts a portion of 4-carboxybenzaldehyde to p-toluic acid. The hydrogen in conduit 230 is fed at a rate of at least 1.5 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude terephthalic acid solution in conduit 220 to p-toluic acid. Preferably, the hydrogen 230 is fed at a rate of at least 2.01im~e~s1he molar ratio necessary fo"convert the 4-carboxybenzaldehyde in the crude terephthalic acid solution 220 to p-toluic acid. The b* color is between 0.5 to 4 in the terephthalic acid decolorized solution in conduit 235. Preferably the b* color of the terephthalic acid solution in conduit 235 is between 0.5 to 2. Most preferably the b* color in the decolorized terephthalic acid solution in conduit 235 is between 0.5 to 1.5. Step (3) comprises, optionally, flashing the decolorized terephthalic acid solution 235 in a flashing zone 245 to remove a portion of the water 250 from the aqueous terepthalic acid solution 235. The flashing of the aqueous terephthalic solution 235 can be accomplished by any means know in the art. Typically, a vessel or a plurality of vessels are used to accomplish the flashing. In the flashing zone 245, water and residual hydrogen can be removed as a vapor via conduit 250. The flash vessel(s) operate at a temperature of 150 °C or higher. Preferably, the flash vessels(s) operate in the range of 155 °C to 260 °C. The flash vessel(s) operate under a pressure of 75 psia to 1400 psia. Specific operating ranges vary depending on the amount of water removed via conduit 250. Alternatively, flashing zone 245 can be omitted as indicated by conduit 240. Step (4) comprises, adding a diol in conduit 270 to the decolorized terephthalic acid solution in conduit 255 in an esteriflcation reactor zone 260 to remove a portion of the water via conduit 265 to form said terephthalic acid/diol mixture in the esteriflcation reactor zone 260. The carboxylic acid and diol react to form a hydroxyalkyester stream"275. The'Hydroxyafkye'stef stream 275 comprises a hydroxyalky ester compound. The diol in conduit 270 is introduced in such a manner as to displace the water as the dominant slurrying iiquid. This can be accomplished by introducing a diol via conduit 270 as a saturated liquid in a temperature range of 150 to 300 °C. Preferably, the diol in conduit 270 (s introduced as a saturated or superheated vapor in the temperature range of 150 to 300 °C in a form with sufficient enthalpy as to evaporate the water to exit via conduit 265. The diol in conduit 270 is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in conduit 270 is ethylene glycol. Alternatively, an external heat source can be used to introduce sufficient enthalpy to vaporize the water, which exits via conduit 265. The hydroxalky! ester stream mixture exits via conduit stream 275. The esterification reactor zone 260 operates at a temperature of 240 °C higher. Preferably the esterification reactor zone 260 operates in the temperature range of 260 °C to 280 °C. The esterification reactor zone 260 operates under a pressure of 40 psia to 100 psia so as to effect esterification of the terephthalic acid/diol mixture 275 to produce a hydroxyethyl ester of terephthaiic acid. In a fifth embodiment of this invention, a process for producing a carboxylic acid/diol mixture comprises removing a portion of contaminated" water in an aqueous slurry by adding a diol in a liquor removal zone to produce said carboxylic acid/diol mixture. The liquor removal zone, the aqueous slurry and a process to produce the aqueous slurry are described subsequently in a sixth embodiment of this invention. In the six embodiment of this invention, a process for producing a carboxylic acid/diol mixture is provided as shown in Figure #3; Step (1) comprises mixing a crude carboxylic acid powder in conduit 305 with water in conduit 315 in a mixing zone 310 to form a crude carboxylic acid solution in conduit 320. The mixing of the crude carboxylic powder in conduit 305 with water in conduit 315 in the mixing zone 310 can be accomplished by any means known in the art. The starting feed material is the crude carboxylic acid powder in conduit 305. Typically, the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof. The mixing zone 310 can be any vessel or equipment capable of mixing the crude carboxylic acid powder in conduit 305 with water in conduit 315. The crude carboxylic acid powder in conduit 305 and water in conduit 315 in mixing zone 310 is heated to a temperature sufficient to dissolve the crude carboxylic acid powder in conduit 305 in the mixing zone 310 to produce the crude carboxylic acid solution in conduit 320. The pressure of the mixing zone 310 is a pressure sufficient to dissolve the crude carboxylic acid powder in conduit 305 in the mixing zone 310. Generally, the concentratiorrof mrde'car&dxylfc'acfd iri the crude carboxylic acid solution is 15% to 35% by weight, Step (2} is decolorizing the crude carboxyfic acid solution in conduit 320 in a reactor zone 325 to form an decolorized carboxylic acid solution in conduit 330. The decolorizing of the crude carboxylic acid solution in conduit 320 can be accomplished by any means known in the art. Preferably, the decolorizing can be accomplished by reacting the crude carboxylic acid solution in conduit 320 with hydrogen in conduit 330 in the presence of a catalyst in a reactor zone 325 to produce a decolorized carboxyfic . acid solution. For the reactor zone 325, there are no special limitations in the form or construction thereof, subject to an arrangement that allows supply of hydrogen in conduit 330 to effect intimate contact of the crude carboxylic slurry 320 with the catalyst in the reactor zone. Typically, the catalyst is usually a single Group VIII metal or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combinations thereof. Most preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably on porous carbon. The reactor zone 325 comprises a hydrogenation reactor that operates at a temperature sufficient to convert the characteristically yellow compounds in the crude carboxylic acid solution 320 to colorless derivatives. The b* color of in the decolorized carboxylic acid solution in conduit 335 is between 0.5 to 4. Preferably the b* color of the carboxylic acid solution-irrconduit-335-is betwe'en 0:5~to~2. "Mbsf preferably the b* color in the decolorized carboxylic acid solution in conduit 335 is between 0.5 to 1.5. . The hydrogen in conduit 330 is fed at a rate sufficient to convert the characteristically yellow compounds in the crude carboxylic slurry in conduit 320 to colorless derivatives; wherein the b* color is between 0.5 to 4 in the decolorized carboxylic acid solution in conduit 335. Step (3) comprises crystallizing the decolorized carboxylic acid solution in conduit 335 in a crystallization zone 345 to form an aqueous slurry in conduit 355. The crystallization zone 345 comprises a vessel or plurality of vessels capable of removing water fr-om -the decolorized carboxyfic acid solution in conduit 335 to produce an aqueous slurry in conduit 355. Typically, the vessels comprise at least one crystallizer. Examples of such systems can be found in U.S patents 5,567,842 and 3,931,305, herein incorporated by reference. Generally, the aqueous slurry in conduit 355 has a carboxylic acid concentration of from 10 to 60 weight percent. The temperature range of the carboxyfic acid solution in the crystallization zone 345 is that which is sufficient to remove a portion of the water. Step (4) comprises removing a portion of contaminated water via conduit 365 in the aqueous slurry 355 by adding a diol in conduit 370 in a liquor removal zone 360 to produce the carboxylic acid/diol mixture in conduit 375. The purpose of the liquor removal zone 360 is to replace the contaminated-water with'aofoTiri condulf 370. The'cdntamiria'ted water comprises water and typical contaminants. The diol in conduit 370 is selected from the group consisting of ethylene gfycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in conduit 370 is ethylene glycol. The diol in conduit 370 is introduced into the liquor removal zone 360 via conduit 370. The removal of the contaminated water via conduit 365 in the liquor removal zone 360 can be accomplished using variety of techniques including; but not limited to, cyclones, centrifuges, and filters. The key factor In the liquor removal zone 360 is to select a temperature range where the typical contaminants preferably remain w'rth the-aqueous mother liquor instead of remaining with the carboxylic acid. The resultant carboxylic acid/diol mixture is removed via conduit 375. The resultant carboxylic acid/diol mixture in conduit 375 is adequate as feed material for the esterification of carboxylic acid with the diol to produce the ester of carboxylic acid. .In a seventh embodiment of this invention, a process for producing a terephthalic acid/diol mixture comprises removing a portion of the p-toJuic contaminated water in a terephthalic acid aqueous aqueous slurry by adding a diol in a liquor removal zone to produce said terephthalic acid/diol mixture. The liquor removal zone, the terephthalic acid aqueous slurry and a process to produce the aqueous slurry are described subsequently in an eight embodiment of this invention. 1n mB~eig!it"embo~dtntent~tif this invention," a prbcesYfbr producing a terephthalic acid/diol mixture is provided as sho'wn in Figure #4. Step (1) comprises mixing a crude terephthalic. acid powder in conduit 405 with water in conduit 415 in a mixing zone 410 to form a crude terephthalic acid solution in conduit 420. The mixing of the crude terephthalic powder in conduit 405 with water in conduit 415 in the mixing zone 410 can be accomplished by any means known in the art. The starting feed material is the crude terephthalic acid powder in conduit 405. The total amount of p-toluic acid and 4-carboxybenzaldehyde in the crude terephthalic acid powder in conduit .405 is less than 6000 ppm on a weight basis. Another characteristic of the crude terephthalic powder 405 is the color as measured by b* is less than 7. Preferably the color measured by b* is between 4 and 6. This crude terephthalic acid powder in conduit 405 is introduced into a mixing zone 410. The mixing zone 410 can be any vessel or equipment capable of mixing the crude terephthalic acid powder in conduit 405 with water in conduit 415. . The crude terephthalic acid powder and water are heated to a temperature of 230 °C or higher to dissolve the crude terephthalic acid powder in conduit 405 in the mixing zone 410 to produce the crude terephthalic acid solution in conduit 420. Preferably, the crude terephthalic acid, solution in the mixing zone 410 is heated to a temperature in the range of 240 °C to 300 °C. The pressure of the mixing zone 410 is 900 psia to 1400 psia to dissolve the crude terephthalic acid powder in conduit 405 in the mixing zone 410. ~Ge"nefany~ th~e~concentration"of crude terephthalic acid powder 405 in the crude terephthalic acid solution 420 is in a range of 15% to 35% by . weight, preferably 20 to 30% by weight. Step (2) is decolorizing the crude terephthalic acid solution in conduit 420 in a reactor zone 425 to form a decolorized terephthalic acid solution in conduit 435. The decolorizing of the crude carboxylic acid solution in conduit 420 can be accomplished by.any means known in the art. Preferably, the decolorizing can be accomplished by reacting the Crude carboxylic acid solution in conduit 420 with hydrogen in conduit 430 in the presence of a catalyst in a reactor zone 425 to produce a decolorized carboxylic aeid solution. For the reactor zone 425, there are no special limitations in the form or construction thereof, subject to an arrangement that allows supply of hydrogen in conduit 430 to effect contact of the crude terephthalic slurry 420 with the catalyst in the reactor zone. The catalyst is usually a single Group VIII metal or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combinations thereof. Most preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably on porous carbon. The reactor zone 425 comprises a hydrogenation reactor which operates at a temperature of 230 °C or higher. Preferably the hydrogenation reactor operates in the range of 240°C to 300 °C. The hydrogenatfon reactor operates at a pressure of 900 psia to 1400 psia and at a hydrogen partial pressure of at least 100 psia. Preferably, the . hydrogen partial pressure is in the range of 100 to 300 psia. By hydrogenation treatment, the characteristically yeHow compounds in the crude terephthalic acid solution 420 are converted to colorless derivatives. In addition, the reactor zone converts a portion of 4-carboxybenzaldehyde to p-toluic acid. The hydrogen in conduit 430 is fed at a rate of at least 1.5 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude terephthalic slurry 420 to p-toluic acid. Preferably the hydrogen 430 is fed at a rate of at least 2.0 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude terephthalic slurry 420 to p-toluic acid. The b* color is between 0.5 to 4 in the decolorized terephthalic acid solution in conduit 435. Preferably the b* color of the terephthalic acid solution in conduit 435 is between 0.5 to 2. Most preferably the b* color in the decolorized terephthalic acid solution in conduit 435 is between 0.5 to 1.5. Step (3) comprises crystallizing said decolorized terephthalic acid solution in conduit 435 in a crystallization zone 445 to form a terephthalic acid aqueous slurry in conduit 455; The crystallization zone 445 comprises a vessel or plurality of vessels capable of removing water via conduit 450 from the decolorized terephthalic acid solution in conduit 435 to produce an terephthalic acid aqueous slurry in conduit 455. Typically the vessels comprise at least one~crystat!Izef as prevfbusly described, "Generally;' fhe'terephYhalic acid aqueous slurry in conduit 455 has a terephthalic acid concentration of from 10 to 60 weight percent, preferably from 20 to 40 weight percent. Examples of such systems can be found in U.S. patents 5,567,842 and y 3,931,305 both of which are herein incorporated by reference. The temperature range of the .terephthalic acid aqueous slurry in conduit 455 is from 120 °C to 270 "C. The pressure range of the crystallizing is from 75 to 1400 psia. Step (4) comprises removing a portion of p-toluic acid contaminated water via conduit 465 in the terephthalic acid aqueous slurry 455 by adding a diol in conduit 470 in a liquor removal zone 460 to produce said terephthatic ac'rdfaiol mixture in conduit 475. The purpose of the liquor removal zone 460 is to replace the p-toluic acid contaminated water with a diol in conduit 470. The dio! in conduit 470 is selected from a group consisting of ethylene glycol, diethylene glycol, n-butyfene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in conduit 470 is ethylene glycol. The diol in, conduit 470 is introduced into the liquor removal zone 460 via conduit 470. The removal of the p-toiuie acid contaminated water via conduit 465 in the liquor removal zone 460 can be accomplished .using variety of techniques including, but not limited to, cyclones, centrifugation, and filtration. The key factor in the liquor removal zone 460 is to select a temperature range where the p-to!uic acid and 4-carboxybenzaldehyde will preferably remain with the aqueous mother liquor instead of remaining with1heterephth"airc~a"cid."TrTe"irq"uor re"rrl6val z6ne~460~ operates in a range of 120 °C to 270 °C, preferably in the range of 120 . °C to 150 °C. The p-toluic acid contaminated water is removed via conduit 465. The resultant terephthalic acid/diol mixture is removed via conduit 475. The resultant terephthalic acid/diol mixture in conduit 475 is adequate as feed material for the esterification of terephthalic acid with 3 diol to produce the ester of terephthalic acid. WE CLAIM: 1. A process for making a hydroxyalkyl ester wherein a carboxylic acid and at least one diol starting materials are esterified in an esterification zone, wherein said process includes obtaining a carboxylic acid and diol slurry without isolation of dry carboxylic acid solid, said process comprising optional steps of mixing a crude carboxylic acid powder with water to make a solution, decolorizing said carboxylic acid solution and flashing said decolorized carboxylic acid solution to form a decolorized carboxylic acid and water solution followed by adding a heated diol to the decolorized carboxylic acid and water solution in an esterification reactor zone to vaporize a portion of the water to form said carboxylic acid and diol slurry; wherein said diol is the dominant liquid and is heated to a temperature of from 150°C to 300°C and said esterification reactor zone is at a temperature of from 240°C to 280°C and a pressure of from 40 psia to 100 psia; wherein said carboxylic acid and diol subsequently reacts in said esterification zone to form a hydroxyalkyl ester. 2. The process as claimed in claim 1 wherein said carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof 3. The process as claimed in claim 1 wherein said process optionally comprises the following steps prior to adding the heated diol to the decolorized carboxylic acid and water solution: (a) mixing a crude carboxylic acid powder with water in a mixing zone operated at a temperature greater than 230°C and a pressure of from 900 to 1400 psia to form a crude carboxylic acid solution; wherein the concentration of said carboxylic acid in said solution is from 15 to 35 weight %: (b) decolorizing said crude carboxylic acid solution in a reactor zone by contacting said carboxylic acid solution with hydrogen at a temperature of from 230°C to 300°C and a pressure of from 900 psia to 1400 psia and in the presence of a hydrogenation catalyst comprising a Group VIII metal to produce a decolorized carboxylic acid solution; and (c) flashing said decolorized carboxylic acid solution in a flashing zone to remove a portion of the water from said decolorized carboxylic acid solution wherein said flashing zone is operated at a pressure of from 75 psia to 1400 psia and a temperature of from 150°C to 260°C to form a decolorized carboxylic acid and water mixture solution. 4. The process as claimed in claim 3 wherein said crude carboxylic acid powder is terephthalic acid powder having a concentration of p-toluic acid and 4- carboxybenzaldehyde of less than 900 ppm by weight. 5. The process as claimed in claim 3 wherein the step (c) optionally comprises the following steps prior to adding the heated diol to the decolorized carboxylic acid and water solution: crystallizing said decolorized carboxylic acid solution in a crystallization zone having a temperature of 120°C to 270°C and a pressure of from 75 psia to 1400 psia to form an aqueous slurry having a carboxylic acid concentration of from 10 to 60 weight % in p-toluic acid contaminated water; and removing a portion of the contaminated water in said aqueous slurry. 6. A process as claimed in claim 3 or 5 wherein said decolorizing reaction occurs at a hydrogen rate sufficient to produce a decolorized carboxylic acid solution with a b* color between 0.5 to 4. 7. The process as claimed in claim 5 wherein said carboxylic acid is terephthalic acid. 8. A process as claimed in claim 5 wherein said crude carboxylic acid is terephthalic acid powder containing a total concentration of p-toluic acid and 4-carboxybenzaldehyde of less than 6000 ppm by weight. 9. A process as claimed in any one of the above claims wherein said diol is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. 10. A process as claimed in claim 8 wherein said crude terephthalic acid powder has a b* color of less than 7. 11. A process as claimed in claim 3 or 5 wherein said decolorization reaction occurs at a hydrogen flow rate of 1.5 times the molar ratio necessary to convert 4-carboxybenzaldehyde to p-toluic acid in said crude terephthalic solution. 12. A process as claimed in claim 1 wherein said adding of said diol occurs at a temperature between 120 °C to 270 °C. 13. A process as claimed in claim 5 wherein said crude carboxylic acid is terephthalic acid aqueous solution has a terephthalic acid concentration between 20% to 40% by weight.

Full Text

The present invention relates of a process for producing a carboxylic acid/diol mixture.

FIELD OF INVENTION
The present invention relates to a process by which a carboxylic acid/diol mixture is obtained from a decolorized carboxylic acid solution without isolation of a substantially dry carboxylic acid solid. More specifically, the present invention relates to a process by which a terephthalic acid/ethylerie glycol mixture suitable as a starting material for polyester production is. obtained from a decolorized terephthalic acid solution without isolation of a substantially dry terephthalic acid solid.
BACKGROUND OF THE INVENTION
Thermoplastic polyesters are step growth polymers that are useful when made to high molecular weights. The first step in a common method of producing a polyester such as polyethylene terephthalate (PET) is an esferification or ester-exchange stage where a diacid (typically terephthalic acid) reacts with an appropriate diol (typically ethylene glycol) to give a bis(h.ydroxyalkyl)ester and some linear oligomers. Water is evolved at this stage and is usually removed by fractional distillation.
Pursuant to the goal of making polyethylene terephthalate and other polyesters, a great deal of patent literature is dedicated to the describing processes for preparing terephthalic acid/ethylene glycol

mixtures suitable as starting material. In general, these inventions describe specific mixing schemes with a purified terephthalic acid solid and liquid ethylene glycol as starting materials. Additionally, there is substantial body of literature devoted to producing a purified terephthalic acid in the powder form that is suitable for use in producing PET. The objective of this invention is to describe a process by which a terephthalic acid/ethylene glycol mixture suitable as starting material for polyester production is obtained from a decolorized terephthalic acid solution without isolation of a substantially dry terephthalic acid solid.
A number of processes for producing the purified terephthalic acid solid have been developed and are commercially available. Usually, the purified terephthalic acid solid is produced in a multi-step process .wherein a crude terephthalic acid is produced. The crude terephthalic acid does not have sufficient quality for direct use as starting material in commercial PET. Instead, the crude terephthalic acid is usually refined to purified terephthalic acid solid.
Liquid phase oxidation of p-xylene produces crude terephthalic acid. The crude terephthalic acid is dissolved in water and hydrogenated for the purpose of converting 4-carboxybenzaldehyde to p-toluic acid, which is a more water-soluble derivative, and for the purpose of converting characteristically yellow compounds to colorless derivatives. Any 4»carboxybenza!dehyde and p-toluic acid in the final purified terephthalic acid product is particularly detrimental to polymerization processes as they act as a chain terminator during the condensation reaction between terephthalic acid and ethylene glycol in

the production of PET. Typical purified terephthalic acid contains on a weight basis less than 25 parts per million (ppm) 4-carboxybenzaidehyde and less than. 150 ppm p-toluic acid.
The crude terephthalic acid typically contains on a weight basis from 800 to 7,000 parts per million (ppm) 4-carboxybenzaldehyde and 200 to 1,500 ppm p-toluic acid as the main impurities. The crude terephthalic acid also contains lesser amounts, 20-200 ppm range, of yellow color aromatic compounds having the structures of benzil, fluorenone, and/or anthraquinone, which are characteristically yellow compounds as impurities resulting from coupling side reactions occurring during oxidation of p-xylene. It is necessary to purify the crude terephthalic acid when using it as a starting material for producing polyester fiber, which requires a purified terephthalic acid as a starting material.
Such a purification process typically comprises adding water to the crude terephthalic acid to form a crude terephthalic acid solution, which is heated to dissolve the crude terephthalic acid. The crude terephthalic acid solution is then passed to a reactor zone in which the solution is contacted with hydrogen in the presence of a heterogeneous catalyst at temperatures of 200° to 375° C. This reduction step converts .the various color bodies present in the crude terephthalic acid to colorless products. The principal impurity, 4-carbpxyber4zaldehyde, is converted to p-toluic acid.
Typical crude terephthalic acid contains excessive amounts of both 4-carboxybenzaldehyde and p-toluic acid on a weight basis.

Therefore, to achieve less than 25 ppmw 4-carboxybenzaldehyde and less than 150 ppmw p-toluic acid in the purified terephthalic acid requires mechanisms for purifying the crude terephthalic acid and removing the contaminants.
Subsequent separation and isolation of the purified terephthalic acid can be accomplished via a wide variety of separation methods including crystallization, centrifugation, filtration, extraction and combinations thereof followed by drying. These processes are described in U.S. patents 4,500,732; 5,175,355; and 5,583,254; all of which are herein incorporated by reference. It Is necessary to perform a separation step" due the nature of the crude terephthaiic acid feedstock to the hydrogenation process.
A number of processes have been developed for producing a purified terephthalic acid solid from crude terephthalic acid. In general, the common features among these processes are as follows:
Step (1) is decolonization of the crude terephthalic acid usually via hydrogenation treatment in an aqueous medium;
Step (2) is purification/separation of the terephthalic acid from partial oxidation products usually via fractional crystallization followed by liquor exchange with contaminant-free water; and
Step (3) is production of a solid purified terephthalic acid product with consistent material handling properties usually via-crystallization of terephthalic acid followed by drying of purified terephthalic acid from water.

The resultant purified terephthalic acid powder along with ethylene glycol are starting materials in the production of polyesters specifically PET. Because the difficulty in handling, mixing, and dissolving terephthalic acid solids,'the purified terephthalic acid solid is usually mixed with ethylene glycol to form a paste prior to introduction into an esterification reactor system.
In the present invention, a novel process has been discovered resulting in fewer steps than the currently employed processes. The primary utility of the invention is reduction of capital and operating costs associated with the isolation of a terephthalic acid powder. In the conventional approach toward producing "terephthalic acid, the post-hydrogenated aqueous solution is passed to a series of crystallizer vessels for the purpose of purifying the terephthalic acid by crystallization and for the purpose of obtaining a uniform particle size distribution necessary for good flowability of purified terephthalic powder. Further, the p-toluic acid contaminated mother liquor from the crystallization process must be removed prior to a drying step .to isolate the purified terephthalic powder.
In on embodiment of the present invention, the crude terephthalic acid solution with low concentrations of p-toluic acid and 4-. carboxybenzaldehyde is hydrogenated to form a decolorized terephthalic acid solution. Starting with crude terephthalic acid with low concentrations of the p-toluic acid and 4-carboxybenzaldehyde
t
eliminates the need for separation of p-toluic acid-contaminated mother liquor from the terephthalic acid. Hence, the decolorized terephthalic

acid solution can be directly combined with ethylene glycol in an esterification zone to produce a terephthalic acid/ethylene glycol mixture. By bypassing conventional processes for producing a purified terephthalic acid powder, the need for the equipment necessary to purify and isolate purified terephthalic powder is eliminated.
Another surprising and seemingly contradictory aspect of the invention is the benefits of addition of large amounts of water to the esterification reaction starting materials. This is directly contrary to accepted esterification procedures. The esterification reaction:
RCOOH + R'OH •» RCOOR1 + H20
is generally not complete". The water formed in the course of the reaction tends to react with the ester to hydrolyze it, i.e. to regenerate the original alcohol and acid. In order to drive the reaction toward the ester, the prior art teaches removal of water from the system by a variety of methods such as distillation or dehydration with a hydrophilic compound. According to .conventional esterification procedures, it is non-intuitive to add large amount of the water to the acid/alcohol starting material.
SUMMARY OF THE INVENTION
The present Invention relates to a process by which a carboxylic
acid/diol mixture is obtained from a decolorized carboxylic acid solution without isolation of a substantially dry carboxylic acid solid. More specifically, the present invention relates to a process for the production of a terephthalic acid/ethylene glycol mixture suitable as feedstock for

the production of commercial PET. The resulting process has fewer steps than currently employed processes and can be operated at lower operating cost and constructed at lower capital cost. Specifically, the present invention incorporates a direct displacement of water with ethylene glycol step following hydrogenation treatment of crude terephthalic acid. Incorporation .of the displacement step eliminates the need to isolate a purified terephthalic acid solid thereby eliminating the need for crystallization, solid-liquid separation, and solids handling equipment normally found in commercial purified terephthalic acid processes.
It is an object of this invention to provide a process for producing a carboxylic acid/diol mixture without isolation of a substantially dry carboxylic acid solid.
It is another object of this invention to provide a process for producing a terephthalic acid/diol mixture without isolation of a substantially dry terephthalic acid solid.
It is another object of this invention to provide a process for producing a terephthalic acid/ethylene glycol mixture without isolation of a substantially dry terephthalic acid solid.
It is another object of this invention to provide a process for producing a terephthalic acid/ethylene glycol mixture without isolation of a substantially dry terephthalic acid solid by vaporization of the water from a decolorized terephthalic acid solution with enthalpy supplied by ethylene glycol in a esterification reactor.

It is another object of this invention to provide a process for producing a terephthalic acid/ethylene glycol mixture without isolation of a substantially dry terephthalic acid solid by removing water from a decolorized terephthalic acid solution through the use of solid liquid displacement devices such as centrifuges, filters or cyclones.
In a first embodiment of this invention, a process for producing a carboxylic acid/diol mixture is provided, the process comprising adding a diol to a decolorized carboxylic acid solution in an esterification reactor zone to remove a portion of the water to form the carboxylic acid/dio! mixture; wherein said carboxylic acid and diol subsequently reacts in the esterification zone to form a hydroxyalky'ester stream. Typically, the carboxylic acid is selected from a group consisting of terephthalic acid, isophthaiic acid, naphthalene dicarboxylic acid, and mixtures thereof
In another embodiment of this invention, a process for producing a carboxylic acid/diol mixture is provided, the process comprising the following steps:
(a) mixing a crude carboxylic acid powder with water in a
mixing zone to form a crude carboxylic acid solution; wherein the
carboxylic acid is selected from a group consisting of terephthalic acid,
isophthaiic acid, naphthalene dicarboxylic acid, and mixtures thereof;
(b) decolorizing the crude carboxylic acid solution in a reactor
zone to produce a decolorized earboxylic acid solution.
(c) optionally, flashing the decolorized carboxylic acid solution
in a flashing zone to remove a portion of the contaminated water from
the decolorized carboxylic acid solution; and

c acid solution in an esterification reactor zone to vaporize a portion of the water to form the carboxylic acid/diol mixture; wherein the carboxylic acid and diol subsequently reacts in the esterification zone to form a hydroxyalky ester stream
In another embodiment of this invention, a process for producing a terephthalic acid/diol mixture is provided, the process comprising vaporizing a decolorized terephthalic acid solution with a diol in an esterification reactor zone to remove a portion of the water to form the terephthalic acid/diol mixture; wherein the terephthalic acid and diol subsequently reactsln the" esterification zone'to form a' hydroxyalky ester stream.
In another embodiment of this invention, a process for producing a terephthalic acid/diol mixture is provided, the process comprising the following steps:
(a) mixing a crude terephthalic acid powder with water in a
mixing zone to form a crude terephthalic acid solution;
(b) decolorizing the crude'terephthalic acid solution in a
reactor zone to form a decolorized terephthalic acid solution.
(c) optionally, flashing the decolorized terephthalic acid
.solution in a flashing zone to remove a portion of water from the
aqueous terephthalic solution; and
(d) adding a diol to the decolorized terephthalic acid solution in
an esterification reactor zone to remove a portion of water to form the

terephthalic acid/diol mixture; wherein the terephthalic acid and diol subsequently reacts to from a hydroxalky ester stream.
• In another embodiment of this invention, a process for producing a carboxylic acid/diol mixture is provided, the process comprising removing a portion of the p-toluic contaminated water in an terephttlalic acid aqueous slurry by adding a diol in a liquor removal zone to produce said carboxylic acid/ethylene glycol mixture.
In another embodiment of this invention, a process for producing a carboxylic acid/dioi mixture is provided, the process comprising the following steps:
(a) mixing a crude carboxylic acid powder with wafer in a
mixing zone to form a crude carboxylic acid solution;
(b) decolorizing the crude carboxylic acid in a reactor zone to
produce a decolorized carboxylic acid solution.
(c) crystallizing the decolorized carboxylic acid solution in a
crystallization zone to form a terephthalic acid aqueous slurry; and
(d) removing a portion of the contaminated water in said
terephthalic acid aqueous slurry by adding a diol in a liquor removal
zone to produce said carboxyiic acid/diol mixture.
In another embodiment of this invention, a process for producing a terephthalic acid/ethylene glycot mixture is provided, the process comprising removing a portion of the p-toltitc contaminated water in an terephthalic acid aqueous slurry by adding a diol in a liquor removal zone to produce the terephthalic acid/diol mixture.

In another embodiment of this invention, B process for producing a terephthalic acid/ethylene glycol mixture is provided, the process comprising the following steps:
(a) mixing a crude terephthalic acid powder with water in a
mixing zone to form a crude terephthalic acid solution;
(b) decolorizing the crude terephthalic acid solution in a
reactor zone to form a decolorized terephthalic acid solution;
(c) crystallizing of the decolorized terephthalic acid solution in
a crystallization zone to form an terephthalic acid aqueous slurry; and
(d) removing a portion of p-toluic acid contaminated water in
the terephthalic"acfd"aqueous slurry by adding a diol in a liquor removal
zone to produce the terephthalic acid/diol mixture.
These objects, and other objects, will become more apparent to others with ordinary skill in the art after reading this disclosure. Brief Description of the Drawings
Figure 1 illustrates one embodiment of this invention. A process is provided utilizing carboxylic acid powder to produce a carboxylic acid/diol mixture with the carboxylic acid and diol subsequently reacting to form a hydroxyalky ester stream
Figure 2 illustrates an alternative embodiment of this invention. A process is provided utilizing a terephthalic acid powder to produce a terephthalic acid/diol mixture with the terephthalic acid and diol subsequently react to form a hydroxyalky ester stream

Figure 3 illustrates another alternative embodiment of this invention. A process is provided which utilizes a carboxylic acid powder to produce a carboxylic acfd/diol mixture.
Figure 4 illustrates yet another alternative embodiment of this invention. A process is provided where a crude terephthalic acid powder is utilized to produce a terephthalic acid/diol mixture.
DETAILED DESCRIPTION OF THE INVENTION
in the first embodiment of this invention a process for producing a carboxylic acfd/diol mixture" the p'rocess comprising the adding a" diol to a decolorized carboxylic acid solution in an esterification reactor zone to remove a portion of the water to form the carboxylic acid/diol mixture; wherein the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof; wherein, said carboxylic acid and diol subsequently reacts in the esterification zone to from a hydroxyalky ester stream.
The esterification reactor zone, the decolorized carboxylic acid solution and a process to produce the decolorized carboxylic acid solution is described subsequently in a second embodiment of this invention.
In the second embodiment of this itwentiorv a process for producing a carboxylic acid/diol mixture is provided as shown in Figure #1.

Step (1) comprises mixing a crude carboxylic acid powder in conduit 105 with water in conduit 115 in a mixing zone 110 to form a crude .carboxylic acid solution in conduit 120; Typically, the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof. The mixing of the crude carboxylic powder in conduit 105 with water in conduit 115 in the mixing zone .110 can be accomplished by any means known in the art. The mixing zone 110 can be any vessel or equipment capable of mixing the crude carboxylic acid powder. The temperature and pressure of the mixing zone 110 is that which is sufficient to properly slurry the crude carboxylic acid powder fn conduit" 105 with water in conduit 115. Typically, the crude carboxylic acid powder in conduit 105 is slurried with water in conduit 115 in mixing zone. 110 at a concentration of 15-35% by weight.
Step (2) is decolorizing the crude carboxylic acid solution in conduit 120 in a reactor zone 125 to produce a decolorized carboxylic acid solution 135.
The decolorizing of the crude carboxylic acid solution in conduit 120 can be accomplished by any means known in the art. Preferably, the decolorizing can be accomplished by reacting the crude carboxylic acid solution in conduit 120 with hydrogen in conduit 130 in the presence of a catalyst in a reactor zone 125 to produce a decolorized carboxylic solution.
For the reactor zone 125, there are no special limitations in the form or construction thereof, subject to an arrangement that allows

supply of hydrogen in conduit 130 to effect intimate contact of the crude carboxylic acid solution in conduit 120 with the catalyst in the reactor zone 125. Typically, the catalyst is usually a single Group VIII metal or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combination thereof. Most preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably on porous carbon.
The reactor zone 125 comprises a hydrogenation reactor that operates at a temperature and pressure sufficient to hydrogenate the characteristically yellow compounds in the crude carboxylic acid solution in conduit 120. By hydrogenation treatment, the characteristically yellow compounds in the crude carboxylic acid solution are converted to colorless derivatives. The b* color of in the decolorized carboxylic acid solution in conduit 135 is between 0.5 to 4. Preferably the b* color of the carboxylic acid solution in conduit 135 is between 0.5 to 2.0. Most preferably the b* color in the carboxylic solution in conduit 135 is between 0.5 to 1.5. The b* is one of the three-color attributes .measured on a spectroscoplc reflectance-based instrument. The color can be measure by any device known in the art. A Hunter Ultrascan XE instrument is typically the measuring device. Positive readings signify .the degree of yellow (or absorbance of blue), while negative readings signify the degree of blue (or absqr-banoe of yellow).
The fiydrogen in conduit 130 is fed at a rate sufficient to convert the characteristically yellow compounds in the crude carboxylic slurry in

conduit 120 to colorless derivatives; wherein the b* color is between 0.5 to 4.0 in the decolorized carboxylic acid solution in conduit 135
. Step (3) comprises, optionally, flashing the decolorized carboxylic
acid solution 135 in a flashing zone 145 to remove a portion of the water
from the decolorized carboxylic acid solution in conduit 135. The
flashing of the aqueous carboxylic solution 135 can be accomplished by
any means know in the art. Typically, a vessel or a plurality of vessels
are used to accomplish the flashing. In the flashing zone 145, water and
residual hydrogen can be removed as a vapor via conduit 150. The
flash vessel(s) operate at a temperature sufficient to remove a portion of
-the water. Alternatively, flashing ~zbne 145 can be omitted as indicated
by conduit 140. .
Step (4) comprises, adding a diol in conduit 170 to the decolorized carboxylic acid solution in conduit 155. A portion of the water via conduit 165 is removed from an esterification reactor zone 160 to form said carboxyfic acid/diol mixture in the esterification reactor zone 160. The carboxylic acid and diol subsequently reacts to form a hydroxyalkyester stream 175.. The hydroxyalkyester stream 175 comprises a hydroxyalky ester compound.
The diol in conduit 170 is introduced in such a manner as to displace the water as the dominant slurrying liquid. This can be accomplished by introdueing a did via-conduit 170 as a saturated liquid at a temperature which is sufficient to vaporize the water. Preferably, the diol in conduit 170 is introduced as a saturated or superheated vapor. The diol in conduit 170 is selected from the group consisting of

ethylene glycot, diethylene glycol, n-butyiene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in conduit 170 isethylene glycol. Alternatively, an external heat source can be used to introduce sufficient enthalpy to vaporize the water, which exits via conduit 165. The hydroxalky ester stream exits via conduit stream 175.
The esterification reactor zone 160 operates at a temperature that is sufficient to produce a hydroxyethyt from the carboxylic acid mixture. The esterification reactor zone 160 comprises an esterification reactor. The esterification can be accomplished by any means know in the art.
In a'tfiird embodiment" of this invention a process for producing a terephthalic acid/diol comprises vaporizing a decolorized terephthalic acid solution with a diol in an esterification reactor zone to remove a portion of the water to form the terephthalic acid/diol mixture; wherein the terephthalic acid and diol subsequently reacts in the esterification zone to form a hydroxyalky ester stream.
The esterification reactor zone, the decolorized terephthalic acid solution and a process to produce the decolorized terephthalic acid solution is described subsequently in a fourth embodiment of this invention.
in the forth embodiment of this invention a process for producing aterepnthaHc aejd/diol mixture is provided as shown in Figure #2.
Step (1) comprises mixing a crude terephthalic acid powder in conduit 205 with water in conduit 215 in a mixing zone 210 to form a crude terephthalic acid solution in conduit 220. The mixing of the crude

terephthalic powder in conduit 205 with water in conduit 215 can be accomplished by any means known in the art. The starting feed material is the crude terephthalic acid powder in conduit 205 with some specific physical characteristics that differ from crude terephthalic add described in U.S. Patent 5,095,146 and U.S: Patent 5,175,355, herein incorporated by reference. Specifically, the total amount of p-toluic acid and 4-carboxybenzaldehyde in the crude terephthalic acid powder in conduit 205 is less than 900 ppm on a weight basis, preferably, less than 500 ppm, and most preferably, less than 250 ppm. Another characteristic of the crude terephthalic powder in conduit 205 is the color as measured by *,„ b*ls less fJiahT". "Preferably, the color measured by b* is between 4 and 6.
The mixing zone 210 can be. any vessel or equipment capable of mixing the crude terephthalic acid powder in conduit 205 with water in conduit 215. The crude terephthalic acid powder in conduit 205 is slurried in water in conduit 215 in the mixing zone 210 to produce the crude terephthalic acid solution in conduit 220. The crude terephthalic acid and water are heated in ,a mixing zone 210 to a temperature of 230 °C or higher to dissolve the crude terephthalic acid powder in conduit 205 in the mixing zone 210 to produce the crude terephthalic acid solution in conduit 220. Preferably, the crude terephthalic slurry in the mixing zone 21t) Is hea'ted to a temperature in the range of 240 °C to 300 °C. The pressure of the mixing zone is 900 psia to 1400 psia to dissolve the crude terephthalic acid powder in conduit 205 in the mixing

zone 210. Generally, the concentration of crude terephthalic acid in the crude terephthalic acid solution is 15% to 30% by weight, preferably, 20 to 30% by weight.
Step (2) \s decolorizing the crude terephthalic acid solution in conduit 220 in a reactor zone 225 to form a decolorized terephthalic acjd solution in conduit 235.
The decolorizing of the crude terephthalic acid solution in conduit 220 can be accomplished by any means known in the art. Preferably, the decolorizing can be accomplished by reacting the crude terephthalic acid solution in conduit 220 with hydrogen in conduit 230 in the presence of a catalyst in a "rea'ctor'zbhe 225" fo~ produce a decolorized terephthalic acid solution.
For the reactor zone 225, there are no special limitations In the form or construction thereof, subject to an arrangement that allows supply of hydrogen in conduit 230 to effect intimate contact of the crude terephthalic acid solution -in conduit 220 with the catalyst in the reactor zone 225. Generally, the catalyst is usually a single Group VIII metal or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combination thereof. Most preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably on porous carbon.
The reactor zone 225 comprises a hydrqgenation reactor Which operates at a temperature of 230 °C or higher. Preferably, the hydrogenation reactor operates in the range of 240°C to 300 °C. The

hydrogenation reactor operates at a pressure of 900 psia to 1400 psia and at a hydrogen partial pressure of at least 100 psia. Preferably, the hydrogen partial pressure is in the range of 100 to 300 psia. By hydrogenation treatment, the characteristically yellow compounds in the crude terephthalic acid solution are converted to colorless derivatives. In addition, the reactor zone converts a portion of 4-carboxybenzaldehyde to p-toluic acid. The hydrogen in conduit 230 is fed at a rate of at least 1.5 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude terephthalic acid solution in conduit 220 to p-toluic acid. Preferably, the hydrogen 230 is fed at a rate of at least 2.01im~e~s1he molar ratio necessary fo"convert the 4-carboxybenzaldehyde in the crude terephthalic acid solution 220 to p-toluic acid. The b* color is between 0.5 to 4 in the terephthalic acid decolorized solution in conduit 235. Preferably the b* color of the terephthalic acid solution in conduit 235 is between 0.5 to 2. Most preferably the b* color in the decolorized terephthalic acid solution in conduit 235 is between 0.5 to 1.5.
Step (3) comprises, optionally, flashing the decolorized terephthalic acid solution 235 in a flashing zone 245 to remove a portion of the water 250 from the aqueous terepthalic acid solution 235. The flashing of the aqueous terephthalic solution 235 can be accomplished by any means know in the art. Typically, a vessel or a plurality of vessels are used to accomplish the flashing. In the flashing zone 245, water and residual hydrogen can be removed as a vapor via conduit 250. The flash vessel(s) operate at a temperature of 150 °C or higher.

Preferably, the flash vessels(s) operate in the range of 155 °C to 260 °C. The flash vessel(s) operate under a pressure of 75 psia to 1400 psia. Specific operating ranges vary depending on the amount of water removed via conduit 250. Alternatively, flashing zone 245 can be omitted as indicated by conduit 240.
Step (4) comprises, adding a diol in conduit 270 to the decolorized terephthalic acid solution in conduit 255 in an esteriflcation reactor zone 260 to remove a portion of the water via conduit 265 to form said terephthalic acid/diol mixture in the esteriflcation reactor zone 260. The carboxylic acid and diol react to form a hydroxyalkyester stream"275. The'Hydroxyafkye'stef stream 275 comprises a hydroxyalky ester compound.
The diol in conduit 270 is introduced in such a manner as to displace the water as the dominant slurrying iiquid. This can be accomplished by introducing a diol via conduit 270 as a saturated liquid in a temperature range of 150 to 300 °C. Preferably, the diol in conduit 270 (s introduced as a saturated or superheated vapor in the temperature range of 150 to 300 °C in a form with sufficient enthalpy as to evaporate the water to exit via conduit 265. The diol in conduit 270 is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in conduit 270 is ethylene glycol. Alternatively, an external heat source can be used to introduce sufficient enthalpy to vaporize the water, which

exits via conduit 265. The hydroxalky! ester stream mixture exits via conduit stream 275.
The esterification reactor zone 260 operates at a temperature of 240 °C higher. Preferably the esterification reactor zone 260 operates in the temperature range of 260 °C to 280 °C. The esterification reactor zone 260 operates under a pressure of 40 psia to 100 psia so as to effect esterification of the terephthalic acid/diol mixture 275 to produce a hydroxyethyl ester of terephthaiic acid.
In a fifth embodiment of this invention, a process for producing a carboxylic acid/diol mixture comprises removing a portion of contaminated" water in an aqueous slurry by adding a diol in a liquor removal zone to produce said carboxylic acid/diol mixture.
The liquor removal zone, the aqueous slurry and a process to produce the aqueous slurry are described subsequently in a sixth embodiment of this invention.
In the six embodiment of this invention, a process for producing a carboxylic acid/diol mixture is provided as shown in Figure #3;
Step (1) comprises mixing a crude carboxylic acid powder in conduit 305 with water in conduit 315 in a mixing zone 310 to form a crude carboxylic acid solution in conduit 320. The mixing of the crude carboxylic powder in conduit 305 with water in conduit 315 in the mixing zone 310 can be accomplished by any means known in the art. The starting feed material is the crude carboxylic acid powder in conduit 305. Typically, the carboxylic acid is selected from a group consisting of

terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof. The mixing zone 310 can be any vessel or equipment capable of mixing the crude carboxylic acid powder in conduit 305 with water in conduit 315.
The crude carboxylic acid powder in conduit 305 and water in conduit 315 in mixing zone 310 is heated to a temperature sufficient to dissolve the crude carboxylic acid powder in conduit 305 in the mixing zone 310 to produce the crude carboxylic acid solution in conduit 320. The pressure of the mixing zone 310 is a pressure sufficient to dissolve the crude carboxylic acid powder in conduit 305 in the mixing zone 310. Generally, the concentratiorrof mrde'car&dxylfc'acfd iri the crude carboxylic acid solution is 15% to 35% by weight,
Step (2} is decolorizing the crude carboxyfic acid solution in conduit 320 in a reactor zone 325 to form an decolorized carboxylic acid solution in conduit 330.
The decolorizing of the crude carboxylic acid solution in conduit 320 can be accomplished by any means known in the art. Preferably, the decolorizing can be accomplished by reacting the crude carboxylic acid solution in conduit 320 with hydrogen in conduit 330 in the presence of a catalyst in a reactor zone 325 to produce a decolorized carboxyfic . acid solution.
For the reactor zone 325, there are no special limitations in the form or construction thereof, subject to an arrangement that allows supply of hydrogen in conduit 330 to effect intimate contact of the crude carboxylic slurry 320 with the catalyst in the reactor zone. Typically, the

catalyst is usually a single Group VIII metal or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combinations thereof. Most preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably on porous carbon.
The reactor zone 325 comprises a hydrogenation reactor that
operates at a temperature sufficient to convert the characteristically
yellow compounds in the crude carboxylic acid solution 320 to colorless
derivatives. The b* color of in the decolorized carboxylic acid solution in
conduit 335 is between 0.5 to 4. Preferably the b* color of the carboxylic
acid solution-irrconduit-335-is betwe'en 0:5~to~2. "Mbsf preferably the b*
color in the decolorized carboxylic acid solution in conduit 335 is
between 0.5 to 1.5. .
The hydrogen in conduit 330 is fed at a rate sufficient to convert the characteristically yellow compounds in the crude carboxylic slurry in conduit 320 to colorless derivatives; wherein the b* color is between 0.5 to 4 in the decolorized carboxylic acid solution in conduit 335.
Step (3) comprises crystallizing the decolorized carboxylic acid solution in conduit 335 in a crystallization zone 345 to form an aqueous slurry in conduit 355.
The crystallization zone 345 comprises a vessel or plurality of vessels capable of removing water fr-om -the decolorized carboxyfic acid solution in conduit 335 to produce an aqueous slurry in conduit 355. Typically, the vessels comprise at least one crystallizer. Examples of such systems can be found in U.S patents 5,567,842 and 3,931,305,

herein incorporated by reference. Generally, the aqueous slurry in conduit 355 has a carboxylic acid concentration of from 10 to 60 weight percent. The temperature range of the carboxyfic acid solution in the crystallization zone 345 is that which is sufficient to remove a portion of the water.
Step (4) comprises removing a portion of contaminated water via conduit 365 in the aqueous slurry 355 by adding a diol in conduit 370 in a liquor removal zone 360 to produce the carboxylic acid/diol mixture in conduit 375.
The purpose of the liquor removal zone 360 is to replace the contaminated-water with'aofoTiri condulf 370. The'cdntamiria'ted water comprises water and typical contaminants. The diol in conduit 370 is selected from the group consisting of ethylene gfycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in conduit 370 is ethylene glycol. The diol in conduit 370 is introduced into the liquor removal zone 360 via conduit 370. The removal of the contaminated water via conduit 365 in the liquor removal zone 360 can be accomplished using variety of techniques including; but not limited to, cyclones, centrifuges, and filters. The key factor In the liquor removal zone 360 is to select a temperature range where the typical contaminants preferably remain w'rth the-aqueous mother liquor instead of remaining with the carboxylic acid. The resultant carboxylic acid/diol mixture is removed via conduit 375. The resultant carboxylic acid/diol

mixture in conduit 375 is adequate as feed material for the esterification of carboxylic acid with the diol to produce the ester of carboxylic acid.
.In a seventh embodiment of this invention, a process for producing a terephthalic acid/diol mixture comprises removing a portion of the p-toJuic contaminated water in a terephthalic acid aqueous aqueous slurry by adding a diol in a liquor removal zone to produce said terephthalic acid/diol mixture.
The liquor removal zone, the terephthalic acid aqueous slurry and a process to produce the aqueous slurry are described subsequently in an eight embodiment of this invention.
1n mB~eig!it"embo~dtntent~tif this invention," a prbcesYfbr producing a terephthalic acid/diol mixture is provided as sho'wn in Figure #4.
Step (1) comprises mixing a crude terephthalic. acid powder in conduit 405 with water in conduit 415 in a mixing zone 410 to form a crude terephthalic acid solution in conduit 420. The mixing of the crude terephthalic powder in conduit 405 with water in conduit 415 in the mixing zone 410 can be accomplished by any means known in the art. The starting feed material is the crude terephthalic acid powder in conduit 405. The total amount of p-toluic acid and 4-carboxybenzaldehyde in the crude terephthalic acid powder in conduit .405 is less than 6000 ppm on a weight basis. Another characteristic of the crude terephthalic powder 405 is the color as measured by b* is less than 7. Preferably the color measured by b* is between 4 and 6. This crude terephthalic acid powder in conduit 405 is introduced into a mixing zone 410. The mixing zone 410 can be any vessel or equipment

capable of mixing the crude terephthalic acid powder in conduit 405 with water in conduit 415.
. The crude terephthalic acid powder and water are heated to a temperature of 230 °C or higher to dissolve the crude terephthalic acid powder in conduit 405 in the mixing zone 410 to produce the crude terephthalic acid solution in conduit 420. Preferably, the crude terephthalic acid, solution in the mixing zone 410 is heated to a temperature in the range of 240 °C to 300 °C. The pressure of the mixing zone 410 is 900 psia to 1400 psia to dissolve the crude terephthalic acid powder in conduit 405 in the mixing zone 410. ~Ge"nefany~ th~e~concentration"of crude terephthalic acid powder 405 in the crude terephthalic acid solution 420 is in a range of 15% to 35% by . weight, preferably 20 to 30% by weight.
Step (2) is decolorizing the crude terephthalic acid solution in conduit 420 in a reactor zone 425 to form a decolorized terephthalic acid solution in conduit 435.
The decolorizing of the crude carboxylic acid solution in conduit 420 can be accomplished by.any means known in the art. Preferably, the decolorizing can be accomplished by reacting the Crude carboxylic acid solution in conduit 420 with hydrogen in conduit 430 in the presence of a catalyst in a reactor zone 425 to produce a decolorized carboxylic aeid solution.
For the reactor zone 425, there are no special limitations in the form or construction thereof, subject to an arrangement that allows

supply of hydrogen in conduit 430 to effect contact of the crude terephthalic slurry 420 with the catalyst in the reactor zone. The catalyst is usually a single Group VIII metal or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combinations thereof. Most preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably on porous carbon.
The reactor zone 425 comprises a hydrogenation reactor which operates at a temperature of 230 °C or higher. Preferably the hydrogenation reactor operates in the range of 240°C to 300 °C. The hydrogenatfon reactor operates at a pressure of 900 psia to 1400 psia and at a hydrogen partial pressure of at least 100 psia. Preferably, the . hydrogen partial pressure is in the range of 100 to 300 psia. By hydrogenation treatment, the characteristically yeHow compounds in the
crude terephthalic acid solution 420 are converted to colorless derivatives. In addition, the reactor zone converts a portion of 4-carboxybenzaldehyde to p-toluic acid.
The hydrogen in conduit 430 is fed at a rate of at least 1.5 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude terephthalic slurry 420 to p-toluic acid. Preferably the hydrogen 430 is fed at a rate of at least 2.0 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude terephthalic slurry 420 to p-toluic acid. The b* color is between 0.5 to 4 in the decolorized terephthalic acid solution in conduit 435. Preferably the b* color of the

terephthalic acid solution in conduit 435 is between 0.5 to 2. Most preferably the b* color in the decolorized terephthalic acid solution in conduit 435 is between 0.5 to 1.5.
Step (3) comprises crystallizing said decolorized terephthalic acid solution in conduit 435 in a crystallization zone 445 to form a terephthalic acid aqueous slurry in conduit 455;
The crystallization zone 445 comprises a vessel or plurality of vessels capable of removing water via conduit 450 from the decolorized terephthalic acid solution in conduit 435 to produce an terephthalic acid aqueous slurry in conduit 455. Typically the vessels comprise at least one~crystat!Izef as prevfbusly described, "Generally;' fhe'terephYhalic acid aqueous slurry in conduit 455 has a terephthalic acid concentration of from 10 to 60 weight percent, preferably from 20 to 40 weight percent. Examples of such systems can be found in U.S. patents 5,567,842 and
y
3,931,305 both of which are herein incorporated by reference. The temperature range of the .terephthalic acid aqueous slurry in conduit 455 is from 120 °C to 270 "C. The pressure range of the crystallizing is from 75 to 1400 psia.
Step (4) comprises removing a portion of p-toluic acid contaminated water via conduit 465 in the terephthalic acid aqueous slurry 455 by adding a diol in conduit 470 in a liquor removal zone 460 to produce said terephthatic ac'rdfaiol mixture in conduit 475.
The purpose of the liquor removal zone 460 is to replace the p-toluic acid contaminated water with a diol in conduit 470. The dio! in conduit 470 is selected from a group consisting of ethylene glycol,

diethylene glycol, n-butyfene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in conduit 470 is ethylene glycol. The diol in, conduit
470 is introduced into the liquor removal zone 460 via conduit 470. The
removal of the p-toiuie acid contaminated water via conduit 465 in the liquor removal zone 460 can be accomplished .using variety of techniques including, but not limited to, cyclones, centrifugation, and filtration. The key factor in the liquor removal zone 460 is to select a temperature range where the p-to!uic acid and 4-carboxybenzaldehyde will preferably remain with the aqueous mother liquor instead of remaining with1heterephth"airc~a"cid."TrTe"irq"uor re"rrl6val z6ne~460~ operates in a range of 120 °C to 270 °C, preferably in the range of 120 . °C to 150 °C. The p-toluic acid contaminated water is removed via conduit 465. The resultant terephthalic acid/diol mixture is removed via conduit 475. The resultant terephthalic acid/diol mixture in conduit 475 is adequate as feed material for the esterification of terephthalic acid with 3 diol to produce the ester of terephthalic acid.

WE CLAIM:
1. A process for making a hydroxyalkyl ester wherein a carboxylic acid and at least one diol starting materials are esterified in an esterification zone, wherein said process includes obtaining a carboxylic acid and diol slurry without isolation of dry carboxylic acid solid, said process comprising optional steps of mixing a crude carboxylic acid powder with water to make a solution, decolorizing said carboxylic acid solution and flashing said decolorized carboxylic acid solution to form a decolorized carboxylic acid and water solution followed by adding a heated diol to the decolorized carboxylic acid and water solution in an esterification reactor zone to vaporize a portion of the water to form said carboxylic acid and diol slurry; wherein said diol is the dominant liquid and is heated to a temperature of from 150°C to 300°C and said esterification reactor zone is at a temperature of from 240°C to 280°C and a pressure of from 40 psia to 100 psia; wherein said carboxylic acid and diol subsequently reacts in said esterification zone to form a hydroxyalkyl ester.
2. The process as claimed in claim 1 wherein said carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof
3. The process as claimed in claim 1 wherein said process optionally comprises the following steps prior to adding the heated diol to the decolorized carboxylic acid and water solution:

(a) mixing a crude carboxylic acid powder with water in a mixing zone operated at a temperature greater than 230°C and a pressure of from 900 to 1400 psia to form a crude carboxylic acid solution; wherein the concentration of said carboxylic acid in said solution is from 15 to 35 weight %:
(b) decolorizing said crude carboxylic acid solution in a reactor zone by contacting said carboxylic acid solution with hydrogen at a temperature of from 230°C to 300°C and a pressure of from 900 psia to 1400 psia and in the

presence of a hydrogenation catalyst comprising a Group VIII metal to produce a decolorized carboxylic acid solution; and
(c) flashing said decolorized carboxylic acid solution in a flashing zone to remove a portion of the water from said decolorized carboxylic acid solution wherein said flashing zone is operated at a pressure of from 75 psia to 1400 psia and a temperature of from 150°C to 260°C to form a decolorized carboxylic acid and water mixture solution.
4. The process as claimed in claim 3 wherein said crude carboxylic acid powder is terephthalic acid powder having a concentration of p-toluic acid and 4- carboxybenzaldehyde of less than 900 ppm by weight.
5. The process as claimed in claim 3 wherein the step (c) optionally comprises the following steps prior to adding the heated diol to the decolorized carboxylic acid and water solution:
crystallizing said decolorized carboxylic acid solution in a crystallization zone having a temperature of 120°C to 270°C and a pressure of from 75 psia to 1400 psia to form an aqueous slurry having a carboxylic acid concentration of from 10 to 60 weight % in p-toluic acid contaminated water; and
removing a portion of the contaminated water in said aqueous slurry.
6. A process as claimed in claim 3 or 5 wherein said decolorizing reaction occurs at a hydrogen rate sufficient to produce a decolorized carboxylic acid solution with a b* color between 0.5 to 4.
7. The process as claimed in claim 5 wherein said carboxylic acid is terephthalic acid.

8. A process as claimed in claim 5 wherein said crude carboxylic acid is terephthalic acid powder containing a total concentration of p-toluic acid and 4-carboxybenzaldehyde of less than 6000 ppm by weight.
9. A process as claimed in any one of the above claims wherein said diol is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof.
10. A process as claimed in claim 8 wherein said crude terephthalic acid powder has a b* color of less than 7.
11. A process as claimed in claim 3 or 5 wherein said decolorization reaction occurs at a hydrogen flow rate of 1.5 times the molar ratio necessary to convert 4-carboxybenzaldehyde to p-toluic acid in said crude terephthalic solution.
12. A process as claimed in claim 1 wherein said adding of said diol occurs at a temperature between 120 °C to 270 °C.
13. A process as claimed in claim 5 wherein said crude carboxylic acid is terephthalic acid aqueous solution has a terephthalic acid concentration between 20% to 40% by weight.

Documents:

936-DELNP-2003-Correspondence-Others-27-05-2008.pdf

936-DELNP-2003-Others Document-27-05-2008.pdf

936-DELNP-2005-Abstract-(07-11-2008).pdf

936-DELNP-2005-Abstract-(16-10-2008).pdf

936-DELNP-2005-Abstract-19-05-2008.pdf

936-delnp-2005-abstract.pdf

936-DELNP-2005-Assignment-(15-09-2011).pdf

936-delnp-2005-assignments.pdf

936-DELNP-2005-Claims-(07-11-2008).pdf

936-DELNP-2005-Claims-(16-10-2008).pdf

936-DELNP-2005-Claims-19-05-2008.pdf

936-delnp-2005-claims.pdf

936-delnp-2005-complete specification (granted).pdf

936-DELNP-2005-Correspondence Others-(15-09-2011).pdf

936-DELNP-2005-Correspondence-Others-(16-10-2008).pdf

936-DELNP-2005-Correspondence-Others-19-05-2008.pdf

936-delnp-2005-correspondence-others.pdf

936-delnp-2005-description (complete)-19-05-2008.pdf

936-delnp-2005-description (complete).pdf

936-DELNP-2005-Drawings-19-05-2008.pdf

936-delnp-2005-drawings.pdf

936-DELNP-2005-Form-1-19-05-2008.pdf

936-delnp-2005-form-1.pdf

936-DELNP-2005-Form-16-(15-09-2011).pdf

936-delnp-2005-form-18.pdf

936-DELNP-2005-Form-2-19-05-2008.pdf

936-delnp-2005-form-2.pdf

936-DELNP-2005-Form-3-19-05-2008.pdf

936-delnp-2005-form-3.pdf

936-delnp-2005-form-5.pdf

936-DELNP-2005-GPA-(15-09-2011).pdf

936-DELNP-2005-GPA-(16-10-2008).pdf

936-DELNP-2005-GPA-19-05-2008.pdf

936-delnp-2005-gpa.pdf

936-DELNP-2005-Others Document-19-05-2008.pdf

936-delnp-2005-pct-101.pdf

936-delnp-2005-pct-210.pdf

936-delnp-2005-pct-220.pdf

936-delnp-2005-pct-308.pdf

936-delnp-2005-pct-408.pdf

936-delnp-2005-pct-409.pdf

936-delnp-2005-pct-416.pdf

936-delnp-2005-pct-notificatian.pdf

936-DELNP-2005-Petition-137-19-05-2008.pdf

936-DELNP-2005-Petition-138-19-05-2008.pdf

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Patent Number

225686

Indian Patent Application Number

936/DELNP/2005

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

20-Nov-2008

Date of Filing

10-Mar-2005

Name of Patentee

EASTMAN CHEMICAL COMPANY

Applicant Address

100 NORTH EASTMAN ROAD, KINGSPORT, TENNESSEE 37660, UNITED STATES OF AMERICA.

Inventors:

#	Inventor's Name	Inventor's Address
1	ROBERT LIN	4533 PALOMINO DRIVE, KINGSPORT, TENNESSEE 37664, U.S.A.

PCT International Classification Number

C07C 51/48

PCT International Application Number

PCT/US2003/031957

PCT International Filing date

2003-10-09

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10/271,058	2002-10-15	U.S.A.