Title of Invention	"METHOD AND SYSTEM FOR SEPARATING AND FILTERING CTA IN PREPARATION OF PURE TEREPHTHALIC ACID"
Abstract	A method for separating and filtering CTA in preparation of pure terephthalic acid, said method comprising: feeding CTA slurry into a rotary pressure filter for solid-liquid separation to obtain wet filter cakes, filtrated mother liquor, washing fluid and dehydrated gas respectively; removing impurities from part of the filtrated mother liquor; and recycling the rest filtrated mother liquor; before impurity removal of the filtrated mother liquor, a gas-liquid separation is performed to the total filtrated mother liquor firstly, to separate the gas therein.

Title of Invention

"METHOD AND SYSTEM FOR SEPARATING AND FILTERING CTA IN PREPARATION OF PURE TEREPHTHALIC ACID"

Abstract

A method for separating and filtering CTA in preparation of pure terephthalic acid, said method comprising: feeding CTA slurry into a rotary pressure filter for solid-liquid separation to obtain wet filter cakes, filtrated mother liquor, washing fluid and dehydrated gas respectively; removing impurities from part of the filtrated mother liquor; and recycling the rest filtrated mother liquor; before impurity removal of the filtrated mother liquor, a gas-liquid separation is performed to the total filtrated mother liquor firstly, to separate the gas therein.

Full Text	Description Method and system for separating and filtering CTA in preparation of pure terephthalic acid Technical Field The present invention relates to a method for separating and filtering CTA in preparation of pure terephthalic acid, and a system of applying the method. Background Art The traditional method for separating and filtering CTA is to apply a rotary vacuum filter (RVF) device, having a large filtering area and high power consumption; moreover, the temperature of feeding slurry of the filter must be within 88-90°C to meet the operation requirements of RVF; for this reason, the third section of crystallization shall be provided with a vacuum system, providing large amounts of cooling water for lowering the temperature of slurry; furthermore, there is no function zone division in RVF, that is, the filtrated mother liquor, washing fluid and dehydrated gas are all extracted from the same central tube, forming a mixed liquid; as a result, the washing fluid and the separated liquid of the dehydrated gas which have little impurity and do not need to be purified are mixed in the filtrated mother liquor needed to be purified, so that the mixed liquid must be delivered to the impurity removal device for purification, thereby increasing the amount of substance to be done i with impurity removal and impurity removal load, and raising the cost of purification treatment. Contents of Invention To overcome the deficiencies of existing technology, the present invention provides a method for separating and filtering CTA in preparation of pure terephthalic acid, and a system of applying the method; through the method and system, the power and water consumptions are greatly decreased, and the workload of impurity removal is reduced. The object of the invention is achieved by following technical schemes: A method for separating and filtering CTA in preparation of pure terephthalic acid comprises: feeding the CTA slurry into a rotary pressure filter for solid-liquid separation to obtain wet filter cakes, filtrated mother liquor, washing fluid and dehydrated gas respectively; removing impurities from part of the filtrated mother liquor; and recycling the rest filtrated mother liquor. The percentage of the filtrated mother liquor for impurity removal treatment generally should ensure that the impurity level of the system meets technical requirements. For example, the proportion between the amount of the filtrated mother liquor for impurity removal and the total amount of the filtrated mother liquor 2 can usually be 8-10%. Before impurity removal of the filtrated mother liquor, a gas-liquid separation shall be performed generally to the total filtrated mother liquor firstly to separate the gas therein; also gas-liquid separations shall be performed respectively to the washing fluid and the dehydrated gas; the wet filter cakes can be led into a drier to be dried. The gases formed after the gas-liquid separation of said filtrated mother liquor, the washing fluid and the dehydrated gas can be condensed in a centralized way, then the gases obtained after the condensation are recycled as inert gases (usually nitrogen) needed by the rotary pressure filter, and the liquid obtained after the condensation and the filtrated mother liquor free of impurity removal are recycled together; the liquids obtained respectively after the corresponding gas-liquid separation of the washing fluid and the dehydrated gas are also recycled together with the filtrated mother liquor free of impurity removal. A system for separating and filtering CTA in preparation of pure terephthalic acid comprises a rotary pressure filter, said rotary pressure filter being provided with CTA slurry inlet, washing fluid inlet, nitrogen inlet and wet filter cake outlet, filtrated mother liquor outlet, washing fluid outlet and dehydrated gas outlet, wherein said 3 filtrated mother liquor outlet is connected with a impurity removal device and a recycling tank which are provided in parallel with each other. The connection mode of said filtrated mother liquor outlet to the impurity removal device and the recycling tank can be in a mode that the filtrated mother liquor outlet is connected with a gas-liquid separation device for filtrated mother liquor through pipe(s), wherein the liquid outlet pipe(s) of said gas-liquid separation device for filtrated mother liquor include two ways, one of which is connected with the impurity removal device, and the other one is connected with said recycling tank. The washing fluid outlet can be connected with the washing fluid inlet of a gas-liquid separation device for washing fluid through pipe(s); the dehydrated gas outlet can be connected with the dehydrated gas inlet of a gas-liquid separation device for dehydrated gas through pipe(s); the wet filter cake outlet can be connected with a wet filter cake drier through a delivering device. The gas outlets of the gas-liquid separation device for filtrated mother liquor, the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas all can be connected with the gas inlet of a gas condenser through pipe(s); the gas outlet of said gas condenser can be connected with the gas 4 inlet of a gas compressor through pipe(s); the liquid outlet of said gas condenser can be connected with said recycling tank through pipe(s); the gas outlet of said gas compressor can be connected with the nitrogen inlet of said rotary pressure filter through pipe(s); the liquid outlets of the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas can be respectively connected with said recycling tank through pipe(s). The recycling tank can be connected to the oxidation reaction unit for the preparation of pure terephthalic acid to realize recycling. The beneficial effects of present invention are as follows: a rotary pressure filter (RPF) is utilized to replace the traditional rotary vacuum filter (RVF) for CTA separation, so as to separately collect the wet filter cakes, filtrated mother liquor, washing fluid and dehydrated gas; the washing fluid and dehydrated gas contain little impurity, thus only the filtrated mother liquor needs to be purified; under the condition that the impurity level of the system can be ensured to meet technical requirements of recycling, the impurity removal is needed for only part of the filtrated mother liquor, thereby effectively reducing the workload of impurity removal, reducing the requestment for handling capacity of relevant devices for impurity removal, lowering the investment, energy consumption, cost of the device, and the amount of the original useful materials 5 discharged along with the impurities; and decreasing CTA and cat loss, and residue emission; the nitrogen formed after the gas-liquid separation of the filtrated mother liquor, washing fluid and dehydrated gas is returned to RPF to be recycled, effectively saving a large number of nitrogen and lowering corresponding cost; most of the filtrated mother liquor and the liquid after the gas-liquid separation is delivered to the oxidation reaction unit to be recycled after centralized collection, therefore it decreases the consumption of relevant materials and saves the corresponding cost; RPF is capable of handling the materials with relatively high temperature, thereby reducing the cooling degree of previous process and the cooling water and relevant energy consumption; due to the wet filter cakes discharged with a higher temperature, thus reducing the vapor consumption in drying the wet filter cakes and the corresponding energy consumption. Description of Drawings Fig.1 is the flow chart of the present invention. Specific Mode for Carrying out the Invention As shown in Fig.1, the present invention applies a rotary pressure filter (RPF) to filter the crude terephthalic acid (CTA); the rotary pressure filter 1 usually comprises a liquid filter area, a acid washing area and nitrogen dehydrating area, and filter cake 6 discharge area; the crude terephthalic acid (CTA) slurry is firstly processed with pressure filtration, then washed with acid and dehydrated by nitrogen, to form wet filter cakes. The liquid filter area is provided with a filtrated mother liquor outlet; the acid washing area is provided with a washing fluid outlet; and the nitrogen dehydrating area is usually provided with a dehydrated gas outlet; consequently, a separation of the wet filter cakes, the filtrated mother liquor, the washing fluid and the dehydrated gas is realized. The filtrated mother liquor outlet is usually connected with the substance inlet of a gas-liquid separation device 2 for filtrated mother liquor through pipe(s); the washing fluid outlet is usually connected with the washing fluid inlet of a gas-liquid separation device 3 for washing fluid through pipe(s); the dehydrated gas outlet is usually connected with the dehydrated gas inlet of a gas-liquid separation device 4 for dehydrated gas through pipe(s); the wet filter cake outlet of the RPF is usually connected with a drier 10 through a delivering mechanism. Usually, the gas-liquid separation devices for filtrated mother liquor, washing fluid and dehydrated gas are all respectively provided with a gas outlet and a liquid outlet. The liquid outlet of the gas-liquid separation device for filtrated 7 mother liquor can be divided into two ways by a liquid flow distribution components 8 that have two outlets, one of which is connected with a impurity removal device 9 through pipe(s), and the other is connected with a recycling tank 7 through pipe(s). The flow distribution components can be a proportional flow control valve or other existing flow distribution devices. Usually, the liquid outlets of the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas are respectively connected with said recycling tank 7 through pipe(s), so that the liquid flowing through them and the filtrated mother liquor free of impurity removal treatment can be mixed there to be recycled. Through liquid filtration, the most impurities of CTA slurry enter into the filtrated mother liquor, the washing fluid and dehydrated gases contain little impurity, thus only the filtrated mother liquor needs to be processed with impurity removal. Before impurity removal, gas-liquid separation for the filtrated mother liquor is necessary so as to degas. Accordingly, the filtrated mother liquor discharged from the RPF usually firstly enters into the gas-liquid separation device for filtrated mother liquor; the filtrated mother liquor inwhich gas is separated out is usually not required to be fed into the impurity 8 removal device entirely; under the condition that the impurity level of the system can be ensured to meet requirements of the system, impurity removal can be performed only to part of the filtrated mother liquor after gas-liquid separation. The filtrated mother liquor delivered for impurity removal usually can be 8-10% of the total filtrated mother liquor, and the rest is usually delivered to the recycling tank to be recycled. The washing fluid and dehydrated gases after gas-liquid separation and degassing will be delivered into the recycling tank together with the filtrated mother liquor free of impurity removal treatment to be recycled. By the gas-liquid separation and recycling for liquid (mostly acid) after the gas-liquid separation, the large amounts of acid used in solid-liquid separation of CTA is effectively processed, thereby saving a large number of resources and investment cost. The gas outlets of the gas-liquid separation device for filtrated mother liquor, the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas are usually respectively connected to a gas condenser 5 through pipe(s), or can be firstly gathered to a main pipe through three pipes, then connected to the gas condenser 5. The gas condenser is usually provided with a gas (N2) outlet 9 and a liquid (acetic acid) outlet, wherein said gas outlet is usually connected with a gas compressor 6 through pipe(s), and said liquid outlet is usually connected with the recycling tank 7 through pipe(s). The gas compressor is usually connected with the nitrogen inlet of the nitrogen dehydrating area of the RPF through pipe(s). A large amount of N2 needs to be consumed for separation and filtration by the RPF; therefore a gas separation shall be performed to the gases discharged from each gas-liquid separation through the condenser, to separate the gaseous acetic acid out through condensation. Usually, cooling water is introduced into the condenser to condense the gaseous acetic acid. After delivering the mixed gases to the condenser to be condensed, the discharged gas (usually N2) enters into the gas compressor and is boosted by 1-1.5 bars, the gas pressure is regulated to the value required, then the gas can re-enter the gas inlet of said nitrogen dehydrating area of the RPF, to be reused. The acid (usually acetic acid) discharged from the condenser enters into the recycling tank along the pipe(s), to be recycled. The recycling tank is connected with the liquid materials inlet of said oxidation reaction unit through pipe(s). Usually following technical parameters are used: the 10 temperature of CTA slurry entering the rotary pressure filter is about 118°C, the washing acid thereinto is about 115°C, and N2 thereinto is about 70°C; the wet filter cake discharged from the rotary pressure filter is about 115°C, the filtrated mother liquor thereout is about 118°C, the washing fluid thereout is about 115°C, and the dehydrated gas thereout is about 100°C. As the CTA slurry enters the RPF at about 118°C, the consumption of the cooling water for temperature reduction used in three sections of crystallization in front procedure will be decreased by abut 40%, meanwhile a vacuum system for said three sections of crystallization and the relevant communal engineering consumptions (e.g. vapor and cooling water) that the vacuum system needed are saved, and the area for the condenser arranged in the three sections of crystallization is reduced by abut 50%. The wet filter cakes discharged from the RPF enters the drier to be dried, and their temperature is about 25°C higher than that of the wet filter cakes discharged from traditional process (the wet filter cakes discharged from the RVF is about 90°C), thereby reducing the amount of vapor used in later drying process. By the present invention, it can realize the recycling and reuses of N2, the filtrated mother liquor and the washing acid, and 11 reduce the handling load of impurity removal, and decrease the cooling degree in front procedures and the heating degree of drying the wet filter cakes in latter procedures. 12 Claims 1. A method for separating and filtering CTA in preparation of pure terephthalic acid, said method comprising: feeding CTA slurry into a rotary pressure filter for solid-liquid separation to obtain wet filter cakes, filtrated mother liquor, washing fluid and dehydrated gas respectively; removing impurities from part of the filtrated mother liquor; and recycling the rest filtrated mother liquor; before impurity removal of the filtrated mother liquor, a gas-liquid separation is performed to the total filtrated mother liquor firstly, to separate the gas therein. 2. The method for separating and filtering CTA in preparation of pure terephthalic acid according to claim 1, wherein the percentage of the filtrated mother liquor for impurity removal treatment should ensure that the impurity level of the system meets technical requirements. 3. The method for separating and filtering CTA in preparation of pure terephthalic acid according to claim 2, wherein the proportion between the amount of the filtrated mother liquor for impurity removal and the total amount of the filtrated mother liquor is 8-10%. 4. The method for separating and filtering CTA in preparation of pure terephthalic acid according to claim 1, 2 or 3, wherein, also gas-liquid separations are performed respectively to the washing fluid and the dehydrated gas; the wet filter cakes are led into a drier to be dried. 5. The method for separating and filtering CTA in preparation of pure terephthalic acid according to claim 4, wherein the gases formed after the gas-liquid separation of the filtrated mother liquor, the washing fluid and the dehydrated gas are condensed in a centralized way, then the gases obtained after the condensation are recycled as nitrogen needed by the rotary pressure filter, and the liquid obtained after the condensation and the filtrated mother liquor free of impurity removal are recycled together; the liquids obtained respectively after the corresponding gas-liquid separation of the washing fluid and the dehydrated gas are also recycled together with the filtrated mother liquor free of impurity removal. 6. A system for separating and filtering CTA in preparation of pure terephthalic acid, said system comprising a rotary pressure filter, and the rotary pressure filter is provided with CTA slurry inlet, washing fluid inlet, nitrogen inlet and wet filter cake outlet, filtrated mother liquor outlet, washing fluid outlet and dehydrated gas outlet, wherein said filtrated mother liquor outlet is connected with a impurity removal device and a recycling tank which are provided in parallel with each other; the connection mode of said filtrated mother liquor outlet to the impurity removal device and the recycling tank is in a mode that the filtrated mother liquor outlet is connected with a gas-liquid separation device for filtrated mother liquor through pipe(s), wherein the liquid outlet pipe(s) of said gas-liquid separation device for filtrated mother liquor include two ways, one of which is connected with the impurity removal device, and the other one is connected with said recycling tank. 7. The system for separating and filtering CTA in preparation of pure terephthalic acid according to claim 6, wherein the washing fluid outlet is connected with the washing fluid inlet of a gas-liquid separation device for washing fluid through pipe(s); the dehydrated gas outlet is connected with the dehydrated gas inlet of a gas-liquid separation device for dehydrated gas through pipe(s); the wet filter cake outlet is connected with a wet filter cake drier through a delivering device. 8. The system for separating and filtering CTA in preparation of pure terephthalic acid according to claim 7, wherein the gas outlets of the gas-liquid separation device for filtrated mother liquor, the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas are all connected with the gas inlet of a gas condenser through pipe(s); the gas outlet of said gas condenser is connected with the gas inlet of a gas compressor through pipe(s); the liquid outlet of said gas condenser is connected with said recycling tank through pipe(s); the gas outlet of said gas compressor can be connected with the nitrogen inlet of said rotary pressure filter through pipe(s); the liquid outlets of the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas are respectively connected with said recycling tank through pipe(s). 9. The system for separating and filtering CTA in preparation of pure terephthalic acid according to claim 6, 7 or 8, wherein the recycling tank is connected to the oxidation reaction unit for the preparation of pure terephthalic acid.

Full Text

Description
Method and system for separating and filtering CTA in preparation
of pure terephthalic acid Technical Field
The present invention relates to a method for separating and filtering CTA in preparation of pure terephthalic acid, and a system of applying the method. Background Art
The traditional method for separating and filtering CTA is to apply a rotary vacuum filter (RVF) device, having a large filtering area and high power consumption; moreover, the temperature of feeding slurry of the filter must be within 88-90°C to meet the operation requirements of RVF; for this reason, the third section of crystallization shall be provided with a vacuum system, providing large amounts of cooling water for lowering the temperature of slurry; furthermore, there is no function zone division in RVF, that is, the filtrated mother liquor, washing fluid and dehydrated gas are all extracted from the same central tube, forming a mixed liquid; as a result, the washing fluid and the separated liquid of the dehydrated gas which have little impurity and do not need to be purified are mixed in the filtrated mother liquor needed to be purified, so that the mixed liquid must be delivered to the impurity removal device for purification, thereby increasing the amount of substance to be done
i

with impurity removal and impurity removal load, and raising the cost of purification treatment. Contents of Invention
To overcome the deficiencies of existing technology, the present invention provides a method for separating and filtering CTA in preparation of pure terephthalic acid, and a system of applying the method; through the method and system, the power and water consumptions are greatly decreased, and the workload of impurity removal is reduced.
The object of the invention is achieved by following technical schemes:
A method for separating and filtering CTA in preparation of pure terephthalic acid comprises: feeding the CTA slurry into a rotary pressure filter for solid-liquid separation to obtain wet filter cakes, filtrated mother liquor, washing fluid and dehydrated gas respectively; removing impurities from part of the filtrated mother liquor; and recycling the rest filtrated mother liquor.
The percentage of the filtrated mother liquor for impurity removal treatment generally should ensure that the impurity level of the system meets technical requirements. For example, the proportion between the amount of the filtrated mother liquor for impurity removal and the total amount of the filtrated mother liquor
2

can usually be 8-10%.
Before impurity removal of the filtrated mother liquor, a gas-liquid separation shall be performed generally to the total filtrated mother liquor firstly to separate the gas therein; also gas-liquid separations shall be performed respectively to the washing fluid and the dehydrated gas; the wet filter cakes can be led into a drier to be dried.
The gases formed after the gas-liquid separation of said filtrated mother liquor, the washing fluid and the dehydrated gas can be condensed in a centralized way, then the gases obtained after the condensation are recycled as inert gases (usually nitrogen) needed by the rotary pressure filter, and the liquid obtained after the condensation and the filtrated mother liquor free of impurity removal are recycled together; the liquids obtained respectively after the corresponding gas-liquid separation of the washing fluid and the dehydrated gas are also recycled together with the filtrated mother liquor free of impurity removal.
A system for separating and filtering CTA in preparation of pure terephthalic acid comprises a rotary pressure filter, said rotary pressure filter being provided with CTA slurry inlet, washing fluid inlet, nitrogen inlet and wet filter cake outlet, filtrated mother liquor outlet, washing fluid outlet and dehydrated gas outlet, wherein said
3

filtrated mother liquor outlet is connected with a impurity removal device and a recycling tank which are provided in parallel with each other.
The connection mode of said filtrated mother liquor outlet to the impurity removal device and the recycling tank can be in a mode that the filtrated mother liquor outlet is connected with a gas-liquid separation device for filtrated mother liquor through pipe(s), wherein the liquid outlet pipe(s) of said gas-liquid separation device for filtrated mother liquor include two ways, one of which is connected with the impurity removal device, and the other one is connected with said recycling tank.
The washing fluid outlet can be connected with the washing fluid inlet of a gas-liquid separation device for washing fluid through pipe(s); the dehydrated gas outlet can be connected with the dehydrated gas inlet of a gas-liquid separation device for dehydrated gas through pipe(s); the wet filter cake outlet can be connected with a wet filter cake drier through a delivering device.
The gas outlets of the gas-liquid separation device for filtrated mother liquor, the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas all can be connected with the gas inlet of a gas condenser through pipe(s); the gas outlet of said gas condenser can be connected with the gas
4

inlet of a gas compressor through pipe(s); the liquid outlet of said gas condenser can be connected with said recycling tank through pipe(s); the gas outlet of said gas compressor can be connected with the nitrogen inlet of said rotary pressure filter through pipe(s); the liquid outlets of the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas can be respectively connected with said recycling tank through pipe(s).
The recycling tank can be connected to the oxidation reaction unit for the preparation of pure terephthalic acid to realize recycling.
The beneficial effects of present invention are as follows: a rotary pressure filter (RPF) is utilized to replace the traditional rotary vacuum filter (RVF) for CTA separation, so as to separately collect the wet filter cakes, filtrated mother liquor, washing fluid and dehydrated gas; the washing fluid and dehydrated gas contain little impurity, thus only the filtrated mother liquor needs to be purified; under the condition that the impurity level of the system can be ensured to meet technical requirements of recycling, the impurity removal is needed for only part of the filtrated mother liquor, thereby effectively reducing the workload of impurity removal, reducing the requestment for handling capacity of relevant devices for impurity removal, lowering the investment, energy consumption, cost of the device, and the amount of the original useful materials
5

discharged along with the impurities; and decreasing CTA and cat loss, and residue emission; the nitrogen formed after the gas-liquid separation of the filtrated mother liquor, washing fluid and dehydrated gas is returned to RPF to be recycled, effectively saving a large number of nitrogen and lowering corresponding cost; most of the filtrated mother liquor and the liquid after the gas-liquid separation is delivered to the oxidation reaction unit to be recycled after centralized collection, therefore it decreases the consumption of relevant materials and saves the corresponding cost; RPF is capable of handling the materials with relatively high temperature, thereby reducing the cooling degree of previous process and the cooling water and relevant energy consumption; due to the wet filter cakes discharged with a higher temperature, thus reducing the vapor consumption in drying the wet filter cakes and the corresponding energy consumption. Description of Drawings
Fig.1 is the flow chart of the present invention. Specific Mode for Carrying out the Invention
As shown in Fig.1, the present invention applies a rotary pressure filter (RPF) to filter the crude terephthalic acid (CTA); the rotary pressure filter 1 usually comprises a liquid filter area, a acid washing area and nitrogen dehydrating area, and filter cake
6

discharge area; the crude terephthalic acid (CTA) slurry is firstly processed with pressure filtration, then washed with acid and dehydrated by nitrogen, to form wet filter cakes. The liquid filter area is provided with a filtrated mother liquor outlet; the acid washing area is provided with a washing fluid outlet; and the nitrogen dehydrating area is usually provided with a dehydrated gas outlet; consequently, a separation of the wet filter cakes, the filtrated mother liquor, the washing fluid and the dehydrated gas is realized.
The filtrated mother liquor outlet is usually connected with the substance inlet of a gas-liquid separation device 2 for filtrated mother liquor through pipe(s); the washing fluid outlet is usually connected with the washing fluid inlet of a gas-liquid separation device 3 for washing fluid through pipe(s); the dehydrated gas outlet is usually connected with the dehydrated gas inlet of a gas-liquid separation device 4 for dehydrated gas through pipe(s); the wet filter cake outlet of the RPF is usually connected with a drier 10 through a delivering mechanism.
Usually, the gas-liquid separation devices for filtrated mother liquor, washing fluid and dehydrated gas are all respectively provided with a gas outlet and a liquid outlet.
The liquid outlet of the gas-liquid separation device for filtrated
7

mother liquor can be divided into two ways by a liquid flow distribution components 8 that have two outlets, one of which is connected with a impurity removal device 9 through pipe(s), and the other is connected with a recycling tank 7 through pipe(s).
The flow distribution components can be a proportional flow control valve or other existing flow distribution devices.
Usually, the liquid outlets of the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas are respectively connected with said recycling tank 7 through pipe(s), so that the liquid flowing through them and the filtrated mother liquor free of impurity removal treatment can be mixed there to be recycled.
Through liquid filtration, the most impurities of CTA slurry enter into the filtrated mother liquor, the washing fluid and dehydrated gases contain little impurity, thus only the filtrated mother liquor needs to be processed with impurity removal.
Before impurity removal, gas-liquid separation for the filtrated mother liquor is necessary so as to degas.
Accordingly, the filtrated mother liquor discharged from the RPF usually firstly enters into the gas-liquid separation device for filtrated mother liquor; the filtrated mother liquor inwhich gas is separated out is usually not required to be fed into the impurity
8

removal device entirely; under the condition that the impurity level of the system can be ensured to meet requirements of the system, impurity removal can be performed only to part of the filtrated mother liquor after gas-liquid separation.
The filtrated mother liquor delivered for impurity removal usually can be 8-10% of the total filtrated mother liquor, and the rest is usually delivered to the recycling tank to be recycled.
The washing fluid and dehydrated gases after gas-liquid separation and degassing will be delivered into the recycling tank together with the filtrated mother liquor free of impurity removal treatment to be recycled.
By the gas-liquid separation and recycling for liquid (mostly acid) after the gas-liquid separation, the large amounts of acid used in solid-liquid separation of CTA is effectively processed, thereby saving a large number of resources and investment cost.
The gas outlets of the gas-liquid separation device for filtrated mother liquor, the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas are usually respectively connected to a gas condenser 5 through pipe(s), or can be firstly gathered to a main pipe through three pipes, then connected to the gas condenser 5.
The gas condenser is usually provided with a gas (N2) outlet
9

and a liquid (acetic acid) outlet, wherein said gas outlet is usually connected with a gas compressor 6 through pipe(s), and said liquid outlet is usually connected with the recycling tank 7 through pipe(s).
The gas compressor is usually connected with the nitrogen inlet of the nitrogen dehydrating area of the RPF through pipe(s).
A large amount of N2 needs to be consumed for separation and filtration by the RPF; therefore a gas separation shall be performed to the gases discharged from each gas-liquid separation through the condenser, to separate the gaseous acetic acid out through condensation. Usually, cooling water is introduced into the condenser to condense the gaseous acetic acid.
After delivering the mixed gases to the condenser to be condensed, the discharged gas (usually N2) enters into the gas compressor and is boosted by 1-1.5 bars, the gas pressure is regulated to the value required, then the gas can re-enter the gas inlet of said nitrogen dehydrating area of the RPF, to be reused.
The acid (usually acetic acid) discharged from the condenser enters into the recycling tank along the pipe(s), to be recycled.
The recycling tank is connected with the liquid materials inlet of said oxidation reaction unit through pipe(s).
Usually following technical parameters are used: the
10

temperature of CTA slurry entering the rotary pressure filter is about 118°C, the washing acid thereinto is about 115°C, and N2 thereinto is about 70°C; the wet filter cake discharged from the rotary pressure filter is about 115°C, the filtrated mother liquor thereout is about 118°C, the washing fluid thereout is about 115°C, and the dehydrated gas thereout is about 100°C.
As the CTA slurry enters the RPF at about 118°C, the consumption of the cooling water for temperature reduction used in three sections of crystallization in front procedure will be decreased by abut 40%, meanwhile a vacuum system for said three sections of crystallization and the relevant communal engineering consumptions (e.g. vapor and cooling water) that the vacuum system needed are saved, and the area for the condenser arranged in the three sections of crystallization is reduced by abut 50%.
The wet filter cakes discharged from the RPF enters the drier to be dried, and their temperature is about 25°C higher than that of the wet filter cakes discharged from traditional process (the wet filter cakes discharged from the RVF is about 90°C), thereby reducing the amount of vapor used in later drying process.
By the present invention, it can realize the recycling and reuses of N2, the filtrated mother liquor and the washing acid, and
11

reduce the handling load of impurity removal, and decrease the cooling degree in front procedures and the heating degree of drying the wet filter cakes in latter procedures.
12

Claims
1. A method for separating and filtering CTA in preparation of pure terephthalic acid, said method comprising: feeding CTA slurry into a rotary pressure filter for solid-liquid separation to obtain wet filter cakes, filtrated mother liquor, washing fluid and dehydrated gas respectively; removing impurities from part of the filtrated mother liquor; and recycling the rest filtrated mother liquor; before impurity removal of the filtrated mother liquor, a gas-liquid separation is performed to the total filtrated mother liquor firstly, to separate the gas therein.
2. The method for separating and filtering CTA in preparation of pure terephthalic acid according to claim 1, wherein the percentage of the filtrated mother liquor for impurity removal treatment should ensure that the impurity level of the system meets technical requirements.
3. The method for separating and filtering CTA in preparation of pure terephthalic acid according to claim 2, wherein the proportion between the amount of the filtrated mother liquor for impurity removal and the total amount of the filtrated mother liquor is 8-10%.
4. The method for separating and filtering CTA in preparation of pure terephthalic acid according to claim 1, 2 or 3, wherein, also

gas-liquid separations are performed respectively to the washing fluid and the dehydrated gas; the wet filter cakes are led into a drier to be dried.
5. The method for separating and filtering CTA in preparation of pure terephthalic acid according to claim 4, wherein the gases formed after the gas-liquid separation of the filtrated mother liquor, the washing fluid and the dehydrated gas are condensed in a centralized way, then the gases obtained after the condensation are recycled as nitrogen needed by the rotary pressure filter, and the liquid obtained after the condensation and the filtrated mother liquor free of impurity removal are recycled together; the liquids obtained respectively after the corresponding gas-liquid separation of the washing fluid and the dehydrated gas are also recycled together with the filtrated mother liquor free of impurity removal.
6. A system for separating and filtering CTA in preparation of pure terephthalic acid, said system comprising a rotary pressure filter, and the rotary pressure filter is provided with CTA slurry inlet, washing fluid inlet, nitrogen inlet and wet filter cake outlet, filtrated mother liquor outlet, washing fluid outlet and dehydrated gas outlet, wherein said filtrated mother liquor outlet is connected with a impurity removal device and a recycling tank which are provided in parallel with each other; the connection mode of said filtrated

mother liquor outlet to the impurity removal device and the recycling tank is in a mode that the filtrated mother liquor outlet is connected with a gas-liquid separation device for filtrated mother liquor through pipe(s), wherein the liquid outlet pipe(s) of said gas-liquid separation device for filtrated mother liquor include two ways, one of which is connected with the impurity removal device, and the other one is connected with said recycling tank.
7. The system for separating and filtering CTA in preparation of pure terephthalic acid according to claim 6, wherein the washing fluid outlet is connected with the washing fluid inlet of a gas-liquid separation device for washing fluid through pipe(s); the dehydrated gas outlet is connected with the dehydrated gas inlet of a gas-liquid separation device for dehydrated gas through pipe(s); the wet filter cake outlet is connected with a wet filter cake drier through a delivering device.
8. The system for separating and filtering CTA in preparation of pure terephthalic acid according to claim 7, wherein the gas outlets of the gas-liquid separation device for filtrated mother liquor, the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas are all connected with the gas inlet of a gas condenser through pipe(s); the gas outlet of said gas condenser is connected with the gas inlet of a gas compressor

through pipe(s); the liquid outlet of said gas condenser is connected with said recycling tank through pipe(s); the gas outlet of said gas compressor can be connected with the nitrogen inlet of said rotary pressure filter through pipe(s); the liquid outlets of the gas-liquid separation device for washing fluid and the gas-liquid separation device for dehydrated gas are respectively connected with said recycling tank through pipe(s).
9. The system for separating and filtering CTA in preparation of pure terephthalic acid according to claim 6, 7 or 8, wherein the recycling tank is connected to the oxidation reaction unit for the preparation of pure terephthalic acid.

Documents:

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Patent Number

279315

Indian Patent Application Number

1279/DELNP/2012

PG Journal Number

03/2017

Publication Date

20-Jan-2017

Grant Date

18-Jan-2017

Date of Filing

10-Feb-2012

Name of Patentee

CHINA NATIONAL PETROLEUM CORPORATION

Applicant Address

NO. 9, DONGZHIMEN NORTH STREET, DONGCHENG DISTRICT, BEIJING 100007, CHINA.

Inventors:

#	Inventor's Name	Inventor's Address
1	RUIKUI YAO	NO. 21, ZENGGUANG ROAD, HAIDIAN DISTRICT, BEIJING 100037, CHINA.
2	WENDE LUO	NO. 21, ZENGGUANG ROAD, HAIDIAN DISTRICT, BEIJING 100037, CHINA.
3	HUATANG ZHOU	NO. 21, ZENGGUANG ROAD, HAIDIAN DISTRICT, BEIJING 100037, CHINA.
4	CHUN ZHANG	NO. 21, ZENGGUANG ROAD, HAIDIAN DISTRICT, BEIJING 100037, CHINA.
5	YINGZHI WANG	NO. 21, ZENGGUANG ROAD, HAIDIAN DISTRICT, BEIJING 100037, CHINA.

PCT International Classification Number

C07C 51/42

PCT International Application Number

PCT/CN2009/075363

PCT International Filing date

2009-12-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	200910090509.9	2009-08-13	China