Title of Invention	"A METHOD FOR THE CONTINUOUS ESTERIFICATION OF TEREPHTHALIC ACID WITH 1, 4-BUTANEDIOL, AN ESTERIFICATION REACTOR FOR PERFORMING THE METHOD AND A DEVICE FOR THE MANUFACTURE OF POLYBUTYLENE TEREPHTHALATE"
Abstract	Method for the coccentraction terephtalic acid with butanediol, method for the manufacture of polybutylene terephtalate and a device therefor The present invention relates to an improved method for the esterification of terephthalic acid with 1,4-butanediol, an improved method for the manufacture of polybutylene terephtalate as well as reactors and devices that are suited for the application in this method.

Title of Invention

"A METHOD FOR THE CONTINUOUS ESTERIFICATION OF TEREPHTHALIC ACID WITH 1, 4-BUTANEDIOL, AN ESTERIFICATION REACTOR FOR PERFORMING THE METHOD AND A DEVICE FOR THE MANUFACTURE OF POLYBUTYLENE TEREPHTHALATE"

Abstract

Method for the coccentraction terephtalic acid with butanediol, method for the manufacture of polybutylene terephtalate and a device therefor The present invention relates to an improved method for the esterification of terephthalic acid with 1,4-butanediol, an improved method for the manufacture of polybutylene terephtalate as well as reactors and devices that are suited for the application in this method.

Full Text	Method for the esterificatiou of terevbtalic acid with butanediol. method for the manufacture of Dolybutvlene terephtalate and a device therefor The present invention relates to a method for the esterification of terephthalic acid with butanediol, a method for the manufacture of polybutylene terephtalate as well as devices appropriate for this method. The manufacture of polybutylene terephtalate (PBT) from terephtalic acid (TPA) and 1,4-butanediol (BD) is known fi-om prior art. in prior art, PBT is usually manufactured in a continuous three-stage method, hi a first reaction stage, the so-called esterification stage, TPA is esterified with BD and hydroxybutyl groups formed in parallel. The esterification product is subsequently subjected to a first polycondensation in a second reaction stage, the so-called prepolycondensation stage. in the terminating third stage, the polycondensation stage, a further polycondensation to the final medium to high viscous product is finally performed. Such methods are known, for example, from the US 6,590,062 B2 as well as the US 6,359,106 Bl. in the methods described therein, in the first esterification stage, TPA is reacted with BD to form an oligomeric esterification product with a number average of the degree of polycondensation of 2 to 5. Subsequently, a usual further processing by condensation reactions is performed. Similar methods are also disclosed in the US citations US 4,680,376 as well as US 5,015,759. These citations include that the TPA turnover in the esterification stage or the esterification degree of the TPA is usually 95%. in this context, the EP 0 869 141 Al discloses that it is preferred to observe a molar ratio of BD:TPA of 1.1 to 1,6 in the esterification stage, in case of turnovers, based on TPA, of approx. 97%. The examples of this European patent application also show that in the manufacture of polybutylene terephtalate, in the esterification stage already, oligomeric products are formed into the esterification reactors. The US 4,656,241 and the US 4,780,527 also describe methods for the manufacture of polybutylene terephtalate where a relatively low molar ratio of BD:TPA is used. The US 4,656,241, for example, describes a molar ratio of 0.4 to 1.3. With regard to the devices that are appropriate for the manufacture of polybutylene terephtalate and in particular for the esterification stage, the prior art discloses usual reactors, in particular stirred tank reactors. The use of such conventional stirred tank reactors is indicated, for example, in the European applications EP 0 431 977 A2 and EP 1 189 968 Al. Similar systems describing the first esterification stage as stirred tank reactor are also disclosed in WO 01/00704 Al, WO 02/098947 Al, and DE 101 27 146 Al. With regard to the reaction procedure of the first discontinuous reaction stage for the esterification, the US 4,346,213 fmally discloses that it is important for the reaction product of the esterification stage to still contain unreacted terephtalic acid, approx. 10 to 30 weight percent, to obtain better polymerisation results. in connection with known continuous manufacturing methods for polybutylene terephtalate, the prior art discloses that the esterification has to be performed in stirring stages by which esterification products with a mean polycondensation degree of approx. 2 to 5 can be obtained. in this case, the TPA turnover should not be too high as it turned out to be advantageous if still unreacted TPA remains in the esterification product as thus an improvement of the polycondensation results can be achieved. Furthermore, the above discussed prior art discloses with respect to the esterification reaction as well as with respect to the polycondensation reaction for the manufacture of polybutylene terephtalate that catalysts are employed, in particular catalysts based on organic titaniimi compoimds. Typical titanium compounds appropriate for this purpose are alkyl titanates, as they are, for example, disclosed in the international patent publications WO 01/00704 Al and WO 02/098947 Al. A disadvantage of the conventional manufacturing methods for polybutylene terephtalate is, however, that the required, comparably large amounts of catalyst lead to the final polymerisation product containing relatively high proportions of imdesired compounds introduced into the method product by the catalyst. Furthermore, the catalysts employed for the polycondensation are liable to hydrolysis, which has negative effects on the reaction procedure as well as on the quality of the final polymer. Due to these disadvantages of the prior art, the following problems in the manufacture of polybutylene terephtalate can occur: - Increasing yellowing in the final p - Superimposed blue and grey - Reduced L-value - Tendency to a secondary photolytic greying of product surfaces and extreme reduction of the white degree in UV-light catalyst precipitations - Polymer turbidity - Risk of formation of residues in continuous operation - Reduced filterability of product melts. The object of the present invention is thus to provide an improved method for the manufacture of polybutylene terephtalate by which the above-mentioned problems are overcome individually, partially or altogether. Short description of the invention The inventors of the present application surprisingly found out that a new design of the esterification stage permits to provide an improved method for the manufacture of polybutylene terephtalate. The essential improvement concerns the procedural method of the esterification stage. A new and inventive esterification method for the reaction of TPA with BD is defined in claim 1 according to the invention. Preferred embodiments of this method are specified in claims 2 to 8. Claim 9 characterises the method according to the invention for the manufacture of polybutylene terephtalate. Claims 10 to 15 define preferred embodiments of this method. Claims 16 to 20 finally disclose devices appropriate for performing the methods according to the invention. Short description of the flgures Figure I shows a flow chart of a continuous method for the manufacture of polybutylene terephtalate in conformity with the present invention. Figures 2 to 4 show preferred embodiments of the reactor according to the invention for the esterification stage. Figure 5 shows a schematic plan view of a reactor in conformity with the present invention. Detailed description of the invention The present invention is in particular ciiaracterised in that a new method procedure for the esterification of TPA and BD is provided. This new method procedure is characterised in that the reaction procedure described in the prior art for the esterification in a stirred tanlc reactor is modified such that in the esterification, after a first stirred esterification zone, a follow-up zone is provided in the esterification stage, the follow-up zone being characterised in that the reaction mixture is not stirred in this follow-up zone. By this reaction procedure, back-mixing is avoided or suppressed in the follow-up zone. The individual stages of the esterification according to the invention will be described below. First, the components necessary for the esterification of TPA and BD, that means in particular the above-mentioned starting products TPA and BD, as well as a common catalyst, preferably on titanium basis, are provided. The catalyst is here preferably provided as solution, preferably in the form of a diolic solution, in particular 1,4-butanediol as main component of the solvent is preferred. The starting compounds TPA and BD can first be transformed to a pasty starting mixture with a molar ratio of BD to TPA of 1.0 to 1.8, where an overall feed-in molar ratio, together with the 1,4-butanedioi to be recycled via the process column, of 2 to 4, preferably 2.8 to 3.8, in particular preferred 3.0 to 3.5, is adjusted. These starting products, i.e. the pasty startmg mixture as well as the catalyst solution, possibly m combination with the recycled process diol, can then be fed into the reactor for the esterification reaction in an appropriate and usual manner. Apart fi"om the components essential according to the invention, appropriate fiirther components can be also introduced into the esterification stage, as long as the esterification reaction is not affected thereby. in this context, in particular common additives for the desired final product, such as stabilizers, etc., or additional components facilitating the reaction procedure, are suited. Furthermore, it is possible according to the invention to add fiirther diol components and/or dicarboxylic acid components to the above-mentioned starting substances TPA and BD, as long as the essential proportion of the starting monomers consists of TPA and BD. By metered addition of further diol components and/or dicarboxylic components, it is possible to produce mixed esterification products from which copolyesters can be obtained in a subsequent condensation. However, the use of TPA and BD as dicarboxylic acid component or diol component, respectively, is preferred. The esterification reaction according to the invention is preferably performed at pressures below atmospheric pressure. in particular, pressures of less than 800 mbar are preferred, in particular preferred are 350 to 600 mbar, more preferred 400 to 500 mbar. The temperature of the esterification reaction in conformity with the present invention is preferably higher than 230°C, in particular prefeired from 235 to 250°C, more preferred from 239 to 246^C. According to the invention, the esterification reaction is fiirthermore preferably controlled such that the mean degree of polycondensation (Pn) is greater than 3, more preferred greater than 3.5, in particular preferred 5 to 6. The TPA turnover is preferably more than 97.5%, more preferred more than 98%; in particular preferred are 99.0% to 99.7%. The average residence time (IR) of the starting components m the esterification reaction is preferably less than 2.5 hours, more preferred less than 2.3 hours; in particular preferred are 1.7 to 2.25 hours. As already illustrated above, the esterification reaction in conformity with the present invention is characterised in that after a stirred first reaction zone, a follow-up zone without stirring is provided. in view of the reaction time stated above (mean residence time), it is preferred for the follow-up phase to make up at least 5% of the complete time, preferably 7 to 15% of the complete esterification time, more preferred 8 to 14%. According to the invention, in the continuous stationary method, it is preferred for the isobaric two-step reaction procedure according to the invention to be designed such that after a stirred reaction zone, a stir-free follow-up zone is provided. According to the invention, it is in particular preferred to realise a plug flow in the follow-up zone where no stirring is performed. The method according to the invention can be preferabl}' performed continuously, the starting products first being infroduced into the first reaction zone in an appropriate maimer (see, for example, the two above-mentioned international applications). An appropriate method procedure principally known to the person skilled in the art ensures that the incorporated starting components are withdrawn from the reactor after the desired reaction time. Furthermore, by corresponding dimensioning of the reactor, comprising the stirred first reaction zone as well as the non-stirred follow-up zone, the advantageous residence time distribution according to the invention between the stirred reaction zone and the non-stirred follow-up zone is ensured. in this context, it is particularly preferred for the follow-up zone to make up at least 5 Voi.-% of the whole volume availabk for the esterification reaction, in particular 7 to 15 Vol.-%, and more preferred 8 to 14 Vol.-% of the whole reaction volume. hi view of the reaction procedure in the follow-up zone it is essential that here no sturing is performed any more, so that back-mixing is excluded as far as possible. According to the invention, a very high turnover, based on TPA, can thus be achieved. Moreover, here BD can be additionally fed in. Appropriate amounts of BD for such a feeding into the follow-up zone are, based on the originally fed-in TPA, up to 10 mole %. it is furthermore preferred if volatile components in the follow-up zone, in particular water and possibly BD, are withdrawn from the reaction mixture. Here, a reduction of the vaporizable product components, in particular water and BD, to approx. 30 to 60% of the concentration in the stirred reaction zone is preferred. To this end, it is also possible to increase the reaction temperature during the foliow-up phase in comparison to the stirred reaction phase. According to the invention, by the esterification stage in conformity with the present application, a homogenous esterification product of TPA and BD is obtained, with a TPA turnover of more than 98%, with a mean polycondensation degree of more than 3. The preferred embodiments illustrated above m connection with the reaction procedure, in particular with respect to the TPA turnover and the degree of polymerization, apply to the product obtained at the end of the esterification reaction. With the homogeneity and gas freedom of the esterification product, accordmg to the invention a stable flow rate control and a stationary flow rate are achieved in the continuous overall process. This product can in particular be used for the manufacture of polybutylene terephtalate, preferably in conformity with a conventional method procedure, as described above in connection whh the prior art. Such a conventional reaction procedure comprises, following the esterification stage, a first and a second condensation stage, i.e. precondensation and polycondensation. According to the invention, it is preferred in this context for the pressure to be further reduced in the ftirther condensation stages, in the first condensation stage (precondensation) pressures of 5 to 50 mbar, particularly preferred 10 to 25 mbar, being observed. For the terminating second condensation stage (polycondensation), the pressure is preferably reduced to 0.5 to 2.0 mbar, tn particular preferred 0.7 to 1.3 mbar. in view of the reaction temperatures, usual process adjustments are appropriate. Preferably, however, the temperature during precondensation is 235 to 245°C, more preferred 238 to 242°C, while the temperature during polycondensation is 240 to 250°C, more preferred 242 to 248°C. The mean residence time for precondensation is preferably 30 to 70 minutes, more preferred 40 to 60 minutes, and for polycondensation 100 to 170 minutes, more preferred 120 to 150 minutes. Precondensation and polycondensation can be appropriately performed in usual reactors. Such reactors are known to the person skilled in the art and described for precondensation for example in the WO 2004/033526 and in the DE 102004038466. hi case of polycondensation, for example the descriptions in DE1745541 and DEi 02004053199 apply. According to the invention, in this context it is in particular preferred if the foUow-up zone of the esterification is followed by an inlet zone in the precondensation which is neither stirred. This inlet zone preferably makes up at least 25%, preferably 35 to 65% of the precondensation time. According to the invention, polybutylene terephtalate can thus be produced with a good yield and satisfying reaction time. it surprisingly showed that by the special reaction procedure in the esterification, the amount of catalyst, in particular titanium catalyst, required for the complete reaction, is clearly reduced. This also reduces the problems occurring in connection with the catalyst employment and discussed above. Thus, product quality can in particular be increased and the method procedure can be simplified. Due to the reduced demand for catalyst, the fiher lives, for example, are increased by more than 50%. Due to the reduced demand for catalyst, furthermore the costs for the manufacture of polybutylene terephtalate are reduced. Quality penalties due to catalysts, such as colour deficiencies and photolytic greying, are also reduced according to the invention. Such an improvement of the reaction results could not be expected on the basis of the information of the prior art. According to the invention, it is particularly preferred if the complete required catalyst amount for the manufacture of polybutylene terephtalate is already fed to the esterification stage. This in particular reduces the amount of equipment required as well as the requirements with respect to the method procedure for the subsequent stages of precondensation and polycondensation. As already illustrated above, by the method design of the first stage according to the invention, the complete catalyst demand for the manufacture of polybutylene terephtalate can be clearly reduced. According to the invention, it was found that the catalyst demand is reduced as the TPA turnover a increases or the residual acid proportion s = 100 - a is reduced. Due to the reduced use of catalyst, there is a reduction of the yellow value b and an increase of the white degree of the manufactured polymeric products. The catalyst component that is preferably introduced into the reaction in the form of a diolic solution according to the invention in addition preferably comprises stabilizing components. in particular, a stabilization of the catalyst solution with TPA is preferred. A method according to the invention for the manufacture of polybutylene terephtalate is described below with reference to Figure 1. TPA is fed to a stirring vessel (1) via line (2) and BD is fed to the stirring vessel (1) via line (3) and they are mixed to form a paste that is fed via line (4) to a stirred tank reactor (7) surrounded by a heating jacket (5) and equipped with an additional heating element (6) for esterification. During esterification, a liquid BD-oligomer mixture and vapour are formed, the latter essentially comprising water, BD and tetrahydrofliran (THF). Esterification in the stirred tank reactor (7) is performed in the presence of the catalyst solution supplied via line (8). The vapour formed in the stirred tank reactor (7) leaves the stirred tank reactor (7) via line (9) and is supplied to the distillation column (10) where water and THF are separated overhead. The overhead product of the distillation column (10) is supplied via line (11) to the cooling apparatus (12) from which the condensate flows to the reflux distributor via line (14). From the reflux distributor (14), water and THF are withdrawn via line (15) and the reflux is returned to the head of the distillation column (10) via line (16). From the bottom of the distillation column, a mixture predominantly consisting of bulanediol is withdrawn via line (17). Via line (18), alkyl titanate is added to the mixture flowing in line (17) by metered addition, resulting in a composition desired for the catalyst solution. The mixture passes a mixture section (19), and via line (8), the produced catalyst solution reaches the stirred tank reactor (7). The catalyst solution can be completely or partially also charged to the stirred vessel (1) via line (20) and/or fed to the paste flow via line (21) into line (4) and/or fed to the transfer line (23) for the esterification product formed in the stirred tank reactor (7) to the precondensation reactor (24). The reactor (24) has a heating jacket (25) and an additional heating element (26). Via line (27), the precondensate from the reactor (24) is supplied to the polycondensation reactor (28). The produced PBT is ptimped off via line (29). The formed vapours are sucked off via line (30) from reactor the (24) and via line (31) from the reactor (28), According to the invention, the reactor (7) comprises, in addition to the indicated stirred reaction zone, a non-stirred follow-up zone. Examples of such reactors are disclosed in Figures 2 to 4. The reaction procedure according to the invention permits a reduction of the catalyst use when the non-stirred fofiow-up zone of the esterification stage is employed. By the method procedure according to the invention, in this case high turnovers of TPA are achieved which are clearly above the prior art as appropriate turnovers. it surprisingly showed according to the invention that it is not a disadvantage to obtain a very high TPA turnover at the end of the esterification stage. The high TPA turnover, in combination with the molar ratio of BD to TPA to be observed according to the invention, ensures stabilization and possibly a reactivation of catalyst proportions which are converted to harmful decomposition products by hydrolysis in the prior art. Due to the method procedure according to the invention, in particular in the follow-up zone of the esterification stage and in the inlet zone of the precondensation, a reactivation of catalyst components can be achieved as the oxidation stage of the catalyst metal can be maintained and the formation of hydroxides liable to precipitation can be prevented. in this context, in particular the futher removal of volatile components in the follow-up zone is advantageous, as with a reduced water content of the esterification mixture and an increased molar ratio of BD to water, a reduced liability to catalyst hydrolysis can be observed. A reactor according to the invention for performing the above-described esterification reaction comprises an esterification reactor with a vertical vessel axis, a beatable jacket, a central inlet chamber with separate connections for feeding the raw materials as paste and the catalyst as diolic solution, a coaxial stirrer for dispersing the charge, and a submerged damper register for transmitting the required process heat. The reactor according to the invention furthermore includes a foliow-up zone, preferably a peripheral follow-up chamber, in particular suited for subsequent dissolution of solid TPA from the inlet chamber and homogenisation of the esterification mixture with a flow with only little back-mixing under isobaric conditions. According to the invention, an appropriate follow-up zone is in particular realized in that the inlet chamber above the damper register is enclosed by a radially enlarged internal container opened at the top, and the follow-up zone is designed between the internal container and the external heated container wall as ring channel with a connection to the common steam room opened at the top. The channel depth for the follow-up zone is preferably less than 800 mm, more preferred 700 mm or less, and in particular preferred 350 mm to 700 mm. in Figure 2, an esterification reactor according to the invention is shown. This reactor comprises a Robert evaporator (RV) and a stirring element (RO) at the bottom with radial discharge. Above the evaporator, the reaction room is conicaJly extended up to a cylindrical head region (ZK). A radially enlarged internal container, consisting of an initial cone (above the external reactor cone situated at the bottom) and a cylindrical board at the edge at the external cone end, divides the reactor into an internal central mlet chamber (EK) and an external follow-up chamber (NK) in the form of a ring channel inclined at the side of the cone with a cylindrical degassing gap at the reactor wall opened at the top. The walls contacted by the product are surrounded by an external heating jacket area. The internal area, with the radial-discharge stirring element at the bottom, is the room for the stirred zone of the esterification, while the follow-up chamber represents the non-stirred follow-up zone. in Figure 3, an alternative conception is disclosed where the upper base plate (OBF) of the evaporator at the same time forms the lower limiting wall of the external follow-up zone in line with the radial enlargement of the reactor room. The first conical, then cylindrical internal container dividing the reaction room into a central internal chamber and an external follow-up chamber at the edge begins at this base plate. A propeller mixer (RO) in the vertical downpipe of the damper register serves for product circulation and improved raw material distribution in the first zone. Figure 4 finally shows a further modified reactor conception with a pear-shaped reactor vessel and a damper register with separate jacket and convex base plates lowered into the tapered bottom space of the reactor. Between the bottom container jacket and the register jacket, there is a free gap for an external down-current of the product corresponding to a vertical up-current in the heating tubes. A stirrer (RO) with upward discharge above the upper tube bottom serves direct admixing and dispersion of the charge fed from above into the central inlet chamber. The division of the upper reaction room into the central inlet chamber (EK) and a peripheral follow-up chamber (NK) in the form of an external ring channel has a design similar to the arrangement already described in Figure 2. in Figures 2 to 4, furthermore the filling level is indicated. Below the line (* ^ ^), there is the (liquid) reaction mixture, the steam room is located above, possibly together with some foam. Figure 5 finally shows a schematic plan view onto a reactor in conformity with the present invention, with an internally disposed stirred reaction zone (GRZ) and an externally surrounding follow-up zone (NZ), as well as a central channel, e.g. for attaching (ZK) a stirring element. Such a reactor for esterification can be connected with further known devices for precondensation and polycondensation. The equipment conception of the continuation of the non-stirred follow-up zone of the esterification into an inlet zone of tfie precondensation in particular preferred according to the invention was already described above. The equipment conception of the prepolycondensation stage as sequence of at least one level bottom and a stirred discharge bottom is already described in the EF 1 478 677 which is incorporated herein by reference. The flow channels are here preferably self-emptying and free from a dead space, as described in the German patent application DE 10 2004 38 466.5. This apphcation, too, is included herein by reference. As end reactor for the polycondensation of the precondensate, all reactor types appropriate for this purpose and known to the person skilled in the art can be used, as in particular storing disk or cage reactors, preferably stirring disk reactors. Example and Comparative Example The degree of polycondensation mentioned in the application which is, for example, described in connection with the esterification, can be determined in confonnity with the following embodiments. The acid number (AN) is measured in mg KOH per gram of esterification product added by weighing. The non-reacted acid end groups of the product dissolved in dimethyl formamide are determined by means of titration with alcoholic KOH from the difference to a blind sample. The saponification number (SN) is also measured in mg KOH per gram of esterification product added by weighing. Here, the esterification product is reacted with boiling alcoholic KOH and the remaining KOH is titrimetrically determined, As the esterification product added by weighing also contains free diol, water and non-reacting additives, their percentage by mass (ADD) also has to be determined. The saponification number corresponds to the complete employed amount of acid end groups, while the acid number represents the not yet reacted acid end groups. Therefore, the TPA turnover e is: Embodiment: in a continuous polycondensation plant with an esterification stage (ES) similar to that of Fig. 2, precondensation (prepoly stage (PP)), equipped with an inlet chamber with a residence time of 15 min, and a polycondensation stage with a ring disk reactor (DRR), the following parameters were adjusted: The esterification was operated with a fed molar ratio of BD to TPA of 3.3, the residence time in the follow-up zone was 12 min, the channel depth was 560 mm, the employed catalyst was 60 ppm in the final product. in the esterification, there was a turnover of 99.6% and a degree of polycondensation of 6, the final product with an intrinsic viscosity of 0.95 had a chromatic value b of 1.2. in the first stirred zone of esterification, aturaover of 97.9% was achieved. The plant was equipped with a prepoly filter which had a mean life of 5 - 6 weeks under the mentioned conditions. Comparative Example: in the same plant, however without follow-up zone in the esterification stage, the following parameters were employed: The fed molar ratio was 2.9 and the employed catalyst was 90 ppm. in the esterification, there was a turnover of 97.8% and a degree ofpolycondensafionof4.7, the final product had an intrinsic viscosity of 0.93 with a chromatic value b of 3. The expected fiUer life in this case was only 3-4 weeks. Laboratory tests in a simple stirring vessel with a residence time of 60 to 90 min at temperatures of 240 to 248°C and pressures of 400 to 500 mbar showed varying turnovers of between 95% and 98%, even at high catalyst concentrations of 120 ppm to 250 ppm. Only by the high preliminary turnover in the stirred zone in connection with the employment of the follow-up zone, the tumover could be increased to more than 99%. At the same time, the required amount of catalyst was reduced, the colour of the final product was clearly improved and the filter lives were increased. Thus, these examples show that the advantages described in the application can be realized by the new and inventive technical teaching of the present application. Patent Claims Method for the continuous esterification of terephtalic acid with 1,4-butanedioi, :haracterised in that terephtalic acid and 1,4-butanediol are reacted in a two-stage sobaric reaction procedure, comprising a first, stirred reaction zone and a second, ion-stirred follow-up zone. Method according to claim 1, wherein the reaction product of the esterification eaction comprises an acid turnover, based on terephtalic acid, of more than 98%. Method according to claim 1 or 2, wherein the reaction product of the sterification reaction comprises a mean polycondensation degree of more than 3. Method according to one of claims 1 to 3, wherein the second reaction zone, the ion-stirred follow-up zone, contains at least 5% of the complete reaction time of he esterification reaction. Method according to one of claims 1 to 4, wherem for the esterification a mean esidence time tR of less than 2.5 hours is observed. 4ethod according to one of claims 1 to 5, wherein an esterification catalyst in the brm of a diolic solution is employed. Method according to claim 6, wherein the esterification catalyst is a catalyst based in titanium. Method for the continuous manufacture of polybutylene terephtalate, comprising he reaction stages of esterification, precondensation and polycondensation, vherein the esterification is designed in conformity with one of claims 1 to 7. Method according to claim 8, wherein the complete amount of catalyst required or the manufacture of polybutylene terephtalate is added in the esterification Method accordii g to one of claims 8 or 9, wherein the non-stirred follow-up zone of esterification iirectly passes over into a non-stirred inlet zone of the precondensation Method accordir g to one of claims 8 to 10, wherein the pressure in the precondensation is lower than the pressure in the esterification and wherein the pressure in the p )lycondensation is lower than the pressure in the precondensation. Method accordii g to one of claims 8 to 11, wherein the pressure in the precondensation is lower than 50 mbar. Method accordir g to one of claims 8 to 12, wherein the temperature in the precondensation is equal to or lower than the temperature during polycondensation. Method accordir g to one of claims 8 to 13, wherein the polycondensation is performed in a stirring disk reactor. Esterification re; ctor, appropriate for performing the method according to one of claims 1 to 7, CO nprising a stirred tank reactor as well as a non-stirred follow-up zone, wherein the follow-up zone is arranged around a stirred internal container as ring channel rad: ally disposed outside. Reactor accordir g to claim 15, wherein the follow-up zone as well as the stirred internal containe comprise a common steam room. Reactor accordir g to one of claims 15 and 16, wherein the follow-up zone designed as ring channel has a channel depth of 300 to 700 mm. Device for the manufacture of polybutylene terephtalate, comprising at least one esterification reactor, at least one precondensation reactor and at least one polycondensatio i reactor, wherein the at least one esterification reactor is selected from reactors in conformity with claims 15 to 17. advice according to claim 18, wherein the at least one polycondensation reactor is tirring disk reactor. Dated this 20 day of August 2008

Full Text

Method for the esterificatiou of terevbtalic acid with butanediol. method for the manufacture of Dolybutvlene terephtalate and a device therefor
The present invention relates to a method for the esterification of terephthalic acid with butanediol, a method for the manufacture of polybutylene terephtalate as well as devices appropriate for this method.
The manufacture of polybutylene terephtalate (PBT) from terephtalic acid (TPA) and 1,4-butanediol (BD) is known fi-om prior art.
in prior art, PBT is usually manufactured in a continuous three-stage method, hi a first reaction stage, the so-called esterification stage, TPA is esterified with BD and hydroxybutyl groups formed in parallel. The esterification product is subsequently subjected to a first polycondensation in a second reaction stage, the so-called prepolycondensation stage. in the terminating third stage, the polycondensation stage, a further polycondensation to the final medium to high viscous product is finally performed.
Such methods are known, for example, from the US 6,590,062 B2 as well as the US 6,359,106 Bl. in the methods described therein, in the first esterification stage, TPA is reacted with BD to form an oligomeric esterification product with a number average of the degree of polycondensation of 2 to 5. Subsequently, a usual further processing by condensation reactions is performed.
Similar methods are also disclosed in the US citations US 4,680,376 as well as US 5,015,759. These citations include that the TPA turnover in the esterification stage or the esterification degree of the TPA is usually 95%.
in this context, the EP 0 869 141 Al discloses that it is preferred to observe a molar ratio of BD:TPA of 1.1 to 1,6 in the esterification stage, in case of turnovers, based on TPA, of approx. 97%. The examples of this European patent application also show that in the manufacture of polybutylene terephtalate, in the esterification stage already, oligomeric products are formed into the esterification reactors. The US 4,656,241 and the US 4,780,527 also describe methods for the manufacture of polybutylene terephtalate where a relatively low

molar ratio of BD:TPA is used. The US 4,656,241, for example, describes a molar ratio of 0.4 to 1.3.
With regard to the devices that are appropriate for the manufacture of polybutylene terephtalate and in particular for the esterification stage, the prior art discloses usual reactors, in particular stirred tank reactors. The use of such conventional stirred tank reactors is indicated, for example, in the European applications EP 0 431 977 A2 and EP 1 189 968 Al. Similar systems describing the first esterification stage as stirred tank reactor are also disclosed in WO 01/00704 Al, WO 02/098947 Al, and DE 101 27 146 Al.
With regard to the reaction procedure of the first discontinuous reaction stage for the esterification, the US 4,346,213 fmally discloses that it is important for the reaction product of the esterification stage to still contain unreacted terephtalic acid, approx. 10 to 30 weight percent, to obtain better polymerisation results.
in connection with known continuous manufacturing methods for polybutylene terephtalate, the prior art discloses that the esterification has to be performed in stirring stages by which esterification products with a mean polycondensation degree of approx. 2 to 5 can be obtained. in this case, the TPA turnover should not be too high as it turned out to be advantageous if still unreacted TPA remains in the esterification product as thus an improvement of the polycondensation results can be achieved. Furthermore, the above discussed prior art discloses with respect to the esterification reaction as well as with respect to the polycondensation reaction for the manufacture of polybutylene terephtalate that catalysts are employed, in particular catalysts based on organic titaniimi compoimds. Typical titanium compounds appropriate for this purpose are alkyl titanates, as they are, for example, disclosed in the international patent publications WO 01/00704 Al and WO 02/098947 Al.
A disadvantage of the conventional manufacturing methods for polybutylene terephtalate is, however, that the required, comparably large amounts of catalyst lead to the final polymerisation product containing relatively high proportions of imdesired compounds introduced into the method product by the catalyst. Furthermore, the catalysts employed for the polycondensation are liable to hydrolysis, which has negative effects on the reaction procedure as well as on the quality of the final polymer. Due to these disadvantages of the prior art, the following problems in the manufacture of polybutylene terephtalate can occur:

- Increasing yellowing in the final p
- Superimposed blue and grey
- Reduced L-value
- Tendency to a secondary photolytic greying of product surfaces and extreme reduction of the white degree in UV-light catalyst precipitations
- Polymer turbidity
- Risk of formation of residues in continuous operation
- Reduced filterability of product melts.
The object of the present invention is thus to provide an improved method for the manufacture of polybutylene terephtalate by which the above-mentioned problems are overcome individually, partially or altogether.
Short description of the invention
The inventors of the present application surprisingly found out that a new design of the esterification stage permits to provide an improved method for the manufacture of polybutylene terephtalate. The essential improvement concerns the procedural method of the esterification stage. A new and inventive esterification method for the reaction of TPA with BD is defined in claim 1 according to the invention. Preferred embodiments of this method are specified in claims 2 to 8. Claim 9 characterises the method according to the invention for the manufacture of polybutylene terephtalate. Claims 10 to 15 define preferred embodiments of this method. Claims 16 to 20 finally disclose devices appropriate for performing the methods according to the invention.
Short description of the flgures
Figure I shows a flow chart of a continuous method for the manufacture of polybutylene terephtalate in conformity with the present invention. Figures 2 to 4 show preferred embodiments of the reactor according to the invention for the esterification stage. Figure 5 shows a schematic plan view of a reactor in conformity with the present invention.

Detailed description of the invention
The present invention is in particular ciiaracterised in that a new method procedure for the esterification of TPA and BD is provided. This new method procedure is characterised in that the reaction procedure described in the prior art for the esterification in a stirred tanlc reactor is modified such that in the esterification, after a first stirred esterification zone, a follow-up zone is provided in the esterification stage, the follow-up zone being characterised in that the reaction mixture is not stirred in this follow-up zone. By this reaction procedure, back-mixing is avoided or suppressed in the follow-up zone. The individual stages of the esterification according to the invention will be described below.
First, the components necessary for the esterification of TPA and BD, that means in particular the above-mentioned starting products TPA and BD, as well as a common catalyst, preferably on titanium basis, are provided. The catalyst is here preferably provided as solution, preferably in the form of a diolic solution, in particular 1,4-butanediol as main component of the solvent is preferred. The starting compounds TPA and BD can first be transformed to a pasty starting mixture with a molar ratio of BD to TPA of 1.0 to 1.8, where an overall feed-in molar ratio, together with the 1,4-butanedioi to be recycled via the process column, of 2 to 4, preferably 2.8 to 3.8, in particular preferred 3.0 to 3.5, is adjusted. These starting products, i.e. the pasty startmg mixture as well as the catalyst solution, possibly m combination with the recycled process diol, can then be fed into the reactor for the esterification reaction in an appropriate and usual manner. Apart fi"om the components essential according to the invention, appropriate fiirther components can be also introduced into the esterification stage, as long as the esterification reaction is not affected thereby. in this context, in particular common additives for the desired final product, such as stabilizers, etc., or additional components facilitating the reaction procedure, are suited. Furthermore, it is possible according to the invention to add fiirther diol components and/or dicarboxylic acid components to the above-mentioned starting substances TPA and BD, as long as the essential proportion of the starting monomers consists of TPA and BD. By metered addition of further diol components and/or dicarboxylic components, it is possible to produce mixed esterification products from which copolyesters can be obtained in a subsequent condensation. However, the use of TPA and BD as dicarboxylic acid component or diol component, respectively, is preferred.

The esterification reaction according to the invention is preferably performed at pressures below atmospheric pressure. in particular, pressures of less than 800 mbar are preferred, in particular preferred are 350 to 600 mbar, more preferred 400 to 500 mbar. The temperature of the esterification reaction in conformity with the present invention is preferably higher than 230°C, in particular prefeired from 235 to 250°C, more preferred from 239 to 246^C.
According to the invention, the esterification reaction is fiirthermore preferably controlled such that the mean degree of polycondensation (Pn) is greater than 3, more preferred greater than 3.5, in particular preferred 5 to 6. The TPA turnover is preferably more than 97.5%, more preferred more than 98%; in particular preferred are 99.0% to 99.7%.
The average residence time (IR) of the starting components m the esterification reaction is preferably less than 2.5 hours, more preferred less than 2.3 hours; in particular preferred are
1.7 to 2.25 hours.
As already illustrated above, the esterification reaction in conformity with the present invention is characterised in that after a stirred first reaction zone, a follow-up zone without stirring is provided. in view of the reaction time stated above (mean residence time), it is preferred for the follow-up phase to make up at least 5% of the complete time, preferably 7 to 15% of the complete esterification time, more preferred 8 to 14%.
According to the invention, in the continuous stationary method, it is preferred for the isobaric two-step reaction procedure according to the invention to be designed such that after a stirred reaction zone, a stir-free follow-up zone is provided. According to the invention, it is in particular preferred to realise a plug flow in the follow-up zone where no stirring is performed.
The method according to the invention can be preferabl}' performed continuously, the starting products first being infroduced into the first reaction zone in an appropriate maimer (see, for example, the two above-mentioned international applications). An appropriate method procedure principally known to the person skilled in the art ensures that the incorporated starting components are withdrawn from the reactor after the desired reaction time. Furthermore, by corresponding dimensioning of the reactor, comprising the stirred first

reaction zone as well as the non-stirred follow-up zone, the advantageous residence time distribution according to the invention between the stirred reaction zone and the non-stirred follow-up zone is ensured. in this context, it is particularly preferred for the follow-up zone to make up at least 5 Voi.-% of the whole volume availabk for the esterification reaction, in particular 7 to 15 Vol.-%, and more preferred 8 to 14 Vol.-% of the whole reaction volume.
hi view of the reaction procedure in the follow-up zone it is essential that here no sturing is performed any more, so that back-mixing is excluded as far as possible. According to the invention, a very high turnover, based on TPA, can thus be achieved. Moreover, here BD can be additionally fed in. Appropriate amounts of BD for such a feeding into the follow-up zone are, based on the originally fed-in TPA, up to 10 mole %.
it is furthermore preferred if volatile components in the follow-up zone, in particular water and possibly BD, are withdrawn from the reaction mixture. Here, a reduction of the vaporizable product components, in particular water and BD, to approx. 30 to 60% of the concentration in the stirred reaction zone is preferred. To this end, it is also possible to increase the reaction temperature during the foliow-up phase in comparison to the stirred reaction phase.
According to the invention, by the esterification stage in conformity with the present application, a homogenous esterification product of TPA and BD is obtained, with a TPA turnover of more than 98%, with a mean polycondensation degree of more than 3. The preferred embodiments illustrated above m connection with the reaction procedure, in particular with respect to the TPA turnover and the degree of polymerization, apply to the product obtained at the end of the esterification reaction.
With the homogeneity and gas freedom of the esterification product, accordmg to the invention a stable flow rate control and a stationary flow rate are achieved in the continuous overall process.
This product can in particular be used for the manufacture of polybutylene terephtalate, preferably in conformity with a conventional method procedure, as described above in connection whh the prior art. Such a conventional reaction procedure comprises, following

the esterification stage, a first and a second condensation stage, i.e. precondensation and polycondensation.
According to the invention, it is preferred in this context for the pressure to be further reduced in the ftirther condensation stages, in the first condensation stage (precondensation) pressures of 5 to 50 mbar, particularly preferred 10 to 25 mbar, being observed. For the terminating second condensation stage (polycondensation), the pressure is preferably reduced to 0.5 to 2.0 mbar, tn particular preferred 0.7 to 1.3 mbar. in view of the reaction temperatures, usual process adjustments are appropriate. Preferably, however, the temperature during precondensation is 235 to 245°C, more preferred 238 to 242°C, while the temperature during polycondensation is 240 to 250°C, more preferred 242 to 248°C. The mean residence time for precondensation is preferably 30 to 70 minutes, more preferred 40 to 60 minutes, and for polycondensation 100 to 170 minutes, more preferred 120 to 150 minutes. Precondensation and polycondensation can be appropriately performed in usual reactors. Such reactors are known to the person skilled in the art and described for precondensation for example in the WO 2004/033526 and in the DE 102004038466. hi case of polycondensation, for example the descriptions in DE1745541 and DEi 02004053199 apply.
According to the invention, in this context it is in particular preferred if the foUow-up zone of the esterification is followed by an inlet zone in the precondensation which is neither stirred. This inlet zone preferably makes up at least 25%, preferably 35 to 65% of the precondensation time.
According to the invention, polybutylene terephtalate can thus be produced with a good yield and satisfying reaction time. it surprisingly showed that by the special reaction procedure in the esterification, the amount of catalyst, in particular titanium catalyst, required for the complete reaction, is clearly reduced. This also reduces the problems occurring in connection with the catalyst employment and discussed above. Thus, product quality can in particular be increased and the method procedure can be simplified. Due to the reduced demand for catalyst, the fiher lives, for example, are increased by more than 50%. Due to the reduced demand for catalyst, furthermore the costs for the manufacture of polybutylene terephtalate are reduced. Quality penalties due to catalysts, such as colour deficiencies and photolytic greying, are also reduced according to the invention.

Such an improvement of the reaction results could not be expected on the basis of the information of the prior art.
According to the invention, it is particularly preferred if the complete required catalyst amount for the manufacture of polybutylene terephtalate is already fed to the esterification stage. This in particular reduces the amount of equipment required as well as the requirements with respect to the method procedure for the subsequent stages of precondensation and polycondensation. As already illustrated above, by the method design of the first stage according to the invention, the complete catalyst demand for the manufacture of polybutylene terephtalate can be clearly reduced. According to the invention, it was found that the catalyst demand is reduced as the TPA turnover a increases or the residual acid proportion s = 100 - a is reduced. Due to the reduced use of catalyst, there is a reduction of the yellow value b and an increase of the white degree of the manufactured polymeric products.
The catalyst component that is preferably introduced into the reaction in the form of a diolic solution according to the invention in addition preferably comprises stabilizing components. in particular, a stabilization of the catalyst solution with TPA is preferred.
A method according to the invention for the manufacture of polybutylene terephtalate is described below with reference to Figure 1.
TPA is fed to a stirring vessel (1) via line (2) and BD is fed to the stirring vessel (1) via line (3) and they are mixed to form a paste that is fed via line (4) to a stirred tank reactor (7) surrounded by a heating jacket (5) and equipped with an additional heating element (6) for esterification. During esterification, a liquid BD-oligomer mixture and vapour are formed, the latter essentially comprising water, BD and tetrahydrofliran (THF). Esterification in the stirred tank reactor (7) is performed in the presence of the catalyst solution supplied via line (8). The vapour formed in the stirred tank reactor (7) leaves the stirred tank reactor (7) via line (9) and is supplied to the distillation column (10) where water and THF are separated overhead. The overhead product of the distillation column (10) is supplied via line (11) to the cooling apparatus (12) from which the condensate flows to the reflux distributor via line (14). From the reflux distributor (14), water and THF are withdrawn via line (15) and the reflux is returned to the head of the distillation column (10) via line (16). From the bottom of the distillation column, a mixture predominantly consisting of bulanediol is withdrawn via line

(17). Via line (18), alkyl titanate is added to the mixture flowing in line (17) by metered addition, resulting in a composition desired for the catalyst solution. The mixture passes a mixture section (19), and via line (8), the produced catalyst solution reaches the stirred tank reactor (7). The catalyst solution can be completely or partially also charged to the stirred vessel (1) via line (20) and/or fed to the paste flow via line (21) into line (4) and/or fed to the transfer line (23) for the esterification product formed in the stirred tank reactor (7) to the precondensation reactor (24). The reactor (24) has a heating jacket (25) and an additional heating element (26). Via line (27), the precondensate from the reactor (24) is supplied to the polycondensation reactor (28). The produced PBT is ptimped off via line (29). The formed vapours are sucked off via line (30) from reactor the (24) and via line (31) from the reactor (28), According to the invention, the reactor (7) comprises, in addition to the indicated stirred reaction zone, a non-stirred follow-up zone. Examples of such reactors are disclosed in Figures 2 to 4.
The reaction procedure according to the invention permits a reduction of the catalyst use when the non-stirred fofiow-up zone of the esterification stage is employed. By the method procedure according to the invention, in this case high turnovers of TPA are achieved which are clearly above the prior art as appropriate turnovers. it surprisingly showed according to the invention that it is not a disadvantage to obtain a very high TPA turnover at the end of the esterification stage. The high TPA turnover, in combination with the molar ratio of BD to TPA to be observed according to the invention, ensures stabilization and possibly a reactivation of catalyst proportions which are converted to harmful decomposition products by hydrolysis in the prior art. Due to the method procedure according to the invention, in particular in the follow-up zone of the esterification stage and in the inlet zone of the precondensation, a reactivation of catalyst components can be achieved as the oxidation stage of the catalyst metal can be maintained and the formation of hydroxides liable to precipitation can be prevented. in this context, in particular the futher removal of volatile components in the follow-up zone is advantageous, as with a reduced water content of the esterification mixture and an increased molar ratio of BD to water, a reduced liability to catalyst hydrolysis can be observed.
A reactor according to the invention for performing the above-described esterification reaction comprises an esterification reactor with a vertical vessel axis, a beatable jacket, a central inlet chamber with separate connections for feeding the raw materials as paste and the

catalyst as diolic solution, a coaxial stirrer for dispersing the charge, and a submerged damper register for transmitting the required process heat. The reactor according to the invention furthermore includes a foliow-up zone, preferably a peripheral follow-up chamber, in particular suited for subsequent dissolution of solid TPA from the inlet chamber and homogenisation of the esterification mixture with a flow with only little back-mixing under isobaric conditions. According to the invention, an appropriate follow-up zone is in particular realized in that the inlet chamber above the damper register is enclosed by a radially enlarged internal container opened at the top, and the follow-up zone is designed between the internal container and the external heated container wall as ring channel with a connection to the common steam room opened at the top.
The channel depth for the follow-up zone is preferably less than 800 mm, more preferred 700 mm or less, and in particular preferred 350 mm to 700 mm.
in Figure 2, an esterification reactor according to the invention is shown. This reactor comprises a Robert evaporator (RV) and a stirring element (RO) at the bottom with radial discharge. Above the evaporator, the reaction room is conicaJly extended up to a cylindrical head region (ZK). A radially enlarged internal container, consisting of an initial cone (above the external reactor cone situated at the bottom) and a cylindrical board at the edge at the external cone end, divides the reactor into an internal central mlet chamber (EK) and an external follow-up chamber (NK) in the form of a ring channel inclined at the side of the cone with a cylindrical degassing gap at the reactor wall opened at the top. The walls contacted by the product are surrounded by an external heating jacket area. The internal area, with the radial-discharge stirring element at the bottom, is the room for the stirred zone of the esterification, while the follow-up chamber represents the non-stirred follow-up zone.
in Figure 3, an alternative conception is disclosed where the upper base plate (OBF) of the evaporator at the same time forms the lower limiting wall of the external follow-up zone in line with the radial enlargement of the reactor room. The first conical, then cylindrical internal container dividing the reaction room into a central internal chamber and an external follow-up chamber at the edge begins at this base plate. A propeller mixer (RO) in the vertical downpipe of the damper register serves for product circulation and improved raw material distribution in the first zone.

Figure 4 finally shows a further modified reactor conception with a pear-shaped reactor vessel and a damper register with separate jacket and convex base plates lowered into the tapered bottom space of the reactor. Between the bottom container jacket and the register jacket, there is a free gap for an external down-current of the product corresponding to a vertical up-current in the heating tubes. A stirrer (RO) with upward discharge above the upper tube bottom serves direct admixing and dispersion of the charge fed from above into the central inlet chamber. The division of the upper reaction room into the central inlet chamber (EK) and a peripheral follow-up chamber (NK) in the form of an external ring channel has a design similar to the arrangement already described in Figure 2.
in Figures 2 to 4, furthermore the filling level is indicated. Below the line (* ^ ^), there is the (liquid) reaction mixture, the steam room is located above, possibly together with some foam.
Figure 5 finally shows a schematic plan view onto a reactor in conformity with the present invention, with an internally disposed stirred reaction zone (GRZ) and an externally surrounding follow-up zone (NZ), as well as a central channel, e.g. for attaching (ZK) a stirring element.
Such a reactor for esterification can be connected with further known devices for precondensation and polycondensation. The equipment conception of the continuation of the non-stirred follow-up zone of the esterification into an inlet zone of tfie precondensation in particular preferred according to the invention was already described above. The equipment conception of the prepolycondensation stage as sequence of at least one level bottom and a stirred discharge bottom is already described in the EF 1 478 677 which is incorporated herein by reference. The flow channels are here preferably self-emptying and free from a dead space, as described in the German patent application DE 10 2004 38 466.5. This apphcation, too, is included herein by reference.
As end reactor for the polycondensation of the precondensate, all reactor types appropriate for this purpose and known to the person skilled in the art can be used, as in particular storing disk or cage reactors, preferably stirring disk reactors.

Example and Comparative Example
The degree of polycondensation mentioned in the application which is, for example, described in connection with the esterification, can be determined in confonnity with the following embodiments.
The acid number (AN) is measured in mg KOH per gram of esterification product added by weighing. The non-reacted acid end groups of the product dissolved in dimethyl formamide are determined by means of titration with alcoholic KOH from the difference to a blind sample.
The saponification number (SN) is also measured in mg KOH per gram of esterification product added by weighing. Here, the esterification product is reacted with boiling alcoholic KOH and the remaining KOH is titrimetrically determined,
As the esterification product added by weighing also contains free diol, water and non-reacting additives, their percentage by mass (ADD) also has to be determined.
The saponification number corresponds to the complete employed amount of acid end groups, while the acid number represents the not yet reacted acid end groups. Therefore, the TPA
turnover e is:

Embodiment:
in a continuous polycondensation plant with an esterification stage (ES) similar to that of Fig. 2, precondensation (prepoly stage (PP)), equipped with an inlet chamber with a residence time of 15 min, and a polycondensation stage with a ring disk reactor (DRR), the following parameters were adjusted:

The esterification was operated with a fed molar ratio of BD to TPA of 3.3, the residence time in the follow-up zone was 12 min, the channel depth was 560 mm, the employed catalyst was 60 ppm in the final product.
in the esterification, there was a turnover of 99.6% and a degree of polycondensation of 6, the final product with an intrinsic viscosity of 0.95 had a chromatic value b of 1.2. in the first stirred zone of esterification, aturaover of 97.9% was achieved. The plant was equipped with a prepoly filter which had a mean life of 5 - 6 weeks under the mentioned conditions.
Comparative Example:
in the same plant, however without follow-up zone in the esterification stage, the following parameters were employed:

The fed molar ratio was 2.9 and the employed catalyst was 90 ppm. in the esterification, there
was a turnover of 97.8% and a degree ofpolycondensafionof4.7, the final product had an

intrinsic viscosity of 0.93 with a chromatic value b of 3. The expected fiUer life in this case was only 3-4 weeks.
Laboratory tests in a simple stirring vessel with a residence time of 60 to 90 min at temperatures of 240 to 248°C and pressures of 400 to 500 mbar showed varying turnovers of between 95% and 98%, even at high catalyst concentrations of 120 ppm to 250 ppm.
Only by the high preliminary turnover in the stirred zone in connection with the employment of the follow-up zone, the tumover could be increased to more than 99%. At the same time, the required amount of catalyst was reduced, the colour of the final product was clearly improved and the filter lives were increased. Thus, these examples show that the advantages described in the application can be realized by the new and inventive technical teaching of the present application.

Patent Claims
Method for the continuous esterification of terephtalic acid with 1,4-butanedioi, :haracterised in that terephtalic acid and 1,4-butanediol are reacted in a two-stage sobaric reaction procedure, comprising a first, stirred reaction zone and a second, ion-stirred follow-up zone.
Method according to claim 1, wherein the reaction product of the esterification eaction comprises an acid turnover, based on terephtalic acid, of more than 98%.
Method according to claim 1 or 2, wherein the reaction product of the sterification reaction comprises a mean polycondensation degree of more than 3.
Method according to one of claims 1 to 3, wherein the second reaction zone, the ion-stirred follow-up zone, contains at least 5% of the complete reaction time of
he esterification reaction.
Method according to one of claims 1 to 4, wherem for the esterification a mean esidence time tR of less than 2.5 hours is observed.
4ethod according to one of claims 1 to 5, wherein an esterification catalyst in the brm of a diolic solution is employed.
Method according to claim 6, wherein the esterification catalyst is a catalyst based in titanium.
Method for the continuous manufacture of polybutylene terephtalate, comprising he reaction stages of esterification, precondensation and polycondensation, vherein the esterification is designed in conformity with one of claims 1 to 7.
Method according to claim 8, wherein the complete amount of catalyst required or the manufacture of polybutylene terephtalate is added in the esterification

Method accordii g to one of claims 8 or 9, wherein the non-stirred follow-up zone of esterification iirectly passes over into a non-stirred inlet zone of the precondensation
Method accordir g to one of claims 8 to 10, wherein the pressure in the precondensation is lower than the pressure in the esterification and wherein the pressure in the p )lycondensation is lower than the pressure in the precondensation.
Method accordii g to one of claims 8 to 11, wherein the pressure in the precondensation is lower than 50 mbar.
Method accordir g to one of claims 8 to 12, wherein the temperature in the precondensation is equal to or lower than the temperature during polycondensation.
Method accordir g to one of claims 8 to 13, wherein the polycondensation is
performed in a stirring disk reactor.
Esterification re; ctor, appropriate for performing the method according to one of claims 1 to 7, CO nprising a stirred tank reactor as well as a non-stirred follow-up zone, wherein the follow-up zone is arranged around a stirred internal container as ring channel rad: ally disposed outside.
Reactor accordir g to claim 15, wherein the follow-up zone as well as the stirred internal containe comprise a common steam room.
Reactor accordir g to one of claims 15 and 16, wherein the follow-up zone designed as ring channel has a channel depth of 300 to 700 mm.
Device for the manufacture of polybutylene terephtalate, comprising at least one esterification reactor, at least one precondensation reactor and at least one polycondensatio i reactor, wherein the at least one esterification reactor is selected from reactors in conformity with claims 15 to 17.

advice according to claim 18, wherein the at least one polycondensation reactor is tirring disk reactor.
Dated this 20 day of August 2008

Documents:

4404 CHENP 2008 FORM 13.pdf

4404 CHENP 2008 PETITION POR.pdf

4404-CHENP-2008 CORRESPONDENCE OTHERS 11-03-2013.pdf

4404-CHENP-2008 AMENDED PAGES OF SPECIFICATION 31-12-2013.pdf

4404-CHENP-2008 AMENDED CLAIMS 31-12-2013.pdf

4404-CHENP-2008 ASSIGNMENT 11-04-2014.pdf

4404-CHENP-2008 CORRESPONDENCE OTHERS 11-04-2014.pdf

4404-CHENP-2008 EXAMINATION REPORT REPLY RECEIVED 31-12-2013.pdf

4404-CHENP-2008 FORM-1 31-12-2013.pdf

4404-CHENP-2008 FORM-3 31-12-2013.pdf

4404-CHENP-2008 OTHER PATENT DOCUMENT 31-12-2013.pdf

4404-CHENP-2008 POWER OF ATTORNEY 31-12-2013.pdf

4404-CHENP-2008 AMENDED CLAIMS 15-04-2014.pdf

4404-CHENP-2008 AMENDED PAGES OF SPECIFICATION 15-04-2014.pdf

4404-CHENP-2008 CORRESPONDENCE OTHERS 04-03-2014.pdf

4404-CHENP-2008 EXAMINATION REPORT REPLY RECEIVED 07-02-2014.pdf

4404-CHENP-2008 EXAMINATION REPORT REPLY RECEIVED 15-04-2014.pdf

4404-CHENP-2008 FORM-13 11-04-2014.pdf

4404-chenp-2008 abstract.pdf

4404-chenp-2008 claims.pdf

4404-chenp-2008 correspondence others.pdf

4404-chenp-2008 description (complete).pdf

4404-chenp-2008 drawings.pdf

4404-chenp-2008 form-1.pdf

4404-chenp-2008 form-18.pdf

4404-chenp-2008 form-3.pdf

4404-chenp-2008 form-5.pdf

4404-chenp-2008 pct.pdf

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Patent Number

260424

Indian Patent Application Number

4404/CHENP/2008

PG Journal Number

18/2014

Publication Date

02-May-2014

Grant Date

30-Apr-2014

Date of Filing

20-Aug-2008

Name of Patentee

LURGI ZIMMER GMBH

Applicant Address

LURGIALLEE 5, 60295 FRANKFURT,

Inventors:

#	Inventor's Name	Inventor's Address
1	WILHELM, FRITZ,	RENDELER STRASSE 79A, 61184 KARBEN,
2	REISEN, MICHAEL,	MERIANPLATZ 1, 60316 FRANKFURT,

PCT International Classification Number

C08G63/183

PCT International Application Number

PCT/EP07/594

PCT International Filing date

2007-01-24

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	6001462.8	2006-01-24	EUROPEAN UNION