Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-12-19
2004-11-02
Trinh, Ba K. (Department: 1625)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S308000, C528S308600, C528S308800, C526S071000, C560S076000, C560S098000
Reexamination Certificate
active
06812321
ABSTRACT:
The present invention relates to a process for the continuous preparation of polybutylene terephthalate (PBT) from terephthalic acid (TPA) and 1,4-butanediol (BDO).
The preparation of polybutylene terephthalate from dimethyl terephthalate (DMT) and 1,4-butanediol is known from the prior art. A disadvantage of this process is that tetrahydrofuran (THF) formed in small amounts as by-product forms an azeotrope with the methanol liberated during the reaction and therefore can be recovered as a material of value only with great difficulty.
The direct preparation of polybutylene terephthalate from terephthalic acid and 1,4-butanediol is made difficult by the formation of relatively large amounts of THF, resulting in loss of 1,4-butanediol required for the reaction. Furthermore, not only THF but also 2,5-dihydrofuran (2,5-DHF) is formed from 1,4-butanediol. The 2,5-dihydrofuran is difficult to separate from THF and therefore contaminates and reduces the quality of the valuable product THF. A further problem in the direct preparation of polybutylene terephthalate from terephthalic acid and 1,4-butanediol is that terephthalic acid is not soluble in 1,4-butanediol and goes into solution only during the esterification with 1,4-butanediol. However, to produce high quality polybutylene terephthalate, it is extremely important for this to be free of contaminants such as free acid groups from terephthalic acid. For this reason, the terephthalic acid should be completely esterified and dissolved before the actual polycondensation commences.
Processes concerned with the direct preparation of polybutylene terephthalate from terephthalic acid and 1,4-butanediol are already known from the prior art.
DD-A 269 296 relates to a continuous process for preparing polyalkylene terephthalates. Setting of appropriate reaction parameters in the esterification step of the dicarboxylic acid used with the glycol used is said to decisively favor removal of water from the esterification phase so that esterification products are obtained both with a high degree of conversion and a high mean degree of polymerization. The esterification step is carried out in a reactor cascade in which the temperature is increased and the pressure is reduced from reactor to reactor. The example described relates to the preparation of polyethylene terephthlate from terephthalic acid and ethylene glycol.
EP-A 0 431 977 describes a process for increasing the direct esterification rate of a diacid and 1,4-butanediol to esterification of >95% of the acid groups. The process can be carried out continuously in three reactors. The process described comprises:
a) mixing 1,4-butanediol and diacid in a ratio of at least 2:1,
b) heating the reaction mixture to 180° C.,
c) adding a suitable catalyst and
d) reacting the mixture at atmospheric pressure and a mean temperature in the range from 180 to 245° C. for a maximum of 60 minutes.
In this process, less than 5% of the 1,4-butanediol is said to be cyclized to THF. However, the content of free acid groups in the end product is high.
DE-A 44 15 220 describes a process for preparing polyesters in a specific apparatus. The process is carried out under decreasing hydrostatic pressure and increasing reaction temperature. No information is given on the formation of THF.
DE-A 35 44 551 relates to the continuous preparation of polybutylene terephthalate from terephthalic acid and 1,4-butanediol. The preparation is carried out in three stages. The first stage, namely the esterification, is carried out at from 225 to 260° C. and a pressure of from 0.1 to 1 bar. The second stage, the precondensation, is carried out at from 230 to 260° C. and a pressure of from 10 to 200 mbar, and the third stage, the polycondensation, is carried out at from 240 to 265° C. and a pressure of from 0.25 to 25 mbar.
It is an object of the present invention to provide a process for preparing polybutylene terephthalate which is improved compared to the prior art. In particular, formation of THF and 2,5-dihydrofuran from the 1,4-butanediol used should be as low as possible and the polybutylene terephthalate obtained should have a very low content of free acid groups.
The achievement of this object starts out from a process for the continuous preparation of polybutylene terephthalate from terephthalic acid and 1,4-butanediol, comprising:
a) direct esterification of terephthalic acid with 1,4-butanediol in a reactor cascade comprising at least two reactors,
b) precondensation of the esterification product obtained in stage a), and
c) polycondensation of the precondensate obtained in stage b).
In the process of the present invention, the reaction pressure decreases and the temperature does not increase along the reactor cascade in stage a).
The polybutylene terephthalate prepared with the aid of the process of the present invention is of excellent quality. It has a low content of acid and alcohol groups. The formation of THF and 2,5-dihydrofuran from 1,4-butanediol is low in the process of the present invention. As a result, only little 1,4-butanediol is lost, so that the yield of polybutylene terephthalate based on 1,4-butanediol is high.
a) Esterification stage
The stage a) is carried out in a reactor cascade comprising at least two reactors, preferably from two to five reactors, particularly preferably three reactors. The reactors used are generally stirred vessels.
According to the present invention, the esterification stage is carried out in a reactor cascade in which the reaction pressure drops from reactor to reactor. The esterification is preferably carried out at a pressure of <1 bar.
In a reactor cascade comprising three reactors, the pressure in the first reactor (p1) is generally set to <1 bar, preferably <900 mbar, particularly preferably <800 mbar. The pressure in the second reactor (p2) is <p1, preferably <p1−100 mbar, particularly preferably <p1−150 mbar. In the third reactor, esterification is carried out at a pressure (p3) of <p2, preferably <p2−100 mbar. Thus, the pressure is preferably from 650 to 900 mbar in the first reactor (p1), from 500 to 700 mbar in the second reactor (p2) and from 350 to 600 mbar in the third reactor (p3), with the pressure in the individual reactors decreasing from reactor to reactor within the specified ranges.
The preferred process conditions with a pressure of less than 1 bar give a still better suppression of THF formation from 1,4-butanediol.
The temperature range for the overall esterification stage is generally from 170 to 250° C., preferably from 180 to 240° C., particularly preferably from 190 to 230° C. According to the present invention, the temperature does not increase along the reactor cascade, i.e. the esterification temperature is approximately equal in each reactor of the reactor cascade or drops from reactor to reactor.
The residence times for the overall esterification stage are generally from 140 to 430 minutes, preferably from 160 to 420 minutes, particularly preferably from 170 to 390 minutes. In the case of a reactor cascade made up of three reactors, the residence time in the first reactor (V1) is generally from 100 to 250 minutes, preferably from 110 to 250 minutes, particularly preferably from 120 to 240 minutes, in the second reactor (V2) generally from 20 to 105 minutes, preferably from 30 to 100 minutes, particularly preferably from 30 to 90 minutes, and in the third reactor (V3) generally from 20 to 75 minutes, preferably from 20 to 70 minutes, particularly preferably from 20 to 60 minutes.
The esterification is generally carried out using a molar excess of 1,4-butanediol in order to push the ester equilibrium in the desired direction. The molar ratios of 1,4-butanediol to terephthalic acid are generally from 1.1:1 to 3.5:1, preferably from 1.5:1 to 2.8:1, particularly preferably from 1.9:1 to 2.5:1.
In a preferred embodiment, a suspension comprising 1,4-butanediol and terephthalic acid in a molar ratio of generally <2:1, preferably <1.5:1, is placed in a reservoir and diluted with hot 1,4-butanediol so
Heitz Thomas
Klatt Martin
Neuhaus Ralf
BASF - Aktiengesellschaft
Keil & Weinkauf
Oh Taylor V
Trinh Ba K.
LandOfFree
Method for the continuous production of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the continuous production of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the continuous production of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3349737