Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1997-08-26
1998-12-29
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528308, 5283086, 5283088, 526 71, C08G 6300
Patent
active
058543775
DESCRIPTION:
BRIEF SUMMARY
This application claims the benefit of international application PCT/EP96/00941 filed Mar. 6, 1996.
The present invention relates to a process for the continuous preparation of thermoplastic polyesters by ester-forming derivatives with a molar excess of a dihydroxy compound, and
Polyesters, especially polyalkylene terephthalates, are widely prepared using (trans)esterification/polycondensation processes in which a first stage involves an esterification or transesterification and the actual polycondensation is carried out in one or more further steps (cf. Chemiefasern/Textilindustrie 40 (1992), 1058-1062, and Ullmann's Enzyklopadie der technischen Chemie, 4th edition, vol. 19, pages 61-88).
DE-A-22 10 655 discloses the esterification of terephthalic acid (TPA) with diols, such as 1,4-butanediol, in the presence of titanium-containing catalysts with subsequent polycondensation in a batchwise manner.
The batchwise preparation starting from TPA is known from DE-A-1135660, DE-A-2120092, DE-A-2621099 and EP-A-46 670.
According to DE-A-35 44 551, the esterification is carried out in one step under reduced pressure at 235.degree.-250.degree. C. This is followed by a second step of reduced pressure precondensation and subsequent polycondensation.
The esterification of TPA with diols in the presence of tin catalysts is known from U.S. Pat. No. 3,936421 and U.S. Pat. No. 4,329,444.
Processes for preparing polyesters starting from dimethyl terephthalate (DMT) and diols are known inter alia from DE-A 2514116 and DE-A 2738 093.
It is evident from the review of the art that the continuous preparation of polyesters is generally problematical, especially with respect to the preparation of polyesters starting from terephthalic acid and predominantly 1,4-butanediol as monomers. At present there is no plant in the world for the continuous preparation of polyesters from TPA and diols including predominantly butanediol.
Nor are there any processes in existence whereby polyester can be prepared selectively starting from TPA or DMT.
It is an object of the present invention to make available a continuous process for preparing polyesters, in particular starting from terephthalic acid, and a process in which the polyester is selectively preparable starting from TPA or DMT. The polyesters obtainable by this process shall have regardless of the starting material a substantially uniform property spectrum such as a low catalyst content, a minimal number of carboxyl end groups, and also be thermally and hydrolytically stable. In addition, the molecular weight of the polyesters should ideally not be subject to any restriction.
We have found that this object is surprisingly achieved on conducting step a) and/or step b) of the process in two or more temperature zones.
Step a) of the process is an esterification or transesterification reaction. It is carried out in at least two, preferably at least three, temperature zones. The temperature of a subsequent zone should be 1.degree.-40.degree. C., preferably 2.degree.-30.degree. C., in particular 5.degree.-10.degree. C., higher than the temperature of the preceding zone. The temperature range for the entire esterification reaction is generally (depending on the starting material) from 200.degree. to 260.degree. C., preferably from 210.degree.-250.degree. C., in particular from 220.degree. to 240.degree. C., and the pressure is generally from 1 to 10, preferably from 1 to 4, in particular from 1 to 2, bar.
Preferably step a) of the process is carried out in two or more temperature zones under substantially identical pressure conditions in the individual zones. The technical requisites for creating different temperature zones, such as apparatus in the form of kettle cascades, for example, are known to the person skilled in the art, making further details superfluous.
Suitable dihydroxy compounds include aliphatic, aromatic or cycloaliphatic diols.
These advantageously have from 2 to 20, in particular from 2 to 12, carbon atoms, and particular preference is given to aliphatic diols having from 2 t
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Schumann, Chemiefasern/Textilindustri, 40/1992 pp. 1058-1062.
Ullmann's Enc. der Tech. Chem., vol. 19, pp. 61-88 "No Date Available".
Acquah Samuel A.
BASF - Aktiengesellschaft
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