Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-05-18
2003-01-28
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S401000, C528S503000, C524S783000, C526S065000
Reexamination Certificate
active
06512080
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process of producing polytrimethylene terephthalate (PTT) with an intrinsic viscosity of at least 0.75 dl/g by esterification of terephthalic acid (TPA) with trimethylene glycol (TMG; this is also referred to as 1,3-propanediol, PDO) in the presence of a catalytic titanium compound to obtain an esterification product, precondensation of the esterification product to obtain a precondensation product, and polycondensation of the precondensation product to obtain PTT.
BACKGROUND OF THE INVENTION
Processes of producing PTT are known (U.S. Pat. Nos. 2,456,319; 4,611,049; 5,340,909; 5,459,229; 5,599,900).
For instance, U.S. Pat. No. 4,611,049 describes the use of a protonic acid as co-catalyst for accelerating the polycondensation of TMG and dimethyl terephthalate, where the addition of p-toluene sulfonic acid in a concentration of 50 mmol % effects an increase of the maximum achievable intrinsic viscosity of 0.75 dl/g in a batch process catalyzed with 50 mmol % tetrabutyl titanate to 0.90 dl/g.
U.S. Pat. No. 5,340,909 proposes to achieve an improvement of the polycondensation capacity and the color of the polytrimethylene terephthalate by using a tin catalyst, which together with titanium can already be present in the esterification. Statements on the influence of recirculation of the vapor condensates obtained during the polycondensation on the polycondensation capacity of the reaction melt cannot be found in U.S. Pat. No. 5,340,909.
U.S. Pat. No. 5,459,229 proposes to reduce the concentration of acrolein in the vapors by adding alkalines to the condensates produced during the esterification of trimethylene glycol and terephthalic acid U.S. Pat. No. 5,459,229 does not contain any details concerning the esterification and polycondensation.
U.S. Pat. No. 5,599,900 describes a process of producing polytrimethylene terephthalate, where in the presence of an inert stripping gas either after the transesterification or after the esterification a polytrimethylene terephthalate with a degree of polymerization of 64 is synthesized. Moreover, it is desired to also adjust higher molecular weights but this is not proven by experiment.
WO 97/23543A describes a process of producing polytrimethylene terephthalate, where it is provided to produce a preproduct with an intrinsic viscosity of 0.16 dl/g by means of transesterification. This preproduct is converted to pastilles by means of dripping, which pastilles directly crystallize at crystallization temperatures up to 130° C. The actual polymer is produced subsequently by solid phase condensation. It is disadvantageous that a high amount of trimethylene glycol and oligomers gets into the process gas and must be recovered or burnt, which is expensive.
U.S. Pat. No. 5,798,433 describes a process of producing PTT by direct esterification of terephthalic acid with 1,3-propanediol and subsequent precondensation and polycondensation. The PTT produced is obtained using a combination of titanium and antimony catalysts. The quantity of the required catalyst is very high and causes severe disadvantages in the product quality especially with regard to the product thermal stability.
From U.S. Pat. No. 4,011,202 the use of glycol jet pumps is known. However, the use of TMG jets is not detailed.
It can be seen that it would be advantageous to create a melt phase process of producing PTT with an intrinsic viscosity between 0.75 and 1.15 dl/g and a good thermal stability, and to achieve at the same time an efficiently long service life of the filters when the polymer melt is filtered prior to processing the same to form the end products. The process may be a batch or continuous process. Additionally, the PTT process should also allow the recycling of TMG and oligomer byproducts.
SUMMARY OF THE INVENTION
The characteristic features of this process, which comprises the catalytic esterification of TPA with TMG, precondensation of the esterification product and polycondensation of the precondensation product, are as follows:
1) The esterification is performed in at least 2 stages, one initial stage and at least one second, subsequent stage connected to a process column.
2) The catalyst used for esterification and polycondensation is a titanium compound, preferably in a stabilized liquid formulation, which is prepared from a catalytic titanium compound, an organic acid and TMG as solvent, in such way that the liquid catalyst feed contains less than 5 percent by weight (wt %) titanium
3) The catalyst used for esterification in the first, initial stage can be alternatively a Ti containing liquid reaction product from TPA and TMG with a degree of esterification of at least 97%, which may be recycled from a later reaction stage and fed to the initial esterification stage together with the raw materials.
4) A defined quantity of the described liquid catalyst feed is introduced into the first, initial esterification stage and separately a second defined quantity of the liquid catalyst feed is added to the at least one subsequent stage of esterification.
5) a major quantity between 65 and 100 wt % of said liquid catalyst feed containing 35 to 110 ppm titanium may be introduced into the at least one subsequent esterification stage, which is operated at a temperature of 245 to 260° C. and a pressure of 0.7 to 1.5 bar,
6) a minor quantity of said liquid catalyst feed containing 0 to 40 ppm titanium and up to 35% of the total catalyst may be directly fed to the initial esterification stage, which direct catalyst feed can be partially or completely substituted by the same quantity of catalyst in a reaction product, which may be recycled from any further reaction stages and which is mixed with the raw materials for further reaction in said initial esterification,
7) In the first, initial esterification stage a total molar feed ratio of TMG/TPA of 1.15 to 2.5, an amount of titanium of 0 to 40 ppm, which is in maximum 35% by weight of the total amount of catalyst, a temperature of 240 to 275° C. and an absolute pressure of 1 to 5.05 bar, preferably 3.5 bar, are adjusted, whereby the reaction is continued until 90 to 95% of the TPA is esterified.
8) In the at least one subsequent esterification stage an additional amount of titanium of 35 to 110 ppm, which is 65 to 100% by weight of the total amount of catalyst, a temperature of 245 to 260° C. and an absolute pressure of 0.7 to 1.5 bar are adjusted, whereby the reaction is continued until 97 to 99% of the TPA is esterified.
9) The precondensation is performed at a temperature of 245 to 260° C. under a reduced pressure in the range from 2 to 200 mbar.
10) The polycondensation is carried out in the melt phase at a temperature increasing from the entry to the exit of the polycondensation reactor from 250 to 270° C. and at an absolute pressure of 0.2 to 2.5 mbar.
11) For generating the vacuum of the precondensation and polycondensation vapor-jet pumps are used, which are operated with TMG vapor, and the vapors sucked off and said TMG vapors are compressed by the vapor jet pumps and condensed by spraying them with a liquid which predominantly consists of TMG, for example the condensate from these spray condensers and optionally fresh make-up TMG.
DETAILED DESCRIPTION OF THE INVENTION
The feed amount of titanium in the first, initial esterification stage preferably is in the range from 5 to 25 ppm. As the catalytic titanium compound to prepare the catalyst liquid there may preferably be used titanium tetrabutylate or titanium tetraisopropylate. As advantageous catalytic titanium compounds there may for instance also be used any catalytic titanium compound, such as titanium alkylates and their derivatives, like tetra-(2-ethylhexyl)-titanate, tetrastearyl titanate, diisopropoxy-bis(acetyl-acetonato)-titanium, di-n-butoxy-bis (triethanolaminato)-titanium, tributyl monoacetyltitanate, triisopropyl monoacetyltitanate or tetrabenzoic acid titanate, titanium complex salts, like alkali titanium oxalates and malonates, potassium hexafluorotitanate, or titanium complexes with hydroxycarboxylic acid
Blackbourn Robert Lawrence
Kelsey Donald Ross
Reitz Hans
Seidel Eckhard
Tomaskovic Robert Stephen
Acquah Samuel A.
Shell Oil Company
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