Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-02-10
2001-03-06
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C528S405000, C528S412000, C528S425000
Reexamination Certificate
active
06197979
ABSTRACT:
The present invention relates to a process for preparing polytetrahydrofuran, tetrahydrofuran copolymers, diesters or monoesters of these polymers having a low color number by polymerization of tetrahydrofuran in the presence of at least one telogen and/or comonomer over a heterogeneous catalyst.
Polytetrahydrofuran (PTHF), also called polyoxybutylene glycol, is a versatile intermediate in the plastics and synthetic fiber industries and is employed, inter alia, for preparing polyurethane, polyester and polyamide elastomers. Furthermore, it is, like some of its derivatives, a valuable auxiliary in many applications, for example as a dispersant or in the deinking of waste paper.
PTHF is advantageously prepared industrially by polymerization of tetrahydrofuran (THF) over suitable catalysts in the presence of reagents whose addition makes it possible to control the length of the polymer chains and thus to set the mean molecular weight to the desired value (chain termination reagents or “telogens”). This control is effected by selection of the type and amount of the telogen. In addition, selection of suitable telogens enables functional groups to be introduced at one end or both ends of the polymer chain. Thus, for example, use of carboxylic acids or carboxylic anhydrides as telogens enables the monoesters or diesters of PTHF to be prepared. Other telogens act not only as chain termination reagents, but are also incorporated into the growing polymer chain of the PTHF; they thus have not only the function of a telogen but also that of a comonomer and can therefore with equal justification be referred to as a telogen or as a comonomer. Examples of such comonomers are water or telogens containing two hydroxy groups, e.g. dialcohols. Examples of such dialcohols are ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, 2-butyne-1,4-diol, 1,6-hexanediol or low molecular weight PTHF. Further suitable comonomers are 1,2-alkylene oxides such as ethylene oxide or propylene oxide, 2-methyltetrahydrofuran or 3-methyltetrahydrofuran. With the exception of water, 1,4-butanediol and low molecular weight PTHF, the use of such comonomers leads to the preparation of tetrahydrofuran copolymers. In this way, the PTHF can be chemically modified.
As comprehensive studies have shown, acid catalysts are suitable for the polymerization of THF on an industrial economical scale, but these have the disadvantageous effect that polymers having yellow to brownish discoloration are obtained. The discoloration increases with the temperature of the polymerization. Furthermore, the purity of the PTHF also depends on the quality of the THF used.
The technical grade contains small amounts of impurities in a concentration of from 10 to 500 ppm. Not all details of the chemical nature of these impurities are known. Although this THF is of very high purity (it normally has a purity of 99.9%), even traces of impurities cause the abovementioned discoloration in the polymerization. In addition, simultaneously with the discoloration, an altered reactivity is observed in the preparation of polyesters or polyurethanes from the polytetramethylene ether glycols. These are serious deficiencies since color and reproducible processing are among the most important properties of a polymer which is to be employed industrially.
For this reason, numerous processes for the pretreatment of technical-grade THF have been proposed for the purpose of improving the quality. Thus, for example, DE-A-2 801 792 describes a process in which THF is treated with bleaching earths prior to the polymerization. Although this gives polymers having an improved color number, this treatment method cannot be applied reproducibly in every case to any available technical grade of THF.
Furthermore, there are processes known for decolorizing the polymers obtained using acid heterogeneous catalysts in a separate decolorization process after conclusion of the polymerization.
According to EP-A 61 668, polytetramethylene ether glycols or polytetramethylene glycol diesters having a low color number are prepared by subjecting the polymers obtained by cationic polymerization of THF to treatment with hydrogen in the presence of a hydrogenation catalyst. If a THF grade as is offered on the market is used in the polymerization, one is forced to carry out the hydrogenative decolorization, at very high hydrogen pressures of, for example, from 50 to 300 bar.
PCT/WO 94/05719 discloses a process for preparing polytetrahydrofuran diesters in which the polymerization of the THF is carried out over acid-activated kaolin, zeolites or amorphous aluminum silicates in the presence of from 1 to 10% by weight of a hydrogenation catalyst and hydrogen.
The processes described in PCT/WO 94/05719 and EP-A 61668 have the disadvantage that an additional catalyst is necessary for preparing pure polytetrahydrofuran diesters.
It is an object of the present invention to find a process for preparing polytetrahydrofuran, tetrahydrofuran copolymers, diesters and monoesters of these polymers which enables polymers and copolymers of THF having a low color number to be prepared simply and economically.
We have found that this object is achieved by a process for preparing polytetrahydrofuran, tetrahydrofuran copolymers, diesters or monoesters of these polymers having a low color number by polymerization of tetrahydrofuran in the presence of at least one telogen and/or comonomer over a heterogeneous catalyst, wherein the polymerization is carried out in the presence of hydrogen.
The novel process allows highly pure polytetrahydrofuran, highly pure tetrahydrofuran copolymers and highly pure diesters or monoesters of these polymers having a low color number to be prepared reliably and reproducibly.
The novel process enables THF polymers and copolymers having color numbers of from 5 to 30 APHA to be prepared even from lower THF grades. The determination of the color numbers is described in the standards DIN 53 409 and ASTM-S-1209.
The preparative process of the present invention is carried out in the presence of hydrogen which is dispersed in the reaction mixture, for example by means of nozzles, gas-introduction rings, gas-introduction stirrers or through a perforated plate. The setting of a particular hydrogen bubble diameter is not critical for the process of the present invention. The polymerization is carried out at hydrogen pressures of from 0.1 to 50 bar, preferably from 0.5 to 5 bar, particularly preferably from 0.7 to 2 bar.
Polymerization catalysts used in the process of the present invention can be sheet silicates which may have been, if desired, activated by acid treatment or supported catalysts comprising an oxidic support material and a catalytically active amount of a tungsten or molybdenum compound or mixtures of such compounds or a metal sulfate, metal hydrogen sulfate and/or metal oxide sulfate.
Suitable supported catalysts comprising an oxidic support material and oxygen-containing molybdenum or tungsten compounds or mixtures of such compounds as catalytically active compounds, which catalysts may also, if desired, be additionally doped with sulfate or phosphate groups, are described in DE-A 44 33 606, which is hereby expressly incorporated by reference.
Also suitable are the supported catalysts described in the German Patent Application No. 194649803.1, which is hereby expressly incorporated by reference, which catalysts comprise as active composition a catalytically active amount of at least one oxygen-containing molybdenum and/or tungsten compound and have, after application of the precursor compounds of the active composition to the support material precursor, been calcined at from 500° C. to 1000° C. and contain a promoter comprising at least one element or compound of an element of groups 2, 3 including the lanthanides, 5, 6, 7, 8 or 14 of the Periodic Table of the Elements.
These catalysts generally contain from 0.01 to 30% by weight, preferably from 0.05 to 20% by weight and particularly preferably from 0.1 to 15% by weight, of promoter, calculated as the sum of its
Becker Rainer
Eller Karsten
Hesse Michael
Rutter Heinz
BASF - Aktiengesellschaft
Keil & Weinkauf
McKane Joseph K.
Solola Taofiq A.
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