Processes for producing poly(alkylene ether) glycol

Details Processes for producing poly(alkylene ether) glycol Processes for producing poly(alkylene ether) glycol

2000-01-13

2002-06-11

Sergent, Rabon (Department: 1711)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C528S365000, C528S366000, C528S405000, C528S408000, C528S409000, C528S410000, C528S411000, C528S416000, C528S417000, C528S421000, C560S240000, C568S613000, C568S621000, C568S623000, C568S624000

Reexamination Certificate

active

06403842

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to processes for producing a poly(alkylene ether) glycol by polymerizing a cyclic ether. More particularly, the invention relates to processes for producing a less colored poly(alkylene ether) glycol. The poly(alkylene ether) glycol is used as a raw material for urethane elastic materials and thermoplastic elastic materials.
DESCRIPTION OF THE RELATED ART
A known process for producing a poly(alkylene ether) glycol comprises subjecting a cyclic ether to ring-opening polymerization using a solid acid catalyst and acetic anhydride as an initiator and then subjecting the polymer to hydrolysis or transesterification (see, for example, JP-B-62-19452 and JP-A-8-231706). (The terms “JP-B” and “JP-A” as used herein mean an “examined Japanese patent publication” and an “unexamined published Japanese patent application”, respectively.)
However, this process has a drawback that the reactions yield a colored poly(alkylene ether) glycol when conducted over a prolonged time period.
SUMMARY OF THE INVENTION
An object of the invention is to provide a process for producing a poly(alkylene ether) glycol which comprises subjecting a cyclic ether to ring-opening polymerization using a solid acid catalyst and a carboxylic acid anhydride as an initiator and in which the coloration of the poly(alkylene ether) glycol being yielded is inhibited.
The present inventors made intensive investigations in order to eliminate the problem described above. As a result, they have found that the coloration can be inhibited to produce a poly(alkylene ether) glycol having an excellent hue by reducing the ketene dimer content of the carboxylic acid anhydride for use in the reaction. They have further found that the ketene dimer can be considerably diminished by treating the carboxylic acid anhydride by contacting with a specific treating agent. The invention has been achieved based on these findings.
The invention provides, according to a first aspect thereof, a process for producing a poly(alkylene ether) glycol which comprises polymerizing a cyclic ether in the presence of at least a catalyst and a carboxylic acid anhydride, wherein the carboxylic acid anhydride has a ketene dimer content of 50 ppm or lower.
The invention further provides, according to a second aspect thereof, a process for producing a poly(alkylene ether) glycol which comprises polymerizing a cyclic ether in the presence of at least a catalyst and a carboxylic acid anhydride, wherein the carboxylic acid anhydride is one which has been treated by contacting with a metal oxide and/or a mixed oxide.
The invention furthermore provides, according to a third aspect thereof: a process for producing a urethane polymer obtained by reacting the poly(alkylene ether) glycol obtained by either of the processes described above with an organic polyisocyanate compound; and an elastic fiber comprising the urethane polymer.
The invention still further provides, according to a fourth aspect thereof, a poly(alkylene ether) glycol which is obtained by polymerizing a cyclic ether in the presence of at least a catalyst and a carboxylic acid anhydride and has a hue of below 20 in terms of APHA unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be explained below in detail with respect to embodiments thereof.
The cyclic ether for use in the invention generally is a cyclic ether having 2 to 10 carbon atoms. Examples thereof include ethylene oxide, propylene oxide, tetrahydrofuran (THF), 1,4-dioxane, tetrahydropyran, and oxetane. Especially preferred of these is THF from the standpoints of availability and handleability.
The carboxylic acid anhydride used as a polymerization initiator is not particularly limited. However, acetic anhydride is generally used from the standpoint of industrial availability.
In general, in the synthesis or decomposition of a carboxylic acid anhydride, e.g., acetic anhydride, a ketene generates in a slight amount and dimerizes to form a ketene dimer.
Known processes for industrially producing a carboxylic acid anhydride, e.g., acetic anhydride, include the following: i) a process comprising pyrolyzing the vapor of acetic acid, acetone, or an acetic ester to yield a ketene gas and causing the ketene to be absorbed by and react with acetic acid; (ii) a process comprising reacting acetic acid with phosgene using anhydrous aluminum chloride or the like as a catalyst; and (iii) a process comprising heating ethylidene diacetate in the presence of a catalyst, e.g., zinc chloride.
These processes each yields a ketene dimer as a by-product. Since the difference in boiling point between acetic anhydride and the ketene dimer is small, acetic anhydride of the industrial grade (hereinafter sometimes referred to as “crude acetic anhydride”) contains the ketene dimer generally in an amount of about 100 ppm. In addition, the carboxylic acid anhydride partly decomposes into the carboxylic acid and a ketene due to thermal equilibrium and this ketene dimerizes to yield a ketene dimer.
It is important that the carboxylic acid anhydride for use in the invention should be regulated so as to have a ketene dimer concentration of generally 50 ppm or lower, preferably 10 ppm or lower, more preferably 5 ppm or lower. In this specification, the values of ketene dimer concentration are by weight.
Methods for reducing the ketene dimer content in the carboxylic acid anhydride to 50 ppm or lower are not particularly limited. Examples thereof include precision distillation, treatment with an ion-exchange resin, treatment with a metal oxide, and treatment with a mixed oxide. These methods may be used in combination of two or more thereof. Preferred of these is treatment with an ion-exchange resin, treatment with a metal oxide, treatment with a mixed oxide, or a combination of two or more thereof.
The metal oxide is not particularly limited. Preferred examples thereof include aluminum oxides such as &ggr;-alumina, zirconium oxide, titanium oxide, niobium oxide, and tantalum oxide.
The mixed oxide may be a crystalline or amorphous compound. Examples thereof include zeolites, activated clays, and mixed oxides each comprising an oxide of two or more elements selected from the elements in Groups 3, 4, 13, and 14 and having an acid strength of +3.0 or lower in terms of H
O
.
The zeolites are not particularly limited. Preferred examples thereof include crystalline aluminosilicates such as the ZSM-5, &bgr;, Y, MCM-22, mordenite, and ZSM-12 types. Also usable are crystalline metallosilicates formed by replacing the aluminum of such crystalline aluminosilicates with another trivalent metal element.
Examples of the mixed oxides each comprising an oxide of two or more elements selected from the elements in Groups 3, 4, 13, and 14 and having an acid strength of +3.0 or lower in terms of H
O
include zirconia-silica, hafnia-silica, silica-alumina, titania-silica, and titania-zirconia.
Methods for the contact treatment of the carboxylic acid anhydride with a metal oxide and/or a mixed oxide are not particularly limited, and the treatment may be conducted by either the suspension or fixed bed method. In the case where the contact treatment is conducted batchwise, the treatment may be accomplished by merely immersing the metal oxide and/or mixed oxide in crude acetic anhydride.
The amount of the metal oxide and/or mixed oxide used in the contact treatment varies depending on the method of contact, and need not be especially specified. However, in the case of, for example, mere immersion in crude acetic anhydride by a batch method, the amount of the metal oxide and/or mixed oxide is generally about from 0.1 to 5 parts by weight per 100 parts by weight of the crude acetic anhydride.
The shape of the metal oxide and/or mixed oxide is not particularly limited, and may be either powdery or particulate. Although the specific surface area thereof is not particularly limited, it is generally selected from the range of from 10 to 1,000 m
2
/g.
The time for the contact treatment varies depending on the method of contact and the

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