Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From heterocyclic reactant containing as ring atoms oxygen,...
Reexamination Certificate
2000-02-11
2002-07-02
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From heterocyclic reactant containing as ring atoms oxygen,...
C502S210000, C502S211000, C502S254000, C502S255000, C502S515000, C502S522000, C568S617000
Reexamination Certificate
active
06414109
ABSTRACT:
The present application relies for priority upon the inventor's Japanese Patent Application Nos. 10-181351, filed Jun. 15, 1998, and 10-183295, filed Jun. 16, 1998, the contents of which are herein incorporated by reference.
TECHNICAL FIELD
The present invention relates to a process for producing polymers of tetrahydrofuran (hereinafter referred to as “THF”) using a heteropoly-acid as a catalyst.
More particularly, the present invention relates to a process for producing polyether glycols containing a THF polymer (homopolymer or copolymer of THF) using as a catalyst a specific compound, namely, a heteropoly-acid low in contents of Al, Cr and free phosphoric acid.
BACKGROUND ART
Polyether glycols are industrially useful polymers used as main starting materials of polyurethane used for polyurethane elastic fibers (spandex) and synthetic leathers, additives for oils, softening agents, etc.
U.S. Pat. Nos. 4,568,775, 4,658,065 and 5,416,240 disclose that heteropoly-acids can be utilized as polymerization catalysts in production of polyether glycols, especially, polyether glycols containing THF polymers. These patents make mention of amount of crystal water in heteropoly-acids and activity of the catalysts.
Moreover, U.S. Pat. No. 4,677,231 discloses a method for removal of heteropoly-acid catalysts.
When THF is polymerized using the same kind of heteropoly-acids under the same conditions, sometimes the catalytic performance of heteropoly-acids differ depending on the difference in production lots of heteropoly-acids. For example, reaction conversion rate of THF to polymers and stability in molecular weight of the polymers differ due to the difference in production lots of heteropoly-acids.
If the reaction conversion rate is low, large energy is consumed in polymerization of THF, and this is not economically preferred.
If the amount of the heteropoly-acid catalyst remaining in the THF polymer is large, the THF polymer is depolymerized due to heating or the like, and molecular weight of the THF polymer changes with time.
Adsorbents or the like are used for the removal of the heteropoly-acid catalyst remaining in THF, but since break through time of adsorbents gradually shortens, the adsorbents must be frequently changed. Therefore, this method is not preferred from both the economical viewpoint and the viewpoint of increase of industrial wastes.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a process for polymerization of THF using a heteropoly-acid catalyst of high performance in production of THF polymers using heteropoly-acid catalysts.
Another object of the present invention is to provide a process for polymerization of THF using a heteropoly-acid which does not change in catalytic performance irrespective of difference in production lots of the heteropoly-acid.
Still another object of the present invention is to provide a process for polymerization of THF using a heteropoly-acid catalyst which is high in reaction conversion rate.
Further object of the present invention is to provide a process for polymerization of THF using a heteropoly-acid catalyst which is low in its residual amount in the THF polymers.
The present invention is a process for producing tetrahydrofuran polymers using a heteropoly-acid catalyst wherein the content of Al of the heteropoly-acid is 4 ppm or less.
Furthermore, the present invention is a process for producing tetrahydrofuran polymers using a heteropoly-acid catalyst wherein the heteropoly-acid is a heteropolyphosphoric acid containing 1 mol % or less of free phosphoric acid.
THF polymers can be produced with high reaction conversion rate and in a high yield by polymerizing THF using as a catalyst a heteropoly-acid lowered in the content of Al element according to the present invention. Furthermore, polymers free from coloration and having an APHA of less than 50 can be obtained by reducing the content of Cr element.
THF polymers less in the amount of heteropolyphosphoric acid remaining therein can be produced by polymerizing THF using a heteropolyphosphoric acid reduced in content of free phosphoric acid as a catalyst, and THF polymers can be produced with high reaction conversion rate by using the catalyst less in content of Al.
BEST MODE FOR CARRYING OUT THE INVENTION
The heteropoly-acids used as catalysts contain impurities such as various metal elements resulting from raw ores.
For stable production of heteropolyphosphoric acid which is a kind of heteropoly-acid, phosphoric acid is used excessively. As a result, the heteropolyphosphoric acid obtained contains free phosphoric acid which does not contribute to the formation of crystal structure effective as a polymerization catalyst for THF.
The present inventors have paid attention to the impurity metal elements and free phosphoric acid in heteropoly-acids and investigated the relation between contents of metal elements and free phosphoric acid and catalytic performance, and, as a result, accomplished the present invention.
Since the content of metal elements in commercially available heteropoly-acids is slight, namely, less than 20 ppm., the relation between the kind and content of the impurities and polymerization behavior of THF has not been hitherto taken into consideration. However, as a result of investigation of the effect of the impurity metal elements in heteropoly-acids on reaction conversion rate of ring opening polymerization of THF, it has been surprisingly found that a specific compound greatly affects the catalytic performance of heteropoly-acids. It has been found that, especially, Al and free phosphoric acid have a great influence on the catalytic performance.
When a large amount of Al is contained in the heteropoly-acid, the reaction conversion rate of THF is lowered. Though the cause therefor is not clear, it is presumed that (1) the resulting THF polymer contains an inorganic acid salt or reacts with the inorganic acid salt to form a kind of organometallic compound, which covers the surface of the heteropoly-acid, and, as a result, the catalytic activity is deteriorated, or (2) Al is dissolved in some form in the heteropoly-acid and, as a result, a Keggin structure which has a strong interaction with THF and is effective as a polymerization catalyst changes to a Dawson structure which has a weak interaction with THF, resulting in reduction of the proportion of the Keggin structure.
This problem is solved by adjusting the content of Al in the heteropoly-acid to 4 ppm or less, and a stable and high reaction conversion rate can be realized.
A solid heteropoly-acid recognizes the polarity of a molecule, and adsorbs the molecule to the surface of the heteropoly-acid or takes the molecule into the crystal of the heteropoly-acid. This property is also seen in catalytic reaction, and it is considered that the ring opening polymerization reaction of THF includes a reaction taking place on the surface of the heteropoly-acid catalyst and a reaction in which the inside of the crystal also participates (bulk reaction). The latter reaction is a phenomenon which is not seen in the conventional solid catalyst reaction and it is one of the specific properties of heteropoly-acids as catalysts.
It is presumed that in the case of using a heteropoly-acid catalyst as a liquid phase, the participation of the bulk reaction is great, but when Al as an impurity is present in an amount exceeding 4 ppm, Al incorporates into the crystal structure of the heteropoly-acid to hinder the bulk reaction. Thus, it is presumed that the coordination of THF to the heteropoly-acid catalyst through water is hindered and, as a result, the reaction conversion rate in ring opening polymerization of THF is deteriorated.
When the Al content of the heteropoly-acid is 4 ppm or less, stable and high reaction conversion rate can be obtained in the ring opening polymerization of THF. Therefore, the Al content of the heteropoly-acid is 4 ppm or less, preferably 2 ppm or less.
In the ring opening polymerization of THF, the lower Cr content of the heteropoly-acid is preferred. If the Cr content of t
Asahi Kasei Kabushiki Kaisha
Lovering Richard D.
Pennie & Edmonds LLP
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