Process for producing a saturated cyclic ether

Details Process for producing a saturated cyclic ether Process for producing a saturated cyclic ether

2002-12-12

2004-03-02

Owens, Amelia (Department: 1625)

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C549S509000

Reexamination Certificate

active

06700003

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for producing a saturated cyclic ether. Particularly, it relates to a process for producing a saturated cyclic ether such as tetrahydrofuran, which comprises reacting a mono- and/or di-fatty acid ester of an &agr;, &dgr;-diol in the presence of a solid acid catalyst.
BACKGROUND ART
A saturated cyclic ether such as tetrahydrofuran is a compound which is extremely useful as an organic solvent, or as a raw material for e.g. polytetramethylene ether glycol.
As a method for producing tetrahydrofuran, a method of hydrogenating butynediol made from acetylene and formaldehyde to convert it to butanediol, followed by dehydration cyclization, or a method of reacting an acetic acid ester of 1,4-butanediol with water in the presence of an acid catalyst, has, for example, been known.
As the acid catalyst, it is known to employ a liquid acid or a solid acid. As a method of using a liquid acid, a method of carrying out the reaction in a liquid phase by using sulfuric acid, is known (JP-A-52-93762, corresponding U.S. Pat. No. 4,105,679). With respect to a method of using a solid acid, as the reaction method, a method wherein the reaction is carried out by liquid/liquid contact of all substrates in a liquid phase (JP-A-52-7909) or a method wherein the reaction is carried out by gas/liquid contact with an ester in a liquid phase and with water in a gas phase (JP-A-52-95655, JP-A-52-95656), is known.
However, such conventional methods have had some problems. Firstly, in the case of a method of using sulfuric acid as the catalyst, a high concentration sulfuric acid is employed, whereby coloration of the reaction liquid tends to be substantial, and separation from the reaction product tends to be difficult. Further, corrosion of the reactor by sulfuric acid is substantial, and the yield is also low.
Also in the case of using a solid acid catalyst, the conventional methods were carried out by a liquid phase reaction by liquid/liquid contact or by a gas liquid mixed reaction by gas/liquid contact. For example, in JP-A-52-95655 or in JP-A-52-95656, a liquid acetic acid ester and steam were reacted to produce a cyclic ether. In these conventional methods, at least an ester as one of substrates is present entirely in a liquid phase in the reaction system, whereby there have been the following problems.
{circle around (1)} Due to clogging of the catalyst, deterioration in the activity will occur.
{circle around (2)} A liquid is adsorbed on the surface of the catalyst, whereby the flow rate control or the contact time control tends to be difficult.
{circle around (3)} The mixing is not uniform, whereby there will be a portion where the concentration of the ester is locally high, thus leading to deterioration in the activity or an increase of a side reaction.
{circle around (4)} The catalyst component will dissolve in a liquid phase carboxylic acid desorbed under a high temperature condition, whereby deterioration in the activity and in the useful life of the catalyst will result.
It is an object of the present invention to solve such problems of the prior art and to provide a process for producing a saturated cyclic ether such as tetrahydrofuran stably in high yield over a long period of time, by reacting a fatty acid ester of an &agr;, &dgr;-diol such as 1,4-butanediol in the presence of a solid acid catalyst.
DISCLOSURE OF THE INVENTION
The present inventors have conducted an extensive study under such circumstances and as a result, have found that in the production of a saturated cyclic ether such as tetrahydrofuran by reacting a fatty acid ester of an &agr;, &dgr;-diol such as 1,4-butanediol in the presence of a solid acid catalyst, the above-described problems can be all solved by reacting the fatty acid ester in such a state that at least 50 mol %, preferably substantially all of the fatty acid ester as the reaction substrate, is in a vaporized gas phase state, and thus have completed the present invention.
According to the process of the present invention, as compared with the case of the conventional liquid phase reaction or the gas/liquid contact reaction, the reaction can be carried out within a wide temperature range from a low temperature to a high temperature, formation of by-products is little, and the flow rate control and the contact time control are easy. Further, even by a high temperature reaction or a reaction for a long time, deterioration of the catalyst is less, and even if the amount of water to be supplied, is reduced, the reaction proceeds completely, and the load in the subsequent separation of water can be reduced. Further, deterioration of the catalyst due to a carboxylic acid formed during the reaction will be low as compared with the gas/liquid contact reaction or the liquid phase reaction. Further, as compared with the gas/liquid contact reaction, in the gas phase reaction, the fatty acid ester and water are uniformly dispersed, whereby the reaction efficiency is good, and the yield will be high, and formation of by-products can be suppressed.
Namely, the gist of the present invention resides in a process for producing a saturated cyclic ether, which comprises reacting a mono- and/or di-fatty acid ester of an &agr;, &dgr;-diol in the presence of a solid acid catalyst, wherein the reaction is carried out in such a state that at least 50 mol % of the fatty acid ester supplied to the reaction system is vaporized.
BEST MODE FOR CARRYING OUT THE INVENTION
Now, the present invention will be described in detail.
In the present invention, the condition that the reaction is carried out in such a state that at least 50 mol % of the fatty acid ester as the reaction substrate supplied to the reaction system, is vaporized, will vary variously depending upon the reaction substrate, the reaction temperature, the reaction pressure and the amount of the inert substance added. However, it is necessary to satisfy the following two points (1) and (2).
(1) In a case where all of the reaction substrates introduced, are gas, the reaction is carried out under such a condition that the molar ratio of raw material components to be introduced into the reaction system, and the saturated vapor pressure of the fatty acid ester at the reaction temperature under the reaction pressure, satisfy the following relation:
(mols corresponding to x mol % of the fatty acid ester/total mols of all materials)<(saturated vapor pressure of the fatty acid ester at the reaction temperature under the reaction pressure/reaction pressure)
where all materials mean the fatty acid ester, water and gaseous inert components, and x represents the vaporized ratio (mol %) of the fatty acid ester supplied to the reaction system.
In the present invention, the vaporized ratio x is 50 mol %.
(2) In a case where the reaction substrates introduced are liquid even partly, it is necessary not only to satisfy the requirement of the above (1), but also to apply, in addition to the calory required to bring all water introduced, to the reaction temperature and to vaporize it, the calory required to bring the ester introduced, to the reaction temperature and to vaporize at least x mol % thereof, after the introduction of the substrates and before the substrates contact the catalyst.
With respect to the above (1) and (2), in the present invention, the vaporized ratio x is at least 50 mol %.
Here, the calory required for vaporization is determined by considering the method for heating the reactor and conditions such as the thermal conductivity of the material of the reactor, the supplied amount of the calory (per unit time), and the space, volume, etc. until the reaction substrates will contact the catalyst in the reactor.
In the present invention, by adding a gaseous inert component to the reaction system, it is possible to reduce the partial pressure of the fatty acid ester and to facilitate vaporization of the reaction substrate within wider reaction temperature and reaction pressure ranges. Such an inert component is not particularly limited. For example, nitrogen, carbon dioxid

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