At present, tetrahydrofuran is a widely used cyclic ether. The primary purposes of tetrahydrofuran are as solvent and binder of various resins, as solvent and extraction solvent of printing inks, as the surfactant of synthetic leather and as the material for synthesizing elastic fibers of polytetrahydrofuran. The purpose of other cyclic ethers has not been fully developed yet.
The process of synthesizing cyclic ethers from alkanediols and the catalysts used therein have been well described in the known literatures and patent references. For example, those wherein phosphoric acid is used as a catalyst are disclosed in U.S. Pat. Nos. 2,251,292, 2,251,835 and 4,124,600; those wherein surfuric acid is used as a catalyst are disclosed in Ger. Offen. 2,509,968, U.S. Pat. Nos. 4,665,205 and 5,099,039, Jpn. Tokkyo Koho 78-43,505 and 78-43,506; those wherein aluminum oxide is used as a catalyst are disclosed in U.S. Pat. No. 4,196,130, Brit. 508,548, Ger. Offen. 2,856,455 and USSR SU 1,158,562.
The process of synthesizing cyclic ethers from alkanediols and the catalysts used therein can be classified into two types: one is a process of homogeneous reaction, the other is a process of non-homogeneous reaction. In the process of homogenous reaction, sulfuric acid and phosphoric acid are the representative catalysts. The drawback of such a process is that part of the catalyst is distilled out with the reaction product, resulting in difficulties of separating the catalyst from the reaction product. Moreover, the acidities of sulfuric acid and phosphoric acid catalysts are strong enough to severely corrode the reactor. In addition, when sulfuric acid and phosphoric acid are used as the catalyst, side reactions easily result in which a great amount of coke is produced. The existence of the coke in the reacting liquid may affect the activity of the catalyst. Therefore, in the continuous synthesis process, while the reacting liquid should be removed from the reactor and part of the reacting liquid should be treated, the problem of acidic waste also results. As to the process of non-homogeneous reaction, aluminum oxide is the representative catalyst. The drawback of this process is that the aluminum oxide catalyst is able to exhibit strong activity at high temperatures only, usually at temperatures higher than 250.degree. C. Such high temperatures generally far exceed the boiling points of many alkanediols. Therefore, the reaction must be carried out in a gasous state and the cost of the equipment and operation will be increased to no avail.
The conversion of alkanediols into cyclic ethers using LaHY, CaHY and H-ZSM-6 zeolites was proposed by C. P. Bezouhanova and F. A. Jabur et al. in React. Kinet. Catal. Lett., Vol. 51, No. 1, pp. 177-181 (1993). However, the reaction was carried out in the condition of a gaseous state at temperatures higher than the boiling points of the reactants. The poor selectivity of cyclic ethers is a drawback of this process. It is not satisfactory because the further step of purification is necessary in the subsequent work-up.
In view of these drawbacks of the above-mentioned conventional arts, the inventor has studied intensively and found that they can be resolved by using a crystalline aluminosilicate zeolite as the catalyst which allows the reaction to be carried out in the liquid phase. Therefore, this invention is able to be achieved.