Study On Skeletel Isomerisition Of N-Butene Over Zeolites

As the raw meterials of methyl tert-butene ether (MTBE), butyl rubber and antioxidants, isobutene is predominantly obtained from catalytic cracking and pylolysis fractions. Since there are too much Linear butene on the market and isobutene is an attractive compound commercially, interest in skeletal isomerization of linear butene to isobutene is growing. Many papers and patents focused on this reaction have been published since late 1 970s, but there are many different views on the catalytic active sites and the prevailing mechanism of the reaction. We performed this reaction over P zeolite owning three-dimensional(3D) channels of 12-membered-ring (12MR) and ferrierite with 1D channels of 1 OMR. With the studies, we got some understandings on the active sites and mechanism of the reaction. The results showed that (1) Acid density of H-Fer is higher than that of H- P, strength of the acid sites are stronger, and BA/LA ratio is significantly larger. (2) As a pair of competing reactions, dimerizing- cracking reaction, which produce by-products and deactivating the catalyst, needs two or more LA located nearby, while skeletal isomerization, which can transfer linear butene into isobutene straightly. will be favored by BA sites with moderate strength. (3) Modifying of the strength and location of acid sites will give higher and more stable yield to isobutene. With its 3D I2NIR channels and low BA/LA ratio, ~B zeolite promotes dimerization products mainly even under temperature as high as 400 ~C. Cracking of dirners gives by-products and coke which will cover active sites. As zhe result of dimerization and cracking reactions, P zeolite is not suitable to be used as a catalyst of skeletal isomerization of linear butenes. On the other hand, ferrierite, owing to its 1 D 1 OMR channels and high BA/LA ratio, depresses dimerising reaction successfully. Its high yield of isobutene can be improved by lowering the BA/LA ratio of Fer, which can be achieved by such means as increasing the framework SIOVA1-~O~ ratio of Fer, modifying the H-Fer with ion-exchanging, or steam treating. Among them, steam treating that can eliminates LA sites used by dimerizing reaction and improves diffusion at the same time, give high and stable yield of isobutene, is a suitable way to modify H-Fer.