Synthesis of Di-t-butyl Polysulfide from Isobutene, Hydrogen Sulfide, and Sulfur (Part 2) Catalytic Behavior of MFI Zeolites

• Published in: Journal of the Japan Petroleum Institute 2009, Vol.52(3), pp.128-138
• Main Authors: Qian, Eika Weihua, Hirabayashi, Kazuo, Hirasawa, Satoko, Yamada, Shigeru, Sakata, Hiroshi, Ishihara, Atsushi
• Format: Article
• Language: English
• Subjects: Aluminum; Boron; Catalysis; Catalysts; Gallium; Liquids; MFI zeolite; Polysulfide synthesis; Polysulfides; Reaction mechanism; Sulfur; Synthesis; Zeolite catalyst; Zeolites
• ISSN: 1346-8804; 1349-273X; 1349-273X
• DOI: 10.1627/jpi.52.128

Synthesis of di-t-butyl polysulfide from isobutene, hydrogen sulfide and sulfur was carried out at 125°C in an autoclave over MFI zeolite catalysts isomorphously framework-substituted with Al, Ga, and B. Performances of the catalysts were studied relative to liquid dicyclohexylamine catalyst. The catalysts were prepared from zeolite powders by kneading with alumina binder, extrusion, calcination, and ion exchange. Liquid products were analyzed with elemental analyzer, X-ray fluorescence spectrometry, HPLC, GPC and 1H-NMR. The Al- and Ga-containing zeolite catalysts were found to be active for the synthesis of di-t-butyl polysulfide. Activities of these catalysts decreased via ion exchange with K+ ion. A higher polysulfide yield was obtained over the Ga-containing catalyst relative to the liquid amine catalyst. The number of bridging sulfurs in the polysulfide ranged from 1 to 9, whereas the average number of bridging sulfur ranged from 4.2 to 4.7 (target 5.0). The distribution of sulfurs in the polysulfide formed over either the zeolite catalyst or the liquid amine catalyst was almost identical. Based on these results, the reaction pathway was discussed. In the case of the catalyst containing B in its framework, products were octenes, thiol, monosulfide, and a very small amount of di-t-butyl polysulfide, while the feed sulfur was not consumed. From the results of NH3 desorption, it is assumed that the strong acid site existing on the zeolite containing Al or Ga in its framework promotes the polysulfide synthesis reaction, whereas the zeolite containing B but having no such strong acid site is incapable of cleaving the elemental sulfur chain to form polysulfide.