Alkyl- transfer (Transalkylation) reactions of alkylaromatics on solid acid catalysts

[摘要] Alkyl-transfer (transalkylation, disproportionation) reactions of alkylaromatics werestudied for the purpose of finding out the principles that governs them. Alkyl-transferof simpler alkylaromatics ranging from mono to polyalkyl-benzenes andalkylnaphthalenes were studied in a fixed bed reactor system on solid acid catalysts(zeolites) at temperatures up to 400 °C. Results showed that alkyl-transfer reactionsare reversible reactions with disproportionation favoured at lower temperatures whiletransalkylation seemed to be dominant at higher temperatures. The outlinedmechanism showed that the catalyst pore sizes and the type of pores as well as thefeed composition of binary mixtures play important roles in the transfer of alkylgroups between aromatic molecules. In alkyl-transfer reactions, the ease ofconversion depends on the number of alkyl groups on the aromatic ring/s, the chainlength, the type of alkyl substituent/s and the ring conjugation of the aromatic moiety.Zeolitic catalysts are rapidly deactivated by carbonaceous material deposition duringalkyl-transfer reactions especially at higher temperatures while deactivation throughmolecular retention is dominant at lower temperatures. Nevertheless, zeolites can beregenerated by high temperatures in oxidizing atmospheres. Bulkier alkylaromatics(those found in coal and petroleum liquids) can be transformed through alkyl-transferreactions if a suitable catalyst with the required strength and appropriate pore sizescan be developed, preferably a tri-dimensional arrangement as shown by the resultsof this study. Thus the alkyl-transfer process has promising future applications inpetrochemical and related industries; especially those interested in the transformationof coal to chemicals.

[发布机构] University of the Witwatersrand