Skeletal isomerisation of n-butenes present in C-4 pyrolysis residue fraction

Butenes present in butadiene and isobutene free C-4 fraction (a stream from the production of methyl-tert-butyl ether - so-called raffinate II) were i somerised over the hydrogen-chlorided and sulphated catalysts at 350-515 de grees C. A natural clay (bentonite) and commercial gamma-alumina were used as catalyst precursors. Hydrogen-chlorided catalysts were deactivated in ab out 6 h by 10-15% with respect to butene conversion, and a regeneration wit h air doped hydrogen chloride did not allow to renew the catalytic activity to full extent. This behaviour should be ascribed to high volatility of ch lorides which, moreover, pollute the product as itself and in the form of c hlorinated organic compounds. On the other hand, catalysts prepared by trea tment of calcinated and evacuated gamma-alumina with diluted sulphuric acid , proved to be sufficiently active in 2500 h lasting experiments, whereas r egeneration with air was necessary every 4-6 h. This stability is probably caused by high melting point of aluminium sulphate which is formed in the c ourse of the catalytic preparation and treatment. The selectivity, 50% of t he isobutene formation, was achieved at approximately 50% conversion of but enes, 450 degrees C, GHSV=0.6 g cm(-3) h(-1). Experiments at higher pressur e allowed to increase the conversion, but larger amount of components with higher molar weight was formed. Methanol and methyl-tert-butyl ether did no t effect the process of skeletal isomerisation significantly, but a presenc e of butadiene strongly enhanced deactivation of the catalyst. (C) 2000 Els evier Science B.V. All rights reserved.