Dehydration of C4 alkanols conjugated with a positional and skeletal isomerisation of the formed C4 alkenes

In the context with our recently published report about skeletal isomerisation of butenes present in C-4 pyrolysis fraction [V. Macho, M. Kralik, L. Jurecek, E. Jurecekova, J. Balazova, Appl. Catal. A: Gen. 203 (2000) 5], the dehydration of C-4 alkanols conjugated with a positional and skeletal isomerisation of the formed C-4 alkenes was studied. Thermally and with diluted sulphuric acid activated gamma-aluminas (A and AA catalysts) were used in a fixed bed reactor at 300-470 degreesC, atmospheric pressure and a catalyst loading GHSW = 0.12-0.8 g cm(-3) h(-1). Under these conditions all the C-4 alkanols were totally dehydrated and underwent subsequent isomerisation, eventually further reactions yielding especially in propene. Depending on the type of origin alcohol and reaction conditions, isobutene was formed mainly from isobutanol and tert butanol; cis-2-butene was generated dominantly in the case of 2-butanol. The lowest yield of isobutene was in the case of l-butanol. Distribution of individual butenes is discussed following reaction steps necessary for obtaining a certain butene isomer and its thermodynamic preference. The reported results showed on the possibility to obtain mainly isobutene from all the C-4 alkanols using a simple dehydration-isomerisation catalyst prepared by the acidification of gamma-alumina. (C) 2001 Elsevier Science B.V. Ail rights reserved.