Dehydration of alcohols in the presence of carbonyl compounds and carboxylic acids in a Fischer-Tropsch hydrocarbons matrix

The dehydration of alcohols in the presence of carboxylic acids, ketones and aldehydes in Fischer-Tropsch hydrocarbon fractions was investigated over eta-alumina at different temperatures and mass hourly space velocities. Quantitative dehydration of the alcohols was achieved while reactions of carbonyl compounds and acids were incomplete and short-lived. At least 70% of the alpha-olefins in the feed were initially isomerised to internal olefins, while primary alcohols were dehydrated to mostly internal olefins. Over a period of 8 days, at 350 degrees C and a liquid hourly space velocity of 6 L feed/(L cat h(-1)), isomerisation of olefins gradually ceased until the fraction of alpha-olefins equalled the original concentration in the feed (16 mass%) plus the fraction formed from the dehydration of alcohols (8 mass%). The conversion of carbonyl compounds and acids also diminished to a negligible level. The isomerisation activity was linked to catalyst sites which were selectively poisoned by carbonyl compounds and acids. Regeneration of the catalyst with oxygen at a temperature of 480 degrees C resulted again in removal of carbonyl compounds and acids as well as olefin isomerisation. The alcohol dehydration reaction appeared not to be affected by the poisoning of the catalyst. (c) 2005 Elsevier B.V. All rights reserved.