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

Abstract

The dehydration of alcohols in the presence of carboxylic acids, ketones and aldehydes in Fischer–Tropsch hydrocarbon fractions was investigated over η-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 α-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 °C and a liquid hourly space velocity of 6 L feed/(L cat h −1), isomerisation of olefins gradually ceased until the fraction of α-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 °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.