Fischer−Tropsch Aqueous Phase Refining by Catalytic Alcohol Dehydration

Polar products from Fischer−Tropsch synthesis, such as short-chain alcohols, carbonyl compounds, and carboxylic acids, on condensation, dissolve in the water formed in the Fischer−Tropsch process to form an aqueous product phase. Recovery of the organic compounds from this aqueous product phase involves complex separations, and catalytic dehydration of alcohols to olefins was investigated as a means to simplify the separations. Dehydration of alcohol mixtures (some containing water) was investigated to determine whether C 2 −C 8 alcohols can be coprocessed and whether branched alcohols can be selectively dehydrated in the presence of linear alcohols. In the presence of an η-alumina catalyst, the ease of alcohol dehydration increased with increasing carbon number, and mixtures could be dehydrated completely with >95% selectivity to olefins. The molar ratio of secondary and tertiary alcohol dehydration to primary alcohol dehydration obtained with a sulfonic acid resin catalyst (Amberlyst 15) at 100−115 °C was >50:1, with a supported phosphoric acid catalyst at 170−180 °C, it was <10:1, and with an η-alumina catalyst at 275 °C, it was <2:1. A processing scheme that simplified the recovery of organic compounds from the aqueous product produced by Fischer−Tropsch synthesis is suggested.