Separation of alcohol/ether/hydrocarbon mixtures in industrial etherification processes for gasoline production

Ether synthesis is growing in importance in the oil industry, due to their increasing use as octane enhancers in gasolines. Ethers are obtained by the addition of an alcohol on an iso-olefin. The main ethers of industrial interest for gasolines are: MTBE (methyl tert-butyl ether) resulting from the addition of methanol on isobutene. TAME (tert-amyl methyl ether) resulting from the addition of methanol on isoamylenes. ETBE (ethyl tert-butyl ether) resulting from the addition of ethanol on isobutene. The reaction step of etherification processes yield rather complex mixtures of alcohols, ethers and hydrocarbons which are difficult to separate due to the existence of numerous azeotropes. After reviewing the use of ethers as gasoline components this paper describes the separation steps which are involved, in the case of ETBE synthesis. It is particularly shown that an accurate knowledge of the thermodynamical behaviour of ethanol/ETBE/Cq mixtures is essential for the design of these separation steps.