ETHERS FROM ETHANOL .3. EQUILIBRIUM CONVERSION AND SELECTIVITY LIMITATIONS IN THE LIQUID-PHASE SYNTHESIS OF 2 TERT-HEXYL ETHYL ETHERS

Alternatives to the conventional isobutylene-derived ethers, namely me thyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), are be ing explored, e.g., those produced from a combination of the branched C-5 and C-6 olefins with methanol or biomass-based ethanol. The conver sion and selectivity of these ethers are thermodynamically limited. Th is paper, thus, describes the determination and analysis of the equili brium limitations in the liquid-phase synthesis of two of the three po ssible isomers of tert-hexyl ethyl ether (THEE) from reactive C-6 olef ins and ethanol in the temperature range 298-353 K. The coupled reacti on network for either of these two ethers involves two simultaneous et herification and one isomerization reactions, all being reversible. Th e equilibrium constants for these reactions, experimentally determined from equilibrium composition and the corresponding activity coefficie nts estimated by the UNIFAC method, decrease in the following order of tertiary olefins: 2M1P > isobutylene > 2,3DM1B approximate to 2M1B > 2M2P > 2M2B > 2,3DM2B for etherification reactions with ethanol, and ( 2,3DM1B reversible arrow 2,3DM2B) > (2M1B reversible arrow 2M2B) > (2M 1P reversible arrow 2M2P) for the isomerization reactions. This is exp lained on the basis of the relative stability of these olefins. The de veloped correlations are used to study the influence of process variab les on the equilibrium conversion and selectivity of THEE formation.