Industrial & Engineering Chemistry Research, Vol.34, No.7, 2237-2246, 1995
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 methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), are being explored, e.g., those produced from a combination of the branched C-5 and C-6 olefins with methanol or biomass-based ethanol. The conversion and selectivity of these ethers are thermodynamically limited. This paper, thus, describes the determination and analysis of the equilibrium limitations in the liquid-phase synthesis of two of the three possible isomers of tert-hexyl ethyl ether (THEE) from reactive C-6 olefins and ethanol in the temperature range 298-353 K. The coupled reaction network for either of these two ethers involves two simultaneous etherification and one isomerization reactions, all being reversible. The equilibrium constants for these reactions, experimentally determined from equilibrium composition and the corresponding activity coefficients 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) > (2M1P reversible arrow 2M2P) for the isomerization reactions. This is explained on the basis of the relative stability of these olefins. The developed correlations are used to study the influence of process variables on the equilibrium conversion and selectivity of THEE formation.