Olefin isomer separation by reactive extractive distillation: Modelling of vapour–liquid equilibria and conceptual design for 1-hexene purification

A thermodynamic model was developed to describe the vapour–liquid equilibria encountered in the reactive extractive distillation of 1-hexene mixed with n-hexane and 2-methyl-1-pentene, used to represent a Fischer–Tropsch stream. Experimentally it is determined that the feed mixture behaves nearly ideal in the absence of any solvent and that the obtained selectivities are near unity. A non-reactive solvent (D2EHPA) increases the activity coefficients but does not significantly improve the selectivity. The selectivity can only be increased by enriching the solvent with a metal-ion (Ag). The model uses the Wilson equation to describe the activity coefficients and can represent the vapour–liquid equilibria accurately as function of composition, pressure and temperature. To produce 1-hexene with a 99% recovery and at 99.5% purity, the solvent-to-feed ratio should be around 5 (at 0.2 bar, T = 311 K). Under these conditions the selectivity is 1.34 (2-methyl-1-pentene/1-hexene) and 1.55 (n-hexane/1-hexene) and the minimum number of equilibrium trays approximately 42.