Functionalized Solvents for Olefin Isomer Purification by Reactive Extractive Distillation

Olefin isomer separations are difficult, energy intensive and thus expensive. An overview is presented to investigate the feasibility of metal–ligand complexes as functionalized solvents applied in a novel separation technology, reactive extractive distillation, for the separation and purification of α-olefins like 1-hexene from other C6-olefin isomers (internal, branched, cyclic and diolefins) and paraffins by using π-complexation. Functionalized metal–ligand complexes were synthesized based on commercial available ligands from hydrometallurgy. In screening experiments they were evaluated for ρ-complexation with ethylene. The best solvents were selected for evaluation of preferential complexation of 1-hexene relative to other olefin isomers. D2EHPA and DNNSA yield both stable metal–ligand complexes and triple the solubility of ethylene. Next, three different phosphoric acid ligands: D2EHPA, DBPA and MEHPA and two sulphonic acid ligands: DNNSA and DBSA, were investigated for a variety of C6-olefin isomers. The highest selectivities were obtained for silver-DBPA (20 wt% Ag, S/F = 3): 1.23 for 2-methyl-1-pentene and 1.42 for n-hexane. An equilibrium model is used to conceptually design a reactive extractive distillation column applying the functionalized solvent silver-D2EHPA. Such a column should be operated at a solvent to feed ratio of around 5(P = 0.2 bar, T = 311 K) for 99.5% purity and 99% recovery. Under these conditions, the minimum number of equilibrium trays (Nmin) to separate 1-hexene from 2-methyl-1-pentene is approximately 42, a dramatic decrease compared to Nmin of about 310 in the absence of silver.