Functionalised 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 a-olefins like 1-hexene from other C6-olefin isomers (internal, branched, cyclic and diolefins) and paraffins by using p-complexation. Functionalized metal-ligand complexes were synthesized based on commercial available ligands from hydrometallurgy. In screening experiments they were evaluated for p-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