Mixed-matrix membranes containing zero-dimension porphyrin-based complex for propylene/propane separation

Abstract

The membrane-based technology for propylene/propane (C3H6/C3H8) separation is very promising due to its low-energy separation process with high effectiveness. Herein, we propose a new type of mixed-matrix membranes (MMMs) containing zero-dimension non-porous porphyrin-based complex (M-TMCPP, M = Zn2+, Cd2+, Ni2+) with coordinatively unsaturated metal sites. Density functional theory calculation results show that M-TMCPP can form π complexation with C3H6 and facilitate C3H6 molecule through membranes. Different from porous nanofillers, M-TMCPP exhibits zero-dimension non-porous molecular structure and can be dissolved in solvent at molecular lever under low concentration. Benefiting from the favorable interaction between C3H6 with metal sites and the uniform distribution of M-TMCPP particles and/or even independent M-TMCPP molecules in polymer, the porphyrin-based complexes are used as nanofillers in fluorinated polyimide (6FDA-DAM). The prepared MMMs exhibit an extraordinary C3H6/C3H8 ideal selectivity of up to 45.6 with a high C3H6 permeability of 70.3 Barrer, far surpassing the previously reported 6FDA-based polyimide MMMs and polymeric membranes. Membrane performances of three different M-TMCPP MMM were studied and the gas transportation mechanism was evaluated. This work provides a new conceptual approach of using non-porous zero-dimensional complexes with coordinatively unsaturated sites as fillers in mixed matrix membranes, which not only can accomplish olefin/alkane separation with ultrahigh performance, but also indicates its high potential for feasible usage.