Green solvent-synthesized polyimide membranes for gas separation: Coupling Hansen solubility parameters and synthesis optimization

In quest of sustainable development, research efforts have been focused on replacing conventional toxic solvents with green solvents to fabricate greener membranes, illuminating the significant role of green chemistry and engineering to promote a circular economy. Nevertheless, the use of green   solvents in membrane technology is still in the early stages since its practicality remains elusive. This work demonstrates the preliminary screening of green solvents using Hansen solubility parameters (HSP), followed by an optimization of the synthesis conditions of polyimide using the selected green solvent. Based on HSP evaluation, TamiSolve® NxG is identified as a potential green solvent for polyimide synthesis. Two synthesis approaches such as chemical imidization and one-step high temperature polymerization are examined by varying monomer concentrations, polymerization temperatures, imidization time, and imidization temperatures. The polyimide membranes developed from the optimized synthesis conditions ameliorate the gas separation performance with more than 30 % increment in O 2 and CO 2 permeabilities without compromising their O 2 /N 2 , CO 2 /N 2 , and CO 2 /CH 4 selectivities. Additionally, the membranes prepared from green solvent-synthesized polyimide exhibit a remarkable enhancement in CO 2 plasticization pressure up to 25 bar which outperform that of conventional membranes within 5–15 bar.