PIM-1-based membranes for gas separation and pervaporation applications

Abstract

PIM-1 belongs to a class of polymers named polymers of intrinsic microporosity (PIMs) that have contorted macromolecular backbone structures with high free volume. The interconnected pores of PIM-1 provide channels to facilitate the quick pass of small molecules therefore; PIM-1 has the potential to be used in membrane-based molecular separation processes such as pervaporation (PV) for alcohol recovery and gas separation for carbon dioxide separation. PIM-1 thin film composite (TFC) PV membranes were designed for butanol (BuOH) recovery from an aqueous solution containing 5 wt.% BuOH at 65 °C. Electrospun polyvinylidene fluoride (PVDF) membranes, due to their high porosity and good hydrophobicity, were used as the support to prepare PIM-1 TFC membranes by the roller coating method. To prevent infiltration of the PIM-1 solution into the support during the membrane fabrication process, the support was impregnated with different PVDF nonsolvents. The membranes showed very high flux in the range of 16.1-35.4 kg m^-2.h^-1, with an acceptable separation factor of 8. In addition, the potential of the PV/distillation hybrid process to decrease the BuOH separation cost was studied using Aspen Hysys. It was concluded that the recovery cost decreased by increasing the selectivity of the PV membrane. PIM-1 gas separation membranes suffer from physical aging resulting in a decrease in membrane permeability over time. PIM-1 mixed matrix membranes (MMMs) were explored to not only suppress physical aging but also to enhance the initial performance of the membranes for CO2/CH4 and CO2/N2 separation. Freestanding PIM-1 MMMs were fabricated by incorporating polyhedral oligomeric silsesquioxane (POSS) and graphene oxide (GO) functionalized with POSS (GO-POSS). Compared to the neat PIM-1, the addition of a very small amount of GO-POSS (in the range of 0.01-0.75 wt.%) to PIM-1 led to membranes with a maximum 69% permeability enhancement and less than half of the reduction in CO2 permeability (26% for the MMM vs 58% for the neat PIM-1) after 5 months. In addition, porous silica nanosheets (SN), exfoliated SN (E-SN), sulfonic acid functionalized SN (S-SN), and amine functionalized SN (N-SN) were synthesized, characterized and embedded into the PIM-1 polymer chain to prepare thick MMMs and thin film nanocomposites (TFNs). Freestanding and thin film membranes containing 0.05 wt.% S-SN showed the best initial performance with 35% and 40% higher CO2 permeability/permeance than the neat PIM-1, respectively; without any sacrifice in selectivity. Moreover, the 150 days-aged freestanding PIM-1/S-SN (1 wt.%) membrane lost 32% of its initial permeability which is substantially lower than that of neat PIM-1 (63%) at the same period. Also, compared to TFC PIM-1, TFN PIM-1/S-SN membrane demonstrated 5 times higher CO2 permeance after 28 days.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Rahul Raveendran Nair (Supervisor) & Patricia Gorgojo (Supervisor)