Experimental study on the performance and long-term stability of PVDF/montmorillonite hollow fiber mixed matrix membranes for CO2 separation process

Abstract

Porous asymmetric polyvinylidene fluoride (PVDF)/montmorillonite (MMT) hollow fiber mixed matrix membranes (MMMs) with different nano-clay loadings were prepared via wet phase inversion technique and was used for membrane contactor. The fabricated MMMs were characterized in terms of morphology, structure, gas permeability, wetting resistance and mechanical stability. From morphology point of view, the fabricated membranes had a finger-like/sponge-like structure in the middle layer with a very porous thin outer skin layer and an inner skinless sponge-like structure. Atomic force microscopy (AFM) revealed an increase in surface roughness with increasing MMT loading. From gas permeation test, the surface porosity of the MMMs was higher than the plain PVDF membrane and the mean pore size of the membranes was small (34-22nm) and decreased slightly at 5wt.% MMT loading. A significant improvement in LEPw and hydrophobicity caused the prepared MMMs to show high wetting resistances. Mechanical stability test of membranes demonstrated an increase in stress at break and collapsing pressure with a slight loss in elongation with clay loading. CO2 absorption tests with water as absorbent showed that the absorption rate of the MMMs was higher than the plain membrane and increased with MMT loading. For example, at MMT loading of 5wt.% and absorbent flow rate of 0.5ms-1, the absorption flux was 1.89×10-3molm-2s-1 that was 48.7% higher than the plain PVDF membrane. Moreover, the absorption rate of the best fabricated MMM was higher than the commercial PVDF membrane. A long-term contactor test of this membrane over 350h showed that wetting did not take place and the absorption flux remained almost constant. It was concluded that, due to the higher surface hydrophobicity, wetting resistance and performance, MMMs can be a promising candidate to be used in contactor applications.