Selectivity as a function of membrane thickness: Gas separation and pervaporation

Abstract

SYNOPSISIn this article, the pervaporation selectivity as a function of the membrane thickness is studied for the dehydration of acetic acid. From this study, it appeared that the selectivity of polysulfone ( P S F ) , poly (vinyl chloride) (PVC ) , and polyacrylonitrile ( P A N ) decreases with decreasing membrane thickness, below a limiting value of about 15 pm. However, in the case of gas separation, the selectivity of PSF membranes is independent of the membrane thickness. This phenomenon could not be explained by a difference in membrane morphology, sorption resistance, thermodynamic interaction, or coupling. It is believed that the decrease in selectivity for thin membranes has to be attributed to defects induced during pervaporation. These defects, crazes (and cracks), result from a reduced value of the critical strain, due to sorption of acetic acid/water and stresses between the polymer chains, due to a concentration gradient across the membrane.

Effects of membrane thickness and heat treatment on the gas transport properties of membranes based on P84 polyimide

“…They observed sharp increases in permeability, solubility, and diffusivity coefficient for increasing film thickness for 13–50 μm range. Koops et al13 studied the pervaporation selectivity as a function of the membrane thickness and found the selectivity of polysulfone (PSF), poly(vinyl chloride) (PVC), and polyacrylonitrile (PAN) decreased with decreasing membrane thickness, below a limiting value of about 15 μm. Huang and Paul14 investigated the relationship between the physical aging and film thickness.…”

Synthesis of magnetite in poly(vinyl alcohol) matrix and its use in separation of acetone/water mixtures via pervaporation, vapor permeation with and without temperature difference methods

“…However, contrary results are also available in literature. Koops et al [34] investigated the pervaporation selectivity for polysulfone, poly (vinyl chloride) and poly (acrylonitrile) membranes and reported that selectivity decreased with decreasing membrane thickness below a limiting value of 15 mm. Brun et al [35] studied the influence of the thickness for rubber membranes and reported that separation factor was constant above a certain (10 mm) membrane thickness.…”

“…It was observed from the figure that the permeation rate increased whereas the separation factor decreased as the temperature increased from 30 to 50 C. Increase in the permeation rate could be attributed to the increase in thermal energy of chain segments which provokes the chain mobility creating an extra free volume within the polymer matrix. As a result, sorption and diffusion rates of both acetone and water molecules increases [31,34,38,39]. Having suitable permeation rate and separation factor, 40 C could be selected as the optimum temperature for the operation.…”

Single layer hydrogenated graphyne membrane for selective hydrogen separation: A molecular dynamics simulation study

“…Comparing these results with what measured using a membrane without any defect, a dramatic reduction in separation selectivity can be observed. Similar to other membrane materials, reducing the number of defects per surface area might lead to a higher separation selectivity [22][23][24].…”