The potential of pervaporation for separation of acetic acid and water mixtures using polyphenylsulfone membranes

Abstract

Conventional pervaporation (PV) membranes usually have limited resistance to acetic acid (HAc), particularly in high pressure and temperature conditions, resulting in a cumbersome water-acetic acid separation. When acetic acid is to be recycled in process conditions in a hybrid pervaporation approach, the PV membrane may experience these conditions of high temperatures and pressures. This study explores the potential of dehydrating acetic acid using pervaporation with novel polyphenylsulfone (PPSU) membranes. These membranes were tested for PV dehydration of mixtures of acetic acid–water with 80 and 90 wt.% acetic acid in the temperature range between 30 and 80 °C. In addition to that, an experimental study of membrane stability was performed at high concentration of HAc and high temperatures. It was found that a higher polymer concentration does not necessary yield a better separation factor: PPSU-based membranes with 27.5 wt.% of the polymer (PPSU-27.5) were similar to 30 wt.% (PPSU-30) in terms of overall performance, considering both flux and separation factor. Although the total flux of PPSU-27.5 (∼0.12–0.83 kg/m 2 h) is lower than PPSU-25 (∼0.24–1.48 kg/m 2 h) the average separation factor can be higher than for the PPSU-30 membrane. For example, in 90 wt.% HAc, the separation factor is 8.4 for PPSU-27.5 and 5.7 for PPSU-30. The swelling degree (DS) was found to decrease with feed temperature, while an increase of the selectivity and flux was observed. The activation energy of permeability ( E p ) shows that PPSU membranes have negative E p values. This indicates that the membrane partial permeabilities decrease with increasing temperature. With the enrichment of acetic acid on the feed side of the membrane, the degree of swelling, flux and separation factor all increase. Regarding on the membrane stability tests, the PPSU membranes showed promising results at tested conditions.