A study on the dehydration performance of pervaporation and vapor permeation processes for an integrated VOCs purification system

Abstract

An integrated VOCs purification system consisting of vapor permeation and pervaporation processes was proposed in this study. Performance evaluation of each process for dehydration of isopropyl alcohol (IPA)-water mixture was conducted experimentally. Different types of hollow-fiber membranes were applied to each process, namely a NaA zeolite membrane coated on a porous alumina tubular support for the pervaporation process and a polyimide membrane with a finger-like structure for the vapor permeation process. The two hollow-fiber modules were evaluated in different operating modes with a cocurrent-flow configuration: a lumen-side feed for vapor permeation (i.e., in-out configuration) and a shell-side feed for pervaporation (i.e., out-in configuration). Parametric investigation was carried out to assess the effect of operating conditions (e.g., feed flow rate, feed concentration, and feed temperature) on each process performance.

In the vapor permeation process, the recovery and purity of IPA increased from 70.3% and 98.4 wt% to 95.0% and 99.6 wt%, respectively, as the feed flow rate increased from 0.107 l/min to 0.535 l/min. The transmembrane flux of IPA decreased slightly from 0.080 kg/m2h to 0.069 kg/m2h, whereas its value of water vapor increased linearly from 0.011 kg/m2h to 0.067 kg/m2h with an increasing feed flow rate. On the contrary, the IPA feed concentration had a negligible effect on the IPA recovery, purity and transmembrane flux of both IPA and water vapor in the higher feed concentration range above 90 wt%.

For the pervaporation process, as the feed temperature increased from 50 C to 70 C, the overall mean transmembrane flux increased from 0.6 kg/m2h to 1.1 kg/m2h, the time required to reach a purity of 99.5 wt% decreased from 11 hours to 7 hours, and the IPA recovery decreased from 85.7% to 82.6%. It was also observed that with an increase in the feed flow rate from 0.5 l/min to 1.0 l/min, the overall mean transmembrane flux decreased from 0.97 kg/m2h to 0.69 kg/m2h, the time required to reach a purity of 99.5 wt% increased from 8 hours to 10 hours, and the IPA recovery increased asymptotically from 82.6% to 85.2%.