Pilot-plant and laboratory studies on vapor permeation removal of VOCs from waste gas using silicone-coated hollow fibers

In a recent bench-scale study the vapor permeation-based removal of individual volatile organic compounds (VOCs), e.g. methanol, toluene from an N₂ stream was studied using microporous polypropylene hollow fibers having a plasma polymerized silicone coating on the outside surface of the fiber. The novel vapor permeation process employed bore-side feed flow and vacuum on the shell-side. The observed separation behavior was described successfully by an analytical solution of a simpler model and by a numerical solution of a more extensive set of model equations based on experimentally-determined behavior of concentration-dependent VOC permeance. The remarkably high separation performance achieved in that study on a bench-scale has led to pilot-plant studies using a larger module. Results of pilot-plant studies using streams containing high concentrations of VOCs, (e.g. 1-8% of methanol, and 0.3-1.3% of toluene) as well as low concentrations of VOCs (e.g. 0.1% or less of methanol, toluene, ethanol, n-butanol, tetrahydrofuran, methylene chloride and acetone together) for a hollow fiber module containing 1000 fibers are reported here. The results for methanol removal from highly concentrated streams have been compared with the results obtained from simulations of theoretical models developed earlier. Model simulation results describe the observed pilot plant separation behavior well. These successes have prompted additional bench-scale laboratory studies with other VOCs (e.g. methylene chloride), results of which are also reported here; these results have also been compared with the predictions from the models developed earlier.