Membrane-Based Absorption of VOCs from a Gas Stream

A regenerative absorption-based process was developed for removing VOCs from N₂ in an inert, nonvolatile, organic liquid flowing in compact hollow-fiber devices. The process eliminates flooding, loading, and entrainment, and can replace activated carbon adsorption. Two types of hollow-fiber membranes were studied: one with a microporous wall and the other with a highly VOC-permeable nonporous coating on the outer surface of a microporous hollow fiber. Criteria for nondispersive operation were developed for each case. Experiments were conducted for the absorption of acetone, methylene chloride, toluene, and methanol from the respective VOC-N₂ gas mixture using two absorbents: silicone oil and mineral oil. The highest mass-transfer coefficient was obtained for toluene followed by methylene chloride, acetone, and methanol. Different resistances making up the overall resistance in VOC absorption were characterized comprehensively to develop a predictive capability and compare the absorption performances of two types of fibers and the two absorbents. The absorbent-filled porous membrane contributed significantly to the total mass-transfer resistance. Numerical simulations of governing equations based on a cell model agree well with experimental results.