Removal of VOCs from air by membrane-based absorption and stripping

Atmospheric emission of volatile organic compounds (VOCs) such as toluene, xylene, acetone etc. from industrial facilities causes serious environmental problems and financial losses. Existing technologies for VOC emission abatement have many strengths as well as considerable limitations. A regenerative absorption-based process for removal of VOCs from N₂ in an inert, nonvolatile, organic liquid flowing in compact hollow fiber devices has been studied here. These devices eliminate flooding, loading and entrainment encountered in conventional absorption units. Detailed experimental results and theoretical analyses for absorption studies were communicated elsewhere. The overall performance of the combined absorption-stripping process is described here; it appears to be controlled by stripping due to the low temperature and the lower membrane surface area in the stripper. The difference between only absorption and combined absorption-stripping results was more pronounced for VOC-absorbent systems having higher Henry's law constant and diffusivity. A theoretical model has been developed from first principles to simulate the behavior of the membrane stripper; this has been combined with the model for the membrane absorber to determine the overall process performance. Simulated results obtained from the mathematical models agree well with the experimental results for combined absorption-stripping. Simulation results suggest that higher stripping temperature and larger stripper area enhance the performance considerably.