A pilot-scale demonstration of a membrane-based absorption-stripping process for removal and recovery of volatile organic compounds

A new membrane-based continuous absorption-stripping process has been developed to separate gas/vapor mixtures, such as volatile organic compounds (VOCs), from a nitrogen/air stream. Two different hollow fiber membrane modules are needed in this process to remove the VOCs. In the first module, VOC-laden nitrogen/air stream flows through the bore of the hollow fibers. A suitable absorbent liquid with a high solubility for the VOC and essentially no solubility for nitrogen/air is pumped countercurrently over the outside of the fibers. This liquid is an inert, nontoxic, and essentially non-volatile, organic solvent. The VOCs are effectively removed from nitrogen/air to a very low level and are concentrated in the absorbent for recovery, while the absorbent is regenerated by heating and subjecting it to vacuum in a separate hollow fiber membrane module called the stripping module. A pilot-scale membrane-based absorption-stripping unit was located next to a paint spray booth at Robins Air Force Base, Warner Robins, GA. Tests were performed on slip-streams of real-time air emissions from scheduled intermittent painting operations, so the concentration of VOC in the exhaust air fluctuated with time. The VOC removal efficiency was determined as a function of the feed air flow rate and the absorbent (silicone oil) flow rate. Depending on the gas/liquid flow rates and the inlet VOC concentration, the process successfully removed as much as 95+% of the VOC present. The experimental results have been compared with theoretical predictions.