Remediation of Cellulose Acetate-Based Hollow Fiber Gas Separation Membranes Contaminated by Nonvolatile Hydrocarbons

Polymeric membranes have been essential to gas processing. The viability of membrane systems for industrial gas applications lies in the tolerance of such membranes to contamination by the impurities present in the gas streams. While membrane contamination from volatile species can be addressed using purge streams and heat treatment, contamination from non-volatile hydrocarbons can cause a significant decline in membrane permselectivity. This study focuses on the characterization and remediation of cellulose acetate based hollow fiber membranes contaminated by heavy hydrocarbons.

Cellulose acetate-based gas separation membranes have a moderate resistance against performance decline caused by hydrocarbons found in natural gas. The hollow fiber membranes were coated with motor oil lubricant to simulate heavy hydrocarbon contamination from large-scale gas compressors and industrial feed streams, and the remediation of the hollow fibers was conducted using solvent exchange and solvent extraction methods. The permeabilities of the membranes to carbon dioxide, helium, hydrogen, methane, nitrogen and oxygen were measured at pressures 300 - 1500kPa and at temperatures 25 - 50°C.  It was shown that even a thin layer of the lubricant oil on the membrane surface could result in substantial losses in membrane performance, with faster permeating gases (e.g., He and H2) suffering the worst losses. Solvent-exchange, in which the membrane was “washed” using a series of solutions of varying organic content, was unable to remediate the membrane effectively, while the removal of the heavy hydrocarbon contaminant on the membrane surface by a direct cyclohexane rinse was found to work well to restore the membrane performance.