Application of Hollow Fiber Membrane Contacting System for CO2/CH4 Separation

Abstract

Carbon dioxide separation using membrane based contacting system is a reliable alternative to traditional gas absorbent techniques such as wet scrubbers. The main objective of this research was to design, develop and implement a hollow fiber membrane based contactor system to absorb and separate CO2 from CH4 in a simulated flare gas stream. Gas-liquid contacting system was constructed using microporous polytetrafluoroethylene (PTFE) hollow fibers as a highly hydrophobic membrane. The module used for the experimental studies has 51 mm diameter and 200 mm effective length. The membrane module had the packing density of 60 % and the PTFE hollow fiber being employed in this module had the mean pore size of 0.48 μm. Experiments conducted in a laboratory-scale plant fed with a simulated flare gas mixture containing 2.5 % of CO2 balanced with CH4 which could produce varying concentrations of inlet gas using mass flow controller. CO2 separation experimentation studies were performed and effect of operational variables on separation efficiency of the system has been studied. In order to optimize the gas separation performance of the membrane module, effects of gas and liquid flow rates, absorbent-phase concentration, and nature of scrubbing liquid were examined. The absorption efficiency of deionized-water and aqueous solutions of sodium hydroxide (NaOH) and diethanolamine (DEA) as the physical and chemical absorbents has been compared. Results indicated that increasing the flow rate and concentration of scrubbing liquid can enhance the separation efficiency; however, increasing the flow rates of the gas-phase has a negative impact on the CO2 absorption performance of the system. The traditional CO2 separation process suffers from many limitations, such as high capital and operational costs, and potential of equipment corrosion. Membrane processes offer attractive opportunities for gas treatment applications including removal of CO2, H2S, and SO2 from flare gas mixtures. This technology offers a variety of practical benefits including low energy and operation costs and at the same time it can help to mitigate the adverse health effects associated with burning the waste gases.