Development of Novel Hydrophobic Composite Hollow Fiber Membranes Intended for Use in Membrane Contactor for CO2 Capture (Keynote Talk)

Carbon dioxide (CO₂) is a greenhouse gas found primarily in flue gas as a main combustion product of fossil fuel as well as a component in natural gas, biogas and landfill gas. The interest to remove CO₂ from those gas streams to reduce CO₂ emission to the atmosphere, and to obtain fuel with enhanced energy content and prevent corrosion problems in the gas transportation system have driven the development of CO₂ separation process technology.

One type of technology which is increasingly seen as a promising alternative to traditional absorption technology using packed towers or bubble columns for CO₂ capture from flue gas or biogas is gas-liquid membrane contactor. In a membrane contactor, a CO₂ containing gas stream and a liquid solution flow counter-currently in both sides of the membrane. CO₂ capture is achieved when CO₂ transports through the hydrophobic microporous membrane matrix and is absorbed by the liquid absorbent. The attractive features offered by this technology include enhanced mass transfer efficiency because of much larger gas-liquid interface, simplicity in design and low cost construction of membrane modules due to its nearly atmospheric pressure of operation, etc. However, membrane contactor has not found practical large-scale applications. One of the main challenges to be addressed is to develop high-performance anti-wetting membranes with high chemical and thermal resistances.

This presentation reports the recent development of novel hollow fiber membranes suitable for use in membrane contactor. Two strategies are used: (1) exploring one-step simple and inexpensive approach for hydrophobic modification of imide group contained polymeric membranes such as polyamide-imide (PAI) hollow fibers using octadecylamine; (2) exploring a novel method to hydrophobically modify the in-house made polyetherimide (PEI) hollow fiber membrane by self-assembling of inorganic fluorinated silica dioxide (fSiO₂) on the PEI membrane surface. The modified membranes were, subsequently, characterized by a series of standard protocols in terms of membrane morphology, chemical structure, contact angle, porosity and critical water entry pressure. Studies of using modified membranes in membrane contactors for CO₂ absorption were also carried out.

Promising results were found through these studies. For example, the incorporation of the fSiO₂ particles on the membrane surface dramatically elevated the membrane hydrophobicity, as evidenced by the dynamic contact angles increment from original 66.7º to 124.8º for advancing values, and from 49.5º to 100.6º for receding values. The system showed a reasonable stability throughout the 31-day long term operation using a 2 M taurinate sodium aqueous solution as the liquid absorbent.