Deep CO2 removal using high pressure membrane contactors with low liquid-to-gas ratio

[Display omitted] •Deep CO2 removal using high pressure membrane contactor was proven able to reduce CO2 content to < 0.005 mol% level, meeting requirement for atural Gas process.•Liquid phase mass transfer resistance was the highest compared to membrane phase and gas phase, showing that liquid was the bottleneck for mass transfer.•High liquid velocity was favored for better liquid phase mass transfer, resulted in high L/G ratio in deep CO2 removal using membrane contactor.•Liquid flow rate reduction could not reduce L/G effectively as this led to more reduction in CO flux than L/G.•Membrane module length increase was able to achieve 70% reduction in L/G, with only 16% reduction in flux, offering lower energy consumption compared to conventional packed column in LNG process. Membrane contactor is a technology that intensifies conventional absorption column. However, liquid-to-gas ratios (L/G) of membrane contactor in existing reports are much higher compared to CO2 absorption column, which results in higher solvent circulation rate and higher consumption in heating energy. This makes the technology less attractive for deep CO2 removal. Direct reduction of liquid flow rate was not effective in lowering down L/G. Experimental results showed that 50% reduction in liquid flow rate could reduce L/G by 25%, but the reduction in CO2 flux (33%) was higher due to decrease in liquid phase mass transfer coefficient which was dependent on liquid velocity. An alternative method to reduce L/G through membrane module length increase was proven, where L/G was reduced 70% with only 16% flux reduction. The flux reduction was only observed when L/G dropped below 0.80L/mol and it was due to depletion of unreacted amine for CO2 absorption. The lowest L/G value obtained in this study was 36% lower than the conventional absorption column in liquefied natural gas (LNG) process, showing that membrane contactor technology is not only energy-viable and more compact for deep CO2 removal, but it also offers energy saving advantage.