CO₂ Capture In A Poly?vinylidene Fluoride? Hollow Fiber Membrane Contactor

With the rapid development of economy,low-carbon renewable energy has attracted people's attention because it can reduce the emission of greenhouse gases.Methane produced by anaerobic fermentation is a source of renewable energy.Normally,the original biogas is composed of methane,CO₂,and trace amounts of H₂S,so it must be purified and removed from biogas before using biogas.Gas-liquid membrane separation is a kind of coupling gas membrane separation technology and gas absorption technology advantages,is a very promising CO₂ separation process,but the technology is still in its infancy,there are many problems to be solved.Based on the new gas-liquid membrane separation system,this paper has carried on the theoretical analysis and the experimental research around the problems such as the aging of membrane,the superhydrophobic modification of the membrane surface,the feasibility of the removal of the acid gas,and the mass transfer process of the membrane gas absorption system.Accelerated aging of polyvinylidene fluoride?PVDF?hollow fiber membranes applied in membrane contactors with solution of MEA was reported.The structure evolution of PVDF membranes before and after the membrane contactor was characterized by Fourier infrared spectroscopy,differential scanning calorimeter,and scanning electron microscopy and contact angle.The reason leading to the decreased hydrophobicity of PVDF membrane after the application in gas absorption was investigated by long-term experiments.The results indicate that it is the elimination reaction that causes the hydrophobicity of PVDF membrane to decrease.To avoid the accelerated aging of the PVDF membranes used in membrane contactors with solution of MEA,some measures were put forward based on the discussion in the article.The wetting of hollow fibre membranes decreases performance of the liquid-gas membrane contactor for CO₂ capture in biogas upgrading.To solve this problem,in this work,a poly?vinylidene fluoride??PVDF?hollow fibre membrane for a liquid-gas membrane contactor was coated with a superhydrophobic layer composed of a combination of hydrophobic SiO₂ nanoparticles and polydimethylsiloxane?PDMS?by the method of spray deposition.A rough layer of SiO₂ deposited on the PVDF membrane resulted in an enhanced surface hydrophobicity.In addition,continuous CO₂absorption tests were carried out in original and modified PVDF hollow fibre membrane contactors,using monoethanolamine?MEA?solution as the absorbent.A long-term stability test revealed the modified PVDF hollow fibre membrane contactor was able to outperform the original membrane contactor and demonstrated outstanding long-term stability,suggesting that spray deposition is a promising approach to obtain superhydrophobic PVDF membranes for liquid-gas membrane absorption.The present work studied the simultaneous separation of H₂S and CO₂ from biogas by gas-liquid membrane contactor?GLMC?using single and mixed absorbents.The results indicated that the use of promoted K₂CO₃ with PS solutions could simultaneously improve the absorption flux of H₂S and CO₂.Increasing the liquid flow rate and absorbent concentration led to an increase in the CO₂ absorption flux,while increasing the gas flow rate led to a significant increase in H₂S absorption;The change of liquid flow rate has little effect on H₂S absorption flux.A long-term stability test revealed that partial wetting of membrane could reduce the CO₂ absorption flux;but has little effect on H₂S absorption flux.The detailed analysis of the mass transfer coefficients showed that liquid side resistance was negligible in comparison with membrane and gas side resistances for H₂S absorption.On the contrary,the mass transfer process of CO₂ was controlled by liquid mass transfer resistance.