Separation Performances Of CO₂ From Landfill Gas By Amino Acid Salt-mdea Mixed Solutions Based On Membrane Contactor

With the rapid development of economy and the continuous improvement of people's living standards,the outputs of municipal solid waste and landfill gas are both increasing.Landfill gas is mainly composed of CH₄ and CO₂.CH₄ is not only a clean energy,but also a more terrible greenhouse gas than CO₂.Therefore,the collection and utilization of landfill gas is of great significance to energy development and environmental protection.However,a large amount of CO₂ in landfill gas will reduce the calorific value of landfill gas,making the efficient separation of CO₂ the primary problem of landfill gas purification and resource utilization.Membrane absorption is a new technology which combines liquid absorption and membrane separation,with the advantages of high selectivity and large mass transfer area.It is a good choice for CO₂separation and CH₄ enrichment.In this paper,the CO₂ separation characteristics of amino acid salt-methyldiethanolamine?MDEA?mixed solutions were experimentally studied based on membrane absorption technology,which provided a theoretical basis for the practical application of CO₂ membrane absorption.In simulated landfill gas atmosphere,CO₂ absorption and desorption characteristics of three kinds of amino acid potassium salts,namely glycine potassium?KGLY?,lysine potassium?KLYS?and arginine potassium?KARG?,mixed with MDEA were studied by cyclic absorption and regeneration experiments.And they were further compared with the corresponding single amino acid potassium salts and traditional amine absorbent ethanolamine?MEA?.The results showed that the CO₂ absorption capacity of single amino acid potassium salt absorbents were similar to that of the traditional amine absorbent MEA,and the CO₂ desorption capacity of the former was better than that of the latter,but not as good as MDEA.Compared with the corresponding single ones,the absorption and desorption performances of amino acid potassium salt solutions with MDEA were significantly improved.Since arginine has more CO₂-reactive sites,the mixed absorbent KARG+MDEA achieved the highest initial CO₂ absorption rate,initial desorption rate and net cyclic loading.Considering CO₂ removal performance and absorbent cost,KARG+MDEA has a broader application prospect in landfill gas purification compared with other tested absorbents.The three amino acid potassium salts-MDEA mixed solutions performed better in terms of CO₂ cyclic absorption and desorption performances were used to remove CO₂in the superhydrophobic PTFE hollow fiber membrane contactor.The results showed that CO₂ removal efficiency decreased with the gas flow rate and increased with the liquid flow rate.Increasing liquid flow rate had a positive effect on CO₂ absorption flux,but gas flow rate had less impact on CO₂ absorption flux than liquid flow rate.The CO₂ removal efficiency of KARG+MDEA was much better than that of the other two mixed absorbents.It has broad application prospects in landfill gas purification in a hollow fiber membrane contactor,and the absorbent performance could be better developed with the liquid-gas ratio of 0.15.The CO₂ separation characteristics of different cationic arginine salt-MDEA mixed solutions were studied,and the CO₂ absorption and desorption characteristics of arginine potassium-MDEA mixed solutions with different concentration ratios were also investigated.The results showed that the CO₂ initial absorption rate and net cyclic loading of the organic amine arginine salt mixed absorbents were higher,while the inorganic amine arginine salt mixed absorbents had more advantages in CO₂ initial desorption rate and absorbent cost.The three arginine salt mixed absorbents all showed better CO₂ separation performances than traditional amine absorbent MEA.The CO₂membrane gas separation efficiencies of inorganic arginine salt mixed absorbents were much higher than that of the organic amino arginine salt mixed absorbent.The order of CO₂ removal efficiency and absorption flux was ARG+MDEA>NaARG+MDEA>MEAARG+MDEA.Besides,KARG+MDEA was less affected by the liquid phase in CO₂ membrane absorption process.In addition,the arginine potassium-MDEA mixed solution with a concentration ratio of 3:7 had a better cyclic CO₂ absorption and desorption performance,a lower viscosity and a higher surface tension,making itself have a greater potential in the application of landfill gas CO₂ membrane absorption.