Recycling CO₂ By Membrane Absorption By Coupling Enhancement Process

The trend of global warming is more significant under the condition of strong El Nino. Temperatures in the Arctic have broken through zero several times. There is no doubt that the continuous emission of greenhouse gases is the major reason for global warming. The reduction of carbon dioxide emission is a important objective at the present stage since CO₂ is the main greenhouse gases. Conventional decarbonization methods have their shortcomings. At the same time, membrane absorption technology is novel gas separating technology that combines membrane separation technology and traditional gas absorption technology. In this thesis, absorption capability in membrane absorption, as well as improvements and application of common absorbents were researched. In order to study the stability of membrane absorption process, sodium hydroxide was used as absorbents. We found that the interaction between sodium hydroxide and membrane results in irregular change of absorption amount and absorption rates in membrane absorption process due to the change of membrane microstructure. Sodium hydroxide absorbent has great effect on the microstructure of polyvinylidene fluoride membrane, and has lest effect on the microstructure of Teflon membrane. When absorbents were changed, the results show that sodium hydroxide absorbent has the most damage on membrane, followed by ammonium hydroxide and N-Methyldiethanolamine.But the absorption rates of N-Methyldiethanolamine is quite slow in the absorption process.To reduce the interaction between absorption solvents and membrane, while guaranteeing the absorbability of carbon dioxide, the method that ammonium hydroxide used as membrane absorbent and coupling generation of ammonium bicarbonate was applicated, which can reduce energy consumption of absorbent regeneration. The researches show that absorbability of membrane absorption can be enhanced through the increasing concentration of ammonium hydroxide. We can found that the best absorbability of carbon dioxide is the membrane of teflon because its microstructure is hardly affected by ammonium hydroxide, followed by the membrane of polyvinylidene fluoride and polypropylene membrane. With the increasing frequency of membrane used, the absorbability of membrane decreases.Four task-specific ionic liquids home-made used as additives mixed with MDEA solvents, which were used as absorbents of CO₂ capture. Four task-specific ionic liquids were 1-aminoethyl-3-butylimidazole bromide, 1-aminoethyl-3-methylimidazolium bromide, 1-aminoethyl-3-methylimidazolium hexafluorophosphate and 1-aminoethyl-3-butylimidazole hexafluorophosphate, respectively. The absorption and absorption mechanism of the new absorbents for CO₂ capture were investigated. The results showed that new absorbents can enhance the absorption rate of MDEA, and the mechanisms of promotion is attributed to the reaction between task-specific ionic liquids and CO₂ so as to provide proton in the form of amphoteric ion for the reaction of MDEA and CO₂. The new absorbents were applied in the membrane absorption process, the experiments show that absorption reates of membrane absorption process coupled with task-specific ionic liquids has been enhanced, and the new absorbents has less effect on the micostructue of membranes.