Preparation Of New Ionic Liquids And Their Application In Biogas Purification

In recent years,with the rapid development of science and technology,the consumption of fossil energy has increased year by year,and the world is facing the shortage of energy.Biogas,as cheap and easily available clean biomass energy,has been paid more and more attention.However,the high CO₂ content in biogas leads to the decrease of energy density and calorific value of biogas,which limits the utilization range of biogas.In order to make better use of biogas resources,CO₂ in biogas should be removed or reduced.Ionic liquids,as an environmentally friendly"green solution",have good solubility and selectivity for CO₂,and have become a hot research topic.In this paper,three kinds of amino acid functionalized ionic liquids were synthesized.It was investigated that the effects of pressure,temperature and mass fraction on CO₂ absorption performance of amino acid ionic liquids,and it was discussed the stability of cyclic regeneration.Different concentrations of absorption solution were prepared with MDEA aqueous solution to investigate the solubility of CO₂.The optimal concentration of the compounding liquid was used in the filler absorption tower for the purification and absorption of the biogas simulation gas,and the purification effect of the simulated gas in the range of the liquid-gas ratio of 10 to 90 L/m³was investigated.The conclusions were as follows:（1）Three kinds of amino acid ionic liquids were synthesized by two-step method:[APMim][Gly],[APMim][Ala],[APMim][Lys],and the synthesized products were confirmed to be the target products by infrared analysis and1HNMR spectra.The three ionic liquids had good thermal stability through thermogravimetric analysis.（2）The effects of pressure,temperature and mass fraction on the absorption of CO₂ by three amino acid ionic liquids.It was known that the absorption rate and absorption capacity of CO₂ by three ionic liquids increase with the increase of pressure.With the increase of temperature and mass fraction the absorption capacity of CO₂ first increase and then decrease.At the pressure of 1 MPa and a temperature of 30°C,the unit absorption of CO₂reached the maximum by the ionic absorbing solution with a mass fraction of20%,which was 1.32 mol/mol,1.25 mol/mol and 1.72 mol/mol,respectively.It was found that the three ionic liquids had good selective absorbability and had no absorption of CH₄.[APMim][Gly],[APMim][Ala],[APMim][Lys]have good recycling performance.After seven times of desorption and regeneration,the absorption rates of CO₂ was 92.4%,87.2%and 88.5%,respectively.（3）In the mixed system of MDEA and amino acid ionic liquid（mass fraction of 27%MDEA+3%ILs,25%MDEA+5%ILs and 22%MDEA+8%ILs）,it could be found that 25%MDEA+5%ILs could effectively improve the absorption rate and absorption capacity of CO₂ in MDEA aqueous solution.The absorption amounts of MDEA and[APMim][Gly],[APMim][Ala],[APMim][Lys]compound solution were 0.932 mol/mol,0.91mol/mol,and 1.11 mol/mol,respectively.When the ratio of liquid to gas was in the range of 15⁸5 L/m³,the compounding solution of 25%MDEA+5%ILs could meet the requirements of purification and absorption of biogas simulated gas in the filler absorption tower.The CO₂ content in the purified gas was less than 3%,which provided a reference for the promotion of industrialization.