Synthesis Of N-（2-cyanoethyl） Diethanolamine And Its CO₂ Absorption Properties

With the intensification of the greenhouse effect,countries around the world pay more and more attention to the emission of carbon dioxide(CO2),and the emission,capture,and utilization of CO2 have become important research topics.The emission of carbon dioxide is mainly based on the flue gas produced by the combustion of fossil fuels in industry.Therefore,the capture and utilization of CO2 in the flue gas will produce good results at the environmental and economic levels.Organic amine absorption method is the main method for capturing CO2 in industry at present.In order to improve the CO2 absorption of organic amines and reduce the energy consumption for desorption,this paper synthesized an organic tertiary amine N-(2-cyanoethyl)diethanolamine,and explored the pKa,ΔH,concentration of various ions and equilibrium solubility of CO2 of this amine solution.First,for the synthesis of N-(2-cyanoethyl)diethanolamine,the paper examines the effects of reaction conditions such as reaction time,reaction temperature,and material ratio on the yield of reactants,and uses regression equations to simulate the optimal reaction conditions.The study found that the most important factor affecting the yield of reactants is the material ratio,followed by the reaction time,and the reaction temperature is the smallest.The optimal reaction conditions explored by the experiment are T=56.4℃,t=45min,δ=1.5.The obtained product was characterized by IR,1HNMR,GC-MS and other characterization methods.The results showed that the structure of the reaction product was exactly the same as that of the expected product.Then the paper comprehensively investigated the CO2 absorption performance of N(2-cyanoethyl)diethanolamine.The investigation shows that as the temperature rises,the pKa of the N-(2-cyanoethyl)diethanolamine aqueous solution gradually decreases,and the relationship is pKa=1887.21/T+2.56.In order to estimate the CO2 desorption performance of N-(2-cyanoethyl)diethanolamine,Gibbs-Helmholtz formula was used to theoretically calculate the absorption heat,and the absorption heat was 36.13kJ/mol,△rGmΘ=50.72kJ/mol.As the CO2 absorption of the solution increases,the concentration of different ions in the solution changes as follows:the concentration of tertiary amine decreases,the concentration of protonated tertiary amine,HCO3-increases,and the concentration of CO32-increases first and then decreases.The change of various ion concentrations in the solution with temperature and pH value is drawn into a threedimensional curved surface graph,which more intuitively shows the change of its ion concentration.Finally,the measured CO2 equilibrium solubility of 2mol/L N-(2cyanoethyl)diethanolamine aqueous solution is 0.68mol CO2/mol amine at a temperature of 283K,a CO2 partial pressure of 101kPa,and an absorption time of 120min.As the temperature rises,its CO2 absorption gradually decreases.