Selective Separation Of High Concentration H₂S And CO₂ System

For high concentrations of acid,chemical absorption requires a large amount of absorbent and it is difficult to achieve H2S recovery.On the contrary,according to its characteristics of high concentration and high pressure,the use of physical solvent absorption method has a great advantage,physical absorption method can achieve the recovery and enrichment of acid gas,after the concentration of acid gas can be used as raw materials to produce downstream products,through recycling to solve the problem of acid gas pollution control,and improve the economy of the whole process.NHD(polyethylene glycol dimethyl ether)solvent has a similar chemical property to the Selexol absorbent and has a high degree of solubility to acidic aerosols,and has a high selectivity for H2S and CO2,so it is widely used in the research of desulfurization and decarbonization.DMI(1,3-dimethylimi-dazolinone)is a weak alkaline solution that can bind to proton hydrogen in H2S and therefore has a good solubility for acidic gas.The solubility,henry coefficient,dissolution thermodynamic parameters,acid gas load,selectivity of the two physical solvents to H2S and CO2 were obtained by experimental calculation using these two physical solvents as absorbent.Thermogravimetric,pH value,and infrared spectroscopy were used to characterize the two solvents.Moreover,using Aspen Plus simulation software,the process flow of selective separation of high concentration acid gas is established,and the best technological conditions are explored to realize the efficient separation of acid gas H2S and CO2.The following conclusions were drawn:(1)The absorption of both acidic gases in both solvents is physical absorption and the solubility of H2S in both solvents is much greater than that of CO2.The Henry coefficient of the corresponding H2S is less than that of the CO2 in the solvent.Compared with the DMI solvent,the NHD force on the H2S is weak,so it is beneficial to the desorption of acid gas.(2)The solubility of H2S in DMI is greater than that of H2S in NHD,and the difference in in NHD and DMI is not significant.The acidic load of the two solvents increases with the increase of pressure and decreases with the increase of temperature.Both solvents have better selectivity for H2S under lower pressure conditions.The overall selectivity of DMI to H2S is higher than that of NHD to H2S.(3)NHD is a neutral solution,while DMI is a weak alkaline solution.The thermal stability of the NHD is better than that of the DMI solvent.Before and after desulfurization,the properties of the two solvents did not change.However,the DMI desulphurization fluid is easily oxidized in the air to produce sulfur.(4)The real condition of the solvent which the PC-SAFT model can better.Through the optimization of the process,the H2S molar fraction can reach 98.7%and the CO2 molar fraction can reach 99.6%,which indicates that the process can make the H2S and CO2 better separation.