Study On Quantitative Calculation And Dissolution Mechanism Of Mercaptan Absorbent

As a kind of clean energy,natural gas has been widely used in production and life.Natural gas must be desulfurized and decarbonized before use.At present,chemical absorption method is usually used.This method has obvious effect on the removal of H2S,CO2 and other acid gases,but poor effect on organic sulfur.Therefore,it is of great significance for the exploitation and use of natural gas to develop a compound absorbent which can simultaneously remove organic sulfur,H2S and CO2.In view of the problem of low removal rate of organic sulfur,this paper proposes to use the method of theoretical simulation and experiment to explore the factors affecting the dissolution process,establish the method of solvent selection,and reveal the thermal effect of the mixed system in the dissolution process.The main research contents and conclusions are as follows:(1)The Henry’s coefficient of methyl mercaptan in 9 different solvents was calculated to characterize the physical absorption capacity of the solvent for methyl mercaptan.It is found,NMP(N-methylpyrrolidone)solvent has the best effect on the absorption of methyl mercaptan.The Pka values of the three chemical solvents are predicted to characterize the chemical absorption of methyl mercaptan by the solvent.It is found that among the three chemical solvents selected,HEP(1-piperidineethanol)is the most basic.Comparing the above calculation results with the experimental values,it is found that the COSMO-RS software can qualitatively predict the Henry coefficient of methyl mercaptan in the solvent,that is,it can accurately predict the solubility trend,but it is slightly insufficient in quantitative analysis.In addition,it was found that the combination of NMP and HEP solvents had the best absorption effect on methyl mercaptan.(2)For the solvent-methyl mercaptan system,the calculation and analysis of RDG and QTAIM were carried out,and the interaction force between the molecules was explored.It was found that the interaction force between the solvent and methyl mercaptan molecules is mainly van der Waals force and hydrogen bonding.The hydrogen bonds between the molecules were studied in more detail,and the atoms forming the hydrogen bonds were located.According to the different bonding atoms,the hydrogen bonds were divided into:C=O------H-S,C-O-----H-S,S=O------H-C,O------H-S,N------H-C,C-S------H-C.The hydrogen bonds were divided into medium-strength hydrogen bonds and weak hydrogen bonds by calculating the hydrogen bond energy.The relationship between different bonding atoms and hydrogen bonding energy is summarized.(3)In order to have a clearer understanding of the physical dissolution process,the three forces of solvent-methyl mercaptan and solvent-solvent,hydrogen bonding force,van der Waals force,and electrostatic force were investigated.It was found that during the dissolution process,the van der Waals force between the solvent and methyl mercaptan is the main driving force for dissolution,and the hydrogen bond plays a role in assisting the promotion.The electrostatic force shows a slight repulsion during the dissolution process.Through the analysis of excess enthalpy,the endothermic and exothermic systems in the dissolution process were confirmed respectively.By analyzing the energy contribution of the three forces to the excess enthalpy,the forces that have a decisive influence on the dissolution process in different systems are confirmed,as well as have a better understanding of the energy changes during the dissolution process.