The Thermal Effect Of Ionic Liquids Absorbing Sulfur Dioxide

As our national strength grows,the speed of industrial development is among the top of the world,but also the dependence on energy dependence is rising.Studies show that at the beginning of this century,China’s energy consumption was still among the highest in the world,with the vast majority of the energy supply coming from the burning of fossil energy.The massive burning of coal energy leads to the emission of large amounts of sulfur dioxide into the atmosphere,which poses a serious threat to the environment and organisms.Compared with traditional desulfurization technologies,ionic liquids have gradually entered the vision of researchers in recent years due to their adjustable structure,extremely low vapor pressure,and environmental friendliness.Certain research results have been achieved.However,the vast majority of the studies only synthesize a new type of absorber from the perspective of improving the absorption capacity,with little research on the thermodynamic parameters exhibited in the absorption process,resulting in slow progress in the industrialization of ionic liquids.At the same time,it has been found that in the process of SO2 desorption,whether by heating or decompression vacuum treatment,there is always a small amount of SO2 present in the ionic liquid,making it difficult to achieve 100%desorption,which requires a new understanding of the reaction mechanism and thermodynamic behavior of the absorption process.Therefore,this paper intends to fill in the thermodynamic data of the sulfur dioxide absorption process using ionic liquids,while focusing on the thermodynamic behavior of the sulfur dioxide absorption process in ionic liquids.Thus,with the help of the industry’s unique reaction calorimeter,variation of specific heat capacity of the system with the absorption process is discussed.The variation of differential absorption enthalpy with this absorption volume in the absorption process was also investigated.Finally,the mechanism of the absorption process was explored in combination with simulation calculations.The main work and conclusions are as follows.(1)Four guanidiniume-based ionic liquids,including 1,1,3,3tetramethylguanidine lactate([TMG]Lac),1,1,3,3-tetramethylguanidine tetrafluoroborate([TMG]BF4),1,1,3,3-tetramethylguanidine octanedioate([TMG]SUB)and 1,1,3,3-tetramethylguanidine dodecanedioate([TMG]DOD),were synthesized to investigate the effect of physical and chemical absorption on the specific heat capacity of the reaction system.It was found that the specific heat capacities of[TMG]Lac and[TMG]BF4 increased with th-e increase of the absorption amount at the same temperature.In this case,the specific heat capacity of[TMG]Lac is higher than that of[TMG]BF4 during absorption.In addition,the specific heat capacity of the reaction system is increased with the increase of temperature for both types at the same absorption amount.Tetramethylguanidine octanedioate([TMG]SUB)and tetramethylguanidine dodecanedioate([TMG]DOD)were synthesized to investigate the effect of anionic side chain length on the specific heat capacity of the reaction system.It was found that the specific heat capacities of[TMG]SUB and[TMG]DOD increased with the increase of the absorption amount at the same temperature.In this case,the specific heat capacity of[TMG]DOD is higher than that of[TMG]SUB during absorption.When the absorption is identical,the specific heat capacity of the system increases gradually with the increase in temperature.Finally,we microscopically explain the variation of the specific heat capacity of the system with the absorption amount during the absorption of the four ionic liquids by simulations.(2)From the specific heat capacity,it can be obtained that the enthalpy of the absorption process.For this purpose,we also synthesized four ionic liquids and passed sulfur dioxide gas in segments to study the effect of the absorption amount on the enthalpy of the system.Firstly,the effect of the anion species on the differential enthalpy of absorption was compared.The differential enthalpy ΔHdiff of both ionic liquids decreased with the increase of the absorption amount at the same temperature.For[TMG]Lac ienic liquids,the differential enthalpy slowly decreases with the increase of absorption,and the overall curve is relatively gentle;for[TMG]BF4 ionic liquids,the differential enthalpy slowly decreases with the increase of absorption,and the overall curve is relatively sharp,when the absorption is between 0.2 mol SO2/mol[TMG]BF4 and 0.6 mol SO2/mol[TMG]BF4 with a linear variation.Then,due to the difficulty of ionic liquids,it is necessary to add solvents to reduce the viscosity of ionic liquids in practical applications,so we chose ethylene glycol and[TMG]Lac ionic liquids to synthesize absorbents according to different molar ratios,and examined the effect of solvent content on the differential absorption heat.With the increase of sulfur dioxide absorption,the differential enthalpy of reaction of ionic liquids gradually decreased.At this time,as the molar ratio of solvent increased,the slope of the molar ratio of absorption to reaction enthalpy curve was gradually decreasing,and at different temperatures,when the same molar ratio of sulfur dioxide was introduced into the kettle,the differential enthalpy of reaction decreased with the increase of temperature.(3)Finally,this thesis combined the simulations and used Gaussian to simulate the calculation process.Taking[TMG]Lac ionic liquid as an example,the anion and cation were optimized separately from the structure,and the lowest energy configuration was obtained by simulating different positions.Then it was combined with sulfur dioxide molecules and the absorption process was simulated,and the combination between the ionic liquid and sulfur dioxide was proved by AIM analysis in a chemical bonding manner.Finally,the conjectural results of the theoretical calculations were corroborated from a calorimetric point of view using calorimetry.