| With the development of the economy,the burning of biomass coal and fossil fuels,which are indispensable in life,emits a large amount of SO2 into the air,and SO2 has serious harm to human health and ecological environment.Therefore,how to effectively capture SO2 becomes the key.Although the traditional desulfurization methods have been applied in practical industries,there is still a problem of high desorption energy consumption.It has been found that after CO2 is absorbed by the phase change absorption solution,the generated product spontaneously separates from the solution as a new phase.Since only one phase of the absorption product enrichment is needed to be sent to the stripper for regeneration,the energy consumption required for heating desorption is significantly reduced.Based on the similarity of structure between SO2 and CO2,it is considered to absorb SO2 with phase change absorbent to solve the problem of high desorption energy consumption.Therefore,in this paper,the absorbents and organic solvents with excellent performance were chosen to prepare phase change absorption solution,and achieved liquid-solid or liquid-liquid phase-change absorption of SO2.Based on the superior performance of ionic liquid,N-heterocyclic tertiary amines were used to provide cations and organic acids were used to provide anions to synthesis ionic liquids in order to achieve liquid-solid phase change absorption of SO2.The specific research content includes the following three aspects:(1)Using a series of tertiary diamines as absorbents,using a higher boiling point and less viscous organic solvent as solvent to form an absorption solution for liquid-solid phase change absorption of SO2.The experiments found that long-chain alkanes were the best solvents for phase change,since the precipitates of absorption products formed therein were far more than those formed in other solvents.Among the diamines studied,N,N,N',N'-tetramethylhexamethylenediamine had the strongest ability for SO2 absorption since its low volatility and strong alkalinity.The SO2 absorption products of the diamine all exhibited intensive hydroscopicity,and they were proved to be pyrosulfltes based on XRD,FTIR and elemental analysis.A single crystal of 1,4-dimethylpIperazine pyrosulfite was obtained by recrystallization and it was found to contain a water molecule.The effects of absorption concentration,temperature and partial pressure on the absorption of SO2 were also investigated.The content of diamine in the liquid phase along with the SO2 absorption was determined by gas chromatography.The results showed that the SO2 absorbed by the diamine completely separated the diamine from the liquid phase.TG analysis showed that the decomposition of the products of SO2 absorbed by diamines were accompanied by the volatilization of the diamines,which meant that the diamines cannot be regenerated by a simple heating method,and the initial decomposition temperature sequence of the absorption products was C10H26N2S2O5>C7H20N2S2O5>C6H16N2S2O5·H2O>C6H18N2S2O5,which was consistent with the order of boiling point of its corresponding absorbents.(2)The use of N heterocyclic tertiary amines and organic acids with different pKa values to synthesize ionic liquids to achieve liquid-solid phase change absorption of SO2.The effects of cations and anions on their absorption properties were investigated.The results showed that the effect of cations on their absorption properties was caused by the N atoms and basicity of the cationic donor amine.The effect of anions on their absorption properties was as follows:the acidity of the anionic donor acid was weaker than that of sulfurous acid,the ability to absorb SO2 for ionic liquids was much higher than that of those whose anionic donor acids'acidity stronger than sulfurous acid.At the same time,the influence of temperature on the absorption performance was investigated.As the temperature increased,the capacity of SO2 absorption decreased.XRD results showed that the washing method had no effect on the structure of the absorption product and the product was very easy to absorb water in the air,in other words,the structure was stable after absorbing water.The absorption product was methylaminomethanesulfonic acid confirmed by infrared,elemental analysis combined with X-ray single crystal diffraction.(3)Using N,N-dimethyl-n-octylamine(DMOA)as absorbent and organic solvents with good physicochemical properties as solvent,DMOA/hexadecane was seleted as an absorption solution capable of realizing liquid-liquid phase change absorption of S02.The absorption product was analyzed by nuclear magnetic and infrared,and the results showed that the absorption product was charge-transfer complex DMOA·SO2.In the influencing factors experiments,the effect of absorbent concentration,temperature and partial pressure on its absorption performance was investigated.The change curves of SO2 absorption capacity,absorbent concentration and temperature on the content of each component in two phases were investigated by gas chromatography.The results showed that with the process of SO2 absorption,the content of DMOA and SO2 in the lower phase gradually increased,in the upper phase gradually decreased,while the solvent hexadecane was just the opposite.The concentration of the absorbent had substantially no effect on the content of each component in the upper and lower phases.The effect of temperature on the content of each component was that with increasing temperature,the mutual solubility of the upper and lower phases increased.The ability of the absorption solution for SO2 in the five-cycle absorption-desorption experiments was substantially unchanged,which indicated that the absorption solution has an excellent cyclic absorption ability for SO2. |
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