| With the rapid development of modern industry,developing new energy and improving the utilization rate of waste resources are conducive to the green and low-carbon development of economy and society.At present,methanol gasoline,ethanol gasoline and other biofuels have gradually become a research hotspot due to their advantages of high calorific value and low pollution,but many binary azeotropes containing low-carbon alcohols will be produced in the process of production and processing.In industry,special separation methods such as extractive distillation are usually used to separate azeotropes.As a new type of ionic liquids,deep eutectic solvents（DESs）have been widely used in the field of azeotrope separation in recent years because of their low vapor pressure,good thermal stability,simple preparation,strong environmental friendliness and designability.The extractive distillation of isopropanol-water azeotrope with choline chloride:ethylene glycol（1:2）and choline chloride:glycerol（1:2）as extractant was studied.Firstly,from the perspective of quantum chemistry,using COSMO-SAC model,the micro mechanism of DESs effective separation of isopropanol-water azeotrope was explained by analyzing the strength of hydrogen bond formed between various extractants and isopropanol.The traditional process using ethylene glycol as extractant and the new process using DESs as extractant were compared from the aspects of economic performance,thermodynamic efficiency and environmental impact.The results showed that with choline chloride:ethylene glycol（1:2）as extractant,the amount of extractant,high-pressure steam and condensate were reduced by 66.67%,32.50%and35.48%respectively,the total equipment cost was reduced by 27.31%,the total annual cost（TAC）was reduced by 30.92%,the thermodynamic efficiency was increased by40.34%,and the emissions of greenhouse gas and acid gas were reduced by more than30%.After adiabatic compression of the heat at the top of the extractive distillation column as a part of the heat source of the reboiler,the TAC was further reduced by7.69%.Three kinds of choline-based DESs（choline chloride:ethylene glycol（1:2）,choline chloride:glycerin（1:2）and choline chloride:urea（1:2））were prepared by using choline chloride as hydrogen bond accepter and ethylene glycol,glycerol and urea as hydrogen bond donors.The types and quantities of hydrogen atoms contained in DESs were verified by ~1HNMR.The liquid-liquid equilibrium data of n-hexane-methanol-DESs,and n-hexane-isopropanol-DESs ternary systems were measured at 298.15 K and 1 atm.The distribution coefficient of methanol and isopropanol in DESs and the selectivity of DESs to them were calculated.The results showed that the distribution coefficient of methanol in the three DESs is more than 10 times that of isopropanol,and the selectivity of DESs to methanol is more than 20 times higher than that of isopropanol.Molecular dynamics simulation was used to study the extraction mechanism of DESs in the process of liquid-liquid equilibrium of methanol and isopropanol.The interaction energies,radial distribution function and spatial distribution function between DESs and two low-carbon alcohols were calculated.The results showed that the interaction force between DESs and methanol is much greater than that between DESs and isopropanol.Among the three DESs,choline chloride:ethylene glycol（1:2）has the best separation effect on low-carbon alcohols-n-hexane azeotropes,and chloride ion plays the largest role in the extraction process.To obtain the general law of DESs extracting low-carbon alcohols from alkanes,the separation effect of DESs on methanol-n-heptane and isopropanol-n-heptane azeotropes was studied by above methods,and compared with the previous work.The results showed that the separation effect of DESs on methanol-n-heptane azeotrope was better,and the separation effect was slightly better than that of methanol-n-hexane.From the above analysis results,it can be concluded that the separation effect of DESs on low-carbon alcohols-n-heptane azeotropes is better than that of low-carbon alcohols-n-hexane azeotropes.Among the three DESs,choline chloride:ethylene glycol（1:2）has the best separation effect on low-carbon alcohols-alkanes azeotropes,and the strength of the interaction between low-carbon alcohols/alkanes and DESs decreases with the growth of carbon chain,which has important reference significance for the efficient and rapid separation of binary azeotropes containing low-carbon alcohols in industry. |
PDF Full Text Request