Physicochemical Properties And Acetylene/Ethylene Dissolution Performance Of Deep Eutectic Solvents

Acetylene(C2H2)and ethylene(C2H4)are the basic raw materials in chemical industry.The development of clean and efficient C2H2/C2H4 separation technology is of great significance.The solvent absorption method is restricted by the volatility of organic solvents.Because of the advantages of deep eutectic solvents(DES)such as low vapor pressure,wide sources,simple synthesis,the study on the absorption of C2H2 and C2H4 by DES was carried out.We designed and synthesized a series of DES,systematically measured their Kamlet-Taft solvatochromic parameters and selected out potential DES with high capacity and selectivity in separation of C2H2 and C2H4 according to the prediction results of COSMO-RS.In the hoping of providing necessary data for the development of new green and efficient separation method based on DES,the dissolution performance of C2H2/C2H4 in these solvents was studied through experiments.Firstly,we synthesized 121 kinds of DES composed of different hydrogen bond acceptor and donor,and determined the Kamlet-Taft solvatochromic parameters aiming at better understanding the influence of the chemical structure,mole ratio,temperature and water content on their polarity.It is shown that an increase of the chain length of hydrogen bond donor and acceptor leads to a decrease on the hydrogen bond acidity(a)value,an increase on the hydrogen bond basicity(β)value and a decrease on the dipolarity/polarizability effects(π*)value.Compared with bromide-based mixtures,the α value of chloride-based mixtures is lower,the β value is higher and the π*value is similar.The a value will decrease with the increase of temperature,but the β and π*value are hardly affected.With the increase of water content,the a value changes nonlinearly with a slight deviation from ideal-additive behavior,while the increase of π*value and the decrease of βvalue are linear.Otherwise,DES formed by tetraalkyl quaternary ammonium salts and carboxylic acids obtain the highest β value(1.16),which are higher than that of all conventional solvents and most ionic liquids.We predicted Henry’s law constants and selectivity of C2H2 and C2H4 in 171 kinds of DES by COSMO-RS method.It is shown that DES composed of fatty acids and ammonium salts with long carbon chain is expected to have higher C2H2 and C2H4 solubility,and the increase of chain length of hydrogen bond donor and acceptor can improve the solubility of C2H2 and C2H4.The separation selectivity of C2H2/C2H4 is mainly affected by the kind of hydrogen bond donor,and the hydrogen bond acceptor plays a certain regulatory role.On the basis of above research,we synthesized 4 kinds of DES composed of fatty acid and ammonium chloride with long chain and determined the solubility and selectivity of C2H2 and C2H4 at temperature from 298.1 to 313.1 K and pressure from 20 to 120 kPa.The effects of chemical structure,temperature and pressure on their absorption performance were investigated.And the absorption thermodynamics,kinetics and recycling performance were preliminarily studied.It is shown that DES composed of tetrabutylammonium chloride(TBACl)and butyric acid(BA)at a molar ratio of 1:2 has good capacity and high selectivity,Henry’s law constants of C2H2,C2H4 and their separation selectivity are 6.0 bar,54.6 bar and 9.1 at 298.1 K respectively.Moreover,the recycle experiment demonstrates that the C2H2-DES bonding is reversible and TBACl/BA(1:2)can be regenerated without loss of C2H2 capacity.