The Study On Volume Properties Of Binary And Ternary Systems Composed Of Alcohol,Amine And Water

In recent years,atmospheric greenhouse effect and global warming are increasingly serious.As the main component of greenhouse gas,CO₂has attracted worldwide attention.The widely used method for CO₂absorption is the chemical absorption method using alcoholamine solution,such as ethanolamine（MEA）,N-methyldiethanolamine（MDEA）and diethanolamine（DEA）.Among them,MEA molecule is more attractive due to the simple sturcuture and the advantages of fast absorption,low price,large capacity and convenient recovery.However,the disadvantages of pure MEA,such as high alkalinity and high viscosity,largely limit its application.Researches show that the binary mixture composed of alcoholamine and organic solvent,and the ternary mixture composed of alcoholamine,organic solvent and water can effectively overcome the drawbacks.Therefore,the research on CO₂absorption mainly focuses on alcoholamine mixture.Meanwhile,the absorption rate and efficiency are closely related to the interaction between the components and the thermodynamic properties.As a result,the widely used absorbent MEA,alcohol and water are selected and the volumetric properties have been systematically investigated in this work.Firstly,the density of a series of alcohol+MEA binary mixture with the whole range of concentration was measured at the temperature ranging from（293.15-323.15）K and at atmospheric pressure.The experimental results show that the density of the pure components follows the decreasing order of MEA>n-butanol>n-propanol>isobutanol>ethanol>isopropanol>tertbutanol.In addition,according to the density of the binary mixture,coefficient of thermal expansion and excess molar volume were also calculated.The obtained results show that the excess molar volume values are all negative.For straight-chain alcohol mixtures,the excess molar volume values follow the increasing order of ethanol+MEA<n-propanol+MEA<n-butanol+MEA at 298.15 K.While for branched-chain alcohol mixtures,the excess molar volume values show the increasing order of tertbutanol+MEA<isobutanol+MEA<n-butanol+MEA at 298.15 K.For smaller ethanol molecule and MEA,the molar volume is quite similar to each other.However,excess molar volume value for ethanol+MEA system is the most negative.Therefore,the formation of hydrogen bonds plays a leading role for excess molar volume in small molecule alcohol systems.On the other hand,for larger butanol molecule+MEAsystems,steric effect leads to a decrease in excess molar volume with the increase in butanol molar volume.Furthermore,the excess molar volume values were correlated with Redlich-Kister polynomial equation with the largest deviation of 0.048.Secondly,the density of binary mixture,H₂O+MEA,H₂O+ethanol and H₂O+n-propanol,with the whole range of concentration was studied at the temperature range of（293.15-323.15）K and at atmospheric pressure.This experimental can provided valuable information for the following ternary systems.The excess molar volumes were also calculated according to the density values.The results show that the excess molar volume of the binary mixture containing H₂O is negative.And excess molar volume values increase with the increasing of temperature.At higher temperature,the molecular kinetic energy increases,which leads to the hydrogen bond weakening.Additionally,Redich-Kister equation was used to correlate excess molar volume values with a maximum deviation of0.033.Finally,the density of ternary system,MEA+ethanol+H₂O,MEA+n-propanol+H₂O,MEA+n-butanol+H₂O,in the temperature range of（293.15-323.15）K and at atmospheric pressure was determined.The results show that excess molar volume values of the ternary mixtures are all negative.However,the values increase with the increasing of H₂O concentration.That is to say,the addition of H₂O results in the mixture’behavior more ideal.According to the results of binary mixture,the formation of hydrogen bonds between MEA and alcohol is mainly responsible for the negative values of excess molar volume.Therefore,the addition of H₂O to the binary mixture can make the hydrogen bonds between MEA and alcohol damaged.Accordingly,the behavior of the ternary mixture becomes more ideal and the values of excess molar volume are closer to zero.