Physicochemical Properties And Application Study On Protic Ionic Liquids Composed Of N-alkylethylenediaminium Cations With Trifluoromethanesulfonate Anion

Ionic Liquid（IL）is a compound consists of cation and anion and its melting point is below100℃.They have unique physicochemical properties,such as good thermal stability,low vapor pressure,wide liquid range,wide electrochemical window and good electric conductivity.Protic ionic liquids（PILs）and aprotic ionic liquids（AILs）are two major classes of ionic liquids.There are proton-donor and acceptor in the ionic liquids,and their characteristics are mainly expressed in the fact that protons in PILs can be moved from Br?nsted acid to Br?nsted base,so PILs not only have the characteristics of ILs,but also show strong polarity.In this study the basic physicochemial properties and applications study of HHex（TFS）,HOct（TFS）and HEtHex（TFS）PILs were investigated by the following four parts:1、Syntheses and characterization of PILs:At first,octylethylenediamine（Oct-en）,2-ethylhexylethylenediamine（EtHex-en）and hexyleth ylenediamine（Hex-en）were prepared by the reaction between alkylbromide and ethylenediamin e.The structural characterisation and purity were identified using IR analysis and ¹³C-NMR sp ectra.The PILs were prepared by neutralization reaction of the bases strong alkaline N-alkyleth ylenediamines with strong acid trifluoromethanesulfonate acid（CF₃SO₃H,HTFS）.Which are HO ct（TFS）,HEtHex（TFS）and HHex（TFS）,respectively.The structural characteristics and purity were identified using ¹³C-NMR spectra,elemental analysis（CHN）,water content and IR spectra.2、The physicochemical properties of PILs:The result of solubility shows that the PILs with TFS are easily soluble in non-polar solvents such as benzene,ether and chloroform and polar solvents such as water,methanol,acetone,n-butanol,ethanol and propanol.In the same time,HEtHex（TFS）is slightly soluble,and HHex（TFS）and HOct（TFS）are poorly soluble in cyclohexane,n-hexane and petroleum ether.The glass transition temperature of HEtHex（T FS）is-58.6℃,it is liquid at room-temperature.The melting points of HHex（TFS）and HOct（TFS）are 48.8℃and 52.8℃,respectively,they are solid state at room temperature.The results of TGA show that the decomposition decrease was in a two-step for the PILs with TFS.The decomposition 10% and 90%of the temperatures were 290.5℃and 373.9℃for HHe x（TFS）,274.5℃and 368.0℃for HOct（TFS）,235.5℃and 342.7℃for HEtHex（TFS）,respectively.The PILs have strong polarity and easy to absorb water,about 0.5%,moisture has a great influence on the physicochemical properties of PILs.The physicochemical properties such as dynamic viscosity（η）ionic electrical conductivity（σ）and density（ρ）of water/HEtHex（TFS）wit h different water content（0.53%,4.78%,6.00%,6.92%,7.97%,10.05%,14.83%,25.54%and54.99%）in the temperature range of T=（303.15-353.15）K and relationship between the physic ochemical properties and temperature was fitted by Arrhenius equation.The fitted curves are nearly straight line.The results show that the effects of temperature and water content on the density,dynamic viscosity and electrical conductivity of HEtHex（TFS）is significant.The viscosity decreases and the conductivity increases with increasing water content and temperature.3、Tribological behaviour of HEtHex（TFS）as Liquid Paraffin additive:Tribological behavior of HEtHex（TFS）as additive in liquid paraffin（LP,simulant of lubricating base oils）with different mass fractions（0.00%,0.25%,0.50%,0.75%,1.00%and 1.25%）for the contact of steel/steel ball was investigated.At the same time,the effects of the temperature（25,50 and 75℃）and load（196,245 and 294 N）on the anti-friction and anti-wear properties were studied.The morphologies and the elemental compositions of the worn surfaces were analyzed using SEM and EDS.The results showed that the value of extreme-pressure increased significantly,and the antifriction and anti-wear properties of the LP improve with the addition of HEtHex（TFS）.The best abilities for the anti-friction and anti-wear property of 0.75 wt.%HEtHex（TFS）in the LP were found at 25℃,294 N and at25℃,196 N,respectively.The results of the elemental analysis showed that a protective boundary film was formed on the steel ball surface and it caused that the anti-friction and anti-wear properties was improved.4、Study on absorption of CO₂ using HHex（TFS）、HOct（TFS）and HEtHex（TFS）PILs/water systems:PILs/water systems with different molar ratio（1:10、1:15、1:20 and 1:25）were prepared.pH value,density（ρ）,viscosity（η）and electric conductivity（σ）of PILs/water systems were studied before and after CO₂ absorption.The results show that pH value,density,viscosity decrease and electric conductivity increases with increasing the water molar ratio.pH and electric conductivity decrease while density and viscosity increase after CO₂ absorption.