Research On Tertiary Amine Type CO₂ Switch Solvent And Its Application In The Cleaning Of Oily Solid Waste

CO2-switchable solvents refer to a new type of solvent whose properties can change reversibly when CO2 entry and removal.In recent years,CO2-switchable solvents have drawn much attention from researchers both at home and abroad because of its characteristics such as environmental protection,easy operation and recyclable,the applications involve solvent separation and oil extraction,etc.However,there are few studies on the treatment of oily solid waste in the field of oil and gas.In addition,the type of tertiary amine CO2-switchable solvents has become a hot spot because of its low cost and stable properties.Therefore,this paper analyzes two systems for the tertiary amine CO2-switchable hydrophilic solvents and CO2-switchable water,respectively.The main contents of this paper are as follows:(1)Five kinds of small molecule tertiary amines(N,N-dimethylcyclohexylamine(DMCHA),N,N-dimethylbutylamine(DMBTA),N,N-dimethylbenzylamine(DMBZA),N-Ethylpiperidine(NEP)and Triethylamine(TEA)were used to construct a CO2-switchable hydrophilic solvent system and its research on the separation and recovery performance of simulated oils.The CO2 absorption capacity of switchable solvents system was studied and the results show that the CO2 absorption rate meets the order of TEA>DMCHA>DMBTA>N EP>DMBZA,i.e.,the switching capacity;the solubility parameters of the system were analyzed using the group contribution method.The results show that DMCHA had a better effect on the oil dissolution compared with TEA.Combined with the boiling point and the flash point of solvents,DMCHA was selected for the next experiment.Using diesel oil,white oil and crude oil as oil phase,the effects of temperature,aeration rate and oil-water volume ratio on the separation efficiency of DMHHA and oil phase were studied.With the temperature higher than 25?,the phase separation conversion ratio of the mixed oil becomes smaller;increasing the aeration rate and When the oil-water volume ratio was 1:3,the separation efficiency is obviously greater than that of 1:1 and 1:2.The reaction kinetics of the conversion of DMCHA from hydrophilic to hydrophobic state was studied.It was found that the process conforms to the first-order reaction kinetics,that is,the reaction rate is proportional to the first-order reaction concentration.When volatilization loss is not considered,the increase of temperature and aeration rate can increase the conversion efficiency of DMCHA from hydrophilic to hydrophobic state,which can improve the recovery efficiency of DMCHA in practical applications.In addition,the effect of temperature and aeration rate on the reaction rate was confirmed by the calculation of half-life and reaction rate constants.The activation energy of the conversion of DMCHA from hydrophilic to hydrophobic state was found to be 30.37kJ·mol-1 by Arrhenius equation,which indicates that the reaction process needs certain energy.As the molecular energy increases,the proportion of excited molecules increases and the reaction rate increases.The 1H NMR and pH test were combined with the experimental results to discuss the application mechanism of the system.(2)Tertiary amine type CO2 switch water system was constructed using a mono-tertiary amine(N,N-dimethylethanolamine)and dibasic tertiary amine(N,N,N',N'-tetramethyl-1,2-ethylenediamine,N,N,N',N'-tetramethyl-1,3-propylenediamine,N,N,N',N'-t etramethyl-1,6-hexanediamine)and analyze its oil recovery performance.The change of ionic strength of four switchable waters was studied and the results show that the two amine groups in N,N,N',N'-tetramethyl-1,6-hexanediamine(TMHDA)can be protonated at the same time with higher ionic strength,which is beneficial to improve the emulsion breaking efficiency.So TMHDA was preferred for the next experiment.Through 1H NMR spectroscopy and conductivity testing,it was proved that TMHDA has good switching performance.Using diesel oil as the oil phase,the effect of the oil phase acid value and oil-water volume ratio on the emulsification process was studied.The results show that both of these factors have a great influence on the stability of the emulsion.The microscopy and particle size analysis verified that the emulsion had better dispensability and stability.The interfacial tension test confirmed that the surface active substances produced by TMHDA and naphthenic acid had higher surface activity.In the demulsification process by CO2,the pH and conductivity tests confirmed that the ionic strength gradually increased,the water phase gradually became clear,and the oil was recovered after the demulsification was complete.The recovery performance of switchable water additive was analyzed.It showed that when the water phase after demulsification was passed through N2 for 60 minutes at 60?,the switchable water additive was converted back to the initial state,but the conversion was not complete and still contained a certain amount of ammonium ions in the solution.After researching and proposing two kinds of schemes to achieve better reuse effect.That is,re-optimize the volume ratio of the oil and switchable water solution or add a small amount of switchable water to the solution again.In addition,combined with the experimental results,the mechanism of emulsion breaking and demulsification in the switch water additive system was discussed.(3)Use CO2-switchable hydrophilic solvent to clean waste oil-based drill cuttings,oil sludge and floor sludge and use CO2 switchable water to clean oily sludge.The results show that the oil content of the residue after one cleaning was less than 2%,which has great potential for application.