| Traditional microemulsions typically consist of oil,water and surfactant,sometimes even need to add co-surfactant which is generally regarded as indispensable for forming microemulsions.However,many studies have shown that microemulsions can be only composed of two immiscible liquids and an amphisolvent in the absence of surfactant in recent years.Such microemulsion calls it "surfactant-free microemulsion"(SFME).SFME avoids the problem of the residue of surfactant in traditional microemulsion applications and contributes to separate and purifies,which has been attracting more and more attention.At the same time,in practical applications,microemulsion is often required to have different properties in different operation units.Therefore,a surfactant-free microemulsion with reversible performance is worthy of further study.The surfactant-free microemulsions were prepared by using n-heptane and N,N-dimethylcyclohexylamine(DMCHA)as oil phase,dipropylamine(DPA),ethanol and diethylamine(DEA)as amphisolvent phase,ethylene glycol and water as water phase.The phase behavior of "n-heptane/DPA/ethylene glycol","DMCHA/ethanol/water" and"DMCHA/DEA/water" ternary CO2-switchable surfactant-free microemulsion systems has been explored,and their microstructure and CO2 switching performance were characterized.In addition,the CO2-switchable SFMEs were used to clean oil-based drill cuttings,and the cleaning effect of drilling cuttings is evaluated.The main research contents are as follows:(1)CO2-switchable SFME based on n-heptane/DPA/ethylene glycolCO2-switchable SFME was prepared by using n-heptane as oil phase,DPA as amphisolvent phase and ethylene glycol as water phase.The phase behavior of the system was studied,and the single-phase microemulsion region was determined by plotting the three-phase diagram of the system.The single-phase region accounts for about 30%of the whole phase diagram.The microstructure ans its transformation were characterized by conductivity,fluorescence spectrum and particle size measurement.The CO2 switching performance of SFME was characterized by visual observations,conductivity and particle size measurement.The oil-based cuttings was cleaned by the SFME,and determination of oil content of cuttings after cleaning by IR petroleum determination instrument.The results showed that the oil content of the cuttings after cleaning was reduced from the initial 9.42%to 0.85%,realizing the CO2-switchable SFME can be used to clean the oil-based drill cuttings.However,it was found that the oil phase n-heptane of the SFME could not be effectively separated from the base-oil of cuttings after entering CO2,which caused the system cannot form SFME after entering N2.Therefore,an solvent which can separate from the base-oil is used as an oil phase to prepare SFME.(2)CO2-switchable SFME based on DMCHA/ethanol/waterAim at problems that the n-heptane could not be effectively separated from the base-oil of cuttings and the recovery of the system is difficult,an new CO2-switchable SFME was prepared by using DMCHA as oil phase,ethanol as amphisolvent phase and water.The single-phase microemulsion region was determined by plotting the three-phase diagram of the system and the single-phase region accounts for about 70%,which is better for further research.The microstructure ans its transformation were characterized by conductivity,droplet Size and maximum absorption wavelength of MO spectrum.The CO2 switching performance of SFME was characterized by conductivity and particle size measurement,proving the system from micremulsion to a bicarbonate solution under the action of C02 by salting out experiments.Then,using the SFME system to clean the oil-based drill cuttings,the results show that under the optimal cleaning conditions,the oil content of the cuttings after cleaning was 0.62%,realizing the CO2-switchable SFME can be used to clean the oil-based drill cuttings.Owing to the amphisolvent ethanol and base oil were difficult to be separated,CO2 was introduced into the SFME after cleaning the cuttings,the system and based oil cannot separate completely.The recovery efficiency of ethanol is a little low,and the system can not form microemulsion after two cycles.(3)CO2-switchable SFME based on DMCHA/DEA/waterIn the light of the fact that the based oil and ethanol could not separate completely,cycle times of SFME was limited,a CO2-switchable SFME is formed by DMCHA,DEA and water.The single-phase microemulsion region was determined by plotting the three-phase diagram of the system and the single-phase region accounts for about 70%.The microstructure ans its transformation were characterized by conductivity,fluorescence spectrum and surface tension.The CO2 switching performance of the SFME was characterized by visual observations,conductivity and particle size measurement.The CO2-switchable SFME system was used to clean the oil-based drill cuttings.It was found that the oil content of the drill cuttings after cleaning was 0.54%under the optimal cleaning conditions.After two recovery times of the SFME cleaning drilling cuttings,the oil content of drilling cuttings after cleaning is 0.82%,and the SFME system can still recover.While CO2 was introduced into the SFME system after cleaning the cuttings,and the DMCHA and DEA eventually completely became hydrophilic hydrogen carbonate salt and dissolved in water,leading to changes the system from microemulsion to salt solution.The system can separated completely from base oil and be reused for cleaning oil-based cuttings. |
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