Research On Mechanism Of Heavy Oil Emulsification/Demulsification And Upgrading Process By Power Ultrasonics

Petroleum resource is still one of the most important energy at present and foreseeable future.Since the beginning of the 21 st century,oil supply keeps heavier and more inferior(High density,high sulfur,high acid,high carbon residue,high metal content,etc),meanwhile,global reserves of heavy crude oil account for up to70% of total oil reserves.Heavy crude oil and the residue(atmospheric residue,vacuum residue,etc.)of crude oil are collectively referred to as heavy oil.In 2020,about 830 million tons of crude oil was processed and 300 million tons of residue was produced.Therefore,the level of heavy oil refining and processing is of great significance to improve the utilization rate of oil resources.Heavy oil is a complex mixture composed of asphaltenes,resins,and aromatics.It shows heavy weight,high viscosity and complex structure,which lead to serious problems such as coking,catalyst deactivation and low processing utilization rate.Therefore,improving the quality of heavy oil by physical and chemical methods is an important way to improve the utilization rate of heavy oil.Power ultrasonic technology enhances characteristics of crude oil and reaction rate of heavy oil,which has been greatly applied in oil viscosity reduction,oil sand separation,oil demulsification and desalination,diesel oxidation desulfurization and other petrochemical fields.It shows broad prospect to heavy oil upgrading,but the research of power ultrasonic technology in heavy oil upgrading is very few,and the mechanism of ultrasonic cavitation,heavy oil emulsification,demulsification and upgrading process in heavy oil needs to be further studied.In view of the above problems,this thesis will study the power ultrasonic heavy oil processing technology from theoretical analysis,molecular dynamics simulation,experimental verification,the specific research content includes the following aspects:In view of the strong degeneration of ultrasonic cavitation and difficulty in macro analysis,ultrasonic cavitation molecular dynamics model was established to study the generation process of steady cavitation and transient cavitation.By optimizing the interfacial curvature and interfacial configuration,the molecular dynamics model with stable colloidal system was obtained.Integrating the ultrasonic cavitation process with heavy oil molecular dynamics model,the model for ultrasonic cavitation in heavy oil was established.The variation of heavy oil colloidal system structure under different sound pressures and frequencies was obtained and the influence of transient cavitation bubble collapse on the interaction between medium molecules was gained.An ultrasonic cavitation sound field testing system based on spectrum analysis was established to fit heavy oil with high viscosity and strong sound attenuation.The ratio of fundamental frequency energy,steady state cavitation energy and transient cavitation energy was measured and effects of transducer type,ultrasonic power and medium type on cavitation state of sound field were analyzed.Transient cavitation effect was mainly researched and found it could reach high energy levels only in a specific range of sound power.Based on GROMACS simulation platform,a molecular dynamics model of power ultrasonic heavy oil emulsification was established to study the effect of sound pressure and frequencies on molecular interactions.Mechanism of power ultrasonic heavy oil emulsification was revealed that transient ultrasonic cavitation broke the interfacial film and forced water phase into oil phase.A heavy oil experimental device was developed and the effect of ultrasonic power,treatment duration,and oil/water ratio on emulsification degree were studied.Moreover,the optimal parameter combination in this experiment was determined.Optimizing the number of interfacial molecules,a spontaneously coalescing molecular dynamics model was set.Variation of droplet coalescence velocity and intermolecular interactions under different acoustic field parameters were probed.Extrusion effect caused by high sound pressure promoted compact arrangement of oil phase between droplets,producing steric hindrance effect to inhibit droplet coalescence and demulsification.Through experimental research,the application range of power ultrasonic demulsification for heavy oil was determined.An experimental system for power ultrasonic heavy oil upgrading was built,in which cavitation state,sound power and oil types can be adjusted to probe the pathway of heavy oil upgrading.Transient cavitaion leads to chain-breaking and ring-opening reactions,maewhile,asphaltene aggregates disassociate,improving5.17% light components during 3 minutes ultrasonic treatment.However,long treatment duration causes condensation and coking and heavy oil properties became deteriorative.Compared to ultrasonic treating alone,synergetic effect of ultrasound and hydrogen donor is supposed to realize a stable upgrading process,which fits a wide range of ultrasonic treatment duration.