Mechanism Study Of Targeted Catalytic Aquathermolisis Of Heavy Oil By Composite Nano-particles

With the continuous exploitation of light crude oil,heavy oil with abundant reserves will have great development potential in the future.However,the high content of asphaltene and wax makes the viscosity of heavy oil increase sharply,which brings difficulties to the process of production and transportation.In addition,when external conditions such as pressure and temperature change,the asphaltene and wax components in heavy oil are easy to precipitate out,causing pipeline blockage.In order to solve the above problems,researchers have put forward catalytic aquathermolysis technology.Through in-situ catalysing of heavy oil underground,part of the heavy components will be converted into light hydrocarbons,achieving the improvement of oil quality and mobility.In this technology,the effective contact between aquathermolysis catalyst and heavy component in heavy oil will directly affect the catalytic efficiency.Therefore,it is particularly critical to develop catalysts with asphaltene and resin targeting functions.Because of the special aromatic groups and aliphatic side chains,the comb copolymer can play a role in the targeted dispersion of asphaltenes,providing an idea for the design of highly efficient catalysts for the targeted aquathermolysis of heavy oil.In this work,aiming at the aggregation/precipitation behavior of asphaltenes,the targeted dispersion effect of comb-type copolymers with different aromatic/aliphatic side chains on asphaltenes was studied.Then,a kind of composite nanoparticle with targeted catalytic function of heavy oil was designed and synthesized,its catalytic performance was evaluated,and the craking products were systematically analyzed to reveal the catalytic reaction mechanism.Main research contents and conclusions are as follows:1.Three series of poly(maleic anhydride-co-vinyl acetate)derivatives(PMVs)were synthesized.According to the difference of side chain,they can be divided into three series:series ? polymers with only aromatic side chains(benzene,naphthalene,benzimidazole),series? polymers with only aliphatic side chains(octane,tetracane and octadecane)and series ?polymers with both aromatic and aliphatic side chains.The effect of different polymers on the precipitation behavior of asphaltene was studied under the model oil system.The initial precipitation point of asphaltene in the model oil was determined by UV-Vis spectrophotometer.Turbidimeter,dynamic light scattering and optical microscope were used to characterize the turbidity,diameter distribution and morphology of asphaltene in model oil.The rheometer was used to measure the apparent viscosity of heavy oil upon adding polymers.Studies show that series ? polymers have no inhibitory effect on the precipitation of asphaltenes,while series ?polymers have some,and series ? polymers with aromatic/aliphatic side chains have significant inhibitory effect on the precipitation of asphaltenes.The mechanism of polymer's targeting and dispersing effect on asphaltenes was put forward:the aromatic side chains enable the polymers to adsorb on the aromatic dense ring of asphaltenes through "?-? conjugation and hydrogen bonding",and the aliphatic side chains could form "steric bloking layer''to prevent the further aggregation of asphaltenes.In the study on the targeting effect of asphaltenes with different aromatic functional groups,it is found that benzene ring with more degree of freedom and smaller steric hindrance is more suitable as the target group of heavy oil than naphthalene ring and benzimidazole ring.2.With polyvinyl imidazole(PVI)as the target group,nano-titanium dioxide(TiO2)as the catalyst carrier and catalytic center ?,and transition metal nickel ion(Ni2+)as the catalytic center?,composite nanoparticle catalysts(TiO2@PVI/Ni2+)were synthesized(TiO2@PVI/Ni2+).The chemical structure,PVI grafting amount,Ni2+ loading amount and morphology of the composite nanoparticles were characterized by infrared spectroscopy,thermogravimetric analysis,inductively coupled plasma emission spectra,scanning electron microscopy and transmission electron microscopy,respectively.The results show that the composite nanoparticles have good thermal stability.For TiO2@PVI-1/Ni2+,TiO2@PVI-22/Ni2+ and TiO2@PVI-80/Ni2+,the grafting amount of PVI reach 5.9%,9.2%and 10.7%respectively,and the corresponding Ni2+ loading amount reach 1.13%,2.69%and 5.26%,respectively.The results show that the loading amount of Ni2+ is positively correlated with the grafting amount of PVI.3.The synthesized composite nanoparticles were used as heavy oil catalytic aquathermolysis catalysts.The effects of reaction conditions(temperature,catalyst dosage and oil-water ratio),cataltsts' Ni2+ loading amount and hydrogen donor on viscosity reduction in heavy oil catalytic aquathermolysis were studied.The results show that higher Ni2+ loading,reaction temperature,catalyst content,moderate oil-water ratio and addition of hydrogen donor all contribut\to the aquathermolysis reaction.Under the optimized reaction conditions(temperature of 240?,the dosage of catalyst 0.6 wt.%,oil-water ratio of 7:3 and reaction time of 24 hours),TiO2@PVI-80/Ni2+ as catalyst,can obtain up to 83.5%of the viscosity reduction of heavy oil.With the further adding of 3 wt.%hydrogen donor,the viscosity reduction can increase to more than 90%.4,The influence of catalytic aquathermolysis on the rheological properties of heavy oil was studied by characterizing the flow curves,thixotropy,viscoelasticity and time-dependent of the unreacted heavy oil,the oil samples without catalyst,the oil samples with catalyst and the oil samples with hydrogen donor.The analysis of flow curve shows that the heavy oil chang from pseudoplastic fluid to Newtonian fluid.The area of thixotropic ring decrease greatly,indicating that the internal microstructure of oil sample was destroyed irreversibly.The decrease of viscosity modulus(G")of oil samples and the shorter time for the viscosity to reach stability under constant shear rate indicate that the internal three-dimensional network structure of heavy oil becomes loose after aquathermolysis reaction,and the apparent viscosity are greatly reduced.5.The reaction mechanism of catalytic aquathermolysis was systematically studied.The relative content changes of asphaltenes,resins,saturates and aromatics in oil samples before and after the reaction were measured by four component separation.The molecular weight,elemental composition and structural parameters of the obtained asphaltenes and resins were characterized by matrix-assisted laser desorption ionization-time of flight-mass spectrometry,elemental analysis,nuclear magnetic resonance hydrogen spectrometry and infrared spectrometry.The composition of saturates,aromatics and water sample were analyzed by gas chromatography-mass spectrometry.The results show that the content of asphaltenes and resins in heavy oil decrease by 2.3%and 5.6%respectively,and the content of saturates and aromatics increase by 6.8%and 1.1%respectively.After the fine characterization of the structure of the separation products,it is found that under the catalytic aquathermolysis system,the resins in the heavy oil undergo dissociation of alkyl side chains while the asphaltenes experience the fragmentation and depolymerization of large aromatics(oxygen-containing).