Study On The Catalytic Oxidation Of Heavy Oil With Cu-based Catalysts

With the development of industrialization in China,the demand for fossil fuels is increasing.As a major petrochemical energy consuming country,China’s crude oil consumption accounted for 13%of the total global consumption in 2017.Air injection oil recovery technology has been applied more and more because of its advantages of gas source and low cost,many experts and scholars around the world have done a lot of research on its oil displacement mechanism and field application.This technology can effectively improve formation energy and reduce heat loss in the later stage of thermal recovery.The key factor for field implementation of this technology is that oxygen content reaches the safety threshold after air breakthrough,so that the production process can be carried out safely.Adding specific catalysts can increase the low temperature oxidation rate of heavy oil and solve the safety problems caused by excessive oxygen content in tail gas.It has been reported that transition metal salt catalyst is used in low temperature oxidation process of heavy oil.Previous exploratory experiments have found that Cu-based catalysts have good catalytic effect on lowtemperature oxidation of heavy oil,but the related heavy oil oxidation process has not been studied in depth.In this paper,heavy oil from a certain oilfield in Xinjiang is taken as the raw material,without the participation of catalyst,the low-temperature oxidation process of crude oil under the conditions of bottom temperature and pressure is simulated by high-pressure reaction kettle.By analyzing the physicochemical properties(viscosity,acid value,four components of SARA,oxygen group,etc.)of heavy oil before and after the reaction and the gas phase composition after the reaction,we infer that the reaction mechanism of the low temperature oxidation process of the heavy oil.Three types of Cu-based catalysts include copper sulfate,nano-copper oxide and copper naphthenate,are selected to study the low-temperature catalytic oxidation process of heavy oil,and compared with the low-temperature oxidation of heavy oil without catalyst,the effects of the addition of accelerator on the physicochemical properties of oxidized heavy oil,especially the changes of acid value and oxygen functional groups,are discussed.The results show that the participation of catalysts reduces the oxygen-containing functional groups,acid value and viscosity of oxidized heavy oil,which essentially accelerates the decarboxylation of oxides.Comparing with the Cu-based catalysts,nano-copper oxide>copper naphthenate>copper sulfate is found.The oxidation/catalytic oxidation process and stage oxidation characteristics of heavy crude oil are studied by differential thermal scanner.The oxidation process of heavy crude oil can be divided into three stages:low temperature oxidation stage(40℃-359℃),fuel deposition stage(359℃-407℃),and high temperature oxidation stage(407℃-539℃).FlynnWall-Ozawa method is used to study the thermal kinetics of oil samples in low temperature oxidation stage and high temperature oxidation stage.The results show that the activation energy of heavy oil at this stage is reduced by adding catalyst.Among them,nano-copper oxide has the best effect in low temperature oxidation stage and the activation energy decreased from 268.88 KJ/mol to 189.08 KJ/mol.Copper naphthenate has the best effect in high temperature oxidation stage,and its activation energy decreases from 386.54 KJ/mol to 285.51 KJ/mol.The air-assisted thermal recovery technology used in a heavy oil field in Xinjiang has an operating temperature between 180℃ and 220℃,and the reaction phase belongs to the low temperature oxidation section of heavy oil.However,the low temperature range temperature obtained by thermodynamic research is too wide,and the oxygen content of tail gas in airinjection assisted thermal recovery is an important index to judge the safety of the process.Therefore,the low-temperature oxidation process of heavy oil is further discussed with the change of oxygen content of tail gas before and after the reaction,and the kinetic parameters are calculated.The results show that the reaction order of low temperature oxidation of heavy oil changes from 0 to 1 with the addition of Cu catalyst,and the reaction becomes more complex.The activation energy generally decreases after adding catalyst.Among them,the activation energy of nano-copper oxide catalyst decreased from 68.39 kJ/mol to 57.66 kJ/mol,indicating that the addition of copper catalyst can accelerate oxygen consumption,promote oxidation reaction and help to increase the safety of injection-production process.