Pyrolysis Behavior And Pyrolysate Characteristics Of Fushun Oil Shale In Sub/Supercritical Water And Anhydrous Water

People’s demand for energy is increasing,and the reserves of fossil fuels are limited.In order to meet the future energy demand,it is necessary to develop all kinds of alternative fossil fuels.Oil shale is a fine-grained sedimentary rock with a high ash content that contains organic matter called kerogen.The shale oil obtained by distillation of oil shale is similar to crude oil,which can be further processed into gasoline,diesel oil,etc.,or directly used as fuel oil.China is rich in oil shale resources with huge reserves,but the current mining methods are still relatively primitive,mainly direct mining,with low mining efficiency and serious ecological damage,and may be replaced by in-situ mining methods in the future.Therefore,based on MTI technology of Taiyuan University of Technology,this paper proposes an in-situ injection sub/supercritical water pyrolysis method for oil shale production.Sub/supercritical water pyrolysis is an effective method to improve the pyrolysis performance of oil shale formations with depths up to 1000 meters.This paper provides basic technical support for the industrial development of oil shale in-situ injection of sub/supercritical water through comparative experimental study.The main conclusions are as follows:（1）Fushun oil shale belongs to high ash oil shale,ash content is 78.08%,oil content is5.62%;The organic kerogen in oil shale is type II and has high hydrocarbon generation potential.The presence of sub/supercritical water promotes the pyrolysis behavior of Fushun oil shale and increases the pyrolysis weight loss rate.The maximum mass loss occurs at SCW-450,with a weight loss rate of 12.30%.The higher ionization constant of sub/supercritical water promotes acid catalyzed carbocation reaction to produce organic acids.These hydride ions act as transfer agents to avoid polymerization into shale coke and promote the formation of shale oil.In addition,sub/supercritical water has swelling effect,which makes the oil production rate of oil shale under sub/supercritical water environment higher than that of anhydrous pyrolysis.The yield of oil discharged in sub/supercritical water environment is 4.2-14.3 times higher than that of anhydrous pyrolysis.In anhydrous pyrolysis,a small part of organic matter is pyrolyzed,and in high-pressure anhydrous environment,shale oil generated from pyrolysis remains in the pores and channels of residual solids,resulting in higher residual oil yield from anhydrous pyrolysis than that from sub/supercritical water pyrolysis at the same temperature.（2）Sub/supercritical water can promote the combination of hydrogen radical and alkyl radical,and more aromatic side chain breaks,resulting in the increase of saturated hydrocarbons and aromatic hydrocarbons.Under the anhydrous pyrolysis condition,there are more residual oil in shale coke,which is difficult to produce,resulting in the content of saturated hydrocarbon,aromatic hydrocarbon,non-hydrocarbon and asphaltene higher than that of sub/supercritical water pyrolysis.Under the condition of anhydrous pyrolysis,the oil is mainly light kerosene with low carbon number and diesel with medium carbon number,and the content of heavy asphaltene is low.Under the sub/supercritical water pyrolysis condition,the oil is mainly diesel with medium carbon number and asphaltene with high carbon number,and the content of heavy asphaltene is slightly higher than that of diesel.Under the anhydrous pyrolysis condition,there is little light kerosene in the residual oil,which is dominated by middle and heavy distillate diesel oil,bitumen and heavy oil,unlike the discharged oil.（3）Sub/critical water and supercritical water have strong extraction ability,which promotes the formation and release of small molecule gas,resulting in higher gas production rate in this environment than anhydrous pyrolysis gas production rate at corresponding temperature,and the pyrolysis gas production increases 1.42-5.22 times.Due to the solvent effect,sub/supercritical water can promote the cracking of aliphatic hydrocarbons and aromatic ring side chains,resulting in higher gas yields of C₁,C₂ and C₃ in sub/supercritical water pyrolysis than in anhydrous pyrolysis.Under the action of supercritical water solvation,the bond energy of cracking is reduced and the formation of smaller hydrocarbon gas of C₄+is promoted.In the pyrolysis process of oil shale,sub/supercritical water exists,and the water-gas transfer reaction（CO+H₂O→CO₂+H₂）takes place,which improves H₂ production.Due to the acid-base catalytic action of water in sub/supercritical state,the decarboxylation of oxygen-containing organic compounds（acids,esters and ethers,etc.）in kerogen is promoted,resulting in the production of more CO₂.（4）Sub/supercritical water can promote the conversion of organic matter to oil and gas,and the TOC and PC contents of shale coke are lower than that of anhydrous pyrolysis.The hydrocarbon generation potential S₁+S₂ of shale coke decreases with the increase of temperature,but sub/supercritical water can promote kerogen cracking to generate more hydrocarbons,and the S₁+S₂ of shale coke is lower than that of anhydrous pyrolysis.Supercritical water has the greatest influence on the release and migration of hydrocarbons generated during oil shale pyrolysis,and the content of hydrocarbons in solid residues is the least.