Mechanism Research On Hydrogen Sulfide Formation During Tetrahydrothiophene Aquathermolysis Reaction

Steam injection thermal recovery is an effective way for heavy oil exploitation at present.When high-temperature steam was injected into the formation,not only the viscosity of heavy oil decreased,but also a series of chemical reactions occurerd,which generated acidic gases such as CO2 and H2S.H2S is a highly toxic and harmful gas,its formation would cause a series of problems,such as equipment corrosion,health and safety and environmental pollution.Therefore,exploring the formation mechanism of H2S in the process of aquathermolysis reaction has great significance for prevention and treatment of H2S in thermal recovery process.The aquathermolysis of sulfur-containing organic compounds in heavy oil is an important source of H2S.Tetrahydrothiophene is a five-membered heterocyclic thiophene sulfide,which is a representative sulfur-containing organic compound in heavy oil.The influence of reaction temperature,time,molar ratio and solution pH on the H2S formation during tetrahydrothiophene aquathermolysis process were investigated through indoor thermal simulation test.The results showed that main gaseous products during tetrahydrothiophene aquathermolysis are H2S,CO2,H2 and related light hydrocarbon gases.Under the same reaction conditions,aquathermolysis dominates.Reaction temperature and time have a positive correlation with the formation of H2S in the process of aquathermolysis.When molar ratio of water to tetrahydrothiophene is less than 3,the increase of water content in reaction system is beneficial to improve the degree of tetrahydrothiophene aquathermolysis.Under acidic conditions,the reaction activity of tetrahydrothiophene will be greatly enhanced;under alkaline conditions,aquathermolysis will be inhibited.A kinetic model of H2S formation during tetrahydrothiophene aquathermolysis was established through kinetic experiments.The reaction order of H2S formation is 0.9,the activation energy is 54.55 kJ/mol,and the frequency factor is 166.47 day^-1.Based on the analysis of liquid products during tetrahydrothiophene aquathermolysis and the related theory,following conclusions have been obtained:The liquid products of tetrahydrothiophene contain a few alkanes and alkenes;the main products are thiols,thioether,disulphide,alkyltetrahydrothiophene,alkylthiophene,thiophene derivatives and other organic sulfides.In the process of aquathermolysis,the C-S bonds formed by heteroatom S break at first time,and then occur opening-ring,which produce small molecular alkanes or alkenes.High-temperature water plays a key role in the process of tetrahydrothiophene aquathermolysis,and would directly participate in the elementary reactions such as hydrolysis and water gas shift reaction?WGSR?,leading to the migration of hydrogen from water to gaseous or liquid products.In addition,the hydrolysis and secondary hydrolysis are the main pathways for the formation of H2S during tetrahydrothiophene aquathermolysis,the formation of H2S by pyrolysis and hydrodesulfurization are weak.In this paper,tetrahydrothiophene was used as a model compound to explore the formation mechanism of H2S in the process of aquathermolysis reaction through indoor thermal simulation test.The research conclusions provide theoretical support for the prevention and control of H2S formation in thermal recovery process,and have an important guiding role.