Performance Research Of Oxidation Catalysts For Natural Gas Desulfurization By Chemical Looping Technology

H₂S is a typical toxic contaminant in natural gas resulting in environmental pollution,equipment corrosion,and by-products increase in practical natural gas applications.However,the traditional natural gas desulfurization methods were energy-intensive,polluting,and costly.The catalytic oxidation of H₂S in natural gas under oxygen atmosphere can effectively solve the shortcomings in the traditional natural gas desulfurization methods,but the issues such as low selectivity of elemental Sulphur,easy deactivation of the catalyst,and low safety remain challenged.Chemical looping technology can effectively avoid direct exposure of O₂ to reactants by transporting lattice oxygen through oxygen carriers（OC）.Combining chemical looping technology with catalytic oxidation of H₂S method can effectively solve the problems generated by catalytic oxidation of H₂S under oxygen atmosphere.Achieve high efficiency,low energy consumption and low cost for H₂S removal and elemental sulfur recovery.The oxygen transport performance of OC is closely related to the support carrier materials,active components and additives loaded on the support.In this research,four different types of OC with oxygen transport and catalytic functions were prepared.The performance of the prepared OC in the selective oxidation of H₂S to elemental sulfur under low temperature chemical looping operation mode was systematically investigated.Combining multiple characterizations means（XRD,BET,H₂-TPR,SEM-EDS,and XPS）to investigate the mechanism of lattice oxygen transport and the role of catalytic active center during the catalytic oxidation of H₂S.Finally,the effects of the reaction conditions（reduction temperature,oxidation temperature,H₂S concentration,O₂ concentration and Packed bed height）on the performance of the desulfurization reaction were investigated,which provide a reference guide for further design and development of highly active and selective OCs.The main contents are summarized as follows.（1）The OCs with V₂O₅ as the active component and Ti O₂ and Al₂O₃ respectively as the supports were prepared by impregnation method.The effects of the active component and supports on the selective oxidation reaction performance of H₂S were investigated.It was found that both V₂O₄(V⁴⁺)and V₂O₅(V⁵⁺)existed in the prepared OCs,and V₂O₄(V⁴⁺)was the dominant components,which played the role of adsorption and transform of H₂S in the desulfurization reaction.When V₂O₅ was loaded on the Ti O₂ and Al₂O₃supports respectively,the activity of lattice oxygen in the V₂O₅ phase was greatly improved due to the interaction between the supports and V₂O_5.V₂O₅ in crystalline form on the Al₂O₃ support,exhibiting low lattice oxygen activity and higher selectivity of elemental Sulphur.The oxygen transports,oxygen transport rate and selectivity of elemental Sulphur had good stability after 20 cycles.（2）Furthermore,taking Cu O as an additive.The effect of Cu O in the OC on the selective oxidation reaction of H₂S was investigated.It was found that the addition of Cu O could significantly enhance the cumulative oxygen transport and SO₂ yield during regeneration.The addition of Cu O improved the activity of the V₂O₅-based OC,which could realize the selective oxidation of H₂S at a lower temperature,while the addition of Cu O could not enhance the reduction of V₂O₅in the OC.（3）The effects of reduction temperature,oxidation temperature,H₂S concentration and O₂concentration on the reaction performance of H₂S selective oxidation were investigated using OCs with Al₂O₃ supports.The results show that,at low reduction temperature（150°C）,the lattice oxygen activity is low leading to poor oxygen transport.At higher reduction temperature（250°C）,the lattice oxygen activity in the OCs were too strong,resulting in decreasing of selectivity of elemental Sulphur.Low oxidation temperature（300°C）will lead to insufficient regeneration of the oxygen carrier,and high oxidation temperature（500°C）will lead to more SO₂ production in the ramp-up phase,which is not conducive to Sulphur recovery.the higher the concentration of H₂S,the oxygen transport rate,oxygen transport capacity and selectivity of elemental Sulphur increased with the increase of H₂S concentration in the reduction stage.The O₂ concentration affected the reaction performance after OCs regeneration,Higher O₂concentration could improving oxygen transport capacity and decreasing selectivity of elemental Sulphur after oxygen carrier regeneration.（4）The effect of Packed bed height on the performance of H₂S selective oxidation reaction performance was investigated using the OCs with Al₂O₃ supports.The results showed that,the oxygen transport,generation of elemental sulfur and SO₂ were significantly improved by increasing the height of the Packed bed height.The penetration curves of OCs to H₂S at the highest of the Packed bed height showed that the OCs without Cu O addition had higher selectivity of elemental Sulphur,and the OCs with Cu O addition had higher H₂S transport.The results provide a guidance for the design and development of highly activity and selectivity of OCs.