Controllable Design Of Ultra-Deep Oxidative Desulfurization Catalyst And Its Application In Diesel Desulfurization

The increasingly stringent sulfur emission and fuel sulfur standards make petrochemical companies must continuously improve the desulfurization process.At present,hydrodesulfurization（HDS）technology is mainly used in the fuel desulfurization process.However,HDS has many disadvantages such as high temperature,high pressure,the large amount of catalyst,high operating cost,and difficulty in removing aromatic organic sulfur compounds in fuel.Oxidative desulfurization（ODS）technology,as a desulfurization process that can replace traditional HDS to remove aromatic organic sulfur compounds in fuel,displays great application prospects in fuel desulfurization.The key to ODS is the catalytic oxidative desulfurization performance of the catalyst.Therefore,the development of new faster,more efficient,and more stable oxidative desulfurization catalyst is of great significance for realizing the industrialization of ODS.Phosphomolybdate is widely used in the oxidative desulfurization of fuel,due to its advantages of easy preparation and modification,great compatibility,non-toxicity,and high catalytic activity.Phosphomolybdate nanodots have a large number of defect sites,which can effectively improve the catalytic performance of the catalyst after being loaded,and improve the problems of easy dissolution and difficult separation.Therefore,the focus of this dissertation is aiming to synthesize the phosphomolybdate nanodots composites with high catalytic activity.The main research contents and results of this dissertation are as follows:（1）Phosphomolybdate nanodots composites（PMND/SNS）were prepared by the one-step method.The structure and morphology were analyzed by XRD and other means,and then they were used in the oxidative desulfurization of fuel.The results showed that the phosphomolybdate grain size of PMND/SNS composites was 26.8 nm.Using H₂O₂as the oxidant,at 60°C,1.6%（m（catalyst）/m（oil））PMND/SNS could almost completely remove DBT,4-MDBT and 4,6-DMDBT within 16 min;at 80°C,1.6%（m（catalyst）/m（oil））PMND/SNS could almost completely remove BT and 3-MBT from model oil within 32 min.（2）The mesoporous phosphomolybdate nanodots composites（PMND/MSN）were prepared by using the templating agent CTAB to adjust the pore structure of PMND/SNS.The results showed that the surface area of PMND/MSN composites increased from 51.44m²/g to 855.27 m²/g,and the pore volume increased from 0.063 cm³/g to 0.628 cm³/g.The improvement of pore structure increased the active sites of PMND/MSN,which was beneficial to the enhancement of catalytic activity.When H₂O₂ was the oxidant,1.4%（m（catalyst）/m（oil））PMND/MSN could achieve almost 100%removal of BT and 3-MBT in 32 min at 70°C.（3）Hollow phosphomolybdate nanodots composites（PMND/HMS）were prepared by constructing the hollow nanoreactor.The morphology and structure of PMND/HMS were analyzed in detail.The catalytic oxidative desulfurization performance of PMND/HMS was also evaluated.The results showed that under the optimal reaction condition,using H₂O₂ as the oxidant,1.0%（m（catalyst）/m（oil））PMND/HMS removed almost 100%of BT and 3-MBT in fuel at 60°C for 28 min.The constructed hollow nanoreactor displayed excellent performance in reducing the amount of catalyst,shortening the reaction time and reducing the reaction temperature.（4）To solve the agglomeration phenomenon of PMND/HMS during oxidative desulfurization,Janus phosphomolybdate nanodots composites（PMND/JMS）were prepared by grafting method.The analysis results showed that the static contact angle of PMND/JMS increased from 16°to 81°by grafting octyl groups,which improved the interfacial activity of the composites,made PMND/JMS had the best catalytic oxidative desulfurization performance.Only 0.6%（m（catalyst）/m（oil））PMND/JMS could achieve almost complete removal of BT,3-MBT,DBT,4-MDBT and 4,6-DMDBT in 10 min at60°C.Its desulfurization activity remained above 90%after repeated use 10 times,showing excellent recycle stability.（5）To reveal the essence of the catalytic oxidative desulfurization reaction in the H₂O₂ system and the O₂ system,the catalytic oxidative desulfurization process of BT,3-MBT,DBT,4-MDBT,4,6-DMDBT and straight-run diesel under these two systems were studied.The oxidation products and oxidative desulfurization mechanism of these two systems were also explored.The results showed that the organic sulfur compounds in the fuel were oxidized by the strong oxidizing molybdenum phosphate and superoxide radicals produced in the H₂O₂ system and the O₂ system,respectively,and finally generated the high value-added sulfone compounds.Additionally,the catalytic oxidative desulfurization reactions of the four phosphomolybdate nanodots composites all conformed to the apparent first-order kinetic law.The sulfur content of straight-run diesel was reduced to below 5 ppm by using both systems,fully meeting the National VI standard.