Studies On The Research And Application Of Acetylene Front-end Hydrogenation Catalyst

High temperature pyrolysis of petroleum hydrocarbons is the most important reaction in the production of ethylene.0.5 2.0 v% acetylene is contained in the process of above reaction,which is an impurity in the subsequent use of ethylene and must be removed by hydrogenation.There are two kinds of hydrogenation techniques,namely front-end hydrogenation process and post hydrogenation process.At present,the new large scale ethylene plants in China have adopted the front-end hydrogenation process,with a total production capacity of 11.74 million tons / year.The demand for the catalyst is huge,which is one of the most important catalysts for petrochemical industry.Due to the complex composition of the front-end hydrogenation feeds,catalyst development is difficult,leading to long-term dependence on imports.Therefore,the development and successful application of catalysts on acetylene front-end hydrogenation have great theoretical and practical significance.In our reseacrches,a Pd-Ag/?-Al₂O₃ catalyst was developed for the pre-hydrogenation of acetylene.The effects of catalyst carrier,composition,preparation method,pretreatment method and other factors on the performance of the catalyst were studied.The catalyst formulation and preparation conditions were determined.The industrial production technology of acetylene pre-hydrogenation catalyst was formed through amplified preparation.On the basis of those,the industrial production of the catalyst was carried out,obtaining 10 tons of prereduced-passivated catalyst.The results showed that the macroscopic properties,microstructure and reaction performance of the catalysts were as good as those of the imported ones.Moreover,the optimum conditions of the catalyst were determined by investigating the effects of CO content,space velocity,pressure,reaction temperature and MAPD content on the catalyst performance.After studing of the industrial application of the catalyst,we confirmed the experimental scheme which the catalyst was used in Daqing Petrochemical plants with 270 thousand tons/year.We believe that our work laid the foundation for the industrial transformation of the catalyst.The main research achievements and technological innovations are as follows:?1?The Al₂O₃ forming process,the carrier heat treatment condition and the carrier modification method were systematically studied,and ?-Al₂O₃ carrier with multi-stage characteristic pore distribution and low surface acidity was developed.One excellent catalyst for acetylene hydrogenation needs to have high activity,selectivity and anti-coking performance.So it is necessary to develop the catalyst carrier that has sufficient active surface area and sufficient material transport channels.Aimed at this demand,a multi-stage characteristic pore distribution Al₂O₃ carrier was designed and prepared with controlling the gelling reaction temperature,the concentration of reactant?sodium aluminate,nitrate?,the pH value of the solution and the content of ?-Al₂O₃ · 3H2 O in mixture of Al₂O₃.The small pores provide enough active surface area to ensure the hydrogenation activity and the macropores provide sufficient transport channels to improve the selectivity of the catalyst hydrogenation.The conditions of heat treatment and modification of carrier were systematically studied,and the optimal conditions were determined.The ?-Al₂O₃ support prepared by high-temperature heat treatment combined with alkali metal modification has low surface acidity,which is beneficial to improve the anti-coking performance of the catalyst.?2?Pd-Ag bimetallic nanocatalyst was prepared with the optimal composition of the catalyst.Using ?-Al₂O₃ with multi-stage characteristic pore distribution as carrier,preparation of Pd-Ag bimetallic nanocatalyst by solution impregnation was systematically studied.The loading capacity and loading technology of active component Pd and auxiliary component Ag were determined.Finally,uniform dispersion Pd-Ag nanocomposite catalyst was prepared.The performance of the catalyst was compared with that of 7741B-R in the 750 mL unit simulating Daqing condition for 700 h.The self-made catalyst was slightly better than that of imported agent,and the selectivity was quite the same as that of imported agent.?3?A new catalyst preparation method was developed,which improved the dispersion of active components and reduced the surface acidity.The catalyst prepared by impregnation method has many residues of acidic substances,which leads to the polymerization of unsaturated hydrocarbons and results in poor coking resistance.The micro-emulsion method and the in-situ growth of MgCO3 on ?-Al₂O₃ support were used to prepare the catalyst.The results show that Pd and Ag nanoparticles are uniformly distributed on the surface of the Pd-Ag / ?-Al₂O₃ nanocomposite catalyst which is prepared by microemulsion method.The properities of Pd-Ag alloy catalyst obtained by high temperature activation were investigated.At the reaction temperature of 62 oC,the conversion of acetylene is 69%,the selectivity of ethylene is 94% and the amount of n-butene is 74?L/L.The Pd-Ag/MgCO3@?-Al₂O₃ catalyst were prepared on the surface of the ?-Al₂O₃ support.The active component Pd-Ag was evenly distributed on the surface of the support,and the dispersion of the active component Pd was optimized.The conversion of acetylene is 86%,the selectivity of ethylene is 86%,and the amount of n-butene is 55?L/L when the reaction temperature is 70 oC.?4?A new method for the activation of micropressure-air flow activator was developed to decrease the surface acidity of the catalyst and improve the anti-coking performance.The effects of pressure,flow rate and atmosphere composition on catalyst which were active by of the micro-positive pressure-air were investigated.The optimum activation conditions were determined.Compared with the traditional activation method,the activation of the catalyst in the micro-positive pressure-air flow atmosphere reduced the total surface acid amount of the catalyst by 28%,which enhanced the anti-coking performance of the catalyst.?5?The reduction and passivation pretreatment technology was developed,and the reduction-passivation catalyst was obtained,and the stability of starting was improved.Because the pre-hydrogenation of industrial devices do not have the catalyst reduction conditions,we carried out the catalytic reduction and passivation pretreatment technological to improve the starting stability of the catalyst.The catalyst pretreatment technology of reduction with passivation of low palladium content catalyst surface micro-oxidation film was formed.By inhibiting the initial activity of the catalyst,the temperature control interval was broadened and the green oil production was greatly reduced in the initial reaction.Adopting this technique,the problem that the industrial device does not have the reduction inside is solved,and the starting stability is improved.