Study On Bifunctional Catalyst For Mercaptan Etherification And Diolefin Removal In LPG

Liquefied gas（LPG）is a by-product of petroleum processing,the main component is a mixture of C3,C4.LPG contains active diolefins and toxic mercaptans and other impurities,which will affect the equipment and catalysts in the subsequent deep processing process.So they need to be removed in the LPG refining process.Conventional dethiol technology has problems such as large discharge of alkali residue and low dethiol efficiency.In recent years,thioetherification technology has become a research hotspot in thioetherification and selective hydrogenation.But at the same time,there is a problem that the selective hydrogenation temperature of diene is too high.Therefore,this paper is devoted to the study of a Ni-based non-precious metal catalyst that can not only remove diolefins well but also completely etherify mercaptans at lower temperatures.In this paper,Ni X/γ-Al₂O₃ series bimetallic catalysts with Ni as the first active metal component and Fe,Ga,Co,and Cu as the second active metal components were prepared.The results of the evaluation and characterization of the thioetherification and selective hydrogenation of diolefins show that the NiFe catalyst has good selectivity for monoolefins,and the removal rate of methyl mercaptan can reach 100%at low temperature of 60℃,which has a good thioetherification effect.Therefore,NiFe catalyst is selected as the optimal Ni X series bimetallic catalyst.On this basis,this paper then investigates the effect of different Fe₂O₃ loadings on the thioetherification of NiFe/γ-Al₂O₃ catalysts.Through the evaluation and characterization results,it is concluded that when the Fe₂O₃ loading reaches 6 wt.%,the NiFe catalyst has the best hydrogenation activity and selectivity,the highest propylene yield,and complete removal of methyl mercaptan under low temperature conditions.The NiFe Mo/γ-Al₂O₃ trimetallic catalyst was prepared by adding the third active metal component Mo to the above-mentioned preferred NiFe catalyst,and the thioetherification performance of different Mo O₃loadings was explored.From the evaluation and characterization results,it is concluded that the introduction of Mo has a significant promoting effect on the hydrogenation performance of the NiFe catalyst,and with the increase of Mo O₃ content,the sulfidation degree of Mo species and Ni species increases.When the loading of Mo O₃ reaches 5wt.%,the NiFe5Mo catalyst can completely remove methyl mercaptan and butadiene at lower temperature,so the thioetherification of NiFe5Mo catalyst achieves the best effect.The research on the reaction conditions of the NiFe5Mo catalyst showed that,the catalyst has the best activity and selectivity under the conditions of temperature of 110℃,space velocity of 3.5 h^-1,hydrogen-hydrocarbon ratio of 6,and pressure of 2.5 MPa.Finally,a preliminary study on the reaction mechanism of LPG thiol etherification was carried out.Methyl mercaptan and hydrocarbons with different components were subjected to thioetherification reaction at different temperatures.The mechanism of the thioetherification reaction was deduced.