Preparation Of Al-Based Catalyst And Its Mechanism Of Catalytic Oxidation Of PH₃ And H₂S In Ore-Furnace Gas

At present,the main industrial waste gas pollution in China is ore furnace gas pollution,mineral smelting methods are diverse,the characteristics of waste gas is complex,containing a variety of toxic and harmful gases,belongs to high energy consumption,high pollution industry.However,the ore furnace gas contains more than80%CO,which is a high-quality chemical feedstock gas.If it can be recycled efficiently,it will bring great economic benefits and also help China to achieve carbon neutral strategy.However,high concentration of impurity gases H₂S and PH₃ in ore furnace gas can easily lead to catalyst deactivation,thus affecting the recovery and utilization of CO.Therefore,the synchronous removal of sulfur and phosphorus from ore furnace gas has practical significance.The aluminum-based catalyst(Ce_0.6-Cu₆₀/Al₄₀)supported with Cu and Ce can achieve the efficient and cooperative removal of H₂S and PH₃.However,the preparation conditions,regeneration,desulfurization and dephosphorization reaction conditions and mechanism of the catalyst have not been solved.Based on this,this paper carried out follow-up research on the above issues,in order to establish a relatively complete catalyst desulfurization and dephosphorization reaction system and to lay a certain experimental and theoretical basis for the promotion and application of the catalyst.The specific research contents and conclusions are as follows:(1)The preparation conditions of the alumina-based catalyst were investigated.It was found that the alumina-based catalyst prepared by drying at 60?had good catalytic performance for the oxidation of H₂S and PH₃.The removal capacities of H₂S and PH₃with 50%conversion were 263.8mg/g and 219.3mg/g,respectively.The reason is that the corresponding catalyst has large and ordered active component CuO particles,which makes it have larger specific surface area and stronger redox ability.It was further obtained that the Al based composite catalyst prepared by calcination at 500?had good catalytic performance for the oxidation of H₂S and PH₃.The removal capacities of H₂S and PH₃ with 50%conversion were 323.2mg/g and 288.3mg/g,respectively.Increasing the calcination temperature to 500?can slightly promote the growth and activity of CuO grains.The higher temperature(>500?)leads to the formation of new phase Cu Al₂O₄ with spinel structure on the surface of Al based composite catalyst,which reduces the relative content of active component CuO on the surface of catalyst to some extent,leading to the deterioration of the performance of high temperature catalyst.The adsorption strength of H₂S and PH₃ on Cu Al₂O₄(100)surface was lower than that of CuO(111)by molecular simulation calculation,which supported our analysis to a certain extent.Finally,on the surface of the experimental results,the Al based composite catalyst prepared with nitric acid has the best performance.The reason is that the specific surface area and pore volume prepared by nitric acid are higher,and the catalyst surface will form more active components CuO and-NH₂functional groups.(2)It was found that when the reaction temperature was 70?,the oxygen concentration was about 1%,and the reaction space velocity was low(?10000h-1),the inlet concentration of 456mg/m³(H₂S)and 455 mg/m³(PH₃),the catalytic oxidation of H₂S and PH₃ of alumina based catalyst performance is the best.In addition,the kinetic equation shows that the catalytic reaction rates of H₂S and PH₃ are proportional to the concentration of H₂S and PH₃,respectively.Moderate reaction temperature can fully activate the activity of the catalyst and do not lead to accelerated accumulation of sulfate.The low space velocity can make O₂,H₂S and PH₃ gas molecules stay on the catalyst surface for a longer time,which is more conducive to the conversion of H₂S and PH₃.The experiments with different H₂S and PH₃ inlet concentrations show that the simultaneous catalytic oxidation of H₂S and PH₃ on the aluminum base catalyst will be influenced by each other,indicating that there is competitive adsorption in this process,and the competitive intensity will be affected by their respective concentrations.In addition,kinetic studies show that the reaction space velocity is negatively correlated with the reaction rate,and the reaction rate decreases with the increase of the reaction space velocity.When the particle size of catalyst is 40?60 mesh,the effect of internal diffusion on oxidation reaction can be overcome to the greatest extent.Through the analysis and fitting of the relevant experimental data,the kinetic equation of the simultaneous catalytic oxidation of H₂S and PH₃ is obtained,which shows that the catalytic reaction rate is proportional to the concentration of H₂S and PH₃.The H₂S has a higher reaction rate than PH₃.Constant speed usually means that it has a faster reaction rate.(3)Deactivation and regeneration of alumina based catalysts were investigated.It was found that the main reasons for deactivation were the accumulation of elemental sulfur(S),elemental phosphorus(P),sulfate(SO₄^2-)and phosphate(PO₄^3-),and the decrease of active components and surface relative oxygen content.The results of regeneration experiment showed that the combined regeneration method of water washing,oxygen heating purge and KOH impregnation was the best method to recover the performance of alumina based catalyst.Further experiments showed that the optimal regeneration conditions were as follows:500?oxygen purge and 1M KOH impregnation solution concentration.The results show that the performance of the regenerated Alumina based catalyst will deteriorate with the increase of regeneration times.There are two main reasons:one is that some products remain on the surface of regenerated alumina based catalyst,occupying part of the active sites;The other is that the active substance on the surface of the alumina based catalyst is partially lost during regeneration.(4)The mechanism of desulfurization and dephosphorization of alumina based catalyst was studied by molecular simulation calculation method.It was found that the adsorption of H₂S and PH₃ on CuO(111)surface is determined by molecular simulation.The adsorption of H₂S and PH₃ on CuO(111)surface is determined by the adsorption process of S...Cu3f and P...The strength of Cu3f is-36.53kJ/mol and-42.96kJ/mol,respectively.The corresponding electrostatic potential is the strongest and the charge transfer is the highest.The same adsorption sites of Cu3f indicate the existence of competitive adsorption behavior,which explains to some extent why adding H₂S to PH₃or H₂S to PH₃ or adding low concentration O₂to H₂S and PH₃ in the experimental stage will decrease the release rate of the corresponding gas.On the CuO(111)surface,the adsorption of PH₃ occurs first,followed by H₂S.The catalytic oxidation of PH₃ on CuO(111)surface will generate H₂O and(Cu3f)-HPO₃,and their conversion to H₃PO₄ is the control step of the whole catalytic oxidation reaction process,and finally H₃PO₄ is adsorbed on Cu3f to form a stable adsorption state.Catalytic oxidation of H₂S on CuO(111)surface yields-OH,(Cu₃f)-SO₃ and(Cu3f)-HSO₃.The controlling step of the whole catalytic oxidation reaction process is the transformation from(Cu3f)-SO₃ to(Cu3f)-HSO₂.Finally,two H atoms in H₂SO₄ form hydrogen bonds with two O atoms on the CuO(111)surface respectively to form a stable adsorption state.This is consistent with the inferences of the kinetic part.In addition,the formation of H₂O in the calculation is also consistent with the phenomenon of water mist generation in the inner wall of the reactor during the experiment.