Study On Simultaneous Catalytic Hydrolysis Of COS, CS2 And Reaction Mechanism Over Walnut Shell Based Catalyst

Reductive industrial furnace tail gas contains a large amount of carbon monoxide?CO?.The content of CO is about 85⁹5%,and CO can be used as the raw material gas for one-carbon chemical industry.Therefore,it has high economic value for the development in one-carbon chemical industry.However,there are a large amount of organic sulfur impurities in the reductive industrial furnace tail gas,such as 700-1100mg/m³ carbonyl sulfur?COS?and 20-80 mg/m³ carbon disulfide?CS₂?,which will corrode the pipe and cause the deactivation of the catalyst.It is necessary to remove these organic sulfur impurities.Meanwhile,further researching and presenting the reaction mechanism can provide the theoretical guidance for the removal of COS and CS₂ in industrial production.So far,the detailed mechanism research and reaction pathway exploration for simultaneous removal of COS and CS₂ are imcomplete.This study focused on the simultaneous catalytic hydrolysis of COS and CS₂according to the characteristics of reductive industrial furnace tail gas.Meanwhile,the catalytic hydrolysis reaction mechanisms were investigated by characterization and theoretical calculation methods.The main research contents included:preparation of walnut shell based biochar catalyst?Fe-Cu-KOH/WSB?,regeneration of Fe-Cu-KOH/WSB,reaction kinetic studies on simultaneous catalytic hydrolysis of COS and CS₂,reaction mechanisms of catalytic hydrolysis of COS and CS₂ over walnut shell biochar carrier and active components.The detail research contents and conclusions were as follows.?1?The walnut shell biochar carrier was prepared by carbonization and chemical activation process,and then it was used to prepare Fe-Cu-KOH/WSB by gel-sol method.In this part,the influences of preparation conditions for simultaneous catalytic hydrolysis of COS and CS₂ were investigated,such as carbonization temperature,activation agent species and content,activation temperature,precursors,first metal active component species and content,calcination temperature,second metal active component species and content,impregnated alkali species and content.The results showed that the sulfur capacity is 48.54mgS/g and the walnut shell based catalyst can effectively simultaneous remove COS and CS₂.The sulfur capacity and anti-poisoning performance of Fe-Cu-KOH/WSB increase by 20%compared with commercial activated carbon and commercial catalyst.?2?The deactivated catalysts were regenerated by water washing regeneration method,nitrogen sweeping regeneration method,alkali steeping regeneration method and water washing+nitrogen sweeping+alkali steeping regeneration method.Under the optimal regeneration conditions,the sulfur capacity of the catalyst recovered to 88%of the fresh catalyst.A small amount of sulfate and a large number of–OH groups were washed away in water washing process.A large number of sulfades were decomposed into SO₂ and metal oxides?such as Fe₂O₃ and CuO?in nitrogen sweeping process.The–OH groups was supplied in KOH steeping process.The catalytic activity decreased with increasing number of regeneration,which was attributed to the following two reasons:1)residue of a small amount of sulfate,such as CuSO₄;2)oxidation consumption of activated carbon under high temperature and oxygen free conditions.?3?The influences of reaction conditions were investigated by using the best catalyst.The results showed that:higher reaction temperature simultaneously accelerated the catalytic hydrolysis rate and deactivation rate of catalyst;higher relative humidity formed water film,which reduced the contact between COS,CS₂ and active component;higher oxygen content accelerated the oxidation of H₂S,which led to the deactivation of catalyst;higher CS₂ inlet concentration reduced the removal efficiency of COS.To carry out the controlling step in the desulfurization processes,the kinetics in the adsorption process,catalytic hydrolysis process and desorption process were investigated by using hyperbola kinetic model.The results showed that the catalytic hydrolysis of CS₂ and COS were the controlling steps in the desulfurization processes.Compared with the experimental results and theoretical models,the kinetic models agreed with the experimental results,and they had similar trends.?4?In situ infrared studies showed that no obvious changes were observed on the surface of carbonized material for-CH and C–OH groups in the reaction process.It indicated that the main desulfurization process on the surface of carbonized material was adsorption.Furthermore,obvious decrease for–C=O,–COO,–CH and C–OH groups,and obvious increase for molecular CO₂,–OH and S–O groups were observed on the surface of activated carbon.It indicated that the main desulfurization process on the surface of activated carbon was hydrolysis.Meanwhile,H₂O molecule could be converted into some groups,such as-CH and C-OH groups,which promoted the hydrolysis reaction.?5?Theoretical calculation results showed that the adsorption of H₂O,COS and CS₂on the surface of Fe₂O₃?001?was formed with Fe…O or C…O interaction.The adsorption of H₂O,COS and CS₂ on the surface of CuO?110?was formed with Cu…O or S…O interaction.H₂O was firstly adsorbed on the surface of metal oxides,and then CS₂ was hydrolyzed,and COS was finally hydrolyzed.The adsorption processes of COS,CS₂ and H₂O on the surface of metal oxides were chemical adsorption processes.Meanwhile,the adsorption of-OH groups was easier to occur on the surface of metal oxides.The controlling step for CS₂ hydrolysis over Fe₂O₃?001?was the COS hydrolysis,and the controlling step for CS₂ hydrolysis over CuO?110?was the first step of CS₂hydrolysis.Compared with the adsorption energies of COS+H₂O and CS₂+H₂O over Fe₂O₃?001?,they were higher over CuO?110?,which indicated that COS+H₂O and CS₂+H₂O were easier to form the stable adsorption states over CuO?110?.CS₂ was first hydrolyzed into COS over Fe₂O₃?001?,and then COS was further hydrolysed into H₂S.