Steam Gasification Of Sludge With Sea Mud Catalyst Supported On Ni-Fe For Hydrogen Production

With the continuous,rapid and stable development of the economy,the scale of urban sewage treatment in China is increasing,resulting in huge sludge production and serious harm to the environment.Sludge gasification has a good prospect of development by utilizing the decomposition of organic matter in sludge to convert it into clean energy gas..During gasification,excellent catalytic performance plays an important role..Considering that sea mud contains Fe₂O₃and has a large specific surface area,which can be used as a catalyst carrier to promote the forward progress of the water-gas shift reaction and methane reforming reaction in the process of sludge gasification.In this study,the sea mud catalyst supported on Ni,Fe,and Ni-Fe were prepared by co-impregnation and mechanochemical method,respectively.To explore the influence of metal loading rate under co-impregnation method,ball-milling time and ball-milling speed under the mechanochemical method,catalyst preparation method and gasification reaction temperature on gas production of municipal sewage sludge gasification.It is expected to provide the theoretical basis and data support for further research on municipal sludge gasification technology.（1）In the study of sludge gasification catalyzed by Ni,Fe and Ni-Fe based catalysts prepared by co-impregnation method,the load of Ni,Fe and Ni-Fe can be realized.Compared with SM,when the loading rate of Ni,Fe,Ni-Fe is 6%,the gas yield and hydrogen yield are the largest.The gas yield and hydrogen yield obtained by SM-Fe-6%catalyst were 0.297Nm³/kg and 6.043 mol/kg,respectively;The gas yield and hydrogen yield obtained by SM-Ni-6%catalyst were 0.346 Nm³/kg and 7.187 mol/kg,respectively;the gas yield and hydrogen yield obtained by the SM-Ni-Fe-6%catalyst were 0.381 Nm³/kg and 8.400 mol/kg,respectively.The catalytic performance of the three conditions is as follows:SM-Ni-Fe-6%>SM-Ni-6%>SM-Fe-6%.Fe-based catalysts promote C-O and C-H cracking and tar cracking,Ni-based catalysts promote C-H bond and C-C bond cracking,Ni-Fe-based catalysts effectively promote tar cracking by synthesizing nickel-iron alloys and improve the activity of composite catalysts.（2）In the study of sludge gasification catalyzed by Ni,Fe,Ni-Fe based catalysts prepared by mechanochemical method.Under the catalyzation of SM-Ni-Fe-6%（the ball milling time of 15 min,and the ball milling speed of 300 r/min）,the hydrogen purity,the gas yield and hydrogen yield were 50.11%,0.327 Nm³/kg and 7.708 mol/kg,respectively,which were increased by 11.88%,50.69%,and 68.04%,respectively when compared with SM.The performance comparison of the three conditions is as follows:SM-Ni-Fe-6%>SM-Fe-6%>SM-Ni-6%.The appropriate ball milling time（15 min）and ball milling speed（300 r/min）can promote the breaking of chemical bonds,and the formation of nickel-iron alloys also strengthens the cracking of C-H bonds of hydrocarbon organic substances to generate the target products.However,excessive ball milling time（>15 min）and ball milling speed（>15 r/min）will destroy the structure of the nickel-iron alloy,which will eventually lead to the collapse of the crystal structure and greatly reduce the performance of the catalyst.Compared with this two preparation methods of catalyst,the gas and hydrogen yield obtained by co-impregnation method higher than the mechanochemical method,while the H₂/CO obtained by mechanochemical method higher than impregnation method.The Ni-Fe distribution in the catalyst prepared by the co-impregnation method is more uniform,and the cracking of the C-H bond is stronger.The mechanochemical method obtain internal energy through grinding,and then promote the forward progress of the water-gas shift reaction,consume a large amount of CO to generate more H₂.（3）With the increase of Ni ratio in the composite catalyst,the value of gas yield from sludge gasification first increased and then decreased.When Ni:Fe=5:5（mol:mol）,the gas yield,H₂yield and Q_L（energy of the yield）all reach the maximum with the value of 0.381Nm³/kg,8.400 mol/kg,5.450 MJ/kg.Appropriate amount of Fe（Ni:Fe=5:5,mol:mol）can effectively improve the performance of hydrogen production by Ni-Fe catalyst for catalytic sludge gasification,while the excess Ni addition will mask the active site.（4）With the increase of the reaction temperature,the performance of the catalyst prepared by the co-impregnation method first increased and then decreased.Compared with no catalyst,when the reaction temperature was 850°C,the gas yield and hydrogen yield of the SM-Ni-Fe-6%catalyst were increased by 74.77%and 105.73%,respectively.At the same gas yield and hydrogen yield,the SM-Ni-Fe catalyst system can effectively reduce the reaction temperature of sludge gasification.High temperature conditions can effectively promote the reduction reaction between alloy and C,promote the generation of more gas,and improve the effect of sludge gasification to produce hydrogen.However,too high temperature（900°C）accelerated the sintering speed of Ni-Fe-based catalysts,and the collapse of support structure,inhibiting the forward progress of the gasification reaction.