Enhanced Hydrogen-rich Gas Production From Sludge Gasification By Honeycomb Ceramic-loaded Metal Catalyst

With the rapid socio-economic development,the continuous urbanization process and the concentration of population,the scale and quantity of urban wastewater treatment facilities in China show a trend of year-on-year growth,which leads to the generation of a large amount of sludge.Sludge gasification technology can convert sludge into reusable energy,such as syngas,at a high temperature,thus achieving sludge reduction,stabilization,harmlessness and resource utilization.The use of catalysts in the sludge gasification process is important to improve the quality and yield of gasification products.However,the conventional granular catalysts used in sludge gasification catalysis have problems of reuse and regeneration and poor structural stability,which are solved by monolithic catalysts,and have the advantages of low price and easier scale-up from laboratory to industrial scale.Thus,in this study,cordierite honeycomb ceramics were used as a monolithic catalyst substrate to catalyze the positive water gas conversion reaction,methane reforming reaction and tar cracking reaction in the sludge gasification process.In this study,cordierite honeycomb ceramics（CHC）monolithic catalysts were used for the first time in the field of sludge gasification treatment,and CHC-loaded Ni,Fe,and Ni-Fe-based monolithic catalysts were prepared by impregnation method using CHC as the monolithic catalyst substrate.The effects of different metals,loading rates,gasification reaction temperatures and reuse of CHC monolithic catalysts on gas production from municipal sludge gasification were investigated and the mechanism of the effects was analyzed to provide theoretical basis and data support for further research on the application of CHC in the field of municipal sludge gasification.The following conclusions were obtained from this study:（1）In the study of Ni,Fe,and Ni-Fe-based monolithic catalysts with different loading rates for catalytic sludge gasification,Ni,Fe,and Ni-Fe-based could achieve effective loading.Among the CHC-loaded Ni-based monolithic catalysts with 0%,3%,6%,9%and 12%loading rates,the gas and hydrogen yields were the largest under CHC-Ni-3%catalytic conditions with0.200 Nm³/kg and 3.690 mol/kg,respectively.Among the CHC-loaded Fe-based monolithic catalysts with 0%,3%,6%,9%and 12%loading,the gas and hydrogen yields were the highest under CHC-Fe-6%catalytic conditions with 0.390 Nm³/kg and 8.272 mol/kg,respectively.Among the CHC-loaded Ni-Fe-based monolithic catalysts with 0%,3%,6%,9%and 12%loadings,the gas and hydrogen yields were the highest at CHC-Ni-Fe-3%with 0.250 Nm³/kg and 5.370 mol/kg,respectively.The best gas and hydrogen production performance among the three metal-based monolithic catalysts was CHC-Fe-6%.The Fe-based catalyst promoted the cracking of C-H and C-C bonds as well as the tar cracking;the Ni-based catalyst promoted the cracking of C-O and C-H bonds;and the Ni-Fe alloy in the Ni-Fe-based catalyst effectively promoted the tar cracking and improved the catalyst activity.Because the catalytic mode of the monolithic catalyst itself determines that it mainly catalyzes the tar in the sludge gasification products,while the Fe catalyzes the tar cracking more strongly,the Fe based catalyst has the best performance in gas and hydrogen production among the three catalysts.（2）The performance of CHC-Fe-6%catalytic gas and hydrogen production showed an increasing and then decreasing trend with the increase of sludge gasification reaction temperature（700-900℃）.High temperature conditions can effectively promote the reduction reaction of iron oxide and promote more hydrogen production,improving the hydrogen production effect of sludge gasification.However,too high temperature（900°C）will accelerate the sintering of the Fe-based catalyst and reduce the catalytic effect.At the reaction temperature of 800°C,the gas yield and hydrogen yield of CHC-Fe-6%catalyzed sludge steam gasification were 0.390 Nm³/kg and 8.272 mol/kg,respectively,which were 114.28%and 119.30%higher than those under the catalyst-free condition.Under the catalyst-free condition,the gas and hydrogen yields were maximum at the reaction temperature of 900℃,0.2794 Nm³/kg and5.909 mol/kg,respectively,while the reaction temperature was only 800℃to achieve these gas and hydrogen yields under the catalyst condition.（3）With the reuse of CHC-Fe-6%,the gas yield and hydrogen yield after sludge gasification decreased.After the fifth reuse,the gas yield and H₂ yield were 0.166 Nm³/kg and3.110 mol/kg,respectively,which were reduced by 57.43%and 62.40%,respectively,relative to the fresh catalyst.Reuse increases the carbon build-up on the surface of the CHC-loaded Fe-based monolithic catalyst,thus causing a decrease in gas yield and hydrogen yield after sludge gasification.