Research For Syngas Preparation By Catalytic Reforming With Modified Nickel Based Alumina

Syngas is one of the most important synthetic raw materials in industrial production.In this study,the syngas was produced based on the biomass derived gas reforming.The influence of relevant parameters on the product distribution of primary gas reforming was studied by thermodynamic equilibrium analysis.The nickel based alumina catalyst was modified and applied for the reforming of biomass derived gas to produce syngas.Firstly,based on the Gibbs free energy minimization method,the thermodynamic equilibrium analysis was carried out for simulated biomass derived gas to optimize the reforming conditions.The influence of temperature,pressure and components on the gas distribution under thermodynamic equilibrium were illustrated.Some conclusions can be drived as follows:when the minimum reforming temperature of biomass derived gas is above 825?,most of the methane can be completely converted;To increase the syngas rich gas,decrease the amount of impurity gas,and obtain the syngas with low ratio of H₂ to CO,the reforming temperature should be raised to a higher temperature,and the reverse water gas shift reaction can be applied to decrease the ratio of H₂ to CO;On the contrary,the reforming temperature should be decreased and the ratio of hydrogen to carbon can be increased by using the positive water gas shift reaction.Increasing the system pressure is not conducive to the preparation of syngas but favor of methanation.The amount of CO₂ and steam is the key factors to increase the syngas yield and adjust the ratio of H₂ to CO.By increasing the amount of CO₂ and steam,the CH₄ conversion ratio can be increased.At a specific temperature,the ratio of H₂ to CO for syngas can be adjusted by changing the amount of steam or CO₂ based on the direction of reverse water gas shift reaction.Then four kinds of nickel based alumina catalysts were prepared by co-precipitation method under different calcination temperatures.The catalytic performance was evaluated with the dry reforming system.And the key structural parameters affecting the catalytic performance of the catalysts were revealed by various characterization methods.The results reveals that the spinel structure can improve the microporous characteristics of the catalyst surface,reduce the crystal size and enhance the interaction between the active metal and the support.When the spinel structure is formed in the catalyst,the existing morphology of nickel in the catalyst changes.To modify the support of catalyst,a series of composite supported catalysts were prepared by adding activated carbon fibers(ACF)into the nickel based alumina catalyst system using co-precipitation method.The catalytic performance of catalysts was studied in a dry reforming system.At the same time,the macro reaction kinetic model was established with the composite support catalyst.The related characterization results show that the coprecipitation coating of Ni and Al₂O₃ can not only keep the great surface properties of the fibers,but also inhibit the carbon from ACF participating reaction with CO₂.The addition of ACF in the catalyst can enhance the basicity and improve the metal dispersion on the catalyst surface,and facilitate the adsorption and activation of feed gas.Moreover,the grain size of the spinel Ni Al₂O₄ can be reduced.In addition,FTIR showed that ACF can provide abundant oxygen-containing and methyl functional groups on the surface,which could be the intermediate product of the reaction and effectively promotes the reforming reaction.For the catalyst Ni-?-Al₂O₃/ACF,when the reforming temperature is below 800?,the apparent activaton energy of CH₄ and CO₂ are 96.28k J·mol^-1 and 50.45 k J·mol^-1,respectively.While the reforming temperature is above 800?,the apparent activaton energy of CH₄ and CO₂ are 5.33 k J·mol^-1 and 4.69 k J·mol^-1,respectively.The apparent activation energy of CO₂ is lower than that of other catalysts reported in the literatures,especially for the temperature above 800?.In addition,four kinds of metal promoters(Mn,Fe,Co and Cu)were added into the catalyst Ni-?-Al₂O₃/ACF by coprecipitation to obtain a series of bimetallic catalysts.The catalytic performance of the obtained catalysts was illustrated in dry reforming of methane and the reverse water gas shift reaction systems.The results show that bimetallic catalyst has the dual functions of catalytic reforming and adjusting the hydrogen carbon ratio of syngas.The addition of metal promoter enhance the sintering resistance and the dispersion of active nickel on the catalyst surface,and significantly improves the catalytic performance of the bimetallic catalysts.For the four kinds of catalysts,the bimetallic catalyst with Co processed the best catalytic performance,and the highest conversion ratio of CH₄ and CO₂.The added metal promoter plays an important role in adjusting the H₂/CO ratio of syngas.For dry reforming of methane,the bimetallic catalyst with Co showed the best performance of adjusting the H₂/CO ratio of syngas.And for the reverse water gas shift reaction system,the bimetallic catalyst with Co processed the best catalytic performance.The conversion ratio of H₂ is 43.4%,44.9%and46.1%at 800?,850?and 900?,respectively.At the same time,the pyrolysis-reforming performance of above three groups of catalysts was investigated in a two-stage reactor.The spinel structure in nickel based alumina catalyst has an important influence on the pyrolysis-steam reforming of rice husk.Increasing calcination temperature during the preparation of catalyst,the amount of syngas in the product is significantly increased by the spinel structure.Compared with the nickel based alumina catalyst,the addition of carbon fiber improved the pyrolysis-reforming performance of biomass.The syngas yield increased from 12.16 mmo L/g to 17.32 mmo L/g.For the bimetallic catalysts,the Fe based bimetallic catalyst possessed the highest yield syngas yield(22.53 mmol/g),and the Cu based bimetallic catalyst possessed the best catalytic performance of shift reaction.