| Biomass is a kind of renewable resources with abundant reserves in China.It is irreplaceable in renewable energy for its composition characteristics.The use of biomass to obtain syngas is an effective way to utilize biomass,which can not only effectively solve the bottleneck problem of the consumption and utilization of distributed biomass by-products,but also develop biomass as a raw material for chemical products.However,the composition of biomass pyrolysis volatiles is complex,and the transformation process is affected by many factors.However,there are few related studies and the theoretical data focus on the conversion from biomass to syngas.In this paper,catalyst assisted chemical looping reforming with catalyst assisting was used as the main pathway for biomass conversion.Via screening appropriate oxygen carriers and catalysts,the main influencing factors of biomass volatiles conversion to syngas,the active materials of oxygen carriers and the synergistic mechanism between the catalyst and the oxygen carrier were studied,and the research results were verified and analyzed by a real biomass pyrolysis non-solid product transformation experiment.The main research contents and conclusions are as follows:The oxygen supply capacity of the oxygen carrier was evaluated by CO-TGA and CH4experiments,and the synthesis method and metal collocation of the oxygen carrier were screened respectively.The results showed that the oxygen carrier prepared by the coprecipitation method had moderate oxygen supply rate,uniform distribution of active metal,low oxygen release temperature and high conversion rate to CH4.Four kinds of spinel oxygen carriers were obtained by combining divalent metals Ni and Cu with trivalent metals Al and Fe.It was found that Ni Fe2O4 spinel has stronger oxygen carrier capacity and exhibits in CH4 reforming experiment.After the Ni Fe2O4 spinel is subjected to four kinds of single metal modified,the results show that the Ni O-modified oxygen carrier exhibits better CH4conversion ability,and its CH4 conversion rate can reach over 90%.The comparison results of four different bimetallic modified oxygen carriers show that the bimetallic Ni-Ce and Ni-Zr modified oxygen carriers exhibit excellent reducing ability.Further analysis of the cyclic stability of the modified oxygen carrier from the characterization structure shows that the addition of the metal additive Zr O2 or Ce O2 sterically hinders the agglomeration and bonding of the active metal which occered in the unmodified or single metal modified oxygen carriers.Moreover,the addition of bimetal promotes the formation of Fe0.64Ni0.36 in the redox process of the oxygen carrier.The presence of the alloy promotes the supply of oxygen in the oxygen carrier,and on the other hand,the presence of the alloy also enhances the oxygen carrying.The ability of the body to react with water vapor promotes the formation of H2.The material evolution of the bimetallic modified oxygen carrier,unmodified and single metal modified oxygen carrier were compared under different reducing atmospheres via the gradual reduction and oxidation reaction.The results showed that the presence of Ni promotes the migration of metal atoms and it also may dope into the spinel structure to promote the formation of more alloys.The effect of Zr O2 addition is different under different reducing atmospheres.The addition of Zr O2 would hinder the release of oxygen in H2atmosphere,while it would promote the faster release of oxygen from oxygen carriers in the CH4 atmosphere.The oxidation test results show that the structure of the oxygen carrier can be restored to the initial state after air oxidation,while the oxidation of steam can only converted oxygen carrier into Fe3O4 and Fe Ni3.By combining the crystal structure of the evolved material,the oxygen release process in the oxygen carrier is analyzed.During the oxidation process,the surface oxygen is first taken,and the internal lattice oxygen is preferentially transferred to the surface,resulting the atomic density in the bulk phase increasing.When the surface layer of oxygen are consumed,the metal atom will relax.Due to the Ni atom is more active and may relax toward the vacuum,the Fe atom does not easily migrate and remains inwardly relaxed,so the Fe atom may exchange with bulk Ni atoms results in a bulk phase transformation to Fe3O4.Since Ni metal exhibits a stronger adsorption capacity for methane,the addition of Ni metal can promote the adsorption of the reactant by the oxygen carrier,and the Ni metal may be doped by oxygen deficiency in Ni Fe2O4 after oxygen supply,thereby promoting The faster release of O atoms in the bulk phase reduces the inward relaxation of Fe and promotes alloy formation.The bimetallic Ni-Zr modified oxygen carrier was combined with three different types of catalysts,and the chemical chain steam reforming experiments of methane and acetic acid were carried out respectively.The results showed that the selectivity of the modified oxygen carrier to CO was low.However,it shows a strong ability to resist carbon deposition.After adding a catalyst to construct a catalytic synergistic reaction system,the reaction can complete the reforming reaction of methane and acetic acid at a reaction space velocity of 5times that of a pure oxygen carrier.The comparison between the catalyst assisted systems shows that the natural ore catalyst exhibits good synergistic effect.In the VR-catalyst assisted systems,methane conversion rate could reach more than 95%,and the content of H2 and CO in the gas production could be more than 90%.The results of mechanistic analysis showed that the catalyst provided more active sites in the system to promote the catalytic conversion of the reactants,and some of the converted gases were adsorbed and oxidized by the oxygen carrier,and the oxidation products further converted the residual carbon accumulated by the catalyst into Gas to complete synergistic conversion.The pyrolysis gas simulants and pyrolysis liquid simulants were used as the research objects,and the performance of the synergistic system was evaluated and screened from four aspects:ratio,temperature,space velocity and water-carbon ratio.The test results show that the CH4 content has a great influence on the gas product.When the CH4 content is 62.5%,the pyrolysis gas can be converted into a synthesis gas with a H2/CO ratio of 2,and its purity is about 95%.In the pyrolysis liquid conversion test,in the catalytic synergistic system constructed by volcanic rock catalyst,when the catalyst addition amount is 20%and the water-carbon ratio is 0.5,the pyrolysis liquid could be convert to the synthesis gas completely with the H2/CO ratio of 2,and the catalytic synergy system still maintains stable properties after 20 cycles.The direct reforming of the pine nut shell pyrolyzed non-solid product shows that the obtained syngas will be more purity and more suitable H2/CO ratio as the pyrolysis temperature increasing.When the pyrolysis temperature is 750°C,the reforming temperature is 800°C,and the water-carbon ratio is 0.5,the biomass pyrolysis non-solid product could be convert to syngas with a ratio of H2/CO about 2.2,and the purity is about 87%. |
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