Catalytic pyrolysis of waste biomass to produce hydrogen-rich gas:Influence of catalyst performance

Catalytic pyrolysis of waste biomass is a promising method for the production of hydrogen-rich gas. HZSM-5 carrier is the premise of ensuring the thermal stability and long life of catalytic materials, and plays a mechanical role in bearing the active component nickel (Ni). At the same time, aluminum ash (ASA), as an important waste in the production process of aluminum industry, is mainly composed of Al₂O₃ and a large number of heavy metal oxides such as Na₂O, CaO, MgO, Fe₂O₃ and so on. In this study, aiming at the technical bottleneck problems such as the low performance of traditional HZSM-5 molecular sieve and the difficulty of resource utilization of aluminum ash, the active component nickel (Ni) and promoter iron (Fe) were combined with HZSM-5 molecular sieve by ultrasonic-assisted excessive impregnation to improve the yield of hydrogen-rich gas. Furthermore, waste aluminum ash (ASA) and HZSM-5 molecular sieve were used as co-carriers to prepare aluminum ash co-supported Ni-Fe catalyst with HZSM-5 molecular sieve, and it was used to enhance the process of hydrogen-rich gas production by the catalytic pyrolysis of biomass. The results showed that the heat transfer efficiency decreased with the increase of heating rate during pyrolysis of biomass. After compensation, the apparent kinetic parameters (E and A) of pyrolysis of different biomass were obtained. At the pyrolysis temperature of 700 ℃, Ni-Fe/HZSM-5 catalyst increased the yield of hydrogen-rich gas to 56.49% (about 230.59 mL/g), hydrogen yield to 63.12%, hydrogen production efficiency to 0.71%, and CO yield to 65.77 mL/g. Sufficient amount of Ni-Fe/HZSM-5 catalyst enhanced the pathway of hydrogen production by the catalytic pyrolysis of biomass, promoted the gasification reaction of carbon deposition, and played a dual role in increasing the yield of H₂ and CO. The synergism between HZSM-5 and ASA carriers enhanced the reforming process of CH₄ and CO₂, inhibited the reverse water vapor shift reaction, obtained 53.37% and 41.56% gas and tar yields. At the same time, the gasification reaction of carbon deposition was also accelerated, reduced the char yield to 5.07%, and obtained the carbon deposition of 0.05 g/g. Ni-Fe/ASA@HZSM-5 had good thermal cracking ability and deoxidization ability, which was helpful to promote the formation of hydrogen-rich gas on HZSM-5 as a base catalyst. From the point of view of proximate analysis and chemical composition of biomass, the composition of different kinds of biomass varied greatly, and the product distribution of catalytic pyrolysis also had a great influence. The order of gas yield of pyrolysis of biomass catalyzed by Ni-Fe/HZSM-5 was PR (74.21%) > WSt (54.71%) > CR (53.5%) > MCh (52.47%) > WSh (52.10%) > CS (46.49%), which provided theoretical support for the development of deep purification and efficient utilization of high temperature pyrolysis gas, and effectively guided the development of a new double catalytic bed for multi-stage catalytic reforming.