Preparation Of Modified Nickel Based Catalyst And Its Application In Straw Catalytic Pyrolysis

Biomass resources play an important role in the future energy structure,so the rational development and utilization of biomass resources is very important.Catalytic pyrolysis is a highly efficient way to produce syngas from biomass.Nickel-based catalysts are the most commonly used catalysts with excellent catalytic performance and low cost.However,the deactivation of the catalyst is fast.In order to improve its service life and catalytic activity,it is necessary to modify the catalyst.In this paper,the catalytic activity and stability of Ni/Al₂O₃ catalyst were studied by modifying and characterizing the support and active components.Based on the above,the research work of this paperis as follows:(1)Rice straw was selected as raw materialfor industrial analysis,element analysis,thermogravimetric analysis and calorific value calculation.The results showed that rice straw had a high volatile content,and the pyrolysis process was divided into three stages,of which the second stage was the main stage of volatile matter precipitation.The low calorific value of rice straw was 13.55 MJ/kg.(2)NiO/fly ash catalysts were prepared by homogeneous precipitation method with fly ash as support.The supports and catalysts were characterized by XRF,XRD,SEM and BET.The results showed that NiO formed a network structure of intertwining on the FA surface.After loading,the specific surface area increased from 0.56 to 31.90 m²·g^-1,and the pore volume increased from 0.0015 to 0.115 cm³·g^-1.Meanwhile,the effects of calcination temperature,reaction temperature,holding time and NiO loading on the syngas content in the pyrolysis gas products of rice straw were investigated in a tubular pyrolysis furnace.When the calcination temperature of the catalyst at 400?,the reaction temperature at600?,the holding time at 20 min,and the NiO load at 20 wt%,the content of syngas produced by the catalytic pyrolysis of rice straw with NiO/FA catalyst was the highest,reaching 75 vol%.The stability of NiO/FA catalyst was tested under the above conditions,and compared with the Ni/Al₂O₃ catalyst.After 6 times of catalysis,the syngas content of NiO/FA catalyst was 46 vol%,which was about 5 vol%higher than that of Ni/Al₂O₃catalyst.(3)The AMS(Al₂O₃-MgO-Sawdust char)supports were prepared by mixing aluminum nitrate,magnesium nitrate and sawdust carbon in different proportion by coprecipitation method,and then Ni and Ni La catalysts were preparedby using the above supports.Characterization methods such as XRD,XRF,SEM-EDX and BETwere used to analyze the supports and catalysts.The effects of the supports ratio and the addition amount of the additive La on the performance of catalytic pyrolysis of rice straw to syngas production were investigated at reaction temperature of 700°C and holding time of 20minin the tubular pyrolysis furnace,and compared with Ni/Al₂O₃ catalyst..The results showed that Ni and La were successfully supported on the AMS support.The addition of La was beneficial to the formation of elemental Ni and the dispersion of Ni/Al₂O₄,and increased the specific surface area of the catalyst.With the increase of the composite ratio of Al₂O₃,MgO,and SC,the content of syngas decreased.The Ni/AMS-5 catalyst had the best activity for syngas production at the composite ratio of 1:1:1.When the content of La increased from 2wt%to 10wt%,the content of syngas increased from 73.3 vol%to 78.9vol%and the Ni-10La/AMS-5 catalyst had the best catalytic activity.Compared with Ni/Al₂O₃ catalyst,Ni/AMS-5 and Ni-10La/AMS-5catalystincreased the content of syngas by 14.9 vol%and 24.6 vol%,respectively.The stability test experiments of Ni-10La/AMS-5 and Ni/Al₂O₃ catalysts show that Ni-10La/AMS-5 catalysts show more stable performance than Ni/Al₂O₃ catalysts during 6 times of catalysis.The syngas content of Ni-10La/AMS-5 catalyst was 63.0 vol%,much higher than 34.3 vol%of Ni/Al₂O₃catalyst.(4)The AZS(Al₂O₃-Zr O₂-Sawdust char)supports were prepared by mixing aluminum nitrate,zirconium nitrate and sawdust char in different proportions by co-precipitation method,and the AZS supported Ni and Ni-La catalysts were prepared by using the above support.XRD,XRF,and SEM analysis were employed to study the physiochemical properties of the supports and catalysts.The effects of the supports ratio and the addition amount of the additive La on the performance of catalytic pyrolysis of rice straw to syngas production were investigated at reaction temperature of 700°C and holding time of 20 min in the tubular pyrolysis furnace,and compared with Ni/Al₂O₃ catalyst.The results showed that the active components of the catalyst mainly exist in the form of NiO and La₂O₃,and some of them may enter the pores of the support.When the composite ratio was 1:1:1,Ni/AZS-5 catalyst had the best activity for syngas production.The content of syngas reached 75 vol%,which was 20.7 vol%higher than that of Ni/Al₂O₃ catalyst.When La content was 10 wt%,the content of syngas reached 80 vol%,which was 5 vol%higher thanthat without La.The stability test experiments of Ni-10La/AMS-5 and Ni/Al₂O₃catalysts showed that after 6 times of catalysis,the Ni-10La/AZS-5 catalyst was about 50vol%,which was higher than 34.3 vol%of Ni/Al₂O₃ catalyst.In this paper,the activity and stability of NiO/FA,Ni-La/AMS-5,Ni-La/AZS-5 catalysts prepared by modification of surpports and additives were superior to Ni/Al₂O₃catalyst.It can improve the service life of Ni/Al₂O₃ catalyst to a certain extent.These studies will help to provide a reference for the further development of nickel-based catalyst modification methods.