Experimental Studies On Biomass Catalytic Pyrolysis Based On Fe/Ni Carbon Nanofiber Materials

Under the background of current industrialization leading to energy shortage and environmental pollution,by transfering biomass to liquid and gaseous products through pyrolysis process,which been further used as the alternative fuel or synthetic raw materials for chemical products has gradually gained widely attention.However,bio-oil has high oxygen content,and pyrolysis gas has low molar ratio of H₂/CO and contains impurities such as tar,which have greatly limited the application prospects of bio-oil and pyrolysis gas.Catalytic cracking,as an effective method to improve the quality of biomass pyrolysis products,has obtained a lot of research and application,but the existing catalysts have defects such as low catalytic activity or carbon deposition inactivation.In order to solve the above problems,a carbon nanofiber supported iron and nickel bimetal composite was prepared as a catalyst for on-line catalytic pyrolysis of biomass,steam reforming of bio-oil and co-pyrolysis of biomass blending with plastics.The variation of yield and composition of liquid and gaseous products were analyzed,at the same time,the catalytic performance and cycle stability of the catalyst for pyrolysis gas modification were evaluated.Firstly,the catalysts composited by Fe/Ni with carbon nanofibers were prepared from wood chips,then were used in the on-line catalytic pyrolysis process of wood.Compared with the result of non-catalyst pyrolysis,the tar removal efficiency of Fe-Ni/carbon nanofiber catalyst reached 85.76%,and the content of monocyclic aromatic hydrocarbons in tar was greatly reduced,and the total yield of pyrolysis gas doubled?0.947 L/g?.In particular,the H₂yield was significantly increased.After 13 cycles of reuse,the tar removal efficiency and pyrolysis gas yield only decreased by 7.25%and 9.07%,respectively.The results showed that the presence of FeCl₃ could promote the formation of pore structure,and combining the catalytic action of NiCl₂,carbon nanofibers were formed;the above aspects all increased the pore volume of catalyst,which was beneficial to the adsorption and cracking of macromolecule tar components.Besides,the Fe_0.64Ni_0.36 alloy detected in the Fe-Ni/carbon nanofiber catalyst was proved to has a relatively high catalytic ability for aromatic compounds.In addition,the interaction between the Fe and Ni can alleviate the carbon deposition of the catalyst,thereby effectively maintaining the performance of the catalyst.Secondly,acetic acid was selected as the model compound of the light component of bio-oil,then used in the steam reforming experiment under the prepared catalyst.By analyzing the influence of catalyst type,water-carbon ratio?H₂O/C?,weight hourly space velocity?WHSV?and reaction temperature on the experimental results,when Fe-Ni/CNF was used as catalyst,the H₂O/C was 8,and the hourly space velocity was set as 4 h^-1,the reaction temperature was 700°C,the best result was obtained.This optimal operating condition was used for the cycling test.It was found that the carbon conversion rate gradually decreased and then stabilized,and the overall reduction was 25.14%.The H₂ selectivity also showed a downward trend,and finally maintained 83.32%of the initial value.The SEM and NH₃-TPD characterization further confirmed that the catalyst has a certain degree of carbon deposition deactivation.In addition,although the H₂ selectivity in the gas product obtained by the steam reforming reaction is relatively high,there is a large content of oxygenated compounds such as CO₂.Finally,the co-catalytic pyrolysis of high density polyethylene?HDPE?blending with wood chips was carried out.The effects of catalyst type,blending ratio and catalytic temperature on the distribution of liquid and gaseous products were investigated.The results showed that when the catalyst is Fe-Ni/CNF,the mixing ratio of wood to HDPE is 1:2,and the catalytic temperature is 700°C,the yield of liquid product was greatly reduced and the 2-3ring light aromatic hydrocarbon was effectively enriched.Also,the H₂/CO ratio in the gas product reached 2.32.Blending wood with HDPE has effectively increased the effective hydrogen to carbon ratio(H/C_eff)of the reactants in the pyrolysis process,thereby reducing the oxygen content of the product;at the same time,HDPE provides H radicals during pyrolysis and combined with the effect of nickel catalyst,has together promoted the formation of H₂.After 13 cycles of experiments,the liquid product yield only increased from2.67%to 4.74%.Integrated with the characterization of the used catalyst,it was proved that the surface morphology of carbon nanofiber has been basically retained and the deposited carbon was also attached as fibrous form without covering the active site,which reflected the excellent cycle stability of catalyst.