Preparation Of Hydrocarbon-rich Fuel By Metal-loaded Biochar-Catalyzed Deoxygenation And Denitrogenization Of Microalgae

Due to the growing concern about global warming and energy crisis,the replacement of fossil energy with renewable and sustainable energy sources is imminent.Algal biomass,as a feedstock for third generation biofuels,is a promising renewable alternative to fossil resources.Although bio-oil produced by microalgae pyrolysis has high calorific value and ideal p H value,it still contains abundant oxygen and nitrogen,which limits its application as a temporary fuel.Therefore,in order to improve the quality of bio-oil,firstly,we need to improve the defect of biomass itself with more oxygen and less hydrogen,of which the use of co-pyrolysis with hydrogen-rich waste is a good solution;secondly,we need to develop new and efficient catalysts for catalytic reforming of pyrolysis volatiles.Biochar-loaded metal catalysts are widely used for the hydrodeoxygenation of oxygenates due to their strong absorption of oxygenates.In this study,a one-pot lignin biochar loaded with nickel metal was used as a catalyst for the preparation of high quality biofuel from the pyrolysis of Chlorella vulgaris.In order to improve the quality of algal bio-oil,low density polyethylene（LDPE）was also introduced as the hydrogen donor feedstock for co-pyrolysis with Chlorella vulgaris,and the lignin biochar-loaded nickel catalyst（Ni/biochar）and HZSM-5 were used as cascade catalysts for the co-pyrolysis of Chlorella vulgaris with LDPE.Four catalysts with different Ni loading ratios（0,5%,10%and 20%）were prepared and characterized by BET,ICP-OES,NH₃-TPD,FT-IR,SEM,TEM,XPS and XRD.The results showed that the prepared catalysts had a specific surface area of 291～459 m²/g,the average pore size of the micropores was 0.47～0.56 nm,the Ni loading ratio was 12.05～42.94%.the ratio of Ni0 was 33.13%.the average particle size of Ni particles was 37.57 nm,and the surface of the metal-modified catalysts was rich in functional groups（O-H,C-O and C=C,etc.）and acidic sites.The experimental data indicate that the catalysts have high specific surface area,microporous pores with diameters close to those of monoaromatic hydrocarbons,and abundant functional groups,which provide good catalytic performance for deoxygenation and denitrogenation of Chlorella and the production of hydrocarbons.The performance of a novel Ni/lignin biochar catalyst for deoxygenation and denitrification of microalgae pyrolysis vapors was evaluated using a pyrolytic cracker.The catalytic reforming of microalgae with pyrolysis vapors was carried out using allosteric catalysis.The effects of the pyrolysis conditions（catalyst nickel loading ratio,catalyst-to-feedstock ratio,and pyrolysis temperature）on the composition and distribution of the catalytic pyrolysis products were investigated.The highest selectivity of 79.2%was obtained for Chlorella aromatic hydrocarbons,including75.6%for BTX（benzene,toluene and xylene）when the nickel loading ratio was 10%,the catalyst-to-feedstock ratio was 20:1,and the pyrolysis temperature was 500℃.In the quantitative analysis,the highest yields of 58.0 mg/g,17.6 mg/g and 6.6 mg/g were obtained for benzene,toluene and xylene.The chemical pathways involved in the mechanism of deoxygenation and denitrification in microalgae were investigated using soy protein,glucose and rapeseed oil to mimic the typical composition of microalgae.In addition,three model compounds corresponding to different nitrogen-containing groups（i.e.amino acids,proline,leucine and phenylalanine）were used to explore the denitrification mechanism in detail.The results showed that the selectivity of aromatic hydrocarbons produced by pyrolysis of glucose and soy protein was 95.7%and 90.8%,respectively.The ability of the three amino acids to produce aromatic hydrocarbons was phenylalanine>leucine>proline,respectively.The pyrolysis of Chlorella produces furans,fatty acids,nitrogenous and oxygen-containing compounds such as nitrogen heterocycles,which are adsorbed on the catalyst Ni⁰,establishing a spatial channel for electron transfer and weakening the bonding energy,thus transforming them into aliphatic hydrocarbons by deoxygenation and denitrogenation,and finally converting them into aromatic hydrocarbons through a series of reactions such as polymerization and aromatization.A thermal cracker was used for thermal cracking of microalgae with hydrogen-rich waste,and Ni/lignin biochar catalyst and HZSM-5 were introduced as co-catalysts and applied in the study of co-pyrolysis of microalgae with LDPE.The effects of catalyst-to-feedstock ratio,Ni/biochar and HZSM-5 ratio and the mixing ratio of the two feedstocks on the composition and distribution of the catalytic pyrolysis products were investigated.In addition,the reaction principle of co-pyrolysis dual catalyst and the synergistic effect between dual catalyst and co-pyrolysis were further investigated.The results showed that when the catalyst-to-feedstock ratio was 40:1,the HZSM-5 and Ni/biochar feeding ratio was 1:3,and the mixing ratio of LDPE and Chlorella was 1:1,the selectivity of hydrocarbon compounds was 100%,including 48.5%of BTX.In addition,the synergistic effect analysis showed that the cascade catalysis of Ni/biochar and HZSM-5 and the co-pyrolysis of Chlorella and LDPE both promoted the denitrogenation and deoxygenation reactions of the microalgae bio-oil.After the initial deoxidation and denitrification,the nitrogenous and oxygenated compounds were catalyzed on the HZSM-5 catalyst to produce hydrocarbons.