Study On The Preparation Of Hydrocarbon Fuel By Microwave Catalytic Pyrolysis Of Peanut Shell By Self-derived Bio-char Catalyst

With the progress of society and the rapid development of mankind,the energy problem is becoming extremely serious.Biomass resources have been studied and analyzed due to they are abundant availability and sustainability.As a large agricultural country,China produces a large amount of agricultural waste every year,but the utilization rate of them is still very low.Therefore,the use of pyrolysis can provide a favorable channel for the effective treatment of agricultural waste.Pyrolysis technology can convert biomass into bio-oil,bio-char and syngas,among which bio-oil can be refined into hydrocarbon fuel and chemicals,biochar can be used as soil improvement,environmental remediation and catalytic materials,etc.Hydrocarbon fuel is a general term for liquid hydrocarbons used in jet engines,and kerosene as a main component of hydrocarbon fuel is consisted of alkane,cyclo-hydrocarbon and aromatic hydrocarbon.However,the bio-oil produced by direct pyrolysis of biomass cannot be directly used as hydrocarbon fuel due to the problems of complex compositions and high oxygen content.Catalytic pyrolysis is the direct modification and upgrading of pyrolysis volatile products by using catalyst in the process of biomass pyrolysis,then the hydrocarbon fuel is obtained,but there are still problems to be solved,such as expensive catalyst costs and poor performance.Compared with ordinary heating methods,microwave-assisted heating has the advantages of short reaction time,less heat loss,and promotion of chemical reactions.In this paper,peanut shell was used as a raw material to prepare hydrocarbon fuel by microwave catalytic pyrolysis,and the biochar by-product generated during pyrolysis was used as the catalyst to treat raw materials.A self-derived biochar catalyst was prepared by transition metal modification,which can catalytically pyrolyze peanut shell to obtain hydrocarbon fuel,and its reaction mechanism and kinetic behavior were investigated as well.The preparation of high activity catalysts derived from pyrolysis by-product which were recycled in catalytic pyrolysis raw materials realized a high value application of the catalytic pyrolysis reaction,increased the biomass utilization,reduced the reaction cost,provided theoretical basis and technical support for the utilization of agricultural waste.The specific contents of this paper are as follows:（1）Microwave pyrolysis of peanut shells was used to obtain biochar as the support of the catalyst.The modified biochar catalyst were prepared by loading transition metal Fe,Zn,and Mo on the biochar support by precipitation method,and then subjected to XRD,SEM,TEM,BET,TPD,etc.Characterization results showed that Fe,Zn,and Mo were all successfully loaded on the biochar support.The Fe-loaded biochar catalyst had the highest acidity and the most active sites,more significantly,compared with other transition metal modified biochar catalysts,it had the largest specific surface area.The analysis of the catalytic performance of the catalyst by the pyrolysis-gas chromatography/mass spectrometer（Py-GC/MS）indicatedthat the hydrocarbon content in the bio-oil reached 38.09%during catalytic pyrolysis of peanut shell over 10%Fe/Bio-char,and the aromatic selectivity was24.57%.And comparing with the control,the hydrocarbon content and aromatic hydrocarbon increased by 34.13%and 22.24%,respectively,showing a good catalytic performance.（2）In order to investigate the effect of self-derived biochar catalysts on the microwave catalytic pyrolysis of peanut shells for hydrocarbon fuels production,Fe/Bio-char with 10%loading was used as the catalyst.The effects of the amount of microwave absorbent on the yield and chemical selectivity of the bio-oil were explored.The results showed that the optimum addition ratio of microwave absorbent（activated carbon）was 15%.Then the central composite design method（CCD）was used to study the influence of the reaction conditions on preparation of hydrocarbon fuel during catalytic microwave pyrolysis of peanut shell by using self-derived bio-char catalyst.The quadratic model of bio-oil yield and its main chemical components（hydrocarbons,phenols,etc.）was established by response surface analysis,and the significance of the model was analyzed to predict whether the model was consistent with the product yield and the distribution of main chemical groups.The results disclosed that phenolic compounds were the major components in the control,accounting for about 80-90%of the chemical components in the obtained bio-oil,while hydrocarbon compounds were only about 3%.With the addition of Fe/Bio-char,the selectivity of hydrocarbons,especially aromatic compounds,was significantly improved（p-value=0.0109）.The optimum reaction conditions for this process were pyrolysis temperature 550℃,the ratio of catalyst to biomass 0.2.And the bio-oil yield was 24.3%,which was 3.9%lower than that of the control,this might be illustrated by the further cracking of volatiles during catalytic reforming at high temperature.While the hydrocarbon selectivity in the bio-oil was 26.97%,and the selectivity of aromatic compounds was 17.95%,which were mainly derivatives of benzene such as ethylbenzene and o-xylene.（3）To further disclose,the reaction mechanism and kinetic study of this process,lignocellulosic biomass（peanut shell）and its major model compounds（lignin,cellulose）were utilized as raw materials,self-derived biochar（Fe/Bio-char with 10%of loading）was used as a catalyst.The results revealed that the addition of biochar catalyst promoted the decomposition of sugars and small molecular oxygen compounds of cellulose which generated chain hydrocarbons and a small amount of aromatic hydrocarbons,at the same time,more significantly,a large amount of phenols derived from the decomposition of lignin were promoted to be converted into aromatic hydrocarbons via a series reactions such as dehydroxylation and aromatization.Therefore,the aromatic hydrocarbons in the obtained bio-oil were mainly derived from the conversion with lignin derived phenols,and the chain hydrocarbons were mainly produced from the decomposition of cellulose sugars.Meanwhile,a self-assembled microwave-TGA device was used to investigate the thermal decomposition behavior and kinetic study of this process.The results displayed that the Fe-loaded biochar catalyst can make the thermal decomposition temperature of peanut shell and its model compound move to the lower temperature zone,and the thermal decomposition behavior was easier and more thorough.Meanwhile,the biochar catalyst also significantly reduced the activation energy of the reaction.The activation energy of lignin,cellulose and peanut shell decreased from82.26 k J·mol^-1,81.71 k J·mol^-1and 116.8 k J·mol^-1to 45.16 k J·mol^-1,37.32 k J·mol^-1and 86.79 k J·mol^-1,respectively.