Experimental Studies Of Effects Of Torrefaction Pretreatment On Characteristics Of Biomass Pyrolysis And Dry Reforming Of Methane Over Pyrolysis Semi-cokes Under Microwave Irradiation

Energy crisis and environmental pollution is a problem that always surrounds all mankind.How to make good use of renewable energy and reduce fossil resources is a topic that every researcher needs to pay attention to.As the only carbon-neutral renewable resource,biomass energy has a very high utilization value.Pyrolysis is one of the common thermochemical conversion methods of biomass energy.Since the three-phase products of biomass after pyrolysis have high utility value,biomass have received extensive attention from scientists.However,due to the high water content and oxygen content,and poor uniformity of biomass,it is necessary to pretreat the biomass before pyrolysis.The torrefaction pretreatment is simple,can greatly reduce the water content and oxygen content of the biomass raw materials,and make the energy and mass distribution of the biomass more uniform.It has high application potential and research value.Hawthorn kernel is a waste in the hawthorn food industry.If the hawthorn kernel can be converted into valued something,the resource utilization of the hawthorn kernel can be realized.Among the pyrolysis products of hawthorn kernel,pyrolysis tar can be used to prepare smoke liquid and is the most valuable product.However,the utilization of pyrolysis semi-coke has not received enough attention.In addition,among the hawthorn kernel pyrolysis gas,CO2 and CH4 are the largest sources of greenhouse gases.Combined with the previous research results of our research team,if semi-coke can be used as a catalyst for the dry reforming of methane,it can realize the utilization of semi-coke,reduce greenhouse gas emissions,and maximize the utilization of hawthorn kernel pyrolysis products.This has high research value.In this study,hawthorn kernel was torrefacted and pyrolyzed,and the effect of torrefaction on pyrolysis was studied.During the torrefaction stage,the hawthorn kernel mainly decomposes hemicellulose,and the amount of gas and liquid precipitation is relatively small.The main components of the gas phase products are CO and CO2;As the torrefaction temperature increases,the degree of hemicellulose decomposition deepens,the degree of deoxygenation and dehydration of the torrefaction product increases,and the amount of gas and liquid released increases,and the yield of solid products decreases.At the same time,the element composition on the surface of the solid product changes,the C element content increases,while the O element content increases.During the pyrolysis stage,the amount of tar precipitation of increases significantly.Phenols,carbonyls,acids,esters,etc.are the main components of tar,so the tar of hawthorn kernel can be used to prepare smoke liquid;the pyrolysis semi-coke has a high carbon content,so it can be used to catalyze chemical reactions;in the hawthorn kernel pyrolysis product torrefaction modified,the content of phenols in tar is significantly increased,reaching more than 70%,the content of carbonyl compounds is reduced to less than 5%,and the content of acids is slightly increased,which improves the quality of tar,beneficial to the improve its smokey flavor.The composition distribution of the pyrolysis gas changes.The order of the relative content of four main gases is CH4>CO2>CO>H2.Among them,the content of CO is relatively reduced,and the content of others has increased in different degrees;The carbonization degree of pyrolysis semi-coke is deepened,which is more conducive to the preparation of catalysts.This is due to the decomposition of hemicellulose and cellulose,and the increasement of the content of lignin after torrefaction.In the dry reforming of methane experiment over semi-cokes,it was found that torrefaction has a significant effect on the performance of the catalyst,and the increase in the pyrolysis temperature also promotes the reaction;in the process conditions,both the increase of microwave power and the decrease of space velocity can increase the activity of the catalyst and increase the conversion rate of reaction gas.Under the reaction conditions of torrefaction temperature of 300℃ pyrolysis temperature of 600℃,space velocity of 2.4 L/(h-1·g-1),and microwave power of 900W,the conversion rates of CO2 and CH4 can respectively reach 85%and 70%.However,under lower microwave power,the performance of the catalyst is poor,and the reaction gas conversion rate is only about 40%.The addition of Ni,La and bimetallic active components has obvious promotion effect on the reaction.When Ni:La=3:1,the catalyst has the highest activity,and the conversion rate of the reaction gas and the selectivity of the generated gas can reach high standards,and the conversion rate of reaction gas will not change within 8h.This is because Ni is uniformly dispersed on the surface of the support and has a smaller particle size.The addition of La can enhance the interaction between Ni and the support,reduce the particle size of Ni and make Ni more uniformly dispersed on the surface of the support.At the same time,the addition of La can effectively inhibit the formation of NiO during the reaction.These all promote the catalyst to catalyze the dry reforming reaction of methane.