Research On Bio-oil Production From Pyrolysis Of Agricultural And Forestry Residues Within Molten Salts

Agricultural and forestry residues is a kind of important biomass resources,and its efficient,clean and energization utilization plays a crucial role in promoting the economic development,relieving the energy shortage and protecting environment.As the core of thermal-chemical conversion technologies,pyrolysis can transformate biomass feedstocks into high quality combustible gas and bio-oil with easily storaged,transportated and high energy density.The application prospect of pyrolysis is promising,so it has attracted extensive attention worldwide.The key technology for getting high yield of bio-oil is to heat rapidly biomass particles to the tempetature which the pyroylsis process needed.Molten salt has the excellent thermal-chemical properties of high capacity and high heat conductivity coefficient,and its ions can promote the reactions during the proylysis process,so it has the potential to act as the heat carrier and catalyst of biomass pyrolysis.The research was sponsored by the National Natural Science Foundation of China "Mechanism study on biomass catalytic pyrolysis and reduction coupling process in molten salt"(20876150)and the Doctoral Foundation of Ministry of Education "Investigation on bio-oil production from agricultural and forestry residues by fast pyrolysis in molten salts"(20103317110001).In this paper,the systematic investigations on bio-oil production from agricultural and forestry residues by pyrolysis with in molten salts were carried out.Taking agricultural and forestry residues including crop straws and sawdust as the research objects,the property parameters related with thermal-chemical conversion,including the contents of three main compositions such as cellulose,hemicellulose and lignin,proximate,ultimate compositions and heat value,were detemined and calculated,which provide base data for analyzing biomass pyrolysis properties.The pyrolysis kinetics of rice straw,synthetic rice straw and three main compositions cellulose,hemicellulose and lignin were investigated by thermogravi-metric analysis coupled with the fourier transform infared spectrometry(TG-FTIR).The kinetics parameters of the pyrolysis process were calculated through using Coats-Redfern method and Ozawa method,respectively.The thermodynamics parameters sush as enthalpy change,Gibbs free energy change and entropy change were also counted under the status of the maximum weight loss rate,meanwhile the mechanism function which matched the pyrolysis process mostly was deduced,and the influences of heating rates and biomass types on pyrolysis properties and products evolution performance were explored.The results showed that the pyrolysis process of rice straw and three main compositions were attributabled to different mechanism functions.When the heating rate was remained unchanged,the thermodynamics parameters of three main compositions were remarkably different.The pyrolysis product evolution rates increased with the increasing heating rates,and the release temperatures delayed to the high temperature area,the product release perfomances were impacted by biomass types.The influences of acid and alkali leaching methods and leaching solution concentrations on the pyrolysis of rice straw and products envolution properties were investigated.The results demonstrated that ash could be removed partially by acid and alkali solution leaching method,the pyrolysis delayed to higher temperature zone,and the pre-exponential factor and the changes of enthalpy and entropy decreased,while the Gibbs free energy change increased.The impacts of solution concentration on pyrolysis and product release properties depended on the removal or destruction extent of biomass structure or functional groups.Meanwhile,the evolution properties of pyrolysis products under the role of metallic chlorate salts and sulfate salts of Fe,Co,Ni and Fe were determined,those of Fe series catalysts such as Fe,Fe2O3,Fe3O4 and ammonia synthesis catalyst were also carried out.These catalysts were added to the molten salts of ZnCl2/KCl and Li2CO3/Na2CO3/K2CO3 in order to observe their effects on rice straw pyrolysis products release process.It could be concluded that Ni2+ and Cu2+ had obvious influence on rice straw pyrolysis when their sulfate salts were added into molten ZnCl2/KCl sytem,while Cu2+and Co2+ affected the pyrolysis process significantly in molten Li2CO3/Na2CO3/K2CO3 system.The chlorate salts of Ni2+and Cu2+could catalyzed the pyrolysis of rice straw both in molten ZnCl2/KCl and Li2CO3/Na2CO3/K2CO3 system,Fe3O4 and Fe could promote the evolution of products,and Fe2O3 could enhance the release of CO2 in the high temperature zone especially.Agricultural and forestry residues such as sawdust and straw were selected as raw materials of pyrolysis,the investigations on bio-oil production by pyrolysis in molten ZnCl2/KCl and Li2CO3/Na2CO3/K2CO3 system were carried out,respectively.The influences of pyrolysis parameters such as temperature,carrier gas flow rate,loading amount of additive and biomass types were discussed.The CoCl2 could promote the generation of bio-oil,restrain the pyrolysis reaction of acids containing methoxyl group,and promote the decarboxylic reactions which produced CO2.The gaseous products mainly were CO2,H2 and CH4.Bio-oil mainly composed of ketones,phenols and esters,which were affected by temperature,carrier gas and biomass types.Amplified pyrolysis equipment for agricultural and forestry residues pyrolysis in molten salts was designed and set up on the basis of labrotary scale experiments,and the exploration of rice straw pyrolysis in ZnCl2/KCl was conducted.The bio-oil yield was up to 30wt.%,and the gaseous products were CO2,CO,H2 and CH4.The content of ketones increased and the concentration of phenols decreased,the compounds containing carbonyl converted into alcohols after dehydration of bio-oil and hydrogenation treatment by Cu/Zn catalyst.This research enriched the understanding on the basic characteristics of agricultural and forestry residues,and the bio-oil production process by proylysis within molten salts.The research results provided some reference for energization utilization of agricultural and forestry waste resources.