Research On Stepwise Pyrolysis Characteristics Of Biomass Based On Its Components

Biomass energy is the only renewable carbon resource,and has the potential to produce high grade energy and chemicals.Pyrolysis of biomass can effectively convert biomass into three state products,but the bio-oil obtained from this method has some disadvantages because of complex components and other factors which means the bio-oil can not be utilized effectively.So it is necessary to focus on improving the quality of bio oil and high added-value component's enrichment and separation.Conversion of hemicellulose,cellulose and lignin can be achieved in three steps of hydrothermal pretreatment,low temperature pyrolysis and high temperature pyrolysis,and corresponding target products can be obtained in each transformation stage.In this paper,three typical lignocellulosic biomass of rice straw,peanut shell and rice straw were chosed as research objects.This paper analyzes the influence of main working conditions of hydrothermal pretreatment,low temperature pyrolysis and high temperature pyrolysis in different characteristics of products,and explores the regulation mechanism of classification of pyrolysis products,which lays the foundation of stepwise pyrolysis of biomass.Firstly,a stirred reactor system was used for hydrothermal pretreatment of biomass,so as to explore the influence of raw material,temperature and solid-liquid ratio on the characteristics of products.As far as raw materials are concerned,contents of ash in three biomass slumped.Furfural was the main component in liquid product.The relative content and yield of furfural in the liquid products of peanut shell after hydrothermal pretreatment were the highest.Among the temperature of 160?~240?,with the increase of hydrothermal temperature,the degradation of hemicellulose further increased.Most of hemicellulose was degraded at hydrothermal temperature from 200 to 220?.Solid-liquid ratio had influence on degradation of hemicellulose and deash effects.When the temperature was 200? and solid-liquid ratio was 1:10,the relative content of furfural in the extraction solution of cornstalk was also the largest,reaching 82.82%.The biomass samples were pretreated by hydrothermal treatment and then analyzed by thermogravimetric analysis and pyrolyzed by fixed bed to explore the influence of temperature on the characteristics of products.The main temperature segments of hydrothermal char degradation were 320~400? according to the weight loss interval.The liquid product yield of low temperature pyrolysis reached its peak at about 380?,and most of the cellulose was degraded above 380 ?.After hydrothermal pretreatment,the enrichment of carbohydrates,especially levoglucosan was obvious.The relative content of levoglucosan in liquid product of corn stalk,peanut shell and rice straw reached 7.96%,29.14% and 29.38% respectively at 380?.When the temperature was risen to above 380?,secondary decomposition reaction occurred rapidly,resulting in the decrease of the yield of levoglucosan.At the same time,degradation of lignin accelerated.So the pyrolysis of peanut shell at 380? was the best condition.Pyrolysis experiments was conducted in a fixed bed.Temperature of 400? to 600?was chosed as working condition.In the distribution of three state products of high temperature pyrolysis of biomass,the yield of solid products was very high,while the yield of gas products and liquid products was very low.Py-GC/MS was used to catalytic pyrolyze samples.After using HZSM-5 catalyst,the main components of products were changed into aromatic hydrocarbons,and the main components of aromatics were toluene,ethylbenzene,p-xylene,4-ethyl toluene and naphthalene.So high-temperature pyrolysis of low-temperature pyrolysis char could produce liquid product which has high content of aromatic hydrocarbon.So peanut shell was chosed as the best raw material.The temperature of 200? and solid-liquid ratio of 1:10 were chosed as the best hydrothermal pretreatment parameters in order to enrich furfural.The highest relative content of furfural was 84.14% and yield of furfural was 4.19%.Temperature of low-temperature pyrolysis temperature was controlled as 380?.In low-temperature pyrolysis process,the enrichment of levoglucosan could be achieved.The relative content of levoglucosan was 29.14% and yield of levoglucosan was 6.59%.In high-temperature pyrolysis process,aromatic hydrocarbon could be achieved by using HZSM-5 as catalyst.