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Liquefication of Sawdust and Separation Processing of Liquefied Products for the Production of Bio-fuels

Author: YangZhongZhi
Tutor: JiangJianChun
School: Chinese Academy of Forestry
Course: Forest Chemical Process Engineering
Keywords: Biomass Liquefication Raw material pretreatment Activated carbon Catalyticcracking Catalytic esterification Catalytic hydrogenation
CLC: TK6
Type: Master's thesis
Year: 2013
Downloads: 17
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Abstract

With the rapid development of Chinese economy, the consumption of fossil oil is growinggradually. At present, the external dependency of crude oil has reached55%in2012, whichappears serious imbalance between supply and demand. On the other hand, biomass resource isabundant in our country. There are approximate700million tons lignocellulosic wastes derivedfrom agriculture and forestry induestry each year. However, most of them are discarded orcombusted directly. Not only does it waste the resources, but also pollutes the environment.Account of the above issue, these abundant biomass resources can be converted to renewablefuel by means of thermo-chemical conversion, which is of great significance to energy security,sustainable economic development and environmental protection. In our investigation, we planto develop an efficient and low cost liquefication technology using mix sawdust and bamboo asraw materials. Furthermore, a new method of upgrading liquefied oil was explored. The maincontents were summarized as follows.1、The mix sawdust and bamboo were soaked in glycerin, then pretreated by defibratorgrinding. The results showed that surface formation of the woody materials were changed bythermal grinding pretreatment. The broken and broomed fibers were observed, which improvesmass loss and mass loss rate in liquefication reaction. But the internal stability of the latticestructure remain the same as the materials before the pretreatment. Through orthogonalexperiment, the optimum liquefication process conditions of bamboo pretreated by thermalgrinding using glycerin as reagent is explored. Under the following conditions: bamboo193.34g （equivalented to absolute dry bamboo60g）, the ratio of concentrated sulfuric acid to absolutedry bamboo is1:40, the ratio of methanol to absolute dry bamboo is4:1, at200℃withreaction time30min, then cooling to room temperature with water, the conversion is95.77%.The smashed bamboo was liquefied at the same condition. The conversion is93.88%, minordifference is observed. Then, the similar experiment results were obtained when sawdust was liquefied by two pretreatment methods. It proved that there is not obvious help for liqueficationreaction pretreated by glycerol soaking and defibrator grinding.2、Liquefication experiment of sawdust using mix solvents. The sawdust was liquefied byglycerin and methanol as mix solvents with0.1L and1L stainless steel high-pressureautoclave respectively using concentrated sulfuric acid as catalyst under the supercritical effectof methanol in high temperature and high pressure. The influences of the particle size and thereaction time on the yield of liquefied residue was investigated. The results showed that theoptimal liquefication conditions in0.1L stainless steel high-pressure autoclave is:methanol-glycerin-oxalic acid-0.28⁰.90mm mix sawdust of mass ratio5:2.5:0.042:1,reaction temperature290℃and reaction time40min, then cooling to room temperature, theconversion of sawdust is up to92.79%. The properties of liquefied oil are as follows: moisture10.78%, acid value4.49mgKOH·g^-1, density1111kg·m^-3, viscosity15.4mm2·s^-1, gross heat19.48MJ·kg^-1. In the1L stainless steel high-pressure autoclave, the optimal liqueficationconditions is: methanol-glycerin-concentrated sulfuric acid-0.28⁰.90mm mix sawdust ofmass ratio5:2.5:0.025:1, in210℃with reaction time1h, then rapid cooling to the roomtemperature, the conversion of sawdust is94.98%.Based on the optimal liquefication conditions of the liquefication experimrnt, a new ideaof integrated utilization of liquefied products was developed. Part of liquefy agent wasreplaced by methanol in stead of glycerol. Not only did it save cost, but also the solid residueof sawdust liquefication can be used to prepare activated carbon. Activated carbon wasprepared by phosphoric acid activation and steam activation using residue as raw material,respectively. The yield and properties of the actived carbon from these two methods werestudied. The results showed that the two methods can prepared activated carbon with high yield.The yield of the activated carbon from phosphoric acid method was69.8%, and yield of37.3%by steam method. Adsorption properties of the two activated carbon is as follows: Theiodine adsorption value and methylene blue adsorption value of the activated carbon fromphosphoric acid method were885.5mg·g^-1and180.0mg·g^-1, respectively; The iodineadsorption value and methylene blue adsorption value of the activated carbon from steam method were971.9mg·g^-1and142.5mg·g^-1, respectively. Through analysis of nitrogenadsorption and desorption isotherm, the activated carbon with phosphoric acid activationappears intensive pore width distribution on the microstructure with average pore diameter of1.99nm. Pore width distribution of activated carbon with steam activation is scattered. Itsmicropore and mesopore appears continuous distribution, average pore diameter is2.46nm.Increasemental volume and BET surface area are less relatively.3、Classification and refining of liquefied oil. The liquefied oil was distilled in rectifyingcolumn, and distillates were obtained below90℃. Then components of the distillates wereanalyzed and their characteristics were investigated. The results showed that the distillatecomponent is complex of different oxygenated compounds Such as esters and ethers, whichhas high protential to be used as fuel additives. The residue after rectification was furthertreated by esterification and catalytic hydrogen. After esterification of the residue with n-butylalcohol to remove water and decrease the acid value, the characteristics of the cracked oil wasas follows: moisture0.85%, acid value3.40mgKOH·g^-1, density944.92kg·m^-3, viscosity7.16mm2·s^-1, gross heat after deducting n-butyl alcohol is28.76MJ·kg^-1. Then, the cracked oil washydrogenated under the catalysis of of Pd/C. Gas chromatography-mass spectrometer （GC-MS）was used to analyzed components of the products. The result showed that after catalytichydrogenation, the content of ketones decreased from5.80%to0.65%, while the alcoholsincreased from54.38%to57.3%. This resulted indicated that the stability of liquefied oil wasimproved.

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