High-Valued Comprehensive Utilization Of Rice Husk Pyrolysis Products

Fast pyrolysis is one of the most promising techniques for biomass utilization.By pyrolysis technology,the organic matter is converted into condensable mixture（bio-oil）,non-condensable mixture（non-condensable gas）and solid（rice husk char）.In order to enhance the utilization rate of rice husk resources,not only is the research on rice husk pyrolysis technology necessary,but also is the high-valued utilization of pyrolysis products significant.This thesis consists of three parts,namely,rice husk pyrolysis process（chapter 2）,bio-oil upgrading and high-valued utilization（chapter 3,4 and 5）and comprehensive utilization of rice husk char（chapter 6）.The first part investigated the rice husk feeder,rice husk dryer system,main pyrolyzer and condenser.The results showed that the commissioning of the device was relatively smooth,and the coordinated operation of each system also works normally.The fluidized bed pyrolyzer could reach the designed temperature of400⁵50 ^oC.The rice husk dryer could reduce the water content of the rice husk to2%and preheat the rice husk to 60 ^oC.The rice husk feeder could well control the quantity of rice husk feeding.The condenser was able to reduce the temperature of pyrolysis steam from 400 ^oC to 60 ^oC rapidly.The rice husk bio-oil,non-condensable gas and rice husk char obtained from rice husk pyrolysis were characterized respectively.The second part used three routes to upgrade and utilize the rice husk bio-oil,which had the disadvantages of high acidity,high water content and high molecular weight,in order to get bio-oil to be used as liquid fuel and high value-added chemicals.For the feasibility of high-valued utilization of bio-oil,the three routes were esterification by acidic catalyst,upgrading by solid alkali catalyst and preparation of bio-oil-phenol-formaldehyde（BPF）adhesive.The performance of the bio-oil had been improved by acidic esterification and upgrading of solid alkali catalysis,so that it could meet the requirements of liquid fuel.The BPF adhesive could be directly used in the production of plywood.1.Ethanol bio-oil and methanol bio-oil were prepared with sulfuric acid as catalyst.The effects of reaction temperature,reaction time and amount of catalyst on pH of bio-oil were investigated.The GC-MS,FTIR and ¹H-NMR analysis of the ethanol bio-oil were compared with the rice husk bio-oil.The results showed that the optimal conditions were 120 ^oC,3 h and 4 g sulfuric acid（60 g raw bio-oil）.The sulfuric acid was separated from the ethanol bio-oil with nano calcium carbonate.The properties of ethanol bio-oil were improved as following,pH increased from 2.83 to4.55,density increased from 0.8853 to 0.9732 g/cm³ and ash content increased from1.2%to 2.9%.In addition,the esters and sugars of the bio-oil increased by 26.1%and6.0%,while the acids and phenols decreased by 15.9%and 12.8%,respectively.The aromatic hydrogen of the bio-oil decreased from 31.32%to 26.74%,and the adipose hydrogen decreased from 68.68%to 65.92%.The molecular weight of the bio-oil was one tenth the molecular weight of raw bio-oil.2.The rice husk bio-oil was upgraded with KF/Al₂O₃ catalysts in order to improve the properties of the bio-oil.The effects of the heat treatment temperature on the structure change of the catalysts,the pH value and corrosiveness of bio-oil and the catalyst recovery were investigated in details.Compared with the rice husk bio-oil,the physical and chemical properties of the ethanol bio-oil were characterized by GC-MS,FTIR and GPC.The results showed that the optimal heat treatment temperature was 500 ^oC,and the ethanol bio-oil（k-5-oil）upgraded with the catalyst had the pH value of 4.45,the aluminum sheet corrosiveness of 0.65%,ash content of0.499%and catalyst recovery of 96.61%.Compared with rice husk bio-oil,the acids and esters of K-5-oil decreased by 12.8%and 8.0%,however,the phenols and sugars increased by 9.8%and 10.5%,respectively.3.Highly substituted bio-oil-phenol-formaldehyde（BPF）adhesives were prepared via the phenolization-copolymerization method,in which furfural was used as a cross-linking agent to improve bonding strength and substitution rate.The phenol percentage decreased by 25%,so that the cost decreased significantly.Firstly,the effects of bio-oil percentage,furfural loading,mole ratio of formaldehyde to phenol（F/P）and amounts of sodium hydroxide on the bonding strength,molecular weight and functional group of BPF adhesives were investigated.Secondly,orthogonal experiments were used to determine the optimal conditions,which were the bio-oil percentage of 75%,furfural loading of 5%,F/P of 0.8,sodium hydroxide of 20%.The BPF adhesive prepared on the optimal conditions had the bonding strength of1.30mpa,free phenol content of 0.32%,free formaldehyde content of 0.20%,and free furfural content of 0.52%.The prepared BPF adhesives can meet the requirements of Chinese National Standard（GB/T14732-2006）.The third part put forward a new route of comprehensive utilization of rice husk char.Carbon and silica of rice husk char was separated.Carbon was activated to carbon adsorbent,silica was converted into calcium silicate and alkali liquor was recycled.1.In the preparation and application of carbon adsorbent,the results showed that（1）the carbon adsorbent was amorphous porous carbon mainly with micropores,and the pore size distribution was mainly concentrated within 1 nm,（2）the optimal decolorization conditions for malachite green solution were pH=7,30 ^oC and 30 min,and the maximum decolorization rate is 99.58%;The maximum absorption wavelength of the pigment in the xylose solution was 410 nm,and the optimal adsorption conditions were 1.5g carbon adsorbent（50 mL xylose solution）,20 min and 50 ^oC,and the maximum decolorization rate is 91.15%.In addition,the conditions had no effects on the yield of the xylose.2.Silica of rice husk char was converted into calcium silicate by reacting with calcium oxide.The sodium hydroxide solution was recycled.The effects of Ca/Si molar ratio and heat treatment temperature on the structural changes were studied.The effects of Ca/Si molar ratio,temperature and time on the recovery rate of sodium hydroxide were investigated.The results showed that（1）at 1000 ^oC,when Ca/Si molar ratio was 3,the crystalline form of clacium silicate wasα_L’.When Ca/Si molar ratio was 1 and 2,the crystalline form of clacium silicate wasβ.（2）the optimal conditions of NaOH recovery were Ca/Si=3,90 ^oC and 1 h.Under the conditions,the recovery rate of NaOH was 100%and the residual rate of Na₂SiO₃ was 0%.In summary,rice husk bio-oil and rice husk char were prepared by rice husk rapid pyrolysis.Ethanol bio-oil and wood adhesive were prepared with the rice husk bio-oil.Carbon adsorbent and calcium silicate prepared by using the rice husk char.This study provides a novel approach for the comprehensive utilization of rice husk resources.