The Study On The Separation And Application Of Main Components Of Rice Husk

As a main byproduct of rice producing, rice husk (RH) reaches its annual output of 40 million tons in China. Most of rice husk is abandoned due to its poor nutrition, high ash content and hardness, which arouse the pollution and waste of RH.However, rice husk is rich in hemi-cellulose, lignin, cellulose and amorphous silica. The content of amorphous silica in rice husk is the highest among all biomass. Therefore, the research of how to separate and utilize the main content in RH is important, which will be helpful to avoid the environmental pollution and resource waste.This dissertation is focus on the separate and utilize of the four main content of rice husk (hemi-cellulose, lignin, cellulose and amorphous silica). The methods of separating and utilizing of them were discussed as the following scheme shown:(?)There are four parts concluded in above mentioned scheme:Part 1:Praparing D-xylose from the hemi-cellulose of rice huskThe hemi-cellulose in RH was hydrolyzed to be D-xylose by dilute sulfur acid solution under controlled conditions. D-xylose was separated from hydrolysis solution through purify. The metal oxides in rice husk were dissolved at the same time, which purified the silica in residue. The conclusions of this step are shown as bellows:(1)When the hemi-cellulose was hydrolyzed at atmosphere, the yield of D-xylose rose with the reaction time and concentration of sulphuric acid. Increasing the concentration of sulphuric acid was helpful to reduce the reaction time. The max yield of 15.97% was reached under the conditions of 6%(wt.%) sulphuric acid, 7 hours, and 6:1(mL:g).(2)When the hemi-cellulose was hydrolyzed in an autoclave, the temperature could be controlled above of 100℃. The yield of xylose could be increased to higher level, the reaction time could be reduced. The max yield of 17.88% was reached under the conditions of 4%(wt.%) sulphuric acid, 3 hours, 130℃and 6:1(mL:g).(3)The influences of variables on the hydrolysis of hemi-cellulose was analyzed by range analysis. The sequence of importance was concentration of sulphuric acid > temperature > ratio of RH and solution > reaction time. The content of metal oxides was reduced to 0.048% from 2.38% under this condition.(4)The residue produced from optimal condition was pyrolyzed at 700℃for an hour. Silica with the purity of 99.87% was obtained. The purity of this silica is almost equal to the fumed silica's, but higher than the precipitated silica's.Part 2: Extracting lignin from the RH residueâ… and applying of lignin in phenol formaldehyde resinLignin was extracted from the RH residueâ… by the method of organic solvent pulping, the organic solvent used are ethanol, 1,2-ethanediol and 1,4-butanediol. Then the lignin was used in the preparation of phenol formaldehyde resin. The conclusions got from this part of research are shown as bellow: (1)For ethanol auto-catalyzed pulping methods, the yield of lignin was influenced by the variables such as temperature, time, concentration of ethanol solution, etc. The max yield of lignin from rice husk reached 12.8% when the conditions were controlled as temperature 220℃, time 5 hours, concentration of ethanol solution 65% and ratio of solid to liquid 1:10. The result of SEM and EDXA analysis proved the lignin precipitated on the surface of rice husk during the separation process, which decreased the yield of lignin.(2)For ethanol auto-catalyzed pulping methods, the max yield of lignin from RH residueâ… reached 10.41% when the conditions were controlled as temperature 230℃, time 5 hours, concentration of ethanol solution 65% and ratio of solid to liquid 1:10. This yield was lower than above mentioned 12.8%, because the acetyl group providing H⁺ in residueâ… was less than in the rice husk, which could not support the auto-catalysis reaction of lignin clearage.(3)The yield of lignin from residueâ… increased with the addition of MgCl₂ as catalyst. The optimal dosage of MgCl₂ was 0.4% of solvent weight, other conditions were temperature 230℃, time 5 hours, concentration of ethanol solution 65% and ratio of solid to liquid 1:10.The max yield reached 13.18%,which increased 26.73% from the yield of auto-catalysis.(4)The regular microballoons were prepared form rice husk via ethanol auto-catalysis, under conditions of temperature 220℃, time 3 hours, concentration of ethanol solution 35% and ratio of solid to liquid 1:10(g:mL). The diameters of microballoons were between 100-500nm. The yield of lignin was 6.26%. The key variable affecting the regular degree of lignin was proved to be the concentration of ethanol solution.(5)For ethanediol auto-catalyzed pulping methods, the max yield of lignin from RH residueâ… reached 11.11% when the conditions were controlled as temperature 200℃, time 4 hours, concentration of ethanediol solution 90% and ratio of solid to liquid 1:6. The sequence of viarables's importance on the yield was temperature>concentration of ethanediol>reaction time > ratio of RH and solution.The yield of lignin from residueâ… increased with the addition of sulphuric acid as catalyst. The optimal dosage of sulphuric acid was 0.5% of solvent volume, other conditions were temperature 200℃, time 4 hours, concentration of ethanediol solution 90% and ratio of solid to liquid 1:6.The max yield reached 18.84%,which increased 69.58% from the yield of auto-catalysis.(6)For 1,4-butanediol auto-catalyzed pulping methods, the max yield of lignin from RH residueâ… reached 11.90% when the conditions were controlled as temperature 200℃, time 2 hours, concentration of ethanediol solution 80% and ratio of solid to liquid 1:8.The yield of lignin from residueâ… increased with the addition of sulphuric acid as catalyst. The optimal dosage of sulphuric acid was 0.5% of solvent volume, other conditions were temperature 200℃, time 2 hours, concentration of ethanediol solution 80% and ratio of solid to liquid 1:8.The max yield reached 28.69%,which increased 141% from the yield of auto-catalysis. When the dosage of sulphuric acid exceed 0.5%, the charry of residueâ… appeared, the yield of lignin decreased.Part 3: Preparing ethanol from cellulose of rice husk residueâ…¡:The cellulose in residueâ…¡was hydrolyzed by dilute sulphuric acid solution to prepare glucose, then glucose was fermented to ethanol. The conclusions drawn from this step are as follows:(1)The variables affecting the yield of glucose are concentration of sulphuric acid, temperature, reaction time, ratio of RH and solution. The importance of variables on the hydrolysis of cellulose was analyzed by range analysis. The sequence of importance was concentration of sulphuric acid > temperature > reaction time>ratio of RH and solution. (2) Concentration of sulphuric acid had the max impact on the yield of glucose. The optimal concentration is 0.25%.(3) Temperature had the second important effect on the yield of glucose, the optimal temperature is 200℃.(4)The results of orthogonal test shown the optimal conditions were: concentration of sulphuric acid 0.20%, temperature 190℃, reaction time 5 hours, ratio of RH and solution 1:10, the max yield of glucose is 24.17%.(5)The solution from cellulose hydrolysis was neutralized and purified, then Anqi yeast was used to ferment the glucose to ethanol under 32-35℃for 60 hours, the max yield of ethanol reached 45%(.wt.%, mass of ethanol/mass of glucose).Part 4: Preparing nano silica particle from the RH residue via pyrolysis and the modification of silicaThe nano silica particle was prepared from residue via pyrolysis, then the surface modification of silica was produced, the conclusions drawn from this step were as following:(1)The pyrolysis temperature varied with the constitution of rice husk. The pyrolysis temperature of rice husk residueâ… ,â…¡,â…¢was 650℃,660℃and 700℃respectively. The content of silica increased in the subsequence of rice husk residueâ… ,â…¡,â…¢.(2)For the one steps pyrolysis of residueâ… at 600℃,no matter what the circumstance flow was, the silica was obviously conglobated. The reason might be the high surface energy of micro-silica. If the pyrolysis temperature was lower than 600℃, the residue could not be pyrolyzed completely under oxygen flow circumstance.(3)For the two step pyrolysis of residueâ… at 600℃,silica nano particle with good disparity was obtained. The first step was: pyrolyzing the organic substance in residueâ… at 600℃under the CO₂ flow for 0.5 hour. The mixer of silica-carbon was obtained. In this way, the carbon was acted as an disseminating agent to prevent the aggregation of silica;The second step was oxidating the carbon at 600℃under the O₂ flow for 0.5 hour. silica nano particle with good disparity was obtained. The TEM analysis shown the silica nano particle was like irregular rice grains with the width of 15nm and length of 20nm。(4)For the two step pyrolysis of RH residueâ… , the aggregation degree raised with the temperature. TEM analysis indicated that when the temperature enhanced from 600℃to 680℃, the average diameter of silica particle increased 20nm; when the temperature enhanced to 780℃, the average diameter of silica particle increased to 100nm with obvious aggregation.(5)For the two step pyrolysis of RH residueâ…¡under 650℃,the irregular silica nano particle with average diameter of 30nm was obtained.(6)For the two step pyrolysis of RH residueâ…¢under 650℃,the regular silica nano particle with average diameter of 30nm was obtained. Its specific surface was 136.4 m²/g,pore size was 40nm.(7)The silica nanoparticle prepared from residueâ… was modified by dimethyl dichlorosilane (DMCS), the optimal condition was temperature 200℃,dosage of active agent 0.3mL/1g, reaction time 40 minutes,activation grade reached100%。The angle of contact changed from 0⁰ to 115⁰, Zeta electric potential changed from -36.60±2.97mV to 14.29±2.45 mV,which proved the modification of–OH on the surface of silica nanoparticle。A new comprehensive utilization method of rice husk was conducted by the study of this dissertation. This method is helpful to the decrement of pollution caused by rice husk and increment of economy profit. 1 tons of D-xylose, 2.19 tons of organic lignin, 0.5 ton of ethanol and 1.7 tons of silica nanoparticle are produced from 10 tons of rice husk, the value of those products is about 65 thousand Yuan. If the 40 million tons rice husk in China were all utilized by this method, the value of those products would be 260 billions Yuan. Therefore, the development of research on the utilization of rice husk would helpful to the industry of rice husk utilization, increasing the income of farmer. There is billions of agriculture waste produced in China. The method of utilizing rice husk has a kind of generality. Therefore, the conclusions in this dissertation would has the consulting value to the utilization of other agriculture waste.