【作者】 张宏喜；

【导师】 王子忱；

【作者基本信息】 吉林大学 ， 物理化学， 2011， 博士

【摘要】 稻壳是大米加工过程的主要副产物之一,资源丰富,仅我国稻壳的年产量就达到4000万吨左右。由于稻壳的营养物质少、灰分含量高、硬度大,目前其利用程度较低。大部分的稻壳被当作农业垃圾废弃,造成了严重的污染和浪费。然而,稻壳中含有丰富的半纤维素、木质素、纤维素和无定形二氧化硅,可用于制备木糖、酚醛树脂、酒精、纳米二氧化硅等各种产品。因此,在化石资源匮乏的今天,开展对稻壳中各种组分的分离与利用的研究,植物秸秆资源化综合利用,即开发了可再生资源,又保护了环境。本文根据稻壳的微观结构和组成特点,对稻壳四种主要组分的转化与应用方法进行了系统研究,主要研究内容包括四个部分,如下图所示:（?）第一部分:水解稻壳中的半纤维素制备木糖通过控制反应条件,利用稀酸溶液将稻壳中的半纤维素水解,从水解液中分离得到食品级的木糖,同时去除了稻壳中的金属氧化物,为从稻壳中提取高纯度无定形二氧化硅打下了基础。研究结果表明:（1）在常压下稀硫酸催化消解稻壳中的半纤维素,木糖的收率与时间成正比,与酸浓度成正比。增加硫酸溶液的浓度,能在较短的时间内得到较高的得率。6%的硫酸溶液以6:1比例（mL:g）下水解7小时,木糖最大收率为15.97%。（2）在水解釜中加热进行反应时,温度可以控制在100℃以上,木糖的得率可以进一步提高,达到最大得率的反应时间可以缩短。经过实验证明最佳的水解条件为:130℃下水解3小时,固液比例为1:6,硫酸浓度为4%。木糖得率达到了17.88%。同时,稻壳中的金属氧化物含量由2.38%降低为0.048%。（3）通过极差分析可知,硫酸浓度水解温度对木糖得率的影响相对较大,而固液比例和水解时间对木糖得率的影响相对较小。各因素对半纤维素水解为木糖的影响大小依次为:硫酸浓度>水解温度>固液比例>水解时间。（4）最佳水解条件下得到的残渣在700℃下灰化1小时后,得到的二氧化硅的纯度为99.87%,此纯度高于沉淀法白炭黑,接近气相法白炭黑。第二部分:稻壳残渣Ⅰ中木质素的提取及其在酚醛树脂中的应用利用乙醇、乙二醇、1,4丁二醇等有机溶剂提取的方法,分别从稻壳、稻壳残渣Ⅰ中提取木质素,并初步研究了利用这种木质素制备酚醛树脂。此种方法提取的木质素,具有灰分、半纤维素和糖等杂质含量低、反应活性高等特点。此部分的研究结果表明:（1）利用乙醇自催化法提取稻壳中木质素时,实验表明反应温度、乙醇浓度、反应时间等因素对木质素的得率有重要影响。在反应温度为220℃,固液比例为1:10,乙醇浓度为65%,反应时间为5小时的条件下,对原始稻壳中木质素的最大得率为12.8%,为木质素理论产量的53%。通过SEM和EDXA分析发现造成得率不高的原因是木质素在稻壳表面的重新沉淀。（2）对除去半纤维素后的稻壳残渣Ⅰ进行乙醇自催化法提取木质素的研究,实验表明木质素的最佳提取条件为温度230℃、固液比例1:10,乙醇浓度65%,反应时间为5小时,最高得率为时的10.41%,明显低于未水解半纤维素稻壳的木质素得率。分析其原因,主要是因为稻壳残渣Ⅰ中的乙酰基在水解半纤维素的过程中被除去,无法提供自催化裂解木质素大分子的H⁺。（3）加入催化剂MgCl₂有利于乙醇法从稻壳残渣Ⅰ中提取木质素的得率。通过加入溶剂质量的0.4%的MgCl₂作为催化剂,在温度230℃、固液比例1:10,乙醇浓度65%,反应时间为5小时条件下,可以提高木质素的得率达到13.18%,较不加催化剂提高了26.73%。催化剂起到的主要作用是与部分反应物乙醇结合,放出H⁺对木质素大分子裂解进行催化。（4）利用乙醇自催化法从原始稻壳中提取木质素,通过控制条件可得到形貌规则的木质素微球。具体条件为温度220℃,固液比例1:10（g:mL）,反应时间3小时,乙醇溶液浓度35%的条件下,木质素微球直径在100-500nm范围。木质素的得率为6.26%。实验证明乙醇浓度是控制木质素的形貌最重要的影响因素。（5）以沸点较高的乙二醇水溶液为溶剂,采取自催化法提取稻壳残渣Ⅰ中的木质素时,最佳的条件是200℃下反应4小时,固液比例为1:6,乙二醇浓度为90%,木质素的得率达到了11.11%。各因素对木质素得率的影响大小依次为:反应温度>乙二醇浓度>反应时间>固液比例。硫酸作为催化剂可提高木质素的得率,在其它条件不变的情况下,加入占溶剂体积0.5%的浓硫酸后,木质素的得率达到了18.84%,较不加催化剂得率提高了69.58%。当硫酸浓度超过0.5%之后,原料有轻微炭化现象,同时木质素得率下降。对此现象的解释为硫酸在反应过程中提供了H⁺,促进了木质素大分子的裂解。但是硫酸过量也会造成有机物的炭化和木质素裂解的副产物引起木质素的收率下降。（6）以1,4丁二醇水溶液为溶剂提取稻壳残渣Ⅰ中的木质素得率最高。在反应温度为200℃,时间2小时,1,4丁二醇的浓度为80%,液固比为1:8（g:mL）的条件下,进行自催化法提取木质素的得率为11.90%。硫酸对木质素的得率有较大提高作用,当加入占溶剂体积的0.5%浓硫酸后,相同条件下木质素的收率达到28.69%,较不加催化剂得率提高了1.41倍。当硫酸浓度超过0.5%之后,原料开始出现轻微的炭化现象,同时木质素得率下降。第3步:稻壳残渣Ⅱ中的纤维素水解为葡萄糖并发酵制备燃料乙醇通过稀酸水解法,对稻壳残渣Ⅱ中的纤维素进行了水解,将得到的葡萄糖进行了酵母发酵的初步研究。本步骤进一步去除了残渣中的金属元素,排除了其对葡萄糖发酵的影响。本部分的研究结果表明:（1）影响葡萄糖产率的因素有硫酸浓度、反应温度、反应时间和固液比例等。通过正交实验的极差分析可知,各因素对葡萄糖得率的影响大小依次为:硫酸浓度>水解温度>水解时间>固液比例。（2）硫酸浓度对葡萄糖和甲基糠醛的得率影响最大,在0.25%以前,硫酸浓度与葡萄糖为正比关系,超过0.25%后,易出现碳化现象。（3）水解反应温度对葡萄糖的得率影响较大,低于200℃时副产物较少,高于200℃后副反应增加。（4）正交试验的结果表明,以浓度为0.20%硫酸为催化剂,固液比例为1:10,在190℃下水解5小时,葡萄糖的收率达到了24.17%的最大值。（5）水解液经中和、纯化和浓缩等处理程序后,使用安琪酵母发酵60小时,乙醇的得率达到45%wt.% （乙醇的质量/葡萄糖的质量）。第四部分:稻壳残渣热解制备纳米二氧化硅及其表面改性以稻壳残渣为原料,通过热解的方法,制备出纳米级无定形二氧化硅粒子,并对其的干法改性进行了初步研究。本部分的研究结果表明:（1）稻壳原料的组成不同,则二氧化硅含量和热解温度有明显不同:稻壳残渣Ⅰ、Ⅱ、Ⅲ中二氧化硅的含量逐渐增加,样品对应的热解温度分别为650、660、700℃。稻壳中半纤维素的去除导致了热解温度上升了100℃,而木质素的去除对热解温度影响不大,纤维素的含量增加会导致热解温度的升高。（2）对于稻壳残渣Ⅰ,在600℃下一步完成有机物的热解得到二氧化硅,无论是通入空气还是氧气流的条件,制得的二氧化硅均有明显的团聚。可能原因是无定型二氧化硅具有粒子直径小,比表面积大,比表面能高的特点,在600℃高温下团聚以降低表面能。但是如果热解温度低于600℃,则即使在通氧气的条件下,稻壳残渣也无法完全热解,有残余的炭存在。（3）改进的二步热解法能制备出了分散性较好的纳米二氧化硅。第一步:在600℃温度下,先通入CO₂进行热解0.5小时,制备炭-二氧化硅复合物。炭作为一种天然的分散剂,阻止二氧化硅纳米粒子的团聚;第二步:同样温度下,再通入氧气热解0.5小时,氧化去除炭,得到分散性较好的纳米二氧化硅。通过高分辨透射电镜分析,二氧化硅纳米粒子为不规则米粒状,宽度约15nm,长度约20nm。（4）提高二步法的热解温度,能缩短稻壳中有机热解的速度,但也会加剧纳米二氧化硅的团聚。TEM测试的结果表明,当热解温度提高到680℃后,二氧化硅粒子的平均粒径增加了约20nm。当二步法热解温度提高到780℃后,二氧化硅粒子的团聚现象严重,形成了直径约100nm的聚集体。（5）对于稻壳残渣Ⅱ,在热解的温度为650℃下二步法热解,所得二氧化硅为形貌不规则的米粒状微粒,粒径约30nm.（6）对于稻壳残渣Ⅲ,在650℃下经过二步法热解得到的纳米二氧化硅形貌相对比较规则,粒径约30nm。其比表面积为136.4 m²/g,孔径分布为单峰形式,最大比例的孔径为40nm。（7）采用二甲基二氯硅烷为改性剂,以稻壳残渣Ⅰ热解得到的纳米二氧化硅为原料,经考察得到最佳改性条件为200℃、活化剂用量为0.3mL/1g,反应时间为40分钟,活化度为100%。改性前后的二氧化硅接触角分别为0⁰和115⁰, Zeta电位分别为-36.60±2.97mV和14.29±2.45mV,红外谱图表明二氧化硅中的-OH与改性剂发生了反应。通过本文的研究,得到了一种综合利用稻壳中四种主要组分的方法。本方法有利于从源头上治理稻壳引起的污染和浪费问题,创造显著的经济效益。根据本文研究的结果,利用10吨稻壳能够生产1吨木糖, 2.19吨有机溶剂木质素、0.5吨乙醇、1.7吨纳米二氧化硅,售价估算约6.5万元。如果我国4000万吨稻壳全部进行利用,可产生产品的价值接近2600亿元。因此对于稻壳资源来说,其开发研究的进展将有力地推动稻壳综合利用的产业化,提高农业产出。我国年产约2亿吨的秸秆,与稻壳一样,均含有四种组分,因此稻壳的利用方法与原理具有一定的普遍适用性,本文的研究结果对其它生物质资源的综合利用具有一定的参考价值。更多还原

【Abstract】 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 residueⅠand applying of lignin in phenol formaldehyde resinLignin was extracted from the RH residueⅠby 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 residueⅠreached 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 residueⅠwas less than in the rice husk, which could not support the auto-catalysis reaction of lignin clearage.（3）The yield of lignin from residueⅠincreased 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 residueⅠreached 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 residueⅠincreased 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 residueⅠreached 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 residueⅠincreased 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 residueⅠappeared, the yield of lignin decreased.Part 3: Preparing ethanol from cellulose of rice husk residueⅡ:The cellulose in residueⅡwas 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 residueⅠ,Ⅱ,Ⅲwas 650℃、660℃and 700℃respectively. The content of silica increased in the subsequence of rice husk residueⅠ,Ⅱ,Ⅲ.（2）For the one steps pyrolysis of residueⅠat 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 residueⅠat 600℃,silica nano particle with good disparity was obtained. The first step was: pyrolyzing the organic substance in residueⅠat 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 residueⅠ, 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 residueⅡunder 650℃,the irregular silica nano particle with average diameter of 30nm was obtained.（6）For the two step pyrolysis of RH residueⅢunder 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 residueⅠwas 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.更多还原