【作者】 安冬敏；

【导师】 王子忱；

【作者基本信息】 吉林大学 ， 物理化学， 2011， 博士

【摘要】 随着全球工业化的快速发展,一次性能源的消耗量不断增加,引起了能源枯竭和环境污染问题,这些问题带来的负面影响正日益加剧,人类为了自身的生存和发展,不断寻找新的能源,以减少和替代一次性能源的消耗。在各种可再生能源中,生物质是储存太阳能的唯一一种可再生的碳源,是可持续再生能源中的重要组成部分。对稻壳热能利用的研究开发已成为开发新能源的一个重要方向,目前生物质能主要用于供热、发电以及合成化学工业产品的需要,大规模推广利用稻壳热能发电,这是我国目前正在研发推广的一项新技术。利用稻壳燃烧的热量的同时,燃烧灰分和燃烧废气的利用也是一个重要研究开发课题。稻壳是稻米加工后的副产品。据统计,我国年产稻壳6000万吨以上,利用稻壳发电,不仅解决了污染问题,而且开发了能源,对我国国民经济的发展有着巨大的作用。但是,稻壳发电燃烧后产生大量的稻壳灰,如不加以处理,对环境仍是一大危害。由于稻壳灰中含有大量的未完全燃烧的碳,是制备活性炭极好的原料。并且稻壳中含有16%-20%的无定形水合二氧化硅,燃烧后主要成分为二氧化硅,其它矿物杂质含量很少,是生产精细化工产品白炭黑的理想原料。本论文首先利用强碱NaOH浸提稻壳灰中的二氧化硅,得到含硅酸钠的滤液。然后用N2和CO2的混合气体模拟工业废气-石灰窑气,作为沉淀剂,碳化法制备了纳米级二氧化硅。通过向碳化后的滤液中加入Ca(OH)2浆液,提取齐NaOH获得了再生,用再生的NaOH滤液又去处理稻壳灰,实现了提取剂NaOH的循环利用。并通过正交实验设计,得出了NaOH处理稻壳灰提取二氧化硅的最佳工艺：NaOH的浓度为4wt.%,提取时间为2.5h,浸渍比为9：1,得到二氧化硅的提取率为99%以上。并对制得的二氧化硅进行了表征,发现制得的产品为无定形结构,IR表征为水合的二氧化硅,粒子平均直径在40nm左右,分散性良好、纯度较高的球形二氧化硅粉末。并对碳化法制备纳米二氧化硅的机理进行了研究。然后,改变传统的Na2CO3熔融石英砂的方法,用Na2CO3浸提稻壳灰中的二氧化硅,得到的滤液采用碳化法制备出分散性较好的纳米级二氧化硅。并对影响二氧化硅提取率的实验条件Na2CO3浓度、提取时间、碳化时间,及其浸渍比等进行了研究。提取剂Na2CO3在提取过程中起到催化剂的作用,反应过程中损失少,通过及时补充,能够实现提取齐Na2CO3的循环利用,并对反应机理进行了初步探讨。此法降低了传统工艺上需要处理大量工业废水的成本,因此上述方法是一种绿色和能够可持续发展的新工艺。稻壳灰经碱煮提硅后,剩余灰残渣中炭的含量有了极大提高,有的甚至高达90%以上,且炭质变得疏松多孔,是制备活性炭的良好原料。在二氧化硅的浸取过程中,由于碱对稻壳灰的刻蚀作用,使得得到的灰残渣产生很多空隙,如若对其进行进一步的活化处理,活化剂能够进入灰残渣内部,对炭进行充分刻蚀,进一步使孔的数量增加,能够更好的达到活化的目的。因此,我们对碳酸钠提取二氧化硅后剩余的灰残渣进行活化,用强碱KOH为活化剂,研究了活化时间、活化温度、活化剂用量对制备的活性炭的孔容、比表面积及其碘吸附性能的影响。得到了最佳的实验条件：活化温度为850℃,活化时间为1h,碱与灰残渣的质量比为2：1,在此条件下制备的活性炭样品的孔容为1.2ml/g,比表面积为1936 m2/g,碘吸附量可达1259.06 mg/g,并对KOH的活化造孔机理进行了探讨。并通过扫描电镜跟踪分析,考察稻壳灰经酸去除金属氧化物、碱提二氧化硅、及其KOH活化对灰的形貌及其孔隙的影响,得出高温是造孔的必需条件。中空二氧化硅微纳米球由于本身的高熔点、高稳定性、无毒等特殊性质,受到了广大研究人士的关注。模板法是在制备特殊形貌材料中应用比较多的一种方法。此方法先以特定的物质作为形貌辅助物-模板,然后根据需要将材料包覆或填充在模板中得到所需的形貌。少数研究者采用易溶于酸的无机盐或氧化物为核,多数以高分子共模板剂做核,并且采用的硅源基本上都为正硅酸乙酯。本论文采用的硅源来自于第二章中氢氧化钠处理稻壳灰得到的硅酸钠滤液,然后以常见模板剂PVP和CTAB胶束为共模板剂,硫酸做沉淀剂合成了二氧化硅中空球,在高温下煅烧后,得到了具有中空结构的二氧化硅微球。并通过设计实验及表征,探讨了中空介孔纳米二氧化硅微球的形成机制,得到了制备二氧化硅中空球的最佳PVP与CTAB的比例。最后,本文对碳化法制备的纳米级二氧化硅产品进行了表面修饰。通过采用不同链长的脂肪醇,实现了对二氧化硅不同程度的表面改性。通过接触角的测试,发现,当所用脂肪醇的量一定时,所得产品的接触角随着脂肪醇链的增长而逐渐增大,并对产生这一现象的机理进行了探讨。最后将改性后的纳米二氧化硅产品添加到高分子聚合物中,通过SEM断面分析,我们证实了经过改性后的二氧化硅在高分子材料里得到了良好的分散,实现了无机粒子与有机基质的良好相容性。总之,本论文通过碱提稻壳灰中的二氧化硅、碳化法制备了纳米级二氧化硅,并对提硅后的碳残渣进行了活化,制备了具有高比表面积和很强吸附性的活性炭,实现了稻壳灰资源的两大成分的充分利用。为稻壳灰的综合利用提供了一个崭新的方案。不仅在基础领域取得了成果,同时将理论分析与实际应用结合起来,具有着重要的社会意义以及经济意义。更多还原

【Abstract】 With the rapid development of global industrialization, the consumption of primary energy is increasing, which causes energy depletion and environmental pollution problems and the negative impact of these problems are increasing. For its own survival and development, the human is constantly looking for new energy sources to reduce or substitute one-time energy consumption. In a variety of renewable energy, biomass, which is the only renewable carbon source to store solar energy, is an important renewable energy component. The research of heat energy utilization of rice husk has become an important direction to develop new energy sources. In the current, biomass is mainly used for heating, power generation and synthetic chemical industry. Large-scale promotion of the use of rice husk to generate power is now a new technology, which is spread by our country. Besides of use of rice husk burning calories, the use of combustion ash and gases is also an important issue.Rice husk is a by-product after processing. According to statistics, China’s annual output of more than 60 million tons of rice husk. The use of rice husk to generate power is not only solving the pollution problem, but also developing energy resources, which plays a huge role to develop our national economy. However, the burning of rice husk to generate power produces large amounts of rice husk ash, if not dealt in time, which remains an environment problem. Because rice hull ash contains large amounts of unburned carbon, it is an excellent raw material for preparation of activated carbon. Moreover, rice husk contains 16% -20%of amorphous hydrated silicon dioxide, and the main component is silicon dioxide after the combustion of rice husk, besides, small amounts of other mineral impurities, which indicates that it is an ideal raw material to produce fine chemical product-white silica. In this paper, silica was leached from RHA as sodium silicate by NaOH treatment and industrial waste gas CO2 was used as precipitator. The silica extraction yield reached 99 wt.% and the effect of parameters, which involved the concentration of NaOH, the extraction time and impregnation ratio, on the silica extraction yield was investigated in this study. The optimum extracted conditions of silica from rice husk ash are as follows:the concentration of NaOH is 4 wt.%, the extraction time is 2.5h and impregnation ratio is 9:1. The extracted yield of silica is up to 99 wt.%. Furthermore, the extraction reagent NaOH could be regenerated by the addition of calcium hydroxide (Ca(OH)2) slurry into the filtrate after carbonation, and calcium carbonate (CaCO3) by-product with high purity was obtained. The X-ray diffraction patterns (XRD) indicated the amorphous structure of the silica powders and Fourier transform-infrared spectroscopy (FTIR) indicated that the product is hydrated silica. The average diameter of silica particle is around 40nm and the silica product has a well dispersion and fine purity. At last, Preparation and carbonization mechanism of nano-silica was studied.Then, the traditional method of Na2CO3 fused silica sand was changed in the second chapter. Na2CO3 was used to extract silica from rice husk ash, the resulting filtrate was then reacted with CO2 to prepare good dispersant nano-silica. The parameter of affecting on the silica extracted yield, such as Na2CO3 concentration, extraction time, carbonization time, and the impregnation ratio were studied. Na2CO3 acts as a catalyst in the extraction process, and only a small amount if it was lost during the reaction, thus, the recycling of extractant Na2CO3 was achieved through the timely supplement of it, and the reaction mechanism was discussed. This method reduced the cost of industrial waste water and predigested the traditional craft, therefore, the above method is a green and sustainable technology. The remained carbon content in the ash residue has been greatly improved after alkali extraction, and some is even as high as 90% or more, and become porous and loosen, thus it is a good material for preparation of activated carbon. In the silica leaching process, due to alkali etching effect of rice husk ash, the resulting ash residue was generated a lot of gaps. If some further activation was done, active agent can enter the ash residue internal to the full etching of carbon, and further increase the number of holes, therefore, better activated effect was achieved. In this chapter, a strong base KOH was used as activated agent to react with ash residue, the effect of parameters, which involved activated temperature, impregnation ratio, and activated time on pore volume, BET surface area and iodine adsorption capacity of activated carbonwas discussed in this study. The activated carbons are found to be a mixture of micropore and mesopore pore structures. The maximum pore volume, BET surface area and iodine adsorption capacity of as-prepared active carbon can reach 1.22 cm3/g,1936.62 m2/g and 1259.06 mg/g, respectively. Field emission scanning electron microscopy (SEM) was used to characterize the morphological features of the ash after step by step treatment, and we found that high temperature is a necessary condition for making pore.Because of their high melting point, high stability, non-toxic, and other special properties, hollow silica microspheres have got the majority of public concern. Template method is a familiar method in the preparation of the application of special shape materials. With this method, a particular material was used as the morphology of aids-templates firstly, and then some materials were needed to be covered or filled in the template to get the required shape. Several researchers used a small number of acid-soluble inorganic salt or oxide as the core, but the majority used polymer template as the core, besides TEOS was usually used as a silica source. Silica source used in this paper was from the second chapter, which was filtrate obtained from dealing with rice husk ash by sodium hydroxide, and PVP and CTAB were used as the co-templates, besides, sulfuric acid was used as precipitng agent to synthesize hollow silica spheres. After calcination at high temperatures, a hollow silica microspheres structure was obtained. The formation mechanism of silica hollow microspheres was raised through the design of experiments and characterization of product. Moreover, we found the key parameter to get silica hollow spheres was the ratio of PVP and CTAB.Finally, the precipitated nano-silica product was modified by fatty alcohol. Different levels of silica surface modification were achieved through the use of different chain length of fatty alcohol. By contact angle test, we found that when a certain amount of alcohol was used, the contact angle of the final product increased with the growth of chain length of fatty alcohol increasing, and the mechanism of this phenomenon was discussed. Finally, the modified nano-silica product was added into the polymer, and we confirmed that after modification of the silica, a good compatibility with organic substrate was achieved through SEM cross section analysis. Thus a good dispersion of inorganic particles in the polymer material was got through this method.In summary, the silica was extracted from rice husk ash by alkali, and nano-silica powder was prepared by carbonation method. Besides, the ash residue after alkali extraction was activated by KOH to obtain the activated carbon with high specific surface area and strong adsorption. The method in this paper makes full use of the two components of rice husk ash, which provides a new solution for the comprehensive utilization of rice husk ash. It is not only fruitful in the basic fields, but also on the combined the practical application with the theoretical analysis, Which has the important social significance and economic significance.更多还原