【作者】 李大伟；

【导师】 朱锡锋；

【作者基本信息】 中国科学技术大学 ， 热能工程， 2011， 博士

【摘要】 生物质快速热解液化是一种高效的生物质转化利用技术,而生物质热解炭的高值化利用,是该技术产业化应用的关键影响因素之一。快速热解稻壳炭（PRH）是一种典型的生物质热解炭,但目前关于PRH高值化利用的研究报道较为少见。本文针对PRH制备多孔炭及多孔二氧化硅,开展的主要研究及取得的创新性结果包括:（1）提出了CO₂活化—碱液常压沸煮工艺高效利用PRH,可以在无机碱不需加热至高温且用量较小的情况下制得中孔率达79%、50%的活性炭,还可以联产硅酸钠或多孔二氧化硅;（2）研究了中孔率不同的两种自制活性炭对亚甲基蓝的吸附特性;（3）采用聚乙二醇为模板剂,H3PO4为酸化剂,在10 h内制得了比表面积高达1018 m²/g的稻壳炭基多孔二氧化硅;（4）首次研究了稻壳炭基多孔二氧化硅对Cu（Ⅱ）的吸附特性。具体内容如下:1、CO₂活化-碱液常压沸煮工艺制备高中孔率的稻壳活性炭提出先用CO₂活化PRH的炭化物,再用碱液常压沸煮,制取活性炭;通过正交试验考察了制备条件对活性炭碘值的影响;探讨了孔隙发育机理。结果表明,采用该工艺,无机碱不需经历高温过程,利于降低耗碱量,并可制得中孔率高达79%的稻壳活性炭,其孔容积、比表面积分别达到0.783 cm³/g、899 m²/g;CO₂活化时间对活性炭碘值的影响最大;孔隙发育机理主要在于CO₂脱除了炭基体中的C,使得孔隙初步发育,之后,碱液沸煮脱除了二氧化硅,使得孔隙进一步发育。2、热解稻壳炭联产硅酸钠和活性炭为以较低的耗碱量在常压下联产出二氧化硅含量高、模数大的硅酸钠,以及比表面积大于800 m²/g的活性炭,采用Doehlert实验设计、Derringer渴求函数、响应面模型相结合的方法优化CO₂活化-碱液常压沸煮工艺。结果表明,最佳联产条件为取用1 mol/L的NaOH溶液、9.7 mL/g的液固比;该条件下可得模数为2.6的硅酸钠,以及比表面积为897 m2/g、中孔率为50%的活性炭;该活性炭对苯酚及Ni²⁺的吸附量均显著超越了优质商业活性炭。3、不同中孔率的稻壳活性炭对亚甲基蓝（MB）的吸附特性通过批量吸附实验,考察了中孔率为79%、50%的自制活性炭对MB的吸附特性,结果表明,当MB的初始浓度不大于280 mg/L时,两种自制活性炭的吸附量均达到了优质商业活性炭的水平;在MB初始浓度为310-380 mg/L时,两种自制活性炭的脱除效率均高于86%。4、热解稻壳炭快速制备大比表面积多孔二氧化硅利用最佳联产条件下所得的硅酸钠,以聚乙二醇（PEG）为模板剂,制得了多孔二氧化硅;研究了PEG用量及pH值对多孔二氧化硅孔隙结构的影响规律及影响机理。结果表明,在较短的时间内（<10 h）,可以制得比表面积高达709-1018 m2/g的稻壳炭基多孔二氧化硅;增大PEG用量、降低pH值均能显著提高多孔二氧化硅的比表面积,其机理在于,增大PEG用量或降低pH值,均能显著提高PEG-二氧化硅复合材料中的PEG含量,致使更多PEG被烧除,形成更为发达的孔隙。5、稻壳炭基多孔二氧化硅对Cu（Ⅱ）的吸附特性以稻壳炭基多孔二氧化硅为吸附剂,在对其进行表征的基础上,通过批量吸附实验,考察了它对重金属离子Cu（Ⅱ）的吸附特性,并探讨了吸附机理。研究表明,在Cu（Ⅱ）初始浓度为20-120 mg/L时,稻壳炭基多孔氧化硅对Cu（Ⅱ）的最大吸附量、最高脱除效率分别达到77 mg/g、97 %;多孔二氧化硅对Cu（Ⅱ）的吸附较好地符合Freundlich等温线和准二级动力学模型;多孔二氧化硅表面硅羟基与Cu（Ⅱ）之间的相互作用,是Cu（Ⅱ）被吸附的重要原因。更多还原

【Abstract】 High value-added utilization of char from biomass pyrolysis is a key factor for industrialization of fast pyrolyzing biomass, a promising technique for efficient conversion of biomass into a liquid product known as biooil. Fast pyrolyzed rice husk （PRH） is a typical char produced by fast pyrolyzing biomass, but currently few researches have been conducted on high value-added utilization of PRH. This study aims to prepare active carbon and porous silica from PRH. The main research and innovative results can be divided into four aspects. （1） A novel process, namely combination of CO₂ activation and boiling in alkaline solution under normal pressure, was proposed to efficiently utilize PRH. By using this process, active carbons with mesopore fraction up to 79% and 50% can be prepared without requiring inorganic alkali to undergo high temperature treatment or consume a large amount of alkali. The process also allows producing sodium silicate or porous silica. （2） The adsorption of methylene blue （MB） onto the active carbons with different mesopore fraction was studied. （3） Porous silica with specific surface area （SSA） up to 1018 m2/g was produced within 10 h by using polyethylene glycol （PEG） as a template and H3PO4 as a acidulant. （4） The adsorption of Cu（Ⅱ） onto porous silica prepared from PRH was studied for the first time. More detailed research contents were given as follows.1 Preparation of PRH-based active carbon with high mesopore fraction by combination of CO₂ activation and boiling in alkaline solution under normal pressure.A new process, namely combination of activating carbonized PRH with CO₂ and then boiling it in alkaline solution under normal pressure, was proposed to prepare active carbon. Effects of process variables on iodine number of active carbons were studied using an orthogonal experimental design, followed by discussion on pore development mechanism. The results indicated that by using the proposed research, PRH-based active carbon with mesopore fraction, pore volume and SSA up to 79%, 0.783 cm³/g and 899 m²/g can be successfully produced without requiring inorganic alkali to undergo high temperature treatment or consume a large amount of alkali. The effect of CO₂ activation time on iodine number was more significant than any other process variable studied. The pore development of active carbons can be attributed to initial pore development resulting from removal of carbon from the precursor by CO₂ activation, and further pore development caused by dissolution of silica in alkaline solution. 2 Co-production of sodium silicate and active carbon from PRHTo produce sodium silicate with large silica content and high modulus, and active carbons with SSA higher than 800 m²/g under normal pressure by using a small quantity of alkali, the proposed process was optimized by using Doehlert experimental design, Derringer desirability function and surface response model. The optimum co-production condition was found to be using 1 mol/L NaOH solution and 9.7 mL/g liquid-solid ratio, under which sodium silicate with modulus reaching 2.6, and active carbon with 897 m²/g SSA and 50% mesopore fraction can be manufactured. The adsorption quantities of phenol and Ni²⁺ by the active carbon were both significantly higher than the corresponding values of excellent commercial active carbon.3 Adsorption characteristics of MB onto PHR-based active carbon with different mesopore fractionThe adsorption characteristics of MB onto PHR-based active carbon with different mesopore fraction were studied using batch adsorption experiments. The results showed that the MB adsorption amounts of the two active carbons were both comparable to that of excellent commercial active carbon at intial MB concentration not larger than 280 mg/L. The removal efficiency of the two active carbons was both higher than 86% at initial MB concentration of 310-380 mg/L.4 Short-period production of high SSA silica from PRHPorous silica was prepared from the sodium silicate produced under the optimum co-production condition by using PEG as a template. Effects of PEG dosage and pH on the textural properties of porous silica were investigated, including the mechanism of the effects. The results showed that PRH-based porous silica with SSA ranging from 709 m²/g to 1018 m²/g was prepared with 10h. Increasing the PEG dosage or reducing pH can significantly enhance the SSA of porous silica. The reason was that more PEG was incorporated into the PEG-silica composites when the PEG dosage increased or the pH decreased, and hence more pores were created after PEG was removed from the composites.5 Adsorption characteristics of Cu（Ⅱ）onto PRH-based porous silicaThe adsorption characteristics of Cu（Ⅱ）onto PRH-based porous silica was studied by batch adsorption experiments after characterization of the adsorbent. The largest adsorption capacity and highest removal efficiency for Cu（Ⅱ）at initial Cu（Ⅱ） concentrations of 20-120 mg/L were 77 mg/g and 97 %, respectively. The adsorption of Cu（Ⅱ） onto the silica could be described by the Freundlich isotherm and the pseudo-second-order model. Interaction of silanol group on porous silica surface with Cu（Ⅱ）was an important reason for adsorption of Cu（Ⅱ）.更多还原