【作者】 孔令照；

【导师】 李光明；

【作者基本信息】 同济大学 ， 环境科学， 2008， 博士

【摘要】 随着能源与资源的短缺和环境污染的日益严重，生物质废弃物资源化的利用研究引起了广泛的关注。水热技术为生物质废弃物的资源化利用提供了一条新的途径。本论文利用水热技术对生物质废弃物进行处理及资源化研究，利用间歇式水热反应器，以生物质废弃物水热降解所产生的还原糖和乳酸为目标产物，较深入地研究了生物质废弃物水热降解的影响因素、反应过程及机理，为工业化应用提供基础。以碳平衡为基础对玉米秆、木屑、稻壳和麦麸等生物质废弃物水热降解的产物分布规律进行了研究，考察了反应温度、反应时间、水的用量和反应物粒径以及添加氧化剂H₂O₂条件下对生物质废弃物水热降解所得液相、气相和固相产物分布的影响，结果表明生物质废弃物水热降解可以分为低温液化、中温气化（油化）和高温碳化三个阶段；延长反应时间、增加水的用量和降低反应物的粒径有利于促进液相产物的生成；氧化剂H₂O₂的增加能促进生物质废弃物完全降解。分析了反应温度和反应时间对还原糖产率和选择性的影响，探讨不同体系（酸性、碱性、氧化剂、金属离子和醇／水混合体系）下还原糖的产率和选择性，确定了还原糖生成的最佳反应条件。结果表明，在300-350℃时有利于生物质废弃物水热降解反应生成还原糖；Na₂CO₃浓度的增大可促进微晶纤维素、玉米秆和木屑水热降解生成还原糖；氧化剂H₂O₂供给量的增加能够提高微晶纤维素和木屑的水热降解还原糖的产率；乙酸的加入能够促进微晶纤维素向还原糖转化；在乙醇／水反应体系中所有反应物的还原糖产率均随乙醇比例的升高而增加，此时玉米秆获得最大还原糖产率为70．30％；因金属离子不同导致所得还原糖的产率和选择性有较大变化。在研究不同条件下微晶纤维素和葡萄糖等模型化合物水热降解产生乳酸的基础上，为增加乳酸产率，进一步考察了金属离子存在下生物质废弃物（玉米秆、木屑、稻壳和麦麸）水热降解产生乳酸的产率和选择性，研究了生物质废弃物水热降解过程及乳酸生成途径，以丙酮醛为原料探讨了金属离子催化条件下乳酸的生成机理。结果表明在400ppm的Ni²⁺和Co²⁺条件下微晶纤维素和葡萄糖水热降解获得最大乳酸产率，分别为6．62％和9．51％；400ppm的Cr³⁺下玉米秆和稻壳最佳乳酸产率分别为9．24％和6．71％；木屑最佳乳酸产率是在400ppm的Zn²⁺存在下获得，为5．47％；非催化条件下能够获得麦麸的最高乳酸产率为7．46％。表明水热条件下水具有较强的离子化倾向，从而使得水成为Br（?）nsted酸碱并具有一定的催化作用，金属离子在水热催化降解丙酮醛生成乳酸中表现出Lewis碱的特性，能与丙酮醛生成金属复合物，最终生成乳酸，此反应过程符合Cannizzaro反应特性。利用热重分析方法研究了微晶纤维素、玉米秆、木屑、稻壳和麦麸的热解行为和特性，确定了相应的动力学模型和参数，结果表明生物质废弃物热解过程的失重明显区主要集中在300-400℃，失重和失重速率曲线随着升温速率的增大向高温区移动，利用Coat-Redfern法模拟所得热解动力学符合一级反应动力学方程。通过对微晶纤维素及其水热降解固相产物的热重、红外、元素、SEM和XRD分析表明微晶纤维素的水热降解主要分成低温水解为主和高温热解为主两个阶段。更多还原

【Abstract】 Under the background of energy and resource shortage and the environment pollution, the utilization and research of biomass wastes as a kind of resource attracting worldwide attention. Hydrothermal reaction provides an effective method for the reutilization of biomass wastes. The disposal and reutilization of biomass wastes were realized by hydrothermal reaction in batch hydrothermal reactor. To obtain high yield of reducing sugar and lactic acid by hydrothermal reaction, the influence factors, decomposition process and reaction network were investigated. The work can provide base for the industrialization of hydrothermal reaction.The product distributions of maize straw, sawdust, rice husk and wheat bran were described on basis of carbon balance. The effects of reaction temperature, time, water volume, grain size and oxidant on the aqueous, residual and gaseous sample of biomass wastes by hydrothermal decomposition were researched. The results showed that the hydrothermal decomposition of biomass wastes was composed by the liquefaction, oily production and gasification according to different temperature region. The increase of reaction time and water volume and the decrease of grain size can promote the liquefaction of biomass wastes. The increased amount of H₂O₂ can realized the complete decomposition of biomass wastes by hydrothermal reaction.The saccharification of micro crystalline cellulose, maize straw, sawdust, rice husk and wheat bran under the hydrothermal conditions was carried out in batch reactors. The effect of reaction temperature, time, water volume, oxidant, acetic acid, ethanol, metal ions (Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺ and Cr³⁺) and sodium carbonate on the yield of reducing sugar were investigated. The optimal conditions for production of reducing sugar were obtained. The results indicated that 300-350℃in favor of the hydrothermal decomposition of biomass wastes to obtain reducing sugar. The yield of reducing sugar increased with increasing Na₂CO₃ for micro crystalline cellulose, maize straw and sawdust. For micro crystalline cellulose and sawdust, H₂O₂ could accelerate the production of reducing sugar. At the same time, the yield of reducing sugar increased much when adding acetic acid for micro crystalline cellulose. Furthermore, adding ethanol could increase the yield of reducing sugar and it reached the maximum 70.30% for maize straw. The yields of reducing sugar changed according to the difference of metal ions.As model compound, the hydrothermal decomposition of micro crystalline cellulose and glucose for the production of lactic acid under different conditions were discussed. To obtain a high yield of lactic acid by hydrothermal reaction, the influences of metal ions(Zn²⁺, Ni²⁺, Co²⁺ and Cr³⁺)on the reaction of biomass-relevant sugars such as maize straw, sawdust, rice husk and wheat bran were investigated. Based on the experimental data, the hydrothermal decomposition process and the catalyst’s mode of operation in this reaction network were investigated. In comparison with non-catalytic process, the addition of 400ppm Ni²⁺ catalyst increased the yield of lactic acid to 6.62% for micro crystalline cellulose. The lactic acid yield for glucose was achieved as 9.51% for 400ppm Co²⁺ catalyst. Compared with non-catalytic conditions, the lactic acid yield is 9.24% and 6.71%, respectively starting from maize straw and rice husk at 400ppm for Cr³⁺. Sawdust obtains the highest lactic acid yield 5.47% at Zn²⁺ 400ppm. But as for wheat bran, the highest lactic acid yield 7.46% is obtained under non-catalytic conditions. Hydrothermal reactions makes water a Bronsted base-acid and act as an effective catalyst and the metal ions represent Lewis base character. The conversion process occurs in a very complex network of parallel, consecutive and equilibrium reactions, and the last step being the catalyzed Cannizzaro-type reaction of pyruvaldehyde to lactic acid.The pyrolysis behavior and character of micro crystalline cellulose, maize straw, sawdust, rice husk and wheat bran were studied by thermo gravimetric analysis （TGA）.The kinetic parameters and model of pyrolysis biomass wastes were established. The experimental results showed that the decomposition of micro crystallite cellulose mainly occurred at the temperature range of 300-400℃.The weight loss（TG） and the rate of weight loss（DTG） shift to higher temperature region with the increase of heating-up rate. The thermal dynamics for biomass wastes was coincidence to the first order reaction dynamics by Coat-Redfern analysis. The Fourier transform spectrum （FTIR）, TGA, element, scanning electron microscopy （SEM）, X-ray diffraction （XRD） analysis indicated that the hydrothermal decomposition of micro crystallite cellulose was composed by low temperature hydrolysis and high temperature pyrolysis.更多还原