基于生物质原料特性的汽爆过程传递规律及其新工艺研究
文献类型：学位论文
| 作者 | 张玉针 |
| 学位类别 | 硕士 |
| 答辩日期 | 2012-05-29 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 陈洪章 ; 邱卫华 |
| 关键词 | 蒸汽爆破 生物炼制 传递过程 孔径分布 抑制物 |
| 其他题名 | Transfer laws and new technology of steam explosion based on biomass characteristics |
| 学位专业 | 化学工程 |
| 中文摘要 | 基于低压无污染汽爆技术，我们已成功建立了清洁制浆、大麻清洁脱胶、秸秆制备腐植酸和活性低聚木糖等一系列汽爆新工艺和产业化示范，并拓宽到粮食、果蔬等自然物料加工领域，以及生物基化学品、材料及能源的开发领域。汽爆技术已形成生物质炼制通用平台技术，但是目前尚未从生物质原料特性的角度对汽爆过程的传递规律及作用机理进行分析。本文在前期研究基础上，系统分析了原料参数、操作参数、设备参数以及产品参数对汽爆效果的影响个关系，揭示了汽爆过程高温蒸煮及机械撕裂作用机制。基于解除预处理过程带来的影响纤维素酶解的二次屏障作用的目的，研究了汽爆过程半纤维素和木质素降解、生成、溶出的热力学和动力学规律，以此开发了新型汽爆分梳二段工艺。论文取得的主要研究结果如下： 1)从传递角度分析了汽爆过程热质传递、动量传递及其细胞壁力学性能间的关系。探索了瞬时泄压阶段作用在物料上的最大耗散能与温度及含水率的关系，基于最大耗散能进一步优化出卸料口面积与物料颗粒尺寸间的关系。结果表明每个温度对应一个最佳含水率 且卸料口面积与物料颗粒尺寸关系为 ，此时作用在物料上的物料撕裂效果最佳，进一步将物料含水率、颗粒尺寸及卸料面积三因素丰富到汽爆强度因子R之中，丰富了汽爆强度的内涵，且为汽爆技术的工艺及设备设计提供指导。 2）从热量传递的角度，分析了汽爆过程的能耗组成及其相互关系；系统考察了初始物料含水率、汽爆罐高径比、装料系数和维压温度等四因素对汽爆能耗的影响，表明初始物料含水量影响最大，其次为维压温度和装料系数，罐体高径比对单位质量干基的耗汽量几乎无影响。优化出在罐体高径比3、装料系数100 kg/m3、物料初始含水率0.44、维压温度167 ℃条件下汽爆能耗最低值为0.1948kg蒸汽/kg干基。构建了常用汽爆条件下能耗检索表，为进一步的物料衡算和经济分析提供参考。 3）研究了汽爆秸秆孔径分布和酶解作用效果的关系，得出汽爆秸秆中微孔和中孔（尺寸为5-300nm）面积占总面积的92%以上，且酶解过程作用位点为微孔和中孔内，指出生物质预处理的目的应强化微孔尺寸的增加，而不再是简单的宏观表面积的增加。 4）基于温度梯度下的汽爆物料的半纤维素降解率、抑制物的产生率、酶解率以及孔径分析等，研究并验证了汽爆的作用位点，比较了汽爆处理中物理、化学作用对各指标的影响。结果表明物理作用为主的低温汽爆过程孔体积和孔面积均增大。而高温蒸煮过程中，中孔/微孔向孔隙/大孔转变，所以物理化学共同作用的高温汽爆过程中孔体积增大，孔面积减小。同时，高温蒸煮作用对物料孔隙率及渗透率的提高大于物理撕裂作用，再次说明高温蒸煮作用对细胞壁内填充物质的降解有助于打开中孔和微孔，提高物料的孔隙率及渗透率。此外，随着温度的升高，物料的孔面积下降但其酶解率升高，其原因为碳水化合物的暴露程度比孔面积对酶解率的影响大得多，碳水化合物的暴露比例显著升高，抵消了孔面积下降对酶解率的负影响，使得酶解率仍然上升。以上，揭示了影响物料酶解效果的主要因素和各自权重系数，为预处理技术的综合评价以及有针对性的强化物料酶解效果提供理论指导。 5）伴随预处理过程木聚糖在纤维底物上的吸附和残留以及酚类物质的生成，均构成后续酶解发酵的二次屏障作用。本文从热力学角度，分析了汽爆预处理中降解物的能量状态及溶出规律。结果表明离子强度越大、液固比越大，自由能 越负，汽爆降解物中可溶性分子的溶解越易发生，溶解率越大。且酚类分子的溶出为吸热过程，糖类分子的溶出为放热过程。因此，低温（常温）水洗汽爆物料即可实现糖类分子的最大溶出或者酚类物质的最小溶出，从溶出过程即可实现糖类和酚类物质的分级分离，省去后续发酵工业的脱毒程序。从动力学角度，分析了汽爆预处理过程中的10类潜在抑制物的生成规律，推导计算出汽爆过程中抑制物生成率方程及其生成率—时间---温度关系，可以预知和计算不同汽爆条件下抑制物产生率，为实现人为调控汽爆的温度和时间并选择性的避免或增加某种抑制物提供理论依据和参考。 6）基于生物质物料结构组织的不均一性，解析了发酵抑制物生成的原因及二段分梳汽爆工艺构建的必要性。建立的新型汽爆分梳二段工艺，结果表明，在1.1MPa/4min-分梳-1.2MPa/4min的条件下，纤维组织和薄壁组织的分离度可达1.6，与一段汽爆（1.2MPa/8min）相比，抑制物含量降低了33%，发酵产物2,3-丁二醇含量提高了209 %。二段汽爆分梳方法，从源头上优化了木质纤维素水解工艺，控制抑制物的产生，降低其含量，省去了脱毒单元操作的引入，简化了工艺。 |
| 英文摘要 | Based on un-polluted steam explosion technology, we have successfully established a series of new technologies and industrialization demonstration projects, such as clean pulping, clean degumming of marijuana, preparation of humic acid and activity xylo-oligosaccharides by straw and so on, and broaden this thchnology to the natural materials processing areas, and bio-based chemicals, bio-based materials and bio-based energy development areas. Steam explosion has formed the common platform technology for biomass refining, but transfer laws and mechanisms of steam explosion has not analysed from the perspective of the biomass characteristics up to the present. Based on the previous research results, this paper systematic analysed the effects of the raw materials parameters, operating parameters, equipment parameters and product parameters on steam explosion, and revealed the mechanisms of temperature cooking and mechanical tearing in steam explosion process. Based on the purpose of eliminating the secondary barriers which were formed in pretreatment processes, the thermodynamics and kinetics of degradation, formation and dissolution of hemicellulose and lignin in steam explosion process were studied, and based on which, a novel steam explosion carding process was developed. The main results obtained in the paper were as follows: 1) Heat transfer, mass transfer, momentum transfer and the relationships with mechanical properties of cell wall in steam explosion process were analysed. The maximum dissipation energy and relationships between temperature and moisture content in instantaneous decompression stage of steam explosion were explored, and the relationship between particle size and the discharge port were further optimized based on the maximum dissipation energy. Results showed that each temperature corresponded with an optimal moisture content , and the relationships of the discharge port area and particle size were , on which occasion tearing effects ofs material reached the best. Furtherly, moisture content of materials, particle size and discharge port area were included in steam explosion strength factor R. Enriched strength factor R provided a guidance for process and equipment design of steam explosion. 2) Based on heat transfer, compositions and mutual relations of the energy consumption in steam explosion process were analyzed. The effects of four factors, such as the initial moisture content of materials, ratio of tank height to diameter, the loading coefficient and holding temperature, on energy consumption were systematically investigated. Results showed that the initial moisture content had the greatest effect on energy consumption, followed by holding temperature and loading coefficient, and the ratio of tank height to diameter almost had no effect on it. Under the conditions of holding temperature 167 °C, the ratio of tank height to diameter 3, loading coefficient 100kg/m3 and initial moisture content 0.44, the energy consumption of steam explosion reached the minimum value 0.1948kg steam/ kg dry basis. An index table of energy consumption in common steam explosion condition was established, which provided a reference for further material balance and economic analysis. 3) Pore size distribution of steam-exploded straw and its relationships with the enzymatic hydrolysis effects were studied. Results showed that micropores and mesopores (size 5-300nm) in steam-exploded straw accounted for more than 92% of the total area, and the locations of enzymatic hydrolysis were in micropores and mesopores. By these, it’s known that pretreatment of biomass should aim to increase the areas of micropores and mesopores, rather than simply increase the macroscopic surface. 4) Based on the analysis of hemicelluloses degradation yield, inhibitors production yield, enzymatic hydrolysis yield and pore size distribution of materials by gradient temperatures steam explosion, the action location of steam explosion was researched. And physical and chemical effects of on various indicators in steam explosion process were compared and analyzed. Results show that pore volume and pore area both increased in low-temperature steam explosion process which based on physical roles. In the process of high-temperature cooking, mesoporous/microporous transferred to macropores/cracks, so pore volume increased and pore area decreased in high temperature steam explosion process which combined both physical and chemical effects. Besides, the effect of improvement material porosity and permeability in the process of high temperature cooking was greater than which in physical tearing, which showed again that degradation of hemicelluloses and lignin in cell wall in high-temperature cooking process were help to open the porous, which improved the material porosity and permeability. In addition, with the increasing of temperature, pore area decreased but the enzymatic hydrolysis yield increased. Reasons for these were the effects of proportion of carbohydrate exposure were much greater than that of the pore area on the enzymatic hydrolysis yield, and the significantly increasing of carbohydrate exposure proportion offset negative impact of pore area decreasing on enzymatic hydrolysis. Above these, revealed the main factors affecting enzymatic hydrolysis and their weight coefficients, provided theoretical guidances for the comprehensive evaluation the pretreatment technologies and purposefully strengthen enzymatic hydrolysis of materials. 5) Adsorption of xylan on lignocellulosic substrates and formation of phenolic compounds along with pretreatment process, both constituted the second barrier to subsequent enzymatic hydrolysis and fermentation. From the viewpoint of thermodynamics, the energy states and dissolution law of degradation products in steam explosion pretreatment were analyzed. Results showed that the greater the ionic strength and the ratio of liquid to solid, the more negative the free energy, then the dissolution of soluble molecules the steam explosion degradation products were more likely to occur and the greater the dissolution yield. Besides, dissolution process of phenolic compounds was an endothermic process, and dissolution of process of sugars was an exothermic process. Therefore, washing steam-exploded materials in low temperature (may be at room temperature) would realize the maximum dissolution of sugars and/or the minimum dissolution of phenolic compounds. Fractionation of sugars and phenolic compounds from the dissolution process could be realized, which eliminated the need for detoxification process in subsequent fermentation industry. Based on kinetic points, formation law of 10 types of potential fermentation inhibitors in steam explosion process was analyzed. And formation equations of inhibitors in steam explosion process were deduced and calculated, which would help for predicting and calculation inhibitors conversions at different steam explosion conditions, and provided a theoretical reference for purposefully controlling the temperature and time of steam explosion to avoid or decrease inhibitors. 6) Based on the heterogeneity of lignocellulosic biomass, formation reasons of fermentation inhibitors and the need for building two-step steam explosion carding process were analyzed. Results showed that under the conditions of 1.1MPa/4min-carding-1.2MPa/ 4min, the separation degree of fibrous tissue and parenchyma was up to 1.6. Compared with control group (1.2 MPa/8min), inhibitor content decreased by 33%, and fermentation product 2,3 - butanediol increased by 209%. Two-step steam explosion carding process, optimized of lignocellulose hydrolysis process from the source, controlling inhibitors generation and reducing its content, eliminated the need for detoxification unit operations and simplified the process. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1814]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 张玉针. 基于生物质原料特性的汽爆过程传递规律及其新工艺研究[D]. 中国科学院研究生院. 2012. |
入库方式： OAI收割
来源：过程工程研究所
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