【作者】 杨静；

【导师】 戴立益；

【作者基本信息】 华东师范大学 ， 物理化学， 2017， 博士

【摘要】 化石能源是一种储备有限且不可再生的资源,世界范围内不断增长的人口以及不断加快的经济发展加剧了化石能源的消耗,能源枯竭不可避免;化石能源在使用过程中会释放大量的温室气体,对全球生态造成威胁。生物质能源因具有储量高、可再生、无二氧化碳排放等优点,被认为是一种潜在的化石替代能源。大力发展生物质能源已成为许多国家的重要发展战略。木质素是生物质能源的重要组成部分,是世界上仅次于纤维素的第二丰富的有机物,然而在造纸工业中木质素往往作为副产物被大量浪费,因此,如何将木质素转化为人类可利用的能源成为了摆在科学家们面前的难题。相比于传统的木质素转化方法(热解和气化),超临界降解是一种木质素转化的有效且快捷的方法。该方法不需要对木质素进行前处理,液化获得的生物油品质较高,还可得到芳烃和单酚类等高附加值化学品。但目前关于在超临界水/醇体系中降解木质素的研究大多局限于提高液态生物油的产率,而对液化获得的主要产物的形成途径、高附加值化学品选择性提升、气态产物分析以及气液产物分布关系鲜有涉及,亟待深入研究。基于以上想法,本论文尝试选取不同的催化剂在不同的超临界体系中催化碱木质素降解,对影响液态产物分布的因素进行探讨。依据获取液态产物的分布,推测主要产物的形成过程,提出碱木质素在超临界体系中的催化降解路径;选择适合于超临界体系的高效催化剂以获取高产率与高选择性的高附加值化学品;通过对液态产物组份随气态产物中氢气选择性和产量的变化趋势的分析,探究液态产物分布与气态产物选择性之间的对应关系。主要研究内容及成果如下:1、超临界异丙醇体系中碱木质素的醇解反应研究。探讨了碱木质素在超临界异丙醇体系中的醇解反应,考察了反应温度(270-350℃)、反应时间(1-5 h)、碱木质素与异丙醇的质量比(1-5wt%)对醇解反应过程的影响,得到了获取最高生物油产率及热值的反应条件为350 ℃反应温度、4 h反应时间和1 wt%木质素加入量。在探究反应温度对液态产物分布的影响规律中发现,高温条件有助于生物油中含两个或两个以上氧原子的愈创木酚和儿茶酚类化合物转化为含有单个氧原子的烷基酚类化合物,为进一步分析高效催化剂对碱木质素降解的催化活性奠定良好的实验基础。2、超临界异丙醇体系中贵金属催化剂催化碱木质素的醇解反应研究。采用正交试验的方法考察了反应温度(270-350 ℃)、反应时间(1-5 h)、碱木质素与异丙醇的质量比(1-3wt%)、贵金属催化剂(Pd/C、Pt/C、Ru/C、Rh/C)、催化剂/碱木质素质量比(10-50 wt%)对碱木质素在超临界异丙醇体系中醇解反应的影响。结果表明,反应温度与催化剂的种类是影响生物油产率及热值的最主要因素。在330 ℃和350 ℃两个反应温度条件下对五种催化剂催化碱木质素降解过程进行了进一步分析,依据催化条件下溶剂异丙醇的稳定性、对含氧链状化合物形成的抑制作用和酚类化合物的加氢脱氧效果判断Rh/C是获得高热值生物油的最优催化剂;通过对比液态生物油与超临界异丙醇热解液态产物组分的区别,推测了含氧链状化合物和环己醇/酮类化合物的形成过程,提出了碱木质素在超临界异丙醇体系中的催化降解路径。3、超临界醇/水体系中多功能负载型催化剂Rh/La2O3/CeO2-ZrO2催化碱木质素的降解反应研究。采用多功能负载型催化剂Rh/La2O3/CeO2-ZrO2催化碱木质素在超临界乙醇体系中的降解,分析了催化剂对液态产物和气态产物分布的影响,实验获取了高选择性的芳香醇类化合物(57%)和氢气(82%);考察了该催化剂催化降解木质素的循环使用性,对比使用前后的催化剂发现,载体团聚、贵金属的流失和积碳率的升高均有可能导致催化剂的失活。测试了催化剂在超临界水/甲酸、甲醇、异丙醇中的催化性能,研究发现在前两种体系中液态产物无苯环加氢饱和现象出现,而在超临界异丙醇体系中得到的液态产物中苯环发生加氢饱和形成了大量的加氢环状化合物;与超临界乙醇体系获得的氢气选择性相比,超临界水/甲酸和甲醇体系中氢气选择性较低,而超临界异丙醇体系中氢气选择性最高。综合考虑液态产物与气态产物,负载型催化剂在超临界乙醇体系中活性最大。4、超临界醇/水体系中碱木质素催化降解的液态产物分布与气态产物选择性的对应关系研究。选取超临界异丙醇/水作为介质进行碱木质素的液化,通过调节异丙醇与水的体积比来达到调节气态产物选择性与产量的目的,实验发现液态产物分布随氢气选择性(93%-77%)和产量(48.95-0.44mmol)呈现有规律变化。为了进一步扩大氢气选择性的可调变范围,在不同的异丙醇/水体积比的体系中引入甲酸,将氢气选择性范围扩大至35%-90%,而氢气的产量调变范围变化不大(38.63-0.65 mmol)。通过对液态产物分布随气态产物选择性的变化趋势分析,发现气态产物中氢气的选择性与液态产物分布之间存在对应关系。考察不同温度、溶剂以及催化剂条件下碱木质素降解获得的液态产物与氢气选择性,发现上述对应关系具有良好的普适性。更多还原

【Abstract】 With the growth of worldwide population and development of economy,the demand for fossil energy is increasing,while the fossil energy is non-renewable with limit storage on the earth.As a result,the exhaustion of fossil energy is inevitable.Meanwhile,the use of it will release a large number of greenhouse gases,which is a threat to global ecology.Biomass energy is considered to be a potential alternative fossil energy because of its high reserves,renewable and no carbon dioxide emissions.The development of biomass energy has become an important development strategy for many countries.Lignin is one of the most important components of biomass energy,which is the second most abundant organic compound in the world.Unfortunately,it is a great waste in the paper industry as a by-product.Therefore,how to convert lignin into available energy has become a difficult problem for scientists.Compared to the traditional treatment of lignin(pyrolysis and gasification),supercritical degradation is an effective and rapid method for lignin conversion.It is because the process of liquefaction not only do not need to pretreat lignin,but also can obtain high quality bio-oil and high value-added chemicals like aromatic hydrocarbons and phenolic compounds.However,there are a lot of researches on the topic of improving the bio-oil yield for the liquefaction of lignin,and only a few researchers put their attention on the fundamental reaction pathway,the selectivity of high-value chemicals,gaseous products distribution and gas-liquid product distribution relationship in present.In my opinion,the later is more significant and meaningful.Based on the above considerations,this paper tried to select different catalysts to degrade kraft lignin in different supercritical systems and discuss how the factors affected the distribution of liquid products.According to the distribution of the liquid products,the formation process of the main components was speculated,and the catalytic degradation path of kraft lignin was put forward in supercritical system.The high efficient catalyst was selected for the supercritical system in order to obtain high value-added chemicals with high yield and high selectivity.Based on the analysis of the variation trend of liquid product composition along with H2 selectivity and yield,the relationship between liquid product distribution and H2 selectivity was investigated.The main work and results were summarized as follows:1.The study of the alcoholysis reaction for kraft lignin in supercritical isopropanol.The alcoholysis reaction of kraft lignin in supercritical isopropanol system was discussed,and the effect of the reaction temperature(270-350 ℃),reaction time(1-5 h)and the mass ratio of kraft lignin to isopropanol(1-3 wt%)on liquefaction process were studied.The optimal reaction conditions(350 ℃ reaction temperature,4 h reaction time,1 wt%lignin concentration)were proposed for the highest bio-oil yield and heating value.By exploring the influence of reaction temperature on liquid products distribution,a conclusion could be drawn that high temperature conditions were conducive to the conversion between guaiacol/catechols(containing two or more oxygen atoms)and alkylphenolic compounds(containing a single oxygen atom),which laid a good experimental foundation for further analysis of catalytic depolymerization of kraft lignin.2.The study of the alcoholysis reaction catalyzed by noble metal catalyst for kraft lignin in supercritical isopropanol.The effect of reaction temperature(270-350℃),reaction time(1-5 h),the mass ratio of kraft lignin to isopropanol(1-3 wt%),noble metal catalysts(Pd/C;Pt/C;Ru/C;Rh/C)and the mass ratio of catalyst to kraft lignin(10-50 wt%)on the liquefaction process of kraft lignin were researched by orthogonal array design(OAD)in supercritical isopropanol.The results showed that the reaction temperature and the kind of catalysts were the main influence factors in the yield and heating value of bio-oil.The degradation process of kraft lignin catalyzed by five kinds of catalysts was further analyzed at 330 and 350 ℃,a conclusion was drawn that Rh/C was the optimal catalyst for obtaining high HHV bio-oil base on the analysis for the stability of isopropanol,the inhibition of the formation of oxygen-containing chain compounds and the effect of the hydrogenation of phenol compounds under the catalysis conditions.By comparisons between bio-oil and liquid products from sole isopropanol depolymerization in high temperature,the formation process of oxygenic-chain compounds and cyclohexanol/ones was deduced presumably.The catalytic degradation pathway of kraft lignin in supercritical isopropanol was proposed.3.The study of the depolymerization catalyzed by multi-functional supported catalyst Rh/La2O3/CeO2-ZrO2 for kraft lignin in supercritical alcohol/water system.The effect of the catalyst Rh/La2O3/CeO2-ZrO2 on liquid products and gaseous products distribution were analyzed during degradation of kraft lignin in supercritical ethanol system.The degradation reaction obtained high selectivity of aromatic alcohols(57%)and H2(82%).The reusability of catalyst was investigated and catalyst deactivation was discovered.By comparison between the fresh and the used catalyst,the carrier aggregation,the loss of precious metals and the increase of carbon deposition rate were observed.The performance of the catalyst was also tested in supercritical water/formic acid,methanol,isopropanol system,and it was found that none hydrogenation of benzene ring saturation appeared in the previous two systems and a large number of cyclic compounds formed from the hydrogenation of benzene ring in supercritical isopropanol system.Compared with the H2 selectivity in supercritical ethanol system,the supercritical water/formic acid and methanol system was lower,and the supercritical isopropanol was the most.Considering the liquid and gaseous products distribution,the supported catalyst showed the highest activity in the supercritical ethanol system.4.The study of the corresponded relationship between the liquid products distribution and the selectivity of gaseous products obtained from kraft lignin depolymerization in supercritical alcohol/water system.Supercritical isopropanol/water system was chosen as the medium for the liquefaction of kraft lignin.By adjusting the volume ratio of isopropanol to water to regulate the selectivity and yield of gaseous products,it was found that the distribution of liquid products changed regularly with H2 selectivity(93%-77%)and yield(48.95-0.44 mmol).In order to further expand the adjustable range of H2 selectivity,formic acid was introduced into supercritical isopropanol/water systems.The selectivity of H2 expand from 35%to 90%,but there was little change in the yield of H2(38.63-0.65 mmol).Based on the analysis of the variation trend of the liquid products distribution with the gaseous product selectivity,the relationship between the liquid product distribution and H2 selectivity was proposed.The corresponded relationship between liquid products distribution and H2 selectivity was checked in the different temperature,solvents and catalysts,and it was found that the relationship was good applicability.更多还原