【作者】 刘武军；

【导师】 江鸿； 俞汉青；

【作者基本信息】 中国科学技术大学 ， 应用化学， 2014， 博士

【摘要】 植物通过自身的生长,可以从富营养化水体中吸收氮磷营养元素,而通过生物吸附过程,又可以吸附水中的重金属等污染物。但是,富含污染物的植物生物质若处理不当,容易造成二次污染。另一方面,随着化石能源的日益耗竭,以及其在使用过程中造成的一系列环境和气候问题日益引起人们的重视。从可再生、环境友好的生物质中获取能源及资源已经成为研究热点,并且具有十分广阔的应用前景。快速热解是一个极具应用潜力的生物质资源化成熟技术,如果将其应用于对污染生物质的处置及资源回收,将会具有重要的环境和经济意义。本论文系统研究了植物生物质在污染物去除和热解资源化应用中的一些基础问题,包括生物质表面化学修饰强化污染物去除,污染物在热解过程中迁移转化的机理,热解生物油提质的绿色可持续方法研究,热解biochar功能化制备及其在环境、催化及能源储存方面的应用。论文主要的研究内容和结果如下：1.生物质的表面化学修饰强化污染物的去除：以二氯亚砜作为活化剂对EDTA进行活化,再将其用于蒲草生物质的表面化学修饰,以增加其表面羧基和氨基功能基团的含量,从而强化其对污染物的去除能力,并对污染物强化去除的相关机制进行了探讨。结果表明,经过表面修饰的生物质对水溶液中的铅离子具有显著强化的去除能力,其最大吸附能力达到263.9mg/g。远远大于未经修饰的生物质的104.5mg/g。吸附机理主要涉及到离子交换、配位和氢键作用,其中离子交换作用主要是在低pH条件下起作用,而配位和氢键作用主要在高pH值条件下发挥作用。2.生物质热解过程中污染物的迁移转化过程及其机理：将吸附了重金属铅的蒲草生物质进行热解,分析了热解过程中重金属铅的迁移,转化和分布情况。结果表明,热解过程中铅的回收率受温度的影响不明显；在整个热解过程,温度从400℃升高至600℃时,铅的回收率为98.8%以上,发现铅的化合物在热解过程中转化为挥发性很弱的氧化铅和金属铅而保存在热解残炭固相中。以三种典型的富氮磷湿地植物为代表,研究了热解过程中氮磷营养元素的迁移转化过程及其机理。结果显示,热解所得生物油的主要成分包括酚类、醛酮类、羧酸类以及一些含氮杂环或者胺类化合物。在热解过程中,大量的氮磷元素从有机态转化为无机离子态或者结合态,仍然集中在biochar中,可通过无机盐溶液浸出的方法分级提取,其中平均76%的氮元素和57%的磷元素可以通过此法得以回收。将生物质和废弃电子垃圾塑料以一定的比例进行混合进行共热解,研究了热解过程中溴化阻燃剂的迁移,转化过程以及溴元素在热解过程中的分布情况,通过TG-FTIR-MS方法对溴化阻燃剂的转化机理进行了深入的研究。结果显示,生物质和WEEEs塑料在热解过程中的协同作用可以大大提高热解油的产率。机理分析表明,热解过程中产生的溴元素既可以被有机组分捕获形成溴代烃类挥发至热解油和气体相中,也可以被WEEEs塑料和生物质中的无机组分捕获而保留在热解残炭中。3.生物油品质提升及其机理研究：提出在常温常压的情况下以零价活泼金属锌对生物油进行原位氢化的方法。结果表明,金属锌对于生物油体系表现出良好的反应性能,可以显著改善生物油的性质,包括降低腐蚀性与提高稳定性和热值等。新生成的主要形成机理包括醛酮类的直接氢化、生成的醇类和生物油中有机酸的酯化以热解木质素碎片的氢化反应等。直接热解具有催化作用的重金属铜负载的生物质,通过铜在热解过程的催化作用,使得热解生物油的产率和品质有显著的提升。结果表明,铜催化所产生物油中所含的芳香化合物比普通生物油的芳香化合物含量大为增加。机理分析表明,铜的存在能促进生物质中木质素组分的分解,从而产生大量的芳香化合物。热解过程中,超过90%的铜元素富集在热解残炭中,并可以通过灼烧的方法加以回收。4.以生物质作为原料,通过热化学方法合成功能碳材料：以废弃木屑生物质为原料,从海水中吸附氯化镁,再进行热解合成介孔碳负载的氧化镁纳米颗粒,并将合成的材料用于二氧化碳的捕集。材料对二氧化碳的最大捕集量可以达到5.45mol/kg。二氧化碳的捕集机理主要涉及物理吸附和化学相互作用,其中的物理吸附作用随着温度的升高而减弱,而化学相互作用主要包括氢键作用以及二氧化碳和氧化镁的化学反应,是二氧化碳捕集的主要贡献。将生物质吸附一定量的氯化铁,通过快速热解获得磁性多孔碳材料,以此为前体,通过磺化反应合成磁性固体酸材料,并将其用于催化有机反应。结果表明,氯化铁的存在可以催化促进热解过程中碳材料的微孔和介孔的生成,而以此法合成的磁性固体酸具有高比表面积和酸强度,并且具有易分离性,高催化活性和循环稳定性。以富氮的湿地植物蒲草为原料,通过快速热解和KOH活化的方式,合成氮掺杂的多孔碳材料,并将其作为超级电容器的电极材料,研究其电化学储能特性。结果显示,合成的氮掺杂多孔碳材料比表面积可达到3000m2/g以上,具有良好的电容性能,其比电容最大能达到257F/g,并且具有优异的循环稳定性,可以稳定循环使用6000次。更多还原

【Abstract】 The plants can construct their fronds by absorbing the nitrogen and phosphorus from the eutrophicated water body, and adsorb heavy metals from the polluted water through biosorption process. However, after these processes, the pollutants are usually enriched in the plant biomass, and may cause secondary pollution problems if the pollutant-enriched biomass is mishandled. On the other hand, due to depletion of fossil energy, and the environmental and climate problems caused by the use of fossil energy, it urgently needs to recover energy and resource from the renewable and environmentally friendly biomass. As a mature and promising technique for the recovery of energy and resource from biomass, it will be great environmental and economical significance if the fast pyrolysis can be used for treating the polluted biomass.In this thesis, the enhanced removal of pollutants by biomass, as well as the migration, transformation, and distribution of pollutants during the fast pyrolysis of biomass were investigated systematically. The mechanism for the migration and transformation of the pollutants during biomass pyrolysis process was explored. Based on the above results, we developed two sustainable methods for the upgrading of bio-oil, and applied the biomass as raw materials to synthesize a series of functional carbon materials and explore their applications in the fields of environment, catalysis, and energy storage. The main contents and results of this thesis are as follows:1. Surface modification of the biomass to enhance the pollutant removal. A chemically modified Typha angustifolia biomass material with abundant carboxyl and amino groups was prepared using SOCl2-activated EDTA as a modification reagent. The results indicate that the chemical modified biomass exhibited significantly enhanced removal ability towards Pb in wastewater, and the maximum adsoption capacity reached263.9mg/g, much higher than that of the raw biomass (104.5mg/g). The main mechanisms involved in the Pb removal process included ion-exchange, complexation, and hydrogen binding interactions, among which the ion-exchange mainly occurred at a low pH, while the complexation, and hydrogen binding interactions contributed mainly at a high pH. 2. Migration and transformation of the pollutants in the fast pyrolysis of biomass as well as the related mechanism. The migration, transformation and distribution of Pb in the fast pyrolysis of Pb polluted biomass were investigated. During the whole pyrolysis process, when the temperature was increased from400to600℃, the Pb recovery efficiency exceeded98.8%. The main mechanism for this phenomenon is that during the pyrolysis process, the adsorbed Pb was transformed to PbO and metallic Pb, which could not volatilize and remained in the char phase.The migration and transformation of N and P in the fast pyrolysis of three typical N-and P-enriched wetland plants were studied. The main compositions of the obtained bio-oil included phenols, aldehydes, ketones, carboxylic acids, and nitrogen-containing heterocyclic compounds. In the pyrolysis process, a large amount of the organic N and P was converted to inorganic forms and remained in the biochar, which could be recovered by leaching. In average,76%of N and57%of P could be recovered in this case.The biomass and plastics of electronic waste were mixed in a certain ratio and co-pyrolyzed, and the fate of brominated flame retardants (BFRs) in the co-pyrolysis process was studied in detail. The mechanism for the transformation of BFRs was further investigated by the TG-FTIR-MS technique. The results show that The synergistic effects between the plastics and biomass can significantly improve the yield of bio-oil. As the mechanism analysis shows, the Br radicals formed in the pyrolysis process can be either captured by the organic species to form brominated hydrocarbons and release to the bio-oil or gas phases, or captured by the inorganic species and remained in the char phase.3. The upgrading of bio-oil and its mechanism. A green method for bio-oil upgrading at ambient pressure and temperature through in-situ hydrogenation by the zero-valent Zn was proposed. The results indicate that zero-valent Zn showed favorable reactivity in the complex bio-oil system, which ccould significantly improve the property of bio-oil, including decreased corrosivity, and increased heating value and stability. The formation mechanism of13newly formed compounds in the upgraded bio-oil involved the direct hydrogenation of aldehydes and ketones, esterification of alcohols and organic acids, and hydrogenation of the fragments of lignin.A new method for selectively improve the quality of bio-oil with Cu catalysis in the pyrolysis of Cu preloaded biomass was developed. The results indicate that the mono-aromatic compounds contents in the Cu catalytzed bio-oil were greatly higher than those in the non-catalyzed bio-oil. The main mechanism for this phenomenon is that the presence of Cu could promote the decomposition of lignin in the biomass, which minght produce various mono-aromatic compounds. After pyrolysis, more than90%of the preloaded Cu was enriched in the biochar phase, which could be easily recovered by a calcination method.4. Synthesis of functional carbon materials by the thermochemical methods using the biomass as raw materials. The waste sawdust biomass was used as adsorbent to adsorb MgCl2from seawater to obtain the MgCl2preloaded biomass, was then pyrolyzed to synthesize mesoporous carbon stabilized MgO NPs, which was further used for CO2capture. The maximum CO2capture capacity of the as-synthesized material was5.45mol/kg. The mechanism involved in the CO2capture process included physical adsorption and chemical interaction, among which the physical adsorption was weaken with the increase in temperature, while the chemical interaction contributed mainly to the CO2capture, which included hydrogen binding and the reaction between CO2and MgO.A magnetic porous solid acid material was synthesized by pyrolysis and then sulfonation of FeCl3preloaded biomass. The as-synthesized material was used as a catalyst for the organic reactions. The results indicate that the presence of FeCl3could catalyze the formation of the porous structure in the pyrolysis process. The magnetic solid acid had a high acid strength and large surface area, which exhibited a high catalytic activity, favorable separability and cycle stability.The nitrogen-doped porous carbon materials were synthesized from an N-enriched wetland plant biomass by a simple fast pyrolysis and KOH activated method. The as-synthesized materials were used as electrode materials for supercapacitor, and their energy storage performance was evaluated. The as-synthesized materials had porous structure with a surface area higher than3000m2/g, and exhibited favorable performance as a supercapacitor with a high capacity (257F/g), large energy and power density (19.0Wh/kg), and could be reused6,000cycles without significant loss of the capacity.更多还原