【作者】 路瑶；

【导师】 魏贤勇；

【作者基本信息】 中国矿业大学 ， 化学工艺， 2013， 博士

【摘要】 随着化石能源的价格上涨和日益枯竭以及人类对环保越来越重视，寻找合适的替代能源是实现可持续发展的必经之路。生物质能源以储量丰富、洁净和可再生等优势，逐渐成为研发与应用的重要目标。然而，目前的生物质利用技术主要基于生物降解和热化学降解，普遍存在能耗高、成本高、反应条件苛刻和不易控制、残渣多、资源浪费和污染环境等问题，亟需开发生物质降解利用新途径。本文选取稻壳（RHP）和麦秆（WSP）作为生物质原料，旨在开发在温和反应条件下实现生物质降解的新方法。以NaOCl水溶液为氧化剂，对两种生物质进行逐级氧化降解，并对降解产物进行详细分离分析与表征，获得稻壳和麦秆降解产物的组成信息，分析各级氧化残渣的成分与形貌以佐证降解产物成分分析，并推测所选生物质分子结构以及氧化降解反应机理。在RHP和WSP的逐级氧化的各级萃取物中检测到多种产物，分为烷烃、芳烃、醛类、酮类、酚类、有机酸、酯类和含氮化合物以及少量烯烃和醇等其它化合物。其中，有机酸、酯类和酮类的含量较高。烷烃是蜡质的降解产物。芳烃、苯甲醛类和酚类化合物可能源于木质素的降解。酮类化合物种类较为丰富，主要有呋喃酮、环烷酮、吡喃酮、烯酮和含苯酮类化合物，其中前三类可能来自于半纤维素或纤维素的氧化降解。有机酸主要有邻苯二甲酸、苯甲酸和脂肪酸。长链脂肪酸可能来自油脂中，也可能是蜡质经NaOCl氧化而成。邻苯二甲酸酯和脂肪酸苯基酯可能是生物质中木质素与蜡质层的连接结构。含氮化合物可分为胺类、氮杂环化合物、腈类、氨基化合物及磺胺等，前两者种类丰富、含量高。在萃取物中检测到的醇类和烯烃极少，可能被NaOCl所氧化。其它化合物主要包括甾烷（或醇和酮）、杂氧烷、醚类和含硫化合物。温和条件下的溶剂分级萃取可将RHP和WSP中的可萃取物提取分离。生物质在溶剂萃取过程中，可能发生组成和结构上的改变，进而影响其在后续加工利用中的转化历程。在萃取物中检测到的有机化合物分为烷烃、烯烃、芳烃、醛、酮、醇、酯、呋喃、含氮化合物、有机酸和甾族化合物。其中，甾族、烷烃和酮类化合物是所检测化合物中种类最丰富、含量最高的化合物。甾族化合物在可萃取物中的相对含量均超过60%，主要包括胆甾烯酮（或烷、醇）和豆甾烯酮（或烷、醇）。长链的烷烃、烯烃和醛类化合物可能来自于稻壳的蜡质层。甾族化合物大多是重要的地球生物标志物，可作为合成药物和有机化学品的原料，用于治疗疾病等。芳烃可能是木质素的降解产物。烷基呋喃类化合物可能来源于半纤维素，而苯并呋喃可能源于木质素。此外，还检测到了维生素E等。因此，可在温和条件下采用简单的溶剂萃取即可从生物质获取甾族化合物。RHP和WSP的萃余物经逐级氧化，对产物的各级萃取物的FTIR分析和GC/MS分析均与非萃取RHP和WSP原料逐级氧化所得化合物种类分布相近；然而产物总体种类和含量与之明显不同。在萃余物各级萃取物中所检测到的化合物包括烷烃、芳烃、酚类、醛类、酮类、有机酸、酯类及其它化合物。其中以短链脂肪酸为主的有机酸含量最高，其次是酮类化合物含量也较高。甾族化合物和烷烃等大多难溶于水，可能会抑制RHP和WSP在NaOCl水溶液中的直接氧化降解。经溶剂分级萃取可将上述化合物萃取分离，与RHP和WSP本身相比，分级萃取后组成结构发生变化，所得萃余物在NaOCl水溶液中更容易氧化降解，产物的组成更简单，氧化进行更为彻底；通过分级萃取后续的逐级氧化既可以使稻壳和麦秆有效降解，又有助于深入了解RHP和WSP中有机质的组成结构。从各原料至各级氧化残渣，随着氧化级数的增加，残渣中的C、H、N和S元素含量均显著降低，H/C也显著降低。萃余物第三级氧化残渣中，C和H含量分别降低到2.63%和1.55%以及7.10%和1.93%，其它成分多为无机矿物质。SEM直接显示有机质在逐级氧化降解过程中的层次性，纤维素和半纤维素首先被降解，随后是构成植物细胞壁骨架结构的木质素，最终这些有机质大多被降解分离，剩余残渣为散乱分布的矿物质。EDS分析结果显示各级氧化残渣中主要存在Si、C和O元素。随着氧化级数的增加，残渣中C元素含量显著降低，最终几乎全部消失，剩余无机残渣可能是SiO2。对残渣的系统分析结果与液相产物的各级萃取物的GC/MS和FTIR分析结果具有很好的一致性。溶剂萃取预处理对生物质逐级氧化的影响也得到印证。NaOCl水溶液可对RHP和WSP生物质的降解过程可能基于多种自由基的氧化反应机理。纤维素的降解过程经历醚键断裂、糖单体开环、重新成环或断裂，生成呋喃、呋喃酮、环烷酮或短链脂肪醇、醛、酮或酸等小分子化合物。半纤维素的氧化降解过程与纤维素类似。NaOCl可有效降解木质素，不仅能使苯环间的芳醚键断裂生成各种羟基、甲氧基和烷基取代的芳香族化合物，甚至能够氧化苯环结构，生成苯醌中间体，进而生成邻苯二甲酸。根据氧化产物各级萃取物的成分分析以及归类总结，可获得生物质中木质素单体的组成类型、比例，再根据单体间连接方式出现的频率，提出了稻壳木质素的结构模型。CS2对含氮化合物、醛、酮、羧酸和酯类化合物具有很好的富集作用，尤其是对酰胺和吡咯烷酮而言，可能是以内CS2中的C=S键与含氮化合物中的C=O键之间强烈的π-π相互作用。NaOCl逐级氧化可快速有效地将RHP和WSP中纤维素、半纤维素和木质素降解为小分子化合物，具有反应条件温和可控、能耗低、成本低和产物附加值高等优势，为揭示生物质分子结构和氧化降解机理提供科学依据，可作为生产高附加值化学的原料，是农作物秸秆和农业废弃物开发利用的可行途径。更多还原

【Abstract】 Biomass is acknowledged as the largest feedstock for the renewable energy, fuels andchemicals, and possesses advantages such as clean and renewable. The methodologies used forthe degradation of biomass are based on biochemical and thermochemical techniques; however,inferiorities such as high energy consumption, high cost, harsh production conditions, highresidue, complicated subsequent treatments, waste of precious components and environmentalpollution are rising to restrict the further development of those techniques. New methods for thedevelopment of utilization of biomass are necessary.Rice husk (RHP) and wheat straw (WSP) were degraded with sequential oxidation of NaOClaqueous solution under mild reaction conditions. The reaction products were analyzed by thecombination of sequential solvents extraction and gas chromatography/mass spectrometer(GC/MS). The residues from sequential oxidation were also analyzed with ultimate analyzer,Fourier transformed inferred spectrometer (FTIR), scanning electronic microscopy (SEM) andX-ray energy dispersive spectroscopy (EDS).The species identified in the extracts from sequential oxidation of RHP and WSP wereclassified as alkanes, arenes, aldehydes, ketones, phenols, carbonic acids (CAs), esters andnitrogen-containing organic compounds (NCOCs), as well as some alkenes and alcohols, etc.Among these groups of species, CAs, esters and ketones were the most abundant. Alkanes werederived from waxes in the biomass. Arenas, benzoic aldehydes and phenols were ascribed to thedegradation of lignin. Various ketones include furanones, cycloalkanones, pyrones, alkenonesand benzene-ring containing ones. The detected long chain fatty acids might be intrinsiccomponents as lipid in biomass, or be produced from the oxidation of waxes with NaOCl. Mostof the esters identified were phthalic esters and fatty acid phenyl esters, which could be interlinkspecies between lignin and waxes. The NCOCs can be classified into amides, N-heterocycliccompounds (NHCs), amines, nitriles, cloro(nitro)methanes, and sulfonamides..Sequential extraction with several solvents were carried out, and the species in the extractscould be classified into alkanes, alkenes, arenes, aldehydes, ketones, alcohols, esters, furans,NCOCs, CAs and steroids. About60%of the relative contents of the extracted species weresteroids, including cholesteric-and stigmastic-ones/anols/enols. Alkanes, alkenes and aldehydeswith long carbonic chain were attributed to the degradation of waxes. Alkyl substituted furansand benzofurans were derived from the hemicellulose and lignin, respectively.Oxidative degradation of residues from sequential extraction of RHP and WSP were alsocarried out. The species identified in the extracts were classified as alkyls, arenes, phenols,aldehydes, ketones, CAs, esters and other species. Short chain fatty acids and ketones were the most abundant species. However, the kinds and contents for most of the identified species weremuch different with that of unextractd RHP and WSP. Steroids and alkanes are water insolvablespecies, which may restraint the degradation of RHP and WSP with NaOCl aqueous solution.After extraction, the steroids and alkanes were extrated and separated, and the micro-structure ofbiomass might be changed; hence, the processes of oxidation of RHP and WSP were accelerated,and the extents of the degradation were also enhanced.The residues from sequential oxidation were characterized in detail. Also, the differencesbetween sequential oxidation with or without extraction pretreatment were confirmed. Theultimate analysis showed that the contents of C, H, N and S were decreased as well as H/C ratio.The SEM spectra presented vivid transformations of surfaces of the residues in the processes ofsequential degradation. Cellulose and hemicellulose were degraded and separated first, and thenthe lignin. The results form EDS analyses showed that Si, C and O were the main elements in theresidues, and SiO2should be the final component. These results for the residues were fullyaccordance with oxidation products in the liquid phase.Mechanisms basing on radical reactions between main components of biomass and radicaloxidative species were proposed. The degradation mechanism of hemicullulose was believed tobe similar with that of cellulose. The products of lignin with the oxidation of NaOCl includinghydroxyl-, methoxyl-and alkyl-substituted arenes and phenols; further oxidation of these speciesespecially on benzene-rings were also taken place to produce benzoquinones, phthalic acids andbenzoic acids. Reaction mechanisms of typical compounds in biomass were proposed, such asNCOCs. A model of lignin in RHP was proposed basing on the lignin-related species identifiedand their distribution as well as linkages.Most of the NCOCs, and various aldehydes, ketones, CAs and esters, were enriched in theCS2-extractable fraction because of the strong π-π interaction between C=S bond in CS2andC=O bonds in the extracted species.Main components in RHP and WSP were degraded effectively with sequential oxidation ofNaOCl under mild reaction conditions without additional energy consumption; furthermore,basing on the species identified in the extracts, the structure of biomass and the mechanisms ofthe oxidative degradation could be proposed. This investigation provides feedstock for theproduction of chemicals, and a possible way for value-added utilization of agricultural wastes.更多还原