生物质燃烧碳烟的物化特性及生成机理研究

以棉花秸秆和木屑为研究对象,设定不同的燃烧工况,在管式炉中进行燃烧并采集碳烟物质,采用TEM、EDS、GC-MS等检测方法对生物质燃烧过程中生成碳烟的物化特性进行研究,并根据检测结果对碳烟生成机理进行分析和推测。检测及分析结果表明,碳烟颗粒典型形貌有胶囊状、球状、链状、网状等。燃烧工况影响燃烧过程使碳烟颗粒表现出不同的微观形貌。碳烟生长过程中伴随着颗粒的碰撞和凝并,形成形貌复杂的链状或网状颗粒聚团。生物质燃烧中碳烟主要由纤维素热裂解生成,成分包括糠醛类、酚类、醛类、呋喃、烷烃、烯烃等含碳化合物。推测碳烟生成机理为,在生物质燃烧过程中,纤维素发生化学键的断裂与重排,生成CO、CO₂和残炭分子碎片等,而残余碳基再通过重整、脱水、碳化、断键等反应生成各种醛类、酮类等产物,醛类、酮类化合物之间通过缩聚、环化反应生成苯环结构,再进一步转化为苯酚、甲苯等化合物。     

生物质气化技术发展分析

生物质气化技术在世界范围内得到了广泛应用.研究综述了生物质气化技术的发展现状和应用情况,阐明了生物质气化技术目前存在的主要问题;对中国生物质气化生活供气和工业供气典型项目的经济性进行了分析,在此基础上对中国生物质气化技术应用前景进行了展望;结合中国生物质气化产业发展面临的新形势,为生物质气化产业的发展提出建议.     

生物质炭燃烧特性与动力学分析

利用小型固定床反应器对棉杆和木屑进行了炭化制焦实验,利用热重分析仪对制得的生物质炭进行氧化实验.基于综合反应速率方程推导了生物质炭氧化过程气固反应机理,并对热重实验结果进行拟合计算.实验结果表明,随着制焦炭化温度的升高,生物质炭的着火温度和燃尽温度升高,燃烧特性指数S减小;棉杆炭综合燃烧性能优于木屑炭.棉杆炭在低温段和高温段燃烧的反应机理不同,低温段燃烧反应的机理是片状内扩散反应机理,高温段燃烧反应的机理是球形界面化学反应机理.木屑炭的反应机理是球形界面化学反应机理.拟合计算求得的活化能并不能反映出生物质炭进行燃烧反应的难易程度.     

基于桔子皮废弃物从含铼废水中高效、高选择地提取钼

以生物质废弃物桔子皮为原料,直接氨化后得到OW-NH2生物吸附剂,OW-NH2对Mo髩的吸附具有很高的选择性,对其他共存离子Re(Ⅶ)、Pb(Ⅱ)、Fe(Ⅲ)、Zn(Ⅱ)、Mn(Ⅶ)、Ca(Ⅱ)和Cu(Ⅲ)基本不吸附,尤其是对Mo(Ⅵ)、Re(Ⅶ)的分离具有高选择性。红外光谱分析表明阴离子形式的H3Mo7O243-、H2Mo7O244-、HMo7O245-、Mo8O264-、Mo7O246-和MoO42-与引入在纤维素上的RNH3+发生离子缔合反应。OW-NH2吸附Mo(Ⅵ)的过程符合Langmiur吸附模型,最大吸附量为1.71 mmol·g-1。另外,OW-NH2对工业实际料液的动态模拟实验的结果表明Mo(Ⅵ)回收率可达99%以上。     

Mechanistic Studies on the Transformation of Ethanol into Ethene over Fe‐ZSM‐5 Zeolite

Ethanol, through the utilization of bioethanol as a chemical resource, has received considerable industrial attention as it provides an alternative route to produce more valuable hydrocarbons. Using a density functional theory approach incorporating the M06‐L functional, which includes dispersion interactions, a large 34T nanocluster model of Fe‐ZSM‐5 zeolite in which T is a Si or Al atom is employed to examine both the stepwise and concerted mechanisms of the transformation of ethanol into ethene. For the stepwise mechanism, ethanol dehydration commences from the first hydrogen abstraction of the ethanol OH group to form the ethoxide‐hydroxide intermediate with a low activation energy of 17.7 kcal mol^?1. Consequently, the ethoxide‐hydroxide intermediate is decomposed into ethene through hydrogen abstraction from the ethoxide methyl carbon to either the OH group of hydroxide or the oxygen of the ethoxide group with high activation energies of 64.8 and 63.5 kcal mol^?1, respectively. For the concerted mechanism, ethanol transformation into the ethene product occurs in a single step without intermediate formation, with an activation energy of 32.9 kcal mol^?1.     

Diverse Banana Pseudostems and Rachis Are Distinctive for Edible Carbohydrates and Lignocellulose Saccharification towards High Bioethanol Production under Chemical and Liquid Hot Water Pretreatments

Banana is a major fruit crop throughout the world with abundant lignocellulose in the pseudostem and rachis residues for biofuel production. In this study, we collected a total of 11 pseudostems and rachis samples that were originally derived from different genetic types and ecological locations of banana crops and then examined largely varied edible carbohydrates (soluble sugars, starch) and lignocellulose compositions. By performing chemical (H₂SO₄, NaOH) and liquid hot water (LHW) pretreatments, we also found a remarkable variation in biomass enzymatic saccharification and bioethanol production among all banana samples examined. Consequently, this study identified a desirable banana (Refen1, subgroup Pisang Awak) crop containing large amounts of edible carbohydrates and completely digestible lignocellulose, which could be combined to achieve the highest bioethanol yields of 31–38% (% dry matter), compared with previously reported ones in other bioenergy crops. Chemical analysis further indicated that the cellulose CrI and lignin G-monomer should be two major recalcitrant factors affecting biomass enzymatic saccharification in banana pseudostems and rachis. Therefore, this study not only examined rich edible carbohydrates for food in the banana pseudostems but also detected digestible lignocellulose for bioethanol production in rachis tissue, providing a strategy applicable for genetic breeding and biomass processing in banana crops.     

Surface characterization of dead microalgae‐based biomass using methylene blue adsorption

To examine the surface characterization of dead chlorella biomass, the chlorella‐manufacturing residue was used as an adsorbent for removal of cationic dye (i.e. methylene blue) from aqueous solutions at low concentrations (less than 5 mg dm^?3). It could be elucidated by considering the ion‐exchange adsorption phenomena on the negative‐charged surface of the adsorbent based on the characterization of functional groups by the Fourier transform infrared (FTIR) analysis. On the basis of monolayer dye adsorption capacity, the specific surface area of this spherical biomass powder was estimated as 11.8 m² g^?1, which was consistent with the rigid cell wall structure of the dead chlorella particles as shown in the SEM observation. Copyright © 2010 John Wiley & Sons, Ltd.     

生物质热解过程中NO、NH3和HCN的释放特性

在氩气气氛下,利用固定床反应器对稻草（DC）、麦杆（MG）和锯末（JM）三种生物质进行热解实验,采用傅里叶变换红外光谱仪（FT-IR）在线检测热解气体产物中的含氮组分,分析各种气相含氮组分的释放规律。实验结果表明,由于锯末中木质素含量较高,锯末热解开始快速释放NO、NH₃和HCN的温度明显高于稻草和麦杆。稻草热解过程中生成的NH₃、HCN和NO量最大。低温下NH₃的生成至少部分与生物质中氨基结构的分解有关,HCN的生成温度较高。不同生物质热解过程中NO、NH₃和HCN释放特性的差异,是由生物质大分子结构不同、灰分含量及成分不同、N含量不同等决定的,以及氮在生物焦、焦油和气相间的分配差异造成的。     

纤维素催化转化为高附加值化学品的研究进展

Currently,under huge pressure from energy demands and environmental problems,much attention is being paid to biomass conversion,which will play an important role in meeting the requirements for a sustainable society.As the most abundant biomass on earth, cellulose is usually used as the first research target for biomass conversion.In this review,the recalcitrant structure of cellulose is discussed and non-catalytic hydrolysis by hot-compressed water and catalytic hydrolysis using solid acids are then considered.We also review the catalytic conversion of cellulose into valuable chemicals including hexitols(sorbitol and mannitol),ethylene glycol,and related compounds using various heterogeneous catalysts.     

Molecular aspects of glucose dehydration by chromium chlorides in ionic liquids

A combined experimental and computational study of the ionic‐liquid‐mediated dehydration of glucose and fructose by Cr^II and Cr^III chlorides has been performed. The ability of chromium to selectively dehydrate glucose to 5‐hydroxymethylfurfural (HMF) in the ionic liquid 1‐ethyl‐3‐methyl imidazolium chloride does not depend on the oxidation state of chromium. Nevertheless, Cr^III exhibits higher activity and selectivity to HMF than Cr^II. Anhydrous CrCl₂ and CrCl₃?6 H₂O readily catalyze glucose dehydration with HMF yields of 60 and 72 %, respectively, after 3 h. Anhydrous CrCl₃ has a lower activity, because it only slowly dissolves in the reaction mixture. The transformation of glucose to HMF involves the formation of fructose as an intermediate. The exceptional catalytic performance of the chromium catalysts is explained by their unique ability to catalyze glucose to fructose isomerization and fructose to HMF dehydration with high selectivity. Side reactions leading to humins by means of condensation reactions take predominantly place during fructose dehydration. The higher HMF selectivity for Cr^III is tentatively explained by the higher activity in fructose dehydration compared to Cr^II. This limits the concentration of intermediates that are involved in bimolecular condensation reactions. Model DFT calculations indicate a substantially lower activation barrier for glucose isomerization by Cr^III compared to Cr^II. Qualitatively, glucose isomerization follows a similar mechanism for Cr^II and Cr^III. The mechanism involves ring opening of D ‐glucopyranose coordinated to a single Cr ion, followed by a transient self‐organization of catalytic chromium complexes that promotes the rate‐determining hydrogen‐shift step.