纤维素和甲醇共催化热解制备对二甲苯（英文）

本文对纤维素和甲醇在不同金属氧化物改性的ZSM5催化剂作用下共催化快速热解实现一步制备可再生对二甲苯的过程进行了研究.结果表明,镧改性的ZSM5催化剂是生产生物基对二甲苯的有效催化剂.对二甲苯的选择性和产率主要由催化剂酸性、反应温度和甲醇含量决定.在20%La_2O_3-ZSM5(80)催化剂作用下,纤维素与33wt%甲醇共催化快速热解获得对二甲苯的最高收率和对二甲苯/二甲苯的最高比率分别为14.5 C-mol%和86.8%.本文详细研究了催化热解过程中催化剂的失活,基于产物的分析和催化剂的表征提出了由纤维素制备对二甲苯的可能反应途径.     

纤维素和甲醇共催化热解制备对二甲苯

本文对纤维素和甲醇在不同金属氧化物改性的ZSM5催化剂作用下共催化快速热解实现一步制备可再生对二甲苯的过程进行了研究. 结果表明,镧改性的ZSM5催化剂是生产生物基对二甲苯的有效催化剂. 对二甲苯的选择性和产率主要由催化剂酸性、反应温度和甲醇含量决定. 在20%La₂O₃-ZSM5(80)催化剂作用下,纤维素与33wt%甲醇共催化快速热解获得对二甲苯的最高收率和对二甲苯/二甲苯的最高比率分别为14.5 C-mol%和86.8%. 本文详细研究了催化热解过程中催化剂的失活,基于产物的分析和催化剂的表征提出了由纤维素制备对二甲苯的可能反应途径.     

水热处理对HZSM-5分子筛催化热解生物质性能的研究

本文利用比表面积测试等手段考察水热氛围对催化剂物理化学性质的影响,并通过Py-GC/MS实验研究水热处理的催化剂对生物质催化热解的效果,研究结果表明:随着水热处理温度的提高,ZSM-5分子筛的比表面积逐渐减小;水热处理对HZSM-5催化剂表面酸性中心密度和活性的优化,催化剂脱氧效果得到增强,温度越高越有利于催化剂表面酸性中心密度和活性的优化,促进热解产物的脱氧和提质,并且改善催化裂解过程中的催化剂结焦现象。     

金属催化剂对褐煤热解气体产物析出影响的实验研究

利用固定床反应器研究了褐煤和添加碱金属K、碱土金属ca、和过渡金属Ni和Fe后的煤样热解时气体产物随温度的变化.实验结果表明,在热解的起始阶段,CO2最先析出,随着温度的升高,CO2的浓度逐渐下降.H2的浓度随温度的升高逐渐增大,到1173 K时,H2的体积分数达80%.CH4的浓度随温度的升高先增大后降低,在某一温度值达到最大值,峰值对应的温度与催化剂种类有关.CO的浓度的变化曲线与催化剂的种类密切相关.碱金属、碱土金属和过渡金属催化剂的添加,改变了煤热解时气体产物的析出过程.原煤及其热解后的焦,以及添加不同金属催化剂的煤和其煤焦均具有不规则的粗糙表面和直的管壁状结构两种表面形态,这两种表面形态与煤中含有的惰性组和镜质组两种显微组织有关.     

正丁烷和异丁烷低压热解的产物鉴定及质谱分析

利用同步辐射真空紫外光电离质谱技术研究了正丁烷和异丁烷在流动反应器中的低压热解,实验温度为823～1823 K. 通过扫描光电离效率(PIE)谱探测并鉴定了20多种热解产物,特别是多种自由基和同分异构体. 在质谱分析的基础上讨论了正丁烷和异丁烷热解的不同特性,从而为丁烷同分异构体分解路径的讨论提供了实验依据. 通过讨论可以发现,丁烷的同分异构体结构对它们的主要分解路径具有强烈的影响,从而导致了它们质谱和PIE谱的差异,如不同的主要产物和丁烯产物结构等. 此外与正丁烷热解相比,异丁烷热解在较低的温度下即可生成苯,这与后者中炔丙基和C4物种等苯前驱体的生成得到了加强是密切相关的,也为解释支链烷烃碳烟生成趋势高于直链烷烃的现象提供了实验线索.     

Identification of Intermediates in Pyridine Pyrolysis with Molecular-beam Mass Spectrometry and Tunable Synchrotron VUV Photoionization

利用可调谐同步辐射真空紫外光电离结合分子束取样技术研究吡啶的热解,温度是1255―1765 K、压力为267 Pa. 通过测量光电离质谱和光电离效率谱,鉴别了近20种产物和中间物,并给出了物种随温度变化的摩尔分数. 主要的产物为H2、HCN、C2H2、C5H3N、C4H2和C3H3N. 根据实验结果分析了吡啶热解的一些主要反应路径.     

催化剂的性质对超临界乙醇条件下热解木质素液化的影响

研究了在超临界乙醇中、氢气存在下,一系列金属-酸双功能催化剂的酸性、孔径大小、负载的金属对热解木质素加氢裂解过程的影响．制备并采用N₂等温吸附和BET比表面、X射线衍射、NH₃-程序升温脱附技术对催化剂进行表征．实验结果表明催化剂酸性增强可促进热解木质素的缩聚反应,从而产生大量的焦炭和水,导致其液化效率降低．微孔催化剂比介孔催化剂孔径小,与强酸共同作用会导致热解木质素裂解生成更多的小分子气体．在催化剂上负载金属Ru可有效地抑制热解木质素的缩聚反应,促进其裂解液化．     

1,2-环氧辛烷的同步辐射光电离解离研究

利用同步辐射产生的真空紫外光和反射式飞行时间质谱仪,在超声冷却条件下测量了1,2-环氧辛烷在光子能量9.8~16.6 eV能区的光电离解离过程,获得了不同能量光子作用下的电离解离产物。通过测量各离子的光电离效率曲线,得到了主要碎片离子的出现势。结合G3理论计算得到了母体离子、中性碎片及离子碎片的结构与能量,通过对比实验测量值与理论值给出了1,2-环氧辛烷的光电离解离通道.     

镍钒复合光催化剂的光谱特征及其光催化性能

以SiO2、活性炭(AC)和Al2O3为载体,采用浸渍法制备了Ni-V-O系负载光催化剂.考察了样品的光谱特征,并在紫外光下评价了样品在甲醇和CO2光催化反应巾的性能;通过吡啶吸附FIIR和UV-Vis分析,结合反应测试结果,比较了催化剂载体对产物选择件的影响.XRD结果表明,在系列催化剂中,SiO2载体上的镍、钒粒子分散程度最高.吡啶吸附FIIR结果显示,系列催化剂表面存在L酸中心;相同的活性组分由于载体不同,所得到的负载催化剂表面酸度不同.负载催化剂表面L酸强度顺序为:Ni-V-O/SiO2>Ni-V-O/Al2O3>Ni-V-O/AC.不同酸度的催化剂,其上的羰基化产物甲酸甲酯(MF)和碳酸二甲酯(DMC)的选择性也不同.催化剂的表面酸强度是影响羰基产物选择性的主要因素.     

固体核磁共振研究固体酸催化剂酸性进展

酸性直接与固体酸催化剂的活性相关,因此研究固体酸催化剂的酸性受到了科研工作者的广泛关注. 固体核磁共振技术已经成为研究固体酸催化剂酸性的一种强有力的工具. 该文介绍了固体核磁共振的特点和各种常用技术,着重综述了固体核磁共振研究固体酸催化剂酸性的进展.     

异补骨脂素热解实验和理论研究

利用同步辐射真空紫外光电离质谱技术,在不同光子能量下,研究了异补骨脂素(C₁₁H₆O₃)的低压热解,探测了不同温度下异补骨脂素的热解产物及其与前驱体的比例. 实验结果表明,异补骨脂素的主要热解产物是CO及其依次消去CO的产物(C₁₀H₆O₂和C₉H₆O). 利用密度泛函理论计算异补骨脂素的解离途径,并利用过渡态理论计算了竞争通道的反应速率常数. 通过实验和理论的结合,确定了异补骨脂素主要解离路径和相应产物的分子结构.     

Pyrolysis study of poplar biomass by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

Pyrolysis is one of the most important methods to convert biomass into biofuel, which is a potential substitute for fossil fuel. The pyrolysis process of poplar biomass, a potential biofuel feedstock, has been studied with tunable synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry (PIMS). The mass spectra at different photon energies, temperatures, and time-evolved profiles of selected species during poplar pyrolysis process were measured. Our results reveal that poplar is typical of hardwood according to its relative contents of three lignin monomeric precursors. As temperature increases from 300 to 700 °C, the overall intensities of pyrolysis products decrease due to the gas-phase cracking. Observed intensities of syringyl and guaiacyl subunits of lignin in poplar at low temperature present different trends: the intensities of syringyl subunits of lignin undergo an increase firstly and then a decrease, whereas those of guaiacyl subunits of lignin show decrease continuously. Time-dependent data demonstrate that hemicellulose pyrolysis is faster than lignin in poplar. This work reports a new application of SVUV PIMS in biomass pyrolysis, which performs very well in products analysis.     

Exploring the pyrolysis chemistry of 1,3,5-trimethylcyclohexane with insight into fuel isomeric and multiple substitution effects

To reveal insights into the combustion mechanism of multiple alkyl substituent cycloparaffins, this work reports an experimental and modeling study of 1,3,5-trimethylcyclohexane (T135MCH) pyrolysis in an extended flow reactor at low and atmospheric pressures. More than 30 species were detected and quantified employing synchrotron vacuum ultraviolet photoionization molecular beam mass spectrometry, and a detailed kinetic model developed based on reaction classes and update kinetic data was validated against the measured species profiles with a reasonable agreement. The reaction flux analyses were performed to reveal the key pathways of the fuel decomposition, intermediates production and aromatics formation. For the primary decomposition, the branching ratios of reaction types show strong dependence on changes of pressures and temperatures, including unimolecular methyl elimination, unimolecular ring-opening isomerization and H-abstraction. Besides the direct dissociation channels, major intermediate hydrocarbons are formed via stepwise dehydrogenation, recombination with ĊH₃ radical or “formally direct” chemically activated reactions triggered by Ḣ atom addition. Monocyclic aromatic hydrocarbons such as benzene and toluene can be produced by traditional H-abstraction/β-C-H scission sequence, cyclopentadiene-related pathways, or recombination mechanism from small linear products. The formations of indene and naphthalene are controlled by C₅+C₅ and C₅+C₄ mechanism respectively. The comparison work of species profiles combined with theoretical calculations of bond dissociation enthalpies (BDEs) was performed to reveal the multiple CH₃-group substituent and isomeric effects of methylcyclohexane (MCH), 1,2,4-trimethylcyclohexane (T124MCH) and T135MCH on pyrolysis activity and ethylene/benzene formation. Besides the increased reaction active sites, the added CH₃-group and ortho-substitution can both weaken the strength of CC and CH bonds, leading to the promoting decomposition activity. The different formation tendencies of products are caused by different BDEs, length of carbon skeleton, as well as complex fuel-specific pathways.     

Conversion of coals with various degree of metamorphism in supercritical water with formic acid

Conversion of coals with various degrees of metamorphism in supercritical water (SCW) was studied under the isochoric conditions at the temperatures of 380–800 °C. At conversion, formic acid, increasing the hydrogenating properties of the medium, was added into SCW. The results of conversion are comparable with the results of pyrolysis under the same temperatures. It was found that the degree of conversion in SCW is 10–15 % higher than that at pyrolysis. An addition of formic acid increases the conversion degree. After processing, there are almost no liquid organic substances escaped into SCW. However, some agglomerates, whose strength is comparable with the strength of lump coal, are formed because of dissolution of the organic matter in the mixture of SCW and formic acid.     

Formation of reaction intermediates and primary volatiles during acid-catalysed fast pyrolysis of cellulose in a wire-mesh reactor

This study aims to understand the fundamental reaction mechanisms during fast pyrolysis of the acid-impregnated cellulose in a wire-mesh reactor at 40–450 °C and 20 °C/s, via quantifying key compounds in the reaction intermediates and primary volatiles. Acid impregnation reduces the onset reaction temperature of cellulose pyrolysis. During acid-catalysed cellulose pyrolysis, 1,6-anhydro-β-d-glucofuranose (AGF), levoglucosenone (LGO) and 5-hydroxymethylfurfural (5-HMF) are identified as major products in the primary volatiles, and the formation of levoglucosan is greatly suppressed. At temperatures < 100 °C, acid catalyses hydrolysis reactions to produce glucose, which is further dehydrated to AGF at 120 °C. At temperatures > 160 °C, acid enhances the dehydration of glucose, levoglucosan and AGF to produce 5-HMF and LGO as major primary products. Once produced, those products can be easily released into the vapour phase, as either aerosols via thermal ejection or vapours via evaporation. As the pyrolysis temperature increases to 240 °C, aromatic compounds can be identified in the primary volatiles, indicating condensation reactions also play important roles during acid-catalysed cellulose pyrolysis under the conditions. As a result, char formation becomes the favoured pathway during acid-catalysed cellulose pyrolysis at temperatures > 300 °C.     

Effects of organic modifiers on the size-controlled synthesis of hydroxyapatite nanorods

Size-controlled synthesis of hydroxyapatite nanorods were carried out by chemical precipitation method using polyethylene glycol (MW 600), Tween 20, trisodium citrate, and d-sorbitol as organic modifiers and starting from calcium nitrate, phosphoric acid, and ammonia solution. The influence of the organic modifiers on the sizes of the resultant HAP nanorods was investigated under different synthesis temperatures. It was found that polyethylene glycol was beneficial to the formation of HAP nanorods with a larger aspect ratio (average length/average diameter) at high synthesis temperature, Tween 20 and trisodium citrate favored the formation of small-sized HAP nanorods, and d-sorbitol helped the formation of HAP nanorods with long length at low synthesis temperatures.     

Exploring fuel molecular structure effects on the pyrolysis chemistry of branched hexenes

3,3-Dimethyl-1-butene (NEC₆D3) and 2,3-dimethyl-2-butene (XC₆D2) are representative branched alkene components in gasoline. This work experimentally investigated the pyrolysis of NEC₆D3 and XC₆D2 in a flow reactor (T = 950–1350 K, P = 0.04 atm) and a jet-stirred reactor (T = 730–1000 K, P = 1 atm) using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC). A pyrolysis model of branched hexenes was proposed and validated against the new experimental data. The combined experimental observations and modeling analyses provide insights into the predominant fuel decomposition pathways and specific formation pathways of products under pyrolysis conditions. NEC₆D3 exhibits a much higher reactivity than XC₆D2 due to the existence of allylic CC bonds. Unimolecular decomposition reactions play the most crucial role in NEC₆D3 decomposition, while in XC₆D2 pyrolysis, fuel consumption is dominated by H-abstraction reactions and the H-assisted isomerization reaction. Fuel-specific pathways can remarkably influence the formation of pyrolysis products, especially the key C₁C₂ products, isomer pairs and dialkenes. Furthermore, the reactions involving propargyl radical dominate the formation of fulvene and aromatic products in the pyrolysis of both fuels, leading to more abundant production of C₆ and larger cyclic products in XC₆D2 pyrolysis.     

A theoretical study on the bimolecular reactions encountered in the pyrolysis of acetamide

Bimolecular reactions of acetamide with acetamide itself, acetimidic acid and acetic acid are investigated to account for the formation of the three major experimental products from the pyrolysis of acetamide, namely ammonia, acetic acid and acetonitrile. This mechanism involves bimolecular deammonation reactions to form acetamide anhydride, acetic anhydride and N‐acetyl acetamide, and the subsequent fragmentation of these intermediates into acetic acid and acetonitrile. It is found that the overall reaction barrier for the formation of the three major experimental products from the bimolecular reaction of acetamide with its enol form (acetimidic acid) amount to a 36.1 kcal/mol barrier. This barrier is in excellent agreement with the corresponding experimental data from the self‐condensation of acetamide. This finding stresses on the role of acetimidic acid as a major intermediate in the pyrolysis of acetamide. The calculated activation barriers for the two available pathways in the bimolecular reaction of acetamide and acetic acid into imide and N‐acetyl acetamide (36.3 kcal/mol and 24.0 kcal/mol) is in accord with the corresponding experimental activation energy of 30.1 kcal/mol for the autocatalytic reaction of acetamide with the acetic acid. Reaction rate constants are obtained for all plausible reactions. Kinetic data presented herein should be instrumental in building a robust model for the decomposition of N‐alkylated amides, that is, a major structural entity in biomass. Copyright © 2011 John Wiley & Sons, Ltd.