Very low-pressure pyrolysis (VLPP) of cyclopentene

The unimolecularity of the thermal dehydrogenation of cyclopentene has been confirmed using the technique of very low-pressure pyrolysis (VLPP). Application of RRKM theory shows that the experimental unimolecular rate constants obtained over the temperature range of 942°–1152°K are consistent with the high-pressure Arrhenius parameters given by where θ = 2.303 RT kcal/mol. These parameters are in good agreement with static and shock tube studies. No firm evidence could be found for any side reactions or reversibility under the experimental conditions used.     

Very low-pressure pyrolysis (VLPP) of t-butylmethyl ether

The thermal decomposition of t-butylmethyl ether has been studied using the VLPP technique. The recommended Arrhenius parameters for the molecular elimination, reaction (1), are A(800°K) = 10^{1 3, 9} sec^?1 and E_a (800°K) = 59.0 ± 1.0 kcal/mole. No radical reactions occur under the conditions used. These parameters are in good agreement with earlier experimental work and with theoretical estimates of both A and E.     

应用分布活化能模型分析伊敏褐煤丝炭腐植酸热解及氢气生成动力学

应用开放体系的热重-质谱(TG-MS)联用技术在5、20和50℃·min-1三个升温速率下对伊敏褐煤丝炭腐植酸(F-HA)和脱灰丝炭腐植酸(DF-HA)的热解行为进行了分析,并利用分布活化能模型(DAEM)分别对其热解和氢气生成动力学进行分析,获得了热解过程和氢气生成的活化能分布函数.结果表明:(1)F-HA热解活化能分布函数呈类Gaussian分布,且具有一定的对称性,主峰位与标准Gaussian分布相一致;DF-HA热解活化能分布函数也呈类Gaussian分布形式,主峰位与Gaussian分布相比,偏向低活化能值.根据转化率与温度、活化能的关系,结合腐植酸的热失重特征,将F-HA热解过程划分为四个阶段,DF-HA热解过程划分为五个阶段,并对腐植酸热解过程中各阶段的化学反应进行了详细讨论.(2)F-HA和DF-HA热解氢气生成活化能分布函数均呈类Gaussian分布,热解氢气生成活化能的整体趋势为随着转化率的升高而增加,但也表现出一定的阶段集中分布特征.根据热解氢气生成的动力学特征,将其生成过程划分为五个阶段,反映了其生成的不同化学反应机制.(3)酸洗脱灰对伊敏丝炭提取出的HA的热解行为、热解过程及热解氢气生成动力学产生了影响.     

1, 3-丁二烯热裂解的动力学计算与模型研究

1, 3-丁二烯是碳氢燃料燃烧和裂解过程中生成的一种重要产物,也是形成多环芳烃(PAHs)的一种重要前驱体。目前,关于1, 3-丁二烯燃烧实验以及机理的研究较多,但是其热裂解机理的研究较少。本文在B3LYP/CBSB7水平下对1, 3-丁二烯裂解过程中相关反应的反应物、产物以及过渡态进行了几何结构优化和频率计算,并通过组合方法CBS-QB3计算得到了单点能和热力学参数。对于紧致过渡态的反应和无能垒反应,分别采用过渡态理论(TST)和可变反应坐标过渡态理论(VRC-TST)计算其高压极限条件下的反应速率常数。计算得到的反应速率常数与已有文献报导的结果吻合较好。通过量子化学计算,对Hidaka等人提出1, 3-丁二烯的热裂解机理模型进行了更新和改进:更新后的机理模型包含45个物种和224步反应,并对更新后的机理模型进行了模拟验证。结果表明,更新的机理模型能更好地预测1, 3-丁二烯激波管裂解实验过程中C₂H₂、1-丁烯-3-炔(C₄H₄)以及苯(C₆H₆)主要产物的浓度分布,为进一步完善核心机理(C₀-C₄)模型提供了可靠的热、动力学参数。     

正癸烷热解的小规模化学动力学机理模型

正癸烷是目前常用的吸热型燃料的替代组分, 但是其热解机理的研究迄今还很少, 且现有的少数几个机理由于规模庞大使用不便. 本文首先构建了一个包含33种组分和75个基元反应的正癸烷热解动力学机理模型(Mech33); 随后, 在该机理的基础上进一步通过灵敏度分析得到影响主要热裂解组分生成的速率控制步, 并采用局部平衡和稳态假设对Mech33机理简化得到了规模更小的、仅包含22种组分和59步反应动力学机理模型(Mech22). 在较宽的温度和压力范围内对流动反应器及激波管中正癸烷热解过程进行了数值模拟, 并与实验数据进行了对比, 结果表明, Mech33和Mech22两个动力学机理模型都能够很好地描述正癸烷热裂解过程,并准确预测主要热裂解产物的浓度分布, 为进一步实现化学反应与计算流体力学(CFD)耦合的工程计算提供了有价值的动力学机理模型.     

Very low-pressure pyrolysis (VLPP) of methyl- and ethynyl-cyclopentanes and cyclohexanes

Studies of the kinetics of thermal unimolecular decomposition of methylcyclopentane, methylcyclohexane, ethynylcyclopentane, and ethynylcyclohexane have been carried out at temperatures in the range 861–1218 K using the technique of very low-pressure pyrolysis (VLPP). Multiple reaction pathways and secondary decomposition of primary products results in a complex array of reaction products. VLPP rate data (fall-off regime) were obtained for the overall decompositions and interpreted via the application of RRKM theory. The data for methylcyclopentane and methylcyclohexane were interpreted in terms of ring-opening bond fission pathways and bond fission to methyl and cycloalkyl radicals. By selecting Arrhenius parameters consistent with the analogous pathways in open-chain alkanes, a good fit to the overall decomposition is obtained. The data for ethynylcyclopentane and ethynylcyclohexane were interpreted in terms of ring-opening bond fission and alkyne to allene isomerization. The A factors for ring opening were based on known values for C-C fission in open-chain alkynes and the Arrhenius parameters for isomerization were chosen to be consistent with previously reported alkyne to allene isomerizations. The VLPP data are consistent with the following high-pressure rate expressions (at < T > = 1100 K) for the dominant primary reaction channel of ring opening adjacent to the substitutent group: where θ = 2.303RT kJ mol^?. Comparison of the activation energies for the ethynyl-cycloalkanes with those for the methyl-cycloalkanes shows that the effect of the ethynyl substituent is consistent with the propargyl resonance energy. This evidence supports the assumption of a biradical mechanism for ring opening in these cycloalkanes.     

Catalytic cracking of low-density polyethylene over H-Beta and HZSM-5 zeolites: Influence of the external surface. Kinetic model

The effect of the addition of H-Beta and HZSM-5 zeolites on the pyrolysis of commercial LDPE has been studied using dynamic experiments in a thermobalance. The H-Beta zeolite shows an important influence on the decomposition of the polymer even at a very low zeolite concentration. A remarkable effect in the first steps of LDPE decomposition on increasing the catalyst loading has been observed and a two-step process occurs in the presence of H-Beta zeolite. A pseudo-kinetic model has been proposed in order to adequately reproduce this behaviour. The model developed has been applied to simultaneously correlate the TG and DTG curves obtained under dynamic conditions at heating rates of 5, 10 and 35 °C/min and at several catalyst concentrations. The model is capable of simultaneously correlating all the experiments, thus demonstrating the validity of the hypothesis suggested and revealing a notable ability as a predictive model.     

乙苯裂解机理和超临界压力下的动力学模拟

基于乙苯燃烧机理的去氧处理获得的乙苯裂解机理, 采用QRRK/MSC算法代码对小分子产物的高压裂解相关参数进行改进, 构建了高压条件下乙苯裂解的136个物种及626步反应的机理. 在超临界压力和高温条件下的动力学模拟表明, 乙苯裂解机理的气相分子产率和转化率的模拟结果与实验结果相吻合. 采用敏感度分析对机理的控速步骤进行验证, 考察了机理中的关键反应, 结果表明本机理能较好地预测高压实验结果, 可应用于超临界裂解换热的计算模拟.     

Gas-phase thermolysis of benzotriazole derivatives. Part 3: Kinetic and mechanistic evidence for biradical intermediates in pyrolysis of aroylbenzotriazoles and related compounds

Gas-phase pyrolysis (static and FVP) of 1-aroylbenzotriazoles gave the corresponding substituted benzoxazole, benzimidazole, benzamide, N-phenylbenzamide, phenanthridin-6(5H)-one derivatives and 1-cyanocyclopentadiene. The present kinetic and mechanistic findings also provide further evidence of the involvement of biradical or carbene reactive intermediates in the reaction pathway of gas-phase pyrolysis of benzotriazoles.     

裂解气相色谱-质谱法研究聚醚酰亚胺的热裂解行为

采用裂解气相色谱-质谱技术研究了聚醚酰亚胺(PEI)在550℃、650℃和750℃裂解温度下的热分解行为.随着裂解温度上升,裂解产物明显增加.在750℃时聚合物分子链断裂完全,共鉴别到25种碎片组分.PEI热分解的碎片中叔丁基苯酚、叔丁基甲基苯酚、苯酚、苯胺、氰苯、2-苯基-1H-异吲哚-1,3(2H)-二酮等5种裂解产物最重要,因此可以依据这几种化合物定性鉴别聚醚酰亚胺.依据热分解产物的数量以及结构推断降解机理为:裂解首先从醚键开始,其次是酰胺基团中的C-N键,然后再经过一系列消除反应、成环反应、重排反应等形成多种裂解碎片.     

A kinetic expression for the pyrolytic decomposition of polytetrafluoroethylene

Despite the fact that the thermal decomposition of polytetrafluoroethylene has been extensively studied over the past six decades, some inconsistencies regarding the kinetic parameters, e.g. the order of the reaction, remain. Representative kinetic data are essential for practical purposes such as reactor design and scaling. In general the literature data refer to homogeneous bulk heating, whereas the case of the non-homogeneous heating of a single particle has not received attention. Data (reaction rate and pre-exponential factor) applicable to this latter case were experimentally determined from isothermal thermogravimetric analyses of the depolymerisation reaction of PTFE. The kinetic data obtained on coarse granules (800-1000 μm) are reported here. The rate law is consistent with a shrinking particle kinetic model, with chemical kinetics controlling phase-boundary movement. The mass loss rate is directly proportional to surface area. A rate law applicable to this case, and useable for geometries of arbitrary shape, is derived.     

热解/红外光谱联用技术用于热解反应的快速检测

详细介绍了快速热解装置CDS2000／红外联用仪(Py／FTIR)的特点。带有样品的热解探头插入并固定在接口装置上，接口装置可直接置于FTIR的光路中，对热解产物进行直接、快速检测，并且可分析重质热解产物。CDS2000热丝裂解器具有极快的升温速度，升温速度从0．01℃／min到20000℃／s，可以有效避免热解过程中的二次反应，有助于推断结构和热解机理；另外，本文对CDS2000／FTIR热解／红外联用仪使用过程中的有关参数进行了分析，如分辨率的选择。本文应用CDS2000／FTIR联用仪对PVC、生物质和模型化合物进行了热解实验，取得了满意的结果。     

Versatile Pectin Grafted Poly (N-isopropylacrylamide); Modulated Targeted Drug Release

This study describes synthesis and optimization of pectin grafted poly(N-isopropylacrylamide) hydrogels as vehicles for colon-targeted theophylline model drug release. The gels were prepared in the presence of N, N′–methylenebisacrylamide (MBAA) crosslinker and ceric ammonium nitrate (CAN) initiator under N₂ atmosphere. Optimum conditions, in terms of percent of grafting (%G), were determined as follows: pectin = 1.0 g, [NIPAAm] = 26.51 mM, [MBAA] = 0.65 mM, [CAN] = 0.073 mM, polymerization temperature = 30°C and time = 4.0 h. Hydrogels were characterized by FTIR, TGA, DSC, XRD and SEM. The formed hydrogel did not have a thermo-sensitivity behavior. The in vitro percent drug release was studied in terms of different percent of grafting and different polymerization temperatures under two pH values namely 5.5 and 7.4. Conclusively, the optimum colon-targeted vehicle properties that provide the least drug release at pH5.5 and the most drug release at pH7.4 were as follows: [NIPAAm] = 26.51 mM and [MBAA] = 0.56 mM, polymerization temperature = 30°C and %G = 55.5.     

碳前驱体CH3ArCH2NH2热解反应的热力学和动力学DFT研究

在实验研究基础上 ,通过量子化学理论计算对碳前驱体 CH3 Ar CH2 NH2 的热裂解机理作了进一步的研究 .利用 Gaussian98程序包中 AM1方法及 DFT UB3 LYP/3 -2 1 G*方法 ,对化合物 5种可能热裂解路径的热力学和动力学计算结果表明 ,CH3 Ar CH2 NH2 热裂解的主反应路径为生成自由基 CH3 Ar CH2 ·和 NH2 · ,其主反应路径 AM1计算的活化能 Ea=2 3 0 .78k J/mol,DFT计算的活化能 Ea=3 2 1 .1 8k J/mol;比较键焓计算的数据与相应的实验数据 ,发现 DFT计算结果与实验结果吻合得较好 ;通过分析优化的反应物及产物自由基的部分结构参数 ,了解了理论支持主反应的原因 ;计算的产物自由基的空间构型表明主反应路径生成的产物自由基相互间若进行稠环缩合反应 ,将获得分子平面取向性很好的稠环芳烃产物     

The Pyrolysis of Azides in the Gas Phase

The chemistry of the non-metallic elements has in recent years passed through a period of rapid development, often referred to as its “renaissance”. To emphasize just one of the key facets: numerous short-lived molecules containing multiple bonds to elements of the third and higher periods have been discovered, often accompanied by the planned synthesis of derivatives which are sterically shielded by bulky groups and thus kinetically stabilized. Thus today molecules such as silabenzenes H₆C_6?nSi_n and silaethenes H₂Si?CH₂ or R₂Si?CR₂, disilenes R₂Si?SiR₂ and diphosphenes RP?PR, silaphenylisonitrile H₅C₆? N?Si, or methylidyne-phosphanes R? C?P, are all well-known species. Sandwich compounds with P₆ rings or silicon centers demonstrate that there are now hardly any barriers to impede the imagination of the non-metal chemist. In sharp contrast is our lack of knowledge regarding the “microscopic” pathways of chemical reactions: thus apart from information provided for example by molecular beam experiments, or from exact numerical calculations involving species consisting of only a few atoms, it remains largely unknown from which directions medium-sized molecules must approach each other to successfully collide and form a “reaction complex”, in which way their structures are changed in such a process or which role is played by molecular dynamics in the energy transfer.–The pyrolysis of azides X? N₃, i.e. compounds which tend to explode violently when ignited in the condensed phase but can be heated in low-pressure gas flow systems without much risk, illustrates that studies of reactive intermediates are of interest not only because novel molecules may be discovered and isolated, and thereby possibilities for synthesis expanded. Moreover, some aspects of the “microscopic” pathways of these azide pyrolyses can be described satisfactorily on the basis of calculated energy hypersurfaces, and the influence of molecular dynamics becomes experimentally visible in the “chemical activation” of intermediates which leads to their “thermal explosion”.     

Pyrolysis behaviour of titanium dioxide-poly(vinyl pyrrolidone) composite materials

Inorganic-organic hybrid materials are studied due to the unique properties they exhibit. As these materials become more widely applied, particularly as precursor materials for forming inorganic materials, it is essential that the pyrolysis behaviour is understood. Transparent yellow hybrid materials consisting of titanium dioxide and poly(vinyl pyrrolidone) were prepared using sol-gel processing techniques. The hybrids maintained their transparency up to the highest achieved inorganic loading of 57 wt.%. These materials were characterised using thermogravimetric analysis in which the organic component was pyrolysed. The resultant chars were then investigated using optical microscopy, x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The inorganic loading had an effect on char formation, with higher loadings leading to the formation of pyrolysis intermediates which were less apparent in samples of lower inorganic content. The pyrolysis intermediates were found to be carbon-rich.     

Pyrolysis of coal-tar asphaltene in supercritical water

Pyrolysis of coal-tar asphaltene, the main active component of coal tar in supercritical water (SCW), is investigated to further understand the upgrading mechanism of coal tar. It is found that coal-tar asphaltene convert to gas, maltene and char both in N₂ and in SCW, but the conversion of coal-tar asphaltene and the yield of maltene in SCW are significant higher than those in N₂. The effect of maltene and char in coal tar on the pyrolysis of coal-tar asphaltene is also studied. The results indicate that the presence of maltene could suppress the formation of char. And the addition of char could reduce the maltene yield. The analysis of pyrolysis product indicates the aromatic nucleus of asphaltene molecule is mainly composed of 2-4 rings aromatic hydrocarbons. Based on these results the pyrolysis mechanism of asphaltene in SCW was discussed.     

聚有机硅倍半氧烷热解研究进展

国防航空工业的发展需求高性能陶瓷,尤其是纳米陶瓷。聚有机硅倍半氧烷可作为前驱体,通过热解制备陶瓷。该方法操作简便,易于控制。本文综述了国外有关聚有机硅倍半氧烷热解理论与应用研究近况,并对这一领域的发展进行了展望。     

用裂解气相色谱法对几株霉菌的分析

本文用带有PYR-2A管式炉裂解器和C-R2AX计算机的岛津GC-9A气相色谱仪,对3株曲霉和3株青霉进行了裂解气相色谱鉴别。通过对指纹图的分析,能够较好地区分出两属之间和各菌株之间的差异,证明了裂解气相色谱分析法用于霉菌鉴别的可能性。