The vacuum and oxidative pyrolysis of poly-p-xylylene

Poly-p-xylylene prepared by pyrolysis of di-p-xylylene has been degraded under vacuum and in the presence of oxygen as a function of temperature and oxygen pressure. The vacuum pyrolysis is mainly due to “abnormal” structures. Volatiles are initially produced quite slowly, but the reaction accelerates subsequently. Arrhenius equations were derived for various ranges of volatile formation. A mechanism has been formulated consisting of random chain scission followed by depropagation (dimers to pentamers); simulatanously another zip reaction produces hydrogen. The thermal, oxidative degradation has been studied above and below the softening point of the polymer as a function of oxygen pressure. A first-order reaction of volatile formation due to “abnormal” chain scission is followed by normal chain scission, which is also first order. The postulated mechanism leads initially to hydroperoxide formation. Arrhenius equations for volatile formation are different below and above the softening point. Oxygen consumption also follows a first-order reaction with an energy of activation of 31.5 kcal/mole.     

Patterns and kinetics of pyrolysis of tobacco under inert and oxidative conditions

The present work is part of a more extensive research carried out in Naples on cigarette combustion. Theoretical and modelling work highlighted the existence of a misdistribution of the gas flow across the cigarette cross-section, which results into locally variable conditions. As a consequence, oxygen-starving versus oxygen-rich conditions do establish in the pre-heat zone of the cigarette, where pyrolysis of cigarette components takes place. More specifically, oxygen-starving conditions should characterize the process of reaction front propagation in the inner part of the cigarette, close to its axis, while oxygen-rich conditions should establish at the cigarette periphery, close to the paper burn line.The present paper addresses the pattern and the kinetics of pyrolysis under inert and under oxidative conditions of three types of tobacco. The experimental work consists of non-isothermal thermogravimetric analysis at heating rates comprised between 5 and 20 °C/min and with different He–oxygen mixtures. Kinetic expressions for the rate of pyrolysis under inert and under oxidative conditions have been obtained for each ingredient investigated.Results, albeit obtained at sample heating rates smaller than those relevant to actual cigarette burning, highlight the profound differences arising under purely pyrolytic or oxy-pyrolytic conditions as regards the number of reaction steps, the rate, the temperature ranges and yields in solid versus gaseous products of thermal decomposition.The effect of inert/oxidative conditions on the chemical composition of the gaseous products of pyrolysis is discussed in a companion paper [O. Senneca, S. Ciaravolo, A. Nunziata, J. Anal. Appl. Pyrol. 78 (2007) 452].     

Crystallization during polymerization of poly-p-xylylene. II. Polymerization at low temperature

The polymerization of p-xylylene was followed with a newly designed differential thermal analysis system at temperatures between ?196°C and ?20°C. It was found that at the lower temperatures the monomer condenses first to the crystalline monomer before simultaneous polymerization and crystallization. At the higher temperatures, polymerization and crystallization are successive. The data are in agreement with the morphology and crystal structure data derived in Part I of this series of papers on crystallization during polymerization of poly-p-xylylene.     

Chromatographic analysis, isolation and partial characterization of two photocatalysed reaction products of haem and quinone

Quinone was reacted in vitro with free haem under ultraviolet light. Two principal products were detected by liquid chromatography and purified by column chromatography. Mass spectral and Fourier transform infrared analyses showed that both products contained pyrroles and that the first product was probably an ether formed after reaction with the haem vinyl moieties. This product was entirely different from the known N-alkyl intermediates in the haem-catalysed epoxidation reactions of porphyrin dimerization by quinone.     

Characteristics and kinetics analysis of Codonopsis pilosula pyrolysis

Eight kinds of Radix Codonopsis (RC) from different origins in China were selected as the experimental samples fort his study. Their pyrolysis processes were researched by the method of thermogravimetry analysis, in which the heating course was set in the ways of programming temperature from room temperature to 500 °C at different heating rates. Research results show that the process in the heating period of RC includes three stages: water loss, fast pyrolysis, and medium rate decomposition. For cultivated RC, the average initial decomposition temperature in the fast pyrolysis stage is 115 °C, whereas the peak temperature of the fast pyrolysis stage is changed from 189 to 225 °C, in which stage the alcohol-soluble substances are mainly decomposed. It is required to control the operational temperatures of drying and concocting processes according to initial decomposition temperature. Kissinger–Akahira–Sunose model can be used to describe the process mechanism of RC pyrolysis, and the kinetic analyses based on the fast pyrolysis stage thermogravimetric data show that the activation energies change from 141 to 207 kJ mol^?1 for cultivated RC samples and 122 to 131 kJ mol^?1for wild RC samples. The alcohol-soluble extract (ASE) content of wild RC samples is lower than that of cultivated RC samples; their thermal stability is also relatively poor.     

水城褐煤热解的气体产物析出特征及甲烷的生成反应类型研究

利用傅里叶红外光谱仪研究了煤中主要官能团的分布,利用热重-质谱联用（TG/MS）在10℃/min的条件下研究了水城褐煤的热解行为,获得了煤热解主要挥发分气体（H₂、CH₄、H₂O、CO、CO₂）生成的速率曲线。采用分峰拟合的方法将甲烷的生成速率曲线分解为五个峰,通过化学动力学分析,结合煤的结构特性、热解特性及其他挥发分气体的生成特征,认为甲烷的生成主要由一个脱吸附过程和四个化学反应组成。     

模拟油品氧化脱硫及反应动力学研究

在H₂O₂/WO₃/ZrO₂氧化体系中对以甲苯为溶剂、二苯并噻吩(DBT)为模型含硫化合物的模拟油品(硫的质量分数为1540×10^-6)进行了氧化脱硫研究,考察了反应温度、反应时间、氧化剂加入量、催化剂用量对DBT转化率的影响。实验结果表明,在反应温度50℃,反应时间90min,氧化剂加入量油/H₂O₂的体积比为20∶1和催化剂用量0.02g/mL的适宜氧化脱硫条件下,96%以上的DBT氧化为容易分离脱除的二苯并噻吩砜(DBTOs);同时研究了DBT氧化反应动力学,得知DBT氧化反应为一级反应,表观活化能E_a为55.37kJ/mol,指前因子A为3.35×10⁷min^-1。     

The influence of fine structure on the pyrolysis of cellulose. I. Vacuum pyrolysis

The effects of crystallinity, orientation and degree of polymerization on the vacuum pyrolysis of cellulose have been investigated. Natural, modified and manmade celluloses were characterized and the kinetics of their pyrolysis at 251°C studied. The high-temperature pyrolysis of these samples was also investigated by means of DSC and TGA. At 251°C all of the samples showed a rapid, initial weight loss followed by a linear (weight loss)^1/2 versus time dependency. Both the initial weight loss and the subsequent reaction rate were dependent upon the crystallinity of the sample. The reaction rate was shown to be inversely proportional to (DP)^1/2 and related to the orientation. Effects of crystallinity and orientation could also be seen in the DSC thermograms and in the apparent energies of activation. Results are interpreted in terms of probable mechanisms of the uncatalyzed pyrolysis of cellulose.     

Vacuum pyrolysis of astronium urundeuva

Petroleum natural gas (PNG) reserves will last even when the oil reserves are exhausted, requiring the development of technologies for PNG storage. Activated charcoal is the best material for such a purpose. Under vacuum samples of aroeira (Astronium Urundeuva) underwent pyrolysis in diverse conditions. The samples were characterized by thermal analysis, scanning electronic microscopy and infrared spectroscopy. When the pyrolysis temperature increased, mechanical anisotropy resistance tended to disappear. The pyrolysis became complete only at high temperatures and using a long time of treatment.     

The study of the pyrolysis products of Ni (II) and Pd (II) chelate complexes as catalysts for the oxygen electroreduction reaction

Journal of Solid State Electrochemistry - Nitrogen-doped carbon materials were prepared by the pyrolysis of carbon black Vulcan XC-72 impregnated with nitrogen-containing Pd (II) and Ni (II)...     

Pulsed laser powered homogenous pyrolysis for reaction kinetics studies: Probe laser measurement of reaction time and temperature

Pulsed laser powered homogeneous pyrolysis (LPHP) is a technique which can be used to measure rate parameters for purely homogeneous unimolecular decomposition reactions at high temperatures (600–1500 K). The reaction temperature in pulsed LPHP may be obtained from the speed of sound in the reacting gas, which may be measured by observing the thermal lens effect of the gas on a probe laser beam. The reaction time may be obtained directly from the thermal lens measurements. In this work experiments were performed using ethyl acetate (EtAc) and isopropyl chloride (2-ClPr), two reactants whose unimolecular decomposition rate parameters are well established. This allowed us to assess the accuracy and precision attainable with this technique. Pulsed LPHP proved capable of providing rate parameters in good agreement with those in the literature. The results for which the measured activation energies were closest to the literature values gave the temperature dependence of the rate constants as log(k_EtAc) = (12.0 ± 0.9) − 47.7 ± 4.4(kcal/mol)/2.303RT and log(k_2-ClPr) = (13.3 ± 1.0) − 50.8 ± 4.8(kcal/mol)/2.303RT. These may be compared with the literature recommendations, log(k_EtAc) = 12.6 − 48.0(kcal/mol)/2.303RT and log(k_2-ClPr) = 13.6 − 51.1(kcal/mol)/2.303RT. In all cases the measured rate parameters agreed with the recommended values to within the error limits of the measured values. Potential sources of error in the temperature measurement and the kinetic parameters are explored. The expected accuracy of the experiments is assessed, and possible improvements in the experiment are suggested. © 1996 John Wiley & Sons, Inc.     

真空液相色谱柱及其应用

混合物的分离是分析测试中的常用技术 ,柱层析是常用的分离方法之一。而传统的色谱柱由于对样品的受纳容量较小和分离速度较慢 ,无法满足某些研究的需要。本法采用并改进了一种分离快速、使用方便、易于制作的ＶＬＣ柱 ,为含磷化合物的复杂反应产物的研究提供了有效工具。ＶＬＣ柱全称为ＶａｃｕｕｍＬｉｑｕｉｄＣｈｒｏｍａｔｏ ｇｒａｐｈｙ ,即真空液相色谱。这是一种制备色谱 ,其流体由于柱下端产生负压而流出。该柱的使用最早于1977年由Ｃｏｌｌ报道[1,2 ] 。Ｃｏｌｌ及其合作者采用这种柱子顺利地进行了一些天然产物的分离 ,但关于柱…     

Vacuum pyrolysis of intruder plant biomasses

Biomass from three invasive plant species of the Western Karoo region in South Africa, namely Kraalbos, Schotzbos and Asbos, was treated by vacuum pyrolysis. The influence of temperature, pyrolysis time, pressure and initial moisture content on the bio-oil and charcoal yields were investigated. Asbos with the largest ash content, 19.9 wt.%, gave chars with an ash content between 40 wt.% and 44 wt.% making it difficult to use commercially. Vacuum pyrolysis of Kraalbos resulted in producing a biochar with a HHV of 23.0-25.5 MJ/kg and an ash content of 13-19 wt.% which compared favourable with commercial charcoal. The bio-oils from both Kraalbos and Schotzbos showed promise as potential heating oil with a HHV of 21.6-26.9 MJ/kg. The tarry phase contained a number of phenolic compounds that can be separated and shows promise as a feedstock for upgrading. Finally ageing which acts on the lignocellulosic structure of biomasses decreased the charcoal and oil yields from the vacuum pyrolysis of intruder plants.     

热重法研究煤的燃烧反应及其动力学

我国是个多煤少油的国家,煤炭是我国的主要能源,在我国的一次能源中所占比列高达70%[1].煤炭被广泛用于人类生产与生活的各个方面,且它的利用主要是通过燃烧直接获得能量.然而由于先进技术的欠缺,我国在煤炭的利用中一直存在着燃烧效率不高和环境污染严重等缺点,这与现今能源短缺和环境保护日益受重视的现状不相适应.本文通过研究分析煤的燃烧反应及燃烧反应动力学,为煤炭在利用时燃烧的清洁化与高效化提供科学依据.     

Real-time method for the identification and quantification of hydrocarbon pyrolysis products: Part II. Application to transient pyrolysis and validation by numerical simulation

A real-time quantification infra red method has been developed with a gas cell to determine the composition of hydrocarbon pyrolysis products. The aim is to chemically characterise the fuel decomposition in case of regenerative cooling. The method can be extended to a large variety of applications. A transient analysis of the method behaviour is conducted to estimate its capacity to be applied to unsteady conditions (one measure per second), which can be encountered in cooling activity and unsteady processes. A numerical tool called RESPIRE (French acronym for Supersonic Combustion Ramjet Cooling with Endothermic Fuel, Transient Reactor Programming) is used to help in understanding the complex phenomena involved in such a chemical reactor. The validation of transient behaviour with respect to the computations shows negligible time delay (lower than few seconds with gasification rate higher than 60 wt.%) due to residence time in the experimental setup. The quantification accuracy is confirmed to be around 2 mol%. The agreement obtained on gas cell measurements is found to be correct over 10-20 wt.% of gasification rate and very satisfactory over 60 wt.% but this depends on the species. An extension of the method has been developed with a dedicated online cell to be specifically applied to supercritical and multiphase flows. The quantification of the gas phase in the pyrolysis mixture in case of biphasic flow is proposed and validated with an uncertainty around 3 wt.%. The coke formation is monitored as a function of time and its quantification is even tested with 50% of uncertainty after a numerical calibration with respect to simulation.     

The reaction kinetics of dimethyl ether. I: High‐temperature pyrolysis and oxidation in flow reactors

Dimethyl ether reaction kinetics at high temperature were studied in two different flow reactors under highly dilute conditions. Pyrolysis of dimethyl ether was studied in a variable‐pressure flow reactor at 2.5 atm and 1118 K. Studies were also conducted in an atmospheric pressure flow reactor at about 1085 K. These experiments included trace‐oxygen‐assisted pyrolysis, as well as full oxidation experiments, with the equivalence ratio (ϕ) varying from 0.32 ≤ ϕ ≤ 3.4. On‐line, continuous, extractive sampling in conjunction with Fourier Transform Infra‐Red, Non‐Dispersive Infra‐Red (for CO and CO₂) and electrochemical (for O₂) analyses were performed to quantify species at specific locations along the axis of the turbulent flow reactors. Species concentrations were correlated against residence time in the reactor and species evolution profiles were compared to the predictions of a previously published detailed kinetic mechanism. Some changes were made to the model in order to improve agreement with the present experimental data. However, the revised model continues to reproduce previously reported high‐temperature jet‐stirred reactor and shock tube results. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet: 32: 713–740, 2000     

The kinetics of tobacco pyrolysis

When tobacco is pyrolysed under non-isothermal flow conditions in an inert atmosphere, variation of the inert gas or its space velocity has only a minor effect on the profiles of formation rate versus temperature for seven product gases. Thus, mass transfer processes between the tobacco surface and the gas phase are very rapid, and the products are formed at an overall rate which is determined entirely by that of the chemical reactions.The effect of radical chain inhibitors (nitrogen oxides) on the pyrolysis is complex because of the resultant oxidation. Nevertheless, no evidence was found for the occurrence of radical chain reactions in the gas phase. A small proportion (less than 10%) of all the gases monitored are formed by homogeneous decomposition of volatile and semi-volatile intermediate products, in the furnace used.At temperatures above about 600°C the reduction of carbon dioxide to carbon monoxide by the carbonaceous tobacco residue becomes increasingly important. However, when tobacco is pyrolysed in an inert atmosphere, only a small amount of carbon dioxide is produced above 600°C and consequently its reduction to carbon monoxide contributes only a small proportion to the total carbon monoxide formed above that temperature. The rate of the tobacco/carbon dioxide reaction is controlled by chemical kinetic rather than mass transfer effects. Carbon monoxide reacts with tobacco to a small extent.When the tobacco is pyrolysed in an atmosphere containing oxygen (9–21% v/v), some oxidation occurs at 200°C. At 250°C the combustion rate is controlled jointly by both kinetic and mass transfer processes, but mass transfer of oxygen in the gas phase becomes increasingly important as the temperature is increased, and it is dominant above 400°C. About 8% of the total carbon monoxide formed by combustion is lost by its further oxidation.The results imply that inside the combustion coal of a burning cigarette the actual reactions occurring are of secondary importance, the rate of supply of oxygen being the dominant factor in determining the combustion rate and heat generation. In contrast, in the region immediately behind the coal, where a large proportion of the products which enter mainstream smoke are formed by thermal decomposition of tobacco constituents, the chemistry of the tobacco substrate is critical, since the decomposition kinetics are controlled by chemical rather than mass transfer effects. tobacco substrate is critical. In addition, the heat release or absorption due to the pyrolytic reactions occurring behind the coal will depend on the chemical composition of the substrate. Thus, together with the differing thermal properties of the tobacco, the temperature gradient behind the coal should depend on the nature of the tobacco.     

Model-free kinetics analysis of ZSM-5 catalyzed pyrolysis of waste LDPE

Both thermal and catalytic decomposition of waste LDPE sample is studied to understand the effect of catalyst (ZSM-5) on the decomposition behaviour. The nonlinear Vyazovkin model-free technique is applied to evaluate the quantitative information on variation of E_α with α for waste LDPE sample under both catalytic and noncatalytic nonisothermal conditions. The literature reported data on such variation under noncatalytic condition and effects of different catalysts on the LDPE sample are compared with the results of the present study.Results show that the optimum catalyst composition is around 20 wt.%, where the reduction in maximum decomposition temperature is around 70 °C. Presence of ZSM-5 shows similar reduction in maximum decomposition temperature as reported for Al-MCM-41 and MCM-41. Similar trend to literature reported data is observed for variation of E_α with α for LDPE under nonisothermal noncatalytic condition. ZSM-5 catalyzed decomposition of the LDPE sample in the present study indicates that E_α is strong and increasing function of α and consists of four steps. Cracking of large polymer fragments on the external surface of the catalyst, oligomerization, cyclization, and hydrogen transfer reactions inside the catalyst pores might be the possible reaction mechanisms involved during catalytic decomposition.