Identification of the principal high molecular weight fragments in the thermal degradation of poly(methyl acrylate)

The pyrolysis of poly(methyl acrylate) has been studied with identification of the major pyrolysis products. The degradation mechanism of Cameron and Kane involving random homolytic scission of the polymer chain followed by a series of intermolecular and intramolecular transfer reactions is extended and confirmed, and it is apparent that a series of saturated and unsaturated oligomers of methyl acrylate are produced.     

Self-inhibition or the lack of it in the pyrolyses of neopentane and n-hexane

Published data show that in its early stages (up to 3% decomposition), the pyrolysis of n-hexane in the ranges 723–823 K and 10–100 Torr is not inhibited by the olefin products, in contrast with neopentane pyrolysis which is very strongly inhibited in similar conditions. Detailed consideration of the chain mechanisms for the two pyrolyses shows that the reactivity of the chain terminating radical towards hydrogen abstraction from an allylic C? H bond in product olefin is the factor which determines whether or not observable self-inhibition occurs. Thus, n-hexane pyrolysis, whose chain decomposition is terminated by recombination and disproportionation of ethyl, is not significantly self-inhibited, whereas that of neopentane which is terminated by recombination of methyl is very strongly inhibited because methyl is 14× more reactive than ethyl. The implications for other alkanes are briefly discussed.     

On-line product analysis of pine wood pyrolysis using synchrotron vacuum ultraviolet photoionization mass spectrometry

The pyrolysis process of pine wood, a promising biofuel feedstock, has been studied with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry. The mass spectra at different photon energies and temperatures as well as time-dependent profiles of several selected species during pine wood pyrolysis process were measured. Based on the relative contents of three lignin subunits, the data indicate that pine wood is typical of softwood. As pyrolysis temperature increased from 300 to 700 °C, some more details of pyrolysis chemistry were observed, including the decrease of oxygen content in high molecular weight species, the observation of high molecular weight products from cellulose chain and lignin polymer, and potential pyrolysis mechanisms for some key species. The formation of polycyclic aromatic hydrocarbons (PAHs) was also observed, as well as three series of pyrolysis products derived from PAHs with mass difference of 14 amu. The time-dependent profiles show that the earliest products are formed from lignin, followed by hemicellulose products, and then species from cellulose.

基于裂解气质联用分析的生物质逐级热解研究

为探究生物质快速热解反应历程,利用裂解气质联用仪对生物质进行逐级热解实验,考察在不同温度区间热解液体产物组分的分布规律。实验结果表明,生物质的化学组成和热解温度区间对热解液体产物都有重要影响。桉木在25℃~400℃热解液体产物较少,主要是吡喃和芳香类化合物,其中5,6-二氢-4-羟基-吡喃-2-酮相对峰面积随温度升高而降低;在450℃~500℃热解液体产物种类和产量均较多,主要以酮类和芳香类化合物为主。玉米芯热解规律和桉木的相似,但在25℃~350℃主要以呋喃类化合物为主,主要热解液体产物是2,3-二氢-苯并呋喃和2-甲氧基-4-乙烯基苯酚,在400℃~450℃热解液体产物以酮类化合物为主。生物质主要化学组分在不同温度区间热解得到不同液体产物,对其进行选择性热解,能够有效实现生物质资源的综合利用。     

The pyrolysis of non-volatile tobacco ingredients using a system that simulates cigarette combustion conditions

This is the second part of a systematic study in which tobacco ingredients are pyrolysed using experimental conditions designed to simulate the average combustion conditions inside a burning cigarette. In the first part, the pyrolysis system was developed and single-substance, mostly semi-volatile tobacco ingredients were pyrolysed. It was predicted that on a cigarette, the majority of these semi-volatile ingredients would transfer to smoke with little pyrolysis.In this part of the study, a further 159 non-volatile and complex ingredients, as well as ingredient mixtures, have been pyrolysed and the pyrolysis products determined using a gas chromatography–mass spectrometric system coupled to the pyrolyser. These non-volatile tobacco ingredients generally decomposed completely in the pyrolysis system, often yielding many products in relatively small amounts. The study has concentrated on the biologically active substances produced by pyrolysis, in particular the “Hoffmann analytes”. These analytes are believed by regulatory authorities in Canada and U.S.A. to be relevant to smoking-related diseases. They are based on lists published by Hoffmann and co-workers of the American Health Foundation in New York. For the pyrolysis of many of the non-volatile ingredients, no “Hoffmann analytes” were detected amongst the products. When they were occasionally formed, they included phenols, benzene, toluene, styrene and furfural (furfural is biologically active but it does not appear on any of the Hoffmann or regulatory authority lists). Those ingredients that did yield such products generally produced them in relatively small quantities although furfural was produced in relatively large quantities by pyrolysis of some ingredients, especially sugars. Those ingredients that produced biologically active constituents during their pyrolysis have been further assessed. This was done by adding them to cigarettes, machine-smoking the cigarette and comparing their smoke yields to those from a control (no ingredient) cigarette. From this comparison, it was found that in general the ingredients added to cigarettes do not increase the smoke components relative to the control cigarette. The pyrolysis technique of the present study tends to over-predict the amount of decomposition that the non-volatile ingredients undergo relative to their behaviour in a burning cigarette. Several examples are discussed, in particular ingredients that produce furfural during pyrolysis.This general pyrolysis technique is thus a first step in the total toxicological assessment of tobacco ingredients and is a useful screening tool for indicating which ingredients may yield biologically active products during decomposition of the ingredients. There are, however, some products such as formaldehyde and the carbon oxides that are not detected by the pyrolyser-gas chromatography–mass spectrometric technique employed here. The generation and detection of these products during the pyrolysis of selected tobacco ingredients is the subject of a parallel paper.     

Mechanism of thermal degradation of poly(alkyl acrylate)s using pyrolysis gas chromatography mass spectrometry

The pyrolyses of homologous poly(alkyl acrylate)s is reported with identification of the major pyrolyses products. A mechanism involving random homolytic scission of the chain followed by a series of intermolecular and intramolecular transfer reactions has been proposed for poly(methyl acrylate) by Cameron and Kane and further developed by Haken, Ho, Houghton, and Gunawan. This mechanism is demonstrated to be generally applicable to the poly(n-alkyl acrylate)s. Reaction mechanisms are postulated for the various products produced and ion fragmentation mechanisms for the mass spectra produced are shown.     

Identification of pyrolysis products of polysulphides by collisionally activated decomposition linked scanning mass spectrometry

Collisionally activated decomposition (CAD) linked scan mass spectra have been used in the identification of pyrolysis products obtained by the direct pyrolysis of some polysulphides in a mass spectrometer. Structures were determined by comparing the CAD spectra of the pyrolysis products with those of authentic compounds. The results are of help in elucidating the thermal degradation mechanisms that occur in the pyrolysis of the polysulphides investigated.     

基于热重红外联用分析的PE、PS、PVC热解机理研究

利用TGA-FTIR联用技术考察了PE、PS、PVC三种典型塑料的热解特性。结果表明,热稳定性从弱到强依次为PVC、PS、PE。PE热解反应过程为典型的一段式反应,红外光谱分析结果表明,PE热解过程为无规则断链形式,生成产物成分复杂,且随热解过程而改变,开始以饱和烃基团为主,中后期以烯烃基团为主,同时有少量炔烃;PS热解过程同样为一段式反应,红外光谱显示主要热解产物为苯乙烯单体,说明热解过程主要是苯乙烯的解聚过程;PVC热解过程较为复杂,主要分为脱氯阶段和共轭多烯重构阶段,红外光谱结果表明,产物中有芳香族化合物。脱氯过程和共轭多烯重构、环化过程在时间和空间上有重合,给二噁英类污染物的生成制造了可能。     

Py-GC/MS在VDF/CTFE共聚物链段结构和其裂解机理研究上的应用

用高分辨裂解气相色谱 质谱联用技术 (Py GC/MS)分析了VDF/CTFE(1∶4)链段结构和裂解机理。通过对实验条件的选择 ,找出了一套适合于VDF/CTFE(1∶4)共聚物的实验操作条件 ,且表明在此条件下所得的裂解谱图的重现性非常好。讨论了该共聚物具有无序的链段结构特征 ;确定此共聚物裂解机理为解聚断裂生成单体 ,还伴随有主链断裂形成低聚物     

Direct mass-spectrometric studies of the pyrolysis of carbonaceous fuels: III. Primary pyrolysis of lignin

The primary pyrolysis of lignins derived from different types of biomass and by the major separation methods has been investigated by molecular-beam sampling mass spectrometry. The lignins separated by the steam-explosion and kraft processes have altered pyrolysis characteristics while ball-milled lignins yield nearly the same product slate as observed in native biomass samples. The predominant and first-formed products, as determined by mass spectrometry, appear to be the precursor monomers, coniferyl and sinapyl alcohol. There is a distinct lack of higher-molecular-weight oligomers as is commonly observed in the pyrolysis of other types of natural and synthetic polymers. A group of peaks, with the most predominant being m/z 272, appear at masses greater than the monomer masses, but are significantly below the dimer mass range. A third group of predominant peaks are present at masses lighter than the monomers and consist of methoxyphenols that have double bonds and carbonyl groups in the alkyl side chains that are in conjugation with the aromatic ring, enhancing thermal stability. The results indicate that the thermolysis of the alkyl-aryl ether linkage, which is the major bonding unit in lignin, and the limited availability of transferable hydrogen, are the major factors that lead to the predominance of these products. The observed product distributions are indicative of specific, sterically favored rearrangement reactions, which allow devolatilization from the hydrogen deficient, solid matrix and favor double bond formation in the alkyl side chain of the products. A discussion of possible mechanisms of formation is given based on these results and the results of other workers in lignin pyrolysis.     

Entrained Flow Gasification of Polypropylene Pyrolysis Oil

Petrochemical products could be produced from circular feedstock, such as waste plastics. Most plants that utilize syngas in their production are today equipped with entrained flow gasifiers, as this type of gasifier generates the highest syngas quality. However, feeding of circular feedstocks to an entrained flow gasifier can be problematic. Therefore, in this work, a two-step process was studied, in which polypropylene was pre-treated by pyrolysis to produce a liquid intermediate that was easily fed to the gasifier. The products from both pyrolysis and gasification were thoroughly characterized. Moreover, the product yields from the individual steps, as well as from the entire process chain, are reported. It was estimated that the yields of CO and H₂ from the two-step process were at least 0.95 and 0.06 kg per kg of polypropylene, respectively, assuming that the pyrolysis liquid and wax can be combined as feedstock to an entrained flow gasifier. On an energy basis, the energy content of CO and H₂ in the produced syngas corresponded to approximately 40% of the energy content of the polypropylene raw material. This is, however, expected to be significantly improved on a larger scale where losses are proportionally smaller.     

Radical processes in the pyrolysis of acetylene

The literature on the pyrolysis of acetylene below 1000 K is reviewed and it is shown that the reaction is a radical chain polymerization initiated by H atoms. The induction period is examined and shown to arise from a rapid autocatalysis produced by the very first product, vinyl acetylene. Data from studies of acetylene polymerization induced by vinyl acetylene and styrene are examined and shown to be in good qualitative agreement with the radical chain process presented. Measured and where needed, estimated rate constants are given to produce numerical estimates of chain length, rates of polymerization, induction period, and rates of initiation. It is further shown that all the products of the polymerization are capable of efficiently initiating chains in the system. An examination of the possible kinetics of vinylidene shows that it does not play any role in acetylene chemistry.     

食品级聚碳酸酯的热释放成分和热分解机理研究

利用程序控温式热裂解-气相色谱/质谱联用技术研究了4种聚碳酸酯(PC)样品在加热情况下的释放物化学成分.分别考察了4个解吸温度和5个裂解温度下PC的降解产物.结果发现在200℃时PC粒料中就有小分子化学物质释放出来,随温度升高,释放和分解出的小分子化学成分的种类和数量都愈加增多,主要成分为酚端基化合物;由不同聚合工艺合成的聚碳酸酯中释放的化学成分有很大的差别.同时通过分析PC的裂解产物成分,阐述了其热分解机理.升温过程中PC分子链发生断裂和重排生成多种以酚类为主的小分子化合物.     

钾元素对生物质主要组分热解特性的影响

采用热重-红外联用仪对松木及生物质主要化学组分半纤维素、纤维素、木质素的热解特性及钾元素对其热解特性的影响进行了研究.结果表明,半纤维素、纤维素、木质素发生热解的主要温度分别为200~350 ℃、300~365 ℃和200~600 ℃;半纤维热解产物中CO、CO₂较多;纤维素热解产物中LG和醛酮类化合物最多;木质素热解主要形成固体产物,气体中CH₄相对含量较高.三种组分共热解过程中发生相互作用使热解温度提高、固体产物增加,气体中CO增加而CH₄减少.添加K₂CO₃后半纤维素和纤维素热解温度区间向低温方向移动,固体产率提高.K对纤维素作用最明显,CO、CO₂气体与固体产物产率明显增加,醛酮类和酸类物质的产率降低;木质素受K影响相对较小,热解固体产物略有增加,挥发分中H₂O和羰基物质增加;三组分共热解减弱了钾元素的催化作用.     

Investigation of some vinyl polymers by pyrolysis—gas chromatography—mass spectrometry

Although much has been published on the thermal degradation behaviour and products of vinyl polymers, the possibilities of using gaschromatography—mass spectrometry in the investigation of pyrolysate composition have much to offer.Results for poly(vinyl chloride), poly(vinyl acetate), polystyrene and poly(α-methyl-styrene) homopolymers and styrene—acrylonitrile copolymer obtained by pyrolysis—gas chromatography—mass spectrometry are presented. Numerous additional fragments not previously specified have been determined. The possible mechanisms of their origin as regards the polymer chain structure are discussed.     

Polymer reactions—X thermal pyrolysis of poly(isoprene)

Poly(isoprene) (97% cis-1,4 and 3% 3,4) has been pyrolysed in a carrier stream of helium from 315 to 384°. The products were online identified and quantitatively analysed by an interfaced pyrolysis GC peak identification system. The first order rate constant for pyrolysis is 1.1 × 10^?2 sec^?1 at 384° with an overall activation energy of 41 kcal mol^?1. The main products are isoprene and 1-methyl-4-isopropenyl cyclohexene. The dominant initiation process has been shown to be β chain scission leading to two allylic radicals. The former product is derived from an unzipping reaction, the latter together with 1.5-dimethyl-5-vinylcyclohexene are the main C₁₀ products from the allylic radicals. All the other minor products can be account for by simple chain propagation reactions with or without intramolecular hydrogen transfers.     

Electron–proton and electron–methyl exchanges in pyrolysis of polyacetylene and polymethylacetylene

Pyrolysis of polyacetylene is marked by high yields of proton-enriched products methane, ethane, ethylene, propane, polypylene, butadiene, cyclopentadiene, 1,3-pentadiene, and toluene in total amounts exceeding benzene. The activation energies for their formation are low. Polyacetylene doped with AsF₅ and iodine produced these products in even higher yields of two to 17 times of undoped polymers. The dominant mechanism is thought to be random-chain scission followed by electron–proton exchange reactions. Polymethylacetylene is thermally less stable than polyacetylene. Pyrolysis gave mesitylene as the expected main product. However, as in the case of polyacetylene, large amounts of proton-enriched products were formed with moderate activation energies. (The yields of methane, propylene, and propane are nearly the same in the pyrolysis of polymethylacetylene as compared to that of polyacetylene at 923°K referenced to mesitylene and benzene, respectively.) By analogy, mechanisms involving both electron-proton and electron–methyl exchange reactions were proposed to account for the formation of all the pyrolyzates of polymethylacetylene. These reactions, not observed in the pyrolysis of polypropylene and polyisoprene, are attributable to the conjugated backbone permitting facile migrations of electrons, protons, and methyl groups.     

压力对塔里木原油四组分热解性能的影响

压力对深层油藏原油热化学过程的影响尚存在较大争议,为研究其在油藏原油热解成气过程中的作用机理,我们在450℃、5~40 MPa压力下对塔里木原油四组分(饱和分、芳香分、胶质和沥青质)进行了封闭体系的热解实验,通过气相色谱(GC)和气相色谱/质谱(GC/MS)分别对原油四组分热解反应的气体产物及饱和分热解过程的液态产物进行了分析。结果表明,在450℃、24 h及不同压力下,沥青质热解产气率高于胶质、芳香分和饱和分;四组分的气相热解产物中,C1的产率明显高于C2~C5组分。增大压力抑制沥青质、胶质及芳香分的热解产气过程而促进饱和分的热解产气过程。随压力的增大,饱和分热解的液态产物的主峰组分碳数先减小,再增大。压力低于20 MPa时,饱和分热解过程中以裂解反应为主;高于30 MPa时,增大压力有利于缩合反应。研究结果可为认识深层油藏原油的稳定程度及天然气的成因提供一定的理论参考。     

Thermal degradation of polymers: Part XXVI—Vacuum pyrolysis of poly(m-acetoxystyrene): Poroducts volatile at ambient temperature

The products obtained on degradation of poly(m-acetoxystyrene) in vacuo are described. The effects of molecular weight and pyrolysis temperature are discussed and compared with those observed for polystyrene under similar conditions. The liquid products of pyrolysis were separated and identified by gas-liquid chromatography and mass spectrometry. Product analysis revealed significant differences between the products of degradation of the two polymers and mechanisms involving O-acetyl bond scission are proposed and discussed to account for this behaviour. Quantitative studies on the liquid fraction are also described and the behaviour compared with results obtained for polystyrene.     

Fast pyrolysis of biomass

The development of viable fast pyrolysis processes for biomass and other carbonaceous feedstocks will offer significant advantages over conventional pyrolysis, flash pyrolysis and gasification processes with respect to product yield quality and flexibility. Fast pyrolysis is defined and related to other biomass thermochemical conversion processes in some detail. Brief references are made to corresponding coal, hydrocarbon and oil conversion research and development. Proposed mechanisms and chemical pathways are reviewed, potential products. product upgrading and product applications are identified. Fast pyrolysis research is reviewed on both the fundamental bench-scale level and the applied process development level.