Study on the structure and pyrolysis characteristics of Chinese western coals

The structure and pyrolysis characteristics of three inertinite-rich Chinese western coals were researched and compared with one relative vitrinite-rich Chinese middle coal by means of XRD, TG-DTG and fixed-bed reactor. The results show that the atomic ratio O/C, aromaticity factor, even ring condensation number and ring condensation index increase and atomic ratio H/C decreases with increasing inertinite content in coal; inertinite contains more aromatic ring structure than that of vitrinite; the crystallite structure order of coal char increases slightly with increasing heat treatment temperature. The higher inertinite content in coal is, the lower pyrolysis reactivity of coal is at lower temperature, and yet they have obvious second pyrolysis reactivity in higher temperature. The pyrolysis reaction in primarily devolatilisation phase that comes mainly from the decomposition of containing hydrogen function groups and the secondary devolatilisation at high temperature is mainly the decomposition of stable containing oxygen function groups in coal matrix with higher inertinite.     

Formation of HCN and NH3 during coal macerals pyrolysis and gasification with CO2

Three coal macerals with high purities were separated from Pingshuo gas coal. The formation rules of HCN and NH₃ during macerals pyrolysis and gasification were investigated. Experiments were carried out in a tubular quartz reactor at atmospheric pressure. The reactor allowed coal particles to be heated up rapidly and held for a prespecified period of time at a peak temperature. The amount of HCN and NH₃ were quantified by ion chromatography. The influence of temperature and macerals type on the formation rules of HCN and NH₃ was discussed. Results showed that the formation of HCN was mainly due to the thermal cracking of volatile, and NH₃ formed both from the thermal cracking of volatile and the cracking of nascent char. The HCN yield increased with an increase in pyrolysis temperature. For three coal macerals (liptinite, vitrinite and inertinite), the yield of HCN depended not only on their volatile contents but also nitrogen-containing functional groups, in which more pyrrole-type nitrogens would form more amount of HCN at lower temperature. The yield of NH₃ depended on the ability of forming ‘H’ radical. Under the experiment condition in this study, inertinite could convert more nitrogen into NH₃ than vitrinite and liptinite. The yield of HCN during gasification was almost the same as that during pyrolysis, the yield of NH₃ during gasification was little higher than that during pyrolysis.     

Pyrolysis behavior of vitrinite and inertinite from Chinese Pingshuo coal by TG-MS and in a fixed bed reactor

The pyrolysis behaviors of vitrinite and inertinite from Chinese Pingshuo coal were investigated by using the thermogravimetry coupled with mass spectrometry (TG-MS) and in a fixed bed reactor, respectively. The results showed that inertinite has lower pyrolysis reactivity, lower tar and gas yields, but higher water yield than vitrinite. At 650 °C, the tar and gas yield of vitrinite is 22.4% and 14.4%, respectively, obviously higher than 13.4% and 10.2% of inertinite. The TG-MS analysis also showed much difference of vitrinite and inertinite in gas evolution profile. The ultimate and XRD analyses of chars indicated that the difference in element composition of vitrinite char and inertinite char decreases with the increase of temperature, and have similar element composition and structure characteristic at 650 °C. The total sulfur removal of both vitrinite and inertinite increases with the pyrolysis temperature, and reaches to 60% at 650 °C, but the organic sulfur in inertinite seems more stable than that in vitrinite.     

神木煤热解的挥发分收率与岩相组成的关系

引　言从构成煤的微观层次的显微组分入手研究煤的组成、结构和性质已成为煤化学研究的一个重要方面 ,在这方面一些研究者已做过许多有意义的尝试 ,主要集中在有关配煤制优质焦炭等方面[1] ,对于煤的热解挥发分收率与岩相组成相关联的研究也有零星报道 .Ｄｕｘｂｕｒｙ[2 ] 对一系列煤及其显微组分的热解研究结果表明 :不同煤的镜质组和惰质组的热解挥发分产率相差不大 ,相同量的不同煤种挥发分量的不同是由壳质组引起的 .其他研究者因不能得到纯度较高的显微组分而仅对热解过程中镜质组和惰质组的相互影响做过推测 .对于煤的挥发分收率与岩…     

基于显微组分化学键特征的宁夏庆华煤热解特性及动力学分析

通过X射线光电子能谱和傅里叶红外光谱表征宁夏宁东庆华煤不同显微组分的官能团种类、表面结构元素价态分布及化学键赋存特征。采用热重-质谱联用考察庆华煤镜质组和惰质组在不同热解温度下的失重行为和关键气体组分变化。进一步基于Coats-Redfern模型从化学键断裂特征和反应动力学角度探讨煤镜质组和惰质组的热解行为差异。结果表明,庆华煤显微组分的热解失重峰与相应化学键断裂信息能够很好地吻合。不同显微组分的热重曲线变化趋同,但相同热解温度下镜质组的失重率始终高于惰质组。快速热解阶段镜质组较惰质组表现出更大的失重率和最大失重速率。其主要原因在于镜质组的脂肪族官能团相对含量更高,快速热解阶段会发生更多的C_al—C_al断裂。不同热解温度下庆华煤显微组分三个主要热解阶段的活化能和频率因子大小次序为：快速热解阶段>快速缩合阶段>缓慢热解阶段。在快速热解阶段,镜质组和惰质组的平均活化能均约为75 kJ/mol,但镜质组的频率因子更高。     

The characterization of coal macerals by diffuse reflectance infrared spectroscopy

Diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy was applied to study the structure of vitrinites, liptinites and fusinites isolated from different rank coals (77.0-91.5%C) using a centrifugal float-sink procedure. Among the macerals separated from a given coal, liptinites are characterized by the highest proportion of aliphatic CH groups, occurring principally as CH₂, and fusinites by the most aromatic structure. Macerals separated from the low rank coals show comparable content of hydroxyl groups that occur as free OH or form similar types of hydrogen bonds. Carbonyl groups appear not only as conjugated ketones and quinones in vitrinites, but also as carboxylic groups in liptinites and low rank fusinites. CH_ar/CH_al ratio does not vary with carbon content in liptinites, but increases in vitrinites and fusinites. In the case of liptinites and vitrinites, a linear relationship between CH_ar/CH_al and reflectance is observed up to vitrinite R₀ value of 1.80%. For all macerals, the ratio CH_ar/CC increases with reflectance, but at different rates. Structural parameters CH_ar/CH_al and CH_ar/CC calculated from DRIFT spectra are very helpful in monitoring the differences among macerals of given coal and following structural rearrangement occurring with rank.     

Correlation of coal volatile yield with oxygen and aliphatic hydrogen

An interesting correlation has been observed between the volatile yield for three coal conversion processes and the oxygen and aliphatic hydrogen (H_al) content of the coal. The three processes are: (1) rapid pyrolysis in vacuum, (2) hydropyrolysis at ≈10 MPa hydrogen, and (3) liquefaction with tetralin at 400 °C. The volatile yield for the first two processes and for low sulphur coals studied in the third process may be predicted with the equation: Yield≈0.8 O_T+15 H_al where: O_T, the organic oxygen concentration measured by ultimate analysis; and H_al is the aliphatic hydrogen concentration determined from Fourier Transform infrared (FTIR) measurements. The similarity of yields for these processes suggests that they are basically controlled by thermal decomposition. Justification for the above equation is offered by considering a recently developed model for thermal decomposition of coal. The correlation does not fit a group of high sulphur coals studied in the liquefaction programme. These coals have extremely high volatile yields which may be a result of catalytic activity.     

A novel semi-empirical relationship between aromaticities measured from 1H and 13C n.m.r. spectra

An empirical correlation between ¹H n.m.r. measured aromaticity (H_ar) and ¹³C n.m.r. measured aromaticity (C_ar) has been found. Over 300 samples which are diverse in origins and structural characteristics have been studied. A semi-empirical functional relationship between H_ar and C_ar has been devised. It is suggested that for distillable samples with, nominally, less than 50% boiling above 320 °C, the derived function can be used to rapidly and conveniently approximate C_ar from H_ar. The difference between observed and calculated C_ar values for 303 such samples shows a standard deviation of just 1.8%.     

中国西部弱还原性煤的结构特征初步研究

对中国西北地区弱还原性、高惰质组煤结构特征进行了初步研究．与同变质程度的其他成煤时代煤相比,中国西北侏罗纪弱还原性煤普遍具有较低的H／C原子比和较高的O／C原子比,同时其芳碳率和分子结构中环缩合程度相对较高．随惰质组含量增加,弱还原性煤芳碳率和平均缩合环数增高．X射线衍射（XRD）研究表明,惰质组芳环缩合程度更高,芳香层片在空间的排列更规则,相互定向的程度高于镜质组．核磁共振（^13C—NMR）研究表明,惰质组分子结构中苯环取代更多,脂肪部分所占比例少．对弱还原性煤中广泛分布的惰质组组分及其分子结构特征需进行深入研究．     

Characterisation of an Egyptian coal by Mossbauer and FT-IR spectroscopy

Six coal samples collected from Maghara Coal Mine, North Sinai, Egypt, at different depths (52-87 m) were characterised by Mossbauer (MS) and Fourier Transform Infrared (FT-IR) spectroscopy. The moisture and ash content and the ultimate analysis are given. The iron minerals were studied by MS. Jarosite (ferric sulphate) and pyrite have been found in the sample taken at 52 m. However, ferrous sulphate and pyrite are present in the other samples. On the other hand, several structural parameters such as H_ar/H_al and H_ar/C_ar were calculated from FT-IR spectra as a function of depth. These parameters give a quantitative determination of the aromaticity, which was found in the range between 0.46 and 0.59, similar to that reported in the literature for subbituminous coals.     

Hydrogenation of liddell vitrinite: Effects of metal halide catalysts in the temperature range 200–480°C

A vitrinite concentrate prepared from the Liddell Seam (high volatile bituminous coal, NSW, Australia) has been hydrogenated in an unstirred 50 cm³, batch autoclave at reaction temperatures between 200 and 480°C in the presence of metal halides (SnCl₁ or ZnCl₁) and/or alumina (α-Al₁O₃). A vehicle was not used. The influence of reaction temperature, metal halide and alumina on the composition of the products was studied by gas chromatography (GC), gel permeation chromatography (gpc), ¹H solution and ¹³C solid-state cross polarization (CP) nuclear magnetic resonance (nmr) spectroscopy and optical microscopy.The metal halides lower the temperature at which softening and agglomeration of vitrinite takes place. The resultant plastic isotropic material forms mesophase at temperatures above 400°C unless an inert diluent, i.e. alumina, is added. The alumina inhibits reactions involved in the formation of mesophase which would otherwise compete with hydrogenation reactions that yield hexane soluble material (oil).Above 400°C carbon monoxide, carbon dioxide and C₁-C₅ alkanes are the principal gaseous products. At lower temperatures, in the presence of alumina, ethylene is formed in the catalysed experiments; the ethylene is converted to ethane at higher temperatures. The structure of the hexane soluble products derived from vitrinite is also temperature dependent. Above 420°C much of the aliphatic component decomposes to yield further quantities of hydrocarbon gases. Tin(II) chloride and zinc chloride produce hexane soluble products of similar molecular composition, which suggests that they operate through a similar mechanism.The addition of alumina to the reaction mixture results in a more aromatic liquid product with shorter aliphatic carbon chains. Whether or not alumina is present, the aromaticity of the solid residues increases with increase in hydrogenation temperature. Thus the increased aromaticity of the liquid products is not caused by the extraction of a greater proportion of aromatic material from the coal with increase in the hydrogenation temperature. It follows that with increase in hydrogenation temperature an increasing proportion of the aliphatic material becomes transformed into aromatic compounds and/or gas.In summary, the results show that over a wide range of temperatures (200–480°C) the structure of the hexane soluble product depends on the thermal stability of the products and the degree of competition from reactions leading to mesophase formation, and not on the nature of the halide catalyst.     

Distribution of aliphatic and aromatic carbons in H-Coal liquids by quantitative 13C FT-n.m.r. spectroscopy

Three H-Coal liquids, ASO, ASB, and VSO, have been characterized by quantitative FT-n.m.r. spectroscopy. FT-parameters were chosen to allow determination of aromatic:aliphatic carbon ratios to within 1% and 2% error of the theoretical and the absolute number of aromatic and aliphatic carbons in a simulated coal liquid, respectively. The aromaticity, f_a, the C_ar:C_al ratio and, the absolute number of both the aromatic and the aliphatic carbons on a per mol basis, have been derived for each H-Coal liquid using c.m.r. in combination with other physical data. By analysis of the chemical shifts of the c.m.r. spectra, the carbon distributions in the H-Coal liquids have been estimated and compared in terms of six structural types. The molecular parameters thus derived are reasonable correlated with the average molecular structures proposed as working hypothesis for the molecular characterization of the three H-Coal liquids.     

Coal flash pyrolysis: 4. Polymethylene moieties in coal macerals

An analysis for polymethylene moieties in purified coal macerals has shown the (CH₂)_n (wheren?5) content, by a liquefaction—¹ H n.m.r. method, to be highest in exinite macerals and lower in vitrinite and inertinite macerals. From any particular coal, the (CH₂)_n content of the vitrinite was higher than the inertinite but lower than the exinite. Pyrolysis of these macerals gave ethylene yields proportional to the (CH₂)_n content.     

Relation between coal aromatic carbon concentration and proximate analysis fixed carbon

Good agreement has been obtained between measured proximate analysis values for fixed carbon (FC) and the predictions of a thermal decomposition model. The model provides a basis for understanding the relation between FC and coal structure and between FC measured under proximate analysis conditions and coke or char measured in other thermal decomposition experiments. The key parameters in the model are the aromatic carbon concentration (C_ar) and the tar yield. C_ar has been determined for 43 coals using quantitative infrared analysis. The aliphatic hydrogen concentration is measured from the absorption near 2900 cm^?1 and the aliphatic carbon concentration is computed assuming a stoichiometry of CH_1.8 C_ar is then computed by difference. The results verify the good correlation between C_ar and FC discussed by van Krevelen. To explain this correlation, use has been made of a coal thermal decomposition model which has been successful in simulating the quantity and composition of volatile components yielded under vacuum pyrolysis conditions. To apply the model to proximate analysis, it was necessary to estimate the tar yields obtained with thick beds and the amounts of O, N, H, and S which remain with the FC. The tar yields for proximate analysis conditions have been estimated to be $\text{1}\text{3}$ to $\text{1}\text{4}$ the yields for thin beds in vacuum. To determine the composition of the FC, measurements were made on a lignite and a bituminous char produced in a thin bed heated by a wire grid for the time (7 min) and temperature (950 °C) used in the proximate analysis, and on the FC residues from a proximate analysis volatile matter determination. Both residues give similar results, showing that approximately 10% of the ‘fixed carbon’ is not carbon. Values of FC computed with the model adjusted for the above conditions are in good agreement with the measured values.     

煤显微组分的性质及燃烧特性研究

本文根据元素分析、工业分析以及差热分析等数据研究了平朔煤、红阳煤、大同煤和东胜煤的显微组分的性质及燃烧特性。结果表明，壳质组具有最大Ｈ／Ｃ比和最高挥发分含量，镜质组的Ｈ／Ｃ比和挥发分含量高于隋质组；显微组分的粘结性，镜质组大于惰质组；镜质组和惰质组相比较，镜质组的着火点低、燃尽温度也低，具有较窄的燃烧区间；壳质组的着火点最低，但是燃尽温度要高于镜质组。     

陕北低阶烟煤显微组分结构特征及分子结构模型

为了更好地利用我国丰富的低阶煤资源,以变质程度较低的陕北低阶烟煤镜质组、惰质组富集物作为研究对象,采用常规的煤质分析、傅立叶变换红外光谱、高分辨固体13C核磁共振、X射线衍射等分析表征手段,对样品结构进行全面分析,得到了陕北低阶烟煤显微组分分子结构特征及结构参数,建立了镜质组和惰质组的部分分子结构模型。结果表明,陕北低阶烟煤镜质组和惰质组氧含量均较高,硫含量很低,所选镜质组的芳碳率为0.634,平均缩合环数约为2.98个;惰质组的芳碳率为0.734,平均缩合环数约为3.15个;相对于镜质组,惰质组的缩合程度更高,芳核尺寸更大,排列也更加规则有序。今后低阶烟煤加工转化工艺的研究应从分子层面揭示其不同显微组分结构特征的差异性,为低阶烟煤清洁高效利用新工艺的开发奠定基础。     

Dynamic nuclear polarization 13C n.m.r. of coal

A novel n.m.r. method for determining the aromaticity of coal has been evaluated. Polarization transfer from the paramagnetic electrons is used to enhance the intensity of the ¹³C n.m.r. spectrum. Analysis of five samples of Gondwana bituminous steam coals shows that the aromaticity of inertinite is far greater than that of vitrinite and that variation of maceral composition is a major factor determining coal aromaticity. This has been confirmed by the study of maceral concentrates.     

Characterization of Canadian coals by nuclear magnetic resonance spectroscopy

Apparent aromaticities of a series of Canadian coals of different rank were estimated by solid state nuclear magnetic resonance spectroscopy. The aromaticities varied from 0.57 for a lignite up to 0.86 for a semi-anthracite coal. The aromaticities correlated well with fixed carbon and oxygen content of the coals as well as with the mean reflectance of the coals. Correlations were also established between aromaticities and the H/C and H_aru/C_ar ratios of the coals. Uncertainties in calculation of the hypothetical H_aru/C_ar ratios, from experimental data were pointed out.Structural parameters of the chars derived from the coals by pyrolysis at 535°C were, also, estimated. The H/C and H_aru/C_ar ratios of the chars were markedly lower than those of coals. This was complemented by higher apparent aromaticities of the chars compared with the coals.     

煤快速热解固相和气相产物生成规律

利用能有效避免二次转化反应的高频炉热解装置对3种不同变质程度的煤进行了600～1200℃条件下的快速热解,考察了在煤热解最初阶段焦产率、焦-C产率、热解气产率、热解气4种主要组分H₂、CO、CH₄和CO₂的比例以及热解气热值随煤阶和热解温度的变化规律。结果表明,焦的产率和焦-C的产率均随煤阶的升高而升高,热解气的产率随煤阶的升高而降低;热解温度的提高能显著降低煤焦和焦-C的产率并提高热解气的产率。热解气组分以H₂相似文献   

Comparative behaviour of coal and maceral concentrates during artificial coalification

A series of experiments were performed in cold-seal autoclaves (confined-pyrolysis) to characterize the behaviour of individual macerais (vitrinite, inertinite, exinite) extracted from the same Lorraine Basin coal during artificial coalification. Rock-Eval pyrolysis, elemental analysis and weight loss determination provided the simple maturation indexes required. Emphasis was laid on the timing of hydrocarbon generation and on the possible similarities existing between inertinite and vitrinite of higher rank. Hydrocarbon potential and hydrocarbon yield were found to increase from inertinite to vitrinite and exinite, but similar mechanisms were involved during the thermal degradation of both inertinite and vitrinite.