Evolution of porous fractal properties during coal devolatilization

The evolution of pore structures during coal devolatilization was studied using the mercury porosimetry to classify pore structures as micro pores or macro pores based on fractal theory. Pyrolysis caused few changes in the total specific surface areas and micro pore surface areas of most samples. However, the specific macro pore surface areas and the ratio of the specific macro pore surface areas to the total specific surface areas were significantly increased, mostly a result of the shapes of some micro pores becoming less complex after pyrolysis. After devolatilization, the fractal dimensions of the macro pores, which reflect the complexity of the geometrical shapes and hence, the resistances to gas diffusion increased. The fractal geometric factor β, which combines the effects of the ratio of the macro pore surface area to the total surface areas and the fractal dimension of the macro pores after char combustion presented in the previous study is also increased. The volatile content in the parent coal affects the changes of the pore structures.     

Evolution of organic oxygen bonds during pyrolysis of coal

Five Czech coals of different rank (70.2, 71.5, 74.5, 75.0 and 83.3 wt% carbon) were heated at different temperatures in the range 250–850 °C and the contents of oxygen-containing functional groups (OH, COOH, CO, OCH₃) were determined in the coals and carbonization residues. The coals and residues were subjected to pyrolysis chromatography at 740 °C and the yields of phenol produced were measured. The dependence of the oxygen functions and the phenol yield on temperature and coal rank is discussed. In the coals studied, the most resistant oxygen groups appear to be hydroxyl and methoxyl; carboxyl and carbonyl oxygen are eliminated below 550 °C.     

Selective alkylation of acidic hydroxyl groups in coal

The organic molecules which make up coal are held together not only by covalent bonds, but also by a substantial network of hydrogen bonds as well as certain other weak intermolecular associations, which together are called the secondary structure. It is believed that acidic hydroxyl groups are responsible for most of the secondary structure. These attractive forces have been diminished traditionally by solvent swelling the coal, then permanently removed by selective silylation or acetylation of the polar functionalities. A new selective alkylation procedure has been developed which converts polar hydroxyls into relatively non-polar ethers and esters, and has been successfully tested on a bituminous and sub-bituminous coal. This selective O-alkylation proceeds rapidly under very mild conditions and renders the coal essentially free from its secondary structure.     

Liquid-phase alkylation of Assam (Baragolai) coal

Liquid paraffin which consists of a large number of alkylated aliphatics and aromatics seems to be acting as an alkyl group transfer medium to receptive complexes like coal. The alkyl group receptive spots could be created in the coal complex by treatment with molten alkalis like sodium or potassium hydroxide. By repeating extractions of fresh coal with the same volume of liquid paraffin on a laboratory scale it was found that a stage was reached when liquid paraffin became rich enough in alkyl groups to become an alkyl group donor. This suggests a method for liquid phase alkylation of coal.     

Solubilization of an lvb coal by reductive alkylation

Pocahontas (lvb) coal, when treated with alkali metal in tetrahydrofuran in the presence of a small amount of naphthalene, is converted to a ‘coal anion’. The coal anion is formed by transfer of negative charges from the alkali metal to the aromatic clusters in coal with naphthalene acting as an electron transfer agent. The coal anion, containing 12 charges per 100 carbon atoms, is readily alkylated by alkyl halides. The alkylated coals contain 8 alkyl groups per 100 carbon atoms and are soluble in benzene at room temperature. Five of the alkyl groups are attached to carbon atoms and the remaining three to oxygen atoms. The molecular weight of the alkylated coals is in the same range (3000–4000) as that of petroleum asphaltenes. The solubility in benzene of alkylated coal and of petroleum asphaltenes is believed to be due to the presence of alkyl groups which prevent stacking of the aromatic clusters.     

煤燃烧过程中碳、氧官能团演化行为

采用X射线光电子能谱（XPS）系统研究燃烧过程中准格尔褐煤及其煤焦颗粒表面中碳、氧的存在形态及演化过程.研究结果表明，准格尔褐煤颗粒表面含碳官能团中石墨化碳含量非常低，但同时具有一定含量的双键碳;含氧官能团中无机氧含量较低，有机氧含量相对较高.随着燃烧的进行，颗粒表面碳、氧官能团呈现不同的变化趋势.     

Changes in hydrogen utilization with temperature during direct coal liquefaction

A method for quantitative measurement of the hydrogen utilized in different modes of reaction has been applied to hydroliquefaction reactions at temperatures ranging from 375 to 450 °C. The analytical approach is capable of differentiating hydrogen utilized in hydrogenation reactions from that used in bond scission chemistry (hydrogenolysis). The hydrogenolysis reactions result in breakdown of the coal matrix, formation of light hydrocarbon gas and elimination of organic heteroatoms. The results indicate that in this small continuous reactor, operated at 13.8 MPa (2000 psig) H₂, little net chemical activity of hydrogen occurs at 375 °C. However, at 400 °C, the slurry has been hydrogenated significantly with little net hydrogen incorporation. At 450 °C comparable amounts of hydrogen are consumed in gas generation, heteroatom removal, hydrogenation and matrix breakdown, with large net hydrogen incorporation. These results indicate that at temperatures below the thermolysis threshold of 400 °C, significant internal hydrogen redistribution occurs in the slurry. At higher temperatures, a more conventional hydroliquefaction chemistry involving significant bond cleavage and aromatization is indicated. This approach to analysis of hydrogen utilization requires integration of a variety of analytical data. The uncertainties in these data and their impact on the resultant utilization profile are discussed.     

COREX系统用煤燃烧过程中含氧官能团的转变研究

COREX是现有熔融还原方法中的主要工艺流程,该系统对煤质量有严格的要求。我们对系统运行中所涉及的主要煤种大同煤和兴隆庄煤燃烧行为进行深入研究。利用同步热分析仪（TG．DSC）研究高温条件下煤的热分解行为;通过电子扫描显微镜（SEM）观察了煤的微观结构,进行了岩相分析;通过傅里叶红外光谱仪（Frm）和湿式化学分析法,定性及定量的研究了煤中含氧官能团,尤其是热解过程中有机含氧官能基团的组分、数量、化学结构和转化机理。全面评价煤炭的质量,为系统稳定运行选用煤种,提高块煤利用率提供了理论基础。     

Side reactions in the reductive alkylation of low-rank coal

The difficulty occasionally encountered of extracting meaningful information from reductive alkylation experiments on low-rank coals is considered.     

The roles of vehicle and gaseous hydrogen during short contact time coal liquefaction

The roles of the vehicle and gaseous hydrogen during short contact time liquefaction (SCTL) in microreactors were examined by using a number of synthetic vehicles. The importance of vehicles during SCTL was evaluated on their ability to convert coal to tetrahydrofuran (THF)-soluble products. Reaction conditions were three minutes at 425 °C following a one minute heat-up. Although the consumption of hydrogen (hydrogen donor or gaseous hydrogen) by reactive coal fragments is minimal during the early stages of liquefaction (as in SCTL reactions), hydrogen donors were important and could be ranked according to the extent of conversion to THF-soluble products (tetrahydroquinoline > hydrogenated pyrene > dihydroanthracene = dihydrophenanthrene > tetralin). The importance of gaseous hydrogen was also studied. Gaseous hydrogen was needed if either quality or quantity of hydrogen donor was not adequate in a SCTL reaction. With certain synthetic vehicles, the SCTL stage of an integrated two-stage liquefaction process could be conducted in the absence of hydrogen. Solubility properties that might enhance solubilization of coal-derived products, and therefore the extent of liquefaction, were examined by varying the concentration of certain components (m-cresol and quinoline) of the synthetic vehicle mixtures. Solubility effects were minimal.     

Chemical structure of coal macerals in Balmer 10 coal and fusinite from Illinois coal as indicated by reductive alkylation

A Canadian Cretaceous coking coal from the Balmer 10 seam, Fernie, British Columbia, was separated by sink-and-float methods into vitrinite and a semifusinite-rich fraction. A portion of the vitrinite fraction was oxidized in air at 100 °C for 72 h to destroy the coking properties. The fresh vitrinite, oxidized vitrinite, and semifusinite of the Balmer coal, and the fusinite from Illinois coal, were each subjected to the reductive alkylation procedure of Sternberg, to cleave the ether linkages and octylate the products. The oxygen functional groups before and after ether cleavage were determined, as were the extractabilities by benzene of the octylated products. Thus the molecular weights of the benzenesoluble fractions of the octylated cleavage products were: fresh vitrinite 1930, oxidized vitrinite 1830, and fusinite 1490. The molecular-weight distribution of the octylated cleavage products was estimated by volatility analysis, which demonstrated the presence of much lower-molecular-weight material. Dilatation analysis of fresh and oxidized vitrinite showed that after cleavage of the ether linkages with potassium in tetrahydrofuran, the two could be brought to the same state. The dilatation behaviour of semifusinite after cleavage of the ether links and octylation showed only contraction, whereas the oxidized vitrinite treated in a similar manner exhibited a large dilatation.     

Effect of Friedel-Crafts alkylation on the caking properties of bituminous coal

Reaction of medium caking Illinois No. 6 and highly caking Kentucky HVB coals under mild Friedel-Crafts alkylation conditions rendered the product non-caking. Use of aluminium chloride alone with coal did not change the caking property, while this catalyst in the presence of either an alkyl chloride or benzene did suppress caking. Gaseous HCl decreased but did not eliminate agglomeration. Alkylation of a non-caking Western subbituminous coal had no effect on its non-caking property.     

Reductive alkylation of Illinois No. 6 coal in liquid ammonia

The reductive alkylation of Illinois No. 6 coal was investigated using alkali metals and alkyl halides in liquid ammonia. Potassium is the most effective reducing agent and butyl iodide is the most effective alkylating agent for the preparation of coal alkylate that is soluble in tetrahydrofuran. The overall yield of soluble product is often improved through the reaction of the tetrahydrofuran-insoluble portion of the initial reaction products with an alkylating agent in the presence of tetrabutylammonium hydroxide. The infrared spectra of these materials suggest that the phase transfer agent catalyses the esterification of residual carboxylic acid functions. The intermolecular interactions between such acid groups and acceptor groups markedly restrict the solubility of the coal alkylate. The gel permeation chromatograms of the soluble reaction products are essentially featureless with only modest maxima at short and long elution volumes. The proton and carbon nuclear magnetic resonance spectra of the reductive methylation products, prepared using methyl-¹³C iodide, suggest that carbon alkylation exceeds oxygen alkylation and that the alkylation of phenolic groups is the dominant O-alkylation reaction. The spectra also suggest that fewer ethers are cleaved in the reaction in liquid ammonia than under the conditions of the Sternberg reaction.     

Evolution of pore structure and active surface areas of coal and char during hydrogenation

A Belgian coal (Beringen) has been used in a fundamental study of the changes in pore structure and active surface area during hydrogenation. The coal was devolatilized under N₂ and then hydrogenated at constant temperature up to various conversion yields. Reactivities of the chars were determined by isothermal thermogravimetric analysis. Changes in total surface area, calculated from CO₂ adsorption isotherms at 298 K, and in macropore distribution, obtained by mercury penetration, were found to lead to the same conclusion. In the first reaction stage, the preponderant phenomenon was the opening of previously closed micropores, induced by the material consumed by the reaction. This stopped completely when conversion yield exceeded 55 wt% when the maximum surface area was observed. Then removal of material from pore walls became predominant, pores were enlarged and pore walls disappeared gradually with increasing hydrogenation yields. Oxygen chemisorption capacities were measured at 383 K and 0.1 MPa air to give a relative indication of the concentration of carbon active sites. Active surface area results were compared to total surface area values and correlated with reaction rates.     

Evolution of the organic sulfur and other components during nitric acid leaching of Mequinenza coal

In this work, desulfurization by nitric acid leaching is studied in Mequinenza coal, whose characteristics are very low contents of sulfide and sulfate sulfurs in comparison with a very high content of organic sulfur that allows the selective attack on organic sulfur with regard to carbon to be clearly determined. Organic matter is made soluble at high temperatures and there is a threshold temperature for the same. The reaction involves an increase of nitrogen and oxygen, and a decrease of carbon contents. These variations reach a limit as the solubility of the organic matter progresses. The attack on inorganic sulfur is very fast, producing an initial leap as in the attack on organic sulfur, while the solubilization of organic matter is slower, because of which shorter times should be applied for the purpose of desulfurization.     

水煤浆气化制氢的气化压力选择

为确定最适合水煤浆制氢装置的气化压力,以石油焦为原料,采用单喷嘴水煤浆气化技术,在20万m~3/h制氢规模下,对4.0和6.5 MPa两种不同气化压力下的装置配置、技术经济指标、消耗、投资进行综合对比。结果表明,4.0 MPa压力等级下的气化装置和净化装置均出现系列数增加或设备结构尺寸变大的情况,导致投资增加;系列数的增加还会导致备用率降低,在线率和装置可靠性下降,不利于连续稳定供氢;4.0 MPa压力等级低,装置消耗增加,尤其对于低温甲醇洗单元,冷量消耗将大幅增加。因此,针对20万m~3/h制氢规模,6.5 MPa气化压力下的装置在投资、消耗、占地、在线率、可靠性以及操作和维修的复杂性、生产成本等方面均优于4.0 MPa气化压力,在选择气化压力时应优先考虑6.5 MPa压力等级。     

Evolution of fuel nitrogen in coal devolatilization

The distribution of fuel nitrogen in the devolatilization products of a lignite and 12 bituminous coals has been observed experimentally. For these coals under isothermal conditions (300 < T < 1000 °Cand 5 < t < 80 s) the behaviour of the nitrogen evolution was found to be similar. Nitrogen which is initially released is contained almost entirely in the tar. The chemical composition, ¹³C-n.m.r. spectra and infrared spectra of the tars and parent coals are strikingly similar and it is reasonable to suspect that the tar nitrogen occurs in the same structures as in the parent coal. Secondary release of nitrogen into nontar volatiles occurs only at high temperature. Results can be described with first-order kinetics using the same rate constant for all the coals studied. Initial nitrogen release is described by the tar release rate constant, k = 81 exp (−5800/T) (s⁻¹), which is similar to the rate constant for initial nitrogen release measured by Pohl and Sarofim. Secondary release of nitrogen is described with a rate constant which is similar to the results measured by Blair, Wendt and Bartok. This rate is smaller than that measured for the decomposition of nitrogen-ring compounds such as pyridines or pyrroles. The results suggest that coal nitrogen is contained almost entirely in tightly bound rings which are released without breakage in the tar during the initial stage of devolatilization; the remainder is released at higher temperatures when rings are ruptured.     

电解煤浆制取氢气的工艺研究

首次对我国煤炭进行了电解制氢的工艺条件探讨,用自制Pt/Ti催化电极和Pt-Ir/Ti催化电极为工作电极,分别研究了反应过程中煤浆浓度、电解温度、电解质硫酸的浓度、不同煤种、不同溶液催化剂Ce4+、Fe(CN)63-、Fe3+及Fe2+/Fe3+对电解制氢的影响。使用不同电极时电流密度相差较大,Pt-Ir/Ti电极比传统的Pt片电极对电解煤炭制氢的催化效果要好。以Pt-Ir/Ti(摩尔比1∶2)为工作电极所得最大电解制氢效率为99.7%,氢气流速为19.7 mL/(cm2.h)。Fe2+/Fe3+的联用大大提高了电解制氢的效率。阳极气体分析主要组分是CO2及少量CO,还有痕量的低沸点有机物气体,且CO2与氢气体积比为1∶(10~20),大大降低了对该方法引起温室效应的预期。