Low-temperature oxidation of Victorian brown coal

A study has been made of low-temperature oxidation of Victorian brown coal at 35 °C and oxygen pressure of 0.1 M Pa and regression analysis of the experimental results shows that the reaction can best be described by the continuous reaction model. The reaction is subject to reaction product inhibition, apparently caused by product adsorption. Progressive conversion is obtained through a series of cycles consisting of a reaction step followed by evacuation of the coal. The rate equation developed from the continuous reaction model describes satisfactorily the progress of the reaction in each of these cycles. A study of earlier findings on the nature of Victorian brown coal oxidation products indicates that the product water may be significant in this reaction inhibition.     

Low-temperature oxidation of brown coal. 1. Changes in internal surface due to oxidation

The low-temperature oxidation of a Yallourn brown coal was found to decrease markedly the internal surface area of the coal. The surface areas were determined by applying the Dubinin-Polanyi approach to carbon-dioxide isotherms measured gravimetrically at 0 °C.     

Low-temperature oxidation of brown coal. 2. Elovich adsorption kinetics and porous materials

Computer-generated diffusion data are shown to be fitted closely for long periods by the Elovich equation. The graphs obtained also show the discontinuities that frequently occur in Elovich plots of experimental adsorption data. Use of the Elovich equation to interpret sorption on porous materials is therefore a dubious procedure.     

Transportation of coal concentrates at negative ambient temperatures

In the cold season, irregular coal supplies to coke plants are aggravated by the need to heat the coal cars. Thawing of rail cars in garages (enclosures) is the least efficient and most expensive approach. Treatment of the coal concentrates with chemical additives reliably prevents freezing in winter during transit from suppliers to consumers.     

Thermal and oxidation chemistry of coal at low temperatures

The chemical reactions which occur when Illinois No. 6 (hv C) and Rawhide (SBB C) coals are thermally pretreated at 100°C and when Illinois No. 6 coal is subsequently oxidized at 100°C with O₂ have been studied using in-situ FT-i.r. differende spectroscopy. Significant spectroscopic changes were seen. Vacuum drying at 100°C resulted in the decomposition of carboxylic acid species to form a variety of new carbonyl species (in Rawhide) and decarboxylated or decarbonylated coal (Illinois No. 6). Oxidation of predried Illinois No. 6 coal leads to the formation of new carbonyl species. The assumption that drying does not alter the chemical composition of coal may not be correct. Thus, overall spectroscopic (and chemical) changes observed in moderate temperature reaction studies may depend upon sample pretreatment, drying and storage. In addition, the time/temperature profile used in a reaction study may affect the overall changes observed by altering the relative contribution of the different reactions.     

Use of a respirometer to measure oxidation rates of polymeric materials at ambient temperatures

The use of a respirometer is introduced as a novel technique for measuring the oxidation rates of thermally degrading polymers. A dual channel respirometer with fuel cell detectors demonstrates sufficient sensitivity to measure the oxidation rates of low-density polymeric samples at ambient temperatures in a relatively short period of time. Samples of low-density polyurethane foam were aged for various lengths of time in sealed chambers at temperatures ranging from 23 to 110 °C. The extent of oxygen depletion was measured by flushing the chamber with air and comparing the oxygen concentration in the chamber flow to that of a reference flow. Oxidation rates of the 0.1 g/cm³ polyurethane foam could be measured in less than 600 h of aging time at 23 °C. This corresponds to approximately 2 ppm oxidation by weight. Oxidation rates of the foam were used to calculate acceleration factors over a wide temperature range, including ambient conditions. Acceleration factors for the compressive force of the polyurethane foam were determined at elevated temperatures. Assuming that the aging behavior of compressive force of the foam is correlated to its oxidation rate, it is possible to calculate acceleration factors for the compressive force and predict the performance of the foam at ambient temperatures.     

胜利褐煤液化初期反应动力学研究

为研究胜利褐煤在初始阶段的煤液化反应动力学,在可快速升降温的微型高压釜中对胜利褐煤进行了加氢液化反应,得到了反应初期煤液化参数,并对胜利褐煤加氢液化反应初期的动力学行为进行分析。结果表明,虽然反应器升温速度较快,但到达反应温度时,仍有一定量的煤发生了转化,在反应温度440℃、反应时间为0时转化率达到28.12%;在较低温度下,胜利褐煤只发生了部分热解反应,反应后期几乎不再转化,在380℃、反应10 min后转化率已达28%,后续基本不变;随着反应温度的升高,反应转化率、油水产率、气产率等指标增大,反应前10 min增速较快,10~25 min时反应速率减缓,主要是沥青烯组分作为中间产物不断向油转化,速率较低。     

Self-ignition and mechanisms of interaction of coal with oxygen at low temperatures. 3. Changes in the composition of coal heated in air at 60 °C

The gradual changes in weight, in elementary composition, in content of oxygen functional groups and in spin concentration have been established for samples of black coal, brown coal and lignite heated in air for a maximum of 1200 h. An intensive oxidative dehydrogenation was found to occur after more than 300 h oxidation. The process was preceded by a decrease in weight and in oxygen content; its start was found to coincide with a sharp increase in the alcoholic content and in coal ability to exchange hydrogen with calcium acetate, and its rate was found to diminish simultaneously with this ability. The acidity ascribed to phenols decreases gradually but it was found to increase at the end of the experiment. A decrease in ignition temperature was established for oxidized black coal, as well as a change in the composition of low-molecular-weight hydrocarbons evolved during the subsequent gradual heating in air. Some of the changes in the composition during coal oxidation may be explained by acid catalysis.     

Calorimetric investigation of chemical additives affecting oxidation of coal at low temperatures

Interactions in the system “coal-chemical additive-oxygen” were studied at the temperature 30 °C with the aim of recognising inhibitors of the coal oxidation process that are able to modify the coal surface in a chemical way. Three coals of different ranks were tested. As possible inhibitors, 14 aqueous solutions (10 wt.%) of both inorganic (chlorides, sulphates, nitrates, phosphates, and sulphites) and organic (formates, acetates, urea, and thiourea) substances were examined. The action of additives on coal was evaluated from the heat effect during immersion of the coal in the additive solution. It was found that most of the studied substances proved immersing heats quite comparable with that of pure water. However, rather a chemical action was ascertained for sodium sulphite, phenol, urea and/or thiourea with heat effects several times exceeding heats for pure water. To quantify oxyreactivity of original coals as well as additive-treated ones, oxidation heats were measured by the pulse flow calorimetric method. Urea was found to be the chemically acting additive with the most significant inhibiting efficiency (up to 70%) of coal oxidation at low temperatures.     

不同温度下原油蒸气的爆炸极限和临界氧含量

注空气采油因其过程中存在可燃性混合物,会有发生爆炸事故的可能。通过实验测定了15～150℃之间5个初始温度点原油蒸气的爆炸极限和临界氧含量,15℃时爆炸极限范围为4.62%～14.01%,150℃时爆炸极限范围变宽为4.24%～15.62%,安全氧含量15℃时为13.15%,150℃时降低到12.47%相似文献   

褐煤弱氧化产物的成分分析

利用石油醚、氯仿对褐煤进行分级萃取,将萃余煤进行碱性弱氧化.GC/MS对褐煤和氧化产物的萃取液进行成份分析,并采用面积归一化法确定各成份的相对含量.实验表明:原煤石油醚萃取液中鉴定了46种组分,主要以烃类(80.2%)和酯类(14.3%)为主;萃余氧化煤的石油醚萃取液中鉴定了44种为氧化产物,与原煤组分相比,其中烃类(43.3%)相对含量减少,酯类(18.9%),醇类(15%),芳香烃(6.5%),酚类(6.1%),烯烃(4.6%),酸类(2.2%)相对含量增加.这表明在该氧化条件下可以使分子结构发生变化从而得到其它有机化学品.     

Low-temperature oxidation of a bituminous coal. Infrared spectroscopic study of samples from a coal pile

A Fourier-Transform i.r. spectroscopic study has been made of coal samples from a test pile of a bituminous coal which was subject to spontaneous heating. Samples taken from the pile at various depths (various temperatures) and at intervals of 3 months were fractionated into four fractions with different particle sizes so as to distinguish ‘macropore’ oxidation effects from ‘micropore’ oxidation effects. The spectra show that initially a carboxylic acid-type compound is formed. This compound seems to decompose in a later stage of the oxidation. Analysis of the results suggests that macropore oxidation (a diffusion-limited process across the macroscopic interface of the particle) predominates. If so, removal of a small proportion of fines with a relatively large, specific macroscopic surface area would result in a reduction of the spontaneous heating of the pile.     

Self-ignition and mechanisms of interaction of coal with oxygen at low temperatures. 1. Changes in the composition of coal heated at constant rate to 250 °C in air

The changes in weight, in elementary composition, in content of oxygen functional groups and in spin concentration of lignite, brown and black coal samples heated in a stream of humid air at a rate of 1 °C/min to various temperatures have been determined I.r. spectra of oxidized and non-oxidized brown coal are recorded and the yields of CO, CO₂ and H₂O were measured. The mixtures of low-molecular-weight hydrocarbons evolved before self-ignition were analysed by gas chromatography, and the temperatures of self-ignition were determined in an oxygen stream using a Leitz microscope. A region of coal oxidation was identified where the hydrogen content remained invariable or increased, indicating an interaction of coal with water in the presence of oxygen. For the next region the atomic ratio H/C of the overall gaseous product was found to be high (6 to 10). Self-ignition was found to occur in this region. The results permit coal oxidation to be considered as a redox process. The aromatic part of coal is believed to act as an oxidizing agent in the region where hydrogen is less affected by molecular oxygen.     

Thermal decomposition of solid oxygenated complexes formed by coal oxidation at low temperatures

Solid oxygenated complexes formed by coal oxidation play an important role in low-temperature oxidation of coal. Using an isothermal-flow reactor, the decomposition behaviour of solid oxygenated complexes was examined under pure nitrogen, at temperatures between 60 and 110 °C. The production of CO₂ and CO during thermal decomposition of the complexes was quantified by an on-line dual-column micro GC. Experiments show that the production rates of CO₂ and CO depend on temperature, but are independent of the particle size of the samples, indicating that the thermal decomposition process is dominated by chemical kinetics rather than diffusion. It was also found that the rates of formation of carbon oxides follow the Elovich equation and the activation energies for the production of CO₂ and CO are 52.1±6.3 and 72.0±5.8 kJ/mol, respectively, indicating two separate reaction pathways proceeding in the decomposition of solid oxygenated complexes.     

Low-temperature gasification of a woody biomass under a nickel-loaded brown coal char

Catalytic gasification of a woody biomass, Japanese cypress, was investigated under a prepared nickel-loaded brown coal (LY-Ni) char in a two-stage fixed-bed reactor. The nickel-loaded brown coal was prepared by ion-exchange method with a nickel loading rate of 8.3 wt.%. Nickel species dispersed well in the brown coal, and the LY-Ni char via devolatilization at 600 °C showed a great porous property with a specific surface area of 382 m² g^− 1.The LY-Ni char was confirmed to be quite active for the Japanese cypress volatiles gasification at a relatively low-temperature range from 450 to 650 °C. For example, at 550 °C, 16.6 times hydrogen gas and 6.3 times total gases were yielded from the catalytic steam gasification of Japanese cypress volatiles under the LY-Ni char, compared with the case of non-catalyst. The biomass tar decomposition showed a dependence on catalyst temperatures. When the catalyst temperature was higher than 500 °C, Japanese cypress tar converted much efficiently, high gas yields and high carbon balances were obtained.     

分子氧一步法氧化环己烷合成己二酸技术进展

传统的环己烷两步法生产己二酸工艺过程复杂,反应条件苟刻,能量消耗较高,且产生大量有害的NOx气体,污染环境。而以分子氧为氧化剂、环己烷为原料一步法直接合成己二酸具有工艺流程短、氧化剂廉价易得、工艺绿色环保等优点,被誉为是最有希望实现己二酸绿色生产的技术之一。根据催化体系的不同从均相催化和多相催化两个维度概述分子氧一步法氧化环己烷合成己二酸的技术进展,内容涵盖可溶性金属催化法、有机小分子催化法、分子筛催化法以及负载金属催化法等,并对各合成方法的优缺点进行对比说明。     

Subaquatic oxidation of coal by water-dissolved oxygen

Subaquatic oxidation of two bituminous coals by water-dissolved oxygen was investigated using batch reactor equipped with membrane oxygen sensor. Effects of time, temperature and coal grain size were studied as basic parameters influencing the oxidation process. Obtained results showed the subaquatic coal oxidation can be considered as interaction of the first reaction order with respect to oxygen. From temperature dependence of oxidation rate, activation energies E = 72 ± 4 kJ mol⁻¹ and/or 50 ± 4 kJ mol⁻¹ were calculated. For the samples, oxygen consumption R_O2 was found to be in the range of 2 × 10⁻⁷ mol O₂ kg⁻¹ s⁻¹ to 6 × 10⁻⁷ mol O₂ kg⁻¹ s⁻¹, such values being quite comparable with R_O2 for aerial oxidation of bituminous coals.     

Reaction mechanism of coal hydrogenation. 3. Effect of coal type

Seven coals have been hydrogenated in naphthalene and phenanthrene under 10 MPa (initial pressure) of hydrogen with a stabilized niekel catalyst at 400°C for 15 min. Preasphaltene, asphaltene and oil conversions and solvent conversion were measured. The amounts of hydrogen absorbed by coal and by solvent were calculated. Coal conversion and the amount of hydrogen absorbed by coal decreased, while the amount of hydrogen absorbed by solvent increased, with increase in coal rank. The ratio of the amounts of hydrogen absorbed by coal and by solvent showed a good correlation with conversion to benzene- and n-hexanesoluble materials. Naphthalene and phenanthrene gave similar results, suggesting that the coal was hydrogenated directly by gaseous hydrogen.     

Depolymerization of Yallourn brown coal: 1. Reduction of molecular weight with repeated reaction

Yallourn (Australian) brown coal (66.6 wt% C) was depolymerized three times in phenol, using p-toluenesulphonic acid as catalyst. After each reaction the product was extracted with pyridine. The pyridine extracts were then methylated and fractionated by g.p.c. to obtain the molecular weight distribution. The yield of lower molecular weight material increased with advancing reaction.     

Model for coal oxidation kinetics. 1. Reaction under chemical control

Rate expressions are presented to describe the oxidation of coal in a fixed-bed reactor under mild conditions, i.e. conditions which are useful in pretreatment for gasification. A model for chemical control is developed based upon the concept of a triple-path coupled burn-off adsorption site. The model incorporates the effects of temperature, oxygen partial pressure, and coal surface area, and is the first to account for the product distribution of gaseous C0₂, CO, and H₂O, as well as oxygen deposited on the coal surfaces. The overall rate of oxidation is limited by the amount of reactive surface area in the coal particles and is assumed to be reduced as a result of the deposited oxygen which covers potentially reactive sites. This model differs significantly from the previously formulated model of Kam, A. Y. et al. Chem. Eng. Sci. 1976, 31, 815 which postulated external mass transfer control.