Kinetics of thermal liquefaction of coal

A model is presented for the kinetic study of the thermal liquefaction of Belle Ayr subbituminous and Burning Star bituminous coals with anthracene oil, hydrogenated anthracene oil and hydrogenated phenanthrene. All experiments were performed in a continuous-feed, stirred tank reactor, at a temperature of 450 °C and a space time of approximately 5 to 55 min. A kinetic model which includes a reaction: coal + oil→more reactive coal, correlates the data reasonably well. This reaction explains the net consumption of anthracene oil during the initial stages of liquefaction. Such a reaction may account for a portion of the swelling of coal at low space times and the sizable increase of viscosity of reaction slurry during these initial stages of liquefaction. It is also observed that the yield of oil increases when solvents of increasing hydrogen donor capacity are used.     

Hydrogen incorporation during coal liquefaction

Coal hydrogenation reactions have been investigated using a deuterium tracer method which makes it possible to determine which structural positions in the coal react with hydrogen gas or donor solvent during liquefaction. ²H₂ and/or tetralin-d₁₂ were reacted with a Pittsburgh Seam coal at 13.8 to 22.1 MPa and 360 to 425 °C for 0.25 to 1.0 h. Hydrogenation and exchange indices were formulated to indicate the relative contribution of each type of reaction to the total H incorporation. In the coal-deuterium gas system, deuterium incorporation in the solvent-separated products increases in the order oil < asphaltene < preasphaltene < residue. However, in the coal-tetralin-d₁₂-deuterium gas system, deuterium incorporation is similar in each of these four fractions. In both systems, ²H incorporation varies with structural position, with the α-aliphatic positions exhibiting the greatest extent of incorporation. The α-tetralyl radical appears to be an important intermediate in hydrogen transfer to and exchange with the coal. The results indicate that in the donor system the abstraction of hydrogen from the solvent by coal-derived radicals is involved in the rate-determining step of the formation of the soluble products. Evidence indicates that considerable direct interaction of the gas-phase hydrogen with the coal also occurs in the donor solvent system.     

Kinetics of donor-vehicle coal liquefaction in a flow reactor

Development of the Exxon Donor Solvent process has necessitated studies to more clearly define the influence of liquefaction conditions on coal conversion. Process studies were conducted in a 22.7 kg/day (fifty-pound-per-day) integrated pilot plant. Illinois No. 6 coal was liquefied at temperatures from 644 to 756 K, pressures of 10 and 17 MPa, and a tenfold range of residence time. A kinetic model was developed in terms of an empirical classification of four reactive coal constituents. The reactive classes are an incorporation of concepts published in other coal-liquefaction kinetic studies. The effect of vehicle vaporization on actual residence time was used in evaluating the kinetic parameters for this study in a tubular flow reactor. The kinetic model accurately predicts distillation bottoms yields, which ranged from 41 to 72 wt % on coal. Material-balanced quadratic equations are presented for other liquefaction products.     

Kinetics and reaction scheme of coal liquefaction over molten tin catalyst

Rates of formation of gases, oils, asphaltenes and preasphaltenes during non-solvent liquefaction of coal over molten tin catalyst have been measured. A probable reaction scheme and the rate constants for the pathways comprising the scheme have been presented. The results show that the catalyst greatly accelerates the conversion of preasphaltenes to asphaltenes. It also accelerates two other reactions, i.e., coal to preasphaltenes and coal to asphaltenes. By contrast, the catalyst does little to promote gasification and formation of oils.     

Reduction of iron sulphates during coal liquefaction

The transformation of pyrite to pyrrhotite and gypsum to anhydrite is well known during coal liquefaction. Most coals, except extremely fresh ones, contain various iron sulphates resulting from the oxidation of pyrite and marcasite. The reduction of iron sulphates to pyrrhotite during liquefaction is shown with the degree of reduction being temperature dependent. The formation of pyrrhotite from the iron sulphates is important because pyrrhotite is considered to catalyse hydrogénation reactions.     

The redistribution of trace and minor elements during coal liquefaction

Radioactivation analysis of four sets of coal liquefaction feed and product materials provided information on the concentrations of forty trace and minor elements. Coal-derived oil was found to have low levels of most elements, comparable to crude petroleum. Aqueous process effluents were shown to have potentially troublesome levels, especially of Cr and Ba. The concentration data derived in this study and relevant process data were combined to construct elemental mass balances around the liquefaction process; these varied widely between about 80 and 140%, depending mostly on analytical errors. Enrichment of chromium and other transition metals in the conversion residues indicated a possible source through equipment erosion while consistent depletion of barium suggested a loss to aqueous stream particulate matter or possible reactor deposits.     

煤直接液化低分油加氢脱硫脱氮反应动力学研究

为了进一步了解煤直接液化油中硫氮化合物的形态和性质,采用石油研究中的先进分析手段GC-PFPD和GC-NCD,对煤直接液化低分油进行了分析,获得了详细的硫氮化合物组成含量。结果发现:煤直接液化低分油中含有大量的杂环化合物,S主要以苯并噻吩类和二苯并噻吩类化合物存在,N主要以五元环化合物形式存在。在高压釜中进行了催化剂添加量和不同温度条件下的加氢实验,对总硫总氮的加氢反应动力学进行了研究。通过计算得到了高压釜煤液化油加氢脱硫反应的一级反应动力学模型,且通过模型计算的S含量与反应实测的S含量相对误差仅为7.8%;对实验得到的震荡式高压釜中煤液化油加氢脱氮反应的一级反应动力学模型进行验证,发现相对误差也仅为0.97%。     

Kinetics of coal liquefaction: effect of catalyst,H2 concentration and coal type

A process for dry coal hydrogenation—liquefaction has been developed that permits short residence times (seconds) and achieves notably high space rate utilization factors. The purpose of the work reported here is to identify more precisely the process variables that determine space rate utilization factors, and to express them in a kinetic scheme, in the hope of establishing more effective control of these variables in the process. A kinetic analysis of work done in a 3 mm i.d. × 1 m long reactor is presented. Some data from a 4.5 mm i.d. × 34 m long reactor is also included. A correlation of hydroaromatic, catalyst and hydrogen concentration is considered. Parameters considered important for an optimum space rate utilization factor are both chemical and physical in nature. Of special importance are heat transfer, catalyst concentration and hydrogen concentration. A large space rate utilization factor is important from the standpoint of reduced reactor volume.     

Solvent degradation during coal liquefaction in a flowing-solvent reactor

We have previously observed that primary coal extracts recovered from the flowing solvent reactor appeared to be of large molecular mass. Short residence times in the reaction zone following the solubilisation of the extracts tended to limit their thermal degradation. This observation offered the vista of detailed characterisation and analysis of most (∼80-90%) of the coal mass in solution-and in a state relatively free of thermal degradation. Point of Ayr coal was extracted with tetralin and with non-donor solvents, quinoline and NMP at 350 and 450 °C. Structural evaluations have been carried out using size exclusion chromatography, UV-fluorescence spectrometry, GC-MS and probe-MS. Little coal derived material could be found in the pentane-soluble part of the reaction mixture; solvent dimers and trimers were prominent and coal-derived components, such as alkanes, were only minor components. In attempting to characterise the main, pentane-insoluble fraction of the coal extract, the level of interference from solvent-derived material emerged as the decisive parameter for the success or failure of the general method. However, the predominantly pentane-insoluble coal extracts from each solvent were contaminated by solvent polymerisation products. For all three solvents, the level of contamination of extracts with solvent derived material tended to interfere with the detailed characterisation/analysis of material extracted from the coal.     

Peculiarities in methanol action during liquefaction of different coal type

The peculiarities in methanol action during liquefaction of coals having different origin and rank were investigated. When liquefying sapropelic coals, the action of methanol does not differ from that of toluene. In the case of humic coals, methylation of aromatic fragments takes place and methylated liquid products are produced. The degree of alkylation increases with decrease in coal rank. The alkylation of model coal substances and some polyaromatic hydrocarbons was small. It was concluded that during coal liquefaction, reactive coal intermediates are subjected to alkylation.     

Investigation of free radicals produced during coal liquefaction using ESR

Coal liquefaction experiments are described which were carried out to dissolve a subbituminous coal in low and high hydrogen content solvents, in which liquid samples were periodically withdrawn and examined by electron spin resonance spectroscopy. The objectives of this study were to gain information on the free radical processes involved in coal liquefaction, to determine the relative effectiveness of two solvents (H-donor and non-donor) in influencing the radical processes involved in coal liquefaction and to investigate changes in radical concentration on storage.     

Synergistic effects between light and heavy solvent components during coal liquefaction

As part of research to examine coal conversion in solvents containing high-boiling-point components, experimental studies were carried out with model compound solvents. The dissolution of bituminous and subbituminous coals was investigated in pyrene-tetralin and 2-methylnaphthalene-tetralin mixtures. The effects of donor level, gas atmosphere, hydrogen pressure and conversion temperature were determined. At 400 °C, in the presence of hydrogen gas, pyrene-tetralin solvent mixtures show synergism in coal conversion. At donor concentrations as low at 15 wt%, the degree of conversion was almost as high as in pure tetralin. This phenomenon was not apparent in 2-methylnaphthalene-tetralin mixtures. The relative ease of reduction of pyrene and its ability to shuttle hydrogen is considered to be a principal reason for this difference in behaviour. Conversion in pure pyrene and in pyrene-tetralin mixtures at low donor concentrations increased with increasing hydrogen pressure. At 427 °C, bituminous coal conversion was higher in a 30 wt% tetralin-70 wt% pyrene mixture than in either pure compound. It was found that in the absence of coal pyrene can be hydrogenated by H-transfer from tetralin as well as by reaction with hydrogen gas. This can provide a means to increase the rate of transfer of hydrogen to the dissolving coal through the formation of a very active donor (dihydropyrene). During coal liquefaction, several pathways appear to be available for hydrogen transfer for a given coal, the optimal route being dependent upon the solvent composition and the conditions of reaction.     

煤直接液化过程中酚类的转化规律及检测方法

主要论述了低阶煤中各种酚羟基种类对煤液化过程的影响,以及煤液化产物中酚类产品的生成原因,并系统性地对煤液化油馏分中酚类产品的分布、分析检测方法及提取方法等进行了总结。     

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.     

Temperature-staged catalytic coal liquefaction

An investigation has been made of the liquefaction of a bituminous and a subbituminous coal under conditions where reaction is conducted in successive stages of increasing temperature and in the presence of a dispersed sulphided Mo catalyst. This sequence has been found to lead not only to high coal conversion but to greatly increase the selectivity of the liquefied products to oils at the expense of asphaltenes. These gains are made with marginal increases in the production of light hydrocarbon gases. Although no systematic attempt has yet been made to determine the specific influence of reaction parameters upon liquefaction behaviour, preliminary results show that there is substantial potential for further improvement through the suitable choice of solvent and reaction conditions in the two stages. The reasons for the effectiveness of temperature staged liquefaction are discussed in terms of the balance between hydrogenation and condensation reactions. Examination of the liquefaction residues by optical microscopy has provided strong supporting evidence to show that the staged reaction sequence favours hydrogenative processes. Moreover, the microscopic examination has proved to be a powerful diagnostic technique, showing, for example, that the first stage temperature should be lower for the subbituminous than the bituminous coal, and providing insight into the processes of catalysed liquefaction.     

神东煤与煤液化残渣共热解研究

为实现煤液化残渣的资源化利用,采用神东煤与液化残渣进行共热解试验,研究了神东煤粒度、残渣粒度、残渣比例对热解产物分布及热解半焦强度的影响,建立了热解半焦强度测试方法。结果表明,共热解后焦油干基收率随着液化残渣加入量的增多而增大,液化残渣的加入对焦油的生成有正协同作用。1 mm液化残渣添加量由10%增加到30%,3~6 mm神东煤共热解半焦转鼓强度增大29.3%,易碎性F值降低22.8%;同样条件下,液化残渣添加量对3~6 mm神东煤共热解半焦转鼓强度的影响更大,1 mm的液化残渣添加量对神东煤共热解半焦易碎性F值影响更大,3 mm神东煤和1 mm的液化残渣共热解半焦转鼓强度小,易碎性F值高,因此热解过程原料煤应当设置粒度下限。     

Changes in surface characteristics of compacted coal during isothermal decomposition

Isothermal decomposition of coal compacts was carried out in nitrogen between 200–700°, and weight loss was recorded against time. Surface area changes, measured by nitrogen adsorption, were determined at 300° and 500°. The porous structure of the coal disappeared for a while during the decomposition owing to blocking of the pores by tarry matter. The surface area then increased when this tarry matter was driven off.     

煤间接液化中费托合成单元装置的分析

在基于PRO/Ⅱ对低温费托合成系统进行模拟及优化的基础上,采用热力学分析方法,对低温费托合成系统进行了量衡算,分析了系统中各主要能耗单元的效率和损失状况。计算结果表明,系统中损失最大的过程是费托合成反应过程。费托合成反应器是损失最大的设备,效率为86.80%,损失占了总损失的85.15%;冷凝液回流泵效率最低,只有6.71%;效率最高的为石蜡收集槽、石蜡泵、石蜡中间槽等,几乎没有损失。采用热力学分析方法可以更准确地揭示系统中各环节和设备的最大损失,为改进设备、节约能源提供目标和对策。     

Kinetics of short contact time coal liquefaction. Part I: Effect of operating variables

The liquefaction kinetics of Powhatan No.5 mine coal (Pittsburgh Seam) in the presence of SRC-II recycle solvent at short contact times (<10 min) and temperature and pressure ranges of 573–723 K and 10.3–13.8 MPa is examined in a well-mixed reactor. In the initial stages of liquefaction, while overall coal conversion (tetrahydrofuran solubles) increases with temperature, oil (pentane solubles) is lost with an increase in temperature. An increase in solvent-to-coal ratio results in an increase of conversion. The initial coal particle size distribution, total pressure, and nature of gas phase (nitrogen or hydrogen) have no significant effect on the production of any of the product of liquefaction for contact times up to 10 min. A lumped kinetic model is presented to describe the product distribution.     

Optimization of coal liquefaction reactors

The method of Lagrangian multipliers of classical calculus is applied to obtain the optimum operating conditions of three continuous stirred tank reactors (CSTR) in series, to liquefy coal with minimum gas yield. In the formulation of the problem, the gas conversion was assumed to be the cost function. Results obtained were supported by the experimental findings in terms of liquefaction temperatures, reaction times, and conversion of coal into various liquefaction products.