Oil agglomeration as a pretreatment for coal liquefaction

Laboratory experiments demonstrated that a variety of distillate coal liquefaction recycle oils were satisfactory agents for cleaning Illinois no. 6 bituminous coal by oil agglomeration. Ash rejection up to 41% with 98% organic recovery was attained with conventionally cleaned coal, and ash rejection up to 67% with 90% organic recovery with run-of-mine coal. Agglomerates of > 1 mm average diameter were produced under a variety of conditions. Similar results were obtained in the scaled-up production of 268 kg of agglomerates. Oils with lower hydrogen aromaticities and higher hydrogen contents performed better than more aromatic oils. Fe, Ti and Mg were selectively enriched in the ash of the product coal, while Ca, Si, and Al were selectively rejected. The mineral pyrite was rejected only ≈ 30–40% as extensively as the bulk of the ashforming minerals. The coal cleaned by oil agglomeration performed similarly to the feed coal in batch donor liquefaction tests. In continuous hydroliquefaction tests, run-of-mine coal cleaned by oil agglomeration performed substantially better than coal cleaned to the same ash level by conventional means, because of the selective enrichment of catalytic iron minerals.     

Effects of solvent pretreatment and solvent incorporation on coal liquefaction

Yields of short-contact-time liquefaction product can be increased by pretreating the coal-solvent slurry at below normal liquefaction temperatures to permit solvent incorporation and/or swelling of the coal before liquefaction. An external pretreatment and an in situ pretreatment produce similar results. A coal-vehicle adduct was isolated from the pretreated coal and had liquefaction characteristics similar to the original coal. The beneficial effect of the solvent pretreatment is therefore believed to be the result of physical solvent incorporation with the coal, which causes solvent-aided liquefaction, in contrast with the thermal decomposition that can occur if some of the coal reaches liquefaction temperatures before it is contacted by vehicle. Pretreatment allows vehicle to be present (in contact with coal) at the reactive site in order to react with, and cap, coal free radicals.     

Two-stage liquefaction of a subbituminous coal

The two-stage conversion of a subbituminous coal has been investigated using an autoclave reactor system. The overall performance of the reaction is found to be determined by the effectiveness of the first-stage operation and by the method of sequencing of the stages. The initial thermal products can undergo condensation reactions which render them unresponsive to subsequent catalytic conversion and which increase the light gas yield. This can occur during the first stage reaction, if there is limited capacity for free-radical stabilization, and upon storage and/or thermal cycling between stages. The latter effects are circumvented by operating the two stages in immediate sequence. Condensation is also reduced by increasing the solvent quality and the solvent:coal ratio. The presence of a catalyst during thermal decomposition of coal can greatly improve conversion and product stability even at short reaction time and can reduce constraints on solvent quality. The more feasible approaches to improving first-stage operation appear to be in controlling the solvent composition and in employing hydrogenation catalysts.     

Performance indices for coal liquefaction solvents

Most coal liquefaction processes are based on the thermal cleavage of activated bonds giving reactive carbon and oxygen radicals which abstract hydrogen atoms from the donor solvent. The role of oil is approximated in this study by using a simple standard reaction. A series of five representative solvents react with phenyl and phenyloxy radicals generated by thermolysis of benzoyl peroxide at 87 °C in tetrachloroethylene. The n.m.r. analysis of the reacting mixture defines four performance indices, i.e. the hydrogen-donor, the efficiency, the recycle and the scavenger indices, which characterize the ability of these solvents as efficient recycle oils in coal liquefaction processes. 9,10-dihydrophenanthrene proves to be by far the most appropriate solvent for this purpose.     

Short contact-time liquefaction of subbituminous coal: Directions for improving coal conversion

This study was undertaken to find ways to solubilize subbituminous coal in high yield at short contact times. Short contact-time hydroliquefaction runs were carried out in a continuous unit using Belle Ayr subbituminous coal with a solvent rich in hydrogen-donor molecules derived from the Lummus ITSL process, and also with solvents lower in donor concentration derived from the SRC processes. Catalysis by pyrite, molybdenum and supported cobalt-molybdenum was also studied. It was found that pyrite and other hydrogenation catalysts enhanced solubilization and also increased production of distillate oil. Solvent quality seemed to have no effect on the solubilization of Belle Ayr coal. The availability of H₂S also appeared to have no effect. Provided that pyrite was present, reaction could be carried out at severities high enough to give insoluble organic matter yields equivalent to those obtained with bituminous coals (5–10 wt% daf coal). At equivalent levels of solubilization, however, hydrocarbon gas and distillate yields were invariably higher for the subbituminous coal. Implications for two-stage processing of Belle Ayr coal are discussed.     

On a possible role for electrochemical oxidation in coal liquefaction

The feasibility of coal conversion via electrochemical liquefaction has been investigated. Because of the complicating presence of inorganic materials in coals, humic acids extracted from lignites have been used as model substrates. Considerable reductions in molecular mass, as revealed by size exclusion chromatography, were achieved by anodic oxidation at 1.7 V for slurries in acid, and more especially for solutions in alkali. NMR spectroscopy of methylated humic acids before and after oxidation suggests cleavage of ether linkages between aromatic clusters, with generation of carboxyl groups.     

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.     

神华上湾煤恒温阶段直接液化反应动力学

为考察神华上湾煤的直接液化性能及反应动力学,以加氢蒽油-洗油混合油作为溶剂、负载型FeOOH作为催化剂,在0.01 t·d^-1煤直接液化连续实验装置上考察了不同反应温度（435~465℃）、不同停留时间（7~110 min）下液化产品组成的演变规律。研究发现,随着煤的裂解及加氢反应的进行,煤及沥青类物质（PAA）收率不断减小,重质液化产物逐步向轻质液化产物转化。当反应温度为455℃、停留时间为90 min时,煤转化率为90.41%（质量分数（,油收率为61.28%（质量分数（。随着反应条件进一步苛刻,油收率下降。基于上湾煤直接液化反应特性及其产物收率变化规律建立了11集总煤直接液化反应动力学候选模型,以BFGS优化算法对实验数据搜索、选优,确定了动力学模型参数。检验结果表明所建立的动力学模型可用于恒温阶段直接液化行为的模拟计算。     

煤炭直接液化溶剂的研究

讨论了煤炭直接液化过程中溶剂的特点、作用及质量要求,煤液化溶剂具有一般溶剂的功能,同时还具有良好的供氢和传递氢的功能特点,起到溶解、分隔煤裂解生成的自由基的作用,溶剂必须具有一定的分子结构和分子大小。初步讨论了表征煤液化循环溶剂供氢性的指标,指出普通溶剂如四氢萘和二氢萘等部分饱和的芳香化合物可直接用作煤液化溶剂,多环芳烃含量较高的煤焦油和石油系重质油,经过预加氢处理提高溶剂的供氢性后,可作为煤液化过程的起始溶剂或替代溶剂。     

Humic acid-Fe as catalyst for coal liquefaction

Research to increase the activity of iron based catalysts focuses on decreasing the particle size, increasing catalyst dispersion. The chelate compound of iron with humic acid (HA), which macromolecules radii can range from 6 to 50 nm, is truly in a highly dispersed state. Fe²⁺ or Fe³⁺ were dispersed finely into the HA matrix through the ion exchange with -COOH groups or chelate with carbonyl group in humic acid macromolecules. X-ray diffraction (XRD) and FT-IR spectrophotometer were used to characterize iron species before or after chelating with humic acid. The results indicate that there exist α-FeOOH, ferrihydrite and amorphous iron in HA-Fe. Most of the work has been conducted on a laboratory scale, and the results show that HA-Fe catalyst was approved for its excellent catalytic activity in coal liquefaction, and the conversion and oil yield of coal have been greatly improved.     

Filtration in coal liquefaction: 1. Influence of coal type

Commercial solvent extraction systems for coal must be able to process coals with various properties. In this study the influence of coal type upon the extraction yield of coal and the filtration of extraction products has been investigated. All the coals used gave high extraction yields in hydrogenated solvent but resultant products exhibited considerable differences in rates of filtration. This variation in filtration rates is dependent upon particle size, concentration and composition of the residual solids. No simple relation was found to relate coal type with filtration rate.     

提高煤直接液化催化剂活性的研究进展及展望

为制备高效的煤直接液化催化剂,综述了提高煤直接液化催化剂活性的方法,分析了各方法对煤直接液化催化剂性能影响的作用原理,指出了煤直接液化催化剂研究中各方法的关键点和难点,各方法之间并非相互孤立,应有机组合以提高催化剂的活性。针对目前煤直接液化催化剂存在的问题提出了发展展望。煤直接液化催化剂活性提升的方法主要有提高催化剂前驱体的分散度,提高活性相的抗聚结性能和利用多元金属/非金属的复合/协同效应,后续研究应加强煤中灰组成对催化剂性能的影响,深入研究非金属元素对催化剂加氢和抑焦性能的影响,探索多种协同复合的催化剂制备系统,针对特定煤种研制专用高效直接液化催化剂。     

Study on industrial catalyst for bituminous coal liquefaction

The catalyst activities and the grinding characteristics of natural iron compounds and sulfides were investigated with the aim of preparing an industrial coal liquefaction catalyst for the NEDOL process large-scale plants. From the viewpoint of economy, since these plants are to be located at coal mining sites, it is economical to utilize a natural compound produced in the vicinity of plant site as the catalyst raw material. The coal liquefaction, using an electromagnetic agitation type autoclave, suggested that iron sulfide (pyrite) is the best raw material for the catalyst, because it contains higher iron and sulfur for producing pyrrhotite, an active component under the reacting conditions, and thereby, it needs no pollutant sulfur addition. However, taking into consideration the grinding characteristics, iron sulfide is not thought to have good grinding characteristics in a fine particle zone. Co-pulverization, using iron sulfide and coal, improves the grinding efficiency, the abrasion and the catalyst activities, so that the industrial catalyst preparation can be realized by means of the co-pulverization method.     

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.     

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.     

Catalytic activity of iron compounds for coal liquefaction

The catalytic activity of pyrite and synthesized -FeOOH in coal liquefaction was investigated using batch autoclaves with the aim of developing an industrial iron catalyst. The results indicate that the presence of H₂S helps gaseous hydrogen transferring and prevents deactivation so that the catalyst promotes hydrocracking of coal and hydrogenation of the products. The activity converges with excess H₂S and sulfur addition equivalent to an S/Fe molar ratio of 2.0 being reasonable for the activation. The active site is located on the outer surface, with finely divided catalysts exhibiting high activity. Both pulverized pyrite and synthesized -FeOOH are sufficiently fine as to exhibit high activity in the process. Pulverized pyrite is an industrially feasible iron catalyst for coal liquefaction process, because it is inexpensive and does not require sulfur addition.     

直接煤液化:悬浮床技术和经济效果

Axens北美有限公司在煤直接液化技术开发和示范方面具有悠久历史,起源于上世纪60年代.煤直接液化技术的开发基于工业氢-油工艺,并证明了悬浮床反应器技术具有显著的通用性.包括氢-油工艺、CTSL(二级催化液化法)和煤/油混合加工工艺在内的这些技术,处于当今世界上煤液化技术的最佳和最先进的地位.本文对这些技术进行了描述,并阐述生产高质量液体燃料的首选工艺和经济性.     

Highly active limonite catalysts for direct coal liquefaction

The properties of limonite in Australia and Indonesia were examined by using X-ray diffraction, Mössbauer spectroscopy, Thermal gravimetric analysis (TGA) and TEM–EDX in relation to the catalytic activities in the liquefaction of low-rank coals. The molar ratio of H₂O/Fe in limonite was determined from the weight loss resulting from the dehydration reaction of FeOOH to Fe₂O₃ during heating from 120 to 400 °C in TGA. The H₂O/Fe molar ratio varied from 0.06 for hematite to 0.60 for limonite YY, depending on the hematite content. Results from the pulverization tests showed that the higher value of H₂O/Fe molar ratio resulted in lesser abrasion of medium balls. A unique limonite YY in Australia, containing no hematite, was easily pulverized to sub-micron particle size and showed an excellent oil yield in coal liquefaction. It appeared that H₂O/Fe molar ratio could be one of the most important factors to select the better limonite catalyst for coal liquefaction. Moreover, it was found that Ni containing limonite SO in Indonesia exhibited a higher liquefaction activity than YY catalyst, because of transformation into a smaller crystallite size of pyrrhotite (Fe_1−xS). The agglomeration of pyrrhotites may be suppressed by a strong interaction between FeOOH and Al(OH)₃ such as Fe–O–Al. TEM–EDX analysis suggests that Ni may be located near the Fe_1−xS structure. Oil yield was significantly increased from 43 to 62 wt% daf by CLB addition to the coal slurry in the liquefaction of Banko coal. Finely pulverized limonite catalyst (SO) can be advantageously used in a commercial plant for coal liquefaction in Indonesia due to the low catalyst cost and a high liquefaction activity to obtain a high oil yield.     

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.     

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.