Coal liquefaction types

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

In most cases, the inert materials are merely held together by matrices of the internally generated solids. It is important to recognize that there are two very distinct types of material generated by coal liquefaction namely carbonaceous (coke-like) solids and carbonates. 

We have studied the thermal decomposition of diaryl ether in detail, since the cleavage of ether linkage must be one of the most responsible reactions for coal liquefaction among the various types of decomposition reaction and we found that the C-0 bond of polynucleus aromatic ethers is cleaved considerably at coal liquefaction temperature. 

The object of this paper is to draw attention to the possible importance of concerted molecular reactions, of the type termed pericyclic by Woodward and Hoffman (1), in the mechanism of coal liquefaction. 

Fundamental studies of coal liquefaction have shown that the structure of solvent molecules can determine the nature of liquid yields that result at any particular set of reaction conditions. One approach to understanding coal liquefaction chemistry is to use well-defined solvents or to study reactions of solvents with pure compounds which may represent bond-types that are likely present in coal [1,2]. It is postulated that one of the major routes in coal liquefaction is initiation by thermal activation to form free radicals which abstract hydrogen from any readily available source. The solvent may, therefore, function as a direct source of hydrogen (donor), indirect source of hydrogen (hydrogen-transfer agent), or may directly react with the coal (adduction). The actual role of solvent thus becomes a significant parameter. 

Many factors affect the rate and extent of coal liquefaction, including temperature, hydrogen partial pressure, residence time, coal type and analysis, solvent properties, solvent-to-coal ratio, ash composition, and the presence or absence of a catalyst. Many kinetic expressions have appeared in the literature, but since they are generally specific to a particular process, they will not be listed here. In general, liquefaction is... 

Aspects of coal liquefaction have been much researched, particularly with the re-emeigence of interest caused by the oil crisis in the 1970 s. The type of reactors used in the studies has been various, ranging from small bomb type microautoclaves through larger autoclaves and bench-scale reactors to larger scale pilot or demonstration plants. The use of differently sized and designed high pressure equipment for liquefaction studies further complicates an already complex system and allows only limited comparison of results. 

Autoclaves provide reactors which can be used readily to acquire data from coal liquefaction studies but are less representative of likely commercial plant tyi reactors than small scale continuous bed-type reactors. Ideally comparisons between reactors are best made by carrying out experiments in various designs of reactors under similar reaction conditions, but, in order to cover the full range of designs adequately, a larger expenditure on equipment (beyond the budgets of most laboratories) would be necessary. However, steps can be taken to cover the... 

All the hydrocracking/hydrogenation experiments were carried out in 500 ml capacity spinning type autoclaves. Two autoclaves of this design were used and the autoclaves were compared in experiments using the model compound phenanthrene, chosen because phenanthrene and its hydro-derivatives represent a large proportion of the solvent which is recycled in coal liquefaction processes. 

The results have shown that spinning/falling basket autoclaves can be used effectively for gathering data on coal hydroliquefaction, a single contact being representative of steady state conditions. As with other types of reactors for coal liquefaction, the catalysts were deactivated to a constant activity but the rate of deactivation was much more rapid in tiie autoclaves. 

The type of quantitative analytical data which are needed for modelling and kinetic studies on coal liquefaction process could not be obtained by using general analytical techniques. We have developed a new analytical approach for obtaining qualitative information as well as quantitative data on coal liquid species. Coal liquefaction produces smaller molecules from coal which is composed of larger molecular species or a matrix of larger molecular species in which smaller species are entrapped. 

Three types of direct coal liquefaction processes have emerged to convert coals to liquid hydrocarbon fuels 8... 

The software system, to meet the needs of the 1980 s, has wide flexibility and capabilities. For processes such as coal gasification or coal liquefaction, it can be used to perform steady state material and energy balances, calculate sizes of equipment, and carry out economic evaluations. Its flexibility can allow for the handling of coal or other solids in streams and equipment, and its capabilities allow for the simulation of many different types of process equipment and the calculations of physical properties under widely different conditions. Included in this is the ability to analyze conventional chemical and petroleum processes. Another valuable feature 1s a good preliminary cost estimation capability that permits the comparison of alternative processes on an economically consistent basis at an early stage of development. 

The potential importance of reactions involving ions or ion pairs in coal and model compound reactions has been emphasized by Ross and co-workers (42) as well as by Brower (43). For many types of reactions there exists considerable debate concerning reactive intermediates and mechanism. However, in the case of water formation, which is known to be rapid during coal liquefaction under relatively mild conditions and appears to occur in certain model compound reactions (15), it is difficult to construct plausible pathways without postulating ionic intermediates (although these intermediates may reside on solid surfaces). 

MAF conversions to pyridine solubles from short contact time coal liquefaction are dependent on the coal type, solvent source, and reaction severity. As reaction severity increases conversions approach a maximum value with a hydrogen-enriched solvent but go through a maximum and decline with a hydrogen-depleted... 

We have studied the transformations of two typical iron sulfides (troilite FeS and monoclinic pyrrhotite FeySg) at high temperatures. They represent the two extremes of the compounds of the type Fe xS. The purpose of this work was to determine the effect of temperature on the pyrrhotites, in the temperature range of interest in coal liquefaction (350-420° C). 

Several processes have been developed for coal liquefaction. Large-scale pilot plants have been in operation for the solvent-refining coal (SRC) process, and a pilot plant is being constructed for the H-Coal process, which is a direct catalytic process. Construction of demonstration plants is under consideration. The coal liquids produced from the current processes contain large amounts of residual fuels. They probably will be used initially as boiler fuels for stationary power plants. However, the nitrogen content of coal liquids is much higher than the petroleum residual fuels. The sulfur contents of coal liquids can vary considerably they depend on the type of coal and the liquefaction process used. Current coal liquefaction processes are capable of produc-... 

When the catalyst is available in a small amount, a microreactor assembly is often used (Miller, 1987). This is a simple T-type reactor heated by a fluidized sand bath. The mixing is provided by mechanical agitation that shakes the reactor up and down within the fluidized bed. Because of the small amount of slurry, and an effective heat transfer in the fluidized sand bath, the heat-up period in such a reactor is small. The nature of mechanical agitation is, however, energy-efficient. The reactor provides only a small sample for the product analysis, which makes the usefulness of the reactor for detailed kinetic measurements somewhat limited. The reactor has been extensively used for laboratory catalyst screening tests in coal liquefaction. 

Synthoil A coal liquefaction process in which coal, suspended in oil from the process, is hydrogenated over a cobalt-molybdenum catalyst on alumina. The process was piloted by the Pittsburgh Energy Research Center at Bruceton, PA, in the 1970s using several types of coal, but it was abandoned in 1978. See also CSF, H-Coal. 

Reactions involving gas, liquid, and solid are often encountered in the chemical process industry. The most common occurrence of this type of reaction is in hydroprocessing operations, in which a variety of reactions between hydrogen, an oil phase, and a catalyst have been examined. Other common three-phase catalytic reactions are oxidation and hydration reactions. Some three-phase reactions, such as coal liquefaction, involve a solid reactant. These and numerous other similar gas-liquid solid reactions, as well as a large number of gas-liquid reactions, are carried out in a vessel or a reactor which contains all three phases simultaneously. The subject of this monograph is the design of such gas-liquid -solid reactors. 

Absorption of carbon dioxide in a suspension of lime and thermal coal liquefaction are examples of Type I reactions. In the first example, calcium carbonate is produced by carbonation of suspensions of lime, whereas, in the second example, coal is liquified in the presence of hydrogen and oil to produce a host of products. These and several other examples of this type of reaction are summarized in Table 1-1. 

The types of industrial gas-liquid-solid reactor used in industry can be largely divided into two categories, i.e., one where the solids are fixed and the other where solids are in a suspended state (fluidized bed). Although the choice of the status of the solid depends mainly on the nature of the reaction system, often both fixed- and fluidized-bed systems are examined for the same reaction system (e.g., coal liquefaction). 

For some reactions listed in Table 1-4A, the fixed-bed reactor is operated under cocurrent-upflow conditions. Unlike the trickle-flow condition, this type of operation is normally characterized by bubble-flow (at low liquid and gas rates) and pulsating-flow (at high gas flow rates) conditions. Normally, the bubble-flow conditions are used. In the SYNTHOIL coal-liquefaction process, both pulsating-and spray-flow conditions are used, so that the solid reactant (coal) does not plug the reactor. In bubble flow, the gas is the dispersed phase and the liquid Ls a continuous phase. In pulsating flow, pulses of gas and liquid pass through the reactor. In the spray-flow regime, the gas is a continuous phase and the liquid is a dispersed phase. 

Continuous catalytic coprocessing and liquefaction experiments were conducted in a computer-controlled 1-liter bench-scale continuous unit of the type diagrammed in Figure I. The feedstocks included Illinois No. 6 coal and Maya atmospheric tower bottoms (ATB) in coprocessing or with a heavy hydrotreated 650 F-975 F recycle distillate (V-1074) from Run 257 at the Wilsonville Advanced Coal Liquefaction Facility in liquefaction experiments. Properties of the two vehicle oils are summarized in Table II. 

Oils and asphaltenes, which constitute a partial characterization of coal liquids according to solvent extraction, are generally considered to be key intermediates in coal liquefaction. In this regard, the present results do reveal that the asphaltenes contain higher molecular weight homologs in many specific-Z series and different compound types than do the oils. However, our study unequivocally demonstrates that compound types are observed in both the oils and asphaltenes that are equivalent in molecular formula and, hence, presumably in molecular structure. Furthermore, the overlap in the compositions of the two fractions is quantitatively appreciable. Thus, isolation of oils and asphaltenes must involve, in addition to solubility, other physical/... 

Typical Lewis acids such as AlCl3 and ZnCl2 display excellent catalytic activity in most Friedel-Crafts type reactions (9, 10) and are also known to catalyze coal liquefaction and solubilization (11-26). Because of this latter property, acid-catalyzed depolymerization has become a useful method for structural investigation of coal (27). The rationale for solubilization is interpreted either in terms of depolymerization via rupture of the bridges or, since the overall reaction in general is that of Friedel-Crafts alkylation or acetylation, in terms of the effect of the sidechains introduced on the aromatic ring system. 

Solvent fractions of coal liquids such as oils, resins, asphaltenes, and carboids may be separated because of their different polarity, molecular weights, and degree of aromatic character. The composition of coal liquids appears to be more closely related to the liquefaction process used rather than to the type of coal used. For example, oils and resins produced in SRC processes appear to have higher molecular weight, more aromatic average molecules than those contained in either pyrolysis or catalyzed hydrogenation coal liquids. This suggests less breakdown of coal and coal liquefaction intermediates to smaller. 

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