Liquefaction reaction conditions

Carbonaceous solids appear as a result of retrogressive reactions, in which organic thermal fragments recombine to produce insoluble semi-cokes (59,65). Coke formation is observed during liquefaction of all coals and its extent can vary widely according to the coal, the reaction solvent, and reaction conditions. The predominant inorganic species produced during the process of coal... 

The liquefaction of coals was studied in a 500 ml magnetically-stirred stainless steel antoclave. Two different reaction conditions were used in this study, hut the experimental procedures were almost the same in both conditions. 

The effects of various reaction conditions on the reaction rate and the mechanism of coal liquefaction were investigated.Conclusions are summarized as follows ... 

Under the same reaction conditions, the reaction rate are depend on the mechanism of coal liquefaction and kinds coal and catalyst. The reaction rate is in the following order Morwell> Bukit... 

Effect of Reaction Conditions on Solubility. Earlier results ( ) suggested investigation of the ZnCl -methanol system as a coal-liquefaction medium based on high product solubility, low... 

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. 

The activated hydrogen molecules can be attracted to each other more than normal hydrogen molecules in the reaction medium and these attractions may result easily in liquefaction of hydrogen in reaction conditions (Fig. 5.12). 

Figure 5.11 shows the plot for yield of hydrogen liquefaction on Pt-supported carbon versus hquefaction time. The yield of hydrogen liquefaction increased with increasing hquefaction time. The nominal liquefaction time was 30 min in reaction conditions. The yield of hquefied hydrogen was 7.4% weight of Pt-catalyzed carbon. 

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... 

Much of the recent research in direct coal liquefaction seeks to develop methods for dissolving coal at low reaction severity (defined as temperatures below 350 and pressures of 1000-1500psig). Most of these efforts have been prompted by several incentives that exist for converting coal at milder reaction conditions than those utilized in conventional processes, including ... 

Liquefaction reactivity experiments were conducted in a 20 cm- tubing bomb reactor attached to an agitator and immersed in a fluidized sandbath. Table II lists reaction conditions used in these runs. A non-hydrogen donor vehicle (1-methylnaphthalene, 1-MN) and a hydrogen donor vehicle (9,10-dihydrophenanthrene, DHP) were used as solvents (2/1 solvent/coal wt. ratio). Coal conversion was monitored using THF extraction data corrected for the intrinsic THF solubility of untreated and treated coals. 

Figure 1. Effect of Mild Propylation on Liquefaction Reactivity of Four Argonne Coals at Low Seventy Reaction Conditions.

Figure 2. Effect of Alkyl Group Size on Coal Liquefaction Reactivity of Treated Wyodak Coal at I w Severity Reaction Conditions.

An enormous amount of work both at bench scale and at pilot plant scale have been conducted to study the production of liquid and gaseous hydrocarbons from coal. Since most of the analytical methods are either very time consuming or very specialized, almost all the data available on the coal liquefaction process are based on distillation data or on the assumption that all products which are not insoluble solids are converted. It is known that products of liquefaction vary based on coal, reaction conditions, and media of reaction hence, conversion and yield may be based on very different products. 

Coal liquefaction research after the second world war focused on moderating reaction conditions in terms of temperature and pressure in order to lower construction costs of the coal liquefaction facility. At present, typical conditions are 150-200 atm and 300-480°C. Moderation was achieved primarily through improvements in catalysts and donor solvents and through... 

The reaction conditions and product analyses of the hexane solubles for SCT liquefaction of Belle Ayr coal in high and low hydrogen solvents are shown in Tables 3 and 4 respectively. 

If the reactor zones were superimposed on Figure 6 or 7, and the comers were to be linked up through the diagram, it seems relatively clear that one or another of the pyrrhotites would be the principal iron-containing reaction product of pyrite throughout the coal liquefaction range of temperatures and reaction conditions. 

The specific reaction ( activation ) conditions for the conversion of catalyst precursors to unsupported catalysts have a direct effect on the catalytic activity and dispersion. The importance of reaction intermediates in decomposition of ammonium heptamolybdate and ammonium tetrathiomolybdate, and the sensitivity of these intermediates to reaction conditions, were studied in coal liquefaction systems. Recent results indicate that optimization of activation conditions facilitates the formation of a highly dispersed and active form of molybdenum disulfide for coal liquefaction. The use of the catalyst precursors ammonium heptamolybdate, ammonium tetrathiomolybdate, and molybdenum trisulflde for the conversion of coal to soluble products will be discussed. 

XRD analysis has revealed the presence of several different types of carbonate minerals in liquefaction residues from a number of coals. Minerals identified included vaterite and calcite (two polymorphs of CaCO,) dolomite (CaMg[C03]2) and in the residue from a high sulfur coal (2.26 db), anhydrite (CaSO,) was identified. The types of mineral deposits formed depend not only on the coal but also on the reaction conditions. Our data indicates that whilst vaterite forms at low temperatures (380°C), as the temperature increases, the vaterite becomes progressively converted to calcite, the more stable form. After further increases in temperature, particularly at long reaction times, dolomite begins to form. 

This statement applies without any restriction to coal liquefaction as well. Hence, for hydrogenation process engineering the optimization of the reaction conditions has precedence over the raw material properties. 

Short-Contact-Time Coal Liquefaction Products and the Initial Structure of Coal. Our own data and those from the literature indicate that no major changes take place in the different elements of coal structure under short-contact-time reaction conditions and at relatively low temperature. It is obvious, however, that fragmentation occurs by... 

PTGL-processes (table Ia,b,c) can be characterized by their operating principle (pyrolysis, gasification or liquefaction) and reaction conditions, their type of reactor and method of heat supply and the possible presence of auxiliary systems. The selection of a particular process will ultimately be based on its proven reliability on one hand and on the quality of the process output on the other [ ]. ... 

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