Reaction coal conversion

Sasol Fischer-Tropsch Process. 1-Propanol is one of the products from Sasol s Fischer-Tropsch process (7). Coal (qv) is gasified ia Lurgi reactors to produce synthesis gas (H2/CO). After separation from gas Hquids and purification, the synthesis gas is fed iato the Sasol Synthol plant where it is entrained with a powdered iron-based catalyst within the fluid-bed reactors. The exothermic Fischer-Tropsch reaction produces a mixture of hydrocarbons (qv) and oxygenates. The condensation products from the process consist of hydrocarbon Hquids and an aqueous stream that contains a mixture of ketones (qv) and alcohols. The ketones and alcohols are recovered and most of the alcohols are used for the blending of high octane gasoline. Some of the alcohol streams are further purified by distillation to yield pure 1-propanol and ethanol ia a multiunit plant, which has a total capacity of 25,000-30,000 t/yr (see Coal conversion processes, gasification). 

Research on catalytic coal Hquefaction was also carried out using an emulsified molybdenum catalyst added to the slurry medium to enhance rates of coal conversion to distiUate (26). Reaction at 460°C, 13.7 MPa (1980 psi) in the presence of the dispersed catalyst was sufficient to greatiy enhance conversion of a Pittsburgh No. 8 biturninous coal to hexane-soluble oils ... 

Heterogeneous catalysts are used to convert solid coal into gasoline and other chemicals. Solid coal is not easily transformed into hydrocarbon chains, so the conversion requires two general steps gasification followed by catalytic hydrocarbon-forming reactions. Coal is first gasified by reaction with steam ... 

Pyrolysis. In this context it is relevant to consider initially the effect of hydrogen contents on tar yields during pyrolysis (carbonization). This is particularly so, since, in all coal conversion processes little happens until the coal is at a temperature above that where active thermal decomposition normally sets in. In other words, all coal conversion processes may be regarded as pyrolysis under a variety of conditions which determine the nature of the primary decomposition and the reactions which follow. 

Hydrogen donors are, however, not the only important components of solvents in short contact time reactions. We have shown (4,7,16) that condensed aromatic hydrocarbons also promote coal conversion. Figure 18 shows the results of a series of conversions of West Kentucky 9,14 coal in a variety of process-derived solvents, all of which contained only small amounts of hydroaromatic hydrocarbons. The concentration of di- and polyaromatic ring structures were obtained by a liquid chromatographic technique (4c). It is interesting to note that a number of these process-derived solvents were as effective or were more effective than a synthetic solvent which contained 40% tetralin. The balance between the concentration of H-donors and condensed aromatic hydrocarbons may be an important criterion in adjusting solvent effectiveness at short times. 

Autoclave Results - Solvent Activity Test. The initial microautoclave work was done with tetralin and methylnaphtha-lene, using Indiana V bituminous coal (Table I). Base line data is shown in Figure 4. All three tests, Kinetic, SRT, and Equilibrium, show an increase in coal conversion with an increase in the concentration of tetralin. The Equilibrium Test shows the highest coal conversion of approximately 86 wt% of the MAF coal (based on the solubility in the tetrahydrofuran) at the 50% tetralin concentration. The Kinetic Test shows lower coal conversion. The hydrogen transferred to the coal from the tetralin in the Equilibrium Test at the 50 wt% tetralin feed concentration is approximately 0.5 wt% of the MAF coal. In the Kinetic Test 50 wt% tetralin feed concentration results in a much smaller transfer at the short reaction time of 10 minutes. 

Many studies on direct liquefaction of coal have been carried out since the 1910 s, and the effects of kinds of coal, pasting oil and catalyst, moisture, ash, temperature, hydrogen pressure, stirring and heating-up rate of paste on coal conversion, asphaltene and oil yields have been also investigated by many workers. However, few kinetic studies on their effects to reaction rate have been reported. 

Coal Conversion Chemical Reaction Steam Conversion... 

Practical conversion processes can only approach the theoretical efficiencies shown in Table 3. The coal conversion reactions do not proceed to completion at ambient temperatures within practical time limitations. As a result, a portion of the coal feedstock must be burned to supply heat so that the reactions can be carried out at elevated temperatures and pressure where the rates of conversion are rapid. In practical systems, this additional heat can only be partially recovered. Consequently, practical conversion processes have actual heat recovery efficiencies of about 60-70% for production of high H/C ratio products. Production of secondary fuels having somewhat lower H/C ratio, i.e. about 2.0, permits attainment of heat recovery efficiencies of 70 to 80j. 

Environmental applications of HRP include immunoassays for pesticide detection and the development of methods for waste water treatment and detoxification. Examples of the latter include removal of aromatic amines and phenols from waste water (280-282), and phenols from coal-conversion waters (283). A method for the removal of chlorinated phenols from waste water using immobilised HRP has been reported (284). Additives such as polyethylene glycol can increase the efficiency of peroxidase-catalyzed polymerization and precipitation of substituted phenols and amines in waste or drinking water (285). The enzyme can also be used in biobleaching reactions, for example, in the decolorization of bleach plant effluent (286). 

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. 

Both reactions act to reduce hydrogen bonding within the coal structure which may have a direct positive impact on liquefaction reactivity. More indirectly, these reactions lower the concentration of OH species in coal-derived products and hence, reduce the extent of retrogressive condensation via ether bridge formation. Reducing production of THF-insoluble condensation products increases the net THF-soluble coal conversion observed during the liquefaction experiment. None of the spectra from coals pretreated with alkyl alcohols and HCl showed any significant evidence of alkylation at carbon sites in the coal. 

In future work we hope to determine whether the reduction of oxygen occurs during the preconversion reactions as we speculate, or during the more severe reactions during coal conversion. 

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. 

Solem, J. K.. McCarthy, G. J. 1992. Hydration reactions and ettringite formation in selected cementitious coal conversion by-products. Material Research Society Symposium Proceedings, 245, 71-79. 

During coal conversion, the coal structure influences both thermal and catalytic reactions. Thermal reactions of solid coals initiate the breakage of weak bonds at rates proportional to their bond dissociation energies. The radicals thus produced require stabilization by hydrogenation or addition of small molecules otherwise the radicals couple to produce much more thermally stable bonds, which eventually leads finally to the formation of infusible and insoluble coke. 

In this work, the conversion refers to the amount of toluene solubles present at the end of the reaction. The conversion products thus include gases, oils and asphaltenes (GOA). Some of the conversion products are due to simple dissolution or to heating of the coal, and some are due to conversion of toluene insolubles to toluene solubles. Only the latter portion of the conversion products should be affected by the toluene density. The former are inherently toluene solubles, having nothing to do with the density or presence of supercritical toluene. These are only combined with the products obtained by reaction for experimental convenience. 

The results of experiments at 673 K and reduced density of 1.0 and 1.5 (supercritical toluene density of 0.301 g/cc and 0.444 g/cc) are given in Figure 4. As observed at 647 K, the coal conversion to gases + oils + asphaltenes (toluene solubles) increase with reaction time and with the density of the supercritical fluid. The retrogressive reactions are more significant now and hence, the toluene solubles show a maxima in conversion with time. 

At the present time, few, if any, details of chemical reaction mechanisms in coal conversion are known with certainty. This situation is particularly distressing in the areas of coal liquefaction and pyrolysis where chemical kinetics may strongly influence process efficiency and product quality. To improve this situation, in recent years a number of research groups have been performing chemical studies of coal and "model" compound reactions. 

This work presents the first systematic application of these methods to coal chemistry. This analysis is intended not only to suggest likely reaction mechanisms, but also to demonstrate the unique power of thermochemical kinetics methods for semi-quantitative analysis of the complex chemistry of coal conversion. 

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