Coal-derived process solvent

LSE [Liquid solvent extraction] A coal liquifaction process, under development in 1990 by British Coal, at Point of Ayr, North Wales. The coal is dissolved in a coal-derived hydrocarbon solvent and then catalytically hydrocracked. 

Using microbore LC columns, a separation method was developed for a series of weakly basic cyclic and noncyclic secondary amines, which were identified as components of coal-derived solvents. As shown in another study, using normal HPLC on silica gel with Freon-113 elution, model mixtures of aliphatic and aromatic hydrocarbons and nonpolar constituents can be separated in coal-liquefaction process solvents. Encouraging results were obtained on both semipreparative (4.6 mm i.d.) and microbore (1 mm i.d.) columns. According to further reports, carbamate pesticides, polymer additives and solvent-refined coal were analysed, and the components of bergamot oil can be identified. GPC/FT-IR can be used to detect components of cold-rolling oil and to analyse polymers, whereas SEC/FT-IR can be applied to the analysis of coal liquids and to improve detection and identification of proteins. 

The Pott-Broche process (101) was best known as an early industrial use of solvent extraction of coal but was ended owing to war damage. The coal was extracted at about 400°C for 1—1.5 h under a hydrogen pressure of 10—15 MPa (100—150 atm) using a coal-derived solvent. Plant capacity was only 5 t/h with an 80% yield of extract. The product contained less than 0.05% mineral matter and had limited use, mainly in electrodes. 

A schematic diagram of the liquid solvent extraction process is illustrated in Figure 1. Where the production of liquid hydrocarbons is the main objective an hydrogenated donor process solvent is used, whereas in the production of needle coke this is not necessary and a coal derived high boiling aromatic solvent may be used (e.g. anthracene oil). An essential economic requirement of the process is that a high extraction yield of the coal is obtained and this will depend upon the coal used and the digestion conditions. 

The liquefaction process is initiated by the thermal generation of coal-derived free radicals which in turn react with solvent to form solvent radicals by hydrogen abstraction. These sol-... 

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. 

In the Solvent Refined Coal Process, coal is dissolved in a coal-derived solvent to produce a filterable liquid. 

Proposed methods for predicting heats of formation and absolute entropies are tested on two fractions of synthetic crude oil obtained by the EDS process, one sample of H-Coal, one sample of Synthoil, two samples of Solvent Refined Coal, and five pure compounds found in coal liquefaction products. For these samples, the heats of combustion are calculated using predicted values of AHf° and compared in Table IV with observed values. Note that Equations 8 and 9 were used to predict AHf° and S° of the EDS heavy naphtha. Equations 6 and 7 are applied to other samples of coal-derived liquids, and Equations 3 and 4 to the pure compounds. 

Combustion tests of fuel oil blends derived from the Exxon Donor Solvent (EDS) process were carried out in a laboratory 50 hp test boiler and a commercial 1425 hp boiler. All tests showed that coal derived fuel oils burn cleanly compared to petroleum fuels with low levels of smoke and particulates. Emissions of N0X were related to fuel nitrogen content for both the petroleum and coal-derived fuels. 

In the studies carried out to date, eight fuels have been tested which include six synfuels and two petroleum derived fuels. The synfuels tested included SRC-II middle and heavy distillate fuels, a blend of these fuels, and one SRC fuel blended with the process donor solvent. Composition data for the various fuels are presented in Table I, where it can be seen that the coal derived liquids have a higher C H ratio than either the diesel or residual petroleum oils, indicative of a higher aromatic hydrocarbon content. The shale-derived DFM on the other hand is a highly processed fuel and has a C H ratio similar to the petroleum diesel oil. Complete analyses of all the actual fuels tested were unfortunately not available at the time of writing, and, where necessary, typical analyses have been taken from previous studies. 

Direct coal liquefaction (DCL) refers to the process of converting coal to liquid products by mixing ground coal with a recycled process solvent and/or petroleum-derived residual oil and reacting the slurry in a hydrogen atmosphere at 750-850°F (400-450°C) and 1000-2500 psig (7-17 MPa). Under these conditions, the coal structure breaks down into... 

PENTANE Asphaltenes (C5). No established method is available for the preparation of pentane asphaltenes. ASTM D-2006 was discontinued in 1976. Another ASTM method (for rubber extender and processing oils) (23) uses a 10-g sample and only 100 mL of pentane, which is insufficient for a correct dispersion of the sample into the solvent. A very precise method for these asphaltenes from coal-derived liquids has been described (24), but some might object to the use of benzene because of the solubilizing properties of this solvent towards asphaltenes. 

Coal-Derived Oils. Coal-derived oil from the solvent fractionation of CLP from the 400-lb coal/day PDU described previously exhibits a slightly higher g value, a broader spectral line, and a significantly lower spin concentration than the process coal from which it was derived (36). Only a limited number of oils have been examined by ESR additional work is needed before the results can be generalized. 

The Kohleoel process is illustrated in Figure 12.3. Coal and iron oxide catalysts are slurried with process-derived recycle solvents. The specific coal feed rate is in the range of 0.5-0.65 t/m3/h. H2 feedstock together with additional H2 recycled from the process, after mixing with the slurry, is sent to an up-flow tubular reactor. The reactor is typically maintained at 30 MPa and 470 °C. Hot effluents from this reactor... 

Adschiri et al. removed 70 wt.% of the nitrogen from coal-derived pitches by catalytically hydrotreating the pitch in a supercritical toluene-tetralin mixture at 450 °C [67]. These pitches could be used for the production of high-quality electrode carbon. The more conventional process for this reaction involves catalytic hydrotreating of the pitch in the liquid phase. The higher dif-fusivities in the SCF resulted in higher reaction rates. Moreover, catalyst coking could be reduced effectively due to the increased pressure and hence the solvent power of the SCF. 

Thus, the solvent extraction of coal, far from being a theoretical study, is, in fact, very pertinent to the behavior of coal in a variety of utilization operations. For example, the liquefaction of coal (Chapters 18 and 19) often relies upon the use of solvent and, in addition, the thermal decomposition of coal can also be considered to be an aspect of the solvent extraction of coal. The generation of liquid products during thermal decomposition can be considered to result in the exposure of coal to (albeit coal-derived) solvents with the result that the solvent materials being able to influence the outcome of the process. And there are many more such examples. 

The majority of the coal liquefaction processes involve the addition of a coal-derived solvent to the coal prior to heating the coal to the desired process temperature. This is, essentially, a means of facilitating the transfer of the coal to a high-pressure region (usually the reactor) and also to diminish the sticking that might occnr by virtue of the plastic properties of the coal (Chapter 9). 

---