Liquefaction products

ANALYSIS OF SHORT RESIDENCE TIME COAL LIQUEFACTION PRODUCTS (3)... 

Processing Short-Contact-Time Coal Liquefaction Products... 

A question then arises as to whether the CSD recovery is being limited by the preasphaltene content produced from direct products of coal liquefaction or whether by low liquefaction severity a more thermally sensitive product is produced resulting in retrogressive reactions of liquefaction products to "post-asphaltenes." There is some indication that "virgin" preasphaltenes, primary products of coal dissolution, are more easily recovered via CSD as shown in Table VII however, "postasphaltenes" made from thermal regressive reactions are not. 

E. Gorin, C. J. Kulik, and H. E. Lebowitz, "Deashing of Coal Liquefaction Products Via Partial Deasphalting. 2. Hydrogenation and Hydro extract ion EffluentsINEC Process Design and Developments, Vol. 16, Jan. 1977. 

The research involved the use of deuterium gas as a tracer to follow the incorporation of hydrogen into coal. Neither donor solvent nor catalyst was used in those experiments. The liquefaction product was solvent fractionated, and the fractions were examined for deuterium incorporation in each structural position. 

Pyrolysis and liquefaction products are in need of substantial treating processes, the chemistry of which is not yet very well understood. There is also a need and an opportunity to improve the selectivity of Fischer-Tropsch type processes. 

H/C = atomic hydrogen-to-carbon ratio V = vitrinite content of coal VM volatile matter St = total sulfur TRM = total reactive macerals The adequacies of these reactivity correlations, expressed as a percentage of the total variation in the data set explained by the model, were 80.0%, 79.2%, and 47.5% respectively. A later paper in the series (21) concentrated on the development of reactivity correlations for a set of 26 high volatile bituminous coals with high sulfur contents, and extended the models previously developed in include analyses of the liquefaction products and coal structural features. These structural features included the usual... 

Quantitative FT-IR Analysis. Selected samples of the liquefaction products, total product, the chloroform extracts, the asphaltenes, and the solid residues were analyzed as KBr pellets by FT-IR. The methods employed for quantitative analysis have been described previously (14-17). Measured amounts of sample are mixed with measured amounts of KBr, so that spectra are reported in absorbance units/mg of sample in a 1.33 cm pellet. A spectral thesis routine was used to obtain peak areas for individual functional groups and previously determined absorbtivities (17) were employed to obtain the reported percentages of each functional group. 

Short-contact time liquefaction products from bituminous coal... 

Among the many reports in the literature on coal liquefaction, several indicate a relationship between the rank of the coal and the complexity of the hydrocarbon groups in the coal and in its liquefaction products. This subject was reviewed in some detail in previous reports (1,2 ) and will only be summarized and updated here. 

Liquid sulfur dioxide was used to separate the liquefaction products from Texas lignite when Tetralin had been used as the hydrogen donor solvent. The large excess of Tetralin present with the lignite liquefaction products did not interfere with the liquid sulfur dioxide separation procedure. The chemical composition of the fractions were similar to that of SRC and SRL. 

Table III. Comparison of Formulae Identified from Extracts, Liquefaction Products, Carbonization Products, or PyMS for Structures Containing Sulfur Plus One Additional Heteroatom...

SULFUR-NITROGEN. Species containing sulfur and nitrogen are slightly more abundant than those containing two sulfurs per molecule. There are species with the empirical formula (IV) in the pyrolysis tar based on the carbon number, but higher alkylated species can not be distinguished from (V). Very small amounts of benzothienopyridine have been positively identified in liquefaction products (21). Species with formula (V) were seen in the PyMS... 

It seems likely that aromatic amines which are found in liquefaction products have been produced by a combination of thermolysis and hydrogenation. There is no evidence for aromatic amines in coals from either selective oxidation degradations (22) or from direct X-ray Photoelectron Spectroscopy measurements (23). Oxidations would produce very stable nitroaromatics which are not seen. Another possible structure for this formula is phenoxazine(Vb). Such a molecule would not survive high temperature combined with long reaction times. Although annelated thiophene with a pyrrole(VI) would appear to be a likely structure in coal, there is no evidence for its existence in any of the coal derived materials. 

The chemistry of coal liquefaction is not very well understood, even after more than two decades of research into the kinetics and mechanism of the process. There have been a number of models for conversion proposed, most of them focused on the several liquefaction products, including preasphaltenes, asphaltenes, oils, and gases. A survey of some of the models has been presented (1 ), and a common feature among them is the multiplicity of paths connecting all of the components. 

Generally, raising the temperature increases the aromaticity of coal liquefaction products. However, there were no significant changes in either the H/C atomic ratios or the hydrogen aromaticities (see Table VII) of the oils or asphaltenes with temperature. Though there was a decrease in the H/C atomic ratio of the extraction residue and possibly of the pre-asphaltene with temperature (see Table VII). The pre-asphaltene content also appears to decrease with increasing extraction temperature. 

Figure 9 shows a modern air-separation plant with front-end cleanup and product liquefaction. Production of such plants can exceed 2800 tons per day of liquid oxygen with an overall efficiency of about 15 to 20% of the theoretical optimum. The recent introduction of molecular sieve technology has provided an arrangement that increases the product to about 85% of the air input to the compressor. Thus, there has been a strong tendency over the past decade to retrofit older air-separation plants with this new arrangement to improve the process. 

Figure 2. Potential coal liquefaction production markets...

Midwest utilities are coal burners. They have the know-how and facilities to utilize solid fuels. Solvent refined coal, which has the potential of being the lowest cost coal liquefaction product because of its low hydrogen content, is of interest to this group. 

Although obviously not a coal liquefaction product, shale oil represents another synthetic fuel option. During the last quarter of 1979, the Department of Defense arranged with Standard Oil of Ohio through the Paraho Development Corporation to refine 100,000 barrels of raw shale oil. EPRI arranged for delivery of 4,500 barrels of the hydrotreated 700°F residue. 

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. 

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