Pyridine extracts of coals

Pyridine extraction of coal appears to afford, as indicated by infrared absorption studies, a two-component system, one rich in carbonyl and hydroxyl functions and the other in nonaromatic... 

In addition, studies of the constitution of the pyridine extracts of coal have led to the conclusion, assuming that there are structural relationships between the extracts and the insoluble material, that coal consists of molecules having four to six aromatic rings carrying aliphatic side chains of four or five carbon atoms the average bituminous coal had molecules with four or five aromatic rings bearing side chains of three or four carbon atoms. 

In Curie-point Py-LVMS studies of maceral concentrates (22). vitrinitic moieties were shown to be the main source of the hydroxy aromatic components. Thus, the hydroxy aromatic signals observed in Figure 2d appear to be primarily derived from vitrinite-like components by means of pyrolytic processes. Presumably, therefore, the "nonmobile phase", rather than the "mobile phase , is the main source of the phenols observed in TG/MS and Py-MS studies of Pittsburgh 8 coal (9,16). Further support for this conjecture comes from the observation that phenolic products are also observed in Py-MS analysis of pyridine extracts of Pittsburgh 8 coal known to contain colloidal matter whereas the corresponding tetrahydrofuran extracts, free of colloidal material, produced no phenols (21). 

TABLE I. H/C Ratios for the Pyridine-extracts of the Illinois No. 6 Coal... 

An example of the difference of the solvent extracts from the bulk material comes from a series of studies on the exhaustive extraction of coal by boiling pyridine and fractionation of the regenerated soluble solids by sequential selective extraction schemes (Berkowitz, 1979). Subsequent analyses showed that the petroleum ether-soluble material was mostly composed of hydrocarbons (e.g., paraffins, naphthenes, and terpenes), while the ether-soluble, acetone-soluble, and acetone-insoluble fractions were resinlike substances with 80 to 89% carbon and 8 to 10% hydrogen. Indeed, this and later work (Vahrman, 1970) led to the concept that coal is a two-component or two-phase system (Derbyshire et al., 1991 Yun et al., 1991). 

The first systematic work on the extraction of coal using nitrogen-containing solvents (e.g., pyridine) resulted in the production of substantial amounts of... 

Quinoline and isoquinoline are heterocycles in which a benzene ring and a pyridine ring are fused through carbon. The isomeric heterocycles 1- and 2-azanaphthalene, better known by their trivial names quinoline and isoquinoline, have been the subject of extensive studies since their discovery in the extracts of coal tar at the beginning of nineteenth century. Since then their heterocyclic ring systems were found incorporated in several hundreds of natural products and were used as pharmacophore units in dozens of pharmaceuticals especially anti-bacterials, better known under the general name of Quinolones . ... 

Substantial increases in the extractability of coal with pyridine have been obtained by reacting coal with sodium hydroxide in ethyl alcohol. The yield of the extract rises with temperature and reaches a maximum at 450°C (840°F) after which the yield of extract decreases and there is also an observed increase in the yield of extract with coal rank. 

FIGURE 11.1 Fractionation of the pyridine extracts from coal. (From Berkowitz, N., An Introduction to... 

The first systematic work on the extraction of coal using nitrogen-containing solvents (e.g., pyridine) resulted in the production of substantial amounts of extract, which was then further fractionated to produce a series of fractions based on their solubility/insolubility in different solvents (Figure 11.3) (Burgess and Wheeler, 1911). 

Thus, it is possible to deduce several preferred options in the solvent extraction of coals using the so-called specific solvents. For example, the yield of extract usually decreases (but may, on occasion, increase) with an increase in the carbon content of the coal over the range 80% to ca. 87% carbon. However, use of a solvent such as pyridine may produce anomalous results and the petrographic composition of the coal may also have an effect. For coals having more than approximately 81% carbon the yield of extract is diminished to such an extent that only negligible yields of extracts are noted for coals having more than approximately 93% carbon. 

Complexing extraction of pyridine bases from coal coking products with organic solvents 97KGS3. 

Analysis of the results presented in Figures 2 and 4 appears to indicate that hydrogenation of the vitrinite is also accompanied by polymerization (see pyridine extract, Figure 4). If this can be confirmed, it would be worth investigating whether it involves specific fractions in the original vitrinite or has a random character. Solvolysis of different molecular weight fractions of a non-reductively alkylated vitrinite (or coal) may furnish some insight. 

Another parameter is the intrinsic extractability of the parent coals by pyridine. As can be seen in Figure 12, the shape of the curve of pyridine extract yield from the various coals vs. their carbon content follows the same trend as the short contact time conversions of these coals. 

If the initial reactions of coal are purely thermal, one might expect that the H-donor level will be of minor importance if times are kept short. In fact, all coals contain a certain portion of material that is extractable by pyridine. On heating coals to liquefaction temperatures, some additional material also becomes soluble in even non-donor solvents. Thus, there is a portion of all coals which can be solubilized with little dependence on the nature of the solvent. 

The product workup consisted of continuously extracting the filter cake with tetrahydrofuran (THF) and combining the THF and filtrate to make up a sample for distillation. In some experiments the THF extracted filter cake was extracted with pyridine and the pyridine extract was included in the liquid products. Extraction with pyridine increased coal conversion to soluble products by an average of 1.6 weight percent. The hot filtrate-THF-pyridine extract was distilled. Distillation cuts were made to give the following fractions, THF (b.p. <100 C), light oil (b.p. 100-232 C), solvent (b.p. 232-482), and SRC (distillation residue, b.p. >482 C). 

We have discovered that ZnC, in combination with methanol, constitutes an active liquid-phase catalytic medium for conversion of coal to pyridine-soluble material. There are several possible explanations for this effect improved contact between coal and melt higher activity of the ZnCl2 in the methanol medium methylation of cleaved bonds resulting in reduced char formation and extraction of the reaction products leaving the coal more accessible. 

I, 4 in hydrocarbons to 2 in pyridine (3 - 11,0) and again decreases to 1,5 in alcohols. Calculated on this basis value 3 of coal increases droningly with increasing the content of carbon from 70 % till 87 % and in a case of more metamorphized coal is sharply decreased again. Data concerning to the extraction of Greta coal are evidence of maximal yield of extract (more than 20 %) under it treatment with ethylendiamine and dimethylformamide (3 -... 

The other component of the coal volatilized material are free molecules existing in orginal coal this was shown by the py-f. i. m. s studies of coal samples and their pyridine extracts /14/. 

Previously the py.-f.i.m.s. of coals and their pyridine extracts has already been described (14) using this novel technique. About 100 micrograms of ground coal sample was heated in the high vacuum of a combined... 

Finally, completely equating the "mobile phase with solvent (e.g. pyridine) extractable "bitumen in coal ignores the potential presence of colloidal particulate matter in the pyridine extracts as well as possible solvent-induced scission of weak chemical bonds. Furthermore, the solvent-extractable fraction may well include macromolecular components, such as resinites. 

The uncrosslinked portion of the coal is obtained by Soxhlet-extraction of the coal with pyridine. Pyridine is a particularly good solvent for coals, and it is thought to remove a majority of the uncrosslinked molecules from the coal matrix. There is evidence that the pyridine-soluble portion is representative of the larger, crosslinked portion,(12) although this aspect remains... 

Finally, due to the extremely heterogeneous nature of coal, x parameters derived from Equation 1 can only represent at best an average interaction between a solvent and coal extract. It is also clear that pyridine extracts contain a substantial amount of low molecular weight material. Thus, an estimate of the degree of polymerization, x, which appears in Equation 1, is required. 

CHARACTERIZATION of the PYRIDINE-EXTRACT. Pyridine is known to cling to coals. The extract was therefore stirred with a methanol/water/HCl mixture for two days as suggested by Buchanan.(lS) Elemental analysis of the extract revealed 1.85% N. The original coal contained 1.92% N (daf) so it is apparent that the methanol/water/HCl treatment followed by drying successfully removed pyridine from the extract. The FTIR spectrum of the extract did not reveal the presence of pyridine. 

The swelling data in Table IV can be used to calculate x parameters for the extract and O-methylated extract using Equation 1. The results are shown in Table V. The x parameters for both extracts are observed to be positive and independent of pressure or concentration of benzene. The magnitude of the parameters are much larger than that determined for the O-octylated extract (0.65) which is consistent with their lower solubilities in liquid benzene. The X parameters are much larger than those determined by Larsen el al. for the pyridine-extracted Illinois No. 6 coal, which was near 0.3.(6) The reason for this are not clear. However, we note that benzene is a very poor solvent for these pyridine-extracts so large x parameters are expected. 

Primary Conversions and Influence of Mobile Phase Yields for the various H-donor and non-donor solvent extractions of Linby coal at 400% are summarised in Table III the conversions for the THF-extracted coal include the extracted material. Surprisingly, pre-extraction with THF significantly increases primary conversions in the polynuclear aromatic compounds (PACs) investigated. These findings appear to be contrary to those of other liquefaction (16) and pyrolysis (17) studies where prior removal of chloroform-extractable material significantly reduced conversions. However, Rincon and Cruz (18) have reported recently that pre-swelling coals in THF increases conversions for both anthracene oil and tetralin. The fact that Point of Ayr (87% dmmf C) coal yielded over 80% pyridine-solubles in pyrene (C.E. Snape, unpublished data) without pre-extraction is consistent with the earlier results of Qarke et al (19) for anthracene oil extraction where UK coals... 

Conversions to pyridine-solubles for non-THF-extracted Linby coal were much greater with naphthalene than with phenanthrene and pyrene (Table m, pre-soaking at 250% has little effect on conversions) and, even after THF extraction, naphthalene conversions are comparable to those of pyrene. 

Figure 1. Conversion of THF-extracted Linby coal with naphthalene at 400 C. Pyridine-solubles and THF-solubles.

Coke Manufacture By-products. In United States practice, coking of coal is done almost exclusively by the high-temperature (900-1200c C) process, For many years, the major source of the pyridines was the chemical-recovery coke oven, The volatiles produced in the coke oven are only partially condensed. The noncondensed gases are passed through a scrubber (the ammonia saturator) containing sulfuric acid. After removal of crystals (ammonium sulfate), a solution of ammonium sulfate and pyridinium sulfates is obtained and treated with ammonia to liberate and contained pyridine bases (— 70% is pyndine itself), See also Coal Tar and Derivatives. The balance of the pyndine bases is extracted from the crude coal tar. i.e., the condensed, main portion of the volatilization products from coking. The crude tar contains approximately 0,1 -0.2% pyridine bases, Further separation of the pyridines involves a rather complex series of extractions, distillations, and crystallizations. 

Synthetic Methods of Manufacture. Due to rising demand, production of the pyridine bases by large-scale synthesis passed the volume of tar bases extracted from coal tar in the 1960s. By the early 1970s. capacity in the United States for the synthetic manufacture of pyridine, the picolines, and 2-methyl-5-ethylpyridine (MEP) was in the tens of millions of pounds. All of these products can be made by condensation reactions of aldehydes and ammonia, MEP is no lunger made in the United Stales,... 

Ultraviolet fluorescence spectroscopy has also been employed to investigate the nature of the aromatic systems in coal and in coal-derived products (Mille et al., 1990). Examination of the pyridine extracts produced data that were characteristic of compounds having three, four, or five condensed aromatic rings. However, it was not possible to obtain an estimation of the ring size within the insoluble coal matrix. 

The effect of pyridine on coal has been known since the late days of the nineteenth century, and extensive follow-up studies were carried out to determine the comparative extractability of pyridine and chloroform (Bedson, 1902 ... 

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