Coal-derived liquids aromaticity

In addition to the Fischer-Tropsch-derived material, coal-derived liquids were also recovered from low-temperature coal gasification (not shown in Figures 18.3 and 18.4). These products were processed separately to produce chemicals, such as phenols, cresols, and ammonia, as well as an aromatic motor gasoline blending stock.34 The latter was mixed with the Fischer-Tropsch-derived motor gasoline. 

LC-MS has been used to study various aromatic fractions from coal derived liquids, and there are also a number of reports on its use in the analysis of porphyrin mixtures [601,602]. The early work by Dark et al. [601] using LC-MS for coal-derived liquids was mainly concerned with the separation and identification of polycyclic aromatic components. However, it is interesting to note that... 

Enthalpy of Formation and Absolute Entropy of Coal Liquids. Coal-derived liquids are of extremely complex compositions including highly aromatic groups. They are also characterized by their high contents of heteroatoms, such as oxygen, nitrogen and sulfur. 

In order to deal with a coal-derived liquid as a mixture which has a statistically average chemical structure, we choose two measurable structural parameters, aromaticity, fa Car/Ctotal) and the degree of substitution of the aromatic ring, a. To identify major atomic groups of coal-derived liquids which contribute to AHf° and S°, the following assumptions are made. 

The newly developed 600 MHz NMR Spectrometer is used to characterize coal-derived liquids and their chromatographically separated fractions. The distinct and well resolved proton resonance lines in both aromatic and aliphatic regions and IR analysis have been used to identify the major compounds and compound types. Double resonance technique has been applied for the chemical shift identification of donor protons (or-CHg, p-CH,) of partially hydrogenated polynuclear aromatic compounds. An NMR difference technique is applied to determine specific compositional changes in upgraded liquids derived under identical process conditions, but from different coal sources. 

Coal and many coal-derived liquids contain polycyclic aromatic structures, whose molecular equivalents form radical cations at anodes and radical anions at cathodes. ESR-electrolysis experiments support this (14). Chemically, radical cations form by action of H2SO4 (15,19), acidic media containing oxidizing agents (15,20,21,22), Lewis acid media (18,23-35) halogens (36), iodine and AgC104 (37,38), and metal salts (39,40). They also form by photoionization (41,42,43) and on such solid catalytic surfaces as gamma-alumina (44), silica-alumina (45), and zeolites (46). Radical anions form in the presence of active metals (76). 

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. 

In many cases we rely on the clay-gel chromatographic technique (17) (modifications related to applications with coal-derived liquids are given in Ref. 18) that separates aromatic furans and thiophenes from polar compounds such as phenols and thiols. Generally, this simple separation enables us to assign reasonable structures to the oxygen compounds. In our experience these are prevalently phenolic, although significant amounts of furans are also present. 

That coal-derived liquids consist largely of aromatic and cyclic structures suggests that, with appropriate hydroprocessing, high yields of benzene, toluene, and xylenes (BTX s) should be obtained. If the by-products of that BTX production could be directed toward linear... 

The extracts were fractionated by a Preparative Liquid Chromatography method - PLC-8 [2], in eight distinct chemical classes FI-saturated hydrocarbons (HC), F2-monoaromatics, F3-diaromatics, F4-triaromatics, F5-polynuclear aromatics, F6-resins, F7-asphaltenes and F8-asphaltols. This method, proposed by Karam et al. as an extension of SARA method [4], was especially developed for coal-derived liquids. It combines solubility and chromatographic fractionation, affording discrete, well-defined classes of compounds which are readable for direct chromatographic and spectroscopic analysis. 

Separation Techniques. The complexity of the organic composition of coal-derived liquids, shale oil, and their related effluents presents a formidable challenge to the analytical chemist. Our approach to this problem has been the classical separation technique based on acid-base-neutral polarity of the organic compounds. We further subdivide the neutral fraction into aromatic and non-aromatic fractions using dimethyl-sulfoxide (DMSO) extraction. DMSO effectively removes multiringed aromatic compounds with great eflBciency (85-95%) for these complex mixtures and thus allows a straightforward analysis for polynuclear... 

The PNA fraction of the shale oil was smaller (6%) than that fraction in the coal liquids (10- 29%). In shale oil, a larger fraction of the PNA compounds are alkylated than in coal-derived liquids. For example, C5 or higher-substituted aromatics were seen in shale oil but C3 substitution was rare in coal liquid. This characteristic difference in alkyl substitution was repeated also when the N-heterocyclic compounds were similarly compared. Few alkylated species were seen in the coal liquids but Ce and higher-substituted pyridines, quinolines, acridines, indoles, and carbazoles were detected in shale oil. For example, the PNA fraction of shale oil contained many indoles which can be seen in the gas chromatogram of this fraction see Figure 7). The different alkyl substitution patterns found in these two syncrude materials may well reflect the underlying structural differences in coal and kerogen. 

The combination of chromatography/mass spectrometry with MS/MS methods can in fact markedly enhance the analytical performance of the identification of phenols. This was demonstrated in the case of hydroxy aromatic components in coal-derived liquids. The analytical performance can be further improved by using chemical derivatization, as also shown in an MS/MS study of some methylphenols and methylnaphthols. In the course of GC/MS/MS analytical studies on nonylphenol in biological tissues, derivatization proved to be favourable in an indirect way The El mass spectrum of nonylphenol... 

Attention in fundamental and applied research on shape-selective catalysis has been largely focused on open-chain and monocyclic compounds. However, we have observed the rapid developments in polymer materials containing multi-ring aromatic units and the need to develop the monomers and other specialty chemicals from polyaromatic hydrocarbons that are rich in coal-derived liquids [Song and Schobert, 1993, 1996]. Scheme 1 shows the structures of some advanced polymer materials containing aromatic ring in the main-chain. 

During the past 7 years, we have developed and applied new methodologies using capillary-column GC for the separation and identification of PACs in coal-derived liquids. The primary samples that were used throughout these studies included a solvent-refined coal (SRC II) heavy distillate and a coal tar. Details of the isolation and identification of polynuclear aromatic hydrocarbons (PAHs) (II), sulfur heterocycles (12, 13), nitrogen heterocycles (14,15), amino- substituted PACs (16-18), and hydroxy-substituted PACs (14, 19, 20) in an SRC II heavy distillate have already been published (II, 13, 15, 18, 21). 

Current evidence indicates that coal-derived asphaltene constituents are a collection of predominantly one-to-four ring condensed aromatic systems that contain basic and nonbasic nitrogen constituents as well as oxygen (acidic and etheric) functions. These functionalities play a role in intramolecular relationships within the asphaltene fraction and also with the other constituents of the coal-derived liquid. This latter effect influences the viscosity of the liquid. Thus, coal-derived asphaltene constituents are an extremely complex solubility class by virtue of their thermal derivation from coal. 

The involvement of aromatic C - N<, especially derivatives from carbazoles, is not definite yet. Such a mechanism would be desired to reduce hydrogen consumption. HDO is not an important reaction for petroleum products, but it is very important in stabilizing coal-derived liquids. HDO of dibenzofuran is very slow. An acidic support is helpful for the HDO of dibenzofuran species. 

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. 

Proof of the existence of benzene in the light oil derived from coal tar (8) first established coal tar and coal as chemical raw materials (see Feedstocks, coal chemicals). Soon thereafter the separation of coal-tar light oil into substantially pure fractions produced a number of the aromatic components now known to be present in significant quantities in petroleum-derived liquid fuels. Indeed, these separation procedures were for the recovery of benzene—toluene—xylene (BTX) and related substances, ie, benzol or motor benzol, from coke-oven operations (8) (see BTX PROCESSING). 

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