Coal liquids, chemical structure

Yen, T. F. Structural Differences Between Asphaltenes Isolated from Petroleum and from Coal Liquid, Chemistry of Asphaltenes-, Bunger, J. W. Li, N. C., Eds. Advances in Chemistry Series No. 195 American Chemical Society Washington, D.C., 1981, p 39. 

The separation of chemical species by size exclusion chromatography is more reproducible than any other type of chromatography. Once the SEC columns, the mobile phase (most often a pure solvent like THF or toluene), and the flow rate are selected, the retention volume (or retention time assuming the flow rate does not change) is primarily a function of linear molecular size, which can be obtained from the valence bond structure if the compound is known. Some of the chemical species can interact with the solvent forming complexes with an effective linear size greater than that of the molecule. This causes the expected retention volume, based on "free" molecular structure, to shift to a lower but very reproducible retention volume. Phenols in coal liquids form 1 1 complex with THF (9,10) and carry the effective linear molecular size to increase. As a result phenolic species elute sooner than expected from their... 

The role of size exclusion chromatography is the separation of rather complex coal liquids into simpler fractions. The retention volume can be used to help Identify the chemical structure where GC-MS is unable to identify its possible structure. For example biphenyl and dihydroacenaphthene have the same molecular formula as well as similar mass spectral fragmentation patterns. Coal liquids contain both species. The one which appears first (lower SEC retention volume) is biphenyl (GC ret. time = 17 min. in Figure 5-6). Dihydroacenaphthene appears later at longer SEC retention volume and is identified in Figure 5-12 at GC retention time of 13 minutes. The former has a longer structure compared to the latter. 

Phenols are a major chemical lump present in coal liquids. Phenols have basically one or more aromatic ring structures with alkyl substituents. Methyl, ethyl and propyl are the most common alkyl substituents. The smallest specie is the one with a hydroxyl group attached to a benzene ring. Addition of a methyl group produces three isomers - o-, m-, and p-cresols. It appears that all three are present in more or less same proportion. The number of possible isomers increases as the possible number and size of alkyl substituents increases. It is expected that higher... 

Very commonly, however, the sample of interest is not a pure compound, but is a complex mixture such as a coal liquid. As a result, a specific structure determination for each molecular type is not practical, although it is possible to determine an average chemical structure. Features which may be determined include the hydrogen distribution between saturate, benzylic, olefinic, and aromatic sites. The carbon distribution is usually split into saturate, heterosubstituted saturate, aromatic + olefinic, carboxyl, and carbonyl types. More details are possible, but depend greatly on the nature of the sample, and what information is desired. 

Coal has been described as an organic rock. In order to better utilize coal supplies, however, the chemical structure of coal needs to be known in much greater detail so that methods can be developed to convert coal to a clean burning liquid or gaseous fuel. 

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. 

Chung, K. E., "Characterization of Coal-Derived Liquids— Relationships to Chemical Structures in Coal," Ph.D. Thesis, University of Utah, June 1980. 

In order to obtain Insight Into the chemical structure of coal, methods are needed to convert coal into substances which are soluble In suitable solvents. This conversion should be conducted at mild conditions so that the coal molecules remain unchanged as much as possible. So far, the most usual method applied to make bituminous coals more soluble In simple liquids Is hydrogenation which, however, requires temperatures exceeding 350° to 400°C consequently cracking reactions also occur. 

SRC, a detailed examination of the composition of these coal liquids is of fundamental importance. Numerous procedures have been published previously for investigating the composition of liquids derived from coal. In general, these procedures combine separation techniques with a variety of spectroscopic methods to provide the desired quantity of structural information. The separation techniques used include methods based on solubility fractionation (4,5), methods combining solubility fractionation and adsorption chromatography (6), and liquid chromatographic procedures for chemical fractionation (7,8). Chemical reactions also have been used to separate coal liquid asphaltenes into acidic and basic fractions (9). 

The gradient elution scheme is a scaled-up procedure originally described by Middleton (10) that has been extended to handle highly refractive materials such as coal liquids. This separation technique uses Alcoa F-20 alumina activated to a 5.5 wt % moisture level as the stationary phase. Details of this separation procedure are given elsewhere (2). This method separates SRC into 13 fractions and these fractions are listed in Table II along with some key chemical and physical descriptions of the cuts. The structural types indicated in Table II for Fractions 1-6 have been assigned based upon model compound studies and low resolution mass spectrometry (MS) (2), whereas the chemical types indicated for Fractions 7-13 are based upon IR observations and additional model compound studies. Recoveries in these separations are normally greater than 90%. 

In this study the USBM-API separation procedure was modified slightly. Monoaromatic and diaromatic compound types were eluted with specific solvents from an adsorption column. A three- to four-ring aromatic fraction was also desorbed with a stronger eluant. These fractions were separated on the basis of the carbon number of alkyl substituents by GPC. The subfractions obtained from LC and GPC separations were analyzed by mass spectroscopy. This technique provides a method of determining the chemical structure of coal liquids, which is complementary to NMR techniques (9). 

Naphthalene (NAF-thuh-leen) is a white crystalline volatile solid with a characteristic odor often associated with mothballs. The compound sublimes (turns from a solid to a gas) slowly at room temperature, producing a vapor that is highly combustible. Naphthalene was first extracted from coal tar in 1819 by English chemist and physician John Kidd (1775- l85i). Coal tar is a brown to black thick liquid formed when soft coal is burned in an insufficient amount of air. It consists of a complex mixture of hydrocarbons, similar to that found in petroleum. Kidd s extraction of naphthalene was of considerable historic significance because it demonstrated that coal had other important applications than its use as a fuel. It could also be utilized as the source of chemical compounds with a host of important commercial and industrial uses. Naphthalene s chemical structure was determined by the German chemist Richard August Carl Emil Erlenmeyer (1825-1909). Erlenmeyer showed that the naphthalene molecule consists of two benzene molecules joined to each other. 

The properties of manufactured graphites are determined by the microstructure of the carbonaceous mesophase which is formed during pyrolysis, usually between the temperatures of 370 C and 500°C. The characteristics of the final product can be measured in a qualitative way by examination of the mesophase micro-structure. Several coal liquid asphaltene and petroleum pitch samples have been screened in this way to determine their suitability as precursors for graphite materials. The physical and chemical properties of the mesophase formed from the samples and their pyrolyses residues were studied(1). It was found that the phenolic oxygen present either in the precursor or by addition during heat treatment suppresses mesophase formation by crosslinking and preventing the development of fluidity(2J>... 

Typically, reactants and products are represented by their atomic or molecular formulas, but molecular structures or simple names may be used instead. Phases are also often shown (s) for solid, ( ) for liquid, and (g) for gas. Compounds dissolved in water are designated (aq) for aqueous. Lastly, numbers are placed in front of the reactants or products to show the ratio in which they either combine or form. These numbers are called coefficients, and they represent numbers of individual atoms and molecules. For instance, to represent the chemical reaction in which coal (solid carbon) burns in the presence of oxygen to form gaseous carbon dioxide, we write the chemical equation... 

Gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are widely used in the chemical and petrochemical industries for processes such as methanol synthesis, coal liquefaction, Fischer-Tropsch synthesis and separation methods such as solvent extraction and particle/gas flotation. The hydrodynamic behavior of gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are of great importance for the design and scale-up of reactors. Although the hydrodynamics of the bubble and slurry bubble columns has been a subject of intensive research through experiments and computations, the flow structure quantification of complex multi-phase flows are still not well understood, especially in the three-dimensional region. In bubble and slurry bubble columns, the presence of gas bubbles plays an important role to induce appreciable liquid/solids mixing as well as mass transfer. The flows within these systems are divided into two... 

HVL-P represents about 70% of condensed-phase product (CPP) (viz. liquid and solid products) which includes light liquid, heavy liquid, and char. An estimate showed that the average aromatic cluster size of CPP is 2.2, which is practically the same as that of HVL-P. This indicates that HVL-P has the average chemical characteristics of CPP. This estimate was made by assuming that the light liquid and the char were similar to Light and Resld of HVL-P, respectively, in molecular weight and cluster size. If we assume that CPP retains any stable structural features of the feed coal then HVL-P would reveal such structural features. 

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). 

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