Sujit K. Chakrabartty

Studies on the structure of coals. 3. Some inferences about skeletal structures

Contrary to the classic (and current) view that coal is a predominantly aromatic solid, its skeletal carbon arrangements appear to be largely made up of non-aromatic structures. Recent evidence from oxidation of coal with sodium hypohalite — a specific reagent which, among other matters, clearly differentiates between Sp2 and Sp3 carbon — indicates that these structures are modified bridged tricycloalkane systems or polyamantanes. Some properties of a structural model developed from polyamantane configurations are briefly explored. And parenthetically it is noted that assignment of a non-aromatic structure to coal is not inconsistent with extant experimental evidence now regarded as pointing to aromatic structure, since data are generally interpreted on the assumption that a high degree of aromaticity is likely.

Studies on the structure of coals. 2. The valence state of carbon in coal

Abstract A specific oxidation method for estimating the valence states of carbon in coal is described. The method, which is also an important tool for more generally exploring the structure of coal, is based on the fact that sodium hypochlorite is a very selective oxidant capable of differentiating between Sp 3 -carbon and Sp 2 -aromatic carbon. Proceeding from this recognition it is estimated that between 55 and 60% of the total carbon in coal exists in the Sp 3 -valence state. This estimate is much higher than the accepted ‘hydroaromaticity’ of coals.

Sodium hypochlorite as a selective oxidant for organic compounds

A study of the reactions of sodium hypochlorite with a wide variety of compounds has been carried out. The data indicate that a structure capable of producing a carbanion stable enough to undergo halogenation is oxidized by sodium hypochlorite to a ketone or a carboxylic acid. How far the oxidation will proceed is determined by enolateion resonance stabilization and by inductive and steric effects of the activating group (e.g.CO, –NO2, –CN, or –CO2H). Unactivated aromatic, hydroaromatic, alicyclic, and alkane systems are not oxidized. Heteroaromatic ring systems capable of undergoing azomethine-type addition can readily be cleaved, whereas benzenoid ring systems undergo no change. Oxidation of an activated alicyclic compound containing a tertiary sp3 carbon system may result in loss of one, two, or three carbon atoms as CO2 or CHCl3via 1,3- and 1,4-halogenation steps. Based on this investigation, a new methodology of oxidation has been developed for structural elucidation of complex materials such as coal.

The role of acid-base sites in the preparation of Al2O3-supported platinum catalysts

Abstract The sorption of hexachloroplatinic acid on variously prepared specimens of alumina has been investigated under equilibrium and kinetic conditions. Relationships between metal dispersibility and sorption are interpreted in terms of interactions with surficial acid-base couple sites on the alumina substrates.

Behaviour of iron catalysts in hydrocarbon synthesis from carbon monoxide and steam

Abstract The function of catalysts in hydrocarbon synthesis from carbon monoxide and steam has been examined by studying changes in the oxidation states, surface areas and crystallographic properties of iron catalysts during such synthesis. Evidence is presented that generation of hydrocarbons follows an antecedent shift reaction, and depends on a dynamic equilibrium between various transient oxidation states of iron as well as on formation of surface-active “free” carbon species in the catalyst. A qualitative set of equilibria for catalytic activity is outlined.

Catalytic hydropyrolysis of western Canadian coal combined with critical gas extraction

ABSTRACT Experimental results of catalytic hydropyrolysis combined with solvent extraction near critical conditions of an Alberta subbituminus coal indicated a conversion of 40 wt% of coal to hydrocarbon products. The effects of catalyst and solvent on the structural parameters of the extracts were evaluated from the modified Brown-Ladners equation. Both alcoholic and aromatic solvents and Lewis acids (ZnCl2 and SnCl2 2HO2) showed Increased yields of hydrocarbon products, but the presence of hydrogen was necessary to improve this yield.

Effects of boron trifluoride sorption on the caking properties of coal

Abstract Reversible and irreversible sorption of boron trifluoride by a suite of low- and medium-volatile bituminous (caking) coals was investigated. Extraction of irreversibly sorbed BF 3 with diethyl ether was used to test the hypothesis that BF 3 interacts with coal by forming adducts. An approximately rectilinear but inverse relation between residual sorbed BF 3 and the free swelling index was found.

SEARCH FOR LOW SEVERITY LIQUEFACTION CONCEPT

ABSTRACT Numerous process-configurations are presently being investigated to produce hydrocarbon liquid from coal. The common step in all the variants is thermal decomposition-dissolution of the coal in a liquid hydrocarbon vehicle; this common step is generally referred to as liquefaction. Unfortunately, up to now, no precise relationship has been established between liquefaction behaviour and coal composition or chemical structure. Extensive Study of the process indicates that liquid yield is high when the fluidity of the feed coal is high or d.a.f. hydrogen content is greater than 5%. The world resource of high-fluidity coal is limited, but in many countries easily mineable subbituminous or lignitic coals are abundant. The little investigation that has been done on the chemistry of liquefaction of low rank coals leaves room to search for an inexpensive method of producing a high yield of liquid from these resources. This paper discusses some relevant experimental data which may lead to development of n...

MASS TRANSFER LIMITATIONS IN COAL LIQUEFACTION

ABSTRACT In a number of contributions to coal liquefaction, gas–liquid mass transfer limitation has been referred by neglecting mass transfer limitation of solvent Into solid coal. Reported apparent activation energies of coal liquefaction reactions are In the range of 10–20 kCal/g–mole, which are too low for thermal reactions, Imply that diffusion Is the rate controlling step. In this study, the solvent diffusion effect on solvolysis of vitrinitic macerals In Alberta subbituminous coal has been studied, by performing petrographlc analyses of original coal and liquefaction residues. Quasi–steady state and transient coal–solvent diffusion-chemical reaction models are developed to Interpret the experimental data. Results indicate that solvent diffusion into the reactive maceral most likely be a rate limiting step In coal liquefaction.

Changes in pore structure of precipitated iron oxide catalysts during pretreatment and hydrocarbon synthesis reaction

Abstract In connection with studies of precipitated iron oxide catalysts for synthesis of hydrocarbons from carbon monoxide and steam, the changes in pore structure during pretreatment and synthesis reactions were investigated. Precipitated iron oxide catalysts initially contain fine ferric oxide particles built up from spheroidal crystals of different diameters which link to form tubular capillaries with varying widths. Upon CO-steam interaction and subsequent sintering of the catalysts, smoothing of the walls of tubular pores produces capillaries having ink-bottle shape. Changes in surface areas with crystallite sizes, as determined by X-ray line broadening, are discussed.