Irwin Charles Lewis

Chemistry of carbonization

Abstract Considerable progress towards understanding the chemistry of carbonization has been achieved through the efforts of a large number of investigators. Advanced analytical techniques such as: chromatographic methods, thermal analysis, mass spectroscopy, and electron and nuclear magnetic resonance, have enhanced our ability to characterize carbonaceous materials. Structural studies using X-ray have demonstrated the relationships of starting structure to final graphitizability. Reaction studies, using model compounds have shown the importance of molecular rearrangement and dehydrogenative polymerization on the overall carbonization process.

Thermal polymerization of aromatic hydrocarbons

Abstract The conversion of the aromatic hydrocarbons, anthracene and naphthalene to pitch was studied using a variety of techniques including gel permeation chromatography (GPC), field desorption mass spectrometry (FDMS), nuclear magnetic resonance (NMR), and hot-stage microscopy. The results show the importance of aromatic polymerizations in carbonization. These reactions lead to a rapid increase in molecular weight but not necessarily to a high degree of aromatic condensation. Average structures for the naphthalene- and anthracene-derived pitches are proposed, and the thermotropic nature of napthalene-derived mesophase is described.

Chemical changes during the mild air oxidation of pitch

Abstract The chemical changes occurring during mild oxidation of petroleum and coal tar pitch were studied by elementary analysis, solubility measurements, IR and nuclear magnetic resonance spectroscopy and chromatography. The oxidized pitches were compared with pitches which were distilled to give similar softening points. A mild oxidation was shown to induce dehydrogenative polymerization of the pitch components without introducing appreciable amounts of oxygen into the products. The greater reactivity of the petroleum pitch constituents to oxygen is attributed to the presence of alkyl substituents. Study of the mesophase formation and X-ray analysis of the derived graphites showed that mild air oxidation did not affect the subsequent graphitic development.

Chemistry of pitch carbonization

Abstract The conversion of pitch to carbon is a complex process encompassing a multitude of physical and chemical transformations among the many pitch components. Studies on both individual aromatic compounds and pitches have shown that polymerization through loss of side chains and hydrogen is the main chemical reaction. Molecular rearrangements are also prevalent. A continual increase in molecular weight through polymerization and loss of low molecular weight volatiles results in the transformation of pitch to mesophase, coke and ultimately carbon. Stable free-radicals are formed during both the polymerization and rearrangement processes. These various aspects are reviewed to develop a general mechanistic sequence for pitch carbonization.

ESR study of the kinetics of carbonization

Abstract Electron spin resonance (ESR) data have been obtained for a well-graphitizing and a poorly-graphitizing pitch as a function of heat-treatment time at reaction temperatures between 400° and 490°C. Measurements of ESR spin concentration and linewidth and of atomic C H ratio have been used to delineate the kinetics of the transformation of pitch to coke. Correlations between the various ESR and constitutional parameters have been used to obtain information concerning the mechanism of carbonization.

Carbonization of naphthalene and dimethylnaphthalene

Abstract A variety of analytical techniques has been utilized to determine the chemical changes which take place during the thermal conversion of the aromatic hydrocarbons naphthalene (N) and dimethylnaphthalene (DMN), to pitch, mesophase, and coke. Aromatic polymerization was shown to play a dominant role at each stage of the coking process. Secondary reactions involving hydrogen transfer and molecular rearrangement were also apparent. Polymerization of (N) occurs largely through the loss of hydrogen while the polymerization of (DMN) involves the elimination of methyl groups. The faster rate of coking for (DMN) compared to (N) is attributed to the activating effect and facile bond cleavage of the methyl group.

An electron spin resonance study of the carbonization of the aromatic hydrocarbon acenaphthylene

Abstract Electron spin resonance measurements have been made on carbonized acenaphthylene in the pure state and in solutions in inert liquids. Well-resolved nuclear hyperfine structure is observed in the liquid solutions. Isotopic substitution experiments prove that nuclear hyperfine interaction is the main source of line broadening in the ESR of these low-temperature chars. The identities and reactions of the free radicals are discussed.

Chemical structure and graphitization: X-ray diffraction studies of graphites derived from polynuclear aromatics☆

Abstract The average semi-lattice spacings as determined by X-ray diffraction measurements of the (001) bands were determined for graphites derived from numerous polynuclear aromatic hydrocarbons and quinones. These values were used as a criterion of the degree of graphitization of the carbonized compound after heating to 3000°C. The results showed that the nature of the final graphite is highly dependent on the chemical structure of the starting material. However, the relationship is not always obvious as two major factors appear to be involved: 1. (1) the planarity and steric overcrowding in the original molecule, and 2. (2) the chemical reaction sequence and nature of the thermally formed intermediates involved in the polymerization stage of carbonization.

Electron spin resonance of stable aromatic radical intermediates in pyrolysis

Abstract This paper presents the results of electron spin resonance measurements on several types of stable aromatic free radicals suspected as intermediates in carbonization. The radicals studied include phenalenyl, 1-methylphenalenyl, 1-phenylphenalenyl, fluorenyl, 9-phenylfluorenyl, and biphenyleneallyl. The radicals all show remarkable stability at high temperatures. For at least a limited group of compounds, a correlation appears to exist between the planarity of free radical intermediates formed during carbonization and the degree of order of the final graphites.

Magnetic orientation studies of synthetic mesophase pitches

Abstract Previous studies have shown that mesophase spheres with Brooks-and-Taylor structure are nematic liquid crystals which oriȩnt with their molecular c -axes perpendicular to a magnetic field. Mesophase spheres in synthetic pitches made from anthracene and naphthalene with AlCl 3 show similar magnetic orientation behavior; however, they have a novel structure, which was elucidated with the use of sensitive tint microscopy and magnetic orientation experiments. In the proposed structure, the aromatic molecules within the bulk of the sphere, are stacked in parallel layers, similar to those in the Brooks-and-Taylor spheres. However, at the interface of the sphere with surrounding isotropic phase, the molecular planes are oriented parallel to the surface, unlike those observed in the Brooks-and-Taylor spheres.