Ronald A. Greinke

Constitution of coexisting phases in mesophase pitch during heat treatment: Mechanism of mesophase formation

Abstract The molecular constitutions of the coexisting anisotropic and isotropic phases of a heat-treated petroleum pitch were studied as a function of heat treatment time. The results show that the coexisting phases, which were isolated by high temperature centrifuging, contain different proportions of similar size molecules. The molecular weight distribution (MWD) of the mesophase did not change during the transformation, but the average MW of the isotropic phase increased significantly. Although the smaller molecules (400–1100 amu) present in the coexisting mesophase polymerize during the transformation, the constant MWD of the mesophase is explained by the stability of the larger pitch molecules (>1100 amu) and by the selective transfer of the smaller molecues (400–1100 amu) from the isotropic phase to the mesophase via stirring and generated gas percolation mechanisms. These transferred smaller molecules, which had been enriched in the isotropic phase, restore molecular equilibrium to the mesophase and result in the growth of mesophase regions. The nucleation of mesophase spheres in the coexisting isotropic phase is due to polymerization of the 400 to 1100 MW molecules in the isotropic phase and to the selective transfer of the 400 to 1100 MW molecules from the isotropic phase to the mesophase.

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.

Kinetics of petroleum pitch polymerization by gel permeation chromatography

Abstract The thermal polymerization kinetics of petroleum pitch molecules with molecular weights (MW) between 400–2000 were studied utilizing gel permeation chromatography (GPC). Two distinctly different reaction mechanisms of the petroleum pitch were observed from the GPC curves during transformation of the pitch to mesophase and semi-coke. When mesophase is forming in the pitch, molecules in the MW range of 400–700 were the most reactive, while molecules with MW greater than 1200 were essentially unreactivc. This lack of reactivity of the larger molecules ensures that the mesophase remains highly fluid during its formation. A change in reaction mechanism occurs after the mesophase has solidified as a result of the thermal polymerization reactions. At this stage, there is an abrupt decrease in the reactivity of molecules with MW less than 1100 and the reactivity of all measured molecules is the same. This significant kinetic change is due to a physical phenomenon in which solid state reactions occur in the infusible (vitrified) polymerized pitch. The significantly reduced reaction rates occurring in petroleum pitch after vitrification are similar to the results observed for other thermosetting materials.

Pyrolysis studies on model aromatic sulfur compounds

Abstract The incorporation of sulfur into pitches made from dinaphthylenethiophene, dibenzyldisulfide and dibenzothiophene, and the subsequent elimination of sulfur during carbonization were studied. Strained fivemembered rings in the dinaphthalenethiophene system were shown to lead to facile removal of sulfur. The ease of sulfur elimination during the conversion of dibenzyldisulfide into pitch shows the relative instability of sulfur in aliphatic side chains substituted on aromatic rings. The sulfur in dibenzothiophene is stabilized in large polymeric structures which eliminate sulfur only at high temperatures.

1H n.m.r. technique for characterization of polymerized petroleum pitches

Abstract A new proton n.m.r. technique has been developed for the chemical characterization of polymerized petroleum pitches with pyridine-insoluble contents as high as 80%. The polymerized pitches were completely solubilized for conventional 1 H n.m.r. evaluation in a mixed solvent system consisting of S 2 Cl 2 -SO 2 Cl 2 . Although solubilization occurs via the addition of chlorine to the polynuclear aromatic rings, the n.m.r. spectra can still be quantitatively interpreted. Several applications are discussed.

Quantitative influence of dealkylation and polymerization reactions on mesophase formation

Abstract The sensitivity of side chains on the isotropic content in a mesophase containing pitch was quantified after subjecting the decant oil based mesophase pitch to a series of Friedel-Crafts alkylation reactions. These data were then used to quantify the relative influence of concurrent thermal dealkylation and polymerization reactions on mesophase formation in another decant oil based pitch. The results show that the dealkylation reactions, which increase the aromaticity and molecular planarity of the pitch molecules, have only a minor influence (approximately 3%) on mesophase formation, while polymerization reactions, which increase the molecular size, have a major influence (approximately 97%) on mesophase development.

An Improved Fluorometric Method of Analysis for Benzo(a)pyrene in.Airborne Participates

This report describes the research employed to improve the tentative fluorometric method recommended by the American Public Health Association for the determination of benzo(a)pyrene in airborne particulars. A number of variables which affected the accuracy and precision of the tentative method were investigated. Five major improvements are suggested as a result of this research. The relative standard deviation of the improved method varied between 3.5% and 6.2% for benzo(a)pyrene levels of 15 to 400 nanograms.

Quantitative determination of anisotropic domain size in mesophase pitch

Abstract The optical texture of the carbonaceous mesophase is related to the nature of the pitch precursor, the mesophase viscosity and mode of preparation. The anisotropic domain size, represented by the distance between extinction lines, has been a useful parameter for characterizing mesophase pitches. A procedure for quantitative determination of mesophase domain size, utilizing annealing techniques and image analysis, is described and applied to several different mesophase pitch systems.

Determination of atmospheric furfural, a nonideal compound, after adsorption on charcoal tubes.

A charcoal tube procedure for the determination of a polar compound, furfural, in the atmosphere is critically examined. A number of solvents were tested in a search for an optimum desorption solvent. The recovery percentage of furfural as a function of the amount of adsorbed furfural, volume of desorption solvent, and weight of the charcoal was evaluated. The reversibility of the exchange reaction of furfural between the charcoal and desorption solvent was studied. Possible loss of furfural during sampling and storage in the charcoal tube, owing to displacement, volatility, or oxidation, was examined. No serious difficulties in the analyses were encountered.