Pitch composition

As seen in Ch. 5, Sec. 2.1, pitch is a by-product of the destructive distillation of coal, crude oil, or asphalt. It meets the conditions for carbon-fiber production stated above (Sec. 2.1) and is inexpensive and readily available. Its carbon yield can exceed 60%, which is appreciably higher than the yield of PAN ( 50%). 

The composition of pitch includes four generic fractions with variable proportions. These are  

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The following is a discussion of factors which can be used to control or influence the size of optical texture of cokes by manipulation of the parent pitch composition and carbonization treatment. 

Analyses of Pitch. Modern analytical facilities of high-pressure liquid chromatography, gel permeation chromatography, an(j 1 nuclear magnetic resonance and mass spectrometry, associated with 1R and UV spectroscopy enable a total molecular constituent analysis of pitch composition to be obtained. The use of such information could then possibly be the route to prediction of pitch quality on carbonization. It would appear that such an approach would not be successful (ignoring the cost factor for such detailed analysis). The pitch cannot be considered as an assembly of molecules which pyrolyse independently of each other. The pitch carbonizes as a multi-phase system and experience today would indicate the impossibility of predicting all interactions, physical and chemical. 

Table II. Effect of Process Temperature on CCB-Distlllate Pitch Composition...

The distillate and residue obtained by high vacuum-distillation of catalytic cracking bottoms were converted into highly aromatic and anisotropic pitches. We used a two-stage high temperature process at 400°C. The effect of various process parameters on pitch composition and rheology was investigated. 

The CCB fractions were thermally-treated at 420°-450°C at atmospheric pressure in a nitrogen atmosphere and then vacuum stripped (0.5-1.Omm Hg) to remove the unreacted fractions. The pitch chemical structure was determined by NMR, and the pitch composition was determined by solvent analysis with toluene (at reflux) and quinoline (at 75°C). Toluene insolubles were determined because it represents a fusable pitch fraction with a 100% optical anisotropy on melting. 

Granda, M., Santamaria, R., and Menendez, R. (2003). Coal tar pitch composition and pyrolysis behavior. Chem. Phys. Carbon, 28, 263-330. 

Pitch viscosity also exerts a strong influence on the process as do the coal-binder interactions (Clarke and Marsh, 1989a). During the briquetting process, the properties of the binder pitch are changed by heat, duration of the process, air, and steam. These factors can change pitch composition in the thin layer present in the heated briquetting matrix. 

Coal-Tar Pitch Composition and Pyrolysis Behavior, M. Granda,... 

Granda M, Santamaria R, Menendez R. Coal-tar pitch, composition and pyrolysis behaviour. 

Fernandez, J. J., Figueiras, A., Granda, M., Bermejo, J., andMenendez, R., Modification of Coal-Tar Pitch by Air-Blowing, I Variation of Pitch Composition and Properties, Carbon, 33(3) 295-307 (1995)... 

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