Pitch-to-solvent ratio

When a model compound is dissolved in a solvent, composition of the precipitate will not differ from those of the solute. However, when the solute is multicomponent, the composition of any insoluble fraction will depend on the relative proportions of the individual components (governed by their individual solubility limits) and their interactions. Therefore, properties of the pitch extracts should relate to the ratio of pitch to solvent used for the separation. As the pitch to solvent ratio increases, the relative proportions of... 

Figure 7. Effect of pitch to solvent ratio on A240 solubility.

Pitch. For the solvent analysis of pitch, a number of methods have been proposed. The solvents may be used sequentially or a fresh sample may be used with each solvent. Either the least or the most powerflil solvent may be used first. The ratio of solvent to pitch or pitch fraction and the temperature and time of extraction vary. 

The condensation products are mainly or wholly insoluble in organic solvents but do not differ markedly in C/H ratio from the high-boiling pitch compounds from which they have separated. The average molecular weight of the pitch shortly before conversion to spheres was about 450 and that of the material of the newly formed spheres was about 1700. Presumably further condensation reactions occur within the ordered structure of the spheres at higher temperatures after complete conversion to low-temperature coke. 

In view of the wide application of Py—GC in industry and research, the development of techniques and equipment for automatic analysis by this method is of great practical interest. An automatic Py—GC system was developed by Coulter and Thompson [69] for Curie-type cells with a filament for specific application in the tyre industry. A typical analysis involves the identification and determination of polymers in a tyre material sample. The material of a tyre is essentially a mixture of polymers, most often natural rubber (polyisoprene), synthetic polyisoprene, polybutadiene and butadiene-styrene copolymer. A tube is normally made of a material based on butyl rubber and a copolymer of isobutylene with small amounts of isoprene. In addition to the above ingredients, the material contains another ten to twelve, such as sulphur, zinc oxide, carbon black, mineral oil, pine pitch, resins, antioxidants, accelerators and stearic acid. In analysing very small samples of the tyre material, the chemist must usually answer the following question on the basis of which polymers is the tyre made and what is their ratio The problem is not made easier by the fact that cured rubber is not soluble in any solvent. 

An Exxon cat cracker bottom pitch was extracted with solvents of varying solubility parameter in order to evaluate the relationships which exist between extraction conditions and the characteristics of the extracted product. The precursor pitch possessed a carbon/ hydrogen ratio of 1.49 and a alculatedO, overall average solubility parameter of 10.48 reflux quinoline insolubles content of the pitch was 2.3% and the refluxing toluene insolubles were at a level of 20.3%. The pitch was not optically anisotropic. Upon heating in N2 to 530 C in a TGA, a coke yield of 37% was obtained. 

Sawicki 49) also monitored carbazole and BaP at three sites near the handling or use of coal tar. These results, presented in Table II, showed that some sources of polycyclics provide considerably more azaarene compounds compared to the amount of BaP they provide. The only other quantitative study of azaarenes in various effluents was conducted by Lao et al, (57), whose results are presented in Table I. Their BaP/BhQ ratio in coke-oven emissions is considerably higher than the value Sawicki et al. (57) found for coal-tar pitch polluted air. This discrepancy may be due to the use of different extraction solvents—Sawicki et al. (57, 52) used benzene, whereas Lao et al. (57) used cyclohexane. 

---