Pitches are extremely complex mixtures of several thousand different hydrocarbon components, and it is therefore impossible to find the exact chemical composition. Traditionally, pitches have been defined by properties such as softening point, coking value, ash content, quinoline and toluene insolubles, density and ash content. Although these parameters give some indication of the pitch behavior during carbonization, more information on the chemical characteristics of the pitch as a whole is needed. It has been anticipated that evaluation of hydrogen transfer properties could give valuable information. This project aims to widen the knowledge of hydrogen transfer reactions in pitches and their relation to pitch composition.

Graphitizable carbons, e.g. coal-tar and petroleum pitches, pass through a fluid stage during carbonization. The aromatic molecules in the starting material undergo dehydrogenative polymerization reactions to create aromatic, lamellar molecules. These aromatic molecules 'associate' to form an intermediate anisotropic nematic liquid crystal phase, mesophase, in the isotropic fluid matrix at a temperature between 350 and 500 ° C. The fluidity of the reaction system is a key factor in obtaining an ordered coke structure. During the carbonization process thermal cleavage of C-C and C-H bonds in reactive components of starting materials gives free radicals. When these thermally induced radicals are stabilized by transferable hydrogen, they may not recombine at a too early stage to form isotropic carbon and small-sized anisotropic carbon structures. Then the growth and coalescence of mesophase takes place under low viscosity/high fluidity conditions, and a more ordered anisotropic coke structure is formed. The hydrogen transfer characteristics of the pitch can be evaluated by hydrogen donor ability (HDa) and acceptor ability (HAa). Pitch and anthracene (hydrogen acceptor) or 9,10-dihydroanthracene (hydrogen donor) are heated to 400 ° C at a heating rate of 5° C/min in a sealed glass tube. The HDa can be measured by the formation of 9,10-dihydroanthracene (DHA) and 1,2,3,4-tetrahydroanthracene (THA) from anthracene, while the HAa can be estimated by the formation of anthracene from DHA. The amount of DHA, THA and anthracene formed during heat treatment can be found by GC-analysis. The figure shows a typical chromatogram from a donor ability test of a petroleum pitch.