Hydrogen donor and acceptor abilities of pitches from coal and petroleum evaluated by gas chromatography

Abstract

Among the characteristics of coal-tar and petroleum pitches, the thermal reactivity of their constituents is one of the most important because it determines the development of mesophase and, consequently, the structure of graphitizable carbons (cokes). At the early stages of the carbonization process the hydrogen transfer reactions and the availability of donatable hydrogen are crucial to give high fluidity/low viscosity systems. In such conditions, aromatic molecular systems have enough mobility to stack parallel to each other resulting in a more ordered coke structure. A chemical procedure for estimating the reactivity of a pitch to supply and consume hydrogen from the reaction system is the co-carbonization with anthracene and 9,10-dihydroanthracene (DHA) as hydrogen acceptor and donor agents, respectively. A series of pitches including impregnation and binder coal-tar pitches, petroleum pitches and pitch-like residues from the by-products coking plants was studied. Carbon disulphide extracts from the co-carbonization systems (pitch+anthracene and pitch+DHA) were analyzed by capillary gas chromatography. Results indicate that pitches with the highest hydrogen donor ability favour the formation of 1,2,3,4-tetrahydroanthracene in the reaction system. The relation between the amount of volatile matter released in the temperature range of 400–500°C and the hydrogen donor and acceptor ability of the pitches can be considered as important factors in the development of coke structure.