Application of extrography for characterization of coal tar and petroleum pitches Marcos Granda, Jenaro Bermejo, Sabino R. Moinelo and Rosa Menendez lnstituto National del Carbdn, CSIC, Apartado 73, 33080 Oviedo, Spain (Received 14 December 1989; revised 12 February 7990) Extrography has been used for fractionation of coal tar and petroleum pitches into six fractions of increasing polarity by a given sequence of solvents. Sample recovery, composition of the fractions and reproducibility of separation into distinct classes of compounds were determined. The results of several samples show the efficiency of extrography for the characterization of pitches of different origin. FT-i.r. and gas chromatography were used to evaluate the separation. Extrography is a rapid, simple and reproducible technique for the characterization of pitch materials. (Keywords: tar; petroleum pitch; extrography) Considerable research has already been carried out on industrial applications of pitches but no detailed explanations exist for the different behaviour of pitches having very similar specifications. This is because pitch is a very complex material, both chemically and physically. It is necessary to develop new procedures to give more precise chemical information on pitch components. Properties traditionally used for pitch characterization, i.e. quinoline insolubles, softening point, etc, do not completely explain pitch behaviour. The characterization of the whole material by spectro- scopic or chromatographic techniques gives only limited information because of its complexity. Previous fraction- ation is necessary to simplify this characterization problem. Solvent extraction techniques have been widely used for pitch characterization, but there are problems because of co-solubilization effects which make it possible to find the same compound in both the soluble and the insoluble fractions’. Preparative liquid chromatography has also been extensively used for the fractionation and characterization of coal and petroleum derived products. It provides good separation into classes of compounds according to their functionality, but it is tedious and time consuming’. Size exclusion chromatography is suitable for the fractionation of complex mixtures of organic molecules according to their molecular size, each fraction being composed of molecules with different functionalities and within the same molecular size range. Extrography is an alternative technique that provides good fractionation in a relatively short time. It has been used under different conditions for the fractionation of low volatile residues from oil distillation3T4, for coal-derived liquidssp8 and also for the fractionation of coal tar and petroleum pitchess-ll. The purpose of this paper is to optimize extrography for the characterization of pitches from various origins. In this work, extrography is applied to the fractionation of eight commercial coal tar pitches (CTP) and petroleum pitches (PP), into aliphatic, aromatic, neutral hetero- aromatic compounds, monophenols, basic nitrogen 0016-2361/90/060702X)4 0 1990 Butterworth-Heinemann Ltd. 702 FUEL, 1990, Vol 69, June compounds and highly polar compounds, by using a sequence of six solvents. The resultant fractions have been characterized by FT-i.r. and g.c.-m.s., giving information not only about the quality of the fractionation but also about the chemistry of the constituent fractions. EXPERIMENTAL Table 1 shows selected properties of the pitches, which were supplied by Quimica de1 Nalbn S.A., Spain and Centre de la Pyrolyse de Marienau, France. Fractionation of pitches Four g of pitch, <0.20 mm in particle size, were solubilized or suspended in carbon disulphide, and 40 g’ of silica gel (63-200 pm) added to the solution. The silica gel was previously activated by heating at 12o”C, and its activity was adjusted by adding appropriate quantities of water. After mixing, the carbon disulphide was removed by vacuum distillation in a rotary evaporator and the solid residue dried under nitrogen. The dried material was placed in a glass column. At the bottom of the column, 18 g of silica gel were also placed to avoid fractions overlapping. When a previously established” sequence of six solvents (Figure I) was used; the solvent volumes were those consumed until no sample was eluted. The flow rate was approximately 5 ml min-‘. Solvents were pushed into the system by nitrogen, the flow of which was continued until all the solvent was removed. Then, the solvent was removed from the collected fractions and the residues dried, weighed and analysed by FT-i.r. and g.c.-m.s.. A last fraction (number 7) was obtained by Soxhlet extraction, with 300 ml of pyridine, of the residual sample retained on the silica gel. Solvents were previously purified by distillation and their quality checked by g.c.. Characterization of the fractions Gas chromatography of the fractions was carried out with a flame ionization detector and a fused silica