In order to prepare the petroleum pitch for use as the blast furnace coke, pitches were produced from Gach Saran and Murban vacuum residue by heat-treatment at 425-440°C. The pitch thus obtained was fractionated by n-pentane, benzene and quinoline into four fractions; PS, PI•BS, BI•QS and QI, and the relationship between the amount of fractions in the pitch and the caking capacity of pitch was investigated. The caking capacity of the pitch was evaluated by a caking index determined by the Roga test.
It was found that there exists a clear relationship between the amount of fractions in the pitch and the Roga index when the pitches were classified into two groups corresponding to the amount of QI. A boundary value of QI was about 25%. When the amount of QI was 25% and below, the Roga index linearly increased with an increase in the amount of PI, and when the amount of QI was greater than 25%, the Roga index mainly depended on the amount of QI. That is, when the amount of QI was 25 and 50%, the Roga index was nearly constant, however when the amount of QI was greater than 50%, the Roga index decreased rapidly as the amount of QI increased. Further, the relationship between the amount of middle fractions (PI•BS+BI•QS) and the Roga index was shown in two separate curves and the turning point corresponded to the maximum value of middle fractions (_??_70%) in the course of heat-treatment and also to the boundary value of QI (_??_25%).