RELATIONSHIPS BETWEEN PITCH COMPOSITION AND OPTICAL TEXTURE OF COKES

The optical texture of cokes obtained at 500 degrees C (60 minutes soa k time) from a range of pitches, coal-tar and petroleum pitches and fr om the extrography fractions of three of the pitches, was related to t he chemical composition of the parent material. Small differences obse rved in the amount of polyaromatic hydrocarbons and basic nitrogen pol yaromatic compounds present in vacuum-distilled and thermally treated binder pitches do not have a significant influence on the optical text ures of the resultant cokes. However, when pitches of very different o rigins (binder pitches, impregnating pitches, petroleum pitches and lo w-temperature tar pitches) are compared, different distributions of cl asses of compounds in terms of molecular size and functional groups (a s determined by extrography) have a definite effect on the optical tex ture of the coke, a wide range of structures being observed. The carbo nization of pitch fractions obtained by extrography gave valuable info rmation on the effect of specific types of compounds on the optical te xture of cokes. Fractions rich in basic PANCs provided cokes with the best developed optical texture, whereas fractions constituted by PAHs were not completely converted into mesophase under the same pyrolysis conditions. It was also observed that pitch material not eluted during the extrographic fractionation, which is highly polar, adversely affe cts the development of the optical texture of the cokes. (C) 1997 Else vier Science Ltd.