Carbons obtained by thermal and catalytic cracking of coal tars

Abstract

Reflected-light microscopy has been used to examine the solids formed during cracking of tar vapours at temperatures between 500 and 1000°C on high-temperature coke as contact material. The tars investigated were of the vertical-retort and the fluidized-bed types. Four types of carbons were distinguished on the basis of microscopic form and optical properties. Of these, two were varieties of pyrolytic carbon, another was (at least in part) similar to isotropic carbon, and the fourth a type of pitch coke. Estimates were made of the relative proportions of these types in the solid products from about sixty test runs. The effects of the following process variables on the properties of the carbon products were assessed: temperature of cracking, contact time, tar composition, the use of catalysts on the contact material, and addition of steam and oxygen to tar vapours prior to cracking.