Most coal chemicals are obtained from high temperrature tar with an average yield over 5% of the coal which is carbonized.
The yield in coking are about 70% of the weight of feed coal.
Tars obtained from vertical gas retorts have a more uniform chemical composition than those from coke ovens.
Two or more coals are usually blended.
The conditions of carbonization vary depending on the coals used and affect the tar composition.
Coal-tar chemicals include phenols,cresols,xylenes,benzene,toluene,naphthalene,and anthracene.