Composition changes in phenols and hydrocarbons during the oxidative pyrolysis of primary coal tars

A study has been made of the changes in the phenols and hydrocarbons yields and compositions during the oxidative pyrolysis of primary coal tars over a wide range of conditions (temperature, pyrolysis period, air supply), compared with pyrolysis in the absence of air. The introduction of atmospheric oxygen greatly intensifies the thermal degradation of primary-tar phenols, notably the higher-boiling polyalkyl homologs. Phenol itself undergoes less degradation. The oxygen becomes particularly active when the conditions prevent stable combustion of gases and vapors for one reason or another, so that more molecular oxygen is available to react directly with the tar vapors. The introduction of atmospheric oxygen suppresses the buildup of hydrocarbons soluble The introduction of atmospheric oxygen suppresses the buildup of hydrocarbons soluble in petroleum ether which characterizes the pyrolysis of primary tars in the absence of air. If the oxygen reacts directly with the tar vapors at 750/sup 0/C, the hydrocarbons contents of the pyrolyzed tar are lowered. The presence of atmospheric oxygen reduces the yields of phenanthrene, anthracene, fluorene, and some alkyl-naphthalenes. Raising the temperature to 900/sup 0/C promotes aromatization processes and increases the yields of naphthalene and more highly condensed hydrocarbons, but the extent of these conversions whenmore » air is supplied in amounts not exceeding the combustion requirements for the primary volatile matter is less than in the absence of oxygen. The amount of oxygen supplied is a very important factor with a major influence on the primary-tar pyrolysis sequence, comparable with the temperature and time factors. At certain ratios of atmospheric oxygen to vapors and gases available for pyrolysis, greater thermal degradation takes place at substantially lower temperatures.« less