Methodological Aspects of Air Blowing of Technical Hydrocarbon Mixtures

摘要

Air blowing is an industrial thermal process where air or another oxygen-bearing mixture is passed through the high-boiling fractions of coal tar or molten pitch, resulting in the oxidative hydrogenation of the hydrocarbons and the formation of water. While the foreign literature refers to this process as air blowing, Russian researchers and scientists refer to it as thermal oxidation, because the direct oxidation of hydrocarbons to produce oxygen functional groups is possible only under certain conditions (lower temperature, prolonged process time, high specific oxidant flow, or sufficient pressure to initiate oxidation). Of paramount importance in this regard is the aggregate state of the feedstock. For example, coal-tar pitches with high softening points readily form oxygen compounds when oxidized in the solid state at 160-200 deg C. This is a widely used industrial process for pre-treating various pitch-based hydrocarbon compositions before baking in order to increase the yield, mechanical strength, and density of the final product. As shown in Fig. 1, oxidation of a solid specimen of lampblack-pitch composition based on pitch with a softening point of 137 deg C results in a considerable initial weight gain due to the formation of oxygen compounds [1]. However, these compounds are not very stable, and they decompose at 190 deg C, as indicated by the weight loss. In this case, with no pitch in the vapor phase, the hydrocarbon-oxygen reaction occurs by a diffusion mechanism; i.e., the oxidation rate is determined by the diffusion rate of oxygen molecules into the pitch.