[Differences in the mechanisms of low-temperature and high-temperature processes in the formation of 3,4-benzopyrene during wood pyrolysis].

In 4 series of experiments a dependence between 3,4-benzpyrene (BP) output and the temperature of fir sawdust pyrolysis under isothermic conditions has been investigated. The experimental series differed in the duration of wood pulp particles stay in the reaction zone (tau). Also EPR spectra of pyrolysis products have been recorded. The experimental series did not differ in an output of ether extract from pyrolysis products, while BP output temperature curves in their shape were found to be largely dependent on tau: with an increased tau these curves definitely showed the maximum in the range of 300-350 degrees C and the BP output raised in the range of this maximum and also at the temperature of 600 degrees C. In the temperature range over 350 degrees C the character of dependence of the EPR signal value on temperature would correlate well with the temperature-dependent BP output, in the range of lower temperatures the EPR signal was not detected. The data obtained are considered as an evidence of two processes of BP formation in wood pyrolysis-a high-temperature process (temperature over 500 degrees C) and low-temperature one (300-350 degrees C). The high-temperature process seems to have the free-radical mechanism of BP formation, whereas in low temperatures it is evidently the result of a ion type reaction.