In Situ High-Temperature EPR Investigation of the Charring of Tobacco and the O_2-Induced and H_2O-Induced Behavior of the Char

摘要

In situ high-temperature EPR has been used to study the 350 and 500 deg C pyrolysis (under a He atmosphere) of tobacco,as well as the EPR-signaled changes in the resulting char under exposure to O_2 and H_2O after quenching to room temperature.Exposure of a char to O_2 leads to a large increase in free radical concentration,especially for the 350 deg C char.Exposure of the char to both O_2 and H_2O yields an additional increase in free radical content (followed by a decrease after a maximum is reached),the magnitude of this increase being roughly half that of the initial O_2-generated increase.The observed patterns result from a complicated chemical interplay involving the creation and destruction of carbon-centered and oxygen-centered free radicals.