Bull. Spec. CORESTA Congress, Lisbon, 2000, p. 156, ST12

Vapor pressure measurements of tobacco tar by non-isothermal Knudsen effusion method

Philip Morris USA, Research Center, Richmond, VA, USA
Vapor pressures of thermal decomposition products of tobacco are an important parameter in understanding pyrolysis behavior of the tobacco. The extent to which the tars can vaporize, before retrograde reactions reincorporate them into a char, plays a key role in determining the volatiles yields and composition. In this study, a molecular effusion/TGA technique was used. The method selected here is based on Knudsen effusion method, in which the vapor of a substance of interest effuses through a small pinhole of known area in an otherwise sealed container or cell. The non-isothermal Knudsen effusion method was used in response to the need to scan a wide range of temperatures in a modest time. Measurements were made on primary tars of tobacco, as well as pure model compounds: levoglucosan, stigmasterol, solanesol. The vapor pressures of anthracene and pyrene were also measured to test the Knudsen effusion equipment. Tars were prepared by heating tobacco in a tube furnace under flowing helium, removing the condensed products from the downstream trap by washing with methanol, and then evaporating the solvent in a vacuum oven at 40 °C. Molecular weight distribution of the tobacco tar was obtained by the Field Ionization Mass Spectroscopy (FIMS) and the chemical characterization of the tars was obtained qualitatively by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies.