Effect of oxygen on the temperatures and conversion of tobacco in an electrically heated system

The goal of Heated Tobacco products (HTPs) is to devolatilize nicotine from the tobacco by a controlled electrical heating without inducing combustion and to thereby reduce the formation of harmful and potentially harmful compounds typically related to self-sustained combustion of tobacco as in conventional cigarettes. Here, we have instrumented a commercial puffing machine and an HTP with a micro-positioning system of a thin thermocouple (0.25 mm). The puffing was conducted under N2 or air. We provide the evolution of temperature as a function of time during standard puffing cycles and along the radial position within the tobacco plugs of tobacco sticks used as part of an electrically heated tobacco system (EHTS) during operation. The temperature profiles are nearly the same for the two atmospheres showing only minor influences of oxygen (maximum temperatures: 318 °C in air, 308 °C in N2, at the end of the puffing cycle). The thermal degradation of the tobacco remains always globally endothermic due to the high flow rate of the cold air flowing the tobacco during the puffing. To better understand the differences between air or N2 puffing, we have imaged the solid residues collected in the tobacco plugs by FTIR spectroscopy. The residues are clearly differentiated whatever their radial positions between air or N2 by principal component analysis of the FTIR spectra. This result highlights similar surface oxidation phenomena of the solid residue independent of the positions. Moreover, analysis of the FTIR spectra indicates that the heating of the tobacco in the EHTS is relatively uniform along the electrically-controlled heater without signs of local hot spots. These experiments were also completed by calorimetry of tobacco upon pyrolysis or oxidation, in a 3D sensor and under a fixed bed configuration (not in the EHTS). We evidence significant exothermic phenomena from about 230 °C mainly due to gas-phase oxidation of primary volatiles in the hot gas stream. During the operation of the EHTS, such potential exothermicity is counter-balanced by strong heat losses and the high flow rate of cold air flowing through the tobacco bed during the puffing. This leads to the observed net endothermic degradation of tobacco during EHTS operation. •Electrically heated tobacco system (EHTS) important to reduce toxic emissions during tobacco consumption.•Effect of air during product use in EHTS evidenced.•Temperature profiles nearly the same between N2 and air.•Globally al