Effect of oxidative atmospheres on the course and products of reconstituted tobacco thermochemical degradation

Tobacco is a rather complex lignocellulosic biomass containing cellulose, hemi-cellulose, lignin, pectin, proteins and various sugars and organic acids. Pyrolysis of tobacco was investigated in the past by tobacco companies as one of the reaction steps which contributed to consumption of combusted cigarettes. Within that context, due to the relevance for consumers' health, attention was devoted not only to the physical and reactive degradation processes, but also to the detailed analysis of resulting emissions, developing a knowledge useful also for the more general context of thermochemical degradation and smoldering combustion of biomass. Notably, the thermochemical degradation of combustible cigarettes include the formation of a hot combustion front (at the tip) with temperature levels reaching more than 900°C, and a high temperature pyrolysis and distillation zone behind the combustion front. On the contrary, the new Heated Tobacco Products (HTPs), based on controlled electric heating, are designed to limit the operating temperature to avoid combustion, while allowing for distillation and low-temperature pyrolysis processes. The current research is therefore aiming to deepen the understanding of distillation and low-temperature pyrolysis in terms of kinetics and products formation. Thermochemical degradation in inert as well as oxidative atmospheres need to be compared, in order to determine the role of oxidative pyrolysis on the degradation chemistry and rate of the reactions. This is of great interest for understanding the operating conditions of HTPs, but also for the general research on biomass thermochemical degradation and oxy-combustion. The present work reports on experiments of thermochemical degradation of tobacco under different inert/oxidative atmospheres, both in TG/DSC and in small scale reactors, with particular attention on the thermal effects and on the formation of gaseous and liquid products. Gaseous products have been monitored as a function of increasing temperature by means of (online) infrared (IR) analysers and Micro-GC (gas chromatography). GC- FID (flame ionization detector) and GC-TCD (thermal conductivity detector) have been further used to integrate the speciation of gaseous products. Condensable products have been quenched and collected in tar traps and characterized by GC-MS (mass spectrometry). Results suggest that oxidative atmospheres can slightly enhance the rate of thermochemical degradation even at temperatures below the onset of heterogenous combustion, leading to early formation of selected species, such as methane.