An insight into the roles of exogenous potassium salts on the thermal degradation of flue-cured tobacco

- An opposite effect of potassium salts on thermal stability of tobacco at low and high temperature ranges, respectively.
- A reduction of the total pore volume and surface area of tobacco pyrolysis residues caused by potassium salts.
- A positive catalysis of potassium slats with oxygen-bearing organic functional groups, but a protective effect on oxygen-free organic species.
- A gentle escape process of volatile molecules at 350-550 °C due to the protection on the tobacco pyrolysis residues.

The effects of exogenous potassium salts on the thermal degradation of flue-cured tobacco were investigated using thermogravimetric analysis (TGA), surface area/porosity measurements (SAPM), real-time fourier transform infrared (RT-FTIR), and thermogravimetric/Fourier transform infrared spectrometry (TG-FTIR), respectively. TGA analysis showed that potassium salts accelerated tobacco's degradation at around 150-350 °C, but improved the thermal stability of char residue at high temperature range. The porous texture analysis displayed that potassium salts reduced the pore volume and surface area of tobacco pyrolysis residues. Further study using RT-FTIR illustrated that there was a positive catalysis of potassium salts with CO, OH and CO bonds at different temperature ranges, but a protective effect was given to CH bond, CC bond and aromatic moieties except for the accelerating degradation of CH by the oxidation effect of KNO3. The evolution comparison of their gaseous products manifested that potassium salts cut down the emission of CO2, H2O, CO, aldehydes and alkanes, but enhanced the release of carbonyl compounds, anhydrides and alcohols at around 150-350 °C. Above 350 °C, the potassium salt-containing samples exhibited a gentle escape process for both the oxygen-bearing molecules (CO2, H2O and CO) and oxygen-free species (alkanes, methane and unsaturated compounds) in comparison with their quick emission for the virgin samples.