Adsorption Equilibria of Sulfur Dioxide on Cork

The adsorption of sulfur dioxide in the gas phase on crude cork is reported for the first time. Close contact between SO2 and cork occurs either by the liquid phase or by the vapor phase from the headspace, making it crucial to understand the thermodynamic interactions occurring between cork and SO2. Adsorption of gaseous SO2 was studied by thermogravimetry and calorimetry at 298 K and for pressures ranging from 10−5 to 40 hPa on cork sample previously outgassed under vacuum. Amounts of SO2 adsorbed on dry cork are rather low and correspond to negligible quantities when extrapolated to an entire cork stopper. The presence of a hysteresis loop on the isotherm and the high adsorption heats measured at low loading (~100 kJ·mol−1) indicates that a reactive adsorption occurs between SO2 and cork. Nevertheless, the chemisorbed amount is very low and the main adsorption mechanism for SO2 on cork corresponds to a physisorption process. Adsorption of SO2 on partially hydrated cork was also studied. When the water content in cork is of 5% of the weight, the amount of SO2 adsorbed is divided by 3. Thus, water does not enhance the adsorption rate for SO2, but decreases the SO2 adsorption activity onto cork, probably because of competitive adsorption mechanisms.