Adsorption Equilibria of Sulfur Dioxide on Cork

Abstract

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.