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Adsorption Equilibria of Sulfur Dioxide on Cork

¹ Institut Universitaire de la Vigne et du Vin, Université de Bourgogne, F-21078 Dijon, France; ² Equipe EMMA, ENSBANA, Université de Bourgogne, F-21000 Dijon, France; and ³ Institut Carnot de Bourgogne, UMR 5209 CNRS, Université de Bourgogne, 9 A. Savary BP 47870, F-21078 Dijon, France.

Acknowledgments: The authors gratefully acknowledge the Bureau Interprofessionnel des Vins de Bourgogne and the Regional Council of Burgundy for financial support of this work (project 2008-9201AAO024S00120).

The authors thank Christian Paulin and Claudie Josse, Institut Carnot de Bourgogne, for assistance with thermogravimetry and SEM, respectively.

^* Corresponding author (email: jean-pierre.bellat{at}u-bourgogne.fr; tel: +33 (0) 3 80 39 5929; fax: +33 (0) 3 80 39 6132)

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.

Key words: cork, wine, sulfur dioxide, adsorption, thermogravimetry, calorimetry