Acidic carbons were prepared by carbonization and in situ sulfonation of glycerin, a by-product from biodiesel production, and glycerol. The synthetic method used allowed the production of solids containing a large amount of surface functional groups, mainly sulfonic groups. The catalytic performance of the prepared materials was evaluated in reactions typically promoted by acidic catalysts. Conversions as high as 78% for the glycerol acetalization at room temperature and 85% for the glycerol etherification at 393 K were obtained. Furthermore we studied the reaction conditions of fructose dehydration using the prepared materials as catalysts, resulting in milder conditions than those found in the literature for this reaction using carbons as catalysts, with a 5-HMF yield close to 69%.