The esterification kinetics of lactic acid with methanol without addition of catalyst and catalyzed by ion-exchange resins are presented in this work. The effect of catalyst type, stirrer speed, catalyst size, catalyst loading, initial reactant ratio, and temperature on reaction kinetics was evaluated. Experimental reaction rates were correlated by some models based on homogeneous and heterogeneous (dual- and single-site mechanisms) approaches. Nonideality of the liquid phase was taken into account by using activities instead of mole fractions. Prediction of the activity coefficients was made by UNIFAC. Parameters of the different models were obtained by the simplex search method.

Proanthocyanidins are supposed to have some therapeutical properties as antioxidants and antineoplasics. Most of the proanthocyanidins, however, are not commercialized since their separation from natural sources is either very expensive or not well-known. In this work, the feasibility of application of mixtures of carbon dioxide and alcohol under supercritical conditions for selective extraction of some phenolic compounds from grape seeds has been studied, among them some low polymerized proanthocyanidins, their main monomer units, (+)-catechin and (-)-epicatechin, and some low molecular weight phenolic compounds, like gallic acid. An analytical-scale supercritical fluid extractor, whose operation was previously optimized, was used to carry out the experiments. A commercial concentrate of complex phenols and tannins from grape seeds was subjected to supercritical extraction in order to find the best operation conditions before directly extracting defatted milled grape seeds. The solvent capacity was found to increase with pressure and with the amount of alcohol used as cosolvent as expected. Such variation in solvent capacity could be used for design of a selective separation process where individual phenolic compounds or groups of them could be obtained. HPLC coupled with two types of detectors, diode array and mass spectrometry, was used for tentative identification and quantification of complex phenols and tannins in the extracts and in the raw materials used for extraction.

The hydrolysis of methyl lactate catalyzed by an acidic cation-exchange resin, Amberlyst 15, is presented in this work. The kinetic experiments were carried out in a stirred tank batch reactor. The effects of catalyst loading, temperature, and feed composition were investigated. The reaction modeling was carried out by correlating the experimental kinetic data obtained for the esterification (previously reported) and the hydrolysis reactions simultaneously. Three models were essayed, the quasi-homogeneous, the Langmuir-Hinshelwood, and the Eley-Rideal models. Because of the high nonideality of the reaction mixture, the kinetics were expressed in terms of activities. The activity coefficients were calculated by using the group contribution method UNIFAC. The quasi-homogeneous model was found to represent the esterification and hydrolysis reactions over Amberlyst 15 fairly well.

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