Chemical Engineering Journal 126 (2007) 111–118 Kinetic study for esterification of lactic acid with ethanol and hydrolysis of ethyl lactate using an ion-exchange resin catalyst Patricia Delgado, Mar´ ıa Teresa Sanz ∗ , Sagrario Beltr´ an Department of Chemical Engineering, University of Burgos, 09001 Burgos, Spain Received 27 July 2006; received in revised form 11 September 2006; accepted 12 September 2006 Abstract The esterification of lactic acid with ethanol and the hydrolysis of the corresponding ester, ethyl lactate, have been studied in the presence of the commercial cation-exchange resin Amberlyst 15. The influence of different operating parameters such as stirrer speed, catalyst particle size, initial reactant molar ratio, reaction temperature and catalyst loading, has been examined. Additionally, the adsorption constants for the four components on Amberlyst 15 were determined by performing adsorption experiments between two non-reacting species. The values found for the adsorption constants follow the order: water > ethanol > lactic acid > ethyl lactate. Experimental kinetic data of the esterification and the hydrolysis reactions were correlated simultaneously with the Langmuir–Hinshelwood (LH) and pseudo-homogeneous (PH) models. The activity coefficients were calculated according to the UNIQUAC model. The LH model gave the best agreement with the kinetic experimental data. The activation energy of esterification and hydrolysis reactions were found to be 52.29 and 56.05 kJ mol -1 , respectively. © 2006 Elsevier B.V. All rights reserved. Keywords: Esterification; Hydrolysis; Lactic acid; Ethyl lactate; Chemical equilibrium 1. Introduction Food industry generates large volumes of carbohydrates which can be substrates for bioconversion to valuable products such as lactic acid and its derivates. Lactic acid and their esters can be used in the food industry for preservation and flavoring purposes, as well as in the pharmaceutical and cosmetic indus- tries. Lactic acid is also used as a monomer for the manufacture of biodegradable polymers as substitutes for conventional petro- chemical polymers. Fermentation-derived lactic acid requires extensive purification operations [1]. Esterification of lactic acid with lower alcohols, such as methanol, ethanol, isopropanol and butanol, can be used as a method to obtain highly purified lactic acid from fermentation broths. The volatile lactate ester pro- duced can be separated from the reactive mixture and hydrolyzed back to pure lactic acid and the corresponding alcohol that can be recovered and reused [2]. In previous work, our research group studied the catalyzed esterification of lactic acid (20 wt.%) with methanol [3] and the hydrolysis of the methyl lactate [4]. Analysis of the experimental ∗ Corresponding author. Tel.: +34 947 258810/09; fax: +34 947 258831. E-mail address: tersanz@ubu.es (M.T. Sanz). data showed that the pseudo-homogeneous (PH) model repre- sented the esterification and hydrolysis kinetics over Amberlyst 15 fairly well. Kinetic studies on the esterification of lactic acid with ethanol are scarce in the literature and usually the hydrolysis of ethyl lactate is not included. Troupe and Dimilla [2] studied this ester- ification reaction in the presence of sulfuric acid as homogenous catalyst. In their experiments lactic acid of 85 and 44 wt.% analytical grade was used. They studied the effect of reac- tion temperature, amount of catalyst and initial reactant molar ratio. Based on their results they suggested that the mecha- nism of reaction changed above an initial reactant molar ratio (n EtOH /n HL ) of 4. Zhang et al. [5] investigated the esterifi- cation of lactic acid (80 wt.%) with ethanol in the presence of five different cation-exchange resins. They found that the Langmuir–Hinshelwood (LH) model based on the selective adsorption of water and ethanol on the catalyst was the most appropriate model to describe the kinetic behavior. Engin et al. [6] carried out also the esterification of lactic acid with ethanol over hetero-poly-acid supported on ion-exchange resins (Lewatit ® S100) showing higher activities than the resin itself. They used lactic acid 92 wt.% and the hydrolysis reaction of lactoyllactic acid (the linear dimer of lactic acid) was taken into account. 1385-8947/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2006.09.004