Biochemical Engineering Journal 137 (2018) 116–124 Contents lists available at ScienceDirect Biochemical Engineering Journal journal homepage: www.elsevier.com/locate/bej Enzymatic kinetics of cetyl palmitate synthesis in a solvent-free system Natália Allana Cirillo, Carolina Gomes Quirrenbach, Marcos Lúcio Corazza, Fernando Augusto Pedersen Voll ∗ Department of Chemical Engineering, Paraná Federal University (UFPR), Polytechnic Center, Jardim das Américas, Curitiba, PR, 82530-990, Brazil a r t i c l e i n f o Article history: Received 13 January 2018 Received in revised form 18 May 2018 Accepted 22 May 2018 Available online 24 May 2018 Keywords: Esterification Wax ester Cetyl palmitate Immobilized lipase Solvent free synthesis Kinetic modeling a b s t r a c t Cetyl palmitate was synthetized by esterification the cetyl alcohol with palmitic acid in a solvent-free system. Reactions were performed in batch mode using commercial lipase Lipozyme RM IM as catalyst. Stirring speed (180, 480 and 720 rpm), temperature (60, 70, 80 and 87 ◦ C), amount of catalyst (0.5, 1.0 and 1.5% wt% related to the mass of substrates) and alcohol:acid molar ratio (0.5:1, 1:1 and 2:1) were evaluated and best reaction conditions obtained were 480 rpm, 70 ◦ C, 1.0% of enzyme and 1:1 M ratio. A novel kinetic model based on random-sequential bi-bi mechanism was proposed and showed a good agreement with experimental data. Furthermore, this model was proved to be suitable for kinetics predictions with a small uncertainty. The catalyst was recycled and showed good stability since reaction conversion decreased only 6.8% after 15 reuses. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Wax esters of fatty acids, or waxes, are long-chain esters with chain lengths of 12 or more carbons with high added value and high degree of biodegradability. Among the industrial applications of waxes are the production of lubricants, cosmetics, personal care products, pharmaceuticals, wood coatings, antifoaming agents, printing inks and varnishes [1]. They are found in nature on the surface of fruits, on the cranium cavity of sperm whales (Physeter macrocephalus), on hives and on the leaves of carnauba (Coperni- cia cerifera) [2]. Despite its high availability from natural sources, the extraction and exploitation from natural sources is not advan- tageous in technical and economic aspects, which motivates the synthetic production of waxes. Cetyl palmitate ester is one of the waxes with large application in the cosmetics industry due to its emollient characteristics. It is used as a surfactant in shampoos, as an emulsifying agent and thickener in creams and adds texture to various make-up products, usually in those that are stick-shaped [3]. The most common method of cetyl palmitate synthesis is the enzyme-catalyzed esterification. Although enzymes have a high cost, they are able to catalyze reactions under milder conditions, ∗ Corresponding author. E-mail address: fernando voll@ufpr.br (F.A.P. Voll). with medium temperatures, moderate pH and near atmospheric pressure, which avoids unnecessary expenses with fuels, steam and robust reactors (which would be necessary to withstand higher pressures). The products also have a higher degree of purity and a lower degree of degradation, so they are easier to purify [4]. Additionally, there is a continuing interest in immobilized enzymes since they are heterogeneous catalysts, which facilitates their appli- cation in continuous reaction processes. Many enzymes have good catalytic activity in organic solvents, and their applications have been studied by many researchers [5–8]. However, there is a growing concern that chemical processes are not only efficient, but also environmentally friendly, economi- cally viable and free from product contamination. Therefore, when there is miscibility between the reagents to promote sufficient con- tact between the molecules and when the enzyme is active in that condition, the use of solvent-free systems is preferable. Numerous researchers applied commercial immobilized lipases Novozym 435 [9–15], Lipozyme RM IM [15] and Lipozyme TL IM [16,17] in esteri- fication reactions in solvent-free systems and reached conversions above 86%, indicating their good activity in this condition. Kinetic modeling of enzymatic reactions have been proposed based in bi-bi mechanisms [8,15,18] and King-Altman mechanism [10]. However, there is a lack of description on how the temperature influences the reactions rate near the optimum temperature for enzyme activity and how the uncertainty on the kinetic parameters affects the uncertainty on the predictions of the model. https://doi.org/10.1016/j.bej.2018.05.021 1369-703X/© 2018 Elsevier B.V. All rights reserved.