Chemical Engineering Journal 150 (2009) 104–113 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Kinetics of the supercritical fluid extraction of carotenoids from microalgae with CO 2 and ethanol as cosolvent Maria Dolores Macías-Sánchez ∗ , Casimiro Mantell Serrano, Miguel Rodríguez Rodríguez, Enrique Martínez de la Ossa Department of Chemical Engineering, Food Technology and Environmental Technologies, Science Faculty, University of Cadiz, Avda. República Saharaui s/n, 11510 Puerto Real (Cádiz), Spain article info Article history: Received 9 September 2008 Received in revised form 26 November 2008 Accepted 4 December 2008 Keywords: Penetration model Carotenoids Microalgae Supercritical fluid extraction abstract The kinetics of the supercritical fluid extraction of carotenoids from microalgae has been studied. The solvent systems used were supercritical carbon dioxide and CO 2 + 5% ethanol as a cosolvent. A penetration model developed by other authors was applied that, due to the spherical form of the cellular microalgae, was based on the application of the mass balance to a spherical particle. The fit of the model is satisfactory and it was able to predict in a reasonable way the extraction yield of the process. The comparison between experimental and calculated data provided a value for the internal diffusion coefficient and this allowed an analysis of the influence of the different variables in the extraction process. © 2008 Elsevier B.V. All rights reserved. 1. Introduction At present, microalgae offer great possibilities for the isolation of natural substances of significant commercial interest in industries such as pharmaceuticals and alimentary or cosmetics products. This situation means that microalgae are raw materials with a great deal of added value. Nowadays, society demands products made with additives that are natural in origin and, wherever possible, are beneficial to human health. In this sense, marine microalgae offer great potential as sources of these substances and have attracted close attention from the aforementioned industries due to the economic and social repercussions that the use of this type of additive has in the pro- duction of their products. Many of these products are designed for direct human consumption and the extraction technique is extremely important in terms of the appropriate technology to apply. There are numerous reports in the literature related to the analy- sis of diverse types of microalgae as potential sources of carotenoids. We report here a study into the extraction and application of three microalgae that represent three of the five groups in which are usually classified algae. Each one has a cellular structure differ- ent: Nannochloropsis gaditana [1–6], Synechococcus sp. [7–10] and Dunaliella salina [11,12]. ∗ Corresponding author. Tel.: +34 956016579; fax: +34 956016411. E-mail address: dolores.macias@uca.es (M.D. Macías-Sánchez). Studies into the effects of pressure, temperature and the addition of a cosolvent to supercritical carbon dioxide in the extraction of carotenoids from the aforementioned three microalgae have been reported previously [13–17]. The results obtained with supercritical carbon dioxide indicate that the optimum extraction conditions, in the cases of N. gaditana and D. salina, are 400 bar and 60 ◦ C, while the best results in the case of Synechococcus sp. were obtained at a pressure of 300 bar and a temperature of 50 ◦ C. The addition to the supercritical carbon dioxide of ethanol (5%) as a cosolvent led to increases in the extraction yields of carotenoids. In these cases, the optimum conditions of pressure and temperature were 500 bar and 60 ◦ C when the raw material was N. gaditana. In the cases of Synechococcus sp. and D. salina the best conditions were 400 bar and 60 ◦ C. Conventional extraction techniques for carotenoids from natural matrices involve the use of organic solvents, and this is a practice that is currently being phased out for environmental, health and safety reasons. Supercritical extraction with carbon dioxide is an advanced technology that has a low environmental impact due to the undisputed advantages of carbon dioxide as a solvent, i.e. low toxicity, low cost and easy separation from extracts [18]. In addi- tion, the use of carbon dioxide gives an extra advantage in terms of quality, as extracts do not suffer the excessive heating that would destroy thermally unstable compounds. The design and scale up of an industrial process for supercriti- cal extraction requires the development of a model that allows the behaviour of the process to be predicted. The most representative 1385-8947/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2008.12.006