J. of Supercritical Fluids 86 (2014) 76–84 Contents lists available at ScienceDirect The Journal of Supercritical Fluids jou rn al hom epage: www.elsevier.com/locate/supflu Supercritical carbon dioxide separation of fish oil ethyl esters by means of a continuous countercurrent process with an internal reflux Marco Maschietti a,∗ , Augusta Pedacchia b a Chalmers University of Technology, Department of Chemical and Biological Engineering, Gothenburg, Sweden b Università degli Studi di Roma “La Sapienza”, Department of Chemical Engineering, Rome, Italy a r t i c l e i n f o Article history: Received 15 October 2013 Received in revised form 3 December 2013 Accepted 4 December 2013 Keywords: Supercritical fluid Fish oil ethyl esters Continuous countercurrent process Internal reflux Peng–Robinson equation of state Omega-3 a b s t r a c t The continuous countercurrent fractionation of fish oil ethyl esters using supercritical carbon dioxide is studied, modelling a process with internal reflux generated by a thermal gradient at the top stage. A methodology for process design is proposed and applied to determine the relationships between the temperature at the top stage (T 1 ), the number of theoretical stages (N), and the solvent to feed ratio (S/F), with the aim of providing a quantitative comparison with the external reflux process. The internal reflux process is viable and, for stated process specifications (mass fraction and recovery of C20 + C22 ethyl esters of 95%), provides comparable or better results than the external reflux process. For example, operating at 13.3 MPa and 50 ◦ C, and keeping T 1 in the range (66–70) ◦ C, the specifications are attained with N and S/F in the range 16–30 and 88–120, respectively. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In the last two decades, the production of oils rich in polyun- saturated fatty acids (PUFA) of the omega-3 series has gained increasing attention, due to valuable applications of these com- pounds in the nutraceutical and pharmaceutical industry. Many anthropological, epidemiological, clinical and biochemical studies emphasize the nutritional value of omega-3 PUFA in the preven- tion of several diseases and indicate that typical Western diets are well below adequate daily intakes of these compounds [1–3]. In particular, the nutritional and pharmacological value of eicosapen- taenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6) in the prevention of cardiovascular diseases [4,5] and the reduc- tion of hypertriglyceridemia [5] has been well ascertained. As a result of these issues, many nutraceutical products based on oils with EPA + DHA mass fraction from 30% to 80% are currently mar- keted as dietary supplements. Furthermore, mixtures with EPA and DHA (in the form of ethyl esters) over 80%, with stated values of EPA/DHA ratio (typically in the range 1–1.6) are recognized by several Pharmacopoeias as Active Pharmaceutical Ingredient (API) against hypertriglyceridemia and myocardial infarction. The raw material for the production of omega-3 oils is typically represented by fish oils. Most of the fatty acid chains in fish oil ∗ Corresponding author. Tel.: +46 0 31 772 2989; fax: +46 0 31 772 2995. E-mail addresses: maschietti@hotmail.com, marcom@chalmers.se (M. Maschietti). triglycerides have a number of carbon atoms ranging from 14 to 22, being PUFA more abundant in the longest chains. By simply selecting fish naturally rich in omega-3 (e.g., sardine, anchovies, mackerel, herring, menhaden, etc.), crude oil containing EPA + DHA from 10% to 25% can be obtained [6]. Since a considerable enrich- ment in a specific fatty acid cannot be achieved on a triglyceride feedstock, fractionation processes are usually performed on fish oil ethyl esters (FOEE), preliminary obtained by transesterification of fish oils. In order to increase EPA and DHA concentration starting from FOEE, the shortest fatty acid chains (C14–C16–C18) must be sep- arated from the longest (C20–C22), as well as saturated and monounsaturated esters from polyunsaturated ones. Separation on the basis of the degree of unsaturation is typically attained by means of crystallization processes, which may be performed in conventional solvents (e.g., methanol, acetone) or in the urea- adduction process [7]. With regard to the separation on the basis of chain length, short alkyl esters are classically separated by distillation processes. However, when dealing with the long polyunsaturated fatty acid chains of fish oils, the conventional vac- uum distillation is not feasible, because the high temperatures required (well above 200 ◦ C) unacceptably degrade PUFA [7,8]. Until now, only two processes have proven to be feasible for FOEE fractionation on chain length basis: short path distillation and supercritical fluid extraction. Short path distillation is a par- ticular kind of distillation, performed at a pressure much lower (0.1–100 Pa) than conventional vacuum distillation, thus with lower operating temperatures and with very short residence time. 0896-8446/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.supflu.2013.12.003