J. of Supercritical Fluids 34 (2005) 143–147 Separation of d-limonene from supercritical CO 2 by means of membranes Luiz Henrique Castelan Carlson ∗ , Ariovaldo Bolzan, Ricardo Ant ˆ onio Francisco Machado Universidade Federal de Santa Catarina, Depto. de Engenharia Qu´ ımica, Caixa Postal 476, 88040-900 Florian´ opolis, SC, Brazil Abstract The extraction of essential oil from vegetable matrices with supercritical fluids is a promising technology which is still searching for an economical method to recycle the dense carbon dioxide (CO 2 ). The use of the reverse osmosis membrane separation process can be an alternative to avoid the intense depressurization step which is necessary for the recovering of the extracts. The membranes exhibit satisfactory permeability for supercritical CO 2 filtration, with very good resistance under the severe experimental operating conditions. In this work, four commercial reverse osmosis and nanofiltration membranes were applied to perform the separation of limonene and supercritical carbon dioxide. The tests were conducted under a pressure of 12 MPa, a transmembrane pressure of 0.5 MPa and a temperature of 40 ◦ C. Pure CO 2 flux, limonene + CO 2 flux and the limonene retention factor were measured. The highest limonene retention factor was above 0.94. © 2004 Published by Elsevier B.V. Keywords: d-Limonene; Membrane separation; Reverse osmosis; Solvent recovering; Supercritical extraction. 1. Introduction The use of supercritical CO 2 for the extraction of natural products is still considered a new process on an industrial scale [1]. This process employs unproblematic, innocuous fluids as solvent and yields solvent-free products in a ther- mally gentle manner. Simple fraction of the products is possi- ble by a variation of pressure and/or temperature. Nowadays, this process has become particularly familiar in the food, cof- fee and tobacco industries [2]. Processes involving extraction with supercritical fluids typically require a pressurization step, a heating or cooling step, an extraction step, and a subsequent separation and sol- vent regeneration step [3]. Although CO 2 is comparatively innocuous in small quantities and is relatively cheap, it cannot be discharged in unlimited quantities and it must be largely recovered in a well-designed process [4]. The costs of recom- pression of gaseous CO 2 to liquid or supercritical CO 2 is high, ∗ Corresponding author. Tel.: +55 48 33319554; fax: +55 48 3319687. E-mail address: carlson@enq.ufsc.br (L.H.C. Carlson). as a powerful compression equipment and often a refrigera- tion step prior to compression are required. The association of a membrane to the supercritical fluid extraction process could avoid the intense depressurization step, reducing the recompression costs [5]. Semenova et al. [6] studied the separation of supercritical CO 2 and ethanol mixtures with an asymmetric polyimide membrane, and a separation factor (α ethanol/CO 2 ) of 8.7 was obtained. The separation factor is defined by Eq. (1): α ethanol/CO 2 = y ethanol /y CO 2 x ethanol /x CO 2 (1) where y i and x i are the mole fraction of the component i (i = ethanol or CO 2 ) in the permeate and in the feed. For the separation of supercritical CO 2 and iso-octane mixtures, a separation factor (α iso-octane/CO 2 ) of 12.8 was obtained [7]. Sarrade et al. [8] characterized the behavior of organomineral nanofiltration membranes in supercritical CO 2 . Permeability variations were investigated as a function of the tempera- ture and pressure. The membranes exhibit satisfactory per- meability for supercritical CO 2 filtration, with very good re- 0896-8446/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.supflu.2004.11.007