J. of Supercritical Fluids 39 (2007) 315–322 Regeneration of used lubricant oil by ethane extraction Jesusa Rinc ´ on a,∗ , Pablo Ca˜ nizares b , Mar´ ıa Teresa Garc´ ıa c a Departamento de Ingenier´ ıa Qu´ ımica, Universidad de Castilla-La Mancha, Facultad de Ciencias del Medio Ambiente, Avda. Carlos III, s/n. 45071 Toledo, Espa˜ na b Departamento de Ingenier´ ıa Qu´ ımica, Universidad de Castilla-La Mancha, Facultad de Ciencias Qu´ ımicas, Avda. Camilo Jos´ e Cela, 10. 13004C Real, Espa ˜ na c Departamento de Ingenier´ ıa Qu´ ımica, Universidad de Castilla-La Mancha, Escuela Universitaria Polit´ ecnica de Almad´ en, Plaza Manuel Meca, 1. 13400, Almad´ en (C. Real), Espa ˜ na Received 10 March 2005; received in revised form 8 February 2006; accepted 6 March 2006 Abstract Liquid and supercritical ethane has been used as a solvent for the recycling of used lubricant oils. The aim of the work has been to identify the best processing conditions to separate base oil suitable for the formulation of new lubricants, avoiding the coextraction of oxidation products and metallic compounds. The effect of pressure (40–145 kg/cm 2 ) and temperature (25–95 ◦ C) on the separation efficiency and yields has been investigated. In the pressure range analyzed no effect on metallic compounds removal was found. However, it did affect the extraction yields (they increased with pressure) and the separation of oxidation products (removed more efficiently at low pressures). As regards to temperature, at a given pressure the extraction yields were found to be independent of the variable as long as ethane remained as a liquid, but they decreased with increasing temperature with supercritical ethane. As expected, gas ethane could not dissolve base oil at all. On the other hand, at constant pressure metallic and oxidation compounds removal increased as temperature was increased. © 2006 Elsevier B.V. All rights reserved. Keywords: Used lubricant oil; Regeneration; Ethane extraction 1. Introduction Large and increasing volumes of lubricating oil are pro- duced each year that, after use, are considered a hazardous waste because of their high content of pollutants (thermal degradation products from the base oil and additives and combustion prod- ucts from the fuel and lubricant). Nevertheless, the used oil still contains a large proportion of valuable base oil that may be used to formulate new lubricants if undesirable pollutants are sepa- rated from the oil by an appropriate recycling procedure. Thus, not only environmental but also economical reasons justify the waste oil regeneration process. It is well known that many processes for the recycling of used lubricant oil involve the use of vacuum distillation fol- lowed by a polishing or decolorizing treatment. However, they present serious problems related to coking and column fouling during distillation and, therefore, some type of pre-treatment ∗ Corresponding author. Tel.: +34 925 26 88 00; fax: +34 925 26 88 40. E-mail address: Jesusa.Rincon@uclm.es (J. Rinc´ on). to remove additives and contaminants from the oil is preferred [1]. In principle, extraction with solvents can be used to this end. The basics of this pretreatment is the use of a solvent to selec- tively extract the base oil components from the waste lubricant oil in a process that would be quite similar to the commonly used in crude oil refining to separate out asphaltenes for producing heavy neutral base oil (bright stock). Although several organic solvents have the desired proper- ties for performing the extraction [2–8], propane has been the most amply used for base oil recycling [9–16]. Nevertheless, the use of this hydrocarbon makes necessary a hydrofinishing step because a percentage of pollutants that are difficult to separate by vacuum distillation [9,10], such as oxidation and metallic com- pounds, are soluble in propane [17] and, therefore, inevitably co-extracted with the base oil. Therefore, other solvents should be explored to overcome this problem. In principle, considering the composition of a typical waste lubricant oil (a stable dispersion of undegraded base oil and additives with high concentration of metals, varnish, gums and other asphaltic compounds coming from overlay of bearing 0896-8446/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.supflu.2006.03.007