7854
Ind. Eng. Chem. Res. 2005, 44, 7854-7859
Waste Oil Recycling Using Mixtures of Polar Solvents Jesusa Rinco´ n,*,† Pablo Can ˜ izares,‡ and Marı´a Teresa Garcı´a§ Departamento de Ingenierı´a Quı´mica, Universidad de CastillasLa Mancha, Espan˜ a
By the proper selection of components and compositions, a composite solvent to recover base oil from used lubricant oil has been formulated. The composite solvent has two single components: methyl ethyl ketone (MEK) and 2-propanol. The best extraction results were obtained when the single solvents selected were mixed at a 2-propanol/MEK ratio of 3 g/g. However, this solvent was still unable to completely remove metals and oxidation products. To solve this problem, very small quantities of KOH (from 1 to 7 g/(kg of solvent)) were added to the composite solvent and its effect on both the extraction yields and the quality of the oil recovered was determined. A KOH concentration of 2 g/(kg of solvent) was found to be the most appropriate. The vacuum distilled oil pretreated with this solvent (2-propanol/MEK at a weight ratio of 3 g/g with 2 (g of KOH)/(kg of solvent)) was almost similar to a SN-130 virgin oil and, therefore, suitable for the formulation of new lubricants. 1. Introduction Waste lubricant oil constitutes a serious pollution problem. It may contaminate water and earth if discharged to the environment and cause air pollution if burnt as a low-grade fuel. Therefore, both the elimination of a pollution source and the need of preserving crude oil reserves justify the interest in the recycling of waste oil. Most of modern recycling processes consist of the following sequence of operations:1-3 dehydration and light hydrocarbon removal by distillation at atmospheric pressure or light vacuum, separation of base oil from contaminant agents by high vacuum distillation (10-30 mmHg), and finishing of the base oil separated in the preceding step by hydrogenation. The second step has several problems related to fouling of heating and distillation equipment and cracking reactions, which usually create both unpleasant smells (mercaptanes) and low-quality base oils (poor stability, color, and smell). However, these problems may be overcome by introducing a pretreatment step before the vacuum distillation as, for example, extraction with solvents. In a previous paper, we showed that, effectively, the treatment of waste oils with single organic solvents such as ketones and alcohols before distillation at high vacuum was an interesting alternative.4 More specifically, it was shown that the flocculating action and subsequent impurities removal promoted by the single solvents studied could be correlated with several characteristics of the solvents such as the difference in the solubility parameters of the solvents and of a typical base oil and the polarity and viscosity of the solvents. In this paper, all these principles will be applied to find a more efficient solvent. Thus, the action of mixtures of single solvents (composite solvent) will be ex* To whom correspondence should be addressed. Tel.: 34925-26 88 00. Fax: 34-925-26 88 40. E-mail: Jesusa.Rincon@ uclm.es. † Facultad de Ciencias del Medio Ambiente, Avda, Carlos III s/n, 45071 Toledo, Espan˜a. ‡ Facultad de Ciencias Quı´micas, Avda, Camilo Jose´ Cela, 10 13004 C Real, Espan˜a. § Escuela Universitaria Polite´cnica de Almade´n, Plaza Manuel Meca, 1 13400 Almade´n (C. Real), Espan˜a.
plored based on the belief that, by proper selection of components and compositions, one can find formulations having a more favorable balance of the above-mentioned properties. 2. Experimental Section 2.1. Materials. The organic solvents used were methyl ethyl ketone and 2-propanol. They were supplied by Panreac, S. A. Used lubricant oil was supplied by Emgrisa, S. A. Prior to the runs, the oil was treated in a rotary evaporator at 60 °C under vacuum (600 mmHg) to eliminate water and light hydrocarbons. Both types of compounds are undesirable for the formulation of new lubricants and may modify the solubility parameters of the base oil components in the solvent. Used oil properties after this treatment are shown in Table 1. As stated in the Introduction, this is a common processing stage of the oil before distillation at high vacuum (10-30 mmHg) to obtain the base oil. 2.2. Extraction Procedure. Mixtures of ∼10 g of used oil and solvent in weight proportions ranging from 1/1 to 15/1 solvent/oil were agitated to ensure adequate mixing for 30 min.4 Then, the mixtures were poured into glass centrifugal tubes that were later introduced in the support of a centrifuge (Selecta/Mixtasel). After centrifugation at 400 rpm for 10 min, a sludge phase (additive, impurities, and carbonaceous particles) was segregated from the mixture of solvent and oil. The solvent was separated from the solvent/oil mixture by distillation at 40 °C in a rotary evaporator under vacuum (100 mmHg), and the recovered oil was weighed. The extraction yield was calculated as the mass of oil, expressed in grams, separated from 100 g of waste oil. The sludge phase was also weighed in all experiments, both before and after solvent evaporation in a heater at 110 °C, where the sludge was maintained until its weight remained constant. It was observed that, on a solvent-free basis, the difference between the mass of raw used oil extracted and those of the two phases separated after extraction (base oil and sludge) was always
