Ind. Eng. Chem. Res. 2003, 42, 4867-4873
4867
Regeneration of Used Lubricant Oil by Propane Extraction Jesusa Rinco´ n,*,† Pablo Can ˜ izares,‡ Marı´a Teresa Garcı´a,† and Ignacio Gracia‡ Facultad de Ciencias del Medio Ambiente, Departamento de Ingenierı´a Quı´mica, University de CastillasLa Mancha, Avenida Carlos III s/n, 45071 Toledo, Spain, and Facultad de Ciencias Quı´micas, Departamento de Ingenierı´a Quı´mica, University de CastillasLa Mancha, Avenida Camilo Jose´ Cela No. 10, 13004 C. Real, Spain
Liquid and supercritical propane 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 (30-60 kg/cm2) and temperature (20-140 °C) on the separation efficiency and yields has been investigated. In the pressure range analyzed, almost no effect of the variable on yields and metallic compounds removal was found. However, it did affect the separation of oxidation products that were removed more efficiently at low pressures. In regards to temperature, at a given pressure the extraction yields were found not to depend on the variable as long as propane remained as a liquid. However, when the temperature was increased at constant pressure, so propane became a gas or a supercritical fluid, extraction yields decreased. Furthermore, the yield decrease observed with supercritical propane was density-dependent: the higher the propane density, the higher the extraction yield. On the other hand, at constant pressure, metallic and oxidation compounds removal was found to increase with increasing temperature. Finally, propane-extracted oil at optimum conditions (30 kg/cm2 and 90 °C) has been compared to two vacuum-distilled oils (5 mmHg), one of them pretreated with propane at optimum conditions. 1. Introduction The used lubricant oil is a serious pollution problem. Its dumping may contaminate water and earth, and if burnt as a low-grade fuel, harmful metals and other pollutants may be released into the air.1 Therefore, to prevent the environmental pollution and to preserve natural sources, used or waste oils should be collected and recycled. The recycling of used lubricant oil provides products or materials for reuse. Basically, it may be accomplished by two methods: reprocessing and re-refining. Reprocessing involves a series of treatments that remove some water and soluble contaminants using chemicals and/ or adsorbents. It includes fuel oil production from waste oil by application of mild cleaning methods (settling, heating, filtration, and centrifugation). Re-refining is the treatment that produces base oils using a specially developed processing. Obviously, in terms of energy and natural sources conservation, re-refining is more attractive than reprocessing. The European Community2 and Spanish laws3 strongly recommend this treatment. Nevertheless, mainly because of the economical aspects of the re-refining processes but also because of environmental issues related to the wastes produced during the re-refining process, at the present time less than 20% of the used oil collected in the European Community is re-refined.4 Consequently, it becomes necessary to optimize the performance of the existing processes or to develop new ones, so they could be competitive from economical and environmental points of view. * To whom correspondence should be addressed. Tel.: 34925-26 88 00. Fax: 34-925-26 88 40. E-mail: Jesusa.Rinco´n@ uclm.es. † Facultad de Ciencias del Medio Ambiente. ‡ Facultad de Ciencias Quı´micas.
Modern waste oil re-refining technologies5 seem to converge on a two-step procedure: (a) separation of base oil from contaminant agents by vacuum distillation and (b) finishing of the base oil separated in the preceding stage by hydrogenation. In this re-refining scheme, however, the first step presents several problems related to fouling of heating and distillation equipment (which makes continuous operation difficult) and cracking reactions, which usually originate both unpleasant smells (mercaptans) and low-quality base oils (poor stability, color, and smell). To overcome these problems, the use of high-vacuum wiped-film evaporators has been proposed.6 However, the investment and operating costs of these units are rather high. They are economically competitive only for large base oil productions, usually more than 60 000 tonnes/year.7 Obviously, the waste oil supply to these large plants becomes an important logistical problem. On the other hand, catalytic hydrofinishing is also a rather expensive treatment and, therefore, substitution or suppression of this step would be desirable. Considering all of these facts, one realizes that other processing schemes should be explored in order to improve the performance of the two-step re-refining procedure mentioned before. It could be accomplished, for example, by introducing a pretreatment step before the vacuum distillation. The objective of this step would be to preclean the oil to be fed to the vacuum column with a double purpose: to prevent cracking and fouling in the column and to eliminate the need of the hydrofinishing stage. In principle, propane extraction is a possible technology that may be used to this end. The basics of this treatment is the use of propane to selectively extract all base oil components from waste oil. The extraction process would be quite similar to that commonly used
10.1021/ie030013w CCC: $25.00 © 2003 American Chemical Society Published on Web 08/26/2003
4868 Ind. Eng. Chem. Res., Vol. 42, No. 20, 2003 Table 1. Comparison of Crude Used Oil and Three Differently Treated Used Oils characteristic viscosity at 40 °C (ASTM-445), cSt viscosity at 100 °C (ASTM-445), cSt sulfur (ASTMD-4294), % phosphorus (FRX), ppm acid number, mg of KOH/g metallic content, ppm zinc magnesium lead iron calcium a
used oil
propanepretreated oil
vacuum-distilled oil pretreated with propane
vacuum-distilled oil not pretreated
33.95 5.73 0.50 5.60 0.86
30.30 5.19 0.45 155 0.79
33.47 5.71 0.60 490 0.82
1.5 nd 2.6 nd nd
27.5 150 16.2 23 242
93.98 13.11 0.66 8.35 3.36 947 352 850 35 2000
390 43 290 13 170
nd: not detected.
Figure 1. Schematic diagram of the experimental extraction system: SC-P, propane cylinder; CS, cooling system; BPR, back-pressure regulator; EX, extractor; MV, metering valve; RE, cool receiver; FM, flowmeter; FC, flow computer.
in crude oil refining to separate out asphaltenes for producing heavy neutral base oil (bright stock). The use of propane to regenerate waste oil was first proposed by the Institut Francais du Petrole8 to improve the classical acid/clay re-refining technology that had become obsolete for technical, economical, and environmental reasons. Then, much descriptive material has been published about this method,9-12 but neither has detailed information been given about the operating conditions nor have influent or effluent process streams been precisely characterized. Accordingly, the major aim of this paper will be to analyze the waste oil propane extraction process in order to select the best extraction conditions leading to both high yield and quality of the base oil obtained. 2. Experimental Section 2.1. Materials. Liquid propane (purity 95%) was supplied by Praxair S.A. (Madrid, Spain). Used lubricant oil was supplied by Emgrisa S.A. Prior to the runs, the oil was treated in a rotary evaporator at 60 °C to eliminate water and light hydrocarbons. Both types of compounds are undesirable for the formulation of new lubricants. Elimination of water was also necessary because it may modify the solubility parameter of base oil components in propane. Used oil properties after this treatment are shown in column 2 of Table 1.
2.2. Apparatus and Extraction Procedure. A schematic of the extraction system used in this study is presented in Figure 1. It was previously described in ref 13 and consists of three main sections: the propane supply system, the extractor assembly, and the separator assembly. Basically, the supply system was a steel cylinder (SC) that provided liquid propane. After cooling and filtering, the propane was compressed by a membrane pump (Leva model HG-140). The pressure was regulated by a back-pressure regulator (BPR) and checked by a manometer (M). The compressed fluid was passed through the central element of the extraction system (EX), a 0.94-L autoclave extraction cylinder (40 mm i.d. × 75 mm) that was filled with the used oil. As indicated in the figure, the extractor design allowed the propane to enter through a 8 mm i.d. tube and, as it went upward through the extractor, to intimately mix with the used oil and to separate the propane-soluble base oil from the rest of the nonsoluble used oil components (additives and oil degradation products). A type J thermocouple was inserted in the extractor to indicate its operation temperature. This variable was controlled by immersing the extractor in an oil bath at the desired temperature. The oil-laden propane from the extractor was passed through a heated metering valve (MV), where the propane was depressurized and the separated oil was collected in a cool receiver (RE). The propane flow through the extractor was measured by a
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turbine flowmeter (FM) and totalized by a flow computer (FC). 2.3. Analysis of the Metallic Content. The metallic content analyses were performed by atomic absorption spectroscopy using a Varian Spectra 220 FS spectrometer. Prior to the analyses, the samples were heated at 200 °C for 4 h and calcined at 650 °C overnight. These samples were further treated with hydrochloric acid, filtered, and diluted with deionized water. 2.4. Other Analyses. The oil yield was determined gravimetrically. The phosphorus content was measured by energy-dispersive X-ray fluorescence spectroscopy using an Oxford ED2000 spectrometer. The acid number, sulfur content, and viscosities at 40 and 100 °C were determined according to ASTMD-664, ASTMD-4294, and ASTM-445 procedures, respectively. 3. Results and Discussion A waste lubricant oil typically consists of a mixture of undegraded base oil and additives with high concentrations of metals, varnish, gums, and other asphaltic compounds coming from overlay on bearing surfaces and degradation of the fresh lubricant components. The bulk of these particles and heavy compounds are usually kept in stable dispersion by dispersant additives and electrostatic interactions between heteroatoms and asphaltic compounds, just as in the crude oil.14 Because propane, under certain conditions, tends to dissolve preferentially the base oil fraction of the lubricant oil and causes the particles, heaviest hydrocarbons, and other nondissolved compounds to precipitate,15 in this study we have tried to produce base lubricating oil from used oil through a deasphalting and purification process using propane. The regeneration experiments have been designed to study the effect of pressure and temperature on both extraction yields and the quality of the extracts. The quality has been assessed through the measurement of metal and oxidation compound concentrations in the extracted base oil. The accuracy of the experimentally determined extraction yields has been determined by comparing the results from four independent runs carried out under identical conditions: pressure (P) ) 40 kg/cm2, temperature (T) ) 80 °C, propane flow (Q) ) 2 L/min, oil load (L) ) 50 g, and extraction time (t) ) 4 h. In these experiments, the extraction yields were similar (72.5, 72.0, 73.0, and 72.0%), indicating that reproducibility of the data was good. Nevertheless, to minimize experimental errors, each run was replicated twice. 3.1. Preliminary Experiments. Two types of experiments were performed before analyzing the effect of the operating pressure and temperature on both the extraction yield and the quality of the oil recovered. The first group of experiments was made to extinction (at the experimental conditions tested) and was designed to determine both exhaustion yields and the evolution with time of extraction yields. It can be observed in Figure 2 that, irrespective of the experimental conditions, no significant yield increase occurred after 4.5 h from the beginning of the experiment. Therefore, as a good compromise between the length of the experiment and the amount of oil that could be extracted, an extraction time of 4.5 h was chosen for performing subsequent experiments. The second group of experiments was carried out in order to ensure that no oil dragging occurred during the extraction runs. In these experiments, the extractor was
Figure 2. Evolution with time of extraction yields. Conditions: L ) 50 g; Q ) 2 L/min.
loaded with different amounts of used oil (25, 50, 75, and 100 g) and the extractions were performed at the following conditions: P ) 40 kg/cm2, T ) 80 °C, and Q ) 2 L/min. Results obtained are shown in Figure 3. It can be seen that both the oil yield and metallic content of the extracted samples decrease with decreasing waste oil loads, i.e., with increasing extractor death volumes. However, while in experiments performed with 25 and 50 g of oil, either the extraction yields or the metallic contents of the extracted samples were comparable; in experiments carried out with 75 and 100 g of oil, both variables were appreciably larger. Obviously, the higher oil yields of lesser quality oil (higher metal concentration) obtained in the two later experiments indicate that some oil dragging occurred. However, results from the former tests suggest that the phenomenon was unimportant at the conditions at which they were performed. Therefore, for subsequent experiments, an oil load of 50 g was selected. It is evident that, for a given oil load in the extractor, oil dragging is also related to the propane flow. Thus, four more experiments were performed to select a fluid flow that did not lead to a dragging situation at the experimental conditions of this study. The results of these experiments are shown in Figure 4. It can be observed in the figure that the extraction yield was practically 100% at 4 L/min, then decreased to 78.5 and 75.0% respectively at 3 and 2 L/min, and was maintained at 75.0% at 1 L/min. It should be noted, however, that in order to reach a 75% yield at 1 L/min, the extraction time necessary was twice as large (9 h) as that employed at 2 L/min (4.5 h). On the other hand, Figure 4 also shows that while in experiments performed at 1 and 2 L/min the metallic concentrations in the extracted samples were similar, they increased smoothly and steadily respectively when the flow was increased from 2 to 3 L/min and from 3 to 4 L/min. These results indicate that below 2 L/min oil drag did not occur but, above this value, it increased with increasing flow. Experimental results also suggest that operating at 2 L/min the flow of propane leaving the extractor is saturated in base oil; i.e., the residence time of propane in the extractor seems to be enough to allow the system to reach equilibrium conditions. Then, to avoid lengthy experiments, the lowest flow tested (1 L/min) was discarded and, for subsequent experiments, a propane flow rate of 2 L/min was selected. 3.2. Base Oil Yields. The effect of temperature and pressure on the yields of base oil obtained with liquid and supercritical propane was investigated in the tem-
4870 Ind. Eng. Chem. Res., Vol. 42, No. 20, 2003
Figure 3. Effect of oil load on extraction yields and metal concentration in the propane-extracted oil. Conditions: P ) 40 kg/cm2, T ) 80 °C, Q ) 2 L/min, t ) 4.5 h.
Figure 4. Effect of propane flow rate on extraction yields and metal concentration in the propane-extracted oil. Conditions: P ) 40 kg/cm2, T ) 80 °C, t ) 4.5 h, L ) 50 g.
Figure 5. Effect of pressure and temperature on extraction yields.
perature range from 25 to 130 °C at pressures of 30, 40, 50, and 60 kg/cm2. The results obtained are presented in Figure 5, where dotted lines are drawn to divide the graphs into two parts, each one corresponding to a different state of the solvent at the conditions at which the extractions were performed. LP, GP, and SCP are used in the graphs respectively to refer to liquid,
gas, and supercritical propane. It can be seen that, independently of the pressure analyzed, base oil yields are about 80% and almost constant along the first part of the temperature range studied, just as long as the propane remains as liquid; then, when propane becomes a gas or a supercritical fluid, they drop to zero, steeply in the first case and smoothly in the second.
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Figure 6. Effect of pressure and temperature on the acid number of the propane-extracted oil.
From these results, it may be inferred that the solvent power of liquid propane is larger than that of supercritical propane, while gas propane cannot dissolve base oil at all. In regards to liquid and supercritical propane, it can be seen that extraction yield, and therefore propane solvent power, increases with decreasing temperature at constant pressure and with increasing pressure at constant temperature. According to the basic principles of fluid extraction,16,17 these results are probably related to the propane density. Thus, because the density of liquid propane is larger than that of supercritical propane and its variation with pressure and temperature conditions is smaller, the extraction yields obtained with liquid propane are larger than that with supercritical propane and their variation with temperature and pressure is smaller. 3.3. Oxidation Compounds Removal. It was observed visually that the extracts obtained at different conditions presented different coloration and concentration of particles in suspension. Most probably, this was due to the presence of degradation compounds coextracted with the base oil. On the other hand, because under normal service conditions a major portion of lubricant degradation is due to the oxidation of the lubricant base oil,18 it is expected that more of these coextracted compounds are oxidation products. Thus, to separate these degradation compounds from used oil, propane should be able to destabilize the dispersion and to dissolve selectively the base oil fraction, throwing out the undesirable oxidation products. Obviously, the extent at which the separation will occur will depend on the operational conditions. The results obtained in this study will be discussed below. First of all, to ensure the presence of oxidation compounds in the extracts, we obtained their IR spectra. Then, once their presence was confirmed, their concentration in the extracted oil was analyzed. Confirming our hypothesis, the spectrum presents a band at 1700 cm-1 characteristic of oxidation compounds. On the other hand, the oxidation compounds have acid characteristics and, therefore, their relative concentration in the extracts may be determined by measuring the extract acid number.19 The values obtained in this work for this parameter are shown in Figure 6. It can be seen that they increase with increasing pressure at constant temperature and with decreasing temperature at constant pressure, depending on whether the extraction was performed with liquid or supercritical propane.
Because the variation of propane density, and therefore of propane solvent power, with pressure and temperature also follows this trend, it is quite obvious that results obtained are related to the value of this parameter. It seems that the solubility in propane of the used oil acid compounds (which usually have higher molecular weights than base oil components) decreases more steadily than the solubility of base oil compounds when the propane density (i.e., propane solvent power) decreases. In other words, as the propane solvent power decreases, its tendency is to throw out the heaviest components, which are chemically and physically most dissimilar to propane. These results agree with those obtained by Wilson et al.,15 who studied the possibility of using liquid propane as a solvent for dewaxing, deasphalting, and refining of heavy oils. It should also be noted that more recently, and also based on similar results, Cheng et al.20 have proposed the use of supercritical propane for the fractionation of wax-bearing residues. Another possible explanation to the favorable effect of increasing temperature (at constant pressure) on the reduction of the extract acid number may be that the increase with temperature of oxidized compounds vapor pressure is less than that of base oil components. In addition to all of these facts, it should be pointed out that coextraction of oxidation compounds together with base oil components may have also been affected by the presence of dispersant-detergent additives in the used oil. These additives are introduced in the fresh oil to keep in suspension small particles and the heaviest compounds and mainly work through the mechanisms of polar interactions. In principle, it is expected that the higher the concentration of these additives in the solution base oilpropane, the higher the number of interactions between them and the oxidation compounds and, therefore, the higher the concentration of these pollutants in the extracted base oil. In other words, the higher the concentration of dispersant additives, the more difficult will be the separation of oxidation products from used oil. To confirm this hypothesis and taking into account that these additives usually contain calcium in their molecules,19 we determined the concentration of this metal in the extracted oil. Figure 7 shows the results obtained in extractions performed in this work. It can be observed that the variation of the Ca concentration with temperature follows the same trend as that of the concentration of oxidation compounds (Figure 7); i.e., at a given pressure, the Ca concentration in the extracted base oil decreases with increasing temperature. However, in contrast to the case of oxidation compounds, no effect of pressure was found. According to these results, a direct correlation between the concentrations of both compounds (dispersant additives and oxidation products) may not be established. The stabilizing action of dispersant additives seems to depend on the interaction strength more than on the interaction number between these additives and the oxidation compounds. Thus, the fact that the stabilizing action decreases with increasing temperature may be imputed to the fact that polar interactions between these additives and oxidation compounds weaken as the temperature rises.19 As a consequence of this, flocculation and oxidation compounds removal would occur more easily at high temperatures.
4872 Ind. Eng. Chem. Res., Vol. 42, No. 20, 2003
Figure 7. Effect of pressure and temperature on the metallic concentration of the propane-extracted oil.
In conclusion, to explain the effect of pressure and temperature on the removal of oxidation compounds, three factors should be considered: propane density, relative vapor pressure of the oxidation compounds and base oil components, and interaction strength between the dispersant-detergent additives and oxidation compounds. Removal of oxidation compounds is found to increase at high temperatures because they reduce the propane density, increase the difference between the oxidation compounds and base oil components vapor pressures, and weaken the interaction strength between dispersant additives and oxidation compounds. In regards to the effect of pressure, oxidation compounds are separated more easily at low values of the variable because propane density is smaller and, therefore, high molecular weight oxidation compounds are more difficult to dissolve. 3.4. Metallic Compounds Removal. Metallic compounds are other important used oil constituents that should be removed in order to obtain a base oil suitable for the formulation of new lubricants. They are introduced into the used oil from different sources: lead may come from overlay on bearing surfaces as well as grease, antiwear, and detergent additives, calcium from dispersant-detergent additives, zinc from the antiwear additive and oxidation and corrosion inhibitors, and iron from gray iron cylinder liners, malleable iron pistons, hardened steel camshafts, crankshafts, gears, etc. As in the case of oxidation products, the bulk of these metallic compounds are kept in stable dispersion by dispersant additives and electrostatic interactions between heteroatoms and asphaltic compounds just as in the crude oil.14
It is expected that used oil treatment with propane may remove an important part of metallic compounds because, as is well-known, under certain conditions propane tends to dissolve preferentially the fraction of base oil and causes particles and the heaviest compounds to precipitate.15 Figure 7 shows the results obtained in experiments carried out in this study. It can be seen that, at a given pressure, the concentration of metallic compounds in the base oil extracted decreases with increasing temperature. On the contrary, no effect of pressure was found in the experimental range analyzed. As in the case of the oxidation compounds removal, these results should be imputed to the variation of propane density with temperature and pressure. In the pressure range analyzed, propane density, calculated from an equation given in ref 21, did vary at constant temperature, but the variation was not large enough (less than 0.05 g/L). However, in the temperature range studied, the propane density variation at constant pressure was larger than 0.10 g/L and the effect of the variable was noticeable. It should be mentioned here that the different pressure effect on metallic and oxidation compounds removal is probably due to the fact that the metallic compounds present in the used oil have a higher molecular weight than the oxidation products (as can be inferred from column 4 of Table 1 showing that after vacuum distillation most metallic compounds are removed, while an important part of oxidation products still remain in the oil) and, therefore, their extraction from the oil is less sensitive to the variation of the propane density. It should be pointed out as well that the greater increase with temperature of the base oil constituents
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vapor pressure as compared to that of metallic compounds and the weakening of the interaction strength between dispersant additives and metallic compounds as the temperature rises could have also contributed to the temperature effect observed. To end this section, we remark that, similar to the case of oxidation products, although propane allows removing metallic compounds up to a certain degree, greater or smaller depending on the extraction conditions, a percentage of these compounds are soluble in propane and, therefore, inevitably coextracted with the base oil. A similar finding has been recently reported by Angulo.7 3.5. Effect of Propane Treatment on the Quality of Vacuum-Distilled Oils. Problems related to fouling of heating and distillation equipment as well as to the quality of the base oil obtained by vacuum distillation had led us to explore the benefits of introducing a propane precleaning step of the used oil before treatment in the vacuum distillation units. Results obtained in this work are shown in Table 1, where we compare the characteristics of raw used oil with those of a propane-extracted oil at optimum conditions (30 kg/cm2 and 90 °C) and two distilled used oils (5 mmHg), one of them pretreated with propane at optimum conditions. It can be observed that all used oil characteristics notably improve after propane pretreatment (column 3) and that when this oil is subjected to vacuum distillation (column 4), an oil almost suitable for new lubricant formulation can be obtained.19 Although the concentration of oxidation compounds is a little higher than that desired for a lubricant oil,19 it can be easily lowered by a soft hydrotreatment. On the other hand, its metallic content is almost imperceptible and sulfur and phosphorus concentrations, as well as viscosities at 40 and 100 °C, are similar to that of an SN-150 virgin oil,19 which are 29 cSt at 40 °C and 5 cSt at 100 °C. On the contrary, vacuum-distilled oil without propane pretreatment (column 5) is still highly contaminated and may not be used in the formulation of new lubricants without being submitted to a severe treatment. 4. Conclusions Many processes for the recycling of used lubricant oil involve the use of vacuum distillation followed by a polishing or decolorizing treatment. However, they present serious problems related to coking and column fouling during distillation and, therefore, some form of pretreatment to remove additives and contaminants from the oil is preferred. In this work we have found that extraction with propane can be used successfully to this end. In the propane extraction process, almost no effect of pressure on the extraction yields and metallic compounds removal has been found. However, this variable did affect to the separation of oxidation products, removed more efficiently at low pressures. The effect of this variable has been attributed to the variation of propane density with pressure and, therefore, to its variable solvent power. In regards to temperature, at a given pressure the extraction yields were found not to depend on the variable as long as propane remained as a liquid. However, when the temperature was increased at constant pressure so that propane became a gas or a supercritical fluid, extraction yields decreased. On the other hand, metallic and oxidation compounds removal
was found to increase with increasing temperature at constant pressure, and this removal decreases with increasing pressure at constant temperature. The effect of this variable was explained by considering the combined effect of fluid density, vapor pressure of the different compounds, and dispersant agents concentration on the solubility of the compounds of interest (base oil components, metallic compounds, and oxidation products). From the experimental results summarized above, the optimum conditions for processing the used lubricant oil were determined: P ) 30 kg/cm2 and T ) 90 °C. Vacuum distillation of used oil extracted at these conditions provided an oil with physical and chemical properties almost similar to those of virgin oils. Consequently, it can be concluded that this oil, after being submitted to a very soft polishing treatment, may become a valuable resource in the formulation of new lubricant oils. Literature Cited (1) Go´mez, J. A.; Martı´nez, V. Aceites usados: Recogida, recuperacio´n y reciclado. Quim. Hoy 1991, 3, 105. (2) Directiva 91/156/CEE, DOCE, Mar 18, 1991. (3) Ley 10/98 de Residuos, BOE No. 96, Apr 21, 1998. (4) Angulo, J. Seminario internacional sobre recuperacio´ n de aceites usados; CER: Madrid, 2002. (5) Martı´n, J. L.; Matias, P. ×c0Que se hace en Espan˜a con los aceites usados?. Ing. Quim. 1995, 309 (1), 113. (6) Che, Y.; Kessler, R. Sixth International Conference of Used Oil Recovery and Reuse, San Francisco, CA, 1991. (7) Angulo, J. Regeneracio´n de aceites usados por extraccio´n con propano. Ing. Quim. 2002, 389 (4), 153. (8) Quang, D. V.; Carriero, G.; Schieppati, R.; Comte, A.; Andrews, J. W. Propane Purification of Used Lubricating Oils. Hydrocarbon Process. 1974, 53 (4), 129. (9) Foster Wheeler Corp. Procedimiento para la purificacio´n y recuperacio´n de aceite usado de ca´rter. Spanish Patent 433,867, 1975. (10) Audibert, F. Huiles Usagees Schemas IFP de Raffinage. Rev. l’IFP. 1978, 6, 935. (11) Quang, D. V.; Audibert, F.; Audibert, J. F.; Boucher, J. F.; Deville, B. Perfectionnement aux proce´de´s de re´ge´ne´ration d’huiles lubricantes usages. French Patent 2,096,690, 1972. (12) Angulo, J.; Ferna´ndez, J.; Martı´n, J. L. La regeneracio´n de aceites usados: Un proceso viable. Ing. Quim. 1996, 320 (1), 173. (13) Can˜izares, P.; Rinco´n, J.; Garcı´a, M. T. Regeneracio´n de aceites lubricantes usados mediante extraccion con propano. VII. Congreso de Ingenierı´a Ambiental; PROMA: Bilbao, Spain, 2001. (14) Alves dos Reis, M.; Silva, M. Waste Lubricating Oil Rerefinig by Extraction-Flocculation. 1. A Scientific Basis To Design Efficient Solvents. Ind. Eng. Chem. Res. 1988, 27 (7), 1223. (15) Wilson, R.; Keith, P. C.; Haylett, R. E. Liquid Propane: Use in dewaxing, deasphalting, and refining heavy Oils. Ind. Eng. Chem. 1936, 28, 1065. (16) Brunner, G. Gas Extraction; Springer-Verlag: Berlin, 1994. (17) Stahl, E.; Quirin, K. W.; Gerard, D. Dense Gases for Extraction and Refining; Springer-Verlag: Berlin, 1988. (18) Fogler, H. S. Elementos de Ingenierı´a de las Reacciones Quı´micas, 3rd ed.; Pearson Education: Naucalpan de Jua´rez, Me´xico, 2001. (19) Delgado, J.; Lo´pez, F. Los productos petrolı´feros: Su tecnologı´a; G.T.S., Eds.: Madrid, 1988. (20) Cheng, J.; Yaohua, F.; Zhan, Y. Supercritical Propane Fractionation of Wax-Bearing Residue. Sep. Sci. Technol. 1994, 23 (11), 1179. (21) Reid, C. R.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed.; McGraw-Hill: New York, 1987.
Received for review January 8, 2003 Revised manuscript received May 16, 2003 Accepted May 23, 2003 IE030013W
