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Figure 4. Summary of the technologies employed at the industrial level for re-refining used lubricant oil. Adapted from [66,67]. In Ecuador, in the city of Quito, the re-refining of used lubricating oils is carried out, in this process methods such as filtration, extraction by solvents, and vacuum distillation are applied, while in the city of Cuenca only filtration, decantation, and sedimentation is performed; in Figure 3 these processes are marked in red.

Figure 4 Summary of the technologies employed at the industrial level for re-refining used lubricant oil. Adapted from [66,67]. In Ecuador, in the city of Quito, the re-refining of used lubricating oils is carried out, in this process methods such as filtration, extraction by solvents, and vacuum distillation are applied, while in the city of Cuenca only filtration, decantation, and sedimentation is performed; in Figure 3 these processes are marked in red.

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Figure 1. Process for the development of this research.
Figure 1. Process for the development of this research.
@ Refers to a screening process to remove large particles (e.g., wipe cloth) prior to storing in the tanks. ° Indicates if the storage container has been under roof conditions or not. © Frequency of collection of the used oils from the used oil generators’ facilities. Table 1. Storage conditions of the used oils in mechanics and car lubricating shops in Cuenca.
@ Refers to a screening process to remove large particles (e.g., wipe cloth) prior to storing in the tanks. ° Indicates if the storage container has been under roof conditions or not. © Frequency of collection of the used oils from the used oil generators’ facilities. Table 1. Storage conditions of the used oils in mechanics and car lubricating shops in Cuenca.
Table 2. The analytical instruments’ specifications. 2.3. Statistical Analysis of the Used Oil Properties
Table 2. The analytical instruments’ specifications. 2.3. Statistical Analysis of the Used Oil Properties
Figure 2. Cluster analysis of the physicochemical properties of the mixtures of used oils (a dendro- gram using the Ward link). indicate homogeneous conglomerates and large distances show diversified conglomerates, it is convenient to stop the grouping process when the horizontal lines become long [32]; this procedure determines the number of clusters. In the second step of the analysis, the inference statistical technique “confidence interval” (with a 95% level of confidence) was employed [33]. In the third step, a comparison of the physicochemical characteristics of the used oils in Cuenca to the properties of used oils in other countries was conducted. Box and whisker plots were employed to summarize the data and to identify outliers (using the SPSS software).
Figure 2. Cluster analysis of the physicochemical properties of the mixtures of used oils (a dendro- gram using the Ward link). indicate homogeneous conglomerates and large distances show diversified conglomerates, it is convenient to stop the grouping process when the horizontal lines become long [32]; this procedure determines the number of clusters. In the second step of the analysis, the inference statistical technique “confidence interval” (with a 95% level of confidence) was employed [33]. In the third step, a comparison of the physicochemical characteristics of the used oils in Cuenca to the properties of used oils in other countries was conducted. Box and whisker plots were employed to summarize the data and to identify outliers (using the SPSS software).
Table 3. Physical properties and metal content of the used oils in Cuenca city.
Table 3. Physical properties and metal content of the used oils in Cuenca city.
Table 4. The physical properties and metal concentration of the used lubricant oils in Cuenca, in comparison with other oils. Table 5 shows a comparison of the physical properties, presence of metals, and con- centration of additives of the used oils in Cuenca with those of used oils in other countries. Some properties are difficult to compare due to a lack of data. However, it is seen that, as with other materials, the water content is below the values reported in other countries. Properties such as viscosity are of interest since they show that the oils have not degraded too much during their use, as well as indicating a lower water content.
Table 4. The physical properties and metal concentration of the used lubricant oils in Cuenca, in comparison with other oils. Table 5 shows a comparison of the physical properties, presence of metals, and con- centration of additives of the used oils in Cuenca with those of used oils in other countries. Some properties are difficult to compare due to a lack of data. However, it is seen that, as with other materials, the water content is below the values reported in other countries. Properties such as viscosity are of interest since they show that the oils have not degraded too much during their use, as well as indicating a lower water content.
Table 5. The physical properties, concentration of wear metals, and additives of the used lubricating oils in Cuenca, in comparison with the properties of the oils used in various countries.
Table 5. The physical properties, concentration of wear metals, and additives of the used lubricating oils in Cuenca, in comparison with the properties of the oils used in various countries.
Table 6. Steps for re-refining used oils and the technologies employed at the laboratory scale.
Table 6. Steps for re-refining used oils and the technologies employed at the laboratory scale.
Table 6. Cont. Re-refining consists of four stages: pre-treatment (i.e., removal of water and solid particles), regeneration (i.e., elimination of degradation products), fractionation of the bases (i.e., separation of light hydrocarbons), and finishing (i.e., improvement of color and smell of the treated oil) [35,59,63]. Some of these processes still have some disadvantages, such as the poor performance of oil regeneration or the generation of other environmentally
Table 6. Cont. Re-refining consists of four stages: pre-treatment (i.e., removal of water and solid particles), regeneration (i.e., elimination of degradation products), fractionation of the bases (i.e., separation of light hydrocarbons), and finishing (i.e., improvement of color and smell of the treated oil) [35,59,63]. Some of these processes still have some disadvantages, such as the poor performance of oil regeneration or the generation of other environmentally
Table 8. The main re-refining processes currently used in European countries and China (adapted from [66,71])
Table 8. The main re-refining processes currently used in European countries and China (adapted from [66,71])
Table 8. Cont.
Table 8. Cont.
The pretreatment of used oil that ETAPA currently carries out (water and sludge removal through sedimentation, centrifugation, and filtration) is similar to that used in the UAE [44] and Egypt [56]. Thus, the preliminary steps required for the solvent extraction process are already being performed. In the re-refining process through solvent extraction, a 1:3 oil-to-solvent ratio is proposed (where the solvents are blends of butanol + toluene + methanol or butanol + KOH), following the processes used in the two aforementioned countries [44,56]. The solvent extraction process is followed by a vacuum distillation step for the recovery of solvents that will be reused in the process to remove metals (especially Pb and Fe) [44]. For the finishing step, different adsorbents can be used. However, better results are obtained with alumina, bentonite, and activated bentonite. The use of almond and palm kernel powders can also be effective [44]. At the moment, ETAPA’s Used Oil Collection Program sends the filtered and ceded oil sludge to the ECOTECNO Foundation attached to HOLCIM, where a thermal destruction of the waste is carried out with the endorsement of the local and regional Environmental Control Entity. The waste generated by the re-refining plants in Europe and China are used as a component in asphalt preparation and as fuel in boilers [66]. These could be an option for re-using the wastes of the re-refining processes since the city has a small asphalt production plant that could process all this by-product. The development of a re-refining plant with a capacity to process higher amounts of used oils than that currently collected in the city is suggested. Our estimates indicate that there could be up to 7330 t/year of used oil to be processed in the proposed plant (which is around 10% of the total lubricant oil consumed in Ecuador; see Section 1). This amount would result from (a) a complete recovery of used oil in Cuenca; and (b) the contribution of neighboring cities in the South of Ecuador (e.g., Loja, Azogues, Machala, and other smaller cities) that are located at distances less than 220 km from Cuenca (Figure 5). According to [72], the added total number of cars in these cities is approximately double that in Cuenca. However, further work is necessary to better define the collection, transport, and storage logistics of used oil in those cities to comply with the requirements of a re-refining plant and Law 042. The benefit for Ecuador is enormous since the import of up to 7330 t/year of lubricant could be avoided in these conditions. In addition to environmental and social benefits, the country could save around US$ 30 million/year, according to data from the Central Bank of Ecuador [73], due to avoiding the import of lubricant oils. Figure 5. Map of Ecuador showing Cuenca and some neighboring cities that could supply used lubricant oils for the operation of a re-refining plant.
The pretreatment of used oil that ETAPA currently carries out (water and sludge removal through sedimentation, centrifugation, and filtration) is similar to that used in the UAE [44] and Egypt [56]. Thus, the preliminary steps required for the solvent extraction process are already being performed. In the re-refining process through solvent extraction, a 1:3 oil-to-solvent ratio is proposed (where the solvents are blends of butanol + toluene + methanol or butanol + KOH), following the processes used in the two aforementioned countries [44,56]. The solvent extraction process is followed by a vacuum distillation step for the recovery of solvents that will be reused in the process to remove metals (especially Pb and Fe) [44]. For the finishing step, different adsorbents can be used. However, better results are obtained with alumina, bentonite, and activated bentonite. The use of almond and palm kernel powders can also be effective [44]. At the moment, ETAPA’s Used Oil Collection Program sends the filtered and ceded oil sludge to the ECOTECNO Foundation attached to HOLCIM, where a thermal destruction of the waste is carried out with the endorsement of the local and regional Environmental Control Entity. The waste generated by the re-refining plants in Europe and China are used as a component in asphalt preparation and as fuel in boilers [66]. These could be an option for re-using the wastes of the re-refining processes since the city has a small asphalt production plant that could process all this by-product. The development of a re-refining plant with a capacity to process higher amounts of used oils than that currently collected in the city is suggested. Our estimates indicate that there could be up to 7330 t/year of used oil to be processed in the proposed plant (which is around 10% of the total lubricant oil consumed in Ecuador; see Section 1). This amount would result from (a) a complete recovery of used oil in Cuenca; and (b) the contribution of neighboring cities in the South of Ecuador (e.g., Loja, Azogues, Machala, and other smaller cities) that are located at distances less than 220 km from Cuenca (Figure 5). According to [72], the added total number of cars in these cities is approximately double that in Cuenca. However, further work is necessary to better define the collection, transport, and storage logistics of used oil in those cities to comply with the requirements of a re-refining plant and Law 042. The benefit for Ecuador is enormous since the import of up to 7330 t/year of lubricant could be avoided in these conditions. In addition to environmental and social benefits, the country could save around US$ 30 million/year, according to data from the Central Bank of Ecuador [73], due to avoiding the import of lubricant oils. Figure 5. Map of Ecuador showing Cuenca and some neighboring cities that could supply used lubricant oils for the operation of a re-refining plant.
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