Chemical Engineering Journal 220 (2013) 343–351Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Waste lubricating oil treatment by extraction and adsorption Rafie R. Mohammed a, Inaam A.R. Ibrahim a, Alladdin H. Taha b, Gordon McKay c,⇑ a Chemical Industries Department, Mosul Technical Institute, Mosul, Iraq Department of Petroleum Refining, Zakho Technical Institute, Zakho, Iraq c Department of Chemical and Biomolecular Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong Special Administrative Region b h i g h l i g h t s " Novel technology combining extraction and adsorption. " 1-Butanol achieved maximum percent sludge removal. " Addition of KOH accelerated the waste sedimentation process greatly. " Acid activated clay gave the give best conditions for treating waste oil. " The optimum solvent-adsorbent pair for spent lubricant oil recovery is 1-butanol/activated clay. a r t i c l e i n f o a b s t r a c t In this work, the recovery of base oils from waste lubricants was investigated using a novel combination of solvent extraction and adsorption on solids. The performance of six extracting solvents (n-hexane, 1butanol, petroleum ether, 1-hexanol, carbon tetra chloride, and acetone) was evaluated experimentally. Solvent to oil ratios from 1:1 to 4:1 were also examined. This research has studied the effect of the use of KOH to enhance flocculation. The results show that 1-butanol achieved the best performance with the maximum percent sludge removal, followed by n-hexane, petroleum ether, 1-hexanol, carbon tetrachloride, and acetone. The percentage of oil sludge was found to increase with the increase of solvent to oil ratio until it reached the maximum at the ratio of 3:1. The application of an adsorption process using different adsorbent materials was investigated. Adsorbent materials such as almond shell, walnut shell, eggshell, and acid activated clay which were prepared locally were used. It was found that the acid activated clay was able to give the best conditions for treating the waste oil followed by the almond shell powder. The results from the test showed that, viscosity increased from 38.3 cst for used lube oil to 85 cst for acid/ clay treatment and the flash point increase from 178 °C to 238 °C, while the density decreased from 912 to 896 kg/m3, the pour point from À6 to À13.2 °C and colour from 0.53 to 0.12. Other results from the different tests showed varying degrees of improvement with the best results obtained using the acid/clay treatment. Ó 2013 Elsevier B.V. All rights reserved. Article history: Received 12 October 2012 Received in revised form 20 December 2012 Accepted 26 December 2012 Available online 11 January 2013 Keywords: Waste lubricating oil Purification Extraction Adsorption 1. Introduction Lubricating oil is one of the most important liquids that are used in almost all vehicles and machines. Lubricating oils play a dual role of heat transfer and that of friction reduction that reduces the heat generated in internal combustion engines. Basically, the main ingredient of lubricant oil is the base oil, which is refined from crude oil or synthesized in the laboratory. Base oil is mixed with additives to enhance the ability of the oil to act as a layer between contact surfaces. Modern lubricating oil is made of base stock or base oil (71.5– 96.2 wt%), blended with a few ppm of chemical additives according ⇑ Corresponding author. Tel.: +852 2358 8412; fax: +852 2358 0054. E-mail address:
[email protected] (G. McKay). 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.12.076 to its grade and specific duty. Additives are added to fulfill the specific requirement for lubrication. Each lubricant oil consisted at least one type of additive or nearly 30% by weight of additives (Table 1) [1]. During usage, lubricating oils undergo changes termed degradation and contamination, which render them ineffective for further application. Lubricating oil goes through normal degradation and about 50% of it is consumed in the process. The rest of the oil picks up a number of contaminants from the working environment, such as, residual components of engine fuels, solids from wear processes along with corrosion products and dirt, soot, combustion products etc. [2]. Degradation involves changes in the desired viscometric properties of oil as a result of alteration in the lubricating oil molecular structure caused by cracking, isomerization and polymerization reactions prompted by high temperatures in the run- The mixture was strongly mixed until all the KOH dissolved into the solvent solution and was ready for solvent extraction. this liquid waste has been disposed of into the environment and creates a lot of problems. The samples were homogenized.3. eggshell) of particle size 30–60 mesh were used. Waste oil can be a very valuable resource.2 2.1. The solvent was recovered by vacuum distillation. Mohammed et al. getting enough oil to conduct the research. walnut shell. the following advantages are anticipated: (a) using less amount of liquid organic solvents.0 0. where it finally either seeps into ground or floats on water surfaces. the used oil sample was weighed (Woil) and mixed with the solvent/KOH mixture in a beaker with solvent to oil ratios of 1:1–3:1 for 15 min under continuous stirring (stirring speed set at 350–400 rpm). garbage heap and sewerage system. The objective of this study is to evaluate the oil recovery efficiency of the combined extraction and adsorption approach. bowls. eggshell.4.2. Solvents used for extraction were n-hexane. settling centrifuge system. Experimental 2. Clay preparation Brownish-red clay was used and the apparatus used included jars. reducing the effect on global warming. There are limitations of many process because they incorporate only physical separation of contaminants and there is usually no appreciable change in the colour of the used oil. Philips re-fined oil process. petroleum ether. the recovered oil is separated from the adsorbent mixture by using a filter paper. acid-clay process. Used lubricant oil is one of the abundant liquid wastes in the country that needs to be further treated.0 to 3. / Chemical Engineering Journal 220 (2013) 343–351 wt% 71. Currently. The overall effect of this degradation is the formation of low molecular weight compounds and oxidation products which include polymerized or condensed molecules called gum and sludge. solvent to oil ratio and adsorbent type parameters will be investigated for their effect on the treatment performance. Solvent type. 1-hexanol. if managed properly. and. During re-refining the properties of the oils are changed stepwise [6]. a number of stages are possible depending on the original source of the used oil. Impurities such as sand and stone settled at the bottom and then they were removed by decanting. and activated clay – which was prepared locally. solvent-oil solution was separated from sludge by filtration. Materials used Waste lubricant oils were gathered at collecting stations in the city of Mosul (Iraq). while activated clay of 100–230 mesh size were tested. Out of these two options the modern method is re-refining. oven and distilled water.R. stored away from light and at room temperature for several days to allow large suspended particles to settle under gravity. fixed bed sand filtration process to produce relatively clean oil [7]. walnut shell. Flocculation. It is then left at room temperature for one hour to allow gravity settling. After that.0 0.0–9. (c) using local resources. The results should provide a sound basis for developing an environmentally friendly and economically competitive method for used lubricant oil treatment. (b) regeneration of base-oil from waste oil and (c) extracting the heat value of waste oil through combustion processes [3]. (b) running half the treatment process at ambient conditions. The washing solvent was mixed with solvent–oil solution. down the sewers. It has varying refined fractions of petroleum and its recovery possibilities are extremely high. The solvents were of analytical grade and supplied by BDH. After that. Used oil is dumped on the ground.344 Table 1 Composition of typical lubricating oil. The most important methods for the recycling of used lubricating oils are re-refining and reclamation [5]. and the sophistication of the technology utilized [8]. sieves. The clay sample was ground and then made into a slurry in distilled water. the level of contamination. The slurry was . Adequate analysis and comparison of regenerative technologies of waste lubricant has been done by Yu-Lung [13]. The sludge was then dried till constant weight at 105 °C (WDry). A number of other studies have been reported which focus on the reclamation of used lubricant oil [9– 12]. carbon tetrachloride and acetone. 2. This compares with 65–75% recoverable base-oil content in used automotive oils.0 0.5–96. (d) generating less waste and (e) having lower capital and operating costs. 2. or sent to landfills.1–3.5 2–15 ppm of the treatment process. Ingredients SAE 30 or 40 base oil stock Additives Metallic detergent Ashless dispersant Oxidation inhibitor Antioxidant/anti wear Friction modifier Pour point depressant Antifoam R.0 0. This is to ensure perfect mixing and at the same time preventing any losses of oil to the sludge.0 g were carefully added to a specified volume of solvent in a beaker. In the recycling process. whereas lube crudes typically have 12–16% base-oil. Adsorption The extracted oil was then mixed with a fixed amount of 15 wt% of different adsorbents into a beaker. 1-butanol. The mixture is then subjected to intense agitation for 10 min. next. Some major recycling processes in use include. conical flask. The recycled oils produced with solvent refining or hydroprocessing can be used as lubricating base oils in modern engines. There are basically three options to deal with the waste oil in the world: (a) dumping the waste oil on land. This necessitates the adoption of a different process route to improve and also enhance the chemical properties of the recycled oil. Sorbents (almond shell.0–10.1–1. By using the combined extraction and adsorption method.0 1. Percentage sludge removal and some physical properties of the used and treated lubricant oil will be tested to show the improvement Percent Sludge Removal ðPSRÞ ¼ ðW Dry =W Oil Þ Â 100% 2.1–2.5–3. 2. Then. After strong agitation. Adsorbents used were almond shell. The sludge was dispersed twice with the same solvent to extract any remaining oil. transferred to an appropriate tank. The percent sludge removal represents the quality of dry waste oil (additives and impurities) removed from the used oil after mixing with solvent according to the experiment above. solvent extraction and filtration process Several weighed portions of potassium hydroxide (KOH) ranging from 1. which if burnt or dumped would mean the loss of a valuable natural resource [4]. Average crude oils have 3–8% base-oil. it was then left under a controlled temperature of 30 °C for 24 h to allow extraction–flocculation. The percentage sludge removal (PSR) can be calculated as shown: ning engine. The yield of oil was calculated on the basis of initial mass of used oil taken and then analyzed for different physical properties. distilled water. 2. the sample was cooled at a specified rate and examined at intervals of 3 °C for flow characteristics. The temperature of the test specimen was increased rapidly at first and then at a slower constant rate as the flash point was approached. 2. The flash point is the lowest liquid temperature at which application of the test flame causes the vapors of the test specimen of the sample to ignite. 2. reducing the amount of lubrication and activating surfaces which may themselves act as catalysts for degradation of the oil. The residue undergoes cracking and coking reactions during a fixed period of severe heating. titration solvent was added in the ratio 2 g to 100 mL and shaken to allow mixing of the sample engine oil with the solvent.6. As far as the affect of residue on performance. The sample contained in a suitable vessel is ignited and allowed to burn until only ash and carbon remain. 2. plastic bowl.R.0641. k of 850 nm. Then the titrant was titrated with 0. N the normality of the titrant = 0. It is the lowest temperature at which movement of the specimen is observed and recorded as the pour point. A weighed quantity of sample was placed in a crucible and subjected to destructive distillation. Colour measurement [19] The colour of the recovered base oil is measured by using a spectrophotometer where the amount of colour absorbed by the spectrophotometer. the test crucible containing the carbonaceous residue was cooled in a desiccator and weighed. Water is an important contaminant in many lubricant oil systems because of its potential to cause failure via a number of mechanisms. The amount of colour absorbed from new virgin oil is also recorded and this value is fixed as a basis where the comparison between this value and the amount of colour absorbed from the recovered base oil samples are made to determine which sample represents the best colour removal. The efflux time is obtained by timing the flow of the fluid samples as it flows freely from the upper meniscus mark to the lower meniscus mark. Clay activation The apparatus involved in the clay activation was an aluminum pan. Mohammed et al.6. After this time duration.1. two drops of para-napthal benzene indicator was added to the titrant before titration begins. Vs the volume of titrant used for titrating blank. Next 50–60 cm3 of sulphuric acid in 0. A period of 10 min was allowed for the sample to come to the bath temperature and after 15 min it reached 100 °C.6. 2. Results are reported as a percentage of the weight of the original sample. 2. The sample is then drawn up to the upper timing mark of the inverted viscometers and next the instrument was turned to its normal vertical position.1 N perchloric acid in glacial acetic acid against the solvent and for visual determination.R. 2. Whatever the equipment.6. Water content test Water contamination may cause different problems in different types of lubricating oil. At specified intervals a test flame was passed across the cup.7. then it was cooled and weighed [20]. 2.35 mol/cm3 concentration was added to the slurry and left for 1 h at a temperature between 90 and 100 °C. The residue remaining is calculated as a percentage of the original sample. Approximately 70 mL of test specimen was placed into a test cup.4. The method was first to make a slurry using 200 g of clay (after dirt. Conradson carbon residue test Carbon Conradson residue is the percent of coked material remaining after a sample of lubricating oil has been exposed to high temperatures. Since compounded oils contain metallic additives that generally leave a residue. although corrosion is always directly associated with water ingress. / Chemical Engineering Journal 220 (2013) 343–351 345 kept in an oven for 12 h at temperature of 110 °C to be dried and then the dried clay was ground into very fine particles and sieved to a mesh size of 100–230 using test sieves on a mechanical shaker. The orange colour changes to green or brown green at end point of titration. Ash can result from oil or water-soluble metallic compounds or from extraneous solids such as dirt and rust. After preliminary heating. one opinion is that the type of carbon is of greater importance than the quantity. A was recorded at a wavelength. The carbonaceous residue was reduced to an ash by heating in a muffle furnace at 775 °C. and reported as Conradson carbon residue [21].6. Analysis of samples A flash point [15] test was performed. To determine the fire point.5. At the end of the specified heating period. Kinematic viscosity test [16] A clean dry viscometer tube was used which would have a flow time above 200 s for the fluid to be tested.6.6.6.5. The engine oil sample to be tested was weighed into a beaker. the mixture was washed with distilled water in order to remove any excess acid. The test is repeated and the kinematic viscosity was calculated by multiplying the efflux time by the viscometer constant. 2. Total base number This test involves titrating a sample of engine oil dissolved in a mixture of titration solvent (chlorobenzene and glacial acetic acid) with a titrant (perchloric acid in glacial acetic). sand and stone have been removed) with distilled water of about 80 cm3.2. Water contamination within lubricating/lube oil storage tanks can lead to microbiologi- . A blank titrant is then prepared by adding 10 mL of titration solvent into a beaker without any sample and then titrated. Ash content test Knowledge of the amount of ash-forming material present in a product can provide information as to whether or not the product is suitable for use in a given application. Pour point test [18] The pour point of a petroleum specimen is an index of the lowest temperature of its utility for certain applications. oven. The pH of the washing water was monitored until it was found to be neutral and finally the washed clay mixture was dried in an oven for 1 h and ground into powder form [14]. The total base number (TBN) can then be calculated using the formula [17]: TBN ¼ ðV s2 À V s Þ Â 56:1 Â N Ws where Vs2 is the volume of titrant used for titrating sample of engine oil. The viscometer was placed into the holder and inverted into the constant temperature bath maintained at 40 °C and depending on which temperature of the sample viscosity is to be determined. Ws is the weight of sample taken for titration.6.3. water can displace the oil at contacting surfaces. other testing should be done to also identify the type of residue rather than just the amount. the test is continued until the application of the test flame causes the test specimen to ignite and sustain burning for a minimum of 5 s. burner clay. The viscometer was charged with the sample by inverting the tubes thinner area into the liquid sample and suction is then applied through the thicker area with a vacuum machine. resulting in reduction of oil losses in the sludge phase and increasing the sludge removal value [24]. 1-hexanol and 2-butanol The base oil percentage increase in the solvent phase with the increase of the extraction phase ratio due to the higher affinity of the oil for the solvent [26].346 R. solvent type. vacuum distillation and finishing stages by clay adsorption or hydro-finishing. Fig. 2nd and 3rd respectively. K+ is the ion of Kalium/ Potassium. while between the ratios 3 and 4. H+ is the ion of Hydrogen. a major increase of the extracted oil was verified. solvent becomes saturated by base oil resulting in reduced oil recovery while at higher solvent/ oil ratio maximum oil could be extracted and oil free sludge is obtained. At lower solvent to oil ratio. The flocculation is enhanced in the presence of OH groups that neutralize the electrostatic repulsion. increasing the solvent to oil ratio. metals and carbonaceous particles. the addition of KOH to any solvent used as a component of extraction–flocculation solvents signifi- Cx À OH þ Kþ ! Cx À OK þ Hþ where CxÀOH is the several type of alcohol. Solvent to oil ratio was varied from 1:1 to 4:1. The efficiency of the extraction agents can also be related to the different interaction between the solvent and oil molecules. Participation of alcohol OH groups in ion exchange reactions with the electrolyte ions helps to neutralize the electrostatic repulsion. 1. solvent-to-oil ratio. all the curves show similar trend. in this case the coagulant is potassium hydroxide (KOH) [23]. Higher percent sludge removal means better quality of re-refined oil. light hydrocarbons. Results and discussion The parameters involved were the amount of potassium hydroxide (KOH). A good extraction–flocculation solvent should dissolve base oil and precipitate other substances to form sludge. / Chemical Engineering Journal 220 (2013) 343–351 cal growth. The graphs show the presence of the best condition (best Percentage Sludge Removal value) after which a further increase in the amount of solvent to oil ratio will result in decreasing or no further change in PSR value. it can be seen that in general. increases the medium mutual solubility of oil in the solvent.R. as shown in Figs. The adsorbents used are: almond shell. such as. Used lubricating oil is a complex mixture of recoverable base oil. 4 and 5. walnut shell. Mohammed et al. mould and bacteria that will clog filters and very rapidly corrode fuel systems [22]. 3. The stoichiometric equation is illustrated as below: Metal complexes are classified as colloidal particles that are destabilized on the addition of coagulant. 1–3. carbon tetrachloride. as show in Figs. thus representing the extraction limit of the systems. Percent sludge removal vs solvent/oil ratio. Solvents used were: 1-butanol. petroleum-ether and 1-hexanol is 1st. break this stability. petroleum-ether and 1-hexanol behave as efficient extraction–flocculation solvents for used oil due to their good solubility parameters for base oil and good antisolvent effect for nonpolar or slightly polar polymeric additives. which will enhance downstream refining stages. The difference between them is related to the solubility of the base oil in these solvents. The water content of lubricant oils can be quickly and accurately determined by dissolving the wet oil in ethyl acetate and measuring the near-infrared absorbance of the solution. n-hexane. This electrostatic repulsion exists since alcohol groups are linked with the ions from the additive. Kamal and Khan [25] found that 1-butanol produced maximum sludge followed by methyl ethyl ketone (MEK). metals and carbonaceous particles. water. Solvent extraction Upon plotting the values of percentage sludge removal (PSR) vs the solvent to oil ratio.1. petroleum ether. . and acetone. forming yeast. and adsorbent type. The amount of KOH added was varied between 1 and 3 g. 1–3. This phenomenon can be attributed to fact that. there was no significant increase in the lubricant oil extraction. 1-butanol. In the interval comprehended between the ratios 1 and 3. which are segregated from the base oil by the solvent. 1-hexanol. polymeric additives. The efficiency for sludge removal capability of 1-butanol. due to the size of the main carbon chain and the solvent molecules’ configuration. As shown in Figs. and acid activated clay. eggshell. Addition of KOH promotes a fast flocculation of the impurities. Addition of a solution containing ions that neutralize those charges. relative to a similar reference solution previously dried by molecular sieves. 3. 3. which include some light ends [28]. this is in agreement with the findings of Ping et al. Mohammed et al. The determination of a KOH optimal concentration may be identified by comparing the settling curves obtained for a fixed solvent to oil composition and several KOH concentrations. Percent sludge removal vs solvent/oil ratio. If the used lube oil was contaminated due the fuel dilution then its specific gravity will be lower. the source of the lube oil and the method of refining.2. Fig. The specific gravity of contaminated oil could be lower or higher than that of its virgin/fresh lube oil depending on the type of contaminated. Percent sludge removal vs solvent/oil ratio. Pour point will vary widely depending on the base. after undergoing combustion and oxidation at high temperature of the combustion engine.R. / Chemical Engineering Journal 220 (2013) 343–351 347 Fig. pour point for the used lube oil is high. This is because of the degradation of additives in the lube oil. 5 quite sharply shows the existence of an optimal concentration of 2 g.R. the oil breaks down into component parts. Fig. 3. If the contaminated is due to water originating from fuel combustion in the engine and accidental contamination by rain. In essence. The decrease in value of flash point of the oil could be as a result of the presence of light ends in the oils. especially if . Effect on oil quality As 1-butanol shows the maximum efficiency for sludge removal so the oil extracted using it is utilized to compare the properties of used and extracted oil (Table 2). From the result obtain for the used oil. 2. its specific gravity will be higher than that of its fresh lube oil or the refined one [29]. The flash point of the fresh oil is 242 °C and for used oil is 178 °C. [27]. From the above results. cantly improves the sludge removal and decreases the oil loss. the specific gravity for the used oil is higher than that for the fresh and refined oil. esters. basic salts of polyacidic bases. have been separated out satisfactorily. and flash point increase with increasing solvent to oil ratio to reach maximum at ratio of 3:1 then they star to decrease. / Chemical Engineering Journal 220 (2013) 343–351 Fig.R. Here. water content. ash content. The used oil contains traces of fuel which lowers the flash point. The increased flash point is an indication that the extracted oil is free of fuel and solvent. Mohammed et al. and total base and acid number. Fig. It is clear that viscosity at 40 °C and 100 °C. treatment has improved its viscosity.348 R. the used lube oil has lost most of its viscosity due to oxidation or contamination. The opposite trend is present in density. The total base number of the oil extracted by 1-butanol has been reduced by 72% showing the removal of basic character constituents (amino compounds. the result for 3:1 solvent:oil ratio falls within the specification of the . the recovery method proved very satisfactory when compared with that of fresh lube oil. This indicates that the solvent precipitates out the non-metallic polymeric material which improves the viscosity. In the density test. The result of the viscosity test shows that. and salts of heavy metals). Percent sludge removal vs KOH weight. phenolic compounds. Total acid number is also reduced significantly indicating that organic and inorganic acids. carbon residue (wt%). dewaxing has been done [30]. However. salts of weak acids. Table 2 summarizes the physical and chemical property results of new virgin oil. used oil and re-refined oil. lactones. 5. 1-butanol has the best performances to remove these additives. resins etc. Percent sludge removal vs KOH weight. pour point. Ash content value shows the presence of metallic impurities which has been reduced by 46% in the extracted oil. 4. 523 0.952 178 À6 3.3. while the other adsorbents used in this work are very low cost and their adsorption capacity is comparable with the commercially available activated clay. and walnut shale powders with a contact time of 1 h.1 2. used.2 2. [32] who used more than one of adsorbents. colour. The results in Table 1 reveal that the viscosity. Abdel-Jabbar et al. 6. Property Density (kg/m ) Viscosity at 40 °C (cst) Viscosity at 100 °C (cst) Water content (wt%) Ash content (wt%) Flash point (°C) Pour point (°C) Carbon residue (wt%) Colour code Total base number (mg HCl/g oil) Total acid number (mg KOH/g oil) 3 349 Fresh 895 131 14 0 0. yet adequate fluidity elsewhere in the system [29].7 0. It can be seen that the acid activated clay has the best performance in treating the waste oil in an adsorption process followed by the almond shale powder and eggshell powder.4 3.1 2:1 905 61 8.861 0. The treated oil was analyzed for density. These properties were compared with fresh and used oil.515 220 À11 1. total base number and total acid number.R.3 1. ash content and all measured properties have been enhanced to reasonable values. Also the findings in the present work Fig.47 4.53 4.8 0. / Chemical Engineering Journal 220 (2013) 343–351 Table 2 Physical properties of fresh.53 4.4 Used 912 38. coincide with the results of Etebu and Josiah [31] in their study on the effect of desludging/adsorption ratios for the recovery of low pour point fuel oil from spent engine oil.76 0. unsaturated and polycyclic material and also organic residues of sulphuric acid and solvents from oils.34 0.2 0.14 0.1 80 Almond 898 75 10.7 1. and treated extracted oil with different adsorbents.463 242. The same trend was found by Udonne [29] who studied the used oil treatment process using acid/clay methods. . it must be able to retain adequate body at elevated film temperature.4 3. Density of oil with different adsorbents.7 0. egg shale. 3.042 3. Mohammed et al.42 0.7 4:1 903 69 9.3549 0.30 0. used.843 195 À7 3.57 0. The treated oil was filtered and the solvent recovered.95 4.2 1. Conradson carbon residue. it is activation with sulphuric acid from an economic view is expensive.21 3.05 1. 6–12.562 0. and extracted oil with different solvent:oil ratio.38 3.7 5.5 0.7 5.463 242.706 211 À8 2.1 Nil 0.R.39 3. almond shale.25 3.12 3.483 238 À13. In view of the desirability of the oil to act as a coolant or heat transfer medium. water content.28 0.4 3.505 228 À11. it can be seen that tests using different adsorbents gave the best physical properties of the treated oil and the oil from the adsorption stage was clear enough.2 0.5 À14 1.3 0. These properties of the fresh and treated oil are shown in Table 3 and Figs.5 0.3 3:1 899 72 10.495 225 À12 1.477 231 À11.125 0.867 0.3 3.8 1:1 909 49 7. This can be attributed to the possible conversion of possible contaminants by the acid and removal by the clay from the lube oil. ash content.742 0.564 218 À10 2.3 6.9 Table 3 Physical properties of fresh. Although activated clay gave better results than the other adsorbents.034 0.44 3. Adsorption The adsorption treatment of oil is based on the ability of an adsorbent to selectively extract resinous and sulphur containing compounds.4 5.8 Clay 896 85 11. water content. Based on the figures in this table.692 0.1 1.523 0.952 178 À6 3. The physical method of refining the spent engine oil with these adsorbents is a surface phenomenon depending on the specific affinity between the adsorbent and the adsorbate dispersed in the spent engine oil. flash and pour points.042 3.4 Used 912 38. The waste oil was treated using different adsorbents such as activated clay.961 0.6 74 Walnut 892 76 10.3549 0. found that activated bentonite gave the best physical properties followed by date palm kernel powder. viscosity. The results also show that refining using the acid/clay method gave the highest viscosity improvements.9 84 Egg 900 80 9.4 78 fresh oil.3 6.15 3.55 3.1 2. Property Density (kg/m3) Viscosity at 40 °C (cst) Viscosity at 100 °C (cst) Water content (wt%) Ash content (wt%) Flash point (°C) Pour point (°C) Carbon residue (wt%) Colour Total base number (mg HCl/g oil) Total acid number (mg KOH/g oil) Yield% Fresh 895 131 14 0 0.1 1.5 À14 1. Conclusions Solvent extraction followed by adsorption has been found to be one of the competitive processes for the recycling of waste lubricating oil. 7. but there are still disadvantages associated with the contact treatment of the spent engine oil with the activated clay. 8. the performance of various solvents for sludge formation has been studied. 11. Fig. Water content of oil with different adsorbents.350 R. 10. 9. Fig. Water content of oil with different adsorbents. The treatment improved the colour of the oil. 12. Colour of oil with different adsorbents. viscosity and carbon residue. In this paper. / Chemical Engineering Journal 220 (2013) 343–351 Fig. Carbon residue content of oil with different adsorbents. Viscosity of oil with different adsorbents. The short comings of this process include the regeneration of the adsorbents and the loss of oil with the adsorbents decomposition. 4. Flash point of oil with different adsorbents. Mohammed et al.R. Fig. Regeneration by pyrolysis might be effective in some cases or selective solvent extraction. its density. Fig. Potassium hydroxide was . Fig. Waste lubricating oil treatment by adsorption process using different adsorbents. carbon residue ash content. Technol.S. Graziano. [24] N. West Conshohocken. Purif. A method of predicting effective solvent extraction parameters for recycling of used lubricating oils. [29] J. Res. American Society for Testing and Materials. Udonne. PA. Rahman. Abdul Mutalib. A comparative study of recycling of used lubrication oils using distillation. Annual Book of Standards. 62 (2010) 9–12. 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