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Reclamation of used hydraulic oil
Oil & Chemical Pollution 6 (1990) 127-135
Reclamation of Used Hydraulic Oil
G. C. O f u n n e & A. U. M a d u a k o Industrial Chemistry Department, PO Box 180, University of Port Harcourt, Choba, Port Harcourt, Nigeria (Received 20 February 1989; accepted 4 July 1989)
ABSTRACT In an attempt to develop a nonpolluting method for used oil disposal, sharp sand bedfiltration and the continuous elution technique were used on a bench scale to carry out the reclamation of used industrial hydraulic oils. Both processes gave quantitative yields of reclaimed oils. Assessment of the qualities of these oils using standard A S T M procedures and IR spectroscopy showed that the reclaimed oils are similar to the base oilfrom which the hydraulic oil was formulated. The metallic impurities in the used oil were completely removed, and the oils totally dehydrated. The yields from the continuous elution process were generally higher than those of the sharp sand filtration technique.
INTRODUCTION Substantial quantities of used oils, disposed by m a n y industries into waste water streams, find their way into the aquatic environments and cause pollution hazards (Nemerow, 1978). M a n y recoverable used industrial hydraulic oils, including emulsifiables, are generally disposed into waste water streams and these interfere with effective and efficient water treatment/oil removal facilities. In addition, used industrial hydraulic oils have been found to be toxic (CONCAWE, 1987), a n d w h e n these get into the soil or the drainage system they can pollute drinking 127 Oil & Chemical Pollution 0269-8579/90/$03.50 © 1990 Elsevier Science Publishers Ltd, England. Printed in Ireland.
128
G. C Ofunne, A. U. Maduako
water. Alternatively if they are burnt in small plants, air will be polluted to an unacceptable level by damaging gases and dusts. Recent sustained increases in prices and shortages combined with stringent environmental regulations leading to higher costs of disposal, have made conservation and recycling of used oil a necessity. Consequently, more and more hydraulic oil users are either reclaiming their own oil or are utilising reclaimed oil (Swain, 1978). For a reclaimed oil to be useful and nontoxic, adequate precaution must be taken to ensure that the fluid has been properly purified and its quality restored to that of the base oil from which it was formulated. Several reclamation processes have been reported (NIPER, 1987), but the main industrial process used for hydraulic oils and straight (nonemulsifiable) metal working oils is the physical treatment technique (Cukar, 1976). This process generally involves oil dehydration, centrifugation, filtration, clay contact/hydrofining and reduced pressure distillation. However, there are very few data to show that this multistage process is the most efficient and economic route to used hydraulic oil reclamation. It is therefore appropriate to investigate the use of other processes such as the continuous elution technique and sharp sand bed filtration as a means of reclaiming used hydraulic oils. In this study, acid treated sharp sand, alumina, kaolin, Fullers' earth and silica gel were used as adsorbents. Although several methods are available for assessing the quality of reclaimed oils (ASTM, 1979), Infrared (IR) spectroscopy has the ability to decipher the condition of the oil at the molecular level. As a result a combination of IR spectroscopy, kinematic viscosity, flash point, and metal, water and ash contents were used to assess the quality of the reclaimed oils. MATERIALS AND METHODS Materials
The used mineral-based hydraulic oil was obtained from D. R. Shaft Hydraulic Systems, at the Delta Steel Company Ltd, Oviwan-Aladja, Nigeria. Chromatographic alumina and silica gel were obtained from Aldrich, Fullers' earth from Nalin, kaolin from Ezinachi, and activated charcoal from BDH. The eluting solvent, a petroleum fraction (50°-70°C), was obtained from straight run gasoline (Warri Refinery). A modified Soxhlet extractor, shown in Fig. 1, was used for the oil elution. Sharp sand was obtained locally (Choba, Port Harcourt).
Reclamation of used hydraulic oil
129
Fig. I. Modified type Soxhlet extractor needed for the continuous elution process A = flask; B = separator tube.
Treatment of sharp sand Sharp sand (20 g) was w a s h e d in w a r m water a n d t h e n deionised water. The semi-dried sand was washed with 300 ml of benzene a n d then 300 ml of diethyl ether before drying. The s a n d was then heated in 300 ml o f 0.3 M nitric a c i d for 1 h a n d w a s h e d with deionised water until the solution was no longer acidic. The sand was finally dried at 350 °C for 6 h.
Continuous elution technique This process involves the use of the separator tube of a modified Soxhlet extractor a n d a bed o f adsorbent. A mixture of 50 g of adsorbent, 10 g o f activated charcoal a n d 20 g of used oil was w r a p p e d in a filter p a p e r o f appropriate thickness a n d inserted into a separator tube to create a column. The p e t r o l e u m fraction (50 °-70 °C) was circulated c o n t i n u o u s l y by heating with a water bath. The solvent was r e m o v e d from the reclaimed oil by distillation.
130
G. C. Ofunne, A. U. Maduako
Adsorption technique The used oil (50 g) was mixed with 3 g of activated charcoal and heated to 70°C for 20 min. The oil was allowed to cool and then passed through a bed of treated sharp sand. 38.6 g of clean oil was obtained (77.2% yield).
Quality of reclaimed oil The quality of the reclaimed oils was assessed using IR spectroscopy, by examining the absorbance in key bands (3400 cm -1, 1700 cm -1 and 845 cm-l). IR spectra were recorded as neat film in a sodium bromide plate using a Shimadzu Model IR408 spectrophotometer. Ash content (ASTM D128), kinematic viscosity (ASTM D445), flash point (ASTM D92), water (ASTM D95) and metal content (AAS) were also used to assess the reclaimed oil quality.
RESULTS AND DISCUSSION The physicochemical characteristics of the used and reclaimed hydraulic oil and the process yields are presented in Table 1. The whitish appearance of the used oil indicated contamination with water and this was confirmed by quantitatively evaluating the oil water content using the standard ASTM procedure, D95. The high water content of the oil (8.4wt%) resulted in a white emulsion. The high flash point and kinematic viscosities of the used oil are the result of the high water content of the oil (Hudgen & Feldhans, 1978). Usually, the shafts of hydraulic systems are made of alloys of iron, zinc, manganese and nickel (Steenberger, 1978) and the presence of these metals in the used oil may either indicate metal wear or shaft corrosion. Furthermore, during service, the hydrocarbon matrix of the hydraulic oil undergoes free radical autooxidation forming peroxides, alcohols, lactones, carboxylic acids, ketones and aldehydes (Bolland & Gee, 1946). The presence of these materials in the used oil is confirmed by the absorption bands found around 3400 cm -1 and 1700 cm -1 in the IR spectrum 'A' in Fig. 2. These bands indicate the presence of water, alcohols (3400 cm -l) and carbonyl compounds (1700 cm-1). However, when the used oils find their way into the environment, they constitute a very strong pollution hazard to the ecosystem, either by causing metal contamination or by introducing toxic materials into the system. Thus, reclamation of used oil, for fuel use, or for synthesis of chemicals and the
Reclamation of used hydraulic oil
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production of base oils, remains one of the best ways of reducing used oil pollution in the environment. Reclamation of used hydraulic oil
Heating used oil with an adsorbent earth/clay has been shown to be one of the most effective reclamation processes and is widely used (Siddiqui Hasnudin, 1968). In this process most of the volatile compounds are eliminated on heating, and the degradation p r o d u c t s - ketones, aldehyde, lactones, carboxylic acids, polymeric materials along with metallic impurities, carbon particles and traces of water are removed by the selective adsorption on clay. In our study, a slurry of the used oil in the adsorbents (alumina, or silica gel, kaolin, sharp sand and Fullers' earth) were packed into the separator tube and eluted with a nonpolar petroleum fraction (50 °70°C) to obtain the eluate. Removal of the solvent by atmospheric distillation gave the reclaimed oils at quantitative yields (see Table 1). All the adsorbents gave yields >80%, which is similar to yields earlier reported for other techniques (Cotton, 1979). The ability of these adsorbents to remove impurities from used oil completely is thought to be dependent on the high adsorptive capacity of the adsorbents and the ability of the eluting solvent to precipitate sludge and high molecular weight polymers. This situation effects a complete but gradual filtration of the used oil. In a separate study, the used hydraulic oil was heated with activated charcoal for 1 h at 70 °C, and passed through a bed of sharp sand, to give a golden yellow clear oil, which was stable on exposure to air. The yield was 77.2%, and is similar to values reported elsewhere (Cukar, 1976). One problem encountered in this process was the slow rate of percolation of the oil (10 ml h-l). However, further investigation has shown that the flow rate could be improved by using sharp sand of various sizes packed in a graduated fashion. In this improved system, a flow rate of 170 ml hwas obtained, with no appreciable loss of yield, this being comparable to that obtained for the continuous elution process. Quality of the reclaimed oils
The quality of the reclaimed oils were assessed, using standard ASTM procedures and IR spectroscopy. The results obtained are summarised in Table 1. All the reclaimed oil was clear and golden yellow in colour, indicating the complete removal of water from the used oil. The kinematic viscosities of the reclaimed oils were similar to those of the
134
G. C Ofunne, A. U Maduako
base oil and fully formulated oil, except for the oil obtained by the continuous elution method using alumina as adsorbent. This deviation cannot be explained easily, but could be attributed to the distribution of hydrocarbon types and molecular weights in the reclaimed oil. However, all the reclaimed oils had flash points similar to the base oil and the formulated oils. Analysis for metal and water in the reclaimed oils gave results below the detection limit. Similarly, the ash contents of the reclaimed oils were negligible. The implication of these observations is that both the continuous elution and adsorption techniques are suitable for the effective reclamation of used hydraulic oil. In order to confirm this, an attempt was made to compare the molecular quality of the base oil with those o~ the reclaimed oils. This was done by using IR spectroscopy, and the results obtained are shown in Fig. 2. The spectrum obtained for the used hydraulic oil (spectrum A) was similar to that reported earlier by Asseff (1977). Here the bands of interest are the 3400 cm -1 (hydroxyl group), 1700 cm -1 (carbonyl group), 1000 c m -1 and 845 cm -~ (antioxidant) absorptions. The spectra of the reclaimed oils are shown in Fig. 2: B (Fullers' earth); C (kaolin); D (sharp sand); F (alumina); G (silica gel). The spectrum of the reclaimed oil, obtained from the adsorption technique is shown as H, while the base oil is shown as E. A close examination of the spectra shows that the absorption around 3400 cm -~, 1700 cm -~, 1000 cm -1 and 845 cm -1 are absent in those of the reclaimed oils. These observations therefore indicate that the great majority of the water, alcohols, carboxylic acids, ketones and aldehydes, metal contaminants and antioxidant degradation products have been removed from the used oil in the two techniques studied. The quality of the reclaimed oils could be said to be similar to that of the base oils at the molecular level.
CONCLUSIONS Used oil reclamation has potential as a very reliable method for nonpolluting disposal of used hydraulic oil. The two techniques studied gave quantitative yields of high quality oils which could be used for the formulation of the hydraulic oil. However, the economics of large scale application of these techniques either for in-plant or out-plant reclamation depends on several factors which are beyond the scope of this paper. ACKNOWLEDGEMENTS The authors wish to express their sincere gratitude to Delta Steel Company Ltd for the supply of the used hydraulic oil, and to our
Reclamation of used hydraulic oil
135
colleages D r N. Umesi and Dr C. O. Okoroafor for their useful suggestions a n d criticisms. Finally, thanks are due to the University of Port Harcourt and Bendel State University (A.U.M.), Ekpoma, for financial support.
REFERENCES Asseff, P. A. (1977). Used engine oil analysis m review. Paper presented at the Fuel and Lubricant Meeting, Tulsa, USA. (SAE paper no. 770642.) ASTM (1979). Petroleum products and lubricants, Parts 23-5. InAnnual Book of ASTM Standards, American Society for Testing and Materials, Philadelphia. Bolland, J. E. & Gee, G. (1946). Trans. Farad. Soc., 42, 236. CONCAWE (1987). Health aspects of lubricants. A report prepared by CONCAWE (The Oil Companies European Organisation for Environmental and Health Protection) special Task Force PPH/STF-10 on behalf of the Petroleum Product Handling and Health Management Groups, Rep. No. 5/87. Cotton, F. O. (1979), Waste Lubricating Oil, Annotated Review BETC/IC 79/4, p. 96. Cukar, P. M. (1976). Waste Oil Recycle Study, Technical, Economic and Environmental Assessment of Used Oil Recovery and Disposal For Ontario, Teknekron Inc. (for the Ontario Energy Management, Canada). Hudgens, R. D. & Feldhans, L. B. (1978). Diesel engine lube filter life related to oil chemistry. SAE paper No. 780974 (Paper presented at the International Fuels and Lubricants meeting, Toronto.) Nemerow, N. L. (1978). Industrial Water Pollution Origins, Characteristics and Treatment, Addison-Wesley, London, p. 551. NIPER (1987). Identification and Evaluation of Processesfor Producing Specification Waste Derived Liquid Fuel, Report Prepared for New Jersey Department of Environmental Protection, NIPER (National Institute for Petroleum and Energy Research) B08640-I. Siddiqui Hasnudin, M. K. (1968). Bleaching Earth. 1st Edition, Pergamon Press, London, pp. 32-55. Steenberger, J. E. (1978). Comprehensive lube oil analysis programme; a costeffective preventive maintenance tool. Lubr. Eng., 34 (11), 625. Swain, J. W. (1978). Assessment of industrial waste management practices. Report from the Petroleum Rerefining Industry, US Environmental Protection Agency, Washington, DC.
Reclamation of Used Hydraulic Oil
G. C. O f u n n e & A. U. M a d u a k o Industrial Chemistry Department, PO Box 180, University of Port Harcourt, Choba, Port Harcourt, Nigeria (Received 20 February 1989; accepted 4 July 1989)
ABSTRACT In an attempt to develop a nonpolluting method for used oil disposal, sharp sand bedfiltration and the continuous elution technique were used on a bench scale to carry out the reclamation of used industrial hydraulic oils. Both processes gave quantitative yields of reclaimed oils. Assessment of the qualities of these oils using standard A S T M procedures and IR spectroscopy showed that the reclaimed oils are similar to the base oilfrom which the hydraulic oil was formulated. The metallic impurities in the used oil were completely removed, and the oils totally dehydrated. The yields from the continuous elution process were generally higher than those of the sharp sand filtration technique.
INTRODUCTION Substantial quantities of used oils, disposed by m a n y industries into waste water streams, find their way into the aquatic environments and cause pollution hazards (Nemerow, 1978). M a n y recoverable used industrial hydraulic oils, including emulsifiables, are generally disposed into waste water streams and these interfere with effective and efficient water treatment/oil removal facilities. In addition, used industrial hydraulic oils have been found to be toxic (CONCAWE, 1987), a n d w h e n these get into the soil or the drainage system they can pollute drinking 127 Oil & Chemical Pollution 0269-8579/90/$03.50 © 1990 Elsevier Science Publishers Ltd, England. Printed in Ireland.
128
G. C Ofunne, A. U. Maduako
water. Alternatively if they are burnt in small plants, air will be polluted to an unacceptable level by damaging gases and dusts. Recent sustained increases in prices and shortages combined with stringent environmental regulations leading to higher costs of disposal, have made conservation and recycling of used oil a necessity. Consequently, more and more hydraulic oil users are either reclaiming their own oil or are utilising reclaimed oil (Swain, 1978). For a reclaimed oil to be useful and nontoxic, adequate precaution must be taken to ensure that the fluid has been properly purified and its quality restored to that of the base oil from which it was formulated. Several reclamation processes have been reported (NIPER, 1987), but the main industrial process used for hydraulic oils and straight (nonemulsifiable) metal working oils is the physical treatment technique (Cukar, 1976). This process generally involves oil dehydration, centrifugation, filtration, clay contact/hydrofining and reduced pressure distillation. However, there are very few data to show that this multistage process is the most efficient and economic route to used hydraulic oil reclamation. It is therefore appropriate to investigate the use of other processes such as the continuous elution technique and sharp sand bed filtration as a means of reclaiming used hydraulic oils. In this study, acid treated sharp sand, alumina, kaolin, Fullers' earth and silica gel were used as adsorbents. Although several methods are available for assessing the quality of reclaimed oils (ASTM, 1979), Infrared (IR) spectroscopy has the ability to decipher the condition of the oil at the molecular level. As a result a combination of IR spectroscopy, kinematic viscosity, flash point, and metal, water and ash contents were used to assess the quality of the reclaimed oils. MATERIALS AND METHODS Materials
The used mineral-based hydraulic oil was obtained from D. R. Shaft Hydraulic Systems, at the Delta Steel Company Ltd, Oviwan-Aladja, Nigeria. Chromatographic alumina and silica gel were obtained from Aldrich, Fullers' earth from Nalin, kaolin from Ezinachi, and activated charcoal from BDH. The eluting solvent, a petroleum fraction (50°-70°C), was obtained from straight run gasoline (Warri Refinery). A modified Soxhlet extractor, shown in Fig. 1, was used for the oil elution. Sharp sand was obtained locally (Choba, Port Harcourt).
Reclamation of used hydraulic oil
129
Fig. I. Modified type Soxhlet extractor needed for the continuous elution process A = flask; B = separator tube.
Treatment of sharp sand Sharp sand (20 g) was w a s h e d in w a r m water a n d t h e n deionised water. The semi-dried sand was washed with 300 ml of benzene a n d then 300 ml of diethyl ether before drying. The s a n d was then heated in 300 ml o f 0.3 M nitric a c i d for 1 h a n d w a s h e d with deionised water until the solution was no longer acidic. The sand was finally dried at 350 °C for 6 h.
Continuous elution technique This process involves the use of the separator tube of a modified Soxhlet extractor a n d a bed o f adsorbent. A mixture of 50 g of adsorbent, 10 g o f activated charcoal a n d 20 g of used oil was w r a p p e d in a filter p a p e r o f appropriate thickness a n d inserted into a separator tube to create a column. The p e t r o l e u m fraction (50 °-70 °C) was circulated c o n t i n u o u s l y by heating with a water bath. The solvent was r e m o v e d from the reclaimed oil by distillation.
130
G. C. Ofunne, A. U. Maduako
Adsorption technique The used oil (50 g) was mixed with 3 g of activated charcoal and heated to 70°C for 20 min. The oil was allowed to cool and then passed through a bed of treated sharp sand. 38.6 g of clean oil was obtained (77.2% yield).
Quality of reclaimed oil The quality of the reclaimed oils was assessed using IR spectroscopy, by examining the absorbance in key bands (3400 cm -1, 1700 cm -1 and 845 cm-l). IR spectra were recorded as neat film in a sodium bromide plate using a Shimadzu Model IR408 spectrophotometer. Ash content (ASTM D128), kinematic viscosity (ASTM D445), flash point (ASTM D92), water (ASTM D95) and metal content (AAS) were also used to assess the reclaimed oil quality.
RESULTS AND DISCUSSION The physicochemical characteristics of the used and reclaimed hydraulic oil and the process yields are presented in Table 1. The whitish appearance of the used oil indicated contamination with water and this was confirmed by quantitatively evaluating the oil water content using the standard ASTM procedure, D95. The high water content of the oil (8.4wt%) resulted in a white emulsion. The high flash point and kinematic viscosities of the used oil are the result of the high water content of the oil (Hudgen & Feldhans, 1978). Usually, the shafts of hydraulic systems are made of alloys of iron, zinc, manganese and nickel (Steenberger, 1978) and the presence of these metals in the used oil may either indicate metal wear or shaft corrosion. Furthermore, during service, the hydrocarbon matrix of the hydraulic oil undergoes free radical autooxidation forming peroxides, alcohols, lactones, carboxylic acids, ketones and aldehydes (Bolland & Gee, 1946). The presence of these materials in the used oil is confirmed by the absorption bands found around 3400 cm -1 and 1700 cm -1 in the IR spectrum 'A' in Fig. 2. These bands indicate the presence of water, alcohols (3400 cm -l) and carbonyl compounds (1700 cm-1). However, when the used oils find their way into the environment, they constitute a very strong pollution hazard to the ecosystem, either by causing metal contamination or by introducing toxic materials into the system. Thus, reclamation of used oil, for fuel use, or for synthesis of chemicals and the
Reclamation of used hydraulic oil
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131
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132
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al
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Reclamation of used hydraulic oil
133
production of base oils, remains one of the best ways of reducing used oil pollution in the environment. Reclamation of used hydraulic oil
Heating used oil with an adsorbent earth/clay has been shown to be one of the most effective reclamation processes and is widely used (Siddiqui Hasnudin, 1968). In this process most of the volatile compounds are eliminated on heating, and the degradation p r o d u c t s - ketones, aldehyde, lactones, carboxylic acids, polymeric materials along with metallic impurities, carbon particles and traces of water are removed by the selective adsorption on clay. In our study, a slurry of the used oil in the adsorbents (alumina, or silica gel, kaolin, sharp sand and Fullers' earth) were packed into the separator tube and eluted with a nonpolar petroleum fraction (50 °70°C) to obtain the eluate. Removal of the solvent by atmospheric distillation gave the reclaimed oils at quantitative yields (see Table 1). All the adsorbents gave yields >80%, which is similar to yields earlier reported for other techniques (Cotton, 1979). The ability of these adsorbents to remove impurities from used oil completely is thought to be dependent on the high adsorptive capacity of the adsorbents and the ability of the eluting solvent to precipitate sludge and high molecular weight polymers. This situation effects a complete but gradual filtration of the used oil. In a separate study, the used hydraulic oil was heated with activated charcoal for 1 h at 70 °C, and passed through a bed of sharp sand, to give a golden yellow clear oil, which was stable on exposure to air. The yield was 77.2%, and is similar to values reported elsewhere (Cukar, 1976). One problem encountered in this process was the slow rate of percolation of the oil (10 ml h-l). However, further investigation has shown that the flow rate could be improved by using sharp sand of various sizes packed in a graduated fashion. In this improved system, a flow rate of 170 ml hwas obtained, with no appreciable loss of yield, this being comparable to that obtained for the continuous elution process. Quality of the reclaimed oils
The quality of the reclaimed oils were assessed, using standard ASTM procedures and IR spectroscopy. The results obtained are summarised in Table 1. All the reclaimed oil was clear and golden yellow in colour, indicating the complete removal of water from the used oil. The kinematic viscosities of the reclaimed oils were similar to those of the
134
G. C Ofunne, A. U Maduako
base oil and fully formulated oil, except for the oil obtained by the continuous elution method using alumina as adsorbent. This deviation cannot be explained easily, but could be attributed to the distribution of hydrocarbon types and molecular weights in the reclaimed oil. However, all the reclaimed oils had flash points similar to the base oil and the formulated oils. Analysis for metal and water in the reclaimed oils gave results below the detection limit. Similarly, the ash contents of the reclaimed oils were negligible. The implication of these observations is that both the continuous elution and adsorption techniques are suitable for the effective reclamation of used hydraulic oil. In order to confirm this, an attempt was made to compare the molecular quality of the base oil with those o~ the reclaimed oils. This was done by using IR spectroscopy, and the results obtained are shown in Fig. 2. The spectrum obtained for the used hydraulic oil (spectrum A) was similar to that reported earlier by Asseff (1977). Here the bands of interest are the 3400 cm -1 (hydroxyl group), 1700 cm -1 (carbonyl group), 1000 c m -1 and 845 cm -~ (antioxidant) absorptions. The spectra of the reclaimed oils are shown in Fig. 2: B (Fullers' earth); C (kaolin); D (sharp sand); F (alumina); G (silica gel). The spectrum of the reclaimed oil, obtained from the adsorption technique is shown as H, while the base oil is shown as E. A close examination of the spectra shows that the absorption around 3400 cm -~, 1700 cm -~, 1000 cm -1 and 845 cm -1 are absent in those of the reclaimed oils. These observations therefore indicate that the great majority of the water, alcohols, carboxylic acids, ketones and aldehydes, metal contaminants and antioxidant degradation products have been removed from the used oil in the two techniques studied. The quality of the reclaimed oils could be said to be similar to that of the base oils at the molecular level.
CONCLUSIONS Used oil reclamation has potential as a very reliable method for nonpolluting disposal of used hydraulic oil. The two techniques studied gave quantitative yields of high quality oils which could be used for the formulation of the hydraulic oil. However, the economics of large scale application of these techniques either for in-plant or out-plant reclamation depends on several factors which are beyond the scope of this paper. ACKNOWLEDGEMENTS The authors wish to express their sincere gratitude to Delta Steel Company Ltd for the supply of the used hydraulic oil, and to our
Reclamation of used hydraulic oil
135
colleages D r N. Umesi and Dr C. O. Okoroafor for their useful suggestions a n d criticisms. Finally, thanks are due to the University of Port Harcourt and Bendel State University (A.U.M.), Ekpoma, for financial support.
REFERENCES Asseff, P. A. (1977). Used engine oil analysis m review. Paper presented at the Fuel and Lubricant Meeting, Tulsa, USA. (SAE paper no. 770642.) ASTM (1979). Petroleum products and lubricants, Parts 23-5. InAnnual Book of ASTM Standards, American Society for Testing and Materials, Philadelphia. Bolland, J. E. & Gee, G. (1946). Trans. Farad. Soc., 42, 236. CONCAWE (1987). Health aspects of lubricants. A report prepared by CONCAWE (The Oil Companies European Organisation for Environmental and Health Protection) special Task Force PPH/STF-10 on behalf of the Petroleum Product Handling and Health Management Groups, Rep. No. 5/87. Cotton, F. O. (1979), Waste Lubricating Oil, Annotated Review BETC/IC 79/4, p. 96. Cukar, P. M. (1976). Waste Oil Recycle Study, Technical, Economic and Environmental Assessment of Used Oil Recovery and Disposal For Ontario, Teknekron Inc. (for the Ontario Energy Management, Canada). Hudgens, R. D. & Feldhans, L. B. (1978). Diesel engine lube filter life related to oil chemistry. SAE paper No. 780974 (Paper presented at the International Fuels and Lubricants meeting, Toronto.) Nemerow, N. L. (1978). Industrial Water Pollution Origins, Characteristics and Treatment, Addison-Wesley, London, p. 551. NIPER (1987). Identification and Evaluation of Processesfor Producing Specification Waste Derived Liquid Fuel, Report Prepared for New Jersey Department of Environmental Protection, NIPER (National Institute for Petroleum and Energy Research) B08640-I. Siddiqui Hasnudin, M. K. (1968). Bleaching Earth. 1st Edition, Pergamon Press, London, pp. 32-55. Steenberger, J. E. (1978). Comprehensive lube oil analysis programme; a costeffective preventive maintenance tool. Lubr. Eng., 34 (11), 625. Swain, J. W. (1978). Assessment of industrial waste management practices. Report from the Petroleum Rerefining Industry, US Environmental Protection Agency, Washington, DC.