Effects Of Acid Types On The Recycling Of Used Lubricating Oil
This study focused on the effects of acid types on the recycling of used lubricating oil. Three different acids, H2SO4, HCl, and HNO3 were used for the treatment of used lubricating oil and subsequent neutralization of the oil with NaOH. The properties of fresh and used oil tested for were kinematic viscosity at 40 OC and 100 OC, viscosity index, flash point, pour point, specific gravity at 40 OC, water content, sulphur content, total base number (TBN), and metals present (Pb, Zn and Cu). The result obtained revealed that the quality of lubricating oil was affected after usage as a result of its property degradation and presence of heavy metals such as Pb, Zn and Cu. The result obtained shows that treatment of used oil with acids greatly improved the quality of the used oil. The extent of the recycled oil quality improvement and its yield varied with acid type. The result showed that flash point increased from 220 OC for used oil to 232 OC, 225 OC and 227 OC for oil sample recycled with H2SO4, HCl and HNO3 respectively. This is compared with 245 OC for fresh oil. Also, viscosity index increased from 91.2 for spent oil to 125, 116 and 119 for oil sample recycled with H2SO4, HCl and HNO3 respectively. It was also compared with 127 of fresh oil. Sulfur content was reduced to 0.046, 0.2 and 0.35 wt % using H2SO4, HCl and HNO3 for used oil treatment. In general, based on the various characterization analysis conducted in this study, acid treatment efficiency of used lubricant with H2SO4 is the best followed by HNO3 and HCl respectively. However, the use of H2SO4 also gives the highest yield of 70 % recycled oil.
Table of Contents
- List of Tables
- List of Figures
- 1.1 Background
- 1.2. Statement of the Problem
- 1.3. Objectives
- 1.3.1. General Objective
- 1.3.2. Specific Objective
- 1.4. Significance of the Study
- 2.1. Lubricating Oil
- 2.2. Used Lubricating Oil
- 2.2.1. Lubricating Oil Properties
- 2.2.2. Degradation of Lubricating Oil
- 2.2.3. Contaminants in Used Lubricating Oil
- 2.2.4. Physical and Chemical Tests of Used Lubricating Oil
- 2.2.5. Impacts of Used Lubricating Oil
- 2.3. Used Oil Recycling and Reuse
- 2.3.1. Importance of Used Oil Recycling and Reuse
- 2.3.2. General Regeneration Scheme
- 2.3.3. Acid-clay Process .
Materials and Methods
- 3.1. Materials
- 3.2. Methods
- 3.2.1. Characterization of Used Generator Engine Oil
- 3.2.2. Treatment of the Used Oil Sample
- 3.2.3. Characterization of Treated Oil Sample
- 3.3. Experimental Design
- 3.3.1. Experimental Factors
- 3.3.2. Response Factors
Results and Discussions
- 4.1. Characterization of Used Lubricating Oil Sample
- 4.2. Experimental Results of Acid-clay Treatment
- 4.3. Effects of Experimental Factors on Results
- 4.3.1. Effects of Acid Quantity
- 4.3.2. Effects of Adsorbent Ratio
- 4.3.3. Statistical Analysis
- 4.4. Properties of Regenerated Base Oil
- 4.5. Light Fuel Characterization
- 4.6. Cost Analysis Consideration
Conclusions and Recommendations
- 5.1. Conclusions
- 5.2. Recommendations
- Appendix A: Viscosity Index Evaluation Data
- Appendix B: Experimental Design and Analysis Data
- Appendix C: Material Balance & Energy Requirement
1.1 Background of the Study
Lubricant is an oil or grease that is applied as a surface coating to moving parts to protect and reduce friction of two surfaces in relative motion, eliminate temperature build up and keep the engine clean (Toolingu, 2013; Udonne 2011; Ogbeide, 2010). It also serves the purpose of transportation of foreign particles, heat transfer, corrosion prevention, cutting of metal and protection against wear (Udonne 2011; Ogbeide, 2010). The lubricating oils are either bio or petroleum based and the petroleum base feedstock are mainly complex mixtures of hydrocarbon molecules (Udonne, 2011; Hamad et al., 2005) ranging from low viscosity oils to high viscosity lubricating oil. T.Y chemicals (1990) analysis shows that the presence of impurities depends on the petroleum process and production method but concluded that lube oil contains aromatics in the range 4 to 12 % free, sulphur and other impurities. Machineries/engines that make use of oil lubricant include all vehicles, motor bikes, generating plants and it is also used in various industries/factories equipments. Spent oil is any petroleum-based or synthetic oil that has been used and as a result, is contaminated and has lost nearly all its physical or chemical properties but do not wear out and the contaminant present in it can be removed to the point that it can be reused as engine or machine oil (Garthe, 2005). Contaminants or impure lubricants are drained off from cars and disposed off as used or waste oil containing undesirable oxidation product, sediments, metallic wear particles, water, degraded additives and lead hazardous substances (James, 1967; Kamal and Khan, 2009; Durrani et al., 2011; Emam and Shoaib, 2012; Abdulkareem et al., 2014).
Disposal of used oil into the environment, used as weed killers, pouring into ditches or dumping illegally is dangerous to life. It contaminates water as research shows that a gallon of used oil can contaminate one million gallons of water. Used oil can also affect plant life if poured on the ground and it sinks down into the water table (EPA 530-F-94-008). It is therefore obvious that indiscriminate disposal of used lubricating oil into the environment constitutes hazards to both fauna and flora. Hence, the need to recycle used lubricating oil. There have been several approaches in an attempt to regenerate used lubricants (Isah et al., 2013; Abdulkareem et al., 2014; Durrani et al., 2011 Jhanani and Joseph, 2011; Ogbeide, 2010; Josiah and Ikiensikimama, 2010; Abdul-Jebbar et al., 2010; Kamal and Khan, 2009; Rahman et al., 2008; Gorman, 2005).
Industries and private users of lubricating oils demand necessitates the need to find ways of regenerating the oil after use due to the rapid depletion of fossil fuel reserve which is the source of oil feedstock, shortage of fresh oil, price increase and high demand (Zambiri, 1988). The increased use of lubricating oil globally for which Nigeria produces 364 166 000 litres of used oil annually disposed as a common practice into gutters, water drains, open plots and farms which led to streams, ground water, lakes and oceans pollution (Isah et al., 2013; EPA 530-F-94-008). The frequent disposal of waste lubricating oils globally is alarming and requires serious attention. Presently, many countries in the world are presently giving serious attention to the problems of environmental degradation and hazards caused by the disposal of waste lubricating oils (Hamad et al., 2005; Jilner, 1997). T.Y Chemicals (1990) referred regeneration of used lubricating oil as the means of removal of contaminants or impurities by sulphonating agents such as sulphuric acid, oleum or sulphur trioxide and concluded that the process is made up of two cycles, the removal of about 80 % aromatics and other impurities in the first cycle and other 20% impurities in the second operation cycle. However, Isah et al. (2013) carried out regeneration of used engine oil treated with sulphuric acid and bleached using industrial bleaching earth and activated carbon for different formulated grades. The results obtained by the group showed that the best grade in comparison with fresh oil in terms of viscosity, specific gravity and total acid number was obtained using industrial bleaching earth. Abdulkareem et al. (2014) compared the performance efficiency of used lubricating oil treatment methods and concluded from their findings that acid and acid/clay treatment methods were the most attractive with consequences of environmental pollution resulting from acid sludge. Emam and Shoaib (2012) also made comparison between acid/clay percolation and solvent/clay methods of recycling lubricating oils and concluded that the used of acid treatment method was the most attractive interms of quality while solvent method gave the highest yield.
The used of sulphonating agents specifically sulphuric acid to treat used lubricant has been fully established by many researchers (Abdulkareem et al., 2014; Isah et al., 2013; Emam and Shoaib, 2012) and its performance has been very competitive but environmental consequences are part of its major limitations. In addition to environmental consequences, there is a dare need to quantitatively and qualitatively analyze the effect of other acids which suggest in this study the investigation of nitric, sulphuric and hydrochloric acids suitability and effects in the treatment stage of used lubricating oil recycling.
1.2. Statement of the Problem
The hazard of environmental pollution through disposing used lubricating oils on the ground in many developing countries is of great concern to public health and ecology. Used lubricating oil contains a number of degraded additives, impurities, and residues resulting from the combustion process and frictions of mechanical parts. Some of these are poisonous or carcinogenic like PCB (poly-cyclic benzenes), PAH (poly-aromatic hydrocarbons) and heavy metals. It takes only one liter of oil to contaminate one million liters of water and the smallest single automotive oil change produces 4 to 5 liters of used oil. Similarly, one gallon of used oil is able to contaminate million gallons of drinking water and can form a thin layer of oil on the surface of the water which prevents oxygen from being dissolved in water. By this process, it hampers all kinds of aquatic life and the processes of photosynthesis. The carbohydrate content of plants grown in oil contaminated soils is significantly lower than that grown in plain soils (Nwachukwu et al., 2012).
In developing countries, used oils are utilized in road construction for dust control, for pest and weed control, wood preservation, as old engines emergency lubricants, for burners, boilers and furnaces which have multiple environmental effects on soil, land and air pollutions. Sometimes it is traditionally used for medication purposes on wound and cuts causing additional health effects (Nwachukwu et al., 2012).
Wise application and disposal of used lubricating oils will be of a great value from protecting the environment and utilizing resources in efficient and effective ways. Recycling makes more sense today than ever in this aspect. Recycling protects the environment by reducing waste generation and simultaneously saving expenses through increasing the reusable potential of once purchased resource several times.
Ethiopia is one of the developing nations in which numerous industries are emerging and urban development is increasing, giving rise to multiple waste generations. As used lubricating oil is one of the hazardous wastes generated at different development sectors, it should not be utilized and/or disposed in ways which are environmentally unsafe, therefore, requires proper management.
This research is based on addressing problems associated with improper application and/or disposal of used lubricating oils using a simple recycling technique which utilizes cheaper chemicals, utilities and equipment relative to other recycling or re-refining options for protecting our environment and conserving resources.
The general objective of the study will be to study the potential of recycling used lubricating oil through acid-clay treatment process
1.5.2. Specific Objective
The specific objectives of the study are the following:
- To determine the contaminants that would characterize used generator engine oil.
- Establishing the operating parameters of the acid-clay process experiment.
- Assess the recovery capacity of the acid-clay process by characterizing the recovered oil and comparing it with the virgin oil.
- Optimizing studied process parameters (acid ratio and adsorbent ratio) that would maximize the efficiency of the process.
- Evaluating the preliminary cost analysis of the process from laboratory results.
1.4. Significance of the Study
The significance of this study will primarily circle around the protection of the environment through recycling resources and minimizing the amount of waste lubricating oil to be disposed which has a vital contribution in hazardous waste management in the country.
On the other hand, the fruitfulness of the study will demonstrate the basic hint of how different industries would benefit from reclaiming used oil for recurrent purposes and save expenses. Various factories could open separate processing plant that would assist the main process in this regard.
In addition to the environmental protection, the research will play a role in national research and development efforts to establish businesses henceforth creating job opportunities through small or large scale re-refining units for the future.
Conclusions and Recommendations
The study proved that the acid-clay treatment is a process that can effectively remove contaminants from used lubricating oil. The recovered oil has a comparable quality with the fresh oil indicating the possibility of reusing it.
Used engine oil properties were determined with standard chemical and physical tests. The characterization implied that the oil was contaminated with light fuel from extraneous and/or products of oil degradation; oxidation and polymerization products; water from extraneous source; soot and carbon originating from incomplete fuel combustion and oil components breakdown; organic acids and soaps of heavy metals; and metals from engine parts wearing.
Operational parameters were established in reference with the common acid-clay process and its modification. Acid and clay percentages of 15%, 20% and 25% were randomly selected to test the effects of these variable factors i.e. above and below the ratios in the common process (20%). Certain procedural rearrangements were made to overcome some difficulties faced during the experiment trial as mentioned in Section 3.2.2. The acid treatment was performed twice in the experiment. The first one was performed at the beginning of the treatment to improve the disturbing odor emission faced during the distillation step. The second acid treatment was carried out after the vacuum distillation to react and settle out degraded products formed during the heat up. The acid treatments were conducted for an hour on a shaker at 40°C (recommended) and 250 rpm. Two neutralization steps, with ethyl alcohol and lime, were conducted for the two acid treatment steps, respectively. Vacuum distillation was carried out at 0.5 bar for at 330-350°C for extended seven hours. The time delay was needed since the vacuum created was not low enough and the condenser setup was inadequate due to unavailability of required equipment. Bentonite clay, activated at 120 °C, was used at room temperature and agitation intensity of 300 rpm for three hours to facilitate the adsorption rate.
Effects of acid and adsorbent ratios were studied on the recovery of usable lubricating oil from spent engine oil. The results showed that the efficiency of the recycling operation depends on these reagent ratios. It was noted that the recovery yield increases with decreased percentage in these ratios. A maximum recovery of 74.7% was obtained when both acid and clay to oil proportion was minimum i.e. 15% and vice-versa. Some of the oil properties were also consistently influenced by acid and adsorbent variations. Maximum average density (0.91 g/ml) was observed when 15% acid and 15% adsorbent is used. The other combinations gave relatively lower values especially when the acid percentage was above 15%. Samples were not influenced by adsorbent ratio variation implying it had no significant effect on the density of the product. Kinematic viscosity of the recovered oil was improved as the percentage of acid and adsorbent increased. Lower kinematic viscosity of 92.7 cSt and higher viscosity of 98.6 cSt was obtained for equal acid and adsorbent ratio of 25% and 15%, respectively. The decreasing viscosity trend could be explained by improved removal of contaminants that gave rise to the increased viscosity of the used oil. It was also concluded that viscosity would later be improved towards the virgin oil value by addition of viscosity improvers. Ash content was significantly reduced from 2.3% in used oil but the variation in acid and adsorbent ratio did not considerably influence the results. Ash contents were between 0.33- 0.356% for all combination of the experimental factors.
Optimization of the experimental results was conducted using design expert software through complete analysis of variance. The combination which applied acid ratio of 20% and adsorbent ratio of 15%, was selected as an optimum operating condition for the used oil recovery process. The combination gave the maximum desirability value of 0.637 than the rest of the combinations as per the optimization goal. The response factors i.e. yield, density, kinematic Viscosity @ 40 °C and ash content gave average results of 69%, 0.886 g/ml, 94.6 cSt and 0.34%, respectively.
Characterization of the product from the optimum experimental run presented relatively better results as compared to the fresh oil. This proved the effectiveness of the acid-clay treatment process to recover usable oil from spent engine oil.
Valuable light fuel oil was also recuperated from the vacuum distillation step. This product had similar characteristics that was comparable with gas oil. It could be used to supply the energy requirement in the larger scale recycling plant.
Regarding cost effectiveness of the process, the difference in the imported oil price and the cost incurred for reclaiming used oil increased the appeal of the recycling process to be implemented and gave an insight of its potential and opportunities for scale up.
Further research is required in order to take this process to the commercial stage. However, while few variables have been studied in this research, there are many others that need thorough investigation such as temperature, pressure, settling time, mixing, centrifugation speed & time and type & size of adsorbent which will have significant effects on the yield and recycled oil qualities. In addition, the following aspects are important concerning the general characteristics of the treatment and recycling of used oils sector:
- Detailed statistical analysis on waste oil generation, from the different development sectors in Ethiopia, will be essential in giving a better insight for the significance of oil recycling and provide concrete justification of its implementation in this country.
- A study on different recycling techniques is necessary to practically evaluate and compare efficiencies to recommend the best method for implementation.
- Sludge analysis should be performed to propose efficient disposal or application area.
- A study on the different additives and their formulation is required to give the recycled oil identical properties as that of the fresh oil or deliver a desired product of interest.
- Exclusive investigation on used oil will help to identify components that are responsible for bad odour emission during distillation step and gives an indication to come up with effective solutions.
- The experiment in this study should be re-demonstrated with an appropriate distillation setup having a vacuum pump of desired capacity, temperature regulated heater and efficient condenser to observe results of final temperature and time taken. It may also have considerable effect on proceeding steps and final product quality.
- Proper scale up of the recycling process can be proposed from which required equipment, machineries and utilities will be clearly identified.
- Detailed cost benefit analysis evaluation can be made that compares the potential benefits of used oil recycling with the anticipated costs of construction and erection of the scaled up plant.
- Further character testing may also be executed to evaluate oxidation stability, thermal stability and foaming character of the recycled oil. If possible practical application of the recovered oil in a real engine system should be experimented.
- Different response factors can be analysed which may be significantly influenced by the variation in experimental factors. Results may be used to compare results with this study and come up with another optimum operating conditions. Similarly, different experimental factors can be variably examined.
- During experiment, proper safety equipment should be strictly applied to avoid possible irritations on eyes, skin and breathing system.
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