Used lubricating oils recycling using solvent extraction

Huge amounts of used lubricating oils from automotive sources are disposed of as a harmful waste into the environment. For this reason, means to recover and reuse these wastes need to be found. Valuable lubricant could be recovered from disposed oil. More importantly, oil may be the most important factor to influence the shape of society in the 21st century. This paper discusses the regeneration of used lubricating oils.


Used lubricating oil Characteristics
The automotive lubricating oil loses its effectiveness during operation due to the presence of certain types of contaminants.Those contaminants can be divided into:

Extraneous Contaminants
Extraneous Contaminants are introduced from the surrounding air and by metallic particles from the engine.Contaminants from the air are dust, dirt and moisture.Air itself may be considered as contaminants since it might cause foaming of the oil.The contaminants from the engine are: ´Metallic particles resulting from wear of the engine.´Carbonaceous particles due to incomplete fuel combustion ´Metallic oxides present as corrosion products of metals ´Water from leakage of the cooling system ´Fuel or fuel additives or their byproducts, which might enter the crankcase of engines.

Products of oil Deterioration
Many products are formed during oil deterioration.Some of these important products are:

Sludge
a mixture of oil, waste, dust, dirt and carbon particles that results from the incomplete combustion of the fuels.Sludge may deposits on various parts of the engine or remains in colloidal dispersion in the oil.

Lacquer
a hard or gummy substance that deposits on engine parts as a result of subjecting sludge in the oil to high temperature operation.

Oil soluble products
The result of oil oxidation products that remain in the oil and can not be filtered out and deposit on the engine parts.The quantity and distribution of engine deposits vary widely depending on the condition at which the engine is operated.At low crankcase temperatures, carbonaceous deposits originate mainly from high temperature, the increase in lacquer and sludge deposits may be caused by the lubricating oil.

Method of Treatment
Used oils (engine, gear, compressor and hydraulic) were regenerated by physical as well as chemical methods e.g.dehydration, solvent treatment, clay treatment and filtration.Different additives were blended in sufficient amount to prepare finished oils of different grades.The whole procedure of the regeneration of used oils has shown in below.

Dehydration
Used engine oils were taken in a twonecked round bottom flask equipped with arrangements for heating and stirring under vacuum.The used lubricating oils were heated at 100°C for 1 h to remove water.After dehydration, the temperature was raised to 250°C to remove light ends and after their removals; the dehydrated oils were allowed to cool to room temperature and filtered.

Solvent Treatment
Dehydrated oils thus obtained were then solvent treated with 1-butanol using 50 percent and 60 percent (v/v) at room temperature with constant stirring for 30 min.The solvent treated oils were allowed to settle over night after 24 h, solvent sludge was removed and supernatant solvent treated oils were recovered.

Clay Treatment and Filtration
To prepare different samples, the solvent treated oils were heated under vacuum with constant stirring to 100°C and the fuller's earth was added in 8 to 10 percent (w/v) for 50 and 60 percent solvent treated oils and then the temperature was raised to the bleaching temperature (250°C , 280°C and 300°C ).Thereafter, the clay treated oils were allowed to cool and filtered.

Characteristics of used lubricating oils
Table 1 shows the characteristics of different types of used engine oils obtained from various sources.The colour of the used engine oils being black; and the ash content in these cases varied from 1.18 to 2.80 percent, this variation may be due to difference in the percentage of additives which would have been initially added to the base stock of these oils.The flash point of the different used engine oils varied from 108°C to 192°C.As the sources of the used engine oils were different, the water content and viscosity of the different oils were found to vary in the range of 0.5 to 4.0 percent and 32.5 to 92.5 cst at 40°C, respectively.The difference in viscosity may perhaps be due to change in additive composition and base stock as well.

Dehydration of used lubricating oils
Initially few samples of used engine oils were dehydrated to remove water as well as light ends in dehydration process and then filtered.However, by later processing during clay treatment it was observed that the process of removal of lower fraction at this stage is not prudent since the clay treatment was observed to be effective only at higher temperatures and the simultaneous removal of lower fraction during the process of bleaching was found to be more economical.Drying to remove water was only carried on table 1 shows that different types of used engine oil contained different percentage of water.The range of water content present in used engine oils varied from 0.5 to 4.0 percent.

Solvent treatment of dehydrated oils
In the solvent refining of dehydrated engine oils 50 and 60 percent (v/v) of 1-butanol was used because below this level of solvent proper settling was not being achieved which may be due to the presence of higher percentage of additives and contaminants present in the used oils.Although, the settling time was slightly higher even for 50 percent solvent treated oils but at the same time the yield was found to be better.Further, there was no improvement in the yield of solvent treated oil above 60 percent of 1-butanol solvent; therefore the solvent treatment was performed only by 50 and 60 percent solvent.The yield of solvent treated oils varied for different types of used engine oils.The variation in yield was due to the break down of additives and carbonaceous matter present in used oils

Clay treatment of solvent treated oils
The used engine oils treated with 50 percent solvent were further treated with 10.0 percent clay, and the oils treated with 60 percent solvent we subjected to clay treatment with 8.0 percent as well as 10.0 percent (w/v) of fuller's earth.The above quantity of clay was chosen for the reasons that below 10.0 percent level of clay , 50 percent solvent treated oils were not showing desired improvement in colour values and 60 percent solvent treated oils were not showing improvement in colour instead the yield was getting decreased therefore , it was not economical to use clay above 10.0 percent.
Tables 2 and 3 show the effect of clay treatment temperature on the colour, viscosity, flash point, pour point and ash content of the refined oils.The improvement in colour is due to the higher efficiency of bleaching of fuller's earth at elevated temperatures.Decrease in ash content particles shows the proper refining as the additives and carbon particles present in used oils are removed in refining process and all the samples of base stocks prepared from different used engine oils passed the corrosion copper strip test.The saponification value was failing within the stipulated limit for baser stock.
Table 2 shows the improvement in colour of the refined oils (solvent-clay treated) from [+ 5.5 to + 3.0], [+ 8.5 to + 4.5] and [+ 5.0 to + 2.5] ASTM units on treatment with 50 percent 1-butanol solvent and 10 percent clay [50S 10C], 60 percent solvent and 8 percent clay [60S 8C] and 60 percent solvent and 10 percent clay [60S 10C] at 250°C, 280°C and 300°C respectively.The percent reduction in colour at 300°C over that at 250°C was 45.5 , 47.0 and 50.0 for refined engine oils under the conditions of [50S 10C], [60S 8C] and [60S 8C], respectively.The colour of refined engine oil under [60S 8C] condition at 250°C was poor, hence it was discarded.The difference in colour and yield of refined engine oils in [50S 10C] and [60S 10C] condition at 300°C was [+0.5]ASTM and 1 percent, respectively, therefore, both the treatments are observed to be suitable for satisfactory and economic refining of used engine oil E 1 .The viscosity and flash point of refined oils were in the range of 39.0 to 57.0 cst at 40°C and from 144°C to 204°C, respectively.The increase in viscosity and flash point was observed at 300°C which is due to higher removal of lower fractions at this temperature.The pour point under the best conditions of refining of E 1 was observed to be -18°C.The ash content of the refined oils was insignificant indicating better processing.Total (organic) acidity was in the range of 0.038 to 0.043 mg KOH/g of oil whereas the inorganic acidity was nil.
Table 3 shows the improvement in colour of the refined oils from [+ 5.5 to + 2.5], [+ 7.5 to + 3.5] and [+ 5.0 to + 2.5] ASTM units on treatment with [50S 10C], [60S 8C] and [60S 10C] at 250°C, 280°C and 300°C, respectively.The percent reduction in colour at 300°C over that at 250°C was 54.5 ,53.0 and 50.0 for refined engine oils under the conditions of [50S 10C], [60S 8C] and [60S 10C], respectively.The refined oils having colour above + 4.5 ASTM units were discarded.There was no difference in colour and yield of the refined oils in [50S 10C], [60S 8C] condition at 300°C, therefore, both the treatment can be applied for satisfactory and economical refining of used engine oil E 2 .The viscosity and flash point of refined oils were in the range of 45.0 to 70.0 cst at 40°C and from 140°C to 210°C, respectively.The ash content of the refined oils was insignificant.The pour point under the best conditions of refining of E 2 was observed to be -7°C.Total (organic) acidity was in the range of 0.041 to 0.045 mg KOH/g of oil whereas the inorganic acidity was nil.

Effect of additive blending on the properties of refined base stocks
The base stocks obtained from refining of used lubricating oils namely, engine, gear, compressor and hydraulic oils which were having different physico-chemical characteristics were used to prepare various grades of finished oils (additive blended).Mono and multi grades of engine oils available in the market for various purposes require different base stocks depending upon their characteristics.Further, a specific amount of suitable additives is needed for a particular grade of oil.As it is vary difficult to prepare specific base stock requirement for gear oil, compressor oil and hydraulic oils are also specific base stocks prepared by refining of used oils.The standard additives for engine, gear, compressor and hydraulic oils were procured and their specific percentage as per requirements were blended with the prepared base stocks to make a particular grade of either of the above oils.
The finished engine oils were prepared and characterized for various properties such as viscosity at 40°C and 100°C, viscosity index, flash point, pour point, inorganic and total acidity and ash content which are depicted in Table 4.All the samples of finished oils prepared from different base stocks passed the corrosion strip test.
To make the engine oil of SAE grade 30, the base stocks prepared from E 1 , E 3 , E 4 , E 6 , E 10 having viscosities of 56.0 and 57.0 (both for E 1 ) , 64.0, 65.5, 61.0 and 84.5 cst at 40°C , respectively were considered suitable as the viscosities of these base stocks were appropriate to prepare SAE 30 grade of engine oil.A certain percent of polyisobutylene has been added to upgrade the quality of oil in terms of corrosion resistance, rust prevention, oxidation inhibition etc. Simultaneously, the proportion of Molybdenum disulfide was varied to obtain oil comparable to that of SAE 30 grade for which the viscosity at 100°C should be from 9.3 to 12.5cst.After using different proportion of VI Improver in the base stocks prepared from E 1 and E 6 it was concluded by addition of 5.8 percent Molybdenum disulfide and 5.2 percent polyisobutylene were meeting the requirement of the specification for this grade.Similarly, addition of 5.0 percent polyisobutylene and 5.2 percent Molybdenum disulfide was observed to the optimum for getting SAE 30 grade oil from base stock prepared from E 3 and E 4 .The quantity needed of Molybdenum disulfide has been observed to be lower in this case as the viscosity for base stocks prepared from E 3 and E 4 was higher than that for the base stocks prepared from E 1 and E 6. .For base stock prepared from E 10 Molybdenum disulfide was not at all required and only 5.2 percent polyisobutylene was added to obtain SAE 30 grade engine oil for reason that the viscosity of base stock itself was failing in the limits prescribed for SAE 30 grade oil.
As shown in Table 4, the viscosity of the engine oil of SAE 30 grade prepared from different base stocks at 40°C and 100°C was increased after additives blending and varied from 83.0 to 92.0 cst and from 10.5 to 12.0 cst, respectively ; the viscosity index for these finished oils varied from 112 to 118.The flash point of the finished oils was in the range of 204°C to 221°C and the pour point varied between -6 to -15°C.As the finished oil was blended with additives, the ash content increased and was in the range of 0.0863 to 0.877 percent.Total acidity was in the range of 0.019 to 0.026 mg KOH /g of oil whereas the inorganic acidity was nil for all the finished oils.Therefore, the oils thus prepared met the quality requirements of SAE 30 grade.
To make the engine oil of SAE grade 40, the base stocks prepared from E 7 , E 8 , E 9 , H 3 , having viscosities of 68.0, 70.0, 88.0 and 125.0 cst at 40°C, respectively were considered suitable as the viscosities of these base stocks were appropriate to prepare SAE 40 grade of engine oil.A certain percent of polyisobutylene was added to upgrade the quality of oil.Simultaneously, proportion of Molybdenum disulfide was varied to obtain viscosity of the oil comparable to that of SAE 40 grade for which the viscosity at 100°C should be from 12.5 to 16.3 cst.After using different proportion of VI Improver in the base stocks prepared from E 7 and E 8, it was concluded that for getting SAE 40 grade oil the results obtained by addition of 6.5 percent Molybdenum disulfide and 5.2 percent polyisobutylene were meeting the requirement of the specification for this grade.Similarly, addition of 5.0 percent Molybdenum disulfide and 5.2 percent polyisobutylene was observed to be optimum for getting SAE 40 grade oil from base stock prepared from E 9. The quantity needed of Molybdenum disulfide has been observed to be lower in this case as the viscosity for base stock prepared from E 9 was higher than that for the base stocks prepared from E 7 and E 8 .For base stock prepared from H 3 , Molybdenum disulfide was not at all required for the reason that the viscosity of base stock itself was failing in the limits prescribed for SAE 40 grade oil.However only 5.2 percent polyisobutylene was added to obtain SAE 40 grade engine oil to upgrade its quality.

CONCLUSIONS
´The colour of the used oils was improved on refining due to the removal of carbonaceous matter, oxidative products and extraneous impurities.´The viscosity of the used oils in increased on refining due to the removal of light ends present in used oils.´The flash point of the used oils increased on their refining which is due to the removal of light ends having lower flash point.´Decrease in ash content shows the proper refining as the additives and carbon particles present in used oils were removed in refining process on solvent treatment.