Rerefining of used lubricating oil

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Re-refining of used lubricating oil by vacuum distillation/thin wiped film
evaporation technique
Article in Petroleum Science and Technology · December 2019
DOI: 10.1080/10916466.2019.1704782
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Re-refining of used lubricating oil by vacuum
distillation/thin wiped film evaporation technique
Hozan Jalal Saleem & Abdulsalam Rahim Karim
To cite this article: Hozan Jalal Saleem & Abdulsalam Rahim Karim (2019): Re-refining of used
lubricating oil by vacuum distillation/thin wiped film evaporation technique, Petroleum Science and
Technology, DOI: 10.1080/10916466.2019.1704782
To link to this article: https://doi.org/10.1080/10916466.2019.1704782
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PETROLEUM SCIENCE AND TECHNOLOGY
https://doi.org/10.1080/10916466.2019.1704782
Re-refining of used lubricating oil by vacuum distillation/thin
wiped film evaporation technique
Hozan Jalal Saleem and Abdulsalam Rahim Karim
Department of Chemistry, College of Science, University of Sulaimani, Sulaimani, Iraq
ABSTRACT
Re-refining of used lubricating oil has appeared as a valuable technique to
re-refining of used engine and industrial oils. This paper focused on the
vacuum distillation thin wiped film evaporation technique of used lubricating oil recycling. The whole process consists of dehydration, gas oil evaporation, thin wiped film evaporation and clay treatment. The produced base
oils are in group I through determination of sulfur contents, percentage
of saturate compounds and viscosity indexes. The obtained results are
practicable with most of the American Society for Testing and Materials
(ASTM) properties and reduced most of worn metals in the refined
base oils.
KEYWORDS
ED-XRF; refined base oils;
re-refining; ULOs; VDTWF
1. Introduction
Lubricating oil is an important liquid used to reduce scraping, abrasions and friction of the tribological pieces of machine parts by putting a film of material between rubbings surface, thereby
reducing the amount of wear metals in the machine oil (Hsu and Liu 2011, Laad and Jatti 2018,
Wolak, Zaja˛c, and GołeR biowski 2019). It can be used to cool and clean the machine parts, but it
is deteriorating during operation because of oxidation and contamination (Speight and Exall
2014). The advanced lubricating oil is made of base oil which is blended with chemical additives
according to its grade and specific demand (Mohammed et al. 2013). The main elements in the
lubricating oil additives are zinc, phosphorous, calcium and sulfur (Fujita, Campbell, and
Zielinska 2006). Used lubricating oil (ULO) often referred to as petroleum derived or synthetic
lube oil which has been contaminated by physical or chemical impurities (Speight and Exall
2014). It contains a blend of base oil, worn metals, water, sludge, and oxidation compounds
(Kashif et al. 2018, Emam and Shoaib 2012). Used lubricating oil can pollute the environment to
a broad extend which affects both living organisms of aquatic ecosystems and human health due
to toxicity and carcinogenicity (Kamal, Naqvi, and Khan 2013). Each volume of used lubricating
oil can ruin at least (250,000) volumes of water (Bridjanian and Sattarin 2006). Due to increasing
demand for natural resource conservation, energy conservation and preserving environment,
development of the re-refining of used lubricating oils become essential (Hani and Al-Wedyan
2011). The processes of re-refining used lubricating oil depends on the nature of base stock and
the amount of impurities in the used lubricating oils (ULOs) (Emam and Shoaib
2013).The oldest and most common re-refining process is acid/clay process, but it may cause
serious environmental pollution due to leaving an enormous amount of spent clay and acidic
CONTACT Abdulsalam Rahim Karim
[email protected]
Department of Chemistry, College of Science,
University of Sulaimani, Kirkuk road, Sulaimani, Iraq.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lpet.
Supplemental data for this article is available online at here.
ß 2019 Taylor & Francis Group, LLC
2
H. J. SALEEM AND A. R. KARIM
sludge after the completion of the process (Izza et al. 2018). Nowadays, various re-refining processes have been developed, including super critical fluid extraction (Liu et al. 2005), vacuum distillation with petroleum atmospheric residuum (Kim, Hwang, and Kim 1997), solvent extraction
process (Al-Zahrani and Putra 2013), Propane extraction (Rincon et al. 2003) and polar solvent
extraction (Rincon, Canizares, and Garcia 2005). The objective of this research is to produce the
best quality of the base oils; SN-150 and SN-200 from used lubricating oils (ULOs) by vacuum
distillation/thin wiped film (VDTWF) evaporation technique. In addition, two grades of lubricating oils; SAE 20W50 and SAE 15W40 were prepared.
2. Experimental
2.1. Material and methods
The used lubricating oils (ULOs) were collected from different city service stations in Iraq, and
transferred to an appropriate tanks. The sample is a mixture of different types of used lubricating
oils, from a variety number of cars, busses, and vehicles. Toluene, acetone and n-pentane are
used for determination of saturate and aromatic contents. 2-propanol, chloroform, potassium
hydroxide and hydrochloric acid were used for the determination of total acid number (TAN)
and total base number (TBN). The solvents were supplied by E. Merck and Scharlau. Activated
clay (particle size 60–120 mesh) was supplied from Shiraz Company. The viscosity index
improver and package additive were supplied by Innov OIL Company. Pour point depressant,
which is a type of (KUSA 50), was supplied by AB petroleum Pvt.Ltd.
2.1.1. Vacuum distillation thin wiped film process
The re-refining used lubricating oils (ULOs) consist of the following sequence steps (Supplementary
Scheme 1): First, dehydration of ULOs at temperature 240 C under atmospheric pressure to remove
water, light distillates and collected 8.6% volume. Then Gas oil was separated from residue of atmospheric
distillation unit by vacuum distillation at 240 C under 80 torr and collected 4.3% volume. Next, base oils
(SN-150 and SN-200) were distilled at temperature 320 C and 360 C respectively under vacuum pressure
80 torr through thin wiped film evaporator, and 54% volume of base stock SN-150 and 26% volume of
base oil SN-200 were collected. Then, the refined base oils (SN-150 and SN-200) are treated with activated
clay to remove the remaining impurities in the oils and impart proper color to the base oils. Finally, the
base oils were filtered through filter press to remove any solid impurities remaining in the base oils.
2.1.2. Blending and synthesis of lubricating oil grades
In blending process, the base stock (SN-200) is mixed with additives (package additives, viscosity
index improver and pour point depressant). The lubricating oil grade (SAE 15W40) consists of 85%
volume of base oil (SN-200), 10.5% volume of stock blend of viscosity index improver (VII), 4%
volume of package additive and 0.5% volume of pour point depressant (polymethacrylate). The
lubricating oil grade (SAE 20W50) was synthesized by blending of 80% volume of refined base oil
(SN-200), 15.5% volume of viscosity index improver (VII), 4% volume of package additive and 0.5%
volume of pour point depressant. The viscosity index improver (stock blend) is a solid pellet, olefin
copolymer (OCP) which was prepared by dissolving 10% weight of dry improver (OCP) under high
agitation in base stock (SN-150) at 100 C for 6 hours until all the solids had been dissolved.
2.1.3. Analysis of used lubricating oil, base oil stocks and lubricating oil grades
Re-refined base and used lubricating oils were characterized according to the American Society
for Testing and Materials (ASTM). These standards are specific gravity (ASTM D-4052), flash
point (ASTM D-92), fuel dilution (ASTM D-8004), pour point (ASTM D-97), kinematic viscosity
PETROLEUM SCIENCE AND TECHNOLOGY
3
Table 1. Characterization of used lubricating oil and refined base oils.
Characterization
Specific gravity @ 15.6 C
Flash point C
Pour point C
Viscosity @ 40 C/Cst
Viscosity @ 100 C/Cst
Viscosity index
Water content% volume
Fuel dilution% volume
TAN mg KOH/g sample
Sulfated ash, mass%
ASTM Color
Copper corrosion
Saturate% weight
Aromatic% weight
Polar% weight
Method
ASTM D 4052
ASTM D92
ASTM D97
ASTM D445
ASTM D445
ASTM D2270
ASTM D98
ASTM D8004
ASTM D664
ASTM D874
ASTM D1500
ASTM D130
ASTM D2007
ASTM D2007
ASTM D2007
ULO
0.8844
176
18
76.5
9
90
0.5
1.1
3.3652
0.6980
>9
–
80.57
13.85
5.57
SN150
0.8716
205
3
31
5.1
95
Nil
Nil
Nil
0.0042
2
1a
87.1
7.32
5.57
SN200
0.8807
218
3
44
6.2
95
Nil
Nil
Nil
0.0091
2.5
1a
86
8.12
5.87
Table 2. Characterization of lubricating oil grades (SAE 20W50 and SAE 15W40).
Characterization
Specific gravity @ 15.6 C
Flash point C
Pour point C
Viscosity @ 40 C/Cst
Viscosity @ 100 C/Cst
Viscosity index
Water content % volume
TBN mg KOH/g sample
Sulfated ash, mass%
ASTM Color
Copper corrosion
Method
SAE 20W50
SAE 15W40
ASTM D 4052
ASTM D92
ASTM D97
ASTM D445
ASTM D445
ASTM D2270
ASTM D98
ASTM D4739
ASTM D874
ASTM D1500
ASTM D130
0.8813
234
24
152.19
18.71
139
Nil
5
0.9462
2.5
1a
0.8805
220
24
113.7
15.95
150
Nil
5
0.8064
2.5
1a
Table 3. Elemental analysis for different samples.
Elements
Method
ULOs
SN150
SN200
SAE 20W50
SAE 15W40
Zinc (ppm)
Sulfur% weight
Lead (ppm)
Calcium (ppm)
Magnesium (ppm)
Iron (ppm)
Copper (ppm)
Cobalt (ppm)
Nickel (ppm)
Silver (ppm)
Tin (ppm)
Cadmium (ppm)
Potassium (ppm)
Sodium (ppm)
ED-XRF
ED-XRF
ED-XRF
FAAS
FAAS
ED-XRF
ED-XRF
ED-XRF
ED-XRF
ED-XRF
ED-XRF
ED-XRF
FAAS
FAAS
762
0.941
22
440
24.28
101
27
21
12
Nil
0.1
0.8
0.1
1.18
3
0.717
0.5
Nil
Nil
16
6
17
8
Nil
Nil
Nil
Nil
Nil
4.5
0.732
0.9
Nil
Nil
17
6
12
8
Nil
Nil
Nil
Nil
Nil
1067
1.010
0.5
400
182.12
37
15
22
21
Nil
Nil
Nil
0.11
1
912
0.894
0.5
300
122.41
41
19
21
15
Nil
Nil
2
0.12
2.1
(ASTM D-445), viscosity index (ASTM D-2270), water content (ASTM D-95), total acid number
(ASTM D-664), total base number (ASTM D-4739), sulfated ash (ASTM D-874), color (ASTM
D-1500), copper corrosion (ASTM D-130), saturate and aromatic content (ASTM D-2007),
carbon distribution and group analysis (ASTM D-3238), refractive index (ASTM D-1218), sulfur
content (ASTM D-4294) and molecular weight (ASTM D-2502). Metal content was determined
by flame atomic absorption spectroscopy, model, Pg instrument/AA500 spectrophotometer and
energy dispersive X-ray fluorescence (ED-XRF), model, Rigaku/(NEX QC series affordable
EDXRF analyser).The IR spectra was recorded on a Perkin-Elmer FT/IR spectrometer in the
range (400–4000 cm 1) using KBr pellets ( max in cm 1), from UK.
4
H. J. SALEEM AND A. R. KARIM
Figure 1. IR spectra of used lubricating oils and refined base oils SN 150 and SN 200.
3. Results and discussion
The base oils (SN-150 and SN-200) were obtained by re-refining of used lubricating oils (ULOs)
through VDTWF evaporation technique. The used lubricating oils (ULOs) have the highest specific gravity value (0.8844) while the refined base oils have the lowest specific gravity values, for
base oil SN-150 is 0.8716 and base oil SN-200 is 0.8807, Table 1. The high specific gravity of
PETROLEUM SCIENCE AND TECHNOLOGY
5
Figure 2. Carbon distribution of refined base oils SN 150 and SN 200, (CA: Aromatic Carbon, CN: Naphthenic Carbon and CP:
Paraffinic Carbon).
used lubricating oils (ULOs) is relating to the high levels of impurities such as water and oxidation products (Onukwuli et al. 1999, Hamawand, Yusaf, and Rafat 2013). The used lubricating
oils have lowest pour point value ( 18 C) due to the presence of oxidation products such as
aldehydes and ketones (Emam and Shoaib 2012). The pour point of refined base oils have highest
values ( 3 C). These results show that the pour point of refined base oils have been improved
by vacuum distillation/thin wiped film (VDTWF) evaporation technique. The total acid number
TAN (mg KOH/g sample) for the used lubricating oil (3.3652 mg KOH/g sample) was higher
than those of the refined base oils due to the presence of organic, inorganic acids and heavy
metal salts during oxidation process in the engine oil at elevated temperature, which leads to
decrease the efficiency of engine oil and more wear (Adeyemi, Adebiyi, and Koya 2017). The total
acid numbers of refined base oils (SN-150 and SN-200) were reduced completely by VDTWF
evaporation technique. The sulfated ash content can be used to indicate the amount of additives
(metal in additives) in the lubricating oils (Hussein, Amer, and Gaberah 2014). As an expected,
the used lubricating oil had highest sulfated ash content that related to the presence of wear
metal, dirt and worn additives in the used oils than the refined base oils. It was found that the
sulfated ash content reduced from 0.6980% weight in the used lubricating oil to 0.0042% weight
and 0.0091% weight in the base oils (SN-150 and SN-200), respectively. The used lubricating oils
(ULOs) have lowest flash point (176 C) while the refined base oils have the highest values (base
oil SN-150: 205 C; base oil SN-200: 218 C). The low flash point values of the used lubricating
oils (ULOs) due to the presence of light distillate (fuel dilution) and oxidation components
(Speight and Exall 2014, Adeyemi, Adebiyi, and Koya 2017). The higher values observed for
refined base oils indicate that some light distillate of the used lubricating oil has been removed
by vacuum distillation/thin wiped film (VDTWF) evaporation technique. The copper corrosion
test shows that the refined base oils are 1a, which indicates that the good behavior of protection
and anti-oxidation characterization of the refined base oils. The used lubricating oils have lowest
value of saturate contents (80.57% weight), while the refined base oils have highest values of
saturate content, (base oil SN-150: 87.1% weight; base oil SN-200: 86% weight). These result
shows that some of the aromatic compound were reduced by VDTWF evaporation technique.
6
H. J. SALEEM AND A. R. KARIM
Figure 3. Structural group analysis of refined base oils SN 150 and SN 200, (RA: Aromatic Ring, RT: Total Ring and RN:
Naphthenic Ring).
The used lubricating oils (ULOs) have the highest kinematic viscosity at temperature 40 C
(76.5Cst) and 100 C (9Cst). The refined base oils have lowest kinematic viscosity at the temperatures 40 C and 100 C. The ULOs have lower viscosity index (90) than the refined base oils (95).
The lower viscosity index indicates the more viscosity affected by changes in temperature. The
high kinematic viscosity of used lubricating oils (ULOs) is due to the presence of higher viscous
materials (Adeyemi, Adebiyi, and Koya 2017). These results show that some of the viscous materials in the used lubricating oils were removed by VDTWF evaporation technique. The used
lubricating oils have the highest values of metal contents compared with refined base oils. The
main sources of metal contents in used lubricating oils are worn additives, wear and corrosion
products of metallic engine parts (Wolak, Zaja˛c, and GołeR biowski 2019). Table 3 shows that the
metal contents of refined base oils have been reduced significantly by (VDTWF) evaporation
technique. A spectral band at (1704-1603cm 1) indicates the presence of oxidized products
because of the peak of carbonyl groups absorb at these frequencies (Speight and Exall 2014). The
peak of carbonyl groups disappeared in the refined base oils while it was appeared in the ULOs
(1631.65 cm 1), Figure 1, which indicate that the vacuum distillation/thin wiped film (VDTWF)
evaporation technique removes oxidation components. Carbon distribution indicates the relative
amounts of carbon atoms in naphthenic, aromatic and paraffinic structures. Structural group analysis indicate the ring content in naphthenic and aromatic structures (Drews 1998). The direct
relation between viscosity and high molecular weight aromatic materials (Mehrkesh, Hajimirzaee,
and Hatamipour 2010). Figures 2 and 3 shows that the refined base oils have lower values of aromatic ring and the percentage of aromatic carbon, while the refined base oils have higher values
of the percentage of paraffinic carbon. These results indicate that the aromatic materials have
been reduced significantly by vacuum distillation/thin wiped film (VDTWF) evaporation technique. The refined base oils are all of API type I which in agreement with ASTM D-2007 test for
classification of base oils through determination of viscosity index (ASTM D-2270) and determination of sulfur content (ASTM D-4294). The color of the refined base oils were improved (from
ASTM >9 to ASTM 2.5) due to the adsorption of chromophore groups by clay treatment. The
PETROLEUM SCIENCE AND TECHNOLOGY
7
lubricating oil grades (SAE 15W40 and SAE 20W50) have total base number (TBN) of 5 mg
KOH/g sample due to the existence of detergents in the package additive. The SAE 15W40 and
SAE 20W50 have lower pour point values ( 24 C) due to the existence of pour point depressant,
Table 2. They also have higher values of flash point (SAE 15W40:220 C; SAE 20W50: 234 C)
and lower values of metal contents especially (zinc, calcium, lead, iron and magnesium), Tables 2
and 3, due to the existence of package additive. The copper corrosion test results of 1a from
lubricating oil grades indicate that the package additive contains anti-corrosion and anti-wear
agent in case of finishing lubricating oil beside the good behavior of protection and anti-oxidation characterization of the refined base oils.
4. Conclusion
The vacuum distillation/thin wiped film (VDTWF) evaporation technique is a useful process to
produce base oils, grade SN-150 and SN-200 from local used lubricating oil in Iraq. Base oils produced are all of API type I as their sulfur content is higher than 0.03% weight, saturated content
less than 90% weight and viscosity index is between 80-120. Metal content of used lubricating oil
is reduced dramatically especially zinc, lead, calcium and iron. As indicated by FTIR spectra, the
refined base oils are completely clean from oxidation products, such as aldehyde, ketone and carboxylic acid. Clay treatment improves the color of the base oil and brings it to the standard
requirements of (2-2.5) ASTM color.
Funding
This work was supported financially by University of Sulaimani (Kurdistan region of Iraq) and Asia oil factory
(Kurdistan region of Iraq/Sulaimani).
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