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102

DOI:10.52113/3/eng/mjet/2025-13-02-/102-113, Vol. (13), Issue (2), (2025)

Muthanna Journal of Engineering and Technology

MJET

Submitted 28 May 2025, Accepted 22 July 2025, Published online 31 July 2025

Reclamation of Base Oil from Depleted Engine Oil by Solvent

Extraction Process: An Insightful Review

Hassan A. Younisa and Yasser I. Abdulazizb

a Department of Chemical Engineering, Al-Nahrain University, Baghdad, Iraq

b Department of Chemical Engineering, Al-Nahrain University, Baghdad, Iraq

*Corresponding author E-mail: [email protected]

Abstract

Lubricating oils are viscous hydrocarbon liquids obtained from crude oil, are essential for lubricating the moving parts of

various machines. Used lubricants are classified as hazardous waste due to their elevated concentrations of environmentally

dangerous organic substances, including Polychlorinated Biphenyl (PCBs), Polycyclic Aromatic Hydrocarbons (PAHs), and

heavy metals. These contaminants, originating from the integrity of lubricating oil, are significantly affected by wear and

tear, additive breakdown, thermal cracking, and oxidation during their operational life, necessitating their replacement.

Direct disposal of this used oil into the environment causes substantial pollution. Incineration of used oil generates significant

ash and carcinogenic byproducts, further contributing to environmental contamination. Recycling lubricants, through the

application of physical-chemical processes, enables the recovery of base oil, a valuable reusable raw material in lubricant

production. Numerous studies have investigated oil reuse and used oil re-refining. Research consistently validates solvent

extraction, frequently enhanced using adsorption, as a more performant and efficacious technique for recycling used

lubricating oil. The present review offers a thorough analysis of the solvent extraction procedure for this application.

Keywords: regeneration used oil, Solvent Extraction for Oil Recycling, Base Oil, Waste Oil Management

1. Introduction

The most stable, least volatile, and highest-boiling component of crude petroleum is lubricating oil. Consisting primarily of

hydrocarbons, its molecules typically contain between 20 and 70 carbon atoms and fall into three main categories: paraffinic,

naphthenic, and aromatic. The molecular structure of paraffinic compounds is primarily characterized by straight-chain

alkanes, resulting in properties like waxiness, elevated pour point, favorable viscosity, and superior temperature stability.

Naphthenic compounds differ structurally, incorporating linear chains with a significant presence of pentamerous rings and

a lesser proportion of hexagonal rings. This leads to a low pour point, making them suitable for applications such as

refrigeration oils. However, due to their high carcinogenic potential, their use in engine oils is limited. Aromatic molecules

consist of linear chains that include hexagonal benzene ring structures. In fact, the distinction between these groupings is

sometimes obscured, as numerous lubricating oil molecules are hybrid structures containing varied quantities of these

different hydrocarbon kinds [1]. The high boiling point of lubricating oil (exceeding 400°C) distinguishes it from other crude

oil fractions [2], with molecular weights ranging from 250 to 1000 [3]. The primary functions of lubricating oil include

minimizing friction, inhibiting corrosion, providing a medium for heat transfer, and acting as a suspending agent for

contaminants [4, 5]. The chemical makeup of lubricating oils typically comprises 80–90% base stock and 10–20% chemical

additions and other compounds [6]. A typical lubricating oil composition is illustrated in Figure 1. Notwithstanding the

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detrimental impact of spent oil on the environment, it is regarded as a significant energy resource, a subject that has been

well investigated. Spent oil can be rerefined into base lubricant oil by eliminating pollutants and can be processed into fuel

oil, combusted to generate energy, or utilised as feedstock for the manufacture of different petroleum-derived goods. The

recycling of spent lubricating oil is an established process that has undergone continuous enhancement, resulting in the

development of several ways, and these include: vacuum distillation, solvent extraction, solvent extraction followed by

adsorption, de-slugging, and adsorption process [7]. The use of solvent extraction has been studied as an alternative method

that involves the use of reduced energy levels relative to alternative approaches, as indicated by several researchers [8, 9].

Solvent extraction is a refining technique employed for spent lubricating oils, relying on the solvent's capacity to remove

basic oil constituents derived from discarded lubricating oil selectively. The solvent will eliminate impurities and additives

existing in used oil and will precipitate according to gravitational forces. The solvent can be reconstituted using distillation

for reutilization. The extraction of oil is contingent upon the properties of both the solvent and the oil, the temperature of

extraction, and the duration of contact between the solvent and the feed [8]. This essay aims to emphasise the significance

of solvent extraction as a method for recycling spent synthetic lubricating oils in Iraq. This will help address the sustainable

development goals related to good health, a clean environment, and environmental sustainability and preservation.

2. Definition of used oil

The term "used oil" designates petroleum-derived or manufactured lubricant that has served its lubricating function and is no

longer capable of performing its original intended purpose. Lubricating oil ages, deteriorates, and loses efficacy owing to

contamination with foreign substances, including metal particles, filings, other oils, and additives [2]. Figure 2 illustrates the

lubricating oil return cycle.

Fig. 1: Typical Lubricating Oil Composition [10].

Fig. 2: Recycling process of re-refined lubricating oils

[11].

3. Substances Contaminating Used Oil

The accumulation of various contaminants during operation leads to a decline in the effectiveness of automotive lubricating

oil. These contaminants can be broadly categorized as follows:

3.1. Extraneous Contaminants

Emanate from the external environment and metal particulates produced within the engine. Environmental pollutants

comprise dusts, dirt, and humidity. Air can also be regarded as a pollutant due to its capacity to cause oil foaming. Engine-

derived contaminants include:

1. Metallic particulates originating from engine abrasion.

2. Carbonaceous particulates arising from inadequate burning of fuel.

3. Metallic oxides generated as corrosion byproducts of metallic components.

4. Water infiltrated through leaks in the system cooling.

5. Water generated as a byproduct of burning of fuel, along with fuel, fuel additions, or its derivatives, which may

infiltrate the engine crankcase [12].

3.2. Products of Oil Deterioration

Oil deterioration leads to the formation of several byproducts, including:

1. Sludges: a complex mixture of oil, water, dusts, dirt, and carbonaceous debris. This sludge can either accumulate on

engine parts or remain colloidally suspended within the oil.

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2. Lacquer: The exposure of oil-borne sludge to high operating temperatures leads to the formation of varnish, a rigid

or viscous accumulation on engine components.

3. Oil-Soluble Compounds: These are the byproducts residuals of oil oxidation dissolved in the oil and can't be

eliminated using standard filtration methods. These soluble compounds may subsequently accumulate on motor

components. The quantity and allocation of engine deposits fluctuate considerably based on engine operating

criteria. At decreased crankcase the temperatures, carbon deposits predominantly arise due to incomplete combustion

of gasoline rather than from the lubricating oil. Conversely, at elevated temperatures, the lubricating oil significantly

contributes to the creation of increased lacquer and sludge deposits [12,13].

4. Causes of Lubricating Oil Degradation

Any lubricating oil, regardless of whether it is sourced from crude or synthetic origins, that has been tainted by chemical or

physical contaminants during its application is classified as wasted lubricating oil, occasionally designated as spent engine

oil or waste oil. Rammohan [14] emphasizes that infrequent oil changes permit the accumulation of pollutants such as dirt

within the engine, obstructing adequate lubrication of moving components. Aljabiri [15] delineated the principal mechanisms

contributing to the depletion of lubricating oil additives, including thermal deterioration, oxidation, neutralization, shearing,

hydrolysis, aqueous cleansing, particle purification, filtration, contamination, frictional interaction, surface adsorption,

condensation, settling, and evaporation. Three principal variables lead to the breakdown of lubricating oil: severe heat,

excessive cold, and prevalent pollutants [14, 2]. Additional contributing factors encompass entrained air, humidity,

incompatible gases, process constituents, inside or outside radiation pollution, and unintentional fluid blending. Water,

frequently originating from condensation, can lead to engine corrosion, a process that is expedited in elevated temperature

oil due to heightened chemical reactivity. The extended presence of water in lubricating oil can result in emulsification,

creating a caustic mixture that may evolve into sludge, potentially obstructing oil passageways or filters [15]. The degradation

process entails the reaction of hydrocarbons with oxygen during an initial phase, resulting in the formation of extremely

reactive peroxide radicals. Hydroperoxides degrade into oxygenated molecules, which then react to generate large-molecule

organic acids and polymeric compounds. The subsequent polymerization and polycondensation of certain substances lead to

the production of insoluble sludge, which may form as a thin layer, formulating lacquers or varnishes for application on both

hot and cold metal substrates [16]. Prolonged exposure to elevated temperatures hastens the deterioration of lubricating oil

characteristics, requiring its extraction and substitution [17]. Used lubricating oil comprises many metals, as lead, zinc,

barium, arsenic, chromium, and cadmium [18, 19]. The principal constituents of old lubricating oil include deteriorated

additive, base oil, metallic particulates, carbon particulates, and oxidation byproducts. A variety of additives are employed

to improve lubricant performance; however, these additives diminish in efficacy with time. Furthermore, lubricating fluid

collects various metals due to component wear. While in storage, lubricating oil may become polluted with chlorinated

solvents, water, uncombusted fuel, carbon, and dust [20]. Moreover, lubricating oil serves as a corrosion-resistant, cooling,

and cleansing agent, accumulating numerous contaminants and additional constituents [21]. These impurities immediately

disrupt the lubricant's viscosity, thereby diminishing its efficacy and execution. Figures 3 the percentage contribution of used

oils.

Fig. 3: Percentage contribution of used oils [20].

5. Ecological Consequences of Spent Lubricating Oil

The pollutants in used oil have harmful effects on the environment and public health. Degraded additives, contaminants, and

degradation byproducts render waste oil significantly more toxic and detrimental to people's health and the environment than

virgin oil bases. These pollutants can elicit a range of harmful health effects in humans and other mammals by inhalation,

ingestion, or dermal exposure. These effects include respiratory conditions like lipid pneumonia and lipid granuloma in the

pulmonary system. Inappropriate disposal of spent oil, including the discharge into stormwater drainage systems or sewage

systems, can adversely influence aquatic ecosystems and marine coastlines. When discarded in soil or landfills, spent oil can

infiltrate ground and surface water via multiple land treatment mechanisms. Moreover, improper disposal of used oil

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endangers flora and fauna, potentially resulting in economic detriment to industries such as recreation and fishing [20].

Nwachukwu et al. assert that one liter of spent lubricating oil can pollute one million liters of water, underscoring the

considerable risk of water pollution [23]. The UN claimed in 2016 that about six million deaths each year are linked to air

pollution, highlighting the extensive effects of pollutants. Even minimal amounts of oil in wastewater, 50 - 100 ppm, entering

sewage treatment facilities can disrupt and compromise treatment operations. Used oil drainage is reported to constitute over

40% of overall oil pollution in American rivers, being the predominant source of this contamination. Emetere [24] indicated

that the combustion of used lubricating oil emits aerosols and greenhouse gases into the environment, capable of dispersing

at significant velocities (10-12 m/s). Table 1, used by Nwachukwu et al. encapsulates several local applications of used oil

along with their direct and indirect detrimental consequences.

Table 1: Assessment of the local environmental impact applications of spent motor oil [23]

Local use of spent oil

Application

Ecological impact

Road construction

On the ground

Contamination of soil

Rust prevention

On a metal device

Contact stains

Emergency lubrication for vintage engines

Automobiles, generators

Air pollution, waste

Timber preservation

Timber; roofing, fencing

Soil contamination

Combined with lubricant for gear oil

Gear box lubricant

Contaminants; Soil degradation

Manufacture of grease

Automobile lubricant

Stain upon touch

Combustion, Boilers, furnaces

Burners, bakery, incinerators

Off-gas, air pollution

For the management of pests, weeds, and dust

Garden, workshops

Soil pollution

Hydraulic oil

Props, Lifts, Jacks

Stain upon touch

Ball joint oil and nuts losing oil

Ball and socket joints, fasteners

Emissions, atmospheric contamination

Block and Balustrade mold lubricant

Block, bricks, balustrade molds

Spills

Medication

Wound and cuts

Spills Supplementary Health Impact

Dust and tick control

Land, floor

Soil contamination, discoloration

6. Spent Lubricating Oil Management

The management of old lubricating Oils encompasses three principal methods: recovery, reprocessing, and regeneration (or

re-refining) [25]. Reprocessing focuses on removing impurities from spent lube oils through various physical treatments,

including heat treatment, precipitation, filtration, dehydration, and centrifugation [2]. Recovery, a similar process, entails the

separation of particles and water from used lubricating oils by physical methods, resulting in a product resembling the original

oil but still containing some metallic contamination [2]. Regeneration, also known as re-refining, is a more comprehensive

procedure designed to yield base oils with optimal contamination removal, rendering them appropriate for the formulation of

new lubricants. The regeneration process generally comprises multiple phases, such as water removal, pollutant dirt

separation, treatment with acids, solvent extraction, clay treatment, hydrogenation, or their combinations [26]. The re-refining

process is generally implemented through four discrete unit operations: pre-treatment (dehydration and particulate removal),

regeneration (removal of oxidation products and other contaminants), fractionation (the separation of light-end

hydrocarbons), and finishing. (Odor and colour enhancement of the re-refined base oil) [27]. Table 2 presents commonly

employed re-refining methods at the laboratory scale, while Figure 4 provides a schematic summary of the sequential steps

involved in these processes.

Table 2: Protocols for the re-refinement of old oils and the employed technology [25]

Technologies

Country

Pre-Treatment

Filtering, centrifuging, Decantation, and sedimentation

Egypt [28], South Africa [29]

Distillation

Filtration

Egypt [30]

Sedimentation, magnetization, heating, and agitation

Nigeria [31]

The Regeneration

Acid treatment

Iran [32], Nigeria [33], Colombia [34], Romania [35]

Caustic treatment

Ghana [36]

Activated carbon/clay treatment

Distillation/clay

South Africa [29]

Acid clay treatment

Irradiation and ultrasonic adsorption

Kazakhstan [37]

Solvent extraction

Spain [38], UAE [39], Egypt [28], Iraq [40], Nigeria [31],

Portugal [41], Egypt [30]

Separation of the Bases

Distillation using vacuum

UAE [39], Iraq [40], Ghana [36], Egypt [30], Ukraine [42]

Atmospheric and vacuum distillations

Spain [38]

Finishing

Adsorption, neutralization, Sedimentation, and filtration

Nigeria [31], Romania [35]

Filtration and heating

South Africa [29]

Filtration

Colombia [34]

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Adsorption

UAE [39], Iraq [40], Nigeria [31], Iran [32], Kazakhstan

[37], Egypt [30]

Fig. 4: Basic processes in the re-refinement of used oils [27].

7. Methods for Re-Refining Spent Oils

The primary methods utilized for the re-refinement of spent oils on an industrial basis are (a) the acids/clay method, (b) the

active clays method, (c) Thin Film evaporation (TFE) utilizing distillation using vacuum, (d) the solvent extraction method,

and (e) the hydrotreatment method [2,43,44]. Figure 5 delineates the procedures for every re-refining technique, together

with the associated recoverable yields. Re-refining typically comprises four distinct stages: pre-treatment (extraction of water

and solid particulates), renewal (removal of degradation byproducts), separation of base oils (separation of lighter

hydrocarbons), and finish (enhancement of the colour and Odor of the processed oil) [27, 28, 45]. Table 3 summarizes the

methods of the process with their advantages and disadvantages.

Fig. 5: Overview of the technologies utilized in the industrial re-refinement of old lubricating oil [43, 46].

Spent Oils

Storage of blended oil

Pre-treatment

• Filtration

• Centrifugation

• Magnetization

• Decantation

• Sedimentation

• Heating

Heavy refuse and water

Regeneration

• Acid treatment

• Caustic treatment

• Active carbon / clay treatment

• Acid clay treatment

• Irradiation and ultrasonic adsorption

• Solvent extraction

Sludges (heavy metals, chlorinated

hydrocarbons, and polycyclic

aromatic compounds)

Fractionation of base oil

• Vacuum distillation

• Sequential vacuum and atmospheric distillation

Complete

• Adsorption

• Neutralization

• Decanting

• Filtration

Additives metals

Solvent reclaimed

Re-refined base oil + Additive

Novel lubricating oils

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Table 3: The primary technologies utilized at an industrial level for the re-refinement of old lubricating oils

Method

Process

Advantages

Disadvantages

Acid–clay [23,47]

Dehydration (elimination of contaminants,

water, antifreeze, and solvents through initial

low-temperature distillation). Vacuum

distillation. Sulfuric acid treatment involves the

reaction with oxygen, sulphur, and nitrogen to

produce sludge. Further purification to exclude

paraffinic and naphthenic hydrocarbons. Clay

adsorption to mitigate Odor and discoloration

Established technology; minimal

production expenses;

uncomplicated and direct

procedure; does not necessitate

highly experienced personnel;

appropriate for small-scale

enterprises; low capital outlay;

lucrative for small facilities;

reduced energy usage; generates

high-quality base oils

Produces contaminating waste;

induces equipment

deterioration; diminished

production due to oil depletion

in mud and clay; fails to adhere

to contemporary pollution

control standards; banned in

numerous nations

Activated clay [23,47]

Dehydration. Vacuum distillation employing a

standard vacuum column. Adsorption utilizing

activated clay at 120°C for a duration of 2 hours.

Filtration

Eliminates the necessity for acid

treatment; straightforward

procedure; appropriate for

small-capacity facilities; yields

high-quality base oils

Excessive clay consumption;

comparatively poor efficacy;

variable quality;

environmental issues

associated with the disposal of

substantial amounts of used

clay; dependence on particular

clay varieties, which may not

be easily accessible

Thin film evaporation

(TFE) [28,47]

Dehydration. Thin-film evaporation using

vacuum distillation, isolating volatile substances

from high-boiling distillates that contain heavy

metals. Two finishing alternatives: (a) hydraulic

finishing (for the elimination of chlorine,

nitrogen, oxygen, and sulphur compounds) or (b)

clay adsorption (for the removal of pollutants

including heavy metals and breakdown

byproducts)

Appropriate for large-capacity

facilities; thin-film evaporators

function under high vacuum and

are ideal for high-value products;

reduces contamination; yields

superior quality base oils

Requires high operating

temperatures and high vacuum;

economically viable only for

high-capacity plants; high

energy consumption

Solvent extraction

[47,46,48]

Dehydration. Removal of impurities by mixing

with solvents (except sulfuric acid) that

precipitate insoluble and suspended materials

(e.g., asphalt, metal compounds, and resins),

yielding non-hazardous sludge waste. Vacuum

distillation employing a standard vacuum

column. Clay adsorption for the mitigation of

Odor and discoloration. Propane may serve as a

solvent

Recyclable solvent; reduces

contamination; facilitates

functional recovery of base oils;

yields high-quality base oils;

propane effectively removes

additives, metals, and tar;

operable at ambient temperature

Economical only for

large-scale plants; requires

higher operating pressures;

necessitates sophisticated

operating systems and

qualified personnel; potential

for solvent losses; risk of

fire/explosion with propane;

high energy consumption

Hydro-treatment

[43,47,46]

Dehydration. Vacuum distillation employing a

standard vacuum column. Treatment involving

hydrogen and a catalyst to eliminate sulphur,

nitrogen, and oxygen. Integrating this with

solvent extraction can further improve oil

quality. Clay adsorption

Enhances oil colour and aroma;

distillation efficiently eliminates

sulphur, nitrogen, metals, and

unsaturated hydrocarbons

Elevated expenses; safety

issues; inappropriate for small-

scale operations; significant

energy consumption;

necessitates high operating

temperatures and pressures

The selection of an appropriate re-refining process for spent lubricating oil is contingent upon the consideration of three

major criteria: technical viability and reliability, safety and health, environmental (HSE) considerations, implications, and

economic viability. Solvent extraction, frequently employed in conjunction with adsorption, has been identified as a

particularly efficacious method for spent lubricating oil regeneration [30]. A critical factor in the efficacy of solvent extraction

lies in the selection of appropriate solvents. These solvents must demonstrate a high solubility parameter to facilitate efficient

base oil reclamation [49,50,51]. While exhibiting limited solvency for additive and carbon-based constituents [49].

8. A COMPREHENSIVE ANALYSIS OF THE SOLVENT EXTRACTION PROCESS

The Solvent extraction involves mixing spent lubricating oil with a solvent capable of selectively extracting the base oil while

causing impurities to flocculate. Several recent studies have investigated this technique, often in connection with other

methods, to improve the recovery and quality of re-refined base oil. Araromi et al. (2016) [52] employed two individual

solvents (ethanol C2H6O and 1-butanol C₄H₁₀O) and a binary solvent mixture (1-butanol+ethanol mixture) for the refinement

of used lubricating motor oil at 35°C, 45°C, and 50°C. The solvent efficacy was examined at solvent-to-oil ratios from 1:1

to 7:1, using percentage oil yield as an efficiency metric. 1-Butanol proved to be the most efficacious single solvent in the

extraction method, followed by the 1-butanol-ethanol mixtures. The overall best presentation for both solvents was achieved

at a temperature of extraction of 50°C.

Abdulaziz and Mahmood (2016) [53] examined the extraction and distillation method for the regeneration of base oil from

used lubricating oil. Multiple solvents, such as 1-butanol C₄H₁₀O, 2-propanol C3H8O, ethanol C2H6O, and binary solvent

mixtures (heptane C7H16 + methyl ethyl ketone C4H8O) combined with acetone C3H6O, were analysed. According to their

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findings, 1-butanol achieved the highest oil recovery (93.7%) and solvent recovery (96.2%) under optimal conditions of a

4:1 solvent-to-oil ratio and temperature of extraction of 40°C.

Epelle et al. (2017) [54] studied how well three cleaning liquids—phenol C6H6O, furfural C5H4O2, and N-Methyl Pyrrolidone-

NMP C5H9NO could remove bad stuff from used oil to improve its viscosity index (VI). At a solvent-to-oil ratio of 4:1 and

a heat of 100°C, NMP demonstrated the best performance in terms of VI improvement, achieving the highest value of 105,

outperforming both furfural and phenol. However, furfural provided the optimal performance in relation to raffinate yield

(90%), surpassing NMP and phenol in this metric.

Osman et al. (2018) [30] conducted experimental work on refining spent oils using novel solvent extraction blends. The

execution of three ternary combinations was assessed: (A) {toluene C6H5CH3 + butanol C4H9OH + methanol CH3OH }, (B)

{toluene C6H5CH3+ butanol C4H9OH + ethanol C2H6O }, and (C) {toluene C6H5CH3+ butanol C4H9OH + isopropanol

C3H8O }. Proportions of oil to solvent varying from (1:1 to 1:3). The findings validated that solvent mixture A had the greatest

efficacy in sludges elimination. The highest percentage of sludges removal enhanced with rising solvent-to-oil ratios.

Combination A eliminated the greatest proportion of sludges (52%), followed by combination B (36.7%), while mixture C

removed the least (18.9%). The disparities were ascribed to the solubility of the base oil in the corresponding solvents and

their dielectric constants.

Ramadhan and Wiyanti (2018) [55] investigated the remediation of used lubricating oil utilizing butanol C4H9OH (solvent),

kaolin (adsorbent), and KOH (coagulant). They observed significant reductions in Ca²⁺ (99.98%), Mg²⁺ (97.31%), Pb²⁺

(79.59%), and Cr⁶⁺ (33.33%), but an increase in Fe²⁺ (112.78%). The ideal circumstances consisted of a 3:1 solvent-to-oil

ratio, 1.5 g of kaolin, and 2.0 g of KOH. Higher butanol and KOH concentrations were found to be more effective in reducing

metal content.

In their investigation of solvent extraction/adsorption for spent lubricating oil regeneration, Oladimeji et al. (2018) [56]

identified optimal process conditions. Employing methyl ethyl ketone C4H8O and propan-2-ol C3H8O as solvents, they

determined that a 4:1 solvent-to-oil ratio with methyl ethyl ketone yielded the most advantageous physical-chemical features

in the regenerated base oil. The oil yield increased with higher solvent-to-oil ratios and mixing speeds, reaching an optimal

temperature of 50°C, beyond which the quality declined. The solvent-to-oil ratio was identified as the primary factor

influencing the quality of the regenerated base oil.

Adewole et al. (2019) [57] evaluated regenerated base oil from composite solvent extraction (hexane C6H14 /butanol C4H9OH

solvent, KOH flocculant) for reuse potential. The regenerated oil's flash point (222°C) was slightly below SAE 20 (224°C),

SAE 30 (226°C), and SAE 40 (268°C) standards, while its 40°C kinematic viscosity (138.92 cSt) exceeded these grades

(SAE 20: 37 cSt, SAE 30: 88 cSt, SAE 40: 110 cSt). Further viscosity and flash point improvements were recommended.

Santos et al. (2019) [58] investigated the impact of engine usage on recovered base oil quality. They observed two engines

utilizing the identical oil type, one for roughly 5,000 km and the other for 10,000 km. Base oil was extracted from the utilized

lubricant utilizing polar organic solvents (1-butanol C₄H₁₀O, 2-propanol C3H8O, and methyl ethyl ketone C4H8O) and

subsequently characterized via physical-chemical and thermal analysis (TG/DTG/DTA). Methyl ethyl ketone provided the

highest base oil yields (approximately 80%), followed by 1-butanol (just above 70%). 2-Propanol yielded unsatisfactory

results.

Nour et al. (2021) [59] compared isopropyl alcohol C3H8O (single solvent) with ethanol C2H6O /isopropyl alcohol C3H8O

/toluene C6H5CH3 (composite solvent) for used engine oil recycling. Both reduced calcium, alkaline, and zinc contamination

from additives. At 40°C, isopropyl alcohol showed better viscosity, VI, and FTIR results than the composite solvent. Zeolite

was proposed for heavy metal removal.

Osman et al. (2021) [60] examined the effects of two changed ternary solvent mixtures: A (xylene C₈H₁₀, butanol C4H9OH,

methanol CH3OH) and B (xylene C₈H₁₀, butanol C4H9OH, isopropanol C3H8O), subsequently subjected to bleaching using

activated alumina as an adsorbent. The used oil was first allowed to settle for one hour, subsequently centrifuged at 1500 rpm

for 30 minutes, and last filtered. The results showed that all tested ratios (1:1, 1:3, and 1:5) of solvent mixture A performed

best, achieving the highest percentage of sludges removal. The sludges removal rate was higher with the methanol-containing

mixture (A) compared to the isopropanol-containing mixture (B), attributed to methanol's higher solubility parameter (29

J/m³)^1/2. Increasing the solvent-to-oil ratio also increased the sludges removal rate, with an optimum ratio of 3:1 at 70°C.

The physicochemical properties of the base oils obtained using solvent mixture A at a 3:1 volume ratio at 70°C, subsequent

to treatment with alumina activation, met the specifications of virgin base oil.

Ayeni et al. (2021) [61] regenerated used base oil using methyl ethyl ketone C4H8O extraction and unripe plantain peel-

derived AC adsorption—a 3:1 solvent-to-oil ratio optimized contaminant removal, viscosity, and TBN, yielding a treated

base oil. Extraction at 60°C increased TBN by 32% (6.90 to 10.21 mg KOH/g). Subsequent adsorption (15 wt% AC, 60°C)

removed >91% of both calcium and zinc. The optimal conditions (3:1, 60°C) resulted in a regenerated oil with properties

(90.23 cSt viscosity, 203 °C flashpoint, 0.909 g/ml density, 0.64 wt% sulphur) similar to fresh Ram SN500.

Dinesh et al. (2021) [62] explored lubricating oil refining using solvent extraction combined with vacuum distillation,

employing three different solvents: 1-propanol C3H8O, n-butanol C4H10O, and ethanol C2H6O. Laboratory experiments were

conducted based on a complete global design. The study found that the kinematic and dynamic viscosities of the recovered

oil were higher using different separation methods at lower temperatures.

Benjamin et al. (2022) [63] compared the treatment of 3-month-old 5W-30 oil using 70:30 methanol CH3OH /n-hexane C6H14

(5:1 solvent-to-oil ratio), KOH coagulation (120°C), and activated charcoal adsorption (150°C, 1 hour, 300 rpm

centrifugation). Eight physicochemical parameters of fresh used and treated oil were analysed. Treatment significantly

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improved all parameters (95% confidence), achieving 95.7% recovery. The method was deemed technically feasible,

sustainable, and environmentally friendly.

Naife et al. (2022) [64] investigated the impact of various operating parameters on the solvent extraction process using

heptane C7H16 and 2-propanol C3H8O. The studied parameters included solvent-to-oil ratios (1:2, 1:4, 1:6, and 1:8), mixing

time (20, 35, 50, and 65 minutes), temperature (30, 40, 50, and 60 °C), and mixing speed (500 rpm). The results confirmed

that 2-propanol exhibited superior performance in sludges removal compared to heptane. Increasing the solvent-to-oil ratio

enhanced waste removal, but economic considerations necessitate optimization. The research determined the ideal operating

parameters for 2-propanol (35 minutes, 1:6 solvent-to-oil ratio, 40 °C) and heptane (50 minutes, 1:6 solvent-to-oil ratio,

50 °C).

Decote et al. (2023) [65] investigated ultrasound (25 °C, 24 kHz, 20% amplitude) and mechanical stirring (225 rpm, 25 °C),

utilizing diverse alcohols (ethanol C2H6O, propan-2-ol C3H8O, 2-methylpropan-1-ol C4H10O, butan-1-ol C4H10O) for oil

extraction (0.5, 1, and 5 minutes). Butan-1-ol yielded the highest recovery after 5 min with both ultrasound (91.4 wt%) and

stirring (88.3 wt%). 2-Methylpropan-1-ol also showed good results (79.4 wt% with ultrasound, 59.8 wt% with stirring).

Recovered oil viscosity with 2-methylpropan-1-ol and butan-1-ol (126.0 and 132.7 mm² s⁻¹) approached fresh locomotive oil

(150.6 mm² s⁻¹). Ca, Cr, Fe, Mo, and Na concentrations were reduced.

Olaremu (2024) [66] investigated the use of two ternary solvent mixtures: Toluene C6H5CH3, 1-butanol C₄H₁₀O, and methanol

CH3OH (TBM), and toluene C6H5CH3, 1-butanol C₄H₁₀O, and ethanol C2H6O (TBE). In their experiments, the respective

solvent mixture was added to the used engine oil at a 3:1 ratio, followed by one hour of stirring using a magnetic stirrer and

a 24-hour settling period. The results indicated that the TBM mixture yielded re-refined oil with properties surpassing those

of fresh virgin oil. Conversely, the TBE mixture produced comparatively poorer results.

Mu'azu et al. (2024) [67] explored a hexane C6H14/ methyl ethyl ketone C4H8O extraction followed by activated charcoal

adsorption for used oil regeneration. Optimal conditions yielded 77.20% base oil recovery (0.29% ash, 11.25% sludges

removal). Adsorption further reduced Zn²⁺ (88.88%) and Fe²⁺ (46.32%), with a slight yield loss (2.77%, 75.06% final yield).

The regenerated oil’s properties (0.8699 specific gravity, 26.1/7.3 cSt viscosity at 40/100°C, 192°C flash point) approached

virgin SN 150 and met ASTM standards, except for slightly elevated TAN (0.96 mg KOH/g) and color. The process shows

promise for safe oil reuse.

Table 4: Important studies on solvent extraction methods for used engine oil.

No.

Researcher (s)

Year

Title of the Research

Conclusion

Reference

Araromi et al.

2016

Application of Solvent Extraction

Process for Revivification of Used

Lubricating Engine Oil

1-butanol produced the best performance in Oil ratio of

5:1 at an extraction setting of 50ºC.

[52]

Abdulaziz and

Mahmood

2016

Recovery of Base Oil from Spent

Automobile Oil Using Elementary

and Binary Solvent Extraction

1-butanol yielded the highest oil recuperation (93.7%)

and solvent recuperation (96.2%) at 40°C with a weight

ratio of 4:1.

[53]

Epelle et al.

2017

Improving the Viscosity Index of

Used Lubricating Oil by Solvent

Extraction

N-Methyl Pyrrolidone-NMP best solvent in terms of VI

improvement, giving value 105. Furfural gave the best

performance of raffinate production of 90% at a solvent-to-

oil ratio of 4:1 at 100°C.

[54]

Osman et al.

2018

Recycling of used engine oil by

different solvent

The solvent mixture (toluene, butanol, and methanol)

exhibits optimal effectiveness for sludges removal at a

solvent-to-oil ratio of 3:1.

[30]

Ramadhan and

Wiyanti

2018

Treatment of Waste Lubricating Oil

by Chemical and Adsorption Process

Using Butanol and Kaolin

The best ratio of butanol to reduce iron, calcium,

magnesium, lead, and chromium in used oil is 3:1, and the

best ratio is 2 grams for KOH.

[55]

Oladimeji et al.

2018

Data on the treatment of used

lubricating oil from two different

sources using solvent extraction and

adsorption

Methyl Ethyl Ketone exhibited superior performance,

achieving the maximum sludges clearance; a 4:1 solvent-to-

oil ratio produced the most favourable physicochemical

characteristics in the regenerate base oil.

[56]

Adewole et al.

2019

Characterization and Suitability of

Reclaimed Automotive Lubricating

Oils Reprocessed by Solvent

Extraction Technology

The binary mixture consisting of 70% butanol and 30%

n-hexane, combined with 3 g of potassium hydroxide

(KOH) at a solvent-to-oil ratio of 5:1 and a temperature of

60°C, resulted in enhanced characteristics of the recovered

oil.

[57]

Santos et al.

2019

Recycling of lubricating oils used in

gasoline/alcohol engines: Thermal

characterization

The optimal solvents for base oil extraction are the

methyl ethyl ketone, approximately 80%, and 1-butanol,

slightly exceeding 70%.

[58]

Nour et al.

2021

Dataset on the recycling of used

engine oil through solvent extraction

Optimal results were attained using isopropyl alcohol as

the sole solvent at the temperature of extraction of 40°C.

[59]

Osman et al.

2021

Optimization of acidic activated

conditions for natural clay and its

application in waste oil bleaching

The spent oil was processed using solvent mixture

(xylene, butanol, methanol) at a solvent-to-oil ratio of 3:1,

thereafter subjected to bleaching utilising activated alumina

and activated clay as adsorbent materials to produce base

oil.

[60]

Ayeni et al.

2021

A two-stage coupling process for the

recovery of base oils from used

lubricating oils

Methyl ethyl ketone served as the extraction solvent,

while activated carbon derived from unripe banana peels

functioned as the adsorbent. The findings validated that a

solvent-to-oil ratio of 3:1 at 60°C produced exceptional

efficiency.

[61]

110

Muthanna Journal of Engineering and Technology

Dinesh et al.

2021

Recycling of Used Lubricating

Engine Oil by A Solvent Extraction

Process

The utilisation of ethanol as a solvent for oil treatment

yielded extracts that facilitated simpler distillation in

comparison to n-butanol and 1-propanol solvents.

[62]

Benjamin et al.

2022

Binary Solvent Pretreatment,

Adsorption and Definite

Characterization of the Used Engine

Lubricants.

A binary solvent mixture (methanol/n-hexane) combined

with activated charcoal shown efficacy as a hybrid

formulation, restoring 95.7% of the quality parameters of

degraded engine oil after three months of application.

[63]

Naife et al.

2022

Treatment of Used lubricant Oil by

Solvent Extraction

The results indicate that the solvent 2-Propanol had

superior efficacy in sludges removal compared to heptane.

[64]

Decote et al.

2023

Quality analysis of oil recovered

from used locomotive engine oil

using ultrasound assisted solvent

extraction

The optimal outcomes for recovered oil were achieved

using ultrasound (5 min); the yield of butan-1-ol was the

highest (91.4 wt%), succeeded by 2-methylpropan-1-ol

(79.4 wt%), propan-2-ol (12.1 wt%), and ethanol (3.6 wt%).

[65]

Olaremu

2024

Treatment and Recycling of Used

Lubricating Oil in Nigeria: Solvent

Extraction Approach

The results indicate that the mixture containing Toluene, 1-

butanol, and Methanol (TBM) outperformed the properties

of the fresh virgin oil.

[66]

Mu'azu et al.

2024

Optimization of Base Oil

Regeneration Using Response

Surface Methodology from Spent

Lubricating Oil Through Binary

Solvent Extraction Process

This paper examined the efficacy of Hexane and Methyl

Ethyl Ketone as solvents, followed by adsorption utilising

activated charcoal.

[67]

9. Conclusion

Energy and environmental concerns are paramount topics of discussion among environmental activists and organizations.

Random disposal of used lubricating oil not only harms the environment but also represents a missed opportunity to utilize a

valuable resource and forfeits potential economic benefits. Therefore, promoting sustainable used oil management should be

prioritized and supported by environmental ministries through grants and incentives, recognizing it as an eco-friendly

technology. Due to the significant health, economic, and ecological implications associated with spent lubricating oil,

research efforts have focused on identifying technologies that maximize environmental protection and socioeconomic gains

at minimal cost. Recycling of used lubricating oils is gaining increasing importance in the context of ecological conservation.

Regeneration, or re-treatment processes, aim to produce base oils suitable for reuse. Solvent extraction has emerged as a

viable alternative to conventional acid-clay and hydrotreatment methods within the research community. The appeal arises

from several significant advantages, such as the generation of superior base oil, diminished pollution levels, solvent

recyclability, and compliance with environmental regulations. Process parameters, including temperature, solvent-to-oil ratio,

mixing speed, mixing duration, and solvent type, have been demonstrated to affect the efficacy of solvent extraction. Despite

its demonstrated success, the economic viability of spent lubricating oil regeneration remains a key challenge. Therefore, to

optimize the regeneration process from both financial and environmental perspectives, further research is needed to establish

a systematic approach for solvent screening.

References

[1] Hsu, Y. L., & Liu, C. C. (2011). Evaluation and selection of regeneration of waste lubricating oil technology.

Environmental monitoring and assessment, vol. 176, 197-212.

[2] Speight, J. G., & Exall, D. I. (2014). Refining used lubricating oils. CRC Press, Taylor & Francis Group, NW.

[3] Bhushan, Z. K., Anil, S. M., Sainand, K., & Shivkumar, H. (2016). Comparison between different methods of waste oil

recovery. International Journal of Innovative Research in Science, Engineering and Technology, vol. 5(11), 2001-2009.

[4] Kannan, S. C., Kumar, M. K., Hussain, S. M., and Priya, D. N. (2014). Studies on Reuse of Re-Refined Used Automotive

Lubricating Oil. Research Journal of Engineering Sciences, vol. 3(6), 8 - 14.

[5] Mynin, V. N., Smirnova, E. B., Katsereva, O. V., Komyagin, E. A., Terpugov, G. V., & Smirnov, V. N. (2004).

Treatment and regeneration of used lube oils with inorganic membranes. Chemistry and technology of fuels and oils,

vol. 40, 345-350.

[6] Rincon, J., Canizares, P., & Garcia, M. T. (2005). Regeneration of used lubricant oil by polar solvent extraction.

Industrial & Engineering Chemistry Research, vol. 44(12), 4373-4379.

[7] Abu-Elella, R., Ossman, M. E., Farouq, R., & Abd-Elfatah, M. J. I. J. C. B. S. (2015). Used motor oil treatment: turning

waste oil into valuable products. International journal of chemical and biochemical sciences, vol. 7, 57-67.

[8] Diphare, M., & Muzenda, E. (2013). Influence of solvents on the extraction of oil from waste lubricating grease: A

comparative Study. 2nd International conference on agriculture, environment and biological sciences, Dec. 17 -18,

Pattaya, Thailand.

[9] Ayeni, A. O., Oyekunle, D. T., Adegbite, O., Alagbe, E., & Ejekwu, O. (2019). Physico-chemical remediation of

polycyclic aromatic hydrocarbons contaminated soil. Journal of Physics: Conference Series, IOP Publishing. vol.

1299(1), p. 12121.

Muthanna Journal of Engineering & Technology

111

[10] Mustapha T., Surajudeen A., & Usman A. (2021). Base Oil Regeneration from Spent Lubricating Oil Using Solvent

Extraction Process: A Review. IOSR Journal of Engineering (IOSRJEN), 11(11). 26-35.

[11] Parekh, K., Gaur, R., & Shahabuddin, S. (2022). Recent advances in reclamation of used lubricant oil. Tailored

Functional Materials: Select Proceedings of MMETFP 2021, 273-282.

[12] Awaja, F., & Pavel, D. (2006). Design aspects of used lubricating oil re refining. 1st edition, Elsevier, Oxford, UK.

[13] Armioni, D. M., Raţiu, S. A., Benea, M. L., & Puţan, V. (2024, December). Overview on the environmental impact of

used engine oil. In Journal of Physics: Conference Series, IOP Publishing. vol. 2927(1), p. 12007.

[14] Rammohan, A. (2016). Engine’s lubrication oil degradation reasons and detection methods: A review. Journal of

chemical and Pharmaceutical Sciences, vol. 9(4), 3363-3366.

[15] Aljabiri, N. A. (2018). A comparative study of recycling used lubricating oils using various methods. Journal of

Scientific and Engineering Research, vol.5 (9), 168-177.

[16] Khuong, L. S., Zulkifli, N. W. M., Masjuki, H. H., Mohamad, E. N., Arslan, A., Mosarof, M. H., & Azham, A. (2016).

A review on the effect of bioethanol dilution on the properties and performance of automotive lubricants in gasoline

engines. RSC advances, vol. 6(71), 66847-66869.

[17] Cerón, A. A., Boas, R. N. V., Biaggio, F. C., & de Castro, H. F. (2018). Synthesis of biolubricant by transesterification

of palm kernel oil with simulated fusel oil: Batch and continuous processes. Biomass and Bioenergy, vol. 119, 166-

172.

[18] Udonne, J. D., & Bakare, O. A. (2013). Recycling of used lubricating oil using three samples of acids and clay as a

method of treatment. International Archive of Applied Sciences and Technology, vol. 4(2), 8-14.

[19] Mekonnen, H. A., & Ababa, A. (2014). Recycling of used lubricating oil using acid-clay treatment process. PhD.

Thesis submitted to Addis Ababa University - Ethiopia.

[20] Diphare, M. J., Muzenda, E., Pilusa, T. J., & Mollagee, M. (2013). A comparison of waste lubricating oil treatment

techniques. In 2nd International Conference on Environment, Agriculture and Food Sciences (pp. 106-109).

[21] Abro, R., Chen, X., Harijan, K., Dhakan, Z. A., & Ammar, M. (2013). A comparative study of recycling of used engine

oil using extraction by composite solvent, single solvent and acid treatment methods. International Scholarly Research

Notices, 2013(1), 952589.

[22] Rodriguez-Hernandez, J., Andrés-Valeri, V. C., Calzada-Pérez, M. A., Vega-Zamanillo, Á., & Castro-Fresno, D.

(2015). Study of the raveling resistance of porous asphalt pavements used in sustainable drainage systems affected by

hydrocarbon spills. Sustainability, vol. 7(12), 16226-16236.

[23] Nwachukwu, M. A., Alinnor, J., & Feng, H. (2012). Review and assessment of mechanic village potentials for small

scale used engine oil recycling business. African Journal of Environmental Science and Technology, vol. 6(12), 464-

475.

[24] Emetere, M. E. (2017). Investigations on aerosols transport over micro and macro-scale settings of West Africa.

Environmental Engineering Research, vol. 22(1), 75-86.

[25] Sánchez-Alvarracín, C., Criollo-Bravo, J., Albuja-Arias, D., García-Ávila, F., & Pelaez-Samaniego, M. R. (2021).

Characterization of used lubricant oil in a Latin-American medium-size city and analysis of options for its regeneration.

Recycling, vol. 6(1), 10.

[26] Diphare, J. M., Pilusa, J., & Muzenda, E. (2013). The effect of degrading agents and diluents on oil recovery from

Lithium based waste lubricating grease. In 2nd International Conference on Environment, Agriculture and Food

Science, Kuala Lumpur, Malaysia.

[27] Widodo, S., Ariono, D., Khoiruddin, K., Hakim, A. N., & Wenten, I. G. (2018). Recent advances in waste lube oils

processing technologies. Environmental Progress & Sustainable Energy, vol. 37(6), 1867-1881.

[28] Emam, E., & Shoaib, A. (2012). Re-refining of used lube oil. II-by solvent/clay and Acid/Clay-Percolation Processes.

ARPN J. Sci. Technol. vol. 2. 1034-1041.

[29] Abdulkareem, A. S., Afolabi, A. S., Ahanonu, S. O., & Mokrani, T. J. E. S. (2014). Effect of treatment methods on used

lubricating oil for recycling purposes. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, vol.

36(9), 966-973.

[30] Osman, D. I., Attia, S. K., & Taman, A. R. (2018). Recycling of used engine oil by different solvent. Egyptian Journal

of Petroleum, 27(2), 221-225.

[31] Isah, A., Abdulkadir, M., Onifade, K., Musa, U., Umar, G., Bawa, A., & Sani, Y. (2013). Regeneration of used engine

oil. Lecture Notes in Engineering and Computer Science, World Congress on Engineering, WCE 2013, London, 3 July

2013-5 July 2013.

[32] Salem, S., Salem, A., & Babaei, A. A. (2015). Preparation and characterization of nano porous bentonite for

regeneration of semi-treated waste engine oil: Applied aspects for enhanced recovery. Chemical engineering journal,

260, 368-376.

[33] Owolabi, R. U., Akinola, A. A., Oyelana, O. A., & Amosa, M. K. (2017). Some Physico-Chemical and Adsorptive

Reclamation Strategies of Spent Automobile Engine Lubricating Oil. Journal of Engineering Research, 22(1), 98-106.

[34] Fong Silva, W., Quiñonez Bolaños, E., & Tejada Tovar, C. (2017). Caracterización físico-química de aceites usados

de motores para su reciclaje. Prospectiva, 15(2), 135-144.

[35] Stan, C., Andreescu, C., & Toma, M. (2018). Some aspects of the regeneration of used motor oil. Procedia

Manufacturing, 22, 709-713.

[36] Mensah-Brown, H. (2015). Re-Refining And Recycling Of Used Lubricating Oil.

112

Muthanna Journal of Engineering and Technology

[37] Syrmanova, K. K., Kovaleva, A. Y., Kaldybekova, Z. B., Botabayev, N. Y., Botashev, Y. T., & Beloborodov, B. Y.

(2017). Chemistry and recycling technology of used motor oil. Oriental Journal of Chemistry, 33(6), 3195-9.

[38] Moya, L., & Botamino, I. (2010). Desde el aceite lubricante usado hasta su puesta en el mercado tras su regeneración.

Madrid, España.

[39] Abdel-Jabbar, N. M., Al Zubaidy, E. A., & Mehrvar, M. (2010). Waste lubricating oil treatment by adsorption process

using different adsorbents. International Journal of Chemical and Molecular Engineering, 4(2), 141-144.

[40] Mohammed, R. R., Ibrahim, I. A., Taha, A. H., & McKay, G. (2013). Waste lubricating oil treatment by extraction and

adsorption. Chemical Engineering Journal, 220, 343-351.

[41] Pinheiro, C. T., Ascensão, V. R., Cardoso, C. M., Quina, M. J., & Gando-Ferreira, L. M. (2017). An overview of waste

lubricant oil management system: Physicochemical characterization contribution for its improvement. Journal of

Cleaner Production, 150, 301-308.

[42] Korchak, B., Hrynyshyn, O., Chervinskyy, T., & Polyuzhin, I. (2018). Application of vacuum distillation for the used

mineral oils recycling. Chemistry & Chemical Technology, 12(3), 365-371.

[43] Kupareva, A., Mäki‐Arvela, P., & Murzin, D. Y. (2013). Technology for rerefining used lube oils applied in Europe: a

review. Journal of Chemical Technology & Biotechnology, 88(10), 1780-1793.

[44] Haro, C., De la Torre, E., Aragón, C., & Guevara, A. (2014). Regeneración de arcillas de blanqueo empleadas en la

decoloración de aceites vegetales comestibles. Revista Politécnica, 34(1).

[45] García González, M.T.(2019). Regeneración de Aceites Lubricantes Usados Mediante Extracción.

[46] Ijadi Maghsoodi, A., Hafezalkotob, A., Azizi Ari, I., Ijadi Maghsoodi, S., & Hafezalkotob, A. (2018). Selection of waste

lubricant oil regenerative technology using entropy-weighted risk-based fuzzy axiomatic design approach. Informatica,

29(1), 41-74.

[47] Jafari, A. J., & Hassanpour, M. (2015). Analysis and comparison of used lubricants, regenerative technologies in the

world. Resources, Conservation and Recycling, 103, 179-191.

[48] Oladimeji, T. E., Sonibare, J. A., Omoleye, J. A., Emetere, M. E., & Elehinafe, F. B. (2018). A review on treatment

methods of used lubricating oil. Int. J. Civ. Eng. Technol, 9(12), 506-514.

[49] Durrani, H. A., Panhwar, M. I., & Kazi, R. A. (2012). Determining an efficient solvent extraction parameters for re-

refining of waste lubricating oils. Mehran University Research Journal of Eng. & Tech, 31(2), 265-270.

[50] Emam, E. A., & Shoaib, A. M. (2013). Re-refining of used lube oil, I-by solvent extraction and vacuum distillation

followed by hydrotreating. Petroleum & Coal, 55(3).

[51] Kamal, A., & Khan, F. (2009). Effect of extraction and adsorption on re refining of used lubricating oil. Oil & Gas

Science and Technology Revue de l'IFP, 64(2), 191-197.

[52] Araromi, D., Aremu, M., & Gbolahan, O. (2016). Application of solvent extraction process for revivification of used

lubricating engine oil. American Chemical Science Journal, 10(4), 1-7.

[53] Abdulaziz, Y. I., & Mahmood, S. M. (2016). Recovery of base oil from spent automobile oil using elementary and

binary solvent extraction. Nahrain University College of Engineering Journal, 19(2), 370-384.

[54] Epelle, E. I., Otaru, A. J., Zubair, Y. O., & Okolie, J. (2017). Improving the viscosity index of used lubricating oil by

solvent extraction. Int. Res. J. Eng. Technol, 4, 1581-1585.

[55] Ramadhan, B., & Wiyanti, D. (2018). Treatment of waste lubricating oil by chemical and adsorption process using

butanol and kaolin. In IOP Conference Series: Materials Science and Engineering (Vol. 349, No. 1, p. 012054). IOP

Publishing.

[56] Oladimeji, T. E., Sonibare, J. A., Omoleye, J. A., Adegbola, A. A., & Okagbue, H. I. (2018). Data on the treatment of

used lubricating oil from two different sources using solvent extraction and adsorption. Data in Brief, 19, 2240-2252.

[57] Adewole, B. Z., Olojede, J. O., Owolabi, H. A., & Obisesan, O. R. (2019). Characterization and suitability of reclaimed

automotive lubricating oils reprocessed by solvent extraction technology. Recycling, 4(3), 31.

[58] Santos, J. C. O., Almeida, R. A., Carvalho, M. W. N. C., Lima, A. E. A., & Souza, A. G. (2019). Recycling of lubricating

oils used in gasoline/alcohol engines: Thermal characterization. Journal of Thermal Analysis and Calorimetry, 137,

1463-1470.

[59] Nour, A. H., Elamin, E. O., Nour, A. H., & Alara, O. R. (2021). Dataset on the recycling of used engine oil through

solvent extraction. Chemical Data Collections, 31, 100598.

[60] Osman, D. I., Elsayed, A., Attia, S., & Taman, A. R. (2021). Optimization of acidic activated conditions for natural

clay and its application in waste oil bleaching. Egyptian Journal of Chemistry, 64(11), 6787-6798.

[61] Ayeni, A. O., Tagwai, S., Dick, D. T., Agboola, O., Ayoola, A. A., Babatunde, D. E., & Oni, B. A. (2021). A two-stage

coupling process for the recovery of base oils from used lubricating oils. In IOP Conference Series: Earth and

Environmental Science (Vol. 655, No. 1, p. 012029). IOP Publishing.

[62] Dinesh, K., Kaithari, K.D., Krishnan, K.P and Al-Rivami, A. (2021). Recycling of Used Lubricating Engine Oil by A

Solvent Extraction Process. International Journal of mechanical and production engineering research, 11(1): 151-158.

[63] Benjamin, W., Mohammed, R., & Gero, M. (2022). Binary Solvent Pretreatment, Adsorption and Definite

Characterization of the Used Engine Lubricants. Science Open Preprints.

[64] Naife, T. M., Rashid, S. A., & Jabbar, M. F. A. (2022). Treatment of Used lubricant Oil by Solvent Extraction. Iraqi

Journal of Chemical & Petroleum Engineering, 23(1).

[65] Decote, P. A., Negris, L., Simonassi, P., Druzian, G. T., Flores, E. M., Vicente, M. A., & Santos, M. F. (2023). Quality

analysis of oil recovered from used locomotive engine oil using ultrasound-assisted solvent extraction. Chemical

Engineering Research and Design, 197, 603-616.

Muthanna Journal of Engineering & Technology

113

[66] Olaremu, A. (2024). Treatment and Recycling of Used Lubricating Oil in Nigeria: Solvent Extraction Approach. SRA-

Archives, 15(1), 9-17.

[67] Mu'azu, M., Abdulsalam, S., & El-Nafaty, U. A. (2024). Optimisation of Base Oil Regeneration Using Response

Surface Methodology from Spent Lubricating Oil through Binary Solvent Extraction Process. Path of Science, 10(10),

2048-2057.