INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIV, Issue X, October 2025
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Developing an Efficient Oil Extraction Process Using Soxhlet
Extractor to Improve Oil Yield of Turmeric Rhizomes in Southern
Kaduna
*1
G.
A. Allems,
1
E.
B. Yawuck,
1
L.A. Magashi, and
2
S. Uba
1
Department of Chemistry, Kaduna State College of Education Gidan Waya, Nigeria
2
Department of Chemistry Ahmadu Bello University Zaria, Nigeria
*Corresponding Author
DOI: https://doi.org/10.51583/IJLTEMAS.2025.1410000029
Received: 30 September 2025; Accepted: 07 October 2025; Published: 06 November 2025
Abstract : The inefficiency often observed in oil extraction methods can be attributed to insufficient kinetic and thermodynamic
data during the design phase. This study aimed to optimize the turmeric oil extraction process using 250 ml of n-hexane and 50 g
of turmeric sample from Southern Kaduna. Six kinetic models and thermodynamic principles were applied to describe the
extraction process. The physicochemical properties of the turmeric oil were analyzed following the methods recommended by the
Association of Official Analytical Chemists. The results showed that the optimal conditions for turmeric oil extraction were
temperature range of 343 to 353 K, an extraction time of 5 to 6 hours and a solvent-to-sample ratio of 1:5. The extraction
followed pseudo-second-order kinetics, with an activation energy (Ea) of 18.8327 kj/molK. Thermodynamic analysis revealed an
enthalpy change (∆H) of 19.6389 kj/mol, an entropy change (∆S) of 0.08710 kj/molK and positive Gibbs’ free energy change
(∆G) at all tested temperatures. These thermodynamic results suggest that the extraction process is endothermic, requiring
continuous energy input, exhibits high randomness and is non-spontaneous. Furthermore, the physicochemical analysis confirmed
that the oil is safe for consumption and suitable for use in soap production, cosmetics and pharmaceuticals.
Key words: Efficient, soxhlet, turmeric oil, kinetic and thermodynamics
I. Introduction
Turmeric (Curcuma longa), a member of the Zingiberaceae family, is commonly cultivated in Nigeria's Middle Belt and Southern
regions, including Kaduna State. The rhizomes of turmeric contain bioactive compounds, particularly curcumin, which are known
for their antioxidant, anti-inflammatory and antimicrobial properties (Fatunmibi et al., 2023). These attributes make turmeric oil
highly sought after in industries like pharmaceuticals, cosmetics, and food production (Tanvir et al., 2018). In Southern Kaduna,
turmeric farming is gaining importance due to the area's fertile loamy, well-drained soils (Federal Ministry of Science and
Technology, 2025). However, traditional oil extraction methods often yield low amounts of oil and may fail to capture the full
spectrum of bioactive compounds present in the rhizomes. As such, improving extraction methods is crucial for enhancing the
economic viability of turmeric cultivation in the region (Ciuca, 2023).
The Soxhlet extraction method is a popular technique for extracting oils and bioactive compounds from plant materials. This
method uses continuous solvent extraction to efficiently isolate compounds over extended periods. Studies have demonstrated
that Soxhlet extraction can achieve turmeric oil yields of up to 10.27%, surpassing other methods such as supercritical fluid
extraction and cold maceration (Fatunmibi et al., 2023). Its effectiveness, ease of use and scalability make it a promising
approach for boosting turmeric oil yield in Southern Kaduna. The aim of this study is to optimize the Soxhlet extraction process
of turmeric rhizomes from the Kachia, Jaba, Kagarko, and Kajuru LGAs in Southern Kaduna. By investigating factors like
extraction time and temperature, the research seeks to enhance oil yield while preserving the bioactive components of turmeric
oil. The findings of this study will provide valuable insights for the regional extraction process and contribute to industrial
production improvements through kinetic and thermodynamic analysis.
II. Materials And Methods
The materials used in the experiment include turmeric rhizomes, hexane (solvent) made in Gunsgdong Gruanghua chemical
factory Co.,Ltd, Chaina with CAS (7778-80-5). The following laboratory equipment and apparatus were used in the study;
Soxhlet and other apparatus used were made in china, round bottom flask 500- 1000ml capacity, heating mantle, thermometer,
mortar and filter paper.
Collection and Preparation of Samples
Turmeric rhizomes were sourced from Kurmin – musa (Kachia LGA), Kuryas (Jaba LGA), Aribi (Kagarko LGA) and Maro
(Kajuru LGA) in Southern Kaduna, Kaduna State Nigeria. The Turmeric were identified by the researchers with the assistance of
a botanist and the voucher number deposited in Department of Biology, Ahmadu Bello University Zaria, Kaduna State. The
Turmeric rhizomes were stored in brown envelopes to Department of Chemistry, Ahmadu Bello University Zaria for the
extraction process.
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In the laboratory, the wet Turmeric rhizomes were washed with tap water, followed by distilled water. The cleaned sample were
dried at 310 - 313K for 30 days (Asoconom et al., 2025). The dried Turmeric rhizomes were chop into uniform size with motar
and pistil. Chop dried Turmeric rhizomes were converted to powder. The samples were sieved through 0.5 - 2 mm mesh
(Nwabanne, 2012). Each location sample was labeled as follows; sample A: Kachia LGA, B: Jaba LGA, C: Kagarko and D:
Kajuru LGA.
Extraction Method of Turmeric oil
The Turmeric oil was extracted from the rhizomes using Soxhlet extractor and n-hexane as the solvent. To study the kinetics and
thermodynamics of the extraction process, 96 experimental runs were carried out. The extraction time varied from 60 to 360
minutes i.e 60 - minute intervals, while the solvent volume and particle size were kept constant at 250 ml and 2.0 mm,
respectively, for all runs. The extraction temperature ranged from 323 to 353 K i.e 10 K intervals, with the solvent volume and
particle size remaining constant. A fixed weight of 50 g of ground Turmeric powder was used in each of the 24 runs for each
sample A, B, C and D, making a total of 96 experimental runs. The percentage oil yield was calculated using Equation 2.
ANOVA was used to compare the oil yield percentage across the four locations at P> 0.05.
Characterization of Extracted Turmeric Oil
The physicochemical properties of the extracted Turmeric oil were assessed, including colour, odour, specific gravity, refractive
index, viscosity, moisture content, oil content, peroxide value, acid value, free fatty acid content, saponification value, iodine
value and ester value. These characteristics were determined using methods outlined by the Standard Association of Official
Analytical Chemists (AOAC, 1990).
Kinetic studies
Six kinetics models proposed in Asoconom et al., (2025) which include: first order, second order, pseudo-first order, pseudo-
second order, intra-particle diffusion model and power law model were used for the study.
Thermodynamic Studies
The thermodynamic parameters of the Turmeric oil extraction process were calculated using the Arrhenius equation, which
defines the relationship between the rate constant (k) and temperature (T), as shown in Equation 3. This equation was then
linearized to produce Equation 4, which allowed for the calculation of the activation energy and Arrhenius constant. The changes
in enthalpy (∆H) and entropy (∆S) were determined using Equation 5, while Equation 6 was applied to calculate Gibbs' free
energy change (∆G) at different temperatures (Agu et al., 2021).
Where k =extraction rate constant, A = Arrhenius’s constant (frequency factor), Ea = Activation energy, R = Universal gas
constant and T = Temperature.
III. Results And Discussion
The study revealed that the Turmeric rhizomes contained 6.50 % oil by mass, as determined by exhaustive extraction (repeatedly
extracting the same sample until all the oil was removed). However, a single extraction using 250 ml of n-hexane and 50 g of 2.0
mm Turmeric rhizome powder particles at 353 K for 360 minutes yielded a maximum oil content of 6.50 %. A similar study in
India by Khanam (2018) reported oil yield range of 5.95 %. From the Analysis of Variance (ANOVA) the means of oil yield
obtained through Soxhlet in different locations in Southern Kaduna show that there is no significance difference is oil yield
percentage across the four locations at P> 0.05 significance figure.
Physicochemical Properties of Turmeric Oil
The physicochemical properties of the extracted Turmeric oil from different locations were summarized in Table 1.
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Table 1: Physicochemical properties of Turmeric oil Extracted from Southern Kaduna
Parameter
Kachia LGA
Jaba LGA
Kagarko LGA
Kajuru LGA
Colour
Pale yellow
Pale brown
Yellow
Pale brown
Odour
Aromatic spicy
Aromatic spicy
Aromatic spicy
Aromatic spicy
Specific gravity
1.45
1.30
1.35
1.40
Refractive index
1.44
1.20
1.32
1.41
Viscosity at 25°C mPa.s
35.50
32.50
33.20
34.40
Moisture content (%)
0.30
0.14
0.20
0.25
Oil Content (%)
13.00
10.00
12.00
12.00
Peroxide value (meq/kg)
20.80
18.16
19.20
20.00
Acid value (mgKOH/g)
11.30
11.08
11.21
11.25
Free fatty acid (%)
5.69
5.58
5.65
5.67
Saponification-value (mgKOH/g)
201.00
190.23
195.23
200.01
Iodine Value (gI
2
/100g)
70.39
53.20
51.39
58.20
Ester value (mgKOH/g)
189.70
179.15
184.02
188.85
(Source: Laboratory work 2025)
Table 1 shows that Turmeric oil produced in the Kachia, Jaba, Kagarko, and Kajuru LGAs of Kaduna State ranges in color from
pale yellow to brown with a spicy aromatic scent, primarily due to its curcuminoid content. Higher levels of curcumin and related
compounds result in a more intense yellow color (Jaiswal & Naik, 2021). These variations in color are likely influenced by
several local factors, including soil composition, climate and harvesting methods. Globally, turmeric oil is typically described as
pale yellow to reddish-brown with a fresh, spicy aroma (Oyemitan, 2017). The specific gravity of turmeric oil from Kachia, Jaba,
Kagarko and Kajuru was recorded as 1.45, 1.30, 1.35, and 1.40, respectively. According to Paul et al., (2011), the specific gravity
of turmeric oil ranges from 1.43 to 1.47, indicating that the oil from Southern Kaduna is denser than oils from other regions.
Typically, turmeric oil from India has a specific gravity between 0.92 and 0.95 (Tanvir et al., 2018), with similar values reported
for oils from Indonesia and China (Venkatramna Perfumers, 2022). The higher specific gravity of turmeric oil from Southern
Kaduna suggests a higher concentration of bioactive compounds, enhancing its effectiveness for therapeutic and cosmetic uses.
The refractive index of turmeric oil from Southern Kaduna ranged from 1.20 to 1.44, while Paul et al., (2011) reported a
refractive index value of 1.45. This value measures how much light bends when passing through the oil, influenced by the oil’s
density. The higher refractive index indicates that turmeric oil from Southern Kaduna has a greater refractive index compared to
oils from other regions. Turmeric oil from India typically has a refractive index between 1.50 and 1.52 (NHR Organic Oils,
2022), with similar values reported for oils from Indonesia and China (Kazima, 2022). This higher refractive index suggests a
higher concentration of bioactive compounds, improving its effectiveness in therapeutic and cosmetic applications. Viscosity
values of turmeric oil from the regions in Southern Kaduna at 25°C were as follows: Kachia (35.50 mPa·s), Jaba (32.50 mPa·s),
Kagarko (33.20 mPa·s), and Kajuru (34.40 mPa·s). These values reflect the oil’s resistance to shear stress and suggest that the
turmeric oil from these areas has moderate thickness, typical of essential oils. Globally, turmeric oil’s viscosity varies based on
factors such as geographical location and extraction methods. Turmeric oil from India has a viscosity of approximately 1.53
mPa·s at 25°C (Jaiswal & Naik, 2021), with similar values found in oils from Indonesia and China. The viscosity of turmeric oil
from Southern Kaduna aligns with international standards, indicating that it is well-suited for use in topical formulations and
aromatherapy products (Venkatramna Perfumers, 2022).
The moisture content of turmeric oil from Kachia, Jaba, Kagarko, and Kajuru LGAs at 25°C was found to be 0.30%, 0.14%,
0.20%, and 0.25%, respectively. These values indicate low moisture content, which enhances the oil’s stability and potency.
According to ISO 5562:1983, turmeric powder should have a maximum moisture content of 12.00% (ISO, 1983), but essential
oils, due to the extraction process, usually have much lower moisture content. Eleazu et al., (2015) found moisture contents in
turmeric varieties ranging from 15.75% to 47.80%, but the oil itself typically has low moisture content, similar to the values
observed in Southern Kaduna. The low moisture content suggests that the turmeric oil from this region is of high quality, with
reduced microbial contamination risks and a longer shelf life, making it suitable for pharmaceutical and cosmetic formulations.
The oil content in turmeric oil at 25°C was measured as follows: Kachia (13.00%), Jaba (10.00%), Kagarko (12.00%), and Kajuru
(12.00%). These values suggest that the turmeric oil from these regions has a moderate oil content, aligning with the typical
characteristics of essential oils. In India, turmeric oil typically has an oil content ranging from 2.42% to 3.91% (Kumari et al.,
2021), while studies in Brazil report an average oil content of 3.97% ± 0.61%, ranging from 3.00% to 5.16% (Guimarães et al.,
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2020). The higher oil content of turmeric oil from Southern Kaduna suggests a higher concentration of bioactive compounds,
enhancing its therapeutic and cosmetic effectiveness.
The peroxide values of turmeric oil from Kachia (20.80 meq/kg), Jaba (18.16 meq/kg), Kagarko (19.20 meq/kg), and Kajuru
(20.00 meq/kg) suggest moderate oxidative stability, which is typical for essential oils. Global studies have shown varying
peroxide values for turmeric oil. Jaiswal & Naik (2021) reported peroxide values between 23.25 and 36.16 meq/kg, which are
higher than those found in Southern Kaduna. Similarly, studies in Bangladesh reported peroxide values ranging from 23.25 to
36.16 meq/kg, showing that turmeric oil from different areas may vary in oxidative stability (Paul et al., 2011). The peroxide
values of turmeric oil from Southern Kaduna align with the typical range for essential oils, indicating desirable oxidative stability
suitable for industrial applications. The Acid Value of turmeric oil in Southern Kaduna was measured as follows: Kachia (11.30
mg KOH/g), Jaba (11.08 mg KOH/g), Kagarko (11.21 mg KOH/g), and Kajuru (11.25 mg KOH/g). AV reflects the free fatty acid
content of the oil. These values suggest moderate acidity, which is typical for essential oils. Studies worldwide have reported
similar acid value for turmeric oil. Jaiswal & Naik (2021) observed acid value ranging from 11.08 to 11.32 mg KOH/g, consistent
with those found in Southern Kaduna. Research from Bangladesh also reported acid value between 11.08 and 11.32 mg KOH/g
(Paul et al., 2011). The moderate acid value in turmeric oil from Southern Kaduna suggest a balanced acidity level, making it
suitable for pharmaceutical and cosmetic applications.
The Free Fatty Acid percentages of turmeric oil from Southern Kaduna at 25°C were as follows: Kachia (5.69%), Jaba (5.58%),
Kagarko (5.65%), and Kajuru (5.67%). These values indicate moderate acidity, which is typical for essential oils. Global research
shows similar free fatty acid values for turmeric oil. Jaiswal & Naik (2021) reported free fatty acid levels ranging from 5.00% to
6.00%, aligning with the values found in Southern Kaduna. Similarly, studies in Bangladesh indicated free fatty acid percentages
between 5.00% and 6.00%, suggesting comparable levels of acidity in turmeric oil across regions (Paul et al., 2011). The
moderate free fatty acid value in turmeric oil from Southern Kaduna suggests balanced acidity, making it suitable for
pharmaceutical and cosmetic industries. The Saponification Value of turmeric oil at 25°C in Southern Kaduna was observed as
follows: Kachia (201.00 mg KOH/g), Jaba (190.23 mg KOH/g), Kagarko (195.24 mg KOH/g), and Kajuru (200.01 mg KOH/g).
Saponification value indicates the amount of alkali needed to saponify a fixed amount of oil. These results show that turmeric oil
from these regions has a moderate saponification value, which aligns with the typical characteristics of essential oils. International
studies report similar saponification value for turmeric oil. Jaiswal & Naik (2021) found saponification value between 195.23 and
205.33 mg KOH/g, which are similar to the values observed in Southern Kaduna. Studies in Bangladesh also reported similar
saponification value, indicating comparable saponification potentials for turmeric oils from different regions (Paul et al., 2011).
The moderate saponification value of turmeric oil from Kaduna State suggests that it has a balanced composition of fatty acids,
making it suitable for pharmaceutical and cosmetic use.
The Iodine Values for turmeric oil from Kachia (70.39 g I₂/100g), Jaba (53.20 g I₂/100g), Kagarko (51.39 g I₂/100g), and Kajuru
(58.20 g I₂/100g) suggest a moderate level of unsaturation, which is typical for essential oils. International studies have reported
varying iodine values for turmeric oil. Paul et al., (2011) found iodine values ranging from 75.53 to 90.47 g I₂/100g in turmeric
oil from Bangladesh, which is higher than the values from Southern Kaduna. In contrast, Ifesan et al., (2012) reported an iodine
value of 46.95 g I₂/100g for turmeric oil in Nigeria, which is lower than the values observed in Southern Kaduna. The moderate
iodine values of turmeric oil from Southern Kaduna suggest a balanced degree of unsaturation, making it suitable for industrial
applications. Ester Values for turmeric oil from Kachia (189.7 mg KOH/g), Jaba (179.15 mg KOH/g), Kagarko (184.02 mg
KOH/g), and Kajuru (188.85 mg KOH/g) suggest a balanced composition of fatty acids and esters in the oil. International studies
report varying Ester value for turmeric oil. Paul et al., (2011) found Ester value ranging from 56.30 to 64.13 mg KOH/g in
turmeric oil from Bangladesh, indicating a lower ester content compared to the values observed in Southern Kaduna. Research in
India also reports Ester value between 50.00 and 70.00 mg KOH/g, further suggesting that turmeric oil from different regions
may exhibit varying ester contents (Tanvir et al., 2018). The moderate Ester value of turmeric oil from Southern Kaduna suggest
a balanced composition of fatty acids and esters, making it suitable for pharmaceutical and cosmetic applications.
Kinetics and Thermodynamics Study
The results from the 96 experiments conducted to study the kinetics and thermodynamics of Turmeric oil extraction are presented
in Table 2. The experiments were carried out at various temperatures and times, while keeping the particle size at 2.0 mm, the
solvent volume at 250 ml, and the sample weight at 50 g constant.
Optimization of Turmeric oil Extraction Process.
This study aimed to optimize turmeric oil extraction using the Soxhlet apparatus, focusing on two key parameters: temperature
and extraction time, with a solvent-to-sample ratio of 1:5.
Effect of Temperature on Oil Yield
Temperature plays a critical role in Soxhlet extraction efficiency. As temperature rises, the solubility of essential oils in the
solvent improves, boosting the extraction rate. In this study, temperatures were varied between 343 and 353 K. From table 3, the
oil yield increased from 5.60 % to 6.00 % after 5 hours at 343 and 353 K, similarly, oil yield increased from 6.20 % to 6.50 %
after 6 hours at 343 to 353 K. The higher temperature of 353 K greatly enhanced the diffusion of essential oils from the turmeric
rhizomes into the solvent, improving extraction efficiency. However, higher temperatures aid extraction, they also risk thermal
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degradation of sensitive compounds like curcuminoids, which are responsible for turmeric’s health benefits. The temperatures of
343 and 353 K were optimal for increasing oil yield without causing significant degradation of bioactive components.
Temperatures exceeding 353 K could lead to the breakdown of volatile compounds, negatively impacting the oil's quality (Chang
et al., 2021).
Table 2: Experimental oil yield at various temperature, time and location in southern Kaduna.
Oil Yield (%)
Temperature
323 K
333 K
343K
353K
Time (min) Location
60 A
B
C
D
1.20
1.40
1.60
1.80
1.50
1.90
2.00
2.20
1.70
2.10
2.20
2.40
2.00
2.20
2.40
2.60
120 A
B
C
D
2.20
2.40
2.50
2.70
2.30
2.50
2.60
2.80
2.50
2.70
2.80
3.20
2.60
2.90
3.30
3.60
180 A
B
C
D
2.30
3.20
3.60
3.70
2.50
3.60
3.90
4.00
2.70
3.80
4.10
4.20
3.00
4.10
4.50
5.20
240 A
B
C
D
3.60
4.20
4.40
5.40
3.80
4.40
4.60
5.60
4.00
4.60
4.80
5.80
4.20
4.80
5.00
6.00
300 A
B
C
D
4.00
5.00
5.40
6.00
4.20
5.30
5.50
6.20
4.40
5.50
5.90
6.60
4.80
5.80
6.50
6.90
360 A
B
C
D
5.20
5.30
6.20
6.50
5.40
5.50
6.40
6.70
5.60
5.80
6.60
6.80
5.80
6.20
6.80
7.20
(Source: Laboratory work 2025)
Key: A= Kachia LGA, B=Jaba LGA, C= Kagarko LGA and D= Kajuru lGA
Table 3: Average Experimental oil yield at various temperature, time and location in southern Kaduna
Oil Yield (%)
Temperature Time (min)
323 K
333 K
343 K
353 K
60
1.50
1.90
2.10
2.30
120
2.45
2.55
2.80
3.10
180
3.20
3.50
3.70
4.20
240
4.40
4.60
4.80
5.00
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300
5.10
5.30
5.60
6.00
360
5.80
6.00
6.20
6.50
(Source: Laboratory work 2025).
Effect of Extraction Time on Oil Yield
Extraction time is another crucial factor in Soxhlet extraction. Table 3 revealed that extending the extraction time from 5 hours at
343 K to 6 hours at 353 K increased the oil yield. Extraction follows mass transfer principles, where the solvent dissolves more
essential oils as it cycles through the plant material. The 6-hour extraction at 353 K produced a higher yield, suggesting that
longer extraction times allow for more efficient extraction of oils. Extending extraction time gives the solvent more opportunities
to interact with the plant material, dissolving more oil (Singh et al., 2021). However, after a certain point, the yield increase
becomes minimal, and longer extraction times may lead to over-extraction, which could extract unwanted compounds that affect
the oil's purity. The 5-hour extraction at 343 K yielded 5.6 %, indicating that a shorter extraction time could provide near-optimal
yields without extending the process further.
Effect of Solvent-to-Sample Ratio
A 1:5 solvent-to-sample ratio was maintained throughout the experiment, meaning 5 mL of solvent was used for every gram of
turmeric rhizome. This ratio is vital in Soxhlet extraction as it affects the efficiency of the process. A higher solvent volume
increases the contact area between the solvent and plant material, potentially improving oil yield. However, excessive solvent use
can dilute the oil, complicating its recovery and raising extraction costs (Michaud et al., 2020). The 1:5 ratio used in this study
seemed to strike an optimal balance, providing enough solvent to dissolve essential oils while minimizing wastage. It also ensured
efficient mass transfer during extraction, leading to higher yields.
Comparing Soxhlet extraction with alternative methods such as supercritical CO₂ extraction and Microwave-assisted extraction.
On efficiency soxhlet extraction method is known for its high extraction efficiency, especially when dealing with non-polar
compounds. However, it requires extended extraction periods, ranging from several hours to even days, and involves a substantial
amount of solvent usage (López et al., 2017). While supercritical CO₂ extraction method is environmentally friendly and highly
efficient, particularly for extracting lipids and essential oils. The process is faster than Soxhlet and requires fewer solvents, which
can be recovered and reused, making it a more sustainable option (Zhang et al., 2019). Microwave-assisted extraction enhances
extraction efficiency by utilizing microwave energy to directly heat both the solvent and sample. This method significantly
reduces extraction time and enhances yield compared to Soxhlet (Zhao et al., 2020). On energy consumption soxhlet method is
energy-intensive due to its continuous need for heating and cooling of solvents, which results in high operational costs (Chemat et
al., 2017). While supercritical CO₂ extraction is more energy-efficient as it uses CO₂ in its supercritical state, which typically
operates at lower temperatures than Soxhlet. This results in lower overall energy consumption (Baker et al., 2019). Microwave-
assisted extraction is an energy-efficient method because it directly heats the solvent and sample using microwave radiation,
reducing both energy use and extraction time (Huang et al., 2020).
On environmental impact, soxhlet extraction significant use solvents and it poses potential environmental risks associated with
their disposal. Additionally, the high energy demand increases its environmental footprint (Chemat et al., 2017). While
supercritical CO₂ is non-toxic, non-flammable and recyclable, making it an environmentally sustainable choice. This method
minimizes environmental impact compared to traditional solvent-based extraction methods (Zhang et al., 2019). Although Micro-
assisted extraction still requires some solvents, it uses considerably less solvent than Soxhlet extraction and is more energy-
efficient, which results in a lower overall environmental impact (Huang et al., 2020). On scalability soxhlet extraction is suitable
for small-scale extractions, Soxhlet becomes less practical for large-scale applications due to the need for larger equipment and
increased solvent consumption, leading to higher costs (López et al., 2017). While supercritical CO₂ extraction is highly scalable
for industrial use. It offers faster extraction times and higher throughput, making it ideal for large-scale commercial production
(Baker et al., 2019). Microwave-assisted extraction can be scaled up to handle larger volumes with systems capable of processing
higher loads. However, scalability may be limited by the size of the microwave units, which could restrict its use for very large-
scale extractions (Zhao et al., 2020).
Table 4; Calculated Turmeric oil Kinetic Model Values
First Order
Second Order
Pseudo First Order
T K
k
1
C
o
)
R
2
k
2
C
O (10
12
)
R
2
kʼ
1
(10
-3
)
qe(10
12
)
R
2
323
6.2181
2.0488
0.9707
0.0011
3.6296
0.5409
6.5372
2.3167
0. 6576
333
6.7575
5.1577
0.7516
0.0091
5.0303
0.7771
5.4584
2.4167
0. 5467
343
8.3696
4.4844
0.7172
0.0072
6.9412
0.6219
7.3969
3.4852
0. 8402
353
5.2969
2.9478
0.9349
0.0015
5.0000
0.7287
6.5372
3.5193
0. 9630
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Pseudo Second Order
Intra Particle Diffusion Model
Power Law Model
T K
kʼ
2 (10
-3
)
q
e (10
12
)
R
2
k
id (10
-3
)
I
R
2
B (10
-3
)
N
R
2
323
6.3182
2.8848
0.9907
2.5117
0.5839
0.7197
8.2635
0.2207
0.8164
333
6.6576
3.4222
0.9616
2.2818
0.6810
0.8436
6.6732
0.4658
0.7515
343
6.3969
4.4036
0.9502
2.3514
0.8204
0.9337
6.2097
0.6191
0.7403
353
6.6273
4.5208
0.9388
2.4817
0.9669
0.8188
6.8732
0.6589
0.9286
(Source; laboratory work 2025).
The regression (R²) values indicated that the oil extraction process followed a pseudo-second-order kinetic model. This type of
reaction occurs when a second-order reaction involves a reactant in excess, making its concentration effectively constant
throughout the reaction. In this case, hexane was used as the solvent and was in excess, with its concentration remaining constant
during the extraction process. The pseudo-second-order model, which is useful for describing chemisorption (chemical
adsorption) phenomena, is particularly applicable to essential oil extraction from plant materials (Zhang et al., 2018). The rate
constants for turmeric oil extraction ranged from 0.0063182 g/l min to 0.0066576 g/l min. These relatively low rate constants
suggest that the extraction process is governed by slower adsorption and desorption interactions, characteristic of pseudo-second-
order behavior, where chemisorption plays a significant role (Rahman et al., 2018).
Additionally, the adherence to pseudo-second-order kinetics highlights the importance of considering both external and internal
mass transfer resistances during extraction. Factors such as particle porosity, the solubility of oil constituents and solvent
diffusivity all influence the extraction kinetics. Optimizing these factors by controlling process conditions more precisely could
improve the overall efficiency of Soxhlet extraction (Ali et al., 2020; Wang et al., 2021). The pseudo-second-order kinetic model
provides a strong framework for understanding and optimizing essential oil extraction. By accounting for chemisorptive
interactions and process variables, this model allows for better control and predictability of the extraction process, which is
crucial for both small-scale and industrial applications (Ahmed et al., 2022).
Figure 1; Graph of In da/t vs In A for turmeric oil extraction process. (Source; laboratory work 2025).
Figure 2; Graph of Ink vs 1/T for turmeric oil extraction process. (Source; laboratory work 2025).
y = -697.34x - 0.2395
R² = 0.9431
-2.45
-2.4
-2.35
-2.3
-2.25
-2.2
0.0028 0.00285 0.0029 0.00295 0.003 0.00305 0.0031 0.00315
ln da/t
In A
ln da/t vs In A
y = -1032.5x + 0.7783
R² = 0.958
-2.45
-2.4
-2.35
-2.3
-2.25
-2.2
-2.15
-2.1
0.0028 0.00285 0.0029 0.00295 0.003 0.00305 0.0031 0.00315
ln k
1/T
ln k vs 1/T
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Table 5; Calculated Thermodynamics Properties
SAMPLE
A
Ea (kj/molK)
∆H°(kj/mol)
∆S° (kj/molK)
∆G° (kj/mol)
323K
333K
343K
353K
TURMERIC OIL
+4.1752
+18.8327
+19.6389
+0.008710
+17.4941
+17.5278
+17.6819
+17.8959
(Source; laboratory work 2025).
The Arrhenius factor (pre-exponential factor) for turmeric oil extraction is 4.1752 min
-1
, indicating the frequency of effective
collisions or successful interactions between molecules during the extraction. This moderate value suggests that the interaction
between the solvent and the turmeric matrix is relatively efficient, contributing to a consistent rate of extraction under Soxhlet
conditions (Nguyen et al., 2019). The activation energy (Ea), which represents the minimum energy needed for a chemical
reaction to occur, was observed to be 18.8327 kj/molK. This relatively low activation energy suggests that the extraction process
requires moderate energy input, meaning the process can proceed at moderate temperatures, minimizing energy requirements
(Sharma & Gupta, 2022). The Soxhlet extraction process relies on repeated solvent refluxing and its interaction with the turmeric
matrix, which helps release the oil compounds. The low activation energy aligns with the continuous contact and solubilization
enabled by this extraction method (Fang et al., 2021).
The enthalpy change (∆H) of 19.6389 kj/mol indicates that turmeric oil extraction is an endothermic process. This means the
process absorbs heat from the environments to breakdown bonds in the turmeric matrix and simplify oil release (Smith & Jones,
2018). In endothermic reactions, temperature is a vital driver for the extraction process, as it increases molecular motion and
enhances interactions between the solvent and turmeric matrix, potentially improving yields (Barbosa & Mendes, 2020). The
positive enthalpy value is consistent with other plant oil extractions, where thermal energy is required to break down plant cell
structures and release volatile compounds (Sulaiman & Abdullah, 2017). Thus, optimizing the temperature for Soxhlet extraction
is essential to maximize oil yield while ensuring energy efficiency. The continuous heat supply in the Soxhlet apparatus makes it
ideal for endothermic extractions of turmeric oil.
The entropy change (∆S) of 0.008710 kj/molK indicates an intensification in randomness during the extraction process, as the
turmeric oil moves from a bound state in the plant matrix to a more dispersed state in the solvent. This increase in entropy is
consistent with the disruption of cellular structures and the release and diffusion of essential oil compounds (Martinez & Hall,
2019). The positive entropy value suggests that the process naturally progresses toward a state of greater disorder, which
facilitates the solubilization and diffusion of turmeric oil into the solvent (Nguyen et al., 2019).
Gibbs free energy (∆G) is a critical thermodynamic parameter that indicates whether a process is spontaneous. The ∆G values for
the extraction process at various temperatures are: 17.4941 kj/mol at 323 K, 17.5278 kj/mol at 333 K, 17.6819 kj/mol at 343 K,
and 17.8959 kj/mol at 353 K. The positive ∆G values suggest that the extraction process is non-spontaneous at standard
conditions. However, the decreasing ∆G values with growing temperature indicate that the process becomes more
thermodynamically favorable at higher temperatures (Lin & Chen, 2017). This is steady with the endothermic nature of the
reaction, where higher temperatures provide the necessary energy to overcome thermodynamic barriers and drive the process
(Zhao et al., 2019). The gradual increase in ∆G values from 323 K to 353 K suggests that increasing the temperature improves the
feasibility of the extraction process, highlighting the importance of temperature optimization to enhance the extraction efficiency
of turmeric
Technically, Activation energy refers to the minimum energy required to initiate the extraction process. A lower activation energy
indicates that less energy is needed for the extraction, making the process more efficient. Techniques that heat the solvent more
effectively, such as microwave-assisted extraction, typically exhibit lower activation energies, resulting in greater energy
efficiency (Huang et al., 2020). Entropy measures the degree of disorder or randomness within a system. Extraction methods that
minimize energy waste and involve fewer steps, like supercritical CO₂ extraction, usually have lower entropy. This is because
such processes are more controlled and efficient, leading to a reduction in the overall randomness of the system (Baker et al.,
2019). Gibbs free energy indicates the spontaneity of an extraction process. A lower Gibbs free energy suggests that the process is
more thermodynamically favorable and energy-efficient. Techniques like microwave-assisted extraction, which reduce extraction
time and energy consumption, are typically associated with a more favorable Gibbs free energy (Zhao et al., 2020).
IV. Conclusion
The optimization of the Soxhlet extraction process for turmeric oil revealed key insights into how temperature and extraction time
impact oil yield. The study showed that increasing both temperature and extraction time resulted in higher oil yields, with the
maximum yield achieved at 353 K for 6 hours using a 1:5 solvent-to-sample ratio. The kinetic and thermodynamic analyses
indicated that the extraction follows pseudo-second-order kinetics, with the rate constant influenced by temperature. The positive
entropy value suggests increased randomness during the extraction, while the positive enthalpy and Gibbs free energy changes
confirm that the process is endothermic and non-spontaneous. Further research is recommended to better understand the
relationship between the physicochemical properties of the oil and its chemical composition or biological activity.
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Acknowledgement
The authors acknowledge the technical support provided by the laboratory technologist in the Department of Chemistry, Ahmadu
Bello University Zaria, Nigeria. The authors also appreciate the financial support from IBR-Tetfund for this research.
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