Extraction of oil from Terminalia catappa L.: Process parameter impacts, kinetics, and thermodynamics

Industrial Crops and Products 77 (2015) 713–723

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Extraction of oil from Terminalia catappa L.: Process parameter impacts, kinetics, and thermodynamics Matthew C. Menkiti a,b,∗ , Chinedu M. Agu b , Theophilus K. Udeigwe c a b c

Department of Civil and Environmental Engineering, Water Resources Center, Texas Tech University, Lubbock, Texas, USA Department of Chemical Engineering, Nnamdi Azikiwe University, Awka, Nigeria Department of Plant and Soil Science, Texas Tech University, Lubbock, Texas, USA

a r t i c l e

i n f o

Article history: Received 16 March 2015 Received in revised form 6 August 2015 Accepted 10 August 2015 Keywords: Terminalia catappa L. Solvent extraction Kinetics Thermodynamics

a b s t r a c t The effects of temperature, time, solvent type, and particle size on oil yield as well as the effects of these parameters (particle size, time, and temperature) on the kinetics and thermodynamics parameters (enthalpy, entropy, and free energy) of oil extraction from Terminalia catappa L. kernel (TCK) were investigated. Among the different extractions solvents examined, n-hexane gave the highest oil yield of 60.45% (by weight) at 55 ◦ C, 150 min, and 0.5 mm particle size. Findings from the physicochemical properties investigation revealed that the viscosity, acidity, and dielectric strength of the TCK oil were 20.29 mm2 s−1 , 4.73 mg KOH/g oil, and 30.61 kV, suggesting the potential suitability of TCK oil as transformer oil. Analysis of the chemical composition of the TCK oil indicated that it is composed of 43.89% and 56.1% saturated and unsaturated fatty acids, respectively. The kinetics of the TCK oil extraction was better described by the pseudo second order model compared to hyperbolic and Elovich models. The G, S, and H values of the TCK oil extraction process were −28.76 kJ/mol, 0.643 kJ/mol, and 182.81 kJ/mol, respectively, indicating spontaneous, irreversible, and endothermic process. © 2015 Published by Elsevier B.V.

1. Introduction Terminalia catappa (TC) is a tree in the Combretaceae family, with a Meridional Asia origin (Cavalcante et al., 1986). It is a large, spreading tree distributed throughout the tropics in coastal environments. The tree grows principally in freely drained, wellaerated sandy soils (Dos Santos et al., 2008). It is mainly found in the southern part of Nigeria, especially in the south-east where they are mainly planted for provision of shade and ornamental purposes (Ezeokonkwo and Dodson, 2004; Agu, 2014). It produces lots of seeds seasonally that are usually consumed minimally as edible fruit, with little attention given to the utilization of the kernels. Hence, the need to evaluate the potential useful application of the kernel, specifically as a raw material for transformer oil production (Agu, 2014). T. catappa kernel (TCK) oil can be extracted by mechanical process or by solvent extraction method (Liu et al., 2009; Amin et al., 2010; Sriti et al., 2011; Sulaiman et al., 2013). Usually, high yield and low turbid oil is obtained using solvent extraction when com-

∗ Corresponding author. E-mail addresses: [email protected], [email protected] (M.C. Menkiti). http://dx.doi.org/10.1016/j.indcrop.2015.08.019 0926-6690/© 2015 Published by Elsevier B.V.

pared to the mechanical process (Amin et al., 2010; Sulaiman et al., 2013). The disadvantage of solvent method is the residual solvent left after the extraction (Chiu et al., 2002; Liu et al., 2009; Agu 2014). N-hexane and petroleum ether are the commonly used solvents for this purpose because of their very high volatility (Sayyar et al., 2009). A number of previous studies have been conducted on the kinetics of oil extraction (Sulaiman et al., 2013; Amarni and Kadi, 2010; Perez et al., 2011). It has been shown that the kinetics of oil extraction using solvent extraction method is highly dependent on the type of solvent, temperature, time, particle size, and solute to solvent ratio (Sayyar et al., 2009; Sulaiman et al., 2013; Agu, 2014). Currently, there is limited study and diffuse information on how these process parameters affect the oil yield of TC kernel and its suitability for use as a transformer fluid. Such information on the effect of process parameters could be vital for optimization of oil extraction under industrial settings. Thus, the objectives of this study were to (1) evaluate the effects of temperature, solvent type, time, and particle size on the oil yield of T. catappa L., and then (2) determine its suitability for use as transformer oil. The physicochemical properties and fatty acid composition of extracted oil was also characterized and the former compared to those in literature. Experimental data were fitted to three kinetic models, namely pseudo second order, hyperbolic, and Elovich to investi-

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Nomenclature ASTM A.O.A.C A.O.C.S GC IEC TC TCK DS RMS TO SD

American Society for Testing and Material Association of Official Analytical Chemist. American Oil Chemist’s Society Gas chromatography International Electrotechnical Commission Terminalia catappa Terminalia catappa kernel Dielectric strength Root mean square Transformer oil Standard deviation

gate how the process parameters related with process kinetics. In addition, the fitting of each model to the experimental kinetic data was estimated using correlation coefficient (R2 ), the root mean square (RMS), and standard deviation (SD). Finally, thermodynamic parameters (entropy, enthalpy, and Gibb free energy) were determined. 2. Materials and methods 2.1. Materials T. catappa seeds were picked from Nsukka, Enugu State, Nigeria. Analytical grade solvents (N-hexane, benzene, chloroform, ethanol, and petroleum ether with boiling point range of 60–80 ◦ C) used for the extraction were purchased from laboratory chemical vendor in Enugu. All reagents were used without further purification.

Table 1 Extraction kinetic model equations. Model

Non-linear

Linear

Hyperbolic

C1 t q¯ = 1 + C2 t

1 1 c2 1 = × + c1 t c1 q¯ q¯ = E0 + E1 Int t 1 t = + Ct CS KC 2

Elovich’s Pseudo second order

dC t 2 = k(Cs − Ct ) dt

S

was extracted. The extract leached through the pores of the thimble and filled the siphon tube. It then flowed down into the round bottom flask. This was allowed to continue for different extraction times (30, 60, 90, 120 and 150 min). It was then removed from the tube, dried in the oven, cooled in the desiccators and the amount of oil extracted was determined. The oil yield was calculated using AOAC method no. 920.85. After each extraction process, the solvent was removed in each case at 60 ◦ C using rotary evaporator (model N- 1000S-W, EYELA, Tokyo, Japan). These extraction temperatures were chosen because they were below the boiling point of the solvents used. The above stated procedure was used for the other four solvents (chloroform, ethanol, petroleum ether and benzene) for oil extraction from TC kernels. The solute to solvent ratio used for the entire extraction was 1:5 (15 g:150 ml). Similarly, the extraction times were 30, 60, 90, 120 and 150 min. The entire extraction process carried out under every set of conditions was performed three times and the average values reported, while the total extraction yield was obtained using the earlier stated standard method. The oil yield of T. catappa L. was calculated using Eq. (1). %Oil yield =

weight of oil extracted (g) × 100 weight of TC kernel (g)

(1)

2.2. Methods 2.2.1. Sample preparation The external coatings of the TC seeds were carefully cracked and the kernels were removed and cleaned. The kernels were then oven dried to a constant weight at 60 ◦ C for 24 h. The dried kernels were then milled using manual hand grinder and separated with five different sieve plates of sizes: 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, and 2.5 mm to obtain 5 different average particle sizes of 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm and 2.5 mm, respectively. 2.2.2. Oil extraction by solvent extraction method Oil extraction from the milled TC kernels was carried out according to Association of Official Analytical Chemists (AOAC) 963.15 method (AOAC, 1990) using soxhlet extractor unit for the five different average particle sizes. Soxhlet extractor was chosen in order to enhance the solubility of TC kernels in the chosen solvents used. 15 g of milled kernels of a particular average particle size was packed in a thimble of the soxhlet extractor and the extractor was filled with 150 ml of n-hexane. Oil extraction was performed at temperatures of 35 ◦ C, 40 ◦ C, 45 ◦ C, 50 ◦ C, and 55 ◦ C using n-hexane and five average particle size (0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm and 2.5 mm). At every temperature, extraction was carried out for 30, 60, 90, 120, and 150 min. The oil yield obtained at the end of every extraction time for every extraction condition was calculated and recorded. The extraction temperature was measured using an electronic thermometer (Hanna HI-9063) while the time was measured using a stop watch. The extractor was then heated to and held constant at a particular chosen temperature (e.g., 55 ◦ C). As the solvent starts to boil, the vapor rose through the vertical tube of the extractor into the condenser at the top of extractor. This makes the liquid condensate and then drip into the filter paper thimble in the center that contained the milled TC kernels sample from where the oil

2.2.3. Physicochemical properties of TCK oil The analyses were done using crude TCK oil extract. The oil density (AOAC 985.19), iodine value (AOAC 993.20) and acid value (AOAC 969.17), were determined following AOAC approved techniques (AOAC, 1990). Oil viscosity and dielectric strength were measured according to ASTM D445 (2011) and IEC 60156 (2003) standard methods, respectively. Each measurement was carried out three times and t average values reported.

2.2.4. Fatty acid composition of the seed oil The fatty acid profile was determined according to AOAC 996.06 (AOAC, 1990). In the method, fatty acid methyl esters were identified with gas chromatography unit (Model 910) equipped with a flame ionization detector and integrator. The injector and detector temperature was 250 ◦ C, and the oven temperature was kept at 190 ◦ C for 15 min and subsequently increased to 230 ◦ C at the rate of 5 ◦ C/min for 15 min. Nitrogen was used as the carrier gas at a pressure of 500 kPa. The fatty acid methyl esters were identified and compared with standard compounds. The quantity of each fatty acid was estimated from the percentage area of the individual fatty acid methyl ester (Zahedi and Azarpour, 2011; Liu et al., 2009). The analysis was conducted in triplicate.

2.3. Kinetics of oil extraction Kinetic parameters were calculated from linearized fms of the models (Table 1) using linear regression. The best fit among the kinetic models was evaluated using coefficient of determination (R2 ), root mean square (RMS) (Kitanovic et al., 2008), and standard deviation (SD) (Rahmanian et al., 2011). The root mean square

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(RMS) was calculated using Eq. (2), while standard deviation (SD) was calculated using Eq. (3):



RMS =

   SD = 

1 N N i=1

1 N−1

N 



q¯ exp − q¯ cal q¯ exp

2 (2)

hydrocarbons from soil contaminated with coal tar (Paterson et al., 1999). A plot of yield q¯ verse In t gives E0 as the intercept and E1 as the slope. Where E0 , E1 are Elovich equation parameters (L). 2.6. Pseudo second order model

2

|

715

¯ ¯ qexperimental (i) − qcalculated (i) | − AARE ¯ qexperimental (i)

(3)

For a second-order rate law, the rate of dissolution of the oil contained in the solid into the solvent can be described by Eq. (11).

i=1

Absolute average relative error (AARE) was calculated using Eq. (4).





¯ ¯ 1  qexperimental (i) − qcalculated (i) | AARE = | × ¯ N qexperimental (i) N

(4)

i=1

The higher the value of R2 and the lower the values of the RMS and SD; the better will be the goodness of fit (Kitanovic et al., 2008). These kinetic models are summarized in Table 1 and are briefly described below:

The hyperbolic model is a kinetic model that is applied in food engineering science as pelegs model: q=

c1 t 1 + c2 t

(5)

It has been used lately to model resinoid extraction from aerial parts of St. John’s wort (Hypericum perforatum L.) as well as to model the extraction of total polyphenols from grapes. (Kitanovic et al., 2008). Hyperbolic model equation was developed from a second order rate law and it was successfully used to model protopine extraction from Fumaria officinalis L. (Rackotondramasy et al., 2007). The extraction is first-order at the beginning,ndreases to zeroorder in the later phase of the process. When C2 t « 1. q¯ ≈ C1 t

(6)

and when t → ∞, the equilibrium. is reached (qi = qe ), so q¯ e =

qe c1 = qo c2

(7)

Eq. (8) is obtained when hyperbolic model equation is linearized. c2 1 1 1 = × + c1 t c1 q¯

(8)

The plot of 1/q¯ that is 1/yield against 1/t gives intercept as C2 /C1 and the slope as 1/C1 . C1, and C2 are hyperbolic model parameters: extraction rate at the beginning (min−1 ) and constant related to maximum extraction ¯ respectively. yield (min−1 ), q, 2.5. Elovich’s equation

(9)

The equation is derived under the assumption that the rate of extraction decreases exponentially with increasing extraction yield: dq¯ ¯ = ˇ × exp(−˛q) dt

(12)

By considering the boundary condition t = 0 to t and Ct = 0 to Ct , the integrated rate law for pseudo second-order extraction was obtained: Ct =

C2s kt 1 + Cskt

(13)

The linearized form of Eq. (13) is: 1 t t = + Ct Cs KCs2

(14)

The initial extraction rate, h, the extraction capacity, Cs and the pseudo second order extraction rate constant, k, can be calculated experimentally by plotting t/Ct versus t (Muhammad et al., 2012). 2.7. Thermodynamic parameters Thermodynamic parameters (H, S and G) were estimated using Eqs. (15)–(17) (Liauw et al., 2008): G = −RT In K

(15)

S H + InK = − RT R

(16)

YT mL = Yu ms

(17)

K=

where K is equilibrium constant, YT is the yield of oil at temperature T, Yu is the percentage of the unextracted oil, mL is amount of TC in liquid at equilibrium temperature T, ms is amount of TC in solid at equilibrium temperature T, R is gas constant (8.314 J/mol K), while H (kJ/mol), S (kJ/mol), and G (kJ/mol) are enthalpy change, entropy change and Gibbs free energy change, respectively (Liauw et al., 2008). 3. Results and discussion

Elovich’s equation is written as a logarithmic relation as: q¯ = E0 + E1 × Int

(11)

where: K = the second-order extraction rate constant (L g−1 min−1 ), Cs = the extraction capacity (concentration of oil at saturation in g L−1 ), Ct = the concentration of oil in the solution at any time (g L−1 ), t (min). The initial extraction rate defined as h when t and Ct approach 0 can be expressed as h = kCS2

2.4. Hyperbolic model

−

dCt = k(Cs − Ct )2 dt

(10)

where ˇ = E1 × exp(E0 /E1 ) and ˛ = 1/E1 . When q¯ → 0, then ¯ (dq/dt) → ˇ, thus ˇ is the initial extraction rate. Elovich’s equation has been used to model the extraction of polycyclic aromatic

3.1. Characteristics of TCK oil The oil yield of TCK was found to be 60.45% (in mass), which was higher than the value reported for cottonseed (Khan et al., 2010), and soybean (Lawson et al., 2010), thus, signifying a potential economic benefit. However, Iha et al. (2014) reported 50% (in mass) for the TCK obtained from Brazil’s coastal region. This value was lower than that obtained in this work. This difference in the oil yield could be attributed to factors such as geographical location, seed variety, and harvest period (Berti et al., 2011; Ejikeme et al., 2010).

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Table 2 Physicochemical properties of the TCK oils Oil property

TCa

TCb

Standard spec. for mineral TO

Standard method

Oil yield (%) Dielectric strength (kV) Viscosity (mm2 s−1 ) Acidity (mg KOH/g oil) Density at 20 ◦ C (gm−3 ) Iodine value (g/I2 /100g oil)

60.45 30.61 20.29 4.73 890 101.86

50 – 36.8 10.5 913 –

– 40 - 60 10 0.5 870 –

IEC 60156 ASTM D445 AOCS CD 3d-63 ASTM D 1298 AOCS CD 1c-85

– Not reported, TO: transformer oil, Spec: specifications. a Experimental value. b Iha et al. (2014). Table 3 Fatty acid composition of the TCK oil. Fatty acid

TC a

TCb

C12:0 (lauric acid) C14:0 (myristic acid) C16:0 (palmitic acid) C16:1 (palmitoleic acid) C18:0 (stearic acid) C18:1 (oleic acid) C18:2 (linoleic acid) C18:3 (linolenic acid) Saturated fatty acids (%) Mono-unsaturated fatty acid (%) Poly-unsaturated fatty acid (%)

0.94 0.54 36.01 – 6.4 33.25 22.26 0.59 43.89 33.25 22.85

– 0.10 28.30 0.90 4.90 30.00 32.80 1.70 34.20 30.00 34.50

– Not detected. a Experimental value. b Iha et al. (2014).

Some selected important physicochemical properties of TC kernel oil shown in Table 2, were determined and compared with those reported by Iha et al., (2014). It could be observed from Table 2 that the viscosity and acidity of TCa (experimental value) oil differ greatly from that of TCb (Iha et al., 2014) oil, with the later having higher viscosity and acidity than the former. The high oil yield and the low acid value of TCa oil could be attributed to the breed of T. catappa L. Thus, breeds of T. catappa L. enhance its yield and oil properties. The iodine value (IV) of the TC kernel oil in this work was higher than the 83.92 g/I2 /100 g oil reported by Dos Santos et al. (2008). This was an indication of the high level of saturation in the oil as could be observed in Table 3. On the other hand, the dielectric strength (DS) value of TCK oil was 30.61 kV. Dielectric strength is the maximum electric field that a pure material/substance can withstand under ideal conditions without experiencing failure of its insulating properties (Derick et al., 2014). This value was lower than that of soybean oil (39 kV) but higher than that of palm kernel oil (25 kV) (Usman et al., 2012). The DS value of TCK oil could be improved with further purification and transesterification to obtain TCK oil transformer fluid (Agu, 2014). Generally, oil with high DS is required for proper insulation and cooling in the transformer since its insulating properties are not easily lost with time during transformer usage. The introduction of natural antioxidant additives would further improve the DS (Agu, 2014). The densities of TCK oil sample in Table 2 was 890 g/cm3 . This density was lower than that of TCb oil reported by Iha et al., (2014) . Fatty acid composition of the TC kernel oil, determined by GC, is presented in Table 3, and compared with that reported by Iha et al., (2014). From the results in Table 3, it could be observed that more than 40% of the TCa kernel oil was composed of saturated fatty acid as compared to approximately 34% in TCb oil reported by Iha et al. (2014). The result of the fatty acid composition for TC kernel oil obtained in this work was in close agreement with those reported by Dos Santos et al. (2008) and Iha et al., (2014). Furthermore, it could be observed that TCa had lauric acid as well as high level of other saturated fatty acid, unlike the TCb . This could most likely be

Fig. 1. Effect of time and particle size on the yield of TC oil at: (a) 45 ◦ C, (b) 50 ◦ C and (c) 55 ◦ C.

due to factors such as geographical location and variety (Ejikeme et al., 2010). 3.2. Effect of particle size The efficiency of extraction process is generally affected by feed material properties, especially the particle size (Sulaiman et al., 2013; Desai et al., 2014). Therefore, the effect of average particle size on the oil yield of TC was investigated using five different particle sizes. Fig. 1 shows the effect of particle size on oil extraction yield using n-hexane as the solvent. This shows that the smaller particle sizes between 1.0 and 1.5 mm extracted more oil by 1–2%

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when compared to its immediate preceding bigger particle size of 2.0 mm. On the other hand, the smallest particle size of 0.5 mm extracted more oil by 5% when compared with its immediate preceding bigger particle size of 1.0 mm. The increasing oil yield with decreasing particle size could be attributed to the bigger interfacial area of the solid. Thus, intraparticle diffusion resistance becomes lesser for small particle sizes due to the shorter diffusion path. Intraparticle diffusion effect appeared to be more pronounced for bigger particles which caused appreciable decrease in oil extraction. In this situation, some of the oil was not extracted due to minimal contact surface area and difficulty in solvent entrainment as well as small oil diffusion from inside the larger particle to the solution (Sayyar et al., 2009; Sulaiman et al., 2013; Doker et al., 2010). However, the rate of extraction would increase, with greater milling, since more oil would be freed from the cells, making it easily available. This was evidently demonstrated in this study by the particles of smaller sizes for which the rate of oil extraction from TCK increased with decreasing particle sizes, from 2.5 mm to 0.5 mm. As already known, this would be attributed to the increased surface area of the milled TCK with decreasing particle size, leading to high rate of oil dissolution from milled sample into the solvent and increased mass transfer rate due to shortened diffusion path. (Salgin et al., 2006; Louli et al., 2004; Kriamiti et al., 2002; Ozkal et al., 2005; Xue et al., 2009). 3.3. Effect of solvent Five different solvents were used to investigate the effect of solvent on the oil yield of TC. The oil yield of n-hexane, benzene, chloroform, ethanol, and petroleum ether at 55 ◦ C and time of 150 min was given in Table 9. The oil yield using n-hexane was higher when compared to the other solvents under the same conditions. Sayyar et al. (2009) and Sulaiman et al. (2013) reported that extraction of oil from Jatropha seed and solid coconut waste, respectively, using n-hexane had more yield when compared to petroleum ether under the same conditions. The high yield achieved with nhexane could be attributed to the non-polar property of the solvent which facilitated easier penetration into the matrix of the kernel particles during extraction. This was supported by the absence of O H end in solvent which otherwise could have interfered with the extraction (Sulaiman et al., 2013; Nwabueze and Okocha, 2008). Meanwhile, further consideration was given to only n-hexane for the rest of the report. The boiling point and the polarity/polarity index (HPLC solvent Guide, 2002) of the solvent used are shown in Table 9. 3.4. Effect of temperature The findings on oil yield of TCK in n-hexane at five temperatures levels of 35, 40, 45, 50, and 55 ◦ C and time intervals of 30, 60, 90, 120 and 150 min at paricle sizes of 0.5 mm and 1.0 mm are presented in Fig. 2a and b. It is evident from the Fig. 2 that oil yield increased with temperature during the extraction process. This was due to the increase in diffusion of the oil and decrease in viscosity as the temperature increased (Meziane and Kadi, 2008; Eikani et al., 2012; Sulaiman et al., 2013). Similarly, slight increase in temperature caused a marginal decrease in fluid density which led to decline in the solubility of the solute (Roop et al., 1989; Bimakar et al., 2011). Temperature increase would also enhance mass transfer cofficient of extraction and improve the extraction yield (Wang et al., 2008; Bimakar et al., 2011; Sulaiman et al., 2013) The extraction process was rapid at the beginning, between 30 and 90 min and gradually slowed between 90 and 150 min, likely due to internal diffusion. The rapid extraction process at the beginning was due to free oil on the surface of the milled TC kernel that was exposed to fresh solvent. This made the oil to be easily solu-

Fig. 2. Effect of temperature and time on yield at particle sizes of: (a) 0.5 mm and (b) 1.0 mm.

ble in the solvent, thus, fast extraction of the oil (Reverchon and Marrone, 2001; Sulaiman et al., 2013; Agu, 2014). In this study, the extraction yield of oil from TC increased with temperature and time and the highest extraction yields of 60.45% and 49.0% were obtained at temperature of 55 ◦ C and time of 150 min for particle sizes of 0.5 and 1.0 mm, respectively. 3.5. Kinetics of oil extraction Tables 5–7 show the calculated oil yields and kinetic parameters obtained at various temperatures and particle sizes using equations for hyperbolic, Elovich and pseudo second order models presented in Table 1. The kinetic parameters for hyperbolic, Elovich and pseudo second order models were obtained by plotting 1/q¯ against 1/t, q¯ versus Ln t and t/Ct versus t, respectively. Where q¯ represents the oil yields for hyperbolic and Elovich’s models while Ct is the oil yield of pseudo second order model. In addition, t is the extraction time. On the other hand, their calculated yields were obtained by substituting the obtained kinetic parameters into equations for hyperbolic, Elovich and pseudo second order models, presented in Table 1. It was observed that for hyperbolic and pseudo second order models, their kinetic parameters C1 , C2 , K, Cs respectively, increased with increase in temperature, which amply explains the reason behind the increase in the oil yield as temperature increases (Agu, 2014). The yield increase with temperature was due to the thermodynamic effect of oil solubilization in the solid seed particles (Liauw et al., 2008). The graphs plotted using the linear form of the models show a linear relationship with R2 values of 0.9584 and 0.9934 for hyperbolic and pseudo second order models, respectively at particle size of 2.5 mm. The highest R2 values of 0.9888 and 0.9995 were obtained for hyperbolic and pseudo second order models, respectively, on particle size of 0.5 mm. The maximum calculated oil yields of 58.84% and 60.08% for both models respectively were obtained at a temperature of 328 K at 0.5 mm particle size. These values were close to the 60.45% obtained experimentally which was an indication that both models fit the extraction of oil from TC kernel using

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Table 4 Comparison of the average percentage RMS, SD and R2 for different kinetic models Kinetic Model

35 ◦ C % RMS

Pseudo second order Hyperbolic Elovich’s a b c

3.95 3.61 3.83

40 ◦ C a

b

2c

45 ◦ C 2

50 ◦ C 2

55 ◦ C 2

% SD

%R

% RMS

% SD

%R

% RMS

% SD

%R

% RMS

% SD

%R

% RMS

% SD

% R2

0.225 0.315 0.765

99.49 97.69 94.18

3.69 3.28 4.25

0.604 0.712 0.81

99.49 97.25 93.1

2.74 2.96 3.67

0.393 0.404 0.568

99.66 97.7 93.82

2.43 2.66 3.38

0.328 0.456 0.411

99.73 98.07 94.23

2.25 2.57 3.28

0.155 0.289 0.4

99.87 97.58 93.64

Root mean square calculated by Eq. (2) (±), %. Standard deviation calculated by Eq. (3), %. Linear correlation coefficient, %.

n-hexane. Therefore, it could be considered that variation in particle size, extraction time, temperature and solubilizing power of solvent significantly influence oil yield (Giri and Sharma, 2000; Agu, 2014). On the other hand, the kinetic parameters E0 and E1 for Elovich model followed different trend with temperature increase. While E0 increased with increase in temperature like the hyperbolic and pseudo second order models, E1 did not have a definite trend as could be observed in Table 6. This indefinite trend observed for kinetic parameter E1 also resulted in generally lower linear correlation coefficient (R2 ) (Table 6) obtained for Elovich model when compared with those of the hyperbolic and pseudo second order models. Still in the case of Elovich model, the maximum calculated oil yield of 60.50% for this model was obtained at a temperature of 328 K on 0.5 mm particle size. This value was slightly above the 60.45% obtained experimentally which was an indication that the model fit the extraction of oil from TC using n-hexane (Agu 2014).

3.6. Comparison of the kinetic models Linear coefficient of determination (R2 ), root mean square (RMS), and standard deviation (SD) were used to evaluate how well models represent the experimental data and to choose the best model. Fig. 3 shows the values of the RMS in the form of histograms for each kinetic model and for all extraction conditions while Table 4 summarizes the percentage average values of the RMS, SD and the linear correlation coefficient for each model. From the histograms in Fig. 3(a)–(c), it was evident that irrespective of the particle size used, individual values of the average RMS were less than ±5% for each of the three models considered. On the other hand, from the histograms in Fig. 5(a)–(c), it was also obvious that regardless of the particle size used, individual values of the average SD were less than 0.014 for each of the three models studied. Thus, based on their low RMS and SD, each of the models examined reasonably described the kinetics of oil extraction form TCK. These findings were in line with the result obtained by Kitanovic et al. (2008) for the resinoid extraction from aerial parts of Hyperium perforatum L. Figs. 3(a)–(c) and 5(a)–(c) show the values of the RMS, and SD, respectively in the form of histograms for each kinetic model at different extraction conditions of temperature and particle size. From the plots, it could be seen that in most cases, the least values of the RMS and SD for the models were obtained at the highest extraction temperature of 55 ◦ C and the smallest particle size of 0.5 mm, hence confirming significant correlation of temperature and particle size with related models irrespective of the kinetic model used (Seikova et al., 1999; Agu, 2014). It could be observed from Table 4 that while the average RMS and SD decreased, the best fit of the models increased in the following order; Elovich’s model → hyperbolic model → pseudo second order. Similarly, the average linear correlation coefficient R2 value increased in the following order; Elovich’s model → hyperbolic model → pseudo second order

Fig. 3. (a)–(c) Comparative variation of RMS with temperature and particle size for: (a) pseudo second order (b) hyperbolic (c) Elovich models.

Based on these results, Pseudo second order, having the highest value of the linear correlation coefficient R2 , and lowest RMS and SD values was chosen as the best extraction kinetics model for TCK oil extraction. Therefore, the rank in ascending order of the kinetic models that gave good fit to the experimental data were Elovich’s, hyperbolic and pseudo second order models. Fig. 4 compares the average RMS for the different kinetic models at different temperatures. Similarly, Fig. 6 compares the average SD for the different kinetic models at different temperatures. As

Table 5 Hyperbolic model kinetic parameters for TC oil using n-hexane at 150 min. 0.5 mm

(K)

C1 min−1

C2 min−1

R2

q¯ wt.%

1.0 mm C1 min−1

C2 min−1

R2

q¯ wt.%

1.5 mm C1 min−1

C2 min−1

R2

q¯ wt.%

2.0 mm C1 min−1

C2 min−1

R2

q¯ wt.%

2.5 mm C1 min−1

C2 min−1

R2

q¯ wt.%

308 313 318 323 328

1.47 1.59 1.72 1.97 2.23

2.21 × 10−2 2.33 × 10−2 2.41 × 10−2 2.78 × 10−2 3.13 × 10−2

0.988 0.9888 0.9909 0.9888 0.9854

51.2 52.92 55.95 59.19 58.84

1.69 1.88 2.14 2.41 2.69

3.36 × 10−2 3.59 × 10−2 4.02 × 10−2 4.46 × 10−2 4.76 × 10−2

0.9822 0.9767 0.988 0.9751 0.9788

41.92 44.16 45.62 47.03 49.56

1.61 1.76 2.2 2.3 2.63

3.42 × 10−2 3.61 × 10−2 4.46 × 10−2 4.42 × 10−2 4.95 × 10−2

0.986 0.9719 0.9749 0.9887 0.9772

39.48 41.18 42.86 45.25 46.85

1.57 1.7 2.18 2.39 2.76

3.54 × 10−2 3.64 × 10−2 4.7 × 10−2 4.93 × 10−2 5.5 × 10−2

0.9628 0.9653 0.9585 0.9734 0.9791

37.39 39.5 40.73 42.76 44.78

1.27 1.49 1.75 2.14 2.49

2.89 × 10−2 3.26 × 10−2 3.72 × 10−2 4.53 × 10−2 5.1 × 10−2

0.9657 0.9598 0.9726 0.9782 0.9584

35.79 37.9 39.81 41.12 43.15

Table 6 Elovich model kinetic parameters for TC oil using n-hexane at 150 min. T

0.5 mm

1.0 mm 2

(K)

E0 L

E1 L

R

q¯ wt.%

308 313 318 323 328

−29.52 −27.86 −27.45 −23.7 −20.1

16.36 16.38 16.85 16.43 16.09

0.987 0.9851 0.988 0.9881 0.9877

52.47 54.23 57 58.64 60.5

E0 L −7.23 −5.54 −3.88 0.338 1.2

1.5 mm 2

E1 L

R

q¯ wt.%

9.86 9.95 9.96 9.37 9.76

0.9486 0.9368 0.96 0.9186 0.9366

42.17 44.32 46.04 47.27 50.1

E0 L −6.64 −4.62 −0.116 −1.18 1.78

2.0 mm 2

E1 L

R

q¯ wt.%

9.25 9.18 8.66 9.35 9.1

0.9547 0.9228 0.9248 0.9558 0.9544

39.69 41.4 43.28 45.66 47.35

E0 L −4.18 −4.1 1.65 2.23 5.23

M.C. Menkiti et al. / Industrial Crops and Products 77 (2015) 713–723

T

2.5 mm 2

E1 L

R

q¯ wt.%

8.3 8.74 7.87 8.16 7.97

0.9069 0.9136 0.8945 0.924 0.9216

37.41 39.68 41.06 43.13 45.14

E0 L −7.81 −5.59 −3.87 0.506 4.18

E1 L

R2

q¯ wt.%

8.67 8.67 8.76 8.15 7.81

0.9116 0.8968 0.9238 0.9249 0.8816

35.62 37.84 40.04 41.34 43.31

719

720

Table 7 Pseudo second order kinetic parameters for TC oil using n-hexane at 150 min. T

1.0 mm

0.5 mm 2

2.0 mm

1.5 mm 2

2

2.5 mm 2

K Lg−1 min−1

Cs gL−1

R

Ct wt.%

K Lg−1 min−1

Cs gL−1

R

Ct wt.%

K Lg−1 min−1

Cs gL−1

R

Ct wt.%

K Lg−1 min−1

Cs gL−1

R

Ct wt.%

K Lg−1 min−1

Cs gL−1

R2

Ct wt.%

308 313 318 323 328

2.63 × 10−4 2.86 × 10−4 2.91 × 10−4 3.22 × 10−4 3.54 × 10−4

70.92 71.43 74.07 74.63 75.19

0.998 0.998 0.9989 0.999 0.9995

52.24 53.85 56.59 58.41 60.08

8.1 × 10−4 8.42 × 10−4 8.43 × 10−4 1.06 × 10−3 9.68 × 10−4

48.31 50.25 52.08 51.81 55.25

0.9976 0.9973 0.9987 0.9979 0.9984

41.27 43.41 45.22 46.2 49.05

8.67 × 10−4 9.55 × 10−4 1.11 × 10−3 9.50 × 10−4 1.04 × 10−3

45.45 46.51 47.62 51.02 52.08

0.9976 0.9967 0.9978 0.9989 0.9993

38.89 40.44 42.27 44.85 46.36

1.06 × 10−3 9.94 × 10−4 1.27 × 10−3 1.20 × 10−3 1.35 × 10−3

42.02 44.64 44.83 47.17 48.54

0.9955 0.996 0.997 0.9982 0.9989

36.53 38.81 40.14 42.2 44.05

9.45 × 10−4 1.01 × 10−3 1.01 × 10−3 1.21 × 10−3 1.41 × 10−3

40.65 42.55 44.84 45.25 46.51

0.9934 0.9938 0.997 0.9983 0.9975

34.64 36.84 39.1 40.34 42.22

Fig. 4. Comparative variation of average RMS for different kinetic models and temperatures.

Fig. 5. (a)–(c). Comparative variation of SD with temperature and particle size for: (a) pseudo second order (b) hyperbolic (c) Elovich models.

already stated, the least RMS and SD values were obtained at highest extraction temperature. Fig. 7 compared the average R2 values for the kinetic models at different temperatures. It could be seen that the highest R2 val-

M.C. Menkiti et al. / Industrial Crops and Products 77 (2015) 713–723

(K)

2.04 598.74 5.43 × 105 9.39 × 106 2.21 × 107 3.78 × 109 1.44 × 1012 503.39

1.76

−40.84 −42.87 −56.35 −60.38 −76.30 8.44 × 106 1.43 × 107 1.80 × 109 5.83 × 109 1.42 × 1012 334.95

1.34

−37.09 −43.00 −53.36 −56.02 −64.11 1.95 × 106 1.50 × 107 5.83 × 108 1.15 × 109 1.62 × 1010 344.89

1.24

−38.44 −42.28 −46.88 −59.91 −60.68 3.31 × 106 1.14 × 107 5.02 × 107 4.88 × 109 4.62 × 109 0.643 4.73 × 102 1.11 × 103 2.51 × 103 9.37 × 103 3.81 × 104 308 313 318 323 328

182.81

S kJ/mol H kJ/mol K H kJ/mol K H kJ/mol

S kJ/mol

G kJ/mol

1.0 mm

K

Table 8 shows the values of equilibrium constant and other thermodynamic parameters for the extraction of oil from TCK. Fig. 8 shows the plots of In K vs. 1/T for particle sizes 0.5 to 2.5 mm which were used to determine the values of the thermodynamic parameters. The enthalpy values for the extraction process were in the range of 182.81–598.74 kJ/mol for the different particle sizes. They increased with increase in the kernel particle size. This was due

(K)

3.7. Thermodynamic parameters

0.5 mm

ues were obtained at highest temperature of extraction irrespective of the kinetic model. Thus, as extraction temperature increased, the R2 values increased. Therefore, R2 is a function of extraction temperature for the solvent extraction of oil from TCK.

T

Fig. 8. Plot of In K (equilibrium constant) vs. 1/T (temperature, K) for the five different particle sizes.

Table 8 Thermodynamic parameters for extraction of TC oil using n-hexane.

S kJ/mol

G kJ/mol

K

H kJ/mol

S kJ/mol

G kJ/mol

2.0 mm 1.5 mm

Fig. 7. Comparative average R2 values for different kinetic models and temperatures.

−15.77 −18.24 −20.69 −24.56 −28.76

S kJ/mol H kJ/mol K G kJ/mol

2.5 mm Fig. 6. Comparative variation of average SD for different kinetic models and temperatures.

−33.81 −41.16 −44.70 −59.22 −76.34

721

G kJ/mol

M.C. Menkiti et al. / Industrial Crops and Products 77 (2015) 713–723

722

M.C. Menkiti et al. / Industrial Crops and Products 77 (2015) 713–723

Table 9 Oil yield, boiling point and polarity/polarity index of solvents used. Solvent

Yielda (%)

Boiling point (◦ C)

Polarity

Polarity index1

Hexane Petroleum ether Benzene Chloroform Ethanol

60.45 56.00 48.50 40.00 30.00

68.7 60–80 80.1 61.2 78.37

Nonpolar Nonpolar Nonpolar Polar Polar

0.0 0.1 2.7 4.1 5.2

a

Experimental oil yield values at 55 ◦ C and 150 min.

to more energy required to extract oil from larger seed particles than from smaller ones. The enthalpy in this report, was comparatively higher than those of melon and rubber seed oil studied by Ibemesi and Attah (1990), olive cake oil by Meziane and Kadi (2008) and coconut by Sulaiman et al. (2013), which were in the range (4–13.5 kJ/mol). This could be attributed to the morphology of the seed which could influence oil extraction (Agu, 2014). The positive enthalpy change indicated that the extraction process was endothermic in nature and as such required external energy source during the extraction (Sulaiman et al., 2013; Amin et al., 2010; Topallar, 2000). The entropy of the mixture increased due to extraction of the oil molecules. The positive values of entropy change for the entire process was an indication that the process was irreversible, thus in line with the findings of Amin et al., (2010), Meziane and Kadi (2008), Sulaiman et al. (2013) and Topalla (2000). The entropy values for the extraction of TCK oil using n-hexane was between 0.643 and 2.04 kJ/mol. The free energy values for the extraction were all negative. This was an indication that the process was feasible and spontaneous. The very high negative values of the free energy were an indication that the process was highly spontaneous. From the thermodynamic study, it was evident that energy needed to break the solute–solute and solvent–solvent interactions was lesser than the energy given up in solute–solvent interaction (Sulaiman et al., 2013). 4. Conclusion Findings from this study suggested that n-hexane was the best solvent for the extraction of oil from TC kernel since it gave the highest oil yield compared to the other solvents (benzene, chloroform, ethanol and petrolume ether) examined. Process parameters such as—temperature, extraction, time and particle size as well as the solvent type influenced the yield of TCK oil. Increase in temperature and time led to increase in the oil yield of TCK, provided that the temperature does not exceed the boiling point of the solvent. It could be concluded that the smaller the particle size, the higher the oil yield since the highest oil yield was obtained at the particle size of 0.5 mm. Maximum oil yield of 60.45% was obtained at 55 ◦ C, 150 min, and 0.5 mm using n-hexane. The physicochemical characteristics of TCK oil showed its potential for use as a transformer oil upon further treatment, while the fatty acid composition showed that TC kernel oil was highly unsaturated. The three kinetic models studied: Elovich, pseudo second order, and hyperbolic all reasonably described oil extraction from TC kernel as indicated by high R2 , low RMS, and SD values. Pseudo second order model gave the best fit followed by hyperbolic model, and then Elovich’s model. The G, S, and H values obtained at the five different particle sizes used during the extraction indicated that the extraction process was spontaneous, irreversible, and endothermic, respectively. References AOAC, 1990. Official methods of Analysis, fifteenth ed. Association of Official Analytical Chemists, Washington, D.C, pp. 1990. ASTM D445, 2011. Standard Test Method for Kinematic Viscosity of Transparent and 451 Opaque Liquids (and Calculation of Dynamic Viscosity).

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Further reading Angela, M., Meireles, A., 2009. Extracting Bioactive Compunds for Food Products. Theory and Application. CRC Press, Taylor & Francis Group, 600 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487–2742, London, New York. Anon, 2002. HPLC Solvent Guide. Solvent Miscibility and Viscosity Chart Adapted from Paul Sadek. Wiley-Interscience, pp. 2002. Bucic-Kojic, A., Planinic, M., Tomas, S., Bilic, M., Velic, D., 2007. Study of solid–liquid extraction kinetics of total polyphenols from grape seeds. J. Food Eng. 81, 236–242. Hou, K., Zheng, Q., Li, Y., et al., 2000. Modeling and optimization of herb leaching processes. Comput. Chem. Eng. 24, 1343–1348. Kim, J.Y., Kim, C.L., Chung, C.H., 2002. Modeling of nuclide release from low-level radioactive paraffin waste. A comparison of simulated and real waste. J. Hazard Mater. 94, 161–178. Linares, A.R., Hase, S.L., Vergara, M.L., Resnik, S.L., 2010. Modeling yerba mate aqueous extraction kinetics: influence of temperature. J. Food Eng. 97, 471–477. Nytro, Taurus Electrical Insulating Oil Product Data Sheet. April 4, 2013. Salgin, U., Salgin, S., 2013. Effect of main process parameters on extraction of pine kernel lipid using supercritical green solvents: solubility models and profiles. J. Supercrit. Fluids 73, 18–27. Salgin, U., Uysal, B.Z., Calimli, A., 2004. Supercritical fluid extraction of jojoba oil. J. Am. Oil Chem. Soc. 81, 293–296. Sepidar, S., Zurina, Z.A., Robiah, Y., Azhari, M., 2009. Extraction of oil from Jatropha seeds — optimization and kinetics. Am. J. Appl. Sci. 6 (7), 1390–1395.