3.1. Physicochemical properties of the blended oil
Presented in Table 2 are the datasets of the physicochemical qualities of the blended oil in a different ratio. Observation from the table indicated that the blended oil in the different ratio has the same percentage moisture content of 0.02%, all other blends have different values, except for the BTO50 and BTO85 having the same viscosity (23.10 mm2/s), and BTO25, BTO30, and BTO75 having the same Saponification value (185.00 mg KOH/g oil).
However, since the major key factor in the selection of any oil is the viscosity and the oil specific gravity, therefore the BTO60 with the low viscosity of 22. 30 mm2/s and a specific gravity of 0.890 were selected as blended oil for FAEE production. This blended oil produced lighter oil with low acid value and high API gravity (Adepoju, [24]).
Table 2: Results of physicochemical properties of the oil blend
Blends
|
Physicochemical Properties
|
Ratio (BTO: WUVO)
|
MC (%)
|
SG
|
V @ 40 oC (mm2/s)
|
AV (mgKOH/g oil)
|
SV (mg KOH/g oil)
|
IV (meq O2/kg oil)
|
API g
|
BTO5
|
0.020
|
0.916
|
26.00
|
0.345
|
194
|
60.22
|
22.98
|
BTO10
|
0.020
|
0.914
|
25.80
|
0.332
|
192
|
60.18
|
23.31
|
BTO15
|
0.020
|
0.911
|
25.40
|
0.310
|
190
|
60.10
|
23.82
|
BTO20
|
0.020
|
0.912
|
24.90
|
0.303
|
189
|
60.03
|
23.65
|
BTO25
|
0.020
|
0.908
|
24.87
|
0.294
|
185
|
60.00
|
24.34
|
BTO30
|
0.020
|
0.910
|
24.60
|
0.296
|
185
|
59.86
|
23.99
|
BTO35
|
0.020
|
0.907
|
23.60
|
0.284
|
184
|
59.82
|
24.51
|
BTO40
|
0.020
|
0.905
|
23.50
|
0.283
|
186
|
59.80
|
24.85
|
BTO45
|
0.020
|
0.902
|
23.00
|
0.280
|
183
|
59.83
|
25.37
|
BTO50
|
0.020
|
0.904
|
23.10
|
0.262
|
185
|
59.56
|
25.03
|
BTO55
|
0.020
|
0.903
|
22.82
|
0.263
|
182
|
59.10
|
25.20
|
BTO60
|
0.020
|
0.890
|
22.30
|
0.249
|
180
|
58.88
|
27.49
|
BTO65
|
0.020
|
0.900
|
22.45
|
0.248
|
184
|
58.70
|
25.72
|
BTO70
|
0.020
|
0.902
|
22.52
|
0.252
|
186
|
58.60
|
25.37
|
BTO75
|
0.020
|
0.909
|
22.64
|
0.263
|
185
|
59.92
|
24.17
|
BTO80
|
0.020
|
0.911
|
22.86
|
0.272
|
188
|
59.94
|
23.82
|
BTO85
|
0.020
|
0.915
|
23.10
|
0.274
|
190
|
59.91
|
23.14
|
BTO90
|
0.020
|
0.913
|
22.94
|
0.276
|
191
|
59.70
|
23.48
|
BTO95
|
0.020
|
0.914
|
22.96
|
0.277
|
191
|
59.89
|
23.36
|
M = Moisture content, SG = Specific gravity, V = Viscosity, AV = Acid value, IV = Iodine value, PV = Peroxide value, SV = Saponification value, API g = API gravity
3.2. Characterization and analysis of catalysts
3.2.1 SEM analysis
The morphological characteristic of the catalysts was carried out by SEM analysis. Fig 1(a, b, and c) displayed the results of SEM analysis of BTCPH, CTCPH, and SFCTCPH at the same magnification of 500x, but different structural outlook performed in 2θ diffraction with a peak from 20o<2θ < 80o at speed of 2 oC/min. The image displayed by BTCPH indicated a highly crystal, cracked, less porous, and non-uniform shape structure whereas. This may be due to the burning process, as thermal burning in the open air, caused fusion and barrier for large surface area. The SEM image of CTCPH showed a uniform, highly porous with aggregated sizes and shape. This observation can be attributed to the surface fermentation process which makes it difficult for microorganisms to maintain homogeneous medium, thereby decreases the mineral content and the surface area of the cocoa pod husk powder. Observation from the morphological structure of SFCTCPH indicated a uniformly distributed structure with smaller sizes and shapes and a high surface area. This could be due to submerged fermentation which involves the growth of the microorganism in a homogeneous medium (inter-particle space and surface area) of the substrate and moisture content. However, it was observed that the release of the CaO from CaCO3 was complete at the calcination temperature of 750 oC [11]
3.2.2 FTIR analysis
The results of FTIR analysis of the burnt and calcined sample powder catalysts are displayed in Fig. 2(a-c). The spectral showed a sinusoidal waveform at different peaks confirming the effects of heat on the thermal degradation of the catalysts. The vivid descriptions of the wavelengths at different peaks for each catalyst which showed the stretches and the bending vibration of organic-inorganic functional groups present are presented in Table 4. The wavelength bands noticed between 693.3 – 913.2 cm-1 for CTCPH, and the bands between 752.9 – 913.2 cm-1 observed for SFCTCPH, and the wavelength stretches found in BTCPH of 879.7 – 1043.7 cm-1, specified the presence chlorocarbon (C-Cl), O = C = O bending vibration, nitrogen to carbon bond waging and twisting, and the presence of CO32- molecules at a lower temperature.
The stretches range between 1036.2 – 1699.7 cm-1 observed in SFCTCPH, and 1032.5 – 1982.9 cm-1 noticed in CTCPH showed similar wavelength due to fermentation process involved, but the value of 1088.4 – 1379.1 cm-1 bands found in BTCPH confirmed the presence of sp3 of C-C in alkane, sp2 delocalized electron of C=C in alkene, C=N of imines, and the bending vibration of O-Ca-O in calcium carbonate. Furthermore, 1420.1 – 1654.3 cm-1 wavelength bands noticed in cm-1 BTCPH, the value range of 1893.5 – 2322.1 cm-1 observed in the wavelength bands of SFCTCPH, and the range between 1982.9 – 2050.0 cm-1 displayed by CTCPH indicated the presence of C=O of ketone, -CHO of aldehyde, C=C of ester, C-C of alkyne/acetylene, C-N of cyanogen, and O-H of complex molecules. Further observation also indicated the presence of O-H bending structure in alcohol and phenol, O=O of dioxygen, and NO of sp were found in BTCPH, CTCPH, and SFCTCPH at wavelength bands of 1923.3 – 2974.5 cm-1, 3623.0 – 3693.8 cm-1 , and 3641.6 – 3753.4 cm-1, respectively, but the long stretches (> 3500) found in CTCPH and SFCTCPH showed the presence of amine and amide bonding structures (Adepoju et al. [24]). This showed that fermentation increased the presence of functional groups and the surface area of the sample, but the calcined fermented submerge Theobroma cacao pod husk SFCTCPH showed more functional groups.
Table 4: FTIR sample spectrum analysis
SN
|
Wavelength (cm-1 )
|
Transmittance (%)
|
Bonds and Functional groups
|
BTCPH
|
1
|
879.7 -1043.7
|
58.079-29.767
|
C-Cl, CO32-, N-H waging and twisting, O=C=O bending vibration
|
2
|
1088.4 - 1379.1
|
29.767 – 79.771
|
C-C, C=C, C=N, and O-Ca-O bending vibration
|
3
|
1420.1 – 1923.3
|
82.562 – 98.503
|
C=O, CHO, CC, CN, O=C=O of low energy, and O-H
|
4
|
2974.5 – 3336.0
|
71.078 – 68.824
|
O-H bending structure, O=O, and NO
|
CTCPH
|
1
|
693.3 - 913.2
|
86.990 – 70.688
|
C-Cl, C-C. CO32-, N-H waging and twisting, O=C=O bending vibration
|
2
|
1032.5 – 1830.1
|
57.307 – 97.256
|
C-C, C=C, C=N, and O-Ca-O bending vibration
|
3
|
1982.9 – 2050.0
|
96.325 – 98.896
|
C=O, CHO, CC, CN, and O-H
|
4
|
3623.0 – 3693.8
|
94.405 – 98.587
|
O-H bending structure, O=O, NO, Amine, and Amide
|
SFCTCPH
|
1
|
752.9 – 913.2
|
83.708 – 84.559
|
C-Cl, C-C. CO32-, N-H waging and twisting, O=C=O bending vibration
|
2
|
1036.2 - 1699.7
|
81.649 – 87.699
|
C-C, C=C, C=N, and O-Ca-O bending vibration
|
3
|
1893.5 – 2322.1
|
92.902 – 90.263
|
C=O, CHO, CC, CN, and O-H
|
4
|
3641.6 – 3753.4
|
75.796 – 88.068
|
O-H bending structure, O=O, NO, Amine, and Amide
|
3.2.3 Brunauer-Emmett-Teller (BET) and XRD analysis
Displayed in Table 5 are the results of the analysis of BET and XRD of the catalysts sample. A strong basic site (176, 188, and 196) was found in the catalysts which suggested that the produced catalyst are capable to be used as heterogeneous catalysts for FAEE production, as well as for other industrial applications. The basic site density does not depend on the pore volume of the catalysts but depends solely on the surface area of the catalysts. The higher the surface area, the lesser the basic site density, hence, the value of 176.00 μmole/m2 obtained for BTCPH, 170.91 μmole/m2 obtained for CTCPH, and 178.18 μmole/m2 obtained for SFCTCPH. The results of XRD analysis showed that the total basic site was responsible for the high transformation of CaCO3 to CaO. Despite the fact that the burning and calcined temperature was responsible for the formation of CaO with gaseous evolution of CO2, the reaction is not complete without the process route. Truly, the fermentation process increased the content of CaO obtained in the catalysts, but SFCTCPH has high conversion with 87.65% with a high FAEE yield of 98.94 (% wt.).
The yield of FAEE was also high for CTCPH with 94.82 (% wt.), but the value produced by BTCPH was the least with 90.20 (% wt.) due to low CaO conversion of 68.20%. This showed that the calcined fermented catalyst produced higher CaO-based content than the burnt and non-fermented catalysts [18].
Table 5: BET and XRD analysis of the catalysts
Catalysts
|
β (m2/g)
|
λ
(cm3/g)
|
CaO (%)
|
BS (μmole.g-1)
400<BS<650 >650
|
TBS
|
BSD (μmole/m2)
|
FAEE
(%wt.)
|
CA (wt.%)
|
BTCPH
|
1.00
|
0.0015
|
68.20
|
36
|
140
|
176
|
176.00
|
91.00
|
2.50
|
CTCPH
|
1.10
|
0.0024
|
81.46
|
26
|
162
|
188
|
170.91
|
94.00
|
2.50
|
SFCTCPH
|
1.10
|
0.0030
|
87.65
|
22
|
174
|
196
|
178.18
|
98.20
|
2.50
|
β = Surface area, λ = Pore volume, BS = Basic site, TBS = Total basic site, BSD = Basic site density, GD = Green diesel, CA = Catalyst amount
3.3. Experimental results and the optimization of transesterification process variables
3.3.1 Experimental results
Displayed in Table 3a are the 16 results obtained for every experimental run carried out and the predicted value by the HD using the three catalysts developed from cocoa pod husk (BTCPH, CTCPH, and CSFCTCPH). From the table, the FAEE highest yield obtained when BTCPH was used was 93. 50 (%wt.) while the predicted value was 93.50 (%wt.) at run 15, the highest value of FAEE yield obtained by CTCPH in FAEE2 was 94.50 (%wt.) at run 15 with the same predicted value of 94.50 (%wt.). However, the highest FAEE value obtained when CSFCTCPH was used as catalyst was 99.80 (%wt.), but the predicted value was 99.84 (%wt.) at run 10. These values indicated that the three developed catalysts are suitable for FAEE synthesis and can serve as feedstock for based catalyst in industrial application, but the calcined submerge fermented cocoa pod husk powder produced highest FAEE3 yield CSFCTCPH when compared with the yield associated with the use of BTCPH (93.50 (%wt.)) and CTCPH (93.50 (%wt.). Meanwhile, based on experimental and the predicted yield of FAEEs, the plots in Fig. 3(a) showed the relationship between the experimental results and the predicted values by the design software, the identifier of an appropriate exponent (Lambda = 1) to transform data into a normal shape due to residual error was as indicated in Fig. 3(b).
Usually, the Lambda values between -5 and +5 showed the transformation data has the highest likelihood of normal data. The value of lambda of 0.47 indicated the data obtained in this study were normal and have the function of Y1 confirming the polynomial model choice accuracy.
Table 3a: Experimental results and the predicted value
SN
|
X1
|
X2
|
X3
|
X4
|
FAEE1
|
FAEE2
|
FAEE3
|
PFAEE1
|
PFAEE2
|
PFAEE3
|
1
|
0.000
|
0.000
|
0.000
|
1.732
|
89.10
|
90.30
|
92.30
|
89.10
|
90.30
|
92.30
|
2
|
0.000
|
0.000
|
0.000
|
-0.269
|
90.20
|
91.40
|
93.80
|
90.20
|
91.40
|
93.80
|
3
|
-1.000
|
-1.000
|
-1.000
|
0.604
|
88.30
|
89.50
|
90.50
|
88.31
|
89.53
|
90.46
|
4
|
1.000
|
-1.000
|
-1.000
|
0.604
|
90.10
|
91.00
|
93.00
|
90.09
|
90.98
|
93.04
|
5
|
-1.000
|
1.000
|
-1.000
|
0.604
|
87.90
|
89.60
|
91.60
|
87.89
|
89.58
|
91.64
|
6
|
1.000
|
1.000
|
-1.000
|
0.604
|
88.60
|
89.80
|
91.70
|
88.61
|
89.83
|
91.66
|
7
|
-1.000
|
-1.000
|
1.000
|
0.604
|
88.60
|
89.90
|
90.90
|
88.59
|
89.88
|
90.94
|
8
|
1.000
|
-1.000
|
1.000
|
0.604
|
90.60
|
92.00
|
96.24
|
90.61
|
92.02
|
96.20
|
9
|
-1.000
|
1.000
|
1.000
|
0.604
|
91.60
|
93.90
|
97.20
|
91.61
|
93.92
|
97.16
|
10
|
1.000
|
1.000
|
1.000
|
0.604
|
92.60
|
94.90
|
99.80
|
92.59
|
94.87
|
99.84
|
11
|
1.518
|
0.000
|
0.000
|
-1.050
|
91.80
|
93.00
|
99.40
|
91.80
|
93.00
|
99.40
|
12
|
-1.518
|
0.000
|
0.000
|
-1.050
|
84.50
|
90.00
|
93.00
|
84.50
|
90.00
|
93.00
|
13
|
0.000
|
1.518
|
0.000
|
-1.050
|
90.30
|
92.00
|
96.00
|
90.30
|
92.00
|
96.00
|
14
|
0.000
|
-1.518
|
0.000
|
-1.050
|
82.50
|
84.40
|
86.80
|
82.50
|
84.40
|
86.80
|
15
|
0.000
|
0.000
|
1.518
|
-1.050
|
93.50
|
95.40
|
97.90
|
93.50
|
95.40
|
97.90
|
16
|
0.000
|
0.000
|
-1.518
|
-1.050
|
80.30
|
83.20
|
85.00
|
80.30
|
83.20
|
85.00
|
3.3.2 Process variables optimization
3.3.2.1 Statistical optimization via ANOVA
Displayed in Table 3b are the results of statistical optimization via ANOVA for the response surface quadratic model and the Fits statistics obtained through the catalytic performance during the transesterification reaction. Observation from the table showed that the Model F-values of 194.16, 159.85, and 263.03 with 14 degree of freedom (df), implied the model were significant with P-values <0.05, but the model 194.16 with an F-value of 11,095.04 is the most significant model (P-value = 0.0075) compared with model 159.85 with F-value of 2283.63, and model 263.03 with model F-value of 1300.18. The table also displayed the significance of the quadratic model factors, values of "Prob > F" < 0.05 shows variable terms are significant.
In this case, all the model terms were significant except X12 and X1X3 when FAEE1 was considered, the non-significant quadratic terms found in FAEE2 production were X32, X1X2, X1X3, and X1X4, while only X4, X42, and X1X4 were found non-significant when the analysis of the significant factors was carried out on FAEE3 production. Based on the results of Fit statistics datasets, the coefficient of determination obtained showed the model's predictions interaction was good (>98%) with low standard deviations (<0.20). The values also showed that there is a certainty above 98% that the model generated explained the data variability [26]. Meanwhile, the mean values obtained depicted the high accuracy of the data obtained for the variable factors.
Based on the optimization, the statistical model predicted a FAEE1 yield of 93.4998 (%wt.), FAEE2 yield of 95.2411 (%wt.), and FAEE3 yield of 99.8081 (%wt.) at the process variables conditions of 78.58 min, 3. 37 (wt.%), 79.23 oC, and 1:6.66 (vol/vol), respectively (Supplementary file). The values were validated by performing three experiments under the same condition, the average values of fatty acid ethyl ester obtained were 92.8100 (%wt.) for FAEE1, 93.0200 (%wt.) for FAEE2, and 99.6400 (%wt.) for FAEE3, respectively. These values indicated that all catalysts developed were good as feedstock for industrial applications, but fermented catalyst developed catalyst produced the highest biodiesel yield among others.
Table 3b: Anova and test of significant table
Source
|
Sum of Squares
1 2 3
|
df
|
Mean Square
1 2 3
|
F-Value
1 2 3
|
Prob > F
1 2 3
|
Model
|
194.16
|
159.85
|
263.03
|
14
|
13.87
|
11.42
|
18.79
|
11095.04
|
2283.63
|
1300.18
|
0.0074
|
0.0164
|
0.0217
|
|
21.80
|
6.94
|
32.54
|
1
|
21.80
|
6.94
|
32.54
|
17442.09
|
1387.81
|
2251.71
|
0.0048
|
0.0171
|
0.0134
|
|
17.70
|
23.83
|
44.26
|
1
|
17.70
|
23.83
|
44.26
|
14159.69
|
4766.88
|
3063.24
|
0.0053
|
0.0092
|
0.0115
|
|
64.58
|
68.17
|
108.11
|
1
|
64.58
|
68.17
|
108.11
|
51663.48
|
13633.9
|
7481.75
|
0.0028
|
0.0055
|
0.0074
|
|
18.59
|
5.93
|
0.56
|
1
|
18.59
|
5.93
|
0.56
|
14874.14
|
1186.82
|
38.91
|
0.0052
|
0.0185
|
0.1012
|
|
0.023
|
2.61
|
12.09
|
1
|
0.023
|
2.61
|
12.09
|
18.03
|
521.63
|
836.54
|
0.1473
|
0.0279
|
0.0220
|
|
2.98
|
3.70
|
2.80
|
1
|
2.98
|
3.70
|
2.80
|
2386.14
|
740.98
|
193.46
|
0.0130
|
0.0234
|
0.0457
|
|
1.42
|
0.55
|
2.62
|
1
|
1.42
|
0.55
|
2.62
|
1134.24
|
110.97
|
181.25
|
0.0189
|
0.0603
|
0.0472
|
|
7.41
|
3.63
|
2.20
|
1
|
7.41
|
3.63
|
2.20
|
5925.43
|
726.94
|
152.05
|
0.0083
|
0.0236
|
0.0515
|
|
0.55
|
0.72
|
3.30
|
1
|
0.55
|
0.72
|
3.30
|
441.00
|
144.00
|
228.54
|
0.0303
|
0.0529
|
0.0420
|
|
0.031
|
0.25
|
3.56
|
1
|
0.031
|
0.25
|
3.56
|
25.00
|
49.00
|
246.67
|
0.1257
|
0.0903
|
0.0405
|
|
8.62
|
0.44
|
1.83
|
1
|
8.62
|
0.44
|
1.83
|
6898.37
|
88.17
|
126.57
|
0.0077
|
0.0675
|
0.0564
|
|
5.95
|
8.00
|
12.65
|
1
|
5.95
|
8.00
|
12.65
|
4761.00
|
1600.00
|
875.46
|
0.0092
|
0.0159
|
0.0215
|
|
13.92
|
9.25
|
9.72
|
1
|
13.92
|
9.25
|
9.72
|
11136.70
|
1849.97
|
672.64
|
0.0060
|
0.0148
|
0.0245
|
|
31.57
|
20.83
|
12.68
|
1
|
31.57
|
20.83
|
12.68
|
25255.75
|
4165.73
|
877.26
|
0.0040
|
0.0099
|
0.0215
|
Residual
|
0.00125
|
0.005
|
0.014
|
1
|
0.00125
|
0.005
|
0.014
|
-
|
-
|
-
|
-
|
-
|
-
|
Cor Total
|
194.16
|
159.86
|
263.04
|
15
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
Significance Factors @ p < 0.0500
|
Non-Significant Factors p > 0.0500
|
FAEE1
|
X1, X2, X3, X4, X22, X32, X42, X1X2, X1X4, X2X3, X2X4, and X3X4
|
X12 and X1X3
|
FAEE2
|
X1, X2, X3, X4, X22, X12, X42, X2X3, X2X4, and X3X4
|
X32, X1X2, X1X3, and X1X4,
|
FAEE3
|
X1, X2, X3, X12 , X22, X32, X1X2, X1X3, X2X3, X2X4, and X3X4
|
X4, X42, and X1X4
|
Fits statistics
|
|
R-Squared
|
Adj R-Squared
|
Pred R-Squared
|
Adeq Precision
|
Std. Dev.
|
Mean
|
|
|
|
FAEE1
|
99.99%
|
99.98%
|
99.99%
|
385.597
|
0.035
|
88.78
|
|
|
|
FAEE2
|
99.99%
|
|
99.96%
|
|
99.98%
|
|
178.192
|
|
0.071
|
90.64
|
|
|
|
FAEE3
|
99.98%
|
|
99.92%
|
|
99.97%
|
|
127.523
|
|
0.12
|
93.45
|
|
|
|
Meanwhile, the second-order mathematical differential equation that correlated the response variables (FAEE1, FAEE2, and FAEE3) with the constraint variables (X1: reaction time, X2: catalyst amount, X3: reaction temperature, and X4: EtOH/OMR) are presented in Eqs. (2), (3), and (4), respectively.
Final equation in terms of coded:
Meanwhile, the least interaction noticed in X3X4 (reaction temperature and EtOH/OMR) depicted that the combination of other factors apart from the catalyst produced a low effect. Hence, the effects of the developed catalysts on biodiesel yield are of great important but fermented submerged calcined Theobroma cocoa pod husk (FSCTCPH) with coefficient 1.26 in X2X3 produced high mutual effects than 1.00 produced by CTCPH and 0.86 observed in BTCPH.
3.4. Catalytic refining and reusability test
Before catalyst reusability, after recycled at the completion of reaction, the catalyst obtained was refined following the step by step procedure of Adepoju et al. [24] with slight alterations. The recycled catalyst was washed with alcohol to eliminate the dirt at the interface of catalyst that occurred during the transesterification, centrifuged at 4500 rpm in an in-built system vacuum centrifuge. The washed catalyst was obtained by filtration, and then oven-dried at 120 oC for 45 min, cooled to room temperature before reused. The reusability test was carried out on the derived catalysts in many cycles, at the following reaction conditions: the reaction time of 70 min, the catalyst amount of 2.50 (%wt.), the reaction temperature of 70 oC, and 1:4 (vol/vol) EtOH/OMR.
The results obtained were illustrated using Microsoft Excel 2010 to plots the data. The plots showed the activities of the catalysts maintained stability from the first cycle to the 4th cycle with a negligible decrease in catalysts strength, however, a significant dropped was noticed in the 5th and 6th cycles, hence, catalysts refining and reusability were stopped at the 4th cycle. This observation was in line with what was earlier reported that catalyst basic strength decreases due to continuous intermediate products monoglyceride and diglyceride resulted as a result of the reaction, which obstructed the catalyst holes. The formation of water to oxygen reaction that occurred at the catalyst surface also reduces the catalyst sensitivity [16, 24, 25].
3.5 Fatty acid ethyl ester (FAEEs) qualities and its comparison with standard
Table 6 displayed the results of the qualities of the blended oil (BTO60) and the FAEEs produced with the references to ASTM and EN. Observation from the table indicated that there were significant changes as the oil was converted to biodiesel due to transesterification with developed catalysts, the effect of alcohol, reaction time, and reaction temperature. However, there were no distinct differences in the values of the properties of the three biodiesel (FAEE1, FAEE2, and FAEE3), except a slight difference noticed in the iodine and acid value of the FAEE1 produced by the BTCPH, this may be attributed to the powder preparation processes. Burning could result in the loss of the volatile nutrient, making the ash more acidic and increase the unsaturation level of the biodiesel when used during the transesterification process (Betiku et al., 2017)[11]. The physicochemical properties of the FAEE2 and FAEE3 remain almost the same; this could be attributed to the calcination process involved in the sample preparation, causing the gaseous evolution of CO2 from the CaCO3 at a controlled temperature more than burning. The properties of biodiesel produced were in the range of recommended standard stated by [22] and [23].
Table 6: Qualities of the produced FAEEs
Parameter
|
BTO60
|
FAEEs (%wt.)
|
ASTM D6751 [22]
|
EN 14214 [23]
|
|
|
FAEE1
|
FAEE2
|
FAEE3
|
|
|
Colour@ 27 oC
|
Brownish-yellow
|
Light yellowish
|
Light yellowish
|
Light yellowish
|
-
|
-
|
State @ room temp
|
Liquid
|
Liquid
|
Liquid
|
Liquid
|
Liquid
|
Liquid
|
Specific gravity
|
0.902
|
0.864
|
0.864
|
0.864
|
-
|
860-900
|
Viscosity @ 40 oC/ (mm2/s)
|
22.30
|
2.78
|
2.78
|
2.78
|
1.9-6.0
|
3.5-5.0
|
Moisture content (%)
|
0.02
|
<0.01
|
<0.01
|
<0.01
|
<0.03
|
0.02
|
%FFA (as oleic acid)
|
0.1745
|
0.032
|
0.021
|
0.018
|
0.40 max
|
0.25 max
|
Acid value (mg KOH/g oil)
|
0.249
|
0.064
|
0.042
|
0.036
|
0.80 max
|
0.50 max
|
Iodine value (g I2/100g oil)
|
58.88
|
56.62
|
53.62
|
53.62
|
ND
|
120 max
|
Saponification value (mg KOH/g oil)
|
180.00
|
178.43
|
176.32
|
172.22
|
236.66-253.04
|
ND
|
Peroxide value (meq O2/kg oil)
|
12.65
|
8.90
|
8.70
|
8.60
|
ND
|
12.85
|
HHV (MJ/kg)
|
41.17
|
41.26
|
41.40
|
41.52
|
ND
|
ND
|
Cetane number
|
63.39
|
64.15
|
65.19
|
65.92
|
57 min
|
51 min
|
API gravity
|
22.30
|
32.27
|
32.27
|
32.27
|
30-42
|
ND
|
Diesel index
|
49.50
|
50.26
|
51.30
|
52.04
|
50.4 min
|
ND
|
ND = Not Determine
3.6 Comparative studies of this work with earlier reported works
Table 7 showed the use of single heterogeneous based catalyst derived from different agricultural wastes for biodiesel production using single/blended oil in a different ratio [8, 27, 28]. Falowo et al. [17] derived a based catalyst from the mixture of three agricultural wastes, while Adepoju et al. in their various reported studies, derived novel based catalysts from the mixture of different biomass wastes for biodiesel synthesis. Except the work of Victoria et al. [29], where the authors established the optimum biodiesel yields from banana fruit peel and cocoa pod husk, no single report has ever derived three CaO-based catalysts from single biomass waste and compares their efficiencies in fatty acid ethyl ester (FAEE) synthesis. Hence, with respect on earlier reports, there exists no basis, but this study showed that the derived catalysts produced a high yield of biodiesel, and the catalysts can be used in industrial as feedstock.
Table 7: Comparing this study with reported literature studies
Blended
Oil
|
Blending ratio (vol/vol)
|
Catalysts
|
Calcination temperature and duration
|
% CaO/KOH conversion
|
Catalyst analysis
|
% Biodiesel yield
|
References
|
Honne+ Rubber seed+ Neem oil
|
20:20:60
|
Cocoa pod
Husk-Plantain peels- kola nut husk
|
500 °C for
4 h
|
KOH = 47.67%
|
XRD, SEM, BET, and FTIR
|
98.45
|
Falowo et al. (2020)[17]
|
Pig fat + Neem oil
|
60:40
|
Mixture of Palm kernel shell husk-
Fermented kola nut pod husk
|
800 °C for
3 h
|
CaO = 71.20%
|
EDS, SEM, BET, and FTIR
|
98.05
|
Adepoju, (2020)[11]
|
Cucurbita pepo + Chrysophyllum albidum + papaya oil
|
33:33:34
|
Mixture of Citrullus lanatus - Musa acuminate
peels
|
700 oC for
4 h
|
CaO = 78.74%
|
XRD, SEM, BET and FTIR
|
93.45
|
Adepoju et al. (2020a)[21]
|
Irvingia gabonensis +Pentaclethra macrophylla + Elais guineensis oil
|
33:33:34
|
Mixture of Wood ash-Snail shell- eggshell
|
900 oC for
3 h
|
CaO = 98.50%
|
SEM, EDX-ray, FTIR and BET
|
97.22
|
Adepoju et al. (2020b)[24]
|
Calophyllum inophyllum-waste
cooking oil
|
50:50
|
Donax deltoids shells
|
105 °C for
24 h
|
CaO = 70.87%
|
XRD, SEM, BET, and FTIR
|
96.50
|
Subramaniapillai et al. (2019)[8]
|
Waste cooking oil (WCO)
|
-
|
Ca(NO3).4H2O
|
500 °C for
5 h
|
CaO
|
XRD and SEM
|
96.00
|
Tadesse et al. (2019)[28]
|
Sunflower oil
|
-
|
Chicken eggshells
|
900 oC for
3 h
|
CaO
|
SEM, TGA, XRD
|
83.20%
|
Fayazishishvan et al. (2018)[27]
|
Palm Kernel oil
|
-
|
Banana fruit peel
Cocoa pod husk
|
650 oC for
4 h
|
CaO
|
|
99.50%
99.30%S
|
Victoria et al. (2017)[29]
|
Carica papaya +Citrus sinesis +Hibiscus sabdariffa + Waste used oil
|
25:25:25:25
|
Mixture of Lattorina littorea-Mactra coralline Shell
|
900 oC for
3 h
|
CaO = 99.02
|
SEM, EDX, FTIR
|
99.78%
|
Adepoju et al. (2020c)[25]
|
Luffa cylindrical+ Datura stramonium+ Lagenaria siceraria oil
|
29:50:21
|
Mixture of Cucurbita pepo- Musa acuminate -Citrullus lanatus peels
|
650 oC for
3 h
|
CaO= 75.65%
|
SEM, EDX-ray, FTIR, and BET
|
96.50%
|
Adepoju et al (2020d)[30]
|
Beef Tallow blend + Waste used vegetable oil
|
60:40
|
Theobroma cacao pod husks
|
|
CaO
|
XRD, SEM, BET, and FTIR
|
|
THIS STUDY
|
Burnt
|
Uncontrolled temperature
|
68.20%
|
92.81%
|
Calcined
|
750 oC for
4 h
|
81.46%
|
|
93.02%
|
Submerged fermented calcined
|
750 oC for
4 h
|
87.65%
|
|
99.64%
|