Figure 1.
(a) XRD result of Na2O/γ-Al2O3, and microstructure of Na2O/γ-Al2O3 with magnification: (b) 2000x, (c) 5000x.
The synthesis of biodiesel via transesterification needs to be improved by the heterogeneous catalysts. So, the study aimed to determine the best conditions for the synthesis of biodiesel produced through a transesterification reaction using waste cooking oil with a Na2O/γ-Al2O3 catalyst assisted by ultrasonic wave. The steps were: catalyst preparation, oil preparation, esterification, trans-esterification reactions using methanol and various Na2O/γ-Al2O3 catalysts, and characterization. The results showed that the refined waste cooking oil using FTIR was known that there was still a carbonyl group indicating the presence of triglycerides. Free Fatty Acid content of waste cooking oil after esterification was 0.40%, so that the transesterification reaction could be carried out. The XRD results of the catalyst showed a conformity with the reference and it was determined by the Scherrer formula that the crystal size of the catalyst was 30.59 nm. The best condition for biodiesel synthesis was obtained at a catalyst ratio of 1:1 as much as concentration 3% w/w for 15 minutes of ultrasonication, 65 ℃, and molar ratio of methanol: oil (12:1), for the yield of 83.51%. After identification through GC-MS, it was known that the main components in the transesterified biodiesel from waste cooking oil were methyl elaidate (38.54%), methyl palmitate (30.90%) and methyl linoleate (16.61%).
Citation: Aman Santoso, Titania Nur Kusumah, Sumari Sumari, Anugrah Ricky Wijaya, Rini Retnosari, Ihsan Budi Rachman, Siti Marfuah, Muhammad Roy Asrori. Synthesis of biodiesel from waste cooking oil using heterogeneous catalyst of Na2O/γ-Al2O3 assisted by ultrasonic wave[J]. AIMS Energy, 2022, 10(5): 1059-1073. doi: 10.3934/energy.2022049
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The synthesis of biodiesel via transesterification needs to be improved by the heterogeneous catalysts. So, the study aimed to determine the best conditions for the synthesis of biodiesel produced through a transesterification reaction using waste cooking oil with a Na2O/γ-Al2O3 catalyst assisted by ultrasonic wave. The steps were: catalyst preparation, oil preparation, esterification, trans-esterification reactions using methanol and various Na2O/γ-Al2O3 catalysts, and characterization. The results showed that the refined waste cooking oil using FTIR was known that there was still a carbonyl group indicating the presence of triglycerides. Free Fatty Acid content of waste cooking oil after esterification was 0.40%, so that the transesterification reaction could be carried out. The XRD results of the catalyst showed a conformity with the reference and it was determined by the Scherrer formula that the crystal size of the catalyst was 30.59 nm. The best condition for biodiesel synthesis was obtained at a catalyst ratio of 1:1 as much as concentration 3% w/w for 15 minutes of ultrasonication, 65 ℃, and molar ratio of methanol: oil (12:1), for the yield of 83.51%. After identification through GC-MS, it was known that the main components in the transesterified biodiesel from waste cooking oil were methyl elaidate (38.54%), methyl palmitate (30.90%) and methyl linoleate (16.61%).
Petroleum exploitation can affects environmental damage [1]. So, currently it is necessary to develop renewable and environmentally friendly fuels such as biodiesel. Biodiesel was an alternative fuel with a composition of fatty acid esters from vegetable oils [2]. One of the renewable natural resources was waste cooking oil because it contained triglycerides [3,4]. It is reusable raw materials and do not compete with food any more [5]. The waste cooking oil which was directly discharged into the environment without any prior processing can cause environmental pollution [6]. In addition, waste cooking oil can also affect the mineral content in clean water [7]. Therefore, the production of biodiesel from waste cooking oil is very profitable because it is cheap and can minimize environmental pollution.
Biodiesel can be produced by transesterification reaction between waste cooking oil and methanol assisted by a heterogeneous catalyst in recent years. For example, transesterification of oil with CuO-Al2O3 catalyst produced 78.5% biodiesel for 4 hours [8]. Study of biodiesel synthesis of waste cooking oil using CaO catalyst yielded biodiesel of 77, 76% with 2 hours duration [9]. Study of Sodium Potassium Silicate as catalyst for transesterification of waste cooking oil showed 93.89% yield at 200 rpm, 2 hours, 2.5% concentration, 70 ℃, and alcohol:oil (9:1) [10], and the use of Tangerine peel ashes for the same reaction showed 92% yield [11]. From the previous study, the biodiesel produced was still very little and required a long time. The reaction could be due to the low basicity of the catalyst. An alternative was to use a metal oxide which has a very strong base as the catalyst support [12]. The metal oxide which has a strong base source for the transesterification process was Na2O [13]. The use of Na2O catalyst needed to be supported or added to solids with large surfaces such as carriers or supports because Na2O easily reacts with free fatty acid to form soap. [14]. Research on biodiesel synthesis using a Na2O(20 wt%)/CNTs catalyst with a 3% concentration resulted in the highest FAME yield at 65 ℃, molar ratio of oil: methanol 1:20 for 3 hours, which was 97% yields [15].
A good buffer was γ-Al2O3 because it was stable at high temperatures and has a larger surface area [16]. Cr/Ca/γ-Al2O3 catalyst in transesterification of cooking oil produced 92.79% yields at 18:1 ratio of methanol:oil, 65 ℃, 6% wt, and 3 hours [17]. K2O/γ-Al2O3 catalyst in transesterification of rapessed oil produced 94% yields at 12:1 ratio of methanol:oil, 70 ℃, 3% wt, and 3 hours [18]. NaOH/γ-Al2O3 catalyst in transesterification of coconut oil produced 90% yields at 2:1 ratio of ethanol:oil, 60 ℃, 3% wt, and 3 hours [19]. However, the reaction took a very long time, so that the other efforts were needed to increase the yield with a short reaction time [20]. The use of ultrasonic wave in the transesterification of waste cooking oil obtained the higher yield as compared to conventional [21]. Ultrasonic waves propagating in a liquid were able to make molecules compressed under pressure and increased the mass transfer rate of immiscible liquids [22,23].
Based on the description above, research on the synthesis of biodiesel from waste cooking oil using a heterogeneous catalyst Na2O/γ-Al2O3 assisted by ultrasonic waves needs to be done. This research was conducted to find the best yield with a catalyst variation of 3–5% w/w oil with a reaction time of < 1 hour at 60 ℃ with a mole ratio of oil: methanol 1:12. The analysis will be represented by characterization and comprehensive understanding.
This research was a laboratory experimental research that aimed to synthesize biodiesel from waste cooking oil. The materials for this research were waste cooking oil from collector (small fried food restaurant) in Malang, active natural zeolite from Chemistry Laboratory of Universitas Negeri Malang (natural zeolite was obtained from Malang, Indonesia), aquadest, KOH 0.01 N & 0.1 N, alcohol 95%, Phenolphthalein indicator, methanol p.a., H2SO4 p.a, MgSO4 anhydrous, oxalic acid p.a., NaOH p.a., AlCl3.6H2O p.a., iodium p.a., and ethyl acetate p.a.. The research tools were a condenser, a 1600 RPM hot plate, a magnetic stirrer, analytical balance (Durasclae DAB 200), an Ostwald viscometer, a 10 mL pycnometer, a set of glass ware (consisted of reflux, three-next flask, Beaker, Erlenmeyer, Biuret), Fourier Transform Infra-Red (FTIR) (Shimadzu IRPRESTIGE 21), gas chromatography-mass spectroscopy (GC-MS) (Shimadzu QP2010PLUS), oven (Memmert), furnace (RMF QUARTECH 2800), scanning electron microscopy (SEM) (FEI Inspect-S50), thermometer 110 ℃, Ultrasonic cleaner (Delta D68H), X-Ray Diffraction (XRD) (PanAnalytical E'xpert Pro).
The synthesis of Na2O/γ-Al2O3 catalyst was carried out by synthesis of γ-Al2O3 and then the synthesis of Na2O/γ-Al2O3. First, the γ-Al2O3 catalyst was prepared by: the γ-Al2O3 catalyst was prepared by 50.001 grams of AlCl3.6H2O (merck) dissolved in 83 mL of distilled water. Then, it was stirred with a magnetic stirrer at a temperature of 100 ℃ for 4 hours. Then NH4OH was added until the pH reached ±9. The obtained precipitate was filtered and then washed with distilled water and washed 4 times with ethanol. The solids were dried at 80 ℃ for 48 hours. It was then calcined at a temperature of 500 ℃ for 2 hours. Second, the preparation of Na2O/γ-Al2O3 catalyst was prepared by: mixing γ-Al2O3 with NaOH which has been dissolved in distilled water with a mole ratio (variations of study were 1:1, 1:2, and 1:3). Then, the mixture was dried at a temperature of 130 ℃ for 3 hours. Then, it was calcined at a temperature of 450 ℃ for 3 hours with a heating rate of 10 ℃/minute. Next, the catalyst was characterized by XRD and SEM. Crystal size from the obtained XRD can be calculated by Scherrer equation [24] with the Equation:
| crystal size = k ×λβcosθ | (1) |
which k = Scherrer constant (0.9), λ = wavelength of X-ray, and β = FWHM (full width at Half Maximum).
The preparation was refining of waste cooking oil. The refining of waste cooking oil was carried out as follow: [2] (1) waste cooking oil was heated at 90 ℃ with stirring of 1000 rpm, (2) active natural zeolite was mixed about 30% of oil weight, (3) stirring was constant for 90 minutes, and (4) oil was separated from the zeolite. Refined oil was identified using the FTIR instrument and Free Fatty Acid (FFA) test. For FFA test, the procedures were: 1 gram of the oil and 5 mL of ethanol 95% were put into Erlenmeyer. The mixture was then heated in waterbath for 1 minute. The mixture was then added phenolphthalein indicator and titrated with KOH 0.01 N. The equation for FFA test was:
| FFA = {Normality(N)× Volume(mL)} of KOH × 265, 687gmolmass of sample × 1000× 100% | (2) |
Transesterification of waste cooking oil was carried out in the following way: the refined oil was put into a three-neck flask. Then, it was added with a certain volume of methanol in a ratio of 1:12. The two materials were mixed and catalyst was added with various variations of the molar ratio (1:1, 1:2 and 1:3) and the concentrations were 3%, 4%, and 5% by weight of the oil. The mixture was stirred with a magnetic stirrer and put into the ultrasonic reactor for 15 minutes at a temperature of 65 ℃. Then, the mixture put into a separating funnel and left for ±24 hours. The top layer was taken and anhydrous MgSO4 was added, filtered with Whatman filter paper Number 41. Next, the product was put into the oven to remove the remaining methanol at 70 ℃ for 3 hours. Mass of the product (synthesized methyl ester) was then weighed by analytical balance. After that, identification of the functional groups used FTIR and identification of the components used GC-MS. The calculation of the biodiesel yield was calculated according to Santoso's research [25] by Eq 3:
| Yield = mass of synthesized methyl estermass of theoretical methyl ester×100% | (3) |
The characterization carried out was density, viscosity, acid number, [25] and Thin-Layer Chromatography test [26]. The characterization procedures were:
Density measuring used a pycnometer and the calculation used Eq 4:
| density (ρ) = sample mass in pycnometer(g)−mass of pycnometer (g)volume of pycnometer (mL) | (4) |
Viscosity measuring used a Ostwald viscometer and the calculation used Eq 5:
| η aquadestη sample = ρ aquadest×t aquadestρ sample×t sample | (5) |
1.00 g of oil was put into a 100 mL Erlenmeyer and then 5.00 mL of alcohol was added. The mixture was heated in a boiling water bath for 10 minutes. The mixture was then added to the phenolphthalein indicator and then it was titrated with 0.1N KOH. The calculation of acid number used Eq 6:
| acid number={volume(mL)× Normality(N)× molecular weigh(gmol)} of KOHsample mass (g) | (6) |
In this study, the catalyst used for transesterification is NaOH which was impregnated into γ-Al2O3 catalyst. Then, the mixture calcined, so that it NaOH changes into Na2O. The synthesis produces a Na2O/γ-Al2O3 catalyst with various mole ratios of 1:2, 1:1 and 1:3. The step aims to determine the effect of basicity given by NaOH in the transesterification reaction of waste cooking oil. The catalyst was characterized by XRD and SEM (Figure 1).
Based on Figure 1(a), the results of data analysis showed that there has been a difference of 2θ angle between Na2O/γ-Al2O3 and γ-Al2O3 standard, namely the appearance of a peak at 2θ angle which was typical for XRD Na2O standards. The XRD peaks of Na2O are at 2θ = 28.01, 32.30, 54.89 and 57.50° are due to Na2O (ICSD-180570) [27]. This was in accordance with the results of this study which showed a peak of 2θ = 33.19° with a weak intensity. The XRD peaks of γ-Al2O3 were at 2θ = 12.35°, 19.89°, 20.38°, 24.88°, 35.02°, 35.95°, 36.06°, 38.35° and 62.37° [28]. This was also in accordance with the results of the study which showed that there were peaks of 2θ = 20.67°, 35.05° and 61.98° and also the similarity of peaks between the XRD results of the study and the standard XRD of γ-Al2O3. The analysed peaks can be able to determine the crystal size with using Scherrer equation. The result of Scherrer equation for this catalyst showed that crystal size of Na2O/γ-Al2O3 was about 30.59 nm. Therefore, the peaks correlated to less than 100 nm, and it was relatively known nanoparticle size of Na2O/γ-Al2O3. In addition, the synthesis of Na2O/γ-Al2O3 catalyst was calcined from 450 to 500 ℃, suggesting the transformation phase of boehmite to γ-Al2O3. In the future, the combination of the XRD, XPS, and FT-IR analysis is needed to reveal the efficient stable transformation of γ-Al2O3.
The microstructure can be analyzed through characterization with SEM at 2000x and 5000x magnification. The results of the microstructure analysis can be seen in Figure 1(b) and 1(c). The results of SEM characterization at 2000x magnification showed that the surface of the sample contained clumps like crystals but they were not clearly visible. The 5000x magnification was more clearly visible than the 2000x magnification which indicated the presence of Na2O. The presence of crystals that look like Na2O grains with fairly large and inhomogeneous particle sizes. The results of the analysis showed that Na2O grain were evenly formed on the surface of γ-Al2O3 and had a fairly large and inhomogeneous particle size. Furthermore, the results of SEM-EDX analysis showed that Na2O had been impregnated into γ-Al2O3. Therefore, the SEM results can strengthen the results of XRD analysis that the catalyst in this study is a Na2O/γ-Al2O3 catalyst.
The results of the study provide the characteristics of waste cooking oil before and after being refined. The color originally changed from brownish to yellow color (in Figure 2(a) and 2(b)). This was because the oxidized compounds have been adsorbed and retained in the activated zeolite cavity. In addition to changes in the color of the oil, the refined oil also experienced a decrease in acid and free fatty acid numbers as shown in Table 1. The results of the FTIR characterization of refined oil can be seen in Figure 2(c). These results indicate the presence of triglycerides which were characterized by the stretching vibrations of C = O, C-O, O-H, C-H alkanes, C-H alkenes, and CH2 bonds. The wave number and absorption intensity data can be seen in Table 2. In this study, the results of refinement showed that there was a reduction in fatty acids in the oil. The obtained free fatty acid was less than 2% as requirement to transesterification process [29], the refined oil can be able as raw materials in transesterification. If the FFA is more than 2%, the transesterification will form a soap, as known as saponification [30]. As competitive reaction, it will probably occur a hydrolysis reaction [2].
| Parameter | Before refining | After refining |
| Density (g/cm3) | 0.9260 | 0.9261 |
| Acid number (mg KOH/g) | 1.98 | 1.73 |
| Viscosity (cSt) | 35.69 | 36.71 |
| Free fatty acid (FFA) (%) | 0.94 | 0.82 |
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| Stretching vibration- | Wave number (cm-1) | Absorption intensity | Wavenumber (cm-1) [31] |
| C-H alkene | 3007.02 | strong, sharp | 3008.28 |
| C-H alkane | 2924.04 2852.72 |
strong, sharp Strong, sharp |
2925.80 2854.60 |
| C=O ester | 1747.51 | strong, sharp | 1746.26 |
| C-O | 1161.53 | strong, sharp | 1163.12 |
| CH2 | 721.38 | strong, sharp | 722.80 |
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The biodiesel synthesis was carried out from waste cooking oil which had been refined using zeolite 30% by weight of oil. This was done with the aim that the color of the oil becomes clearer and reduces free fatty acid of the oil. The free fatty acid of the oil after being refined was 0.82%, so that the transesterification process can be continued. The transesterification process was carried out using a Na2O/γ-Al2O3 catalyst with a variation of the mole ratio of the catalyst 1:1, 1:2, 1:3 and the concentration of the catalyst with variations of 3%, 4% and 5% by weight of oil. It aims to determine the best condition of biodiesel synthesis. In this study, biodiesel was formed through a transesterification process using a mole ratio of oil: methanol, which is 1:12 with ultrasonic wave at a temperature of 65 ℃.
The result of transesterification formed two layers, the top layer was methyl ester (biodiesel) and the bottom layer was glycerol (Figure 3(a)). In this study, the transesterification process was assisted by ultrasonic wave for 15 minutes, so that the reaction rate increased. Increasing the reaction rate can result in the formation of higher methyl esters in a shorter time that compared to the process without using ultrasonic wave [32].
The yield of transesterification from waste cooking oil in this study can be seen in Figure 4. Based on Figure 4, the results of transesterification assisted by ultrasonic waves using a 1:1 mole ratio catalyst with a concentration of 3% have a higher yield than the catalyst with a mole ratio of 1:2 and 1:3. However, at 1:1 catalyst the yield decreased from 83.51%, 75.59% and 60.94% yields. The decrease in yield indicated that the amount of the used catalyst was in excess. This was because the use of excess catalyst can result in saponification. The presence of soap in the transesterification reaction can complicated the formation of the product, so the product was difficult to separate from glycerol, and the results did not show a significant increase [33]. Therefore, the best Na2O/γ-Al2O3 catalyst used for the transesterification reaction was at a concentration of 3% with a catalyst ratio of 1:1 mole ratio. In addition, the presence of ultrasonic waves can shorten the reaction time to less than 30 minutes [34].
The product resulting from the transesterification reaction was carried out by the Thin-Layer Chromatography (TLC) test (see Figure 3(b)). The test aims to determine that the result of transesterification is biodiesel instead of oil. Based on Figure 3(b), the produced spot from oil and some samples from the transesterification have different Rf value. Rf value of oil was 0.32 and Rf value of biodiesel was 0.5, so it can be concluded that biodiesel synthesis was successful.
The transesterification yield was characterized to determine whether the resulting product was suitable, namely in the form of biodiesel with the standard quality requirements of SNI Biodiesel. The data from the characterization results were listed in Table 3. Based on the results of the characterization of biodiesel that was in accordance with Indonesian National Standard (SNI) for Biodiesel, it can be concluded that this biodiesel meets the quality requirements as biodiesel and can be investigated further.
| Parameter | Research results | SNI 7182:2015 |
| Density (g/m3) | 0.886 | 0.850−0.890 |
| Viscosity (cSt) | 3.191 | 2.3−6.0 |
| Free fatty acid (mg-KOH/g) | 0.39 | max 0.8 |
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The trans-esterified product was further identified using the FTIR instrument. It aims to determine the functional groups present in the product. The IR spectrum of the trans-esterified product was shown in Figure 3(b). Based on the IR spectrum, there were six typical absorption bands as shown in Table 4. Based on Table 4, the indications of the detected absorption bands were the presence of CH alkene bond stretching vibrations, CH alkane bond stretching vibrations, typical bond stretching vibrations of C = O as ester, vibration CO bond stretching, and CH2 bond stretching vibrations. Based on the results of the IR spectrum analysis, it can be seen that the trans-esterification product has a C = O functional group as R-COOR as an ester.
| Stretching vibration- | Wavenumber of the study (cm-1) | Absorption intensity | Wavenumber (cm-1) [35] |
| C-H alkene | 3008.33 | Strong, sharp | 3008.9 |
| C-H alkane | 2924.09 2854.65 |
Strong, sharp Strong, sharp |
2925.76 2855.76 |
| C=O ester | 1743.65 | Strong, sharp | 1743.54 |
| C-O | 1165.00 | weak, sharp | 1172.42 |
| CH2 | 725.23 | Strong, sharp | 722.75 |
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Furthermore, GC-MS analysis was carried out to determine the components present in biodiesel. Based on the results of the GC analysis, there were 8 peaks on the chromatogram as shown in Figure 5a, and MS results of the sample in Figure 5(b). Then the peaks were analyzed by MS to produce an MS spectrum (Table 5).
| Retention time (minutes) | Content (%) | C content (hydrocarbon) | Compound |
| 7.202 | 1.39 | (C13:0) | Methyl Laurate |
| 8.744 | 2.26 | (C15:0) | Methyl Miristate |
| 10.021 | 0.80 | (C17:1) | Methyl Palmitoleate |
| 10.176 | 30.90 | (C17:0) | Methyl Palmitate |
| 11.270 | 16.61 | (C19:2) | Methyl Linoleate |
| 11.323 | 38.54 | (C19:1) | Methyl Elaidate |
| 11.436 | 8.62 | (C19:0) | Methyl Stearate |
| 12.599 | 0.88 | (C21:0) | Methyl Arachidate |
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MS spectrum peaks were compared with library data. The first peak (retention time of 7.202 minutes) had fragments with m/z 43.74, 101, 143, 171, 214, 253, 281, 331, and 405. Based on data from the NIST17.L library, the first peak has a similarity percentage of 98% with the methyl laurate compound which was 1.39%. The second peak (retention time of 8.744 minutes) had fragments with m/z 43.74, 101, 143, 171, 199, 242, 281, 326, 355, and 405. Based on data from the NIST17.L library, the second peak has a 99% similarity percentage with the methyl myristate compound as much as 2.26%. The third peak (retention time of 10.021 minutes) had fragments with m/z 55.87, 123, 155, 194, 236, 268, 315, 355, 403, and 477. Based on data from the NIST17.L library, the third peak has a 99% similarity percentage with methyl palmitoleate as much as 0.80%. The fourth peak (retention time of 10.176 minutes) had fragments with m/z 43, 74, 101, 143, 185, 227, 270, 297, 327, 355, and 401. Based on data from the NIST17.L library, the fourth peak has a 99% similarity percentage with methyl palmitate compounds as much as 30.90%. The fifth peak (retention time of 11.270 minutes) has fragments with m/z 31, 67, 109, 150, 187, 220, 262, 294, 355, 389, 429, and 470. Based on library data NIST17.L, the fifth peak has a 99% similarity percentage with methyl linoleic compounds as much as 16.61%. The sixth peak (retention time of 11.323 minutes) had fragments with m/z 55, 97, 137, 180, 222, 264, 296, 255, 389, 429, and 470. Based on data from the NIST17.L library, the sixth peak has a 99% similarity percentage with methyl elaidate compounds as much as 38.54%. The seventh peak (retention time of 11.436 minutes) had fragments with m/z 74, 143, 199, 255, 298, 355, 415, 460, and 503. Based on NIST17.L library data, the seventh peak has a 99% similarity percentage with methyl stearate compounds as much as 8.62%. The eighth peak (retention time of 12.599 minutes) had fragments with m/z 39, 74, 109, 143, 207, 241, 283, 326, 377, 429, and 470. Based on the NIST17 library data. L, the eighth peak has 99% similarity with methyl arachidate compound as much as 0.88%.
This study was clear for the identification and characterization of the synthesized biodiesel. Recent studies for the best condition compare to this study as listed in Table 6. Based on Table 6, this study has more effective transesterification than previous study because of ultrasonic wave (for 15 minutes). Besides, Na2O/γ-Al2O3 catalyst needs to low amount for the transesterification of waste cooking oil.
| Catalyst | alcohol to oil molar ratio/temperature (℃)/catalyst (%wt)/time (h)/reactor | Yield (%) | Ref. |
| CaO-K2O | 15:1/65/8/5/ultrasonic wave | 92.37 | [5] |
| SrO–ZnO/Al2O3 | 10:1/75/15/5 | 95.7 | [36] |
| CaO/Al2O3 | 12:1/65/3/3/ | 30.91 | [37] |
| K2CO3/Al2O3 | 12:1/65/10/3 | 98.6 | [38] |
| KOH/Al2O3 | 12:1/65/7/2 | 73.7 | [39] |
| K/Al2O3, | 17:1/70/8.25/7 | 82.01 | [40] |
| NaOH/Al2O3 | 7:1/70/1.5/4 | 92 | [41] |
| K/Fe2O3/γ-Al2O3 | 9.73/65/4.6/7.84 | 99 | [42] |
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Based on the research, The results showed that the refined waste cooking oil using FTIR was known that there was still a carbonyl group indicating the presence of triglycerides. FFA content of waste cooking oil after esterification was 0.40%, so that the transesterification reaction could be carried out. The XRD results of the catalyst showed a conformity with the reference and it was determined by the Scherrer formula that the crystal size of catalyst was 30.59 nm. The best condition of biodiesel synthesis from waste cooking oil was obtained, namely with the catalyst concentration of 3% with a mole ratio of 1:1 of Na2O:γ-Al2O3 of ultrasonication, 65 ℃, and molar ratio of methanol: oil (12:1), the yield was 83.51%. The best conditions correlate to the best yield, so it is understood that the results will probably be higher than this study in the future [43]. The results of the characterization of viscosity, density, acid number and Free Fatty Acid of biodiesel were in accordance with Standar Nasional Indonesia (SNI) for Biodiesel (SNI 7182:2015). The TLC test showed that there was a difference in Rf between waste cooking oil and biodiesel so it could be concluded that the biodiesel synthesis was successful. The FTIR results showed that the transesterification product was an ester and further identified using GC-MS, the biodiesel component of the transesterification product contained 38.54% methyl elaidate, 30.90% methyl palmitate, 16.61% methyl linoleate, 8.62% methyl stearate, 2.26% methyl myristate, 1.39% methyl laurate, 0.88% methyl arachidate, and 0.80% methyl palmitoleate.
The authors would like to thank LPPM UM, who provided PNBP research funds.
The authors declare no conflict of interest.
Aman Santoso contributed with conceptualization and formal analysis. Thitania Nur Kusumah contributed with investigation, methodology and writing—original draft. Sumari Sumari, Anugrah Ricky Wijaya, and Siti Marfuah contributed with writing—original draft and writing—review & editing. Rini Retnosari, Ihsan Budi Rachman, and Muhammad Roy Asrori contributed with writing—review & editing.
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| 1. | Basem Al Alwan, Shahd Alamri, Atef El Jery, Mumtaj Shah, Taher Sahlabji, Development of Novel Mussel-Shell-Derived CaO-Based Transition Metal Catalysts for Efficient Microwave-Assisted Biodiesel Production, 2025, 13, 2227-9717, 522, 10.3390/pr13020522 | |
| 2. | D. Christopher Selvam, Yuvarajan Devarajan, T. Raja, Radioactive Remnants to Renewable Resources: A Comprehensive Review of Nuclear Waste Conversion to Biodiesel, 2025, 2522-5758, 10.1007/s42250-025-01262-8 |
Aman Santoso, Titania Nur Kusumah, Sumari Sumari, Anugrah Ricky Wijaya, Rini Retnosari, Ihsan Budi Rachman, Siti Marfuah, Muhammad Roy Asrori. Synthesis of biodiesel from waste cooking oil using heterogeneous catalyst of Na2O/γ-Al2O3 assisted by ultrasonic wave[J]. AIMS Energy, 2022, 10(5): 1059-1073. doi: 10.3934/energy.2022049
| Parameter | Before refining | After refining |
| Density (g/cm3) | 0.9260 | 0.9261 |
| Acid number (mg KOH/g) | 1.98 | 1.73 |
| Viscosity (cSt) | 35.69 | 36.71 |
| Free fatty acid (FFA) (%) | 0.94 | 0.82 |
DownLoad:
CSV
| Stretching vibration- | Wave number (cm-1) | Absorption intensity | Wavenumber (cm-1) [31] |
| C-H alkene | 3007.02 | strong, sharp | 3008.28 |
| C-H alkane | 2924.04 2852.72 |
strong, sharp Strong, sharp |
2925.80 2854.60 |
| C=O ester | 1747.51 | strong, sharp | 1746.26 |
| C-O | 1161.53 | strong, sharp | 1163.12 |
| CH2 | 721.38 | strong, sharp | 722.80 |
DownLoad:
CSV
| Parameter | Research results | SNI 7182:2015 |
| Density (g/m3) | 0.886 | 0.850−0.890 |
| Viscosity (cSt) | 3.191 | 2.3−6.0 |
| Free fatty acid (mg-KOH/g) | 0.39 | max 0.8 |
DownLoad:
CSV
| Stretching vibration- | Wavenumber of the study (cm-1) | Absorption intensity | Wavenumber (cm-1) [35] |
| C-H alkene | 3008.33 | Strong, sharp | 3008.9 |
| C-H alkane | 2924.09 2854.65 |
Strong, sharp Strong, sharp |
2925.76 2855.76 |
| C=O ester | 1743.65 | Strong, sharp | 1743.54 |
| C-O | 1165.00 | weak, sharp | 1172.42 |
| CH2 | 725.23 | Strong, sharp | 722.75 |
DownLoad:
CSV
| Retention time (minutes) | Content (%) | C content (hydrocarbon) | Compound |
| 7.202 | 1.39 | (C13:0) | Methyl Laurate |
| 8.744 | 2.26 | (C15:0) | Methyl Miristate |
| 10.021 | 0.80 | (C17:1) | Methyl Palmitoleate |
| 10.176 | 30.90 | (C17:0) | Methyl Palmitate |
| 11.270 | 16.61 | (C19:2) | Methyl Linoleate |
| 11.323 | 38.54 | (C19:1) | Methyl Elaidate |
| 11.436 | 8.62 | (C19:0) | Methyl Stearate |
| 12.599 | 0.88 | (C21:0) | Methyl Arachidate |
DownLoad:
CSV
| Catalyst | alcohol to oil molar ratio/temperature (℃)/catalyst (%wt)/time (h)/reactor | Yield (%) | Ref. |
| CaO-K2O | 15:1/65/8/5/ultrasonic wave | 92.37 | [5] |
| SrO–ZnO/Al2O3 | 10:1/75/15/5 | 95.7 | [36] |
| CaO/Al2O3 | 12:1/65/3/3/ | 30.91 | [37] |
| K2CO3/Al2O3 | 12:1/65/10/3 | 98.6 | [38] |
| KOH/Al2O3 | 12:1/65/7/2 | 73.7 | [39] |
| K/Al2O3, | 17:1/70/8.25/7 | 82.01 | [40] |
| NaOH/Al2O3 | 7:1/70/1.5/4 | 92 | [41] |
| K/Fe2O3/γ-Al2O3 | 9.73/65/4.6/7.84 | 99 | [42] |
DownLoad:
CSV
| Parameter | Before refining | After refining |
| Density (g/cm3) | 0.9260 | 0.9261 |
| Acid number (mg KOH/g) | 1.98 | 1.73 |
| Viscosity (cSt) | 35.69 | 36.71 |
| Free fatty acid (FFA) (%) | 0.94 | 0.82 |
| Stretching vibration- | Wave number (cm-1) | Absorption intensity | Wavenumber (cm-1) [31] |
| C-H alkene | 3007.02 | strong, sharp | 3008.28 |
| C-H alkane | 2924.04 2852.72 |
strong, sharp Strong, sharp |
2925.80 2854.60 |
| C=O ester | 1747.51 | strong, sharp | 1746.26 |
| C-O | 1161.53 | strong, sharp | 1163.12 |
| CH2 | 721.38 | strong, sharp | 722.80 |
| Parameter | Research results | SNI 7182:2015 |
| Density (g/m3) | 0.886 | 0.850−0.890 |
| Viscosity (cSt) | 3.191 | 2.3−6.0 |
| Free fatty acid (mg-KOH/g) | 0.39 | max 0.8 |
| Stretching vibration- | Wavenumber of the study (cm-1) | Absorption intensity | Wavenumber (cm-1) [35] |
| C-H alkene | 3008.33 | Strong, sharp | 3008.9 |
| C-H alkane | 2924.09 2854.65 |
Strong, sharp Strong, sharp |
2925.76 2855.76 |
| C=O ester | 1743.65 | Strong, sharp | 1743.54 |
| C-O | 1165.00 | weak, sharp | 1172.42 |
| CH2 | 725.23 | Strong, sharp | 722.75 |
| Retention time (minutes) | Content (%) | C content (hydrocarbon) | Compound |
| 7.202 | 1.39 | (C13:0) | Methyl Laurate |
| 8.744 | 2.26 | (C15:0) | Methyl Miristate |
| 10.021 | 0.80 | (C17:1) | Methyl Palmitoleate |
| 10.176 | 30.90 | (C17:0) | Methyl Palmitate |
| 11.270 | 16.61 | (C19:2) | Methyl Linoleate |
| 11.323 | 38.54 | (C19:1) | Methyl Elaidate |
| 11.436 | 8.62 | (C19:0) | Methyl Stearate |
| 12.599 | 0.88 | (C21:0) | Methyl Arachidate |
| Catalyst | alcohol to oil molar ratio/temperature (℃)/catalyst (%wt)/time (h)/reactor | Yield (%) | Ref. |
| CaO-K2O | 15:1/65/8/5/ultrasonic wave | 92.37 | [5] |
| SrO–ZnO/Al2O3 | 10:1/75/15/5 | 95.7 | [36] |
| CaO/Al2O3 | 12:1/65/3/3/ | 30.91 | [37] |
| K2CO3/Al2O3 | 12:1/65/10/3 | 98.6 | [38] |
| KOH/Al2O3 | 12:1/65/7/2 | 73.7 | [39] |
| K/Al2O3, | 17:1/70/8.25/7 | 82.01 | [40] |
| NaOH/Al2O3 | 7:1/70/1.5/4 | 92 | [41] |
| K/Fe2O3/γ-Al2O3 | 9.73/65/4.6/7.84 | 99 | [42] |
