Influence of temperature on the rate of epoxidation
The temperatures needed to be adjusted started at 55 °C, 65 °C, and lastly, 75 °C. Data were collected during the experiment based on the observations made. RCO was calculated using the weight of the sample taken and the amount of hydrogen bromide used. As shown in Fig. 1B, the RCO changed over time. Specifically, at a temperature of 55 °C, the RCO reading increased significantly until the twentieth minute, after which it immediately decreased. Then, for a temperature of 65 °C, the optimum RCO had already been achieved at the tenth minute, and the RCO reading slowly decreased by two points below the optimum RCO achieved just then. Lastly, at a temperature of 75 °C, the same as the previous temperature, the optimum RCO was reached for the tenth time, and the temperature then moderately decreased.
Vegetable oil in situ epoxidation typically requires temperatures below 70 °C, as high temperatures during epoxidation lead to excessive epoxy ring-opening events. Furthermore, peroxy acids can explode at a temperature of 80–85 °C and easily break down when heated; however, as this epoxide mixture contained sulphuric acid as the catalyst, the ideal temperature needed to be slightly higher than the standard range of temperature for epoxidation, which was from 50 to 80 °C since the catalyst did react together with a peracid that would facilitate formation regarding an active epoxidizing species. The long-term stability of the produced epoxide was not extensively addressed in this study. Oxirane groups are sensitive to moisture, heat, and acidic conditions, which can promote spontaneous ring-opening and degradation over time22. To preserve epoxide stability, storage under low temperatures, in dry conditions, and away from light or acidic environments is recommended.
Influence of hydrogen peroxide on the corn oil molar ratio
For the last parameter, the molar ratio of hydrogen peroxide was investigated. Hydrogen peroxide was used to react with formic acid during the epoxidation process to form a peracid, specifically peroxyformic acid. For the previous experiment, the ratio of hydrogen peroxide used was 1:1; however, for this parameter, the ratio would change to 0.5, 1.0, and 1.5 molar ratios. Based on Fig. 5, the highest yield of RCO was achieved at the twentieth minute, with a molar ratio of 1.5, and it subsequently decreased significantly thereafter. The highest RCO yield achieved in this parameter was approximately 43%; meanwhile, for the other molar ratios of 0.5 and 1.0, the RCO yields achieved were around 32% and 19%, respectively. At a molar ratio of 1.0, the graph fluctuated slightly.
In Fig. 2, the graph of the 1.5 molar ratio of hydrogen peroxide immediately decreased after it passed the highest epoxidation yield. This likely occurred due to the instability of the oxirane ring and may also be attributed to the side reaction that resulted from the excess hydrogen peroxide. This result was also quite contradictory to the finding from23, which, according to the data, obtained a larger proportion of RCO when the hydrogen peroxide concentration was raised. The oxirane ring showed poor stability at the lowest mole ratio of 1:1 between hydrogen peroxide and oleic acid.
Effect of hydrogen peroxide on the molar ratio of the corn oil epoxidation rate of corn oil.
Influence of catalyst loading on the rate of epoxidation
In this experiment, sulphuric acid was used as the catalyst, and the weight of sulphuric acid was measured to determine the ideal amount of catalyst needed to reach the highest epoxidation yield. Based on Fig. 3, the graph for the catalyst loading of 3 g of sulphuric acid shows that the RCO yield reached its highest point, exceeding 70%. As the graph decreased, the RCO values remained the same at the twentieth and thirtieth minutes, indicating that the duration required to reach a lower point was longer than for other amounts of catalyst loading. For the 6 g and 9 g of sulphuric acid, the RCO yield didn’t achieve its high value, and both graphs just moderately went down after barely reaching their optimum point. Too many catalysts wouldn’t help the experiment reach its ideal RCO value; yet, the best amount proven in this experiment was only 3 g of sulfuric acid.
However, this finding contradicts the statement that the reaction time required to obtain the maximal conversion of oxirane value decreased when the acid concentration was raised from 1 to 2 g. Additionally, it was noted that glycol production increased as the acid concentration rose. Higher oxirane cleavage and a proportionally lower oxirane value were seen when the catalyst loading was raised to 3%. Therefore, a 2 g loading of sulphuric acid produced the best conversion to oxirane. As for the corn oil used in the experiment, the amount of sulphuric acid needed was the lowest among the others, which was only 3 g of catalyst. Too much sulphuric acid could lead to an oxirane ring opening and produce an unintended epoxide24. In this study, corn oil, a renewable and biodegradable resource, was used as the raw material, promoting bio-based feedstocks and supporting waste reduction initiatives. However, a comprehensive life cycle assessment (LCA) and waste management evaluation would be necessary for future work to thoroughly assess the environmental benefits of using corn oil for epoxide production.
Effect of catalyst loading on epoxidation rate of corn oil.
FTIR characterization
Figure 4 shows the FTIR spectra show clear differences between the corn oil before and after epoxidation. A strong peak near 1650 cm¹ is observed in the original corn oil, which corresponds to the C = C stretching vibration from unsaturated fatty acids. After epoxidation, the intensity of this peak decreases, indicating that the double bonds have reacted. A new absorption band appears around 820–850 cm-1 in the epoxidized sample, assigned to the C–O–C stretching of the oxirane group, confirming the formation of epoxide structures. Small changes are also seen in the C–H stretching region between 2850 and 2950 cm¹, suggesting slight modifications in the fatty acid chains. Overall, the FTIR results provide supporting evidence for successful epoxidation, complementing the wet chemical analysis for RCO determination25.
FTIR spectra of corn oil and epoxidized corn oil.
Kinetic modelling of epoxidation of corn oil
The ideal reaction conditions for the epoxidation process were determined using kinetic modeling with MATLAB software; the reaction rate values, k, are listed in Table 2. For every chemical, the experimental data’s reaction rates, k, match the initial concentration. For the reaction rate (:{k}_{11}) The rate was a second slower than (:{k}_{12}). This was because the reaction only formed performic acid and its byproduct, water. The rate constant k11 (0.043 mol L-1 min-1) represents the epoxide formation, while k12 (12.53 mol L-1 min-1) reflects the consumption rate of intermediates in a secondary reaction pathway. The significantly higher value of k12 suggests that this step is much faster, which may impact the overall epoxide yield if not controlled.
The constants k2 (0.110 mol L-1min-1) and k3 (0.066 mol L-1min-1) correspond to the rates of epoxide formation and degradation through ring-opening, respectively. The lower value of k3 indicates a slower degradation rate, which is beneficial for preserving the oxirane content. The R2 value of 0.85 indicates a reasonable agreement between the experimental and simulated data, demonstrating the model’s ability to capture the reaction kinetics, though some minor discrepancies remain. The low sum of error (0.14) also supports the model’s reliability in describing the process. These results highlight the efficiency of the epoxidation process while identifying areas where further model refinement could enhance predictive accuracy.
Figure 5 illustrates a notable discrepancy between the simulation and the OOC experiment. The simulation graph was quite low, with its highest point only reaching below 0.6 OOC. Meanwhile, the experiment graph showed that the OOC could reach a higher value, almost 0.8, yet after the twentieth minute, it significantly decreased. This could be happening because of the purity of the solutions used or the efficiency of the epoxidation reaction. The deviations between the simulation and experimental results, especially near the peak oxirane content, are mainly due to simplified modeling assumptions that do not fully capture side reactions and oxirane degradation in linoleic acid-rich corn oil. Secondary ring-opening reactions, oxirane instability, and minor experimental variations may also contribute to the discrepancies. While the model predicts the overall trend well, the observed gaps highlight the need for more detailed kinetic mechanisms in future work.
Comparison of the oxirane content between experiment and simulation.