Preparation method of soybean oil-based cyclic carbonate

Abstract

The invention discloses a preparation method of soybean oil-based cyclic carbonate, which comprises the following steps: mixing epoxidized soybean oil and a catalyst in a closed environment, discharging air in the closed environment, filling CO2 into the closed environment, regulating the pressure of the CO2 to 1.0-2.0 MPa, reacting for 10-12 hours at the temperature of 100-120 DEG C under the stirring condition, and purifying to obtain the soybean oil-based cyclic carbonate, the catalyst is composed of tetrabutylammonium bromide and triethanolamine borate, and the molar ratio of tetrabutylammonium bromide to triethanolamine borate is (1-4): 1. According to the method, tetrabutylammonium bromide and triethanolamine borate form a catalyst, the catalyst is used for preparing the soybean oil-based cyclic carbonate through the reaction of epoxidized soybean oil and CO2, the yield of the soybean oil-based cyclic carbonate is increased, the production cost is reduced, the used reaction temperature and CO2 pressure are low, the reaction time is short, and the reaction conditions are mild.

Description

Technical Field

[0001] This invention belongs to the field of cyclic carbonate technology, specifically relating to a method for preparing soybean oil-based cyclic carbonates. Background Technology

[0002] Vegetable oil-based cyclic carbonates are key raw materials for the preparation of NIPU (nitrogenous polyphenol oxidase), obtained by converting epoxidized vegetable oils with CO2 to cyclic carbonates. Currently, the long fatty acid chains and steric hindrance of the active groups in the structure of epoxidized vegetable oils result in harsh conditions for the cycloaddition reaction in the catalytic chain, making it difficult to synthesize high-yield vegetable oil-based cyclic carbonates. To ensure high yields during synthesis, the reaction gas pressure must reach above 10 bar, and the reaction time must be at least 16 hours. These conditions are not only difficult to simultaneously achieve mild conditions, but also often lead to low cyclic carbonate yields. In actual catalytic cycloaddition reactions, it is difficult to simultaneously achieve relatively mild reaction temperatures, pressures, and times; usually, one must be sacrificed to ensure a high yield. For example, to conduct the reaction under normal pressure, the reaction time may need to be extended to 70 hours; or to shorten the reaction time to 16 hours, supercritical CO2 pressure is required. Therefore, a method for preparing soybean oil-based cyclic carbonates with high yields needs to be developed using epoxidized soybean oil (ESO) as a raw material. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing soybean oil-based cyclic carbonates, in order to solve the problem of harsh reaction conditions and low yield in the process of converting epoxidized soybean oil and CO2 into cyclic carbonates.

[0004] According to one aspect of the present invention, a method for preparing soybean oil-based cyclic carbonates is provided, comprising the following steps: Epoxidized soybean oil and catalyst are mixed in a closed environment. After the air in the closed environment is purged, CO2 is introduced into the closed environment and the pressure of CO2 is adjusted to 1.0-2.0 MPa. Then, the reaction is carried out at a temperature of 100-120℃ and under stirring for 10-12 hours. After purification, the product is obtained. The catalyst is composed of tetrabutylammonium bromide and triethanolamine borate, with a molar ratio of tetrabutylammonium bromide to triethanolamine borate of (1-4):1.

[0005] This invention reveals that using tetrabutylammonium bromide as the main catalyst and triethanolamine borate as the co-catalyst, the combination of the two as a binary homogeneous catalyst significantly reduces the activation energy of the chemical reaction compared to using tetrabutylammonium bromide alone, thereby accelerating the efficient formation of soybean oil-based cyclic carbonates. Specifically, the activation energy of the co-catalyzed reaction of tetrabutylammonium bromide and triethanolamine borate is reduced to 57.16 kJ / mol, corresponding to a pre-exponential factor of 1.79 × 10⁻⁶ kJ / mol.5 The combination of these two components can improve the conversion rate and selectivity of epoxidized soybean oil during the reaction with CO2, thereby increasing the yield of soybean oil-based cyclic carbonates. Simultaneously, the preparation method of this invention utilizes lower reaction temperatures and CO2 pressures, achieving high yields of soybean oil-based cyclic carbonates in shorter reaction times. In this process, they not only act as catalysts, promoting the reaction, but also serve as solvents, providing a suitable medium for the reaction. The triethanolamine borate used in this invention possesses excellent lipid solubility, enabling it to fully integrate with the substrate epoxidized soybean oil; this characteristic helps to increase the rate of the cycloaddition reaction.

[0006] In some embodiments, the molar ratio of tetrabutylammonium bromide to triethanolamine borate is 2:1. This invention has found that in a binary homogeneous catalyst, when the molar ratio of tetrabutylammonium bromide to triethanolamine borate is 2:1, the yield of soybean oil-based cyclic carbonate obtained at 100°C is 44.4%, which is significantly higher than the yield obtained when the molar ratio is 1:1 or 4:1.

[0007] In some implementations, the temperature is 120°C.

[0008] In some embodiments, the molar amount of tetrabutylammonium bromide is 4%-6% of the molar amount of epoxy groups in epoxidized soybean oil; the molar amount of triethanolamine borate is 1.25%-5% of the molar amount of epoxy groups in epoxidized soybean oil. Preferably, the molar amount of tetrabutylammonium bromide is 5% of the molar amount of epoxy groups in epoxidized soybean oil; the molar amount of triethanolamine borate is 2.5% of the molar amount of epoxy groups in epoxidized soybean oil.

[0009] In some embodiments, the method for purging air from a confined environment is to introduce CO2 into the confined environment 3-5 times. This invention ensures that the air in the confined environment is completely replaced by CO2 by introducing CO2 into the confined environment at least 3 times.

[0010] In some implementations, the stirring speed is 400 rpm.

[0011] In some embodiments, the reaction time is 12 hours. At this reaction time, the yield of soybean oil-based cyclic carbonates is the highest.

[0012] In some implementations, the CO2 pressure is adjusted to 2.0 MPa.

[0013] In some embodiments, the purification method involves dissolving the crude product obtained after the reaction in an organic solvent to obtain an organic phase, washing and drying the organic phase, then filtering and rotary evaporating the organic phase, and finally drying the product at 80°C. The purpose of washing is to remove the catalyst, the purpose of drying is to remove the moisture from the crude product, the purpose of filtering is to further remove the residual moisture in the dried crude product, and the purpose of rotary evaporation is to remove the organic solvent.

[0014] In some embodiments, the organic solvent is ethyl acetate.

[0015] In some embodiments, the washing method involves washing the organic phase with saturated brine.

[0016] In some embodiments, the organic phase is washed 8-10 times with saturated brine. The purpose of washing the crude product at least 8 times is to ensure complete removal of the catalyst from the crude product and improve product purity.

[0017] In some embodiments, the method for drying the organic phase is to add anhydrous magnesium sulfate to the organic phase.

[0018] The beneficial effects of this invention are: (1) This invention uses tetrabutylammonium bromide and triethanolamine borate to form a binary homogeneous catalyst for the preparation of soybean oil-based cyclic carbonates, thereby improving the yield of soybean oil-based cyclic carbonates. Moreover, the appropriate addition of triethanolamine borate can significantly reduce the amount of halogen elements used and also helps to reduce the amount of tetrabutylammonium bromide added. This reduces corrosion to production equipment and is expected to lower production costs.

[0019] (2) The preparation method of the present invention significantly improves the yield of soybean oil-based cyclic carbonates by selecting the amount of tetrabutylammonium bromide and triethanolamine borate.

[0020] (3) The preparation method of the present invention uses a low reaction temperature and CO2 pressure, a short reaction time, and mild reaction conditions. Attached Figure Description

[0021] Figure 1 The preparation process of CSO; Figure 2 For CSO 1 H NMR spectrum; Figure 3 The conversion, selectivity, and yield of CSO at different reaction temperatures; Figure 4 The conversion, selectivity and yield of CSO under different CO2 pressures; Figure 5 The conversion, selectivity, and yield of CSO at different reaction times; Figure 6GPC characterization of ESO and CSO; Figure 7 FT-IR spectra of ESO and CSO; Figure 8 The diagrams show the kinetics of the catalytic cycloaddition reaction of TBAB and TBAB-TEOAB, where a is the kinetics of the catalytic cycloaddition reaction of TBAB and b is the kinetics of the catalytic cycloaddition reaction of TBAB-TEOAB. Figure 9 Arrhenius spectra of Lnk and 1 / T for TBAB and TBAB-TEOAB; Figure 10 This is a schematic diagram of the catalytic cycloaddition reaction mechanism of TBAB-TEOAB. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0023] 1. Experimental Materials and Methods 1.1 Main experimental materials and reagents The main reagents and raw materials used in the experiment are shown in Table 1.

[0024] Table 1. Main Reagents and Raw Materials

[0025] It should be noted that the epoxy value of the epoxidized soybean oil used in this invention is 4.2.

[0026] 1.2 Main Experimental Instruments The main instruments used in this experiment are shown in Table 2.

[0027] Table 2 Main Instruments for the Experiment

[0028] 1.3 Experimental Section 1.3.1 Preparation of soybean oil-based cyclic carbonates (CSO) The preparation process of CSO is as follows: Figure 1As shown. 10.0 g of ESO and catalysts (TBAB and TEOAB) were added to a 250 mL liner and stirred until homogeneous. The liner was then placed in a sealed high-pressure reactor equipped with a magnetic stirrer and thermocouple, and the reactor was sealed. Subsequently, CO2 was introduced into the high-pressure reactor at 1.5 MPa. This process was repeated three times to ensure complete replacement of the air inside the reactor. The reactor was then preheated for 30 minutes, followed by pressurization to the required pressure. The stirring speed was adjusted to 400 rpm and maintained until the predetermined reaction time was reached. The high-pressure reactor was then closed, and after it cooled naturally to room temperature, any unreacted CO2 gas remaining inside the reactor was promptly released. The liner was then removed. After the reaction was complete, an appropriate amount of ethyl acetate was added to the system to dissolve the crude sample, and the resulting crude product was transferred to a 100 mL beaker for further processing. First, the crude product was washed eight times with saturated brine at 60°C to remove TBAB and TEOAB. Anhydrous magnesium sulfate was added to dry the crude product, which was then allowed to stand for 12 hours. Residual moisture was removed by vacuum filtration using a vacuum pump. Finally, ethyl acetate was removed by rotary evaporation under reduced pressure. The soybean oil-based cyclic carbonate obtained by rotary evaporation was dried in a vacuum oven at 80°C for 12 hours to obtain pure CSO.

[0029] 1.3.2 Kinetic Experiment 10.0 g of ESO and TBAB (5% of the molar amount of ESO epoxy functional groups) and TBAB / TEOAB (5% / 2.5% / 1.25% of the molar amount of ESO epoxy functional groups) were added to a 250 mL liner and stirred until homogeneous. The liner was placed in a high-pressure reactor and sealed. CO2 at 1.5 MPa was then introduced into the reactor, followed by venting the CO2 out of the reactor. CO2 at 2.0 MPa was then added back into the reactor. The reactions were carried out at 100℃, 110℃, and 120℃, with six reaction times at each temperature: 2 h, 4 h, 6 h, 8 h, 10 h, and 12 h. After the reaction was complete, a certain amount of ethyl acetate was added to dissolve the crude sample, and the crude product was transferred to a 100 mL beaker for subsequent processing. First, the crude product was washed eight times with saturated brine at 60°C to remove TBAB and TEOAB. Anhydrous magnesium sulfate was added to dry the crude product, which was then allowed to stand for 12 hours. The product was then filtered using a vacuum pump to remove residual moisture. Finally, ethyl acetate was removed by vacuum distillation using a rotary evaporator. The resulting soybean oil-based cyclic carbonate (CSO) was then dried in a vacuum oven at 80°C for 12 hours to obtain pure CSO.

[0030] 1.4 Characterization Methods 1.4.1 Fourier Transform Infrared Spectroscopy FT-IR testing was used to determine the chemical structures of ESO and CSO. The liquid products were coated onto potassium bromide slides, and the functional group structures were qualitatively analyzed using an infrared spectrometer (a Nicolet IS10 FTIR spectrometer from Thermo Fisher Scientific). The wavenumber range used in the tests was 400–4000 cm⁻¹. -1 The resolution is 4 cm. -1 The number of scans was 32.

[0031] 1.4.2 Proton NMR Spectroscopy 1 1H NMR was used to determine the chemical structures of ESO and CSO, and the results were used to calculate the conversion, selectivity, and yield of ESO to CSO, as well as the functionality of the cyclic carbonate groups of CSO. The products were dissolved in deuterated chloroform and characterized by 1H NMR using a Bruker AV 600M 181 spectrometer (Germany), with tetramethylsilane as an internal standard.

[0032] 1.4.3 Reaction Kinetics TBAB was selected as the catalyst and reacted with epoxidized soybean oil under different temperature conditions (100℃, 110℃, 120℃) and different reaction times (2 h, 4 h, 6 h, 8 h, 10 h, 12 h). Based on the conversion rate data of soybean oil-based cyclic carbonates under each condition, the activation energy and pre-exponential factor of the catalyst catalyzing the entire reaction system were further calculated.

[0033] 1.4.4 Calculation Methods for Conversion Rate and Selectivity of Soybean Oil-Based Cyclic Carbonates use 1 ¹H NMR spectra can be used to calculate the number of hydrogen atoms on each functional group, thus effectively determining the conversion rate (%C) and selectivity (%S) of soybean oil. Specifically: according to 1 The number of epoxy and cyclic carbonate functional groups in ESO and CSO was calculated by integrating the H NMR spectra. For example... Figure 2 As shown, the signal of a single hydrogen atom (K) on the triglyceride bond was used as the proton spectrum normalization factor. The number of epoxy functional groups (E) was calculated using the signal corresponding to epoxy (I) (Equation (2.1)). Similarly, the number of cyclic carbonate functional groups (C) was calculated from the relevant signal (M) using Equation (2.2). Finally, the conversion, yield, and selectivity were obtained using Equations (2.3), (2.4), and (2.5):

[0034]

[0035]

[0036]

[0037]

[0038] 1.4.5 Gel permeation chromatography GPC was used to characterize the molecular weight distribution of ESO and CSO. The test was performed on a Waters e2695 gel permeation chromatograph with a 2414 RI Detector detector, using polystyrene as the standard, chromatographic grade tetrahydrofuran as the elution solvent, at a test temperature of 30°C, and a column flow rate of 1.0 mL / min. -1 .

[0039] 1.5 Results and Analysis 1.5.1 Screening of main catalyst / co-catalyst Multiple different main catalysts and co-catalysts were paired, and three different quaternary ammonium salt main catalysts (TBAC, TBAB, and TBAI) and four different types of co-catalysts (boric acid, triethylamine, a combination of boric acid and triethylamine, and triethanolamine borate) were used for synergistic catalysis to study the effect of main catalysts and co-catalysts on the yield of soybean oil-based cyclic carbonates. The reaction conditions were set as follows: 10.0 g of ESO feedstock, reaction temperature 100℃, CO2 pressure 1.0 MPa, reaction time 6 h, and reaction speed 400 rpm. The effects of different main catalysts and co-catalysts on the yield of soybean oil-based cyclic carbonates were systematically investigated, and the experimental results are shown in Table 3. In Table 3, the "%" column for main catalyst and co-catalyst indicates the percentage of the molar amount of the main catalyst or co-catalyst relative to the molar amount of the ESO epoxy group.

[0040] Table 3 Effect of main catalyst / co-catalyst on the yield of soybean oil-based cyclic carbonates

[0041] Table 3 shows that the composite catalytic system composed of TBAB and TEOAB exhibits the best performance in catalyzing the cycloaddition reaction of CSO and CO2. Specifically, when using 5 mol% TBAB with ESO epoxy groups and 2.5 mol% TEOAB with ESO epoxy groups, the yield of soybean oil-based cyclic carbonates can reach as high as 44.4%. In the catalytic reaction, TEOAB exhibits excellent solubility and is completely compatible with the epoxidized soybean oil substrate, effectively solving the problem of insufficient yield caused by insufficient reaction surface area. The addition of the co-catalyst TEOAB significantly increases the rate of the cycloaddition reaction.

[0042] Besides the choice of co-catalyst, the main catalyst determines the efficiency of soybean oil-based cyclic carbonate (CSO) formation. When TBAC was chosen as the main catalyst, the CSO yield decreased from 44.4% to 18.7%. Similarly, when TBAB was replaced with tetrabutylammonium iodide (TBAI), the yield also decreased to 28.6%. Experimental results show that when choosing the quaternary ammonium salt TBAX as the main catalyst, bromide ions (Br) have the best catalytic effect for cycloaddition reactions as halogen atoms. In cycloaddition reactions, the nucleophilicity order of halogen atoms is Cl... - >Br - >I - The order of departure ability after opening the loop is Cl. - <Br - <I - Based on the nucleophilic and leaving properties of halogen atoms, combined with experimental results, Br - It plays a central role in the cycloaddition reaction. Based on the above analysis, it can be concluded that the combined use of TBAB and TEOAB as a binary homogeneous catalyst exhibits optimal performance in the catalytic synthesis of soybean oil-based cyclic carbonates. This chapter selects TBAB as the main catalyst and TEOAB as the co-catalyst as a composite catalyst, and this composite catalyst will continue to be used in subsequent experiments.

[0043] 1.5.2 Effect of catalyst concentration on cycloaddition reaction To investigate the effect of the ratio of TBAB to TEOAB on the CSO yield, a series of experiments were conducted under the conditions of a reaction temperature of 100℃, a CO2 pressure of 1.0 MPa, a reaction time of 6 h, and a reaction speed of 400 rpm. The results are shown in Table 4.

[0044] Table 4 Effect of main catalyst / main catalyst dosage on the yield of soybean oil-based cyclic carbonates

[0045] Table 4 shows that when only 5% TBAB was used as the main catalyst, the yield of soybean oil-based cyclic carbonates was only 23.0%. However, when 1.25% TEOAB was added as a co-catalyst, the yield increased to 27.6%, which preliminarily confirms the positive effect of TEOAB on improving the yield of soybean oil-based cyclic carbonates. Furthermore, when the amount of TEOAB increased from 1.25% to 2.5%, the yield significantly increased to 44.4%. It is noteworthy that when the amount of TEOAB continued to increase to 5%, the yield decreased to 24.3%. This indicates that excessive TEOAB addition may inhibit the reaction. A possible reason is that although the Lewis acid sites in TEOAB facilitate ring-opening reactions, their ring-opening efficiency is lower than that of halogen atoms. Therefore, considering various factors, the amount of co-catalyst should not be excessive. Based on the comprehensive experimental results, TBAB with a molar amount of 5% ESO epoxy group and TEOAB with a molar amount of 2.5% ESO epoxy group were selected as the optimal catalyst addition amounts.

[0046] 1.5.3 Effect of reaction temperature on cycloaddition reaction This section investigates the CSO yield at different reaction temperatures. The reaction conditions were set as follows: 10.0 g ESO, 5% TBAB / 2.5% TEOAB, CO2 pressure maintained at 1.0 MPa, reaction time 6 h, and reaction speed 400 rpm. The results are as follows: Figure 3 As shown.

[0047] from Figure 3 It can be seen that when the reaction temperature is set at 80℃, the synthesis yield of soybean oil-based cyclic carbonate is only 32.2%, which is mainly attributed to insufficient conversion. As the temperature gradually increases, the yield of soybean oil-based cyclic carbonate shows an increasing trend. When the temperature reaches 120℃, the yield of soybean oil-based cyclic carbonate significantly increases to 60.5%. However, if the temperature continues to rise to 140℃, although the conversion rate increases somewhat, the increase is limited, and the selectivity decreases significantly, resulting in a yield reduction to 57.5%. Experiments at higher temperatures were not conducted because the catalyst tetrabutylammonium bromide decomposes under high-temperature conditions, producing triethylamine, hydrogen bromide, butanone, and other substances. These decomposition products reduce the selectivity of the reaction, thus affecting the yield. Furthermore, excessively high temperatures can promote the formation of the byproduct ketone. Therefore, considering both conversion and selectivity, as well as avoiding the formation of byproducts, the optimal reaction temperature was ultimately determined to be 120℃, and this set temperature was consistently used in all subsequent experiments.

[0048] 1.5.4 Effect of CO2 pressure on the yield of soybean oil-based cyclic carbonates This section investigates the effect of different CO2 pressures on CSO yield. The reaction conditions were set as follows: reaction temperature 120℃, catalyst dosage of 5% TBAB and 2.5% TEOAB, 10.0 g ESO, reaction time 6 h, and reaction speed 400 rpm. The results are as follows: Figure 4 As shown.

[0049] from Figure 4 It can be seen that under the condition of only 0.1 MPa in the system, the yield of soybean oil-based cyclic carbonates is only 17.5%, which is mainly due to the insufficient solubility of CO2 in vegetable oil. As the CO2 pressure gradually increases, when the pressure increases from 0.1 MPa to 2.0 MPa, the yield of soybean oil-based cyclic carbonates significantly increases to 66.7%, an increase of 49.2% in this process. During this growth stage, both conversion and selectivity increase, but the main increase in yield is attributed to the increase in conversion. When the reaction pressure reaches 1.5 MPa and 2.0 MPa, the yields of soybean oil-based cyclic carbonates are 64.2% and 66.7%, respectively, with an increase of only 2.5% between the two. This indicates that at this pressure, the CO2 concentration has reached a suitable level, and further increasing the CO2 pressure has no significant effect on the yield of soybean oil-based cyclic carbonates.

[0050] The experimental results indicate that at low CO2 pressure, the contact area of ​​the reaction system is small, leading to a low CSO yield. When the CO2 pressure is increased to a certain threshold, the increase in product formation tends to plateau. This is mainly because the concentration of CO2 as a reactant has reached saturation at this stage, and further increases in pressure do not effectively promote the reaction. It is worth noting that the yield of cyclic carbonates is also affected by various factors, including but not limited to the type and amount of catalyst, reaction temperature, and reaction time. Accordingly, simply increasing the CO2 pressure is insufficient to achieve a continuous increase in cyclic carbonate yield. Based on this, the reaction pressure was set at 2.0 MPa, and the reaction time parameter was kept constant thereafter to investigate the effects.

[0051] 1.5.5 Effect of reaction time on the yield of cyclic carbonates This section systematically investigated the effect of reaction time on the yield of CSO. The reaction conditions were set as follows: reaction temperature 120℃, catalyst dosage of 5% TBAB and 2.5% TEOAB (relative to the amount of epoxy groups), 10.0 g ESO, reaction time 6 h, reaction speed 400 rpm, and CO2 pressure 2.0 MPa. The results are as follows: Figure 5 As shown.

[0052] from Figure 5It can be seen that when the reaction time is 2 h, the CSO yield is only 20.4%. When the reaction time is extended to 12 h, the CSO yield increases to 91.2%. However, when the reaction time is increased from 10 h to 12 h, the CSO yield only increases by 1%. At this time, the selectivity of cyclic carbonates decreases from 92.0% to 91.3%, and the yield of soybean oil-based cyclic carbonates remains almost unchanged.

[0053] Experimental results show that the CSO formation rate exhibits a trend of first increasing and then decreasing within the 0-12 h reaction time, a phenomenon possibly related to the chemical composition of the substrate ESO. The changes in CSO yield across the five time periods show a positive correlation with the compositional proportions of various fatty acids in the ESO. During the entire reaction, methyl epoxide (PEO) undergoes ring-opening first, and due to its single epoxy group, its CSO formation rate is the fastest at this stage. Subsequently, methyl epoxide (PEL) and methyl epoxide (PEL-linolenic acid), which have greater steric hindrance, undergo ring-opening sequentially, increasing the difficulty of ring-opening and thus slowing down the CSO formation rate. When PEL reacts, the epoxy group tends to open first at the C-9 and C-15 positions, with the epoxy group at the C-12 position, located at the center of the carbon chain, exhibiting the greatest steric hindrance. When the reaction time is extended from 10 h to 12 h, the yield of soybean oil-based cyclic carbonates increases by only 1% from 90.2%. In conclusion, 12 h was ultimately determined as the optimal reaction time to ensure maximum cyclic carbonate yield.

[0054] 1.5.6 Product Characterization Analysis CSO 1 The H NMR characterization results are as follows: Figure 2 As shown, the characteristic peaks corresponding to the epoxy groups in ESO (2.80-3.20 ppm) disappeared after conversion, and were replaced by the characteristic peaks corresponding to the cyclic carbonate groups in CSO (4.45-5.10 ppm). The molecular weight distributions of ESO and CSO were determined using GPC, and the results are as follows. Figure 6 As shown, the elution position of CSO is lower than that of ESO (18.32 min), indicating that the molecular weight increases after the conversion of ESO to CSO. Furthermore, CSO only shows a single peak at 17.9 min, suggesting that the synthesized compound has high purity. The FT-IR spectra of ESO and CSO are shown below. Figure 7 As can be seen from the figure, the infrared characteristic peak representing the epoxy group in the CSO spectrum is at 824 cm⁻¹. -1 and 845 cm -1 It disappeared at 1795 cm. -1 and 1047 cm -1Two new infrared characteristic peaks appeared, which are attributed to the stretching vibration of C=O and the deformation and stretching vibration of CO, respectively. These results indicate that ESO was successfully converted into CSO.

[0055] To further investigate the conversion efficiency of epoxy groups in ESO to cyclic carbonate groups in CSO, the -CH- groups in triglycerides were used as a starting point. 1 Using the characteristic peaks of 5.20–5.30 ppm in the ¹H NMR spectrum as a standard reference, the normalized integral areas of the epoxy groups in ESO and the cyclic carbonate groups in CSO were calculated. The epoxy groups in ESO (E m The quantity of cyclic carbonate groups (Cb) can be calculated from the b signal (2.80–3.20 ppm), i.e., formula (2.1). Similarly, according to formula (2.2), the number of cyclic carbonate groups (Cb) in CSO can be calculated from the c signal (4.45–5.10 ppm) related to cyclic carbonates. m The quantity of E. mi E represents the initial number of epoxy groups (i.e., the number of epoxy groups that did not participate in the reaction). mf This represents the final number of epoxy groups (i.e., the number of epoxy groups remaining at the end of the reaction). The conversion (%C), yield (%Y), and selectivity (%S) of ESO to CSO can be calculated using formulas (2.3) to (2.5). The calculated conversion %C = 99.8%, selectivity %S = 91.3%, and yield %Y = 91.2%.

[0056] 1.6 Kinetic Study of Cycloaddition Reaction 1.6.1 Calculation of the rate constant for cycloaddition reactions To investigate the kinetic model governing the conversion of epoxidized soybean oil epoxy groups (EPO) to cyclic carbonates catalyzed by the catalyst tetrabutylammonium bromide-triethanolamine borate, this experiment was conducted under conditions of excess CO2 and a fixed TBAB concentration. The reaction order of EPO with CO2 was assumed to be first-order, and the reaction was carried out at 100-120℃ in 10℃ increments. The change in the molar amount of epoxy groups in epoxidized soybean oil over time was obtained experimentally. Furthermore, equation (2.6) provides the basic rate equation for the TBAB-catalyzed cycloaddition reaction between CO2 and ESO, providing a theoretical basis for establishing the kinetic model.

[0057] EPO is the molar concentration of the epoxy functional group after reaction time t. Then, equation (2.6) can be simplified to equations (2.7) and (2.8). Experimental results show that the reaction rate is consistent with equation (2.8) and has a linear relationship with the EPO concentration.

[0058]

[0059]

[0060]

[0061] Given that both CO2 and catalyst are in excess, it is reasonable to assume that the reaction follows first-order kinetics. Based on this, by performing a logarithmic transformation on both sides of equation (2.8), equation (2.9) can be further derived.

[0062]

[0063] At a CO2 pressure of 2.0 MPa, linear relationships were plotted according to equation (2.9) for using TBAB alone as a catalyst and for the TBAB / TEOAB binary composite catalytic system, with -Ln(EPO) as the ordinate and t as the abscissa. Figure 8 a and Figure 8 As shown in b in the figure. Experimental results show that the obtained R 2 The values ​​are all higher than 0.93, proving that the first-order reaction kinetic model proposed above is correct. Based on the experimental results, the reaction kinetic constant "k" of TBAB and TBAB-TEOAB under different temperature conditions was calculated. Tables 5 and 6 show the reaction rate constant "k", intercept "b", and correlation coefficient R of the two types of catalysts under different temperature conditions, respectively. 2 .

[0064] As shown in Tables 5 and 6, at the same temperature, the rate constant (k) of the TBAB-TEOAB catalytic system is higher than that of TBAB. This indicates that the addition of TEOAB promotes the CSO yield. The difference in catalytic efficiency between the TBAB and TBAB-TEOAB catalytic systems is related to temperature; as the reaction temperature increases, the reaction rate constant k also increases, and this increasing trend is positively correlated with the extension of reaction time. This confirms that both temperature and reaction time have a positive impact on the reaction rate constant and also demonstrates that the ESO-CO2 cycloaddition reaction is an endothermic process.

[0065] Table 5. k, b values ​​and R of catalyst TBAB at different temperatures 2

[0066] Table 6. k, b values ​​and R of catalyst TBAB-TEOAB at different temperatures 2

[0067] 1.6.2 Calculation of the Arrhenius equation and pre-exponential factors In the field of chemical reactions, there is a close relationship between the reaction rate constant (k) and temperature (T), which is described by the Arrhenius equation within a certain temperature range. Specifically, this equation can be expressed in the following form:

[0068]

[0069]

[0070] Among them, k, A, E a R and T are the Arrhenius equation for the reaction rate constant, pre-exponential factor, activation energy (kJ / mol), gas constant k, and temperature T, as shown in the figure. Figure 9 As shown.

[0071] Figure 9 The kinetic characteristics of CSO catalytic production by TBAB and TBAB-TEOAB were presented. Linear fitting analysis was performed using the Arrhenius equation, yielding the following expressions: for TBAB, the equation is Lnk = 15.5955 - 8.4253 / T, while for the TBAB-TEOAB system, the equation is Lnk = 20.5567 - 10.1305 / T. Further calculations were made of the activation energy (E). a Based on the calculation of (A) and the pre-exponential factor (A), the activation energy of the TBAB system is found to be 70.05 kJ / mol, with a corresponding pre-exponential factor of 5.92 × 10⁻⁶. 6 In contrast, the activation energy of the TBAB-TEOAB system is 57.16 kJ / mol, and its pre-exponential factor is 1.79 × 10⁻⁶. 5 This indicates that the introduction of TEOAB as a co-catalyst significantly reduced the activation energy of the reaction process, thereby accelerating the cycloaddition reaction and promoting the formation of soybean oil-based cyclic carbonates.

[0072] 1.6.3 Speculation on the Mechanism of Cycloaddition Reactions This experiment used TBAB and TEOAB as the catalytic system. Under the optimal reaction conditions explored above, high-yield CSO was successfully synthesized. Therefore, the mechanism of the cycloaddition reaction of CSO and CO2 by the TBAB-TEOAB catalytic system was investigated in depth.

[0073] In this catalytic system, TBAB acts as the main catalyst, while TEOAB acts as a Lewis acid-base pair, serving as a co-catalyst. Experimental results show that the introduction of TEOAB significantly increases the rate of the cycloaddition reaction and the yield of cyclic carbonates. This phenomenon can be attributed to the Lewis acid-base pair effect provided by TEOAB: during the cycloaddition reaction, the B atom exhibits the characteristics of a Lewis acid, successfully activating the CO bond in the epoxide group through hydrogen bonding with the oxygen atom in the epoxide group, effectively promoting the ring-opening reaction process of the epoxide group; simultaneously, the N atom can effectively absorb CO2 from the reaction environment to generate the corresponding aminocarbonate, a process that can effectively increase the effective concentration of CO2 in the vegetable oil in the reaction system. Based on the above analysis, a possible mechanism for the cycloaddition reaction of ESO and CO2 is proposed, such as... Figure 10 As shown.

[0074] The mechanism of TBAB and TEOAB co-catalyzed synthesis of cyclic carbonates can be summarized into three key stages: First, hydrogen bonds are formed between the B atom in the TEOAB molecule and the oxygen atom in the epoxy group, which significantly enhances the activity of the epoxy group. Simultaneously, the Br ion in TBAB attacks the epoxy group, leading to its ring-opening reaction and generating intermediate A, successfully improving the formation efficiency of soybean oil-based cyclic carbonates. Second, the N atom in TEOAB has the ability to adsorb CO2, which helps increase the CO2 content in the reaction solvent. Subsequently, CO2 interacts with the oxygen anion in the ring-opened epoxy group to form intermediate B3. In the final step, intermediate B3 undergoes an intramolecular cyclization reaction to generate a five-membered ring carbonate, at which point Br... - It is released. This step also reflects the Br in TAB. - The advantage lies in the fact that halogen elements, being more nucleophilic, not only facilitate the ring-opening of the epoxide group but also exhibit stronger leaving ability after attacking the epoxide group. In this cycloaddition reaction step, the Lewis acid bond involved in the activation of the epoxide group also undergoes a bond-breaking process.

[0075] 2. Summary This invention utilizes a binary homogeneous catalytic system composed of TBAB and the widely available and cost-effective TEOAB to catalyze the cycloaddition reaction of epoxidized soybean oil with CO2. The effects of the types and concentrations of the main and co-catalysts, reaction temperature, CO2 pressure, and reaction time on the cycloaddition reaction yield were investigated in detail. Furthermore, the kinetic characteristics of the reaction were studied, and through experimental and theoretical analysis, the potential mechanism of the cycloaddition reaction under the TBAB-TEOAB catalytic system was revealed. Finally, the chemical structure of the product was confirmed using techniques such as infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography (GPC).

[0076] Among numerous main / co-catalyst combinations, TBAB as the main catalyst and TEOAB as the co-catalyst exhibited the best catalytic performance. Through single-factor optimization experiments, the optimal reaction conditions were determined: a TBAB to TEOAB molar ratio of 2:1, a TBAB addition of 5 mol%, a TEOAB addition of 2.5 mol%, and a reaction time of 12 h at 120℃ and 2.0 MPa CO2 pressure. Under these conditions, the yield of cyclic carbonate soybean oil reached the highest, reaching 91.2%.

[0077] In terms of kinetic studies, the activation energy of TBAB alone was found to be 70.05 kJ / mol, while the activation energy of TBAB combined with TEOAB decreased to 57.16 kJ / mol, with corresponding pre-exponential factors of 5.92 × 10⁻⁶. 6 and 1.79×10 5 This data indicates that the addition of TEOAB as a co-catalyst to the TBAB catalytic system significantly reduces the activation energy of the chemical reaction, thereby accelerating the efficient formation of soybean oil-based cyclic carbonates.

[0078] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing soybean oil-based cyclic carbonates, characterized in that, Includes the following steps: Epoxidized soybean oil and catalyst are mixed in a closed environment. After the air in the closed environment is purged, CO2 is introduced into the closed environment and the pressure of CO2 is adjusted to 1.0-2.0 MPa. Then, the reaction is carried out at a temperature of 100-120℃ and under stirring for 10-12 hours. After purification, the product is obtained. The catalyst is composed of tetrabutylammonium bromide and triethanolamine borate, with a molar ratio of tetrabutylammonium bromide to triethanolamine borate of (1-4):

1.

2. The method for preparing soybean oil-based cyclic carbonates according to claim 1, characterized in that, The molar ratio of tetrabutylammonium bromide to triethanolamine borate is 2:

1.

3. The method for preparing soybean oil-based cyclic carbonates according to claim 1 or 2, characterized in that, The molar amount of tetrabutylammonium bromide is 4%-6% of the molar amount of epoxy groups in epoxidized soybean oil; the molar amount of triethanolamine borate is 1.25%-5% of the molar amount of epoxy groups in epoxidized soybean oil.

4. The method for preparing soybean oil-based cyclic carbonates according to claim 1, characterized in that, The method to remove air from a confined environment is to introduce CO2 into the confined environment 3-5 times.

5. The method for preparing soybean oil-based cyclic carbonates according to claim 1, characterized in that, The temperature is 120℃.

6. The method for preparing soybean oil-based cyclic carbonates according to claim 1, characterized in that, The stirring speed is 400 rpm.

7. The method for preparing soybean oil-based cyclic carbonates according to claim 1, characterized in that, The reaction took 12 hours.

8. The method for preparing soybean oil-based cyclic carbonates according to claim 1, characterized in that, The CO2 pressure was adjusted to 2.0 MPa.

9. The method for preparing soybean oil-based cyclic carbonates according to claim 1, characterized in that, The purification method involves dissolving the crude product obtained after the reaction in an organic solvent to obtain an organic phase, washing and drying the organic phase, then filtering and rotary evaporating the organic phase, and finally drying the obtained product at 80°C.

10. The method for preparing soybean oil-based cyclic carbonates according to claim 9, characterized in that, The organic solvent is ethyl acetate; The washing method is to wash the organic phase 8-10 times with saturated saline solution; The method for drying the organic phase is to add anhydrous magnesium sulfate to the organic phase.

Images