Synthesis of Sulfonic Acid-Functionalized Zirconium Poly(Styrene-Phenylvinyl-Phosphonate)-Phosphate for Heterogeneous Epoxidation of Soybean Oil

: In this paper, a solid acid catalyst (ZPS–PVPA–SO 3 H) was prepared by anchoring thiol group on zirconium poly(styrene-phenylvinyl-phosphonate)-phosphate (ZPS–PVPA), followed by oxidation of thiol groups to obtain sulfonic acid groups. The solid acid catalyst was characterized by XPS, X-ray, EDS, SEM, and TG-DSC. The successful preparation of sulfonic acid-functionalized ZPS–PVPA was conﬁrmed. Subsequently, the catalytic performance of ZPS–PVPA–SO 3 H was investigated in the epoxidation of soybean oil. The results demonstrated that ZPS–PVPA–SO 3 H can e ﬀ ectively catalyze epoxidation of soybean oil with TBHP as an oxidant. Moreover, there was no signiﬁcant decrease in catalytic activity after 5 repeated uses of the ZPS–PVPA–SO 3 H. Interestingly, the ZPS–PVPA–SO 3 H was kept in 2 mol / L of HCl overnight after the end of the seventh reaction, and the catalytic activity was gradually restored during the eighth to tenth cycles.


Introduction
The epoxidation of vegetable oil has attracted much attention because the obtainable epoxides are useful for producing a wide range of products, such as plasticizers and stabilizers of polyvinyl chloride (PVC) [1]. Currently, these products are mainly prepared by using a peracid [2,3] in the presence of protonic acid catalysts, such as sulfuric acid [4]. However, separation and reuse of such protonic acid catalysts are still problematic for the reaction mixture [3]. In addition, protonic acid catalysts can also pollute the environment, posing a hazard and causing more by-products. Therefore, a new type of effective catalyst is urgently needed for epoxidation of soybean oil.
In the last few decades, a large number of functional catalytic materials containing -SO 3 H groups have been reported [5][6][7][8]. The -SO 3 H-based functionalized catalytic materials can not only replace liquid acids to catalyze various reactions and reduce wastewater, but also have significant shape-selective catalysis. Their nature also increases the selectivity of the reaction and reduces the by-products of the reaction. Until now, the main choices of catalytic materials have been zeolites, silica,

The Acidity of the Samples of Solid Particles
The calculated acidities of ZPS-PVPA, ZPS-PVPA-SH and ZPS-PVPA-SO 3 H are presented in Table 1. The acidity of ZPS-PVPA microcrystals is mainly caused by the -OH within ZPS-PVPA layers [17]. When -SH group terminated chains were grafted onto ZPS-PVPA, the acidity of ZPS-PVPA-SH decreased, indicating the successful condensation reaction between the -OH of individual ZPS-PVPA and the -Si(OMe) 3 groups of MPTMS. After the ZPS-PVPA-SH nanosheets were oxidized to ZPS-PVPA-SO 3 H, the acidity was sharply enhanced to 418.9 µmol/g from 0.12 µmol/g, which in turn confirms the formation of -SO 3 H groups.

X-Ray Photoelectron Spectroscopy
The XPS results for ZPS-PVPA, ZPS-PVPA-SH and ZPS-PVPA-SO 3 H are summarized in Figure 1. The appearance of S and Si elements on the surface of ZPS-PVPA-SH confirmed the successful grafting of MPTMS on the ZPS-PVPA. Moreover, the XPS spectra of P 2p for ZPS-PVPA, ZPS-PVPA-SH, and ZPS-PVPA-SO 3 H were recorded and are shown in Figure 2. Compared to ZPS-PVPA, the binding energy of the P 2p peak of ZPS-PVPA-SH increased from 134.04 to 134.08 eV after functional reaction. This result is consistent with the formation of P−O−Si bonds between the -OH on the surface of ZPS-PVPA and the -Si(OMe) 3 groups of MTPMS. In addition, the binding energy values of P 2p for ZPS-PVPA-SH and ZPS-PVPA-SO 3 H are both 134.08 eV, which indicates that the oxidation of ZPS-PVPA-SH has no effect on the chemical bonds between the ZPS-PVPA and the grafted chains, ensuring that the chains remain grafted on the ZPS-PVPA surface after oxidation reaction. To further confirm that the -SH groups were oxidized into -SO 3 H groups under the influence of H 2 O 2 and HCl, the XPS spectra of S 2p3/2 were carried out, and the results are shown in Figure 3. A higher binding energy of S 2p3/2 (168.1 eV Vs 163.4 eV) was obtained after the oxidation, which in turns proves that the ZPS-PVPA-SH were successfully oxidized into ZPS-PVPA-SO 3 H.

X-Ray Photoelectron Spectroscopy
The XPS results for ZPS-PVPA, ZPS-PVPA-SH and ZPS-PVPA-SO3H are summarized in Figure 1. The appearance of S and Si elements on the surface of ZPS-PVPA-SH confirmed the successful grafting of MPTMS on the ZPS-PVPA. Moreover, the XPS spectra of P 2p for ZPS-PVPA, ZPS-PVPA-SH, and ZPS-PVPA-SO3H were recorded and are shown in Figure 2. Compared to ZPS-PVPA, the binding energy of the P 2p peak of ZPS-PVPA-SH increased from 134.04 to 134.08 eV after functional reaction. This result is consistent with the formation of P−O−Si bonds between the -OH on the surface of ZPS-PVPA and the -Si(OMe)3 groups of MTPMS. In addition, the binding energy values of P 2p for ZPS-PVPA-SH and ZPS-PVPA-SO3H are both 134.08 eV, which indicates that the oxidation of ZPS-PVPA-SH has no effect on the chemical bonds between the ZPS-PVPA and the grafted chains, ensuring that the chains remain grafted on the ZPS-PVPA surface after oxidation reaction. To further confirm that the -SH groups were oxidized into -SO3H groups under the influence of H2O2 and HCl, the XPS spectra of S 2p3/2 were carried out, and the results are shown in Figure 3. A higher binding energy of S 2p3/2 (168.1 eV Vs 163.4 eV) was obtained after the oxidation, which in turns proves that the ZPS-PVPA-SH were successfully oxidized into ZPS-PVPA-SO3H.         Figure 4 presents the XRD patterns of ZPS-PVPA, ZPS-PVPA-SH, and ZPS-PVPA-SO3H. It can be seen from the XRD spectrum that there has no obvious peak, indicating that the surface morphologies of the ZPS-PVPA, ZPS-PVPA-SH, and ZPS-PVPA-SO3H are amorphous. The broad peak at 2θ = 15.0−30° is mainly attributed to the amorphous silica. Furthermore, the fine diffraction peaks in ZPS-PVPA, ZPS-PVPA-SH and ZPS-PVPA-SO3H are attributed to the special structure of the organic-inorganic hybrid zirconium phosphate. Theoretically, each of the composite zirconium salt particles is composed of a plurality of layered composite zirconium salt crystallites, and the arrangement of the crystal planes of the respective zirconium salt crystal grains is random. Therefore, the results are very likely to present a form of "short-range order, long-range disorder".   Figure 4 presents the XRD patterns of ZPS-PVPA, ZPS-PVPA-SH, and ZPS-PVPA-SO 3 H. It can be seen from the XRD spectrum that there has no obvious peak, indicating that the surface morphologies of the ZPS-PVPA, ZPS-PVPA-SH, and ZPS-PVPA-SO 3 H are amorphous. The broad peak at 2θ = 15.0−30 • is mainly attributed to the amorphous silica. Furthermore, the fine diffraction peaks in ZPS-PVPA, ZPS-PVPA-SH and ZPS-PVPA-SO 3 H are attributed to the special structure of the organic-inorganic hybrid zirconium phosphate. Theoretically, each of the composite zirconium salt particles is composed of a plurality of layered composite zirconium salt crystallites, and the arrangement of the crystal planes of the respective zirconium salt crystal grains is random. Therefore, the results are very likely to present a form of "short-range order, long-range disorder".

Microscopic Analysis
SEM images provide direct information on the microstructure and morphology of ZPS-PVPA and ZPS-PVPA-SO3H, as shown in Figure 5. In this context, Figure 5a indicates that the ZPS-PVPA was amorphous and loose, and various cavities, holes, and pores were present in every particle in ZPS-PVPA. These pores and cavities of varying sizes are caused by the disorderly arrangement of organic polymer and layered crystallites of inorganic zirconium phosphate. Figure 5b shows that the structure of ZPS-PVPA-SO3H is still amorphous, loose, and porous. However, compared to ZPS-PVPA, the channels and pores of ZPS-PVPA-SO3H are more closely packed, which is mainly due to

Microscopic Analysis
SEM images provide direct information on the microstructure and morphology of ZPS-PVPA and ZPS-PVPA-SO 3 H, as shown in Figure 5. In this context, Figure 5a indicates that the ZPS-PVPA was amorphous and loose, and various cavities, holes, and pores were present in every particle in ZPS-PVPA. These pores and cavities of varying sizes are caused by the disorderly arrangement of organic polymer and layered crystallites of inorganic zirconium phosphate. Figure 5b shows that the structure of ZPS-PVPA-SO 3 H is still amorphous, loose, and porous. However, compared to ZPS-PVPA, the channels and pores of ZPS-PVPA-SO 3 H are more closely packed, which is mainly due to the insertion of the -SO 3 H group and results in an increase in the interaction between the particles during the sulfonation process. The EDS surveys of ZPS-PVPA and ZPS-PVPA-SO 3 H are presented in Figure 5c

Microscopic Analysis
SEM images provide direct information on the microstructure and morphology of ZPS-PVPA and ZPS-PVPA-SO3H, as shown in Figure 5. In this context, Figure 5a indicates that the ZPS-PVPA was amorphous and loose, and various cavities, holes, and pores were present in every particle in ZPS-PVPA. These pores and cavities of varying sizes are caused by the disorderly arrangement of organic polymer and layered crystallites of inorganic zirconium phosphate. Figure 5b shows that the structure of ZPS-PVPA-SO3H is still amorphous, loose, and porous. However, compared to ZPS-PVPA, the channels and pores of ZPS-PVPA-SO3H are more closely packed, which is mainly due to the insertion of the -SO3H group and results in an increase in the interaction between the particles during the sulfonation process. The EDS surveys of ZPS-PVPA and ZPS-PVPA-SO3H are presented in Figure 5c

Thermal Gravimetric Analysis
The thermal stability of the catalyst ZPS-PVPA-SO3H was determined by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) (Figure 7). The weight loss of the catalyst ZPS-PVPA-SO3H is divided into four processes. It can be seen from the TG-DSC curve that the first process is the temperature increase from room temperature to 120 °C, where weight loss occurs at 8.7%, and the corresponding endothermic peak appears at 63.2 °C in the DSC curve, which is attributed to the desorption of surface adsorption water and crystal water in the solid catalyst. The second process was the temperature increase from 155 to 222 °C where a weight loss of 2.9% occurs, which is still due to the removal of residual solid water from the catalyst. The third stage is the temperature increase from 222 to 706 °C, resulting in mass loss of 43.8% and two obvious exothermic peaks occurring simultaneously at 426.3 and 530.4 °C, which is mainly attributed to the decomposition of organic groups and burning of species carbon in the catalyst ZPS-PVPA-SO3H. Furthermore, the organophosphine is oxidized to pentavalent phosphorus and Zr(HPO4)2 is formed at this stage, and the organic group is almost completely destroyed at 706 °C. The fourth stage is the

Thermal Gravimetric Analysis
The thermal stability of the catalyst ZPS-PVPA-SO 3 H was determined by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) (Figure 7). The weight loss of the catalyst ZPS-PVPA-SO 3 H is divided into four processes. It can be seen from the TG-DSC curve that the first process is the temperature increase from room temperature to 120 • C, where weight loss occurs at 8.7%, and the corresponding endothermic peak appears at 63.2 • C in the DSC curve, which is attributed to the desorption of surface adsorption water and crystal water in the solid catalyst. The second process was the temperature increase from 155 to 222 • C where a weight loss of 2.9% occurs, which is still due to the removal of residual solid water from the catalyst. The third stage is the temperature increase from 222 to 706 • C, resulting in mass loss of 43.8% and two obvious exothermic peaks occurring simultaneously at 426.3 and 530.4 • C, which is mainly attributed to the decomposition of organic groups and burning of species carbon in the catalyst ZPS-PVPA-SO 3 H. Furthermore, the organophosphine is oxidized to pentavalent phosphorus and Zr(HPO 4 ) 2 is formed at this stage, and the organic group is almost completely destroyed at 706 • C. The fourth stage is the temperature increase from 706 to 800 • C, accompanied by a strong endothermic peak at 667.2 • C. After heating to 800 • C, white residual powder is obtained, which is mainly due to the dehydration of Zr(HPO 4 ) 2 to form zirconium pyrophosphate ZrP 2 O 7 . The quality loss is not obvious. From the above thermogravimetric analysis, it can be stated that the thermal stability of the catalyst ZPS-PVPA-SO 3 H is reached at about 230 • C.
Catalysts 2019, 9, x FOR PEER REVIEW 7 of 13 temperature increase from 706 to 800 °C, accompanied by a strong endothermic peak at 667.2 °C. After heating to 800 °C, white residual powder is obtained, which is mainly due to the dehydration of Zr(HPO4)2 to form zirconium pyrophosphate ZrP2O7. The quality loss is not obvious. From the above thermogravimetric analysis, it can be stated that the thermal stability of the catalyst ZPS-PVPA-SO3H is reached at about 230 °C.  Table 2 summarizes the results of the epoxidation of soybean oil over the catalyst ZPS-PVPA-SO3H. All reactions proceeded smoothly, and these results are significantly better than those catalyzed by the Schiff base molybdenum (VI) [18] and the Cu(salen) complex [19] under optimal catalytic conditions. The excellent catalytic activity is mainly attributed to the special structure of ZPS-PVPA-SO3H, which facilitate self-assembly into a plurality of micro-reactors. Thus, the particles of one catalyst are randomly stacked by hundreds of solid catalyst crystallites. The catalytic active centers are typically located in the channels or inner or outer layers of ZPS-PVPA. When the catalyst is in the TBHP oxidation system, the layers of ZPS-PVPA are expanded or even partly decomposed, more secondary channels are formed, and the original secondary channels are enlarged, meaning some of the embed catalytic active sites are exposed in the solution of the reaction and the substrates and the reactants can diffuse to these catalytic sites easily through these secondary channels. As the reaction time raise, the conversion rate increases gradually, but the selectivity decreases accordingly. Similar results were obtained in our earlier reports [13,20].

Catalytic Reaction
In order to determine the optimal amount of ZPS-PVPA-SO3H, the reaction was firstly carried out in the presence of different amounts (1-20 wt%, based on soybean oil) at 80 °C in 1,2-dichloroethane using TBHP as an oxidant. The results showed that the conversions were increased from 32.1 to 81.3% with an increase in yield from 16.27 to 60.06% when the amount of catalyst was increased from 1 to 20 wt%. Moreover, an additional increase in the amount of catalyst did not show any positive effect on the conversion and selectivity of the soybean oil epoxide (Table 2, entry 5). Blank experiment showed that the ZPS-PVPA-SO3H alone is inactive towards epoxidation of soybean oil, and a yield of only 0.34% was achieved ( Table 2, entry 6). In addition, we screened the effects of different temperatures on the epoxidation of soybean oil. The results show that the conversion and selectivity  Table 2 summarizes the results of the epoxidation of soybean oil over the catalyst ZPS-PVPA-SO 3 H. All reactions proceeded smoothly, and these results are significantly better than those catalyzed by the Schiff base molybdenum (VI) [18] and the Cu(salen) complex [19] under optimal catalytic conditions. The excellent catalytic activity is mainly attributed to the special structure of ZPS-PVPA-SO 3 H, which facilitate self-assembly into a plurality of micro-reactors. Thus, the particles of one catalyst are randomly stacked by hundreds of solid catalyst crystallites. The catalytic active centers are typically located in the channels or inner or outer layers of ZPS-PVPA. When the catalyst is in the TBHP oxidation system, the layers of ZPS-PVPA are expanded or even partly decomposed, more secondary channels are formed, and the original secondary channels are enlarged, meaning some of the embed catalytic active sites are exposed in the solution of the reaction and the substrates and the reactants can diffuse to these catalytic sites easily through these secondary channels. As the reaction time raise, the conversion rate increases gradually, but the selectivity decreases accordingly. Similar results were obtained in our earlier reports [13,20]. Note: [a] Reactions were carried out at 80 • C in 1,2-dichloroethane (5 mL) with soybean oil (10 g), TBHP (5.0 mmol), and the ZPS-PVPA-SO3H catalyst (10 mol%(wt%)); [b] conversions and selectivity were determined by GB/T1676-008 and GB/T 1677-2008 method.

Catalytic Reaction
In order to determine the optimal amount of ZPS-PVPA-SO 3 H, the reaction was firstly carried out in the presence of different amounts (1-20 wt%, based on soybean oil) at 80 • C in 1,2-dichloroethane using TBHP as an oxidant. The results showed that the conversions were increased from 32.1 to 81.3% with an increase in yield from 16.27 to 60.06% when the amount of catalyst was increased from 1 to 20 wt%. Moreover, an additional increase in the amount of catalyst did not show any positive effect on the conversion and selectivity of the soybean oil epoxide (Table 2, entry 5). Blank experiment showed that the ZPS-PVPA-SO 3 H alone is inactive towards epoxidation of soybean oil, and a yield of only 0.34% was achieved ( Table 2, entry 6). In addition, we screened the effects of different temperatures on the epoxidation of soybean oil. The results show that the conversion and selectivity increases with increasing temperature but the selectivity decreases when the temperature increases above 80 • C. A similar trend was found for the effect of reaction time on catalytic reactions. This is mainly attributed to the slow decomposition of TBHP, making formation of a by-product more likely at higher temperatures and over longer durations. Therefore, 80 • C and 6 h were chosen as the reaction time and temperature of the system.

Reusability of the ZPS-PVPA-SO 3 H
To assess the recyclability of the ZPS-PVPA-SO 3 H, the reaction system was separated by centrifugation after the reaction is completed, the catalyst was left untreated, and the reaction was continuously reacted according to the initial ratio. As shown in Table 3, it is obvious that the catalyst worked well for up to five cycles with no considerable decrease in reactivity (yield% from 60.06 to 55.25%). An unexpected discovery was that the catalytic activity of the catalyst was gradually restored at the 8th to 10th cycles of the catalyst when the ZPS-PVPA-SO 3 H was allowed to stand in 2 mol/L of dilute hydrochloric acid overnight after the 7th reuse; similar results have been reported in the asymmetric epoxidation of olefin catalyzed by ZPS-PVPA-SalenMn [12]. This novel phenomenon is probably due to the nano-layered self-supporting function [21] of the inorganic zirconium phosphate portion of the catalyst structure. The catalyst may have a certain "memory function" and can be roughly restored to the original morphology in acid medium. However, the specific reasons remain to be further studied. Note: [a] Reactions were carried out at 80 • C in 1,2-dichloroethane (5 mL) with soybean oil (10 g), TBHP (5.0 mmol), and the ZPS-PVPA-SO3H catalyst (10 mol%(wt%)); [b] conversions and selectivity were determined by GB/T1676-2008 and GB/T 1677-2008 method.

Methods
XPS were recorded on ESCALab250 instrument (Thermo Fisher Scientific, USA). SEM were performed on SU8010 (JEOL, Japan) microscopy. EDS were performed on a JSM-7800F (JEOL, Japan) apparatus. TG-DSC analyses were performed on a SBTQ600 Thermal Analyzer (USA) with a heating rate of 20 • C·min −1 from 25 to 1000 • C under flowing N 2 (100 mL·min −1 ). The interlayer spacings were recorded on a LabXRD-6100 automated X-ray power diffractometer using Cu-Kα radiation and internal silicon powder standard for all samples (Shimadz, Japan). The patterns were generally measured between 2.00 and 80.00 • and X-ray tube settings of 40 kV and 5 mA. The synthesis and characterization of ZPS-PVPA (Scheme 1) has been reported earlier by our group [22].

Methods
XPS were recorded on ESCALab250 instrument (Thermo Fisher Scientific, USA). SEM were performed on SU8010 (JEOL, Japan) microscopy. EDS were performed on a JSM-7800F (JEOL, Japan) apparatus. TG-DSC analyses were performed on a SBTQ600 Thermal Analyzer (USA) with a heating rate of 20 °C·min −1 from 25 to 1000 °C under flowing N2 (100 mL·min −1 ). The interlayer spacings were recorded on a LabXRD-6100 automated X-ray power diffractometer using Cu-Kα radiation and internal silicon powder standard for all samples (Shimadz, Japan). The patterns were generally measured between 2.00 and 80.00° and X-ray tube settings of 40 kV and 5 mA. The synthesis and characterization of ZPS-PVPA has been reported earlier by our group [22].  [23]. Here, 0.50 g of (ZPS-PVPA) was swelled and ultrasounded in toluene (30 mL) for an hour. Subsequently, MPTMS (2 mL) was dropped into the suspension and then refluxed under vigorous stirring for 24 h in a N2 atmosphere. After the reaction, the mixture was filtered and the obtained solid was washed with toluene (30 mL × 3) to remove the residual MPTMS and dried at 60 °C overnight in a vacuum oven. The obtained product Scheme 1. Synthesis of ZPS-PVPA.

Synthesis of Sulfonic Acid-Functionalized Zirconium
Poly(styrene-phenylvinyl-phosphonate)-phosphate ZPS-PVPA was functionalized by the condensation reaction between the -OH on the ZPS-PVPA surface and the -Si(OMe) 3 groups of MPTMS [23]. Here, 0.50 g of (ZPS-PVPA) was swelled and ultrasounded in toluene (30 mL) for an hour. Subsequently, MPTMS (2 mL) was dropped into the suspension and then refluxed under vigorous stirring for 24 h in a N 2 atmosphere. After the reaction, the mixture was filtered and the obtained solid was washed with toluene (30 mL × 3) to remove the residual MPTMS and dried at 60 • C overnight in a vacuum oven. The obtained product was abbreviated as ZPS-PVPA-SH. ZPS-PVPA-SO 3 H was obtained as follows: a certain amount of H 2 O 2 (5.5 mL) was slowly added to the dispersion of ZPS-PVPA-SH (0.3 g) in 12.0 mL of methanol. The reaction was kept at room temperature for 24 h. The obtained solid was further treated with HCl (2.5 mL, 37 wt%) at ambient temperature for complete protonation [24]. The sample was separated by centrifugation and then washed with water and ethanol. After drying at 60 • C for 24 h in a vacuum oven, ZPS-PVPA-SO 3 H was obtained (Scheme 2). was abbreviated as ZPS-PVPA-SH. ZPS-PVPA-SO3H was obtained as follows: a certain amount of H2O2 (5.5 mL) was slowly added to the dispersion of ZPS-PVPA-SH (0.3 g) in 12.0 mL of methanol. The reaction was kept at room temperature for 24 h. The obtained solid was further treated with HCl (2.5 mL, 37 wt%) at ambient temperature for complete protonation [24]. The sample was separated by centrifugation and then washed with water and ethanol. After drying at 60 °C for 24 h in a vacuum oven, ZPS-PVPA-SO3H was obtained (Scheme 2). Scheme 2. Synthesis of sulfonic acid-functionalized zirconium poly(styrene-phenylvinylphosphonate)-phosphate (ZPS-PVPA).

Epoxidation of Soybean Oil
The epoxidation of soybean oil in the present of ZPS-PVPA-SO3H was performed as follows. A solution of 10 g soybean oil (about 50.43 mmol in double bonds) and ZPS-PVPA-SO3H (10%, wt%) in 1,2-dichloroethane (10 mL) was mixed at desired temperatures. Then, TBHP (5.43 mmol) was slowly added over 10 min. After the completion of the reaction, the catalyst was centrifuged and the filtrate was washed with hot water until neutral and dried. The evolution over time of the epoxidation reaction, in terms of double bonds conversion and yield and selectivity to epoxide, was followed by

Conclusions
This paper provides a new solid acid catalyst for catalyzing epoxidized soybean oil. The catalytic results showed that the ZPS-PVPA-SO3H can efficiently promote the epoxidation of soybean oil. Furthermore, the ZPS-PVPA-SO3H could be easily separated from the products and recycled at least five times without significant loss of catalytic activity. Interestingly, the ZPS-PVPA-SO3H was kept in 2 mol/L of HCl overnight at the end of the 7th reaction, and the catalytic activity was gradually restored during the 8th to10th cycles. Scheme 2. Synthesis of sulfonic acid-functionalized zirconium poly(styrene-phenylvinyl-phosphonate)phosphate (ZPS-PVPA).

Epoxidation of Soybean Oil
The epoxidation of soybean oil in the present of ZPS-PVPA-SO 3 H was performed as follows. A solution of 10 g soybean oil (about 50.43 mmol in double bonds) and ZPS-PVPA-SO 3 H (10%, wt%) in 1,2-dichloroethane (10 mL) was mixed at desired temperatures. Then, TBHP (5.43 mmol) was slowly added over 10 min. After the completion of the reaction, the catalyst was centrifuged and the filtrate was washed with hot water until neutral and dried. The evolution over time of the epoxidation reaction, in terms of double bonds conversion and yield and selectivity to epoxide, was followed by

Conclusions
This paper provides a new solid acid catalyst for catalyzing epoxidized soybean oil. The catalytic results showed that the ZPS-PVPA-SO 3 H can efficiently promote the epoxidation of soybean oil. Furthermore, the ZPS-PVPA-SO 3 H could be easily separated from the products and recycled at least five times without significant loss of catalytic activity. Interestingly, the ZPS-PVPA-SO 3 H was kept in 2 mol/L of HCl overnight at the end of the 7th reaction, and the catalytic activity was gradually restored during the 8th to10th cycles.