A selective hydrogenation catalyst for nitrile rubber and a preparation method thereof

Abstract

The application discloses a nitrile butadiene rubber selective hydrogenation catalyst and a preparation method thereof, and belongs to the technical field of catalyst preparation. The preparation method of the catalyst is as follows: sodium alginate powder is calcined at 250-500 DEG C for 2-4 hours to obtain sodium alginate-based carbon, the obtained sodium alginate-based carbon is ground, treated with hydrochloric acid or nitric acid for 20-80 minutes, and then subjected to suction filtration to obtain a carrier; the carrier is dispersed into a noble metal precursor solution, impregnated and stirred for 6-12 hours, a reducing agent is added, and the mixture is continuously stirred for 20-60 minutes; the mixture is subjected to suction filtration, dried, and the catalyst is prepared. The catalyst has high C=C unsaturated bond selectivity and hydrogenation activity in the reaction of catalytic hydrogenation of nitrile butadiene rubber (NBR) to prepare hydrogenated nitrile butadiene rubber (HNBR). The catalytic efficiency is more than 90% under a low addition amount (0.5-2 wt%). The preparation process is simple, the prepared catalyst has high dispersion of active components, the carbon precursor is widely available, the carrier is simple to prepare, the production cost is low, and the catalyst is beneficial to large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer hydrogenation catalyst preparation, and particularly relates to a nitrile rubber selective hydrogenation catalyst and a preparation method thereof. BACKGROUND

[0002] Nitrile rubber (NBR) is widely used as oil-resistant rubber and adhesive due to its good strength and elasticity. However, the aging resistance of NBR is poor due to the presence of unsaturated C=C in the molecular chain, and NBR is easily degraded in extreme environments, which seriously affects the practical application of NBR. At present, the main solution to this problem is to retain the cyano group (-CN) on the acrylonitrile segment and selectively hydrogenate the C=C on the butadiene segment of NBR to obtain hydrogenated nitrile rubber (HNBR) with high saturation. HNBR is prepared by catalytic hydrogenation of NBR solution. According to the state of the catalyst, it is mainly divided into homogeneous solution catalytic hydrogenation and heterogeneous solution catalytic hydrogenation. The homogeneous solution hydrogenation catalyst has high activity and good selectivity. Japanese Zeon and German Lanxess company both use NBR solution homogeneous catalytic hydrogenation to produce HNBR. However, the homogeneous hydrogenation catalyst has poor stability, is expensive and difficult to separate, and the solution residue in the product affects the performance of HNBR. The heterogeneous catalyst is easy to separate, not only can avoid this problem, but also can be reused, so the heterogeneous catalytic NBR solution hydrogenation to prepare HNBR has become a research hotspot in the preparation of special rubber.

[0003] Currently, the main catalyst for NBR heterogeneous hydrogenation is noble metal catalyst. However, the noble metal catalyst used for hydrogenation of nitrile rubber still faces some problems: on the one hand, the loading is relatively high, on the other hand, the active component (noble metal) is prone to agglomeration, leading to deactivation, thus greatly increasing the cost. In view of this problem, modification of the carrier is used to achieve high dispersion of the active component, such as coordination design, defect design and space confinement is an effective strategy. CN103418413A controls the pH and reaction temperature, and reacts dopamine hydrochloride with a silica carrier in an oxygen atmosphere to obtain a modified carrier, thereby achieving high dispersion of noble metal (RhCl3 dosage is 20 mL, 100 mM, SiO2 carrier is 2 g), and the catalyst has a hydrogenation degree of NBR up to 99.1%; CN114832843A mixes the pretreated foamed nickel with the precursor solution to perform hydrothermal reaction, and then filters, washes and dries to obtain a foamed nickel carrier containing hydrotalcite; the mass ratio of Na2PdCl4 to the carrier is controlled to be 0.3:1, the catalyst carrier is mixed with a Pd salt solution under a nitrogen atmosphere and stirred for 12 h to load the active component, and the hydrogenation degree of NBR reaches 92.8%. For the problem of low dispersion of noble metal catalyst, CN116832861A uses a high-pressure reaction kettle to synthesize a covalent organic framework as a palladium-based catalyst carrier by aldehyde-ammonia condensation reaction under a nitrogen atmosphere, and then realizes space confinement of the active component by impregnation loading (Pd loading is 4.1-5.7%), thereby improving the dispersion degree and the hydrogenation degree of NBR is more than 90%. Although modification of the carrier can achieve high dispersion and high catalytic activity of the noble metal catalyst, the modification process is relatively complicated, and the loading of noble metal is still relatively high, so the preparation and application cost of the catalyst is high, which is not conducive to practical application.

[0004] Sodium alginate (SA) is a natural linear anionic biopolymer obtained from brown algae derived from alpha-L-guluronate and 1,4-linked-beta-D-mannuronate residues, and has low cost. In addition, sodium alginate has similar cellulose structural units and relatively high carbon content, and is rich in oxygen-containing functional groups, and the carrier obtained by carbonization is expected to retain part of the functional groups, thereby achieving high dispersion of noble metal. In view of this, we propose a method for conveniently preparing a palladium-based catalyst using sodium alginate-based carbon as a carrier. The palladium-based catalyst prepared by the method has good dispersion, high catalytic activity, high selectivity, simple process, low production cost, is conducive to large-scale production, and has certain significance for the preparation of other noble metal catalysts. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide a synthesis method of a Pd-based catalyst with high dispersion, high C=C hydrogenation catalytic activity and selectivity in the reaction of preparing HNBR by hydrogenation of NBR.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] (1) calcining sodium alginate, then treating with acid, filtering, washing and drying to obtain a catalyst carrier;

[0008] (2) dispersing the carrier obtained in (1) into a noble metal precursor solution, and then impregnating and stirring;

[0009] (3) adding a reducing agent into the system of (2), and then continuing to stir, filter, wash and dry to obtain a catalyst.

[0010] Preferably, the calcining in step (1) is performed in an air atmosphere, the heating rate is 2-10℃ / min, the calcining temperature is 250-500℃, and the constant temperature time is 2-4h.

[0011] Preferably, the acid treatment in step (1) is hydrochloric acid, nitric acid or sulfuric acid, the concentration of the acid is 0.5-2mol / L, and the acid treatment time is 20-80min.

[0012] Preferably, the noble metal in step (2) is Pd, the amount of the carrier is 0.3g, and the Pd loading amount is 0.2-3wt%.

[0013] Preferably, the noble metal precursor solution in step (2) is PdCl2 solution, and 10-100mg of citric acid is added, and the impregnation time is 6-12h.

[0014] Preferably, the reducing agent in step (3) is sodium borohydride (NaBH4), which is prepared with deionized water, the concentration is 0.1mol / L, the amount is 2-10mL, and the stirring time is 20-60min.

[0015] Preferably, the drying temperature in step (3) is 80-100℃, and the drying time is 5-10min.

[0016] The prepared catalyst is applied to the selective hydrogenation of butyl nitrile rubber to prepare hydrogenated butyl nitrile rubber, and the hydrogenation efficiency is 55-98%.

[0017] The reaction of the selective hydrogenation of butyl nitrile rubber to prepare hydrogenated butyl nitrile rubber is that butyl nitrile rubber solution and the prepared noble metal catalyst are mixed and stirred uniformly in a high-pressure reaction kettle at 60-100℃, 1-5MPa H2, and the stirring time is 2-6h. The NBR polyacrylonitrile content is 32-34%, and the solvent is one of 2-butanone, acetone, toluene and xylene.

[0018] The present application has the following advantages:

[0019] (1) The palladium-based catalyst prepared by the method has high dispersibility and low loading amount;

[0020] (2) The palladium-based catalyst prepared by the method has high selectivity and high catalytic activity in the NBR hydrogenation reaction;

[0021] (3) The method uses sodium alginate, which has low cost, simple preparation process, easy operation, and is easy to mass-produce. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM image of the sample prepared in Example 1;

[0023] Figure 2 EDS image of Example 1 and Comparative Example 1;

[0024] Figure 3 XRD spectrum of the sample prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0025] Figure 4 XRD spectrum of the catalyst prepared in Example 2 at different carbonization temperatures;

[0026] Figure 5 XRD spectrum of the catalyst prepared in Example 3 at different loadings;

[0027] Figure 6 XRD spectrum of the catalyst prepared in Example 4 with different acid treatments;

[0028] Figure 7 Infrared spectrum of HNBR and NBR prepared in Application Example 1 and Comparative Example 1;

[0029] Figure 8 Infrared spectrum of HNBR and NBR prepared in Application Example 3;

[0030] Figure 9 Infrared spectrum of HNBR and NBR prepared in Application Example 4. DETAILED DESCRIPTION

[0031] In order to make the content of the present application more convenient to understand, the technical solutions described in the present application will be further described below in conjunction with specific embodiments, but the present application is not limited thereto.

[0032] Example 1 (Pd / C SA-HCl-300 Preparation of catalyst)

[0033] This embodiment provides a method for preparing an NBR hydrogenation catalyst:

[0034] (1) The sodium alginate powder was calcined at 300℃ in a muffle furnace for 3h with a heating rate of 5℃ / min to obtain a sodium alginate-based carbon carrier;

[0035] (2) The sodium alginate-based carbon carrier obtained in (1) was ground, 0.3 g of which was added to 30 mL of a hydrochloric acid solution (1 mol / L) and stirred for 40 min, and then suction filtration was performed to obtain a catalyst carrier;

[0036] (3) The catalyst carrier prepared in (2) was mixed with a Pd precursor solution and stirred for impregnation for 9 h, the Pd precursor solution being 0.003 g of PdCl2 dissolved in 50 mL of deionized water (55 mg of citric acid was added as a complexing agent);

[0037] (4) After impregnation, 5 mL of 0.1 mol / L NaBH4 was added for stirring reduction for 40 min, suction filtration was performed, and drying was performed in a 90°C blast drying oven for 5 min to obtain a 1wt% Pd / C catalyst. SA-HCl-300 Catalyst.

[0038] Preparation of a Pd / C catalyst of Comparative Example 1 SA-300 Catalyst.

[0039] The same method as in Example 1 was used to prepare a comparative sample, except that the sodium alginate-based carbon was not pretreated with hydrochloric acid (i.e., step 2 was omitted), and a 1wt% Pd / C catalyst was prepared. SA-300 Catalyst.

[0040] Figure 1 (a) and (b) are SEM images of the catalyst prepared in Comparative Example 1, and it can be seen from the images that the catalyst carrier that has not been treated with hydrochloric acid has a blocky structure and is relatively dense; (c) and (d) are SEM images of the catalyst prepared in Example 1, and it can be seen from the images that the catalyst carrier that has been treated with hydrochloric acid has a large number of pores on the surface. Figure 2 (a) and (b) are EDS images of Examples 1 and Comparative Example 1, respectively, and it can be seen from the images that the carrier that has not been treated with hydrochloric acid contains a large amount of C, O, and Na elements. After the catalyst carrier is treated with hydrochloric acid, only C and O elements exist, and Na is basically not detected. This indicates that the pores of the carrier after acid washing may be formed by the removal of sodium compounds on the carrier after calcination by reaction with the acid.

[0041] Preparation of a Pd / AC catalyst of Comparative Example 2

[0042] The same method as in Example 1 was used to prepare a catalyst, except that 0.3 g of sodium alginate-based carbon was replaced with 0.3 g of commercial activated carbon (AC), and a 1wt% Pd / AC catalyst was obtained.

[0043] Figure 3XRD patterns of the samples prepared in Example 1, Comparative Example 1 and Comparative Example 2. As can be seen from the figure, the different samples only observed the C peak, indicating that after calcination of sodium alginate, the carbon carrier obtained is amorphous carbon (consistent with the crystal phase of commercial activated carbon), and there is no obvious change before and after acid washing. In addition, no Pd-related species peak was observed in XRD, which may be due to the high dispersion of Pd on the carrier.

[0044] Example 2 (Preparation of Pd-based catalysts with different calcination temperatures)

[0045] This example is consistent with the preparation method of Example 1, the only difference is that the calcination temperature of sodium alginate is different, which is 275, 300, 325, 350, 400, 500°C, respectively. The carrier with different calcination temperatures is prepared, and Pd is loaded on the carrier according to the method of Example 1 to obtain Pd / C SA-HCl-275 , Pd / C SA-HCl-300 , Pd / C SA-HCl-325 , Pd / C SA-HCl-350 , Pd / C SA-HCl-400 , Pd / C SA-HCl-500 catalysts.

[0046] Figure 4 XRD patterns of different samples prepared in Example 2, as can be seen from the figure, when the calcination temperature is 275-325°C, no Pd phase is observed in the catalyst, indicating that Pd is uniformly dispersed on the catalyst carrier prepared at 275-325°C. However, as the calcination temperature increases (350-500°C), the prepared catalyst can detect the Pd phase, indicating that at a higher calcination temperature, the properties of the carrier change, and Pd is easy to agglomerate. This shows that the calcination temperature of sodium alginate has a significant effect on the dispersion of the active component.

[0047] Example 3 (Preparation of Pd-based catalysts with different loadings)

[0048] This example is consistent with the preparation method of Example 1, the only difference is that the Pd loading of the catalyst carrier is different, which is 0.5, 0.7, 1, 1.2, 1.6, 2wt%, respectively. The carrier calcined at 300°C is prepared, and Pd is loaded on the carrier according to the method of Example 1 to obtain 0.5wt% Pd / C SA-HCl-300 , 0.7wt% Pd / C SA-HCl-300 , 1wt% Pd / C SA-HCl-300 , 1.2wt% Pd / C SA-HCl-350 , 1.6wt% Pd / C SA-HCl-300 , 2wt% Pd / C SA-HCl-300 catalysts.

[0049] Figure 5XRD patterns of catalysts with different Pd loadings prepared in Example 3 were prepared. As can be seen from the figure, no Pd phase was observed for all catalysts, indicating that different amounts of Pd were uniformly dispersed on the catalyst carrier.

[0050] Example 4 (catalyst carrier treated with different acids)

[0051] This example is consistent with the preparation method of Example 1, the only difference is that the sodium alginate-based carbon is treated with different acid solutions, 1 mol / L, 30 mL of hydrochloric acid, nitric acid, sulfuric acid solution respectively, and then Pd is loaded on the catalyst according to the method of Example 1, to obtain 1wt% Pd / C SA-HCl-300 , 1wt% Pd / C SA-HNO3-300 , 1wt% Pd / C SA-H2SO4-300 catalyst.

[0052] Figure 6 XRD patterns of catalysts with different acid treatments prepared in Example 4 were prepared. As can be seen from the figure, no Pd phase was observed for all catalysts, indicating that different amounts of Pd were uniformly dispersed on the catalyst carrier.

[0053] Application Example 1 (catalytic hydrogenation of NBR)

[0054] In a high-pressure reaction kettle, 75 mg of catalyst (catalyst prepared in the above examples or comparative examples, commercial 5% Pd / C catalyst) was added, 5000 mg of butyl nitrile rubber (Taiwan Nantai 1052, acrylonitrile content 33%), 10 mL of 2-butanone, 4 MPa of H2was filled, and stirred at 60°C for 6h. After the reaction system was cooled to room temperature, the remaining hydrogen was removed, and the catalyst and rubber solution were separated, and the activity of the catalyst was evaluated by FTIR analysis. In addition, in order to make a comparison, a commercial Pd / C (5wt%) was used to carry out the hydrogenation reaction of NBR under the same conditions.

[0055] Figure 7 The infrared spectra of NBR and HNBR prepared in Application Example 1. As can be seen from the figure, the NBR has peaks at 970 cm -1 and 920 cm -1 corresponding to 1,4 trans C=C and 1,2-vinyl terminal C=C. After catalytic hydrogenation by Pd / C SA-HCl-300 , the peak intensity of C=C is significantly reduced, and a new peak of saturated (—CH2—)n produced by hydrogenation of C=C appears at 723 cm -1 , indicating that Pd / C SA-HCl-300 has good hydrogenation activity. It is worth noting that the peak of (-CN) at 2236 cm -1 does not change, and there is no peak at 3500 cm -1 or at 3310-3450 cm -1No new peaks appeared at Pd / C, indicating that (-CN) was well retained and the selectivity for C=C bond was 100%. SA-300 After catalytic hydrogenation, the -1 , 920cm -1 and 723cm -1 The change at the Pd / AC is not obvious, indicating that the removal of Na-related species by acid washing is a key process to improve the activity of the catalyst. In addition, compared with Pd / AC (Table 1), Pd / C SA-HCl-300 The catalytic activity was significantly improved, indicating that using sodium alginate as a precursor to prepare carbon support is beneficial to the improvement of catalytic activity. SA-HCl-300 The catalytic activity is also better than that of commercial Pd / C (5wt%), indicating that the catalyst prepared by this method has higher activity at a lower loading and can significantly reduce the Pd loading.

[0056] Table 1 Hydrogenation degree of different catalysts

[0057]

[0058] Application Example 2

[0059] The activity evaluation conditions for the catalytic NBR hydrogenation reaction in this application example are basically the same as those in application example 1, except that the catalysts used were those synthesized in example 2 and calcined at different temperatures. The results are shown in Table 2.

[0060] Table 2 Hydrogenation degree of catalysts at different calcination temperatures

[0061]

[0062] Figure 8 The infrared spectra of HNBR and NBR prepared in Application Example 2. As can be seen from the figure, the catalyst prepared by the carrier obtained by calcining at a temperature of 275-325 ° C has an NBR at 970 cm -1 and 920cm -1 The intensity of the peak at 723 cm -1 A new peak appeared at 2236cm -1 The (-CN) peak at 3500 cm -1 Or at 3310~3450cm -1 No new peaks appear at the positions, indicating that these catalysts have hydrogenation effects and high hydrogenation selectivity. However, as the carbonization temperature of the support increases further, the peaks at various positions do not change significantly after the prepared catalyst catalyzes NBR hydrogenation, indicating that the catalytic activity of these catalysts is poor. Therefore, the catalyst support obtained by calcining at a higher temperature has poor activity. Combined with the previous XRD results, it can be seen that ( Figure 4), which might be the reason of the agglomeration of Pd on the support prepared at high temperature.

[0063] Application Example 3

[0064] The activity evaluation conditions of the present application example and the catalytic hydrogenation of NBR in application example 1 are basically the same, except that the catalyst used is the Pd catalyst with different Pd loadings synthesized in example 3. The results are shown in table 3. Figure 4 As shown in table 3, it can be seen that with the increase of the loading, the hydrogenation degree of NBR also gradually increases, but when the loading exceeds 1.0wt%, the hydrogenation degree exceeds 90%, and tends to be stable.

[0065] Table 3 Hydrogenation degree of catalysts with different loadings

[0066]

[0067] Application Example 4

[0068] The activity evaluation conditions of the present application example and the catalytic hydrogenation of NBR in application example 1 are basically the same, except that the catalyst used is the Pd catalyst with different Pd loadings synthesized in example 3. The results are shown in table 3. As shown in table 4, it can be seen that when the support is washed with hydrochloric acid and nitric acid, the activity of the catalyst is higher, while the hydrogenation degree of the Pd-based catalyst with the support treated by sulfuric acid is only 48.9%, which might be that SO4 2+ is left on the support during the acid treatment process, affecting the hydrogenation activity of the catalyst.

[0069] Table 4 Hydrogenation degree of catalysts with different acid treatments

[0070]

[0071] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be covered by the present application.

Claims

1. A method for preparing a catalyst for selective hydrogenation of nitrile rubber, characterized in that: The steps include: (1) calcining sodium alginate powder, treating it with acid, and filtering it to obtain a catalyst support; (2) Dispersing the catalyst support into the noble metal precursor solution and stirring and impregnating it; (3) adding a reducing agent to the system of step (2), continuing stirring, filtering, and drying to obtain the nitrile rubber selective hydrogenation catalyst; In step (1), the calcination temperature of sodium alginate is 275-325°C; In step (1), the acid is hydrochloric acid or nitric acid.

2. The preparation method according to claim 1, wherein: In step (1), the calcination time of sodium alginate is 2 to 4 h, and the heating rate is 2 to 10 °C / min.

3. The preparation method according to claim 1, wherein: In step (1), the concentration of the acid is 0.5-2 mol / L, and the acid treatment time is 20-80 min.

4. The preparation method according to claim 1, wherein: In step (2), the precious metal is Pd, and the loading amount is 0.2~3 wt.%.

5. The preparation method according to claim 1, wherein: In step (2), the noble metal precursor solution is a PdCl2 solution, citric acid is used as a complexing agent, and the immersion time is 6 to 12 hours.

6. The preparation method according to claim 1, wherein: In step (3), the reducing agent is sodium borohydride, which is prepared into a solution with a concentration of 0.1 mol / L using deionized water.

7. a nitrile rubber selective hydrogenation catalyst that makes as described in any one of claim 1-6.

8. an application of a nitrile rubber selective hydrogenation catalyst prepared by the method as claimed in any one of claims 1 to 6 in preparing hydrogenated nitrile rubber by selective hydrogenation of nitrile rubber.

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