Binary metal catalyst and application thereof in efficient catalytic synthesis of diol from hemicellulose

Abstract

The application discloses a binary metal catalyst and application thereof in efficient catalytic synthesis of diols from hemicellulose, wherein the binary metal catalyst is prepared by co-precipitation, calcination and reduction of active metal precursors and carrier precursors. The catalyst can directly convert hemicellulose into diols in one step under the action of water as a solvent and hydrogen atmosphere. The catalyst is simple in preparation and synthesis, and has high selectivity, and can hydrogenolyze part of by-products such as erythritol and tetrahydrofurfuryl alcohol into diols, thereby improving the diol yield. Meanwhile, the catalyst has excellent stability, and can overcome the problem of deactivation in the recycling process of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of fine chemicals, specifically relating to a binary metal catalyst and its application in the efficient catalytic synthesis of diols from hemicellulose. Background Technology

[0002] Diols (including ethylene glycol, propylene glycol, butane glycol, pentane glycol, etc.) are multifunctional, high-value platform chemicals and important intermediates in the chemical industry, with wide applications and significant market demand. Traditionally, diols are produced from fossil resources. Ethylene glycol is primarily produced via a petroleum route using ethylene as a raw material, producing ethylene glycol through ethylene oxide. Another route uses coal or natural gas as raw materials, first producing syngas (CO+H2), and then directly or indirectly producing ethylene glycol. Propylene glycol is industrially produced mainly through the selective oxidation of non-renewable petroleum-derived propylene to propylene oxide and subsequent hydrolysis. Butane glycol is industrially produced mainly through the acetylacetonate process, maleic anhydride process, butadiene process, and propylene oxide process. However, fossil resources are finite, non-renewable, and have serious environmental impacts.

[0003] Hemicellulose is a heteropolysaccharide found in plant cell walls, accounting for approximately 15%–35% of the dry weight of plant cells. Catalytic conversion of hemicellulose into diols is considered a promising route for diol synthesis. However, hemicellulose is a polypentose sugar with a complex composition. Therefore, current research focuses on the hydrolysis products of hemicellulose, xylose and xylitol, with limited studies on the direct conversion of hemicellulose into diols. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a simple and easily scalable method for preparing supported metal catalysts and applying them to the efficient one-pot catalytic synthesis of diols from hemicellulose. This invention improves the catalytic activity of the catalyst by adjusting the type and ratio of the active metal precursor and the support precursor, enabling the catalyst to achieve highly efficient one-pot synthesis of diols from hemicellulose in water. Furthermore, it can convert byproducts such as erythritol and tetrahydrofurfuryl alcohol from the hydrogenolysis of hemicellulose into diols, thereby increasing the yield of diols.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] One of the objectives of this invention is to protect a binary metal catalyst for the catalytic synthesis of diols from hemicellulose, wherein the catalyst uses one of Cu, Ni, and Co as the active metal and one or two of CeO2, ZnO, Al2O3, TiO2, and ZrO2 as the support.

[0007] Furthermore, the loading of the active metal in the binary metal catalyst is 10%-90%.

[0008] Furthermore, the preparation of the binary metal catalyst involves dissolving the active metal precursor and the support precursor in deionized water, then adding sodium carbonate solution dropwise to the mixed solution at 60°C under stirring to precipitate the catalyst until the pH of the mixed solution reaches 8.5. The resulting slurry is then heated to 80°C and stirred for aging for 3 hours. After cooling to room temperature, the slurry is filtered, and the resulting filter residue is dried overnight at 110°C. The dried product is then ground in a mortar, passed through a 100-mesh sieve, calcined in a muffle furnace at 300-800°C for 4 hours, and then reduced in a tube furnace at 200-800°C for 5 hours under a 5 vol% hydrogen atmosphere.

[0009] Furthermore, the active metal precursor is one of Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, or Co(NO3)2·6H2O.

[0010] Furthermore, the carrier precursor is one or more of Ce(NO3)3·6H2O, Zn(NO3)2·6H2O, Zr(NO3)4·5H2O, Al(NO3)3·9H2O, and TiO2.

[0011] Furthermore, the stirring speed is 600-1000 rpm.

[0012] Furthermore, the concentration of the sodium carbonate aqueous solution used is 0.5~1.5 mol / L.

[0013] The second objective of this invention is to protect the application of the binary metal catalyst in the efficient one-pot catalytic synthesis of diols from hemicellulose.

[0014] Further, the application method involves adding hemicellulose to water, adding a binary metal catalyst, and then reacting in a closed system at 180-260°C for 1-6 hours under a hydrogen pressure of 2-8 MPa and a stirring speed of 500 rpm, followed by cooling to room temperature to obtain the diol.

[0015] Furthermore, the ratio of hemicellulose, binary metal catalyst, and water used is 0.01~1g:0.01~1g:20ml.

[0016] The significant advantages of this invention are:

[0017] (1) This invention provides a simple and easy-to-scale method for preparing binary metal catalysts. The desired catalyst can be obtained through simple co-precipitation, calcination and reduction. Furthermore, by adjusting the type and ratio of active metal precursor and support precursor, the catalytic activity of the catalyst can be improved, enabling the catalyst to achieve efficient one-pot synthesis of diols from hemicellulose in water.

[0018] (2) Compared with the method of catalytic conversion of xylose and xylitol to prepare diol, the catalyst of the present invention can realize the direct one-pot catalytic conversion of upstream product hemicellulose into diol, reducing the process of hydrolysis into xylose, and can also convert by-products such as erythritol and tetrahydrofurfuryl produced during the hydrogenation of hemicellulose into diol.

[0019] (3) The catalyst prepared by the present invention has stable performance, and its catalytic activity and selectivity do not decrease significantly after multiple cycles. Attached Figure Description

[0020] Figure 1 SEM image of the 30CuZnO catalyst prepared for the example.

[0021] Figure 2 The image shows the EDS spectrum of the 30CuZnO catalyst prepared for the example. The spectrum indicates that the catalyst exhibits good dispersion. Detailed Implementation

[0022] A method for efficient one-pot catalytic synthesis of diols from hemicellulose, comprising the following steps:

[0023] 1) The active metal precursor and the support precursor were dissolved in deionized water. Then, under stirring at 60℃ and 600-1000 rpm, 0.5-1.5 mol / L sodium carbonate solution was added dropwise to the mixed solution to precipitate the metal. The precipitation was stopped when the pH of the mixed solution reached 8.5. The resulting slurry was then heated to 80℃ and stirred at 600-1000 rpm for 3 h. After cooling to room temperature, the slurry was filtered. The filter residue was dried at 110℃ overnight. The dried product was then ground in a mortar and passed through a 100-mesh sieve. It was then calcined in a muffle furnace at 300-800℃ for 4 h and then reduced in a tube furnace at 200-800℃ for 5 h under a 5 vol% hydrogen atmosphere to obtain a binary metal catalyst with an active metal loading of 10%-90%.

[0024] 2) Add 0.01~1g hemicellulose and 20ml water to the reactor, and add 0.01~1g of binary metal catalyst. Pass H2 through to completely remove the air from the reactor. Then, charge the reactor with 2-8 MPa of hydrogen gas. After sealing the reactor, stir at 500rpm and heat to 180~260℃ for 1-6 hours. After the reaction is completed, quickly cool the reactor to room temperature to obtain the diol.

[0025] In step 1), the active metal precursor is one of Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, and Co(NO3)2·6H2O. The support precursor is one or more of Ce(NO3)3·6H2O, Zn(NO3)2·6H2O, Zr(NO3)4·5H2O, Al(NO3)3·9H2O, and TiO2.

[0026] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0027] Examples 1-5

[0028] Accurately weigh 5.11 g Zn(NO3)2·6H2O and 2.28 g Cu(NO3)2·3H2O, dissolve them in 200 ml deionized water under magnetic stirring, and then add 0.1 mol / L sodium carbonate aqueous solution dropwise to the mixed solution at 60℃ to precipitate until the pH of the mixed solution is 8.5 (the mixed solution is continuously stirred at a stirring rate of 800 rpm during the hydrolysis process). After the hydrolysis is completed, the resulting slurry is heated to 80℃ and stirred at the same rate for 3 h for aging. After cooling to room temperature, the slurry is filtered, and the resulting filter residue is dried at 110℃ overnight. The dried product is then ground in a mortar, passed through a 100-mesh sieve, calcined in a muffle furnace at 500℃ for 4 h, and then reduced in a tube furnace at 500℃ for 5 h under a 5 vol% hydrogen atmosphere to obtain a CuZnO catalyst with a loading of 30%, denoted as 30CuZnO.

[0029] Catalysts with loadings of 10%, 50%, 70%, and 90% were prepared according to the above method and denoted as nCuZnO (n is the loading of Cu).

[0030] Add 0.3 g hemicellulose and 20 mL pure water to a 100 mL high-pressure reactor, then add 0.15 g catalyst. Replace the air in the reactor with hydrogen three times, then purge with 6 MPa H2. Seal the reactor and stir at 500 rpm while heating to 240℃ and maintaining for 4 h. After the reaction is finished and cooled to room temperature, centrifuge the reaction mixture, take the supernatant, and perform quantitative analysis using liquid chromatography and qualitative analysis using gas chromatography-mass spectrometry. The results are listed in Table 1.

[0031] As shown in Experiments 1-5 of Table 1, among the nCuZnO catalysts with different loadings, 30CuZnO exhibits the highest diol yield, reaching 69.35%. This is because initially, with the increase of Cu content, the active metal of the catalyst increases, resulting in stronger catalyst activity while maintaining a certain degree of dispersibility and stability. However, after reaching a certain critical value, the dispersibility and stability of Cu in the support decrease, and Cu particles tend to agglomerate, leading to a reduction in particle size and consequently a decrease in reaction activity.

[0032] Examples 6-10

[0033] Add 0.5 g hemicellulose and 20 mL pure water to a 100 mL high-pressure reactor, then add 0.15 g 30CuZnO catalyst. Replace the air in the reactor with hydrogen three times, then purge with 6 MPa H2. Seal the reactor and stir at 500 rpm. Simultaneously heat to 180℃, 200℃, 220℃, 240℃, and 260℃ respectively and maintain for 2 h. After the reaction is completed and cooled to room temperature, the reaction mixture is centrifuged and the supernatant is collected. Quantitative analysis is performed using liquid chromatography, and qualitative analysis is performed using gas chromatography-mass spectrometry. The results are listed in Table 1.

[0034] As shown in Experiments 6-10 of Table 1, when the reaction temperature is below 200℃, hemicellulose is mainly converted into its hydrogenation product xylitol, with only a small amount of diols. With increasing reaction temperature, the highest diol selectivity is observed at 240℃, with increased yields of ethylene glycol and 1,2-propanediol, but still a small amount of xylitol. When the reaction temperature exceeds 240℃, although xylose and xylitol are completely hydrogenated, the diol selectivity decreases. This is because high temperatures affect product distribution; reaction intermediates and products are difficult to stabilize at higher temperatures and are converted into other byproducts, thus reducing the selectivity of the target product.

[0035] Examples 11-13

[0036] 0.5 g of hemicellulose and 20 mL of pure water were added to a 100 mL high-pressure reactor, followed by 0.15 g of 30CuZnO catalyst. The air in the reactor was replaced with hydrogen three times, and then 2, 4, 6, and 8 MPa of H2 were introduced respectively. The reactor was sealed and stirred at 500 rpm, while being heated to 240℃ and maintained for 2 h. After the reaction was completed and cooled to room temperature, the reaction mixture was centrifuged and the supernatant was collected. Quantitative analysis was performed using liquid chromatography, and qualitative analysis was performed using gas chromatography-mass spectrometry. The results are listed in Table 1.

[0037] As shown in Experiments 11-13 of Table 1, the conversion rate of hemicellulose is low when the hydrogen pressure is 2 MPa, with xylitol as the main product and a total yield of diols and glycerol of 26.31%. When the pressure continues to rise above 4 MPa, all hemicellulose is converted, with xylitol, ethylene glycol, and 1,2-propanediol as the main products. The total yield of diols reaches its highest level at 6 MPa, at 55.10%. When the pressure increases to 8 MPa, the selectivity for xylitol increases, while the selectivity for the products decreases. This is because hydrogen itself has poor solubility in water, and increasing the hydrogen pressure facilitates the dissolution of hydrogen in aqueous solution, making it easier for hydrogen to contact the active sites of the catalyst and the reactants, thus increasing the rate of hydrogenation. However, excessively high pressure also inhibits the dehydrogenation of xylitol to form xylose intermediates, resulting in a decrease in the yield of diols.

[0038] Examples 14-16

[0039] 0.5 g of hemicellulose and 20 mL of pure water were added to a 100 mL high-pressure reactor, followed by 0.2, 0.4, and 0.6 g of 30CuZnO catalyst, respectively. After replacing the air in the reactor with hydrogen three times, 6 MPa of H2 was introduced. The reactor was sealed and stirred at 500 rpm while being heated to 240 °C and maintained for 2 h. The reaction was then stopped and cooled to room temperature. The reaction mixture was centrifuged, and the supernatant was collected. Quantitative analysis was performed using liquid chromatography, and qualitative analysis was performed using gas chromatography-mass spectrometry. The results are listed in Table 1.

[0040] As shown in Experiments 14-16 of Table 1, the number of catalytically active species is relatively small at low catalyst dosages, resulting in low conversion and product yield. The highest diol yield of 70.92% was obtained at a catalyst dosage of 0.4 g.

[0041] Examples 17-18

[0042] 0.5 g of hemicellulose and 20 mL of pure water were added to a 100 mL high-pressure reactor, followed by 0.4 g of 30CuZnO catalyst. After replacing the air in the reactor with hydrogen three times, 6 MPa of H2 was introduced. The reactor was sealed and stirred at 500 rpm while being heated to 240 °C and maintained for 1 and 4 h. The reaction was then stopped and cooled to room temperature. The reaction mixture was centrifuged and the supernatant was collected. Quantitative analysis was performed using liquid chromatography, and qualitative analysis was performed using gas chromatography-mass spectrometry. The results are listed in Table 1.

[0043] As can be seen from experiments 17-18 in Table 1, increasing the reaction time promotes the conversion of hemicellulose into diols. After 1 hour of reaction, the diol yield was 58.44%, and after extending the reaction time to 4 hours, the diol yield increased to 71.84%.

[0044] Examples 19-23

[0045] 0.5 g hemicellulose and 20 mL pure water were added to a 100 mL high-pressure reactor, followed by 0.15 g 30CuZnO catalyst. After replacing the air in the reactor with hydrogen three times, 6 MPa H2 was introduced. The reactor was sealed and stirred at 500 rpm while being heated to 240 °C and maintained for 4 h. The reaction was then stopped and cooled to room temperature. The reaction mixture was centrifuged, and the supernatant was collected. Quantitative analysis was performed using liquid chromatography, and qualitative analysis was performed using gas chromatography-mass spectrometry. The corresponding catalyst was recovered, dried, and subjected to a cycle experiment. The results are listed in Table 1.

[0046] As shown in Experiments 19-23 of Table 1, the catalyst performance did not decrease significantly in 5 cycles, indicating that the catalyst is relatively stable. Based on ICP-OES analysis of the ion concentration in the reaction solution, almost no Cu was lost, while the loss of ZnO was less than 1%.

[0047] Examples 24-29

[0048] Accurately weigh 5.11 g Zn(NO3)2·6H2O and 2.97 g Ni(NO3)2·6H2O, dissolve them in 200 ml deionized water under magnetic stirring, and then add 0.1 mol / L sodium carbonate aqueous solution dropwise to the mixed solution at 60℃ to precipitate until the pH of the mixed solution is 8.5 (the mixed solution is continuously stirred at a stirring rate of 800 rpm during the hydrolysis process). After the hydrolysis is completed, the resulting slurry is heated to 80℃ and stirred at the same rate for 3 h for aging. After cooling to room temperature, the slurry is filtered, and the resulting filter residue is dried at 110℃ overnight. The dried product is then ground in a mortar, passed through a 100-mesh sieve, calcined in a muffle furnace at 400℃ for 4 h, and then reduced in a tube furnace at 500℃ for 5 h under a 5 vol% hydrogen atmosphere to obtain a NiZnO catalyst with a loading of 30%, denoted as 30NiZnO.

[0049] Catalysts 30CoZnO, 30Cu10CeOZnO, 30CuAl2O3, 30CuTiO2, and 30Cu10ZrO2ZnO were prepared using the methods described above.

[0050] Add 0.3 g hemicellulose and 20 mL pure water to a 100 mL high-pressure reactor, then add 0.15 g catalyst. Replace the air in the reactor with hydrogen three times, then purge with 6 MPa H2. Seal the reactor and stir at 500 rpm while heating to 240℃ and maintaining for 4 h. After the reaction is completed and cooled to room temperature, centrifuge the reaction mixture, collect the supernatant, perform quantitative analysis using liquid chromatography, and perform qualitative analysis using gas chromatography-mass spectrometry.

[0051] The results showed that all catalysts could catalyze the complete conversion of hemicellulose. Among them, the products obtained by NiZnO catalysis were mainly ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol and xylitol, with a diol yield of 41.94%.

[0052] The main products obtained by 30CoZnO catalysis were ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, glycerol, and xylitol, with minor amounts of 1,4-pentanediol and furfuryl alcohol. The diol yield was 45.95%.

[0053] The main products obtained by catalysis with 30CuAl2O3 were ethylene glycol, 1,2-propanediol, and glycerol, with minor amounts of 1,2-butanediol and 1,2-pentanediol. The diol yield was 66.41%.

[0054] The main products obtained by 30CuTiO2 catalysis were ethylene glycol, 1,2-propanediol and glycerol, with minor amounts of 1,2-butanediol and 1,2-pentanediol. The diol yield was 60.00%.

[0055] The products obtained by catalysis with 30Cu10CeOZnO were mainly ethylene glycol, 1,2-propanediol, and glycerol, with minor amounts of 1,2-butanediol and 1,2-pentanediol. The diol yield was 68.28%.

[0056] The hemicellulose obtained by catalysis of 30Cu10ZrO2ZnO mainly consists of ethylene glycol, 1,2-propanediol, 1,2-butanediol and glycerol, with the remaining minor products being 1,2-pentanediol and furfuryl alcohol. The diol yield is 69.87%.

[0057] Table 1

[0058]

[0059] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. The application of a binary metal catalyst in the catalytic synthesis of diols from hemicellulose, characterized in that: The binary metal catalyst is prepared by dissolving an active metal precursor and a support precursor in deionized water, then adding sodium carbonate solution dropwise to the mixed solution at 60°C with stirring to precipitate the catalyst until the pH of the mixed solution reaches 8.

5. The resulting slurry is then heated to 80°C and stirred for 3 hours for aging. After cooling to room temperature, the slurry is filtered, and the resulting filter residue is dried at 110°C overnight. After grinding and passing through a 100-mesh sieve, the residue is calcined in a muffle furnace at 300-800°C for 4 hours and then reduced in a tube furnace at 200-800°C for 5 hours under a 5 vol% hydrogen atmosphere. The active metal precursor is one of Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, and Co(NO3)2·6H2O; The carrier precursor is one or more of Ce(NO3)3·6H2O, Zn(NO3)2·6H2O, Zr(NO3)4·5H2O, Al(NO3)3·9H2O, and TiO2; The loading of active metal in the binary metal catalyst is 10%-90%; The application method involves using hemicellulose as raw material and water as solvent, adding the binary metal catalyst, and reacting in a closed environment at 240-260℃ for 1-6 h under a hydrogen pressure of 4-8 MPa and a stirring speed of 500 rpm to obtain diol; wherein the ratio of hemicellulose, binary metal catalyst and water is 0.01~1g:0.01~1g:20ml.

2. The application according to claim 1, characterized in that: The stirring speed is 600-1000 rpm.

3. The application according to claim 1, characterized in that: The concentration of the sodium carbonate aqueous solution used is 0.5~1.5 mol / L.

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