A heterogeneous unsupported tin-based catalyst, its preparation method and use

Abstract

This invention provides a heterogeneous unsupported tin-based catalyst, its preparation method, and its application, belonging to the field of tin-based catalyst materials. The preparation method of the heterogeneous unsupported tin-based catalyst provided by this invention includes the following steps: first, tin tetrachloride and an aqueous solution of an organic alcohol are mixed, followed by the addition of a soluble aluminum salt, and then the mixture is allowed to stand for a first time to obtain a mixed solution; second, the mixed solution is mixed with ammonia water, and the mixture is allowed to stand for a second time, followed by high-temperature hydrolysis and drying to obtain the heterogeneous unsupported tin-based catalyst; the temperatures of the first and second standing periods are both -12 to -20°C. The heterogeneous unsupported tin-based catalyst prepared by the method provided by this invention is stable (it will not transform into tin dioxide), and can convert glucose to lactic acid with a yield of over 90%. Furthermore, the catalyst can achieve 93% of its initial efficiency even after 10 repetitions, exhibiting good stability and catalytic effect.

Description

Technical Field

[0001] This invention relates to the field of tin-based catalyst materials, and more particularly to a heterogeneous unsupported tin-based catalyst, its preparation method, and its application. Background Technology

[0002] Converting glucose, especially the high-concentration sugars in organic wastewater generated during biomass processing such as bamboo blanching and bamboo shoot steaming, into lactic acid, and then processing it into polylactic acid products that can be used as plastic substitutes, is an effective way to deeply process agricultural and forestry by-products.

[0003] Among various technological pathways for converting carbohydrates into lactic acid, chemical catalysis has attracted considerable attention compared to biological fermentation due to its advantages such as shorter process, higher efficiency, and no need for pH adjustment. Tin (Sn)-based catalysts, especially tetravalent tin (Sn... 4+ The Lewis catalyst, due to its Lewis acidity, can efficiently promote key reactions such as glucose isomerization and reverse aldol condensation, thereby generating lactic acid with high selectivity, showing significant potential.

[0004] Compared to homogeneous catalysts, heterogeneous catalysts are easier to separate and recover from the reaction system, can be reused, and better meet the requirements of green chemistry and industrialization, making them a research hotspot. Currently, typical heterogeneous catalysts are supported Sn-based catalysts, such as Sn-Beta molecular sieves. Their preparation process faces significant technical bottlenecks: First, the synthesis of aluminum-free Beta molecular sieve supports relies on precise template agents and harsh hydrothermal conditions, resulting in long crystallization cycles, poor reproducibility, and low production efficiency. Second, if aluminum-containing precursors are used for post-processing modification, the dealumination step often requires strong acids, which may lead to framework collapse, pore structure destruction, and the generation of large amounts of acidic waste liquid, violating the principles of green chemistry. Furthermore, in the Sn active component introduction stage, high-temperature calcination is usually required to allow Sn to enter the framework. This process easily causes framework shrinkage and Sn species aggregation, leading to a reduction in the exposure of active sites. To ensure effective loading, excessive Sn sources are often used, which not only wastes resources but also results in residual free SnO2 impurities that reduce catalytic selectivity and increase purification difficulty. Therefore, unsupported heterogeneous catalysts are a hot topic for future development. Since SnCl4 hydrolyzes in an aqueous phase to form water-insoluble stannic acid sol, its main component can be represented as SnO. x (OH) 4-2x This includes highly reactive α-stannic acid (often abbreviated as Sn(OH)4). However, Sn(OH)4 is chemically unstable in the aqueous phase and readily transforms into less reactive β-stannic acid through dehydration condensation reaction, ultimately forming SnO2 nanoparticles. SnO2 nanoparticles have poor lactic acid catalytic ability.

[0005] Therefore, how to prepare a heterogeneous, unsupported tin-based catalyst with good stability and catalytic performance has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a heterogeneous, unsupported tin-based catalyst, its preparation method, and its applications. The preparation method provided by this invention enables the prepared heterogeneous, unsupported tin-based catalyst to possess good stability and catalytic performance.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a heterogeneous, unsupported tin-based catalyst, comprising the following steps: After first mixing tin tetrachloride with an aqueous solution of an organic alcohol, a soluble aluminum salt is added, followed by a first settling period to obtain a mixed solution. The mixed solution was mixed with ammonia water for a second time and then allowed to stand for a second time. Then, it was subjected to high-temperature hydrolysis and drying in sequence to obtain a heterogeneous unsupported tin-based catalyst. The temperature for both the first and second static periods is -12 to -20°C.

[0008] Preferably, the mass ratio of tin tetrachloride to soluble aluminum salt is 1:(0.01~0.05).

[0009] Preferably, the temperature of the first mixture is -4 to 0°C.

[0010] Preferably, the mass concentration of tin tetrachloride in the mixed solution is 25-35%.

[0011] Preferably, the first settling time is 12 to 36 hours.

[0012] Preferably, the second settling time is 0.5 to 2 hours.

[0013] Preferably, the mass ratio of tin tetrachloride to ammonia is 1:(0.01~0.03). The mass concentration of the ammonia water is 5-10%.

[0014] Preferably, the high-temperature hydrolysis temperature is 130~190℃, and the high-temperature hydrolysis time is 2~6h.

[0015] The present invention also provides a heterogeneous unsupported tin-based catalyst prepared by the preparation method described in the above technical solution.

[0016] This invention also provides the application of the heterogeneous unsupported tin-based catalyst described in the above technical solution in the catalytic conversion of sugars to lactose.

[0017] This invention provides a method for preparing a heterogeneous, unsupported tin-based catalyst, comprising the following steps: first, mixing tin tetrachloride with an aqueous solution of an organic alcohol, then adding a soluble aluminum salt, followed by a first settling period to obtain a mixed solution; second, mixing the mixed solution with ammonia, followed by a second settling period, and then sequentially performing high-temperature hydrolysis and drying to obtain the heterogeneous, unsupported tin-based catalyst; the temperatures of the first and second settling periods are both -12 to -20°C. This invention introduces Al element into the tin tetrachloride aqueous system (a mixture of tin tetrachloride and an aqueous solution of an organic alcohol) and performs hydration pretreatment at low temperature. By limiting the low temperature, the hydrolysis pathway can be effectively controlled, forming [Al-OHO-Sn] bonds and constructing an interfacial water cluster hydrogen bond network. This can synergistically inhibit the dehydration process of Sn(OH)4, improve the stability of the heterogeneous, unsupported tin-based catalyst, and allow it to be directly used for the catalytic conversion of biomass sugars, giving the heterogeneous, unsupported tin-based catalyst excellent catalytic performance. The results of the examples show that the heterogeneous unsupported tin-based catalyst prepared by the preparation method provided by the present invention can exist stably (without transforming into tin dioxide), and can convert glucose into lactic acid with a yield of over 90%. Moreover, the catalyst can achieve 93% of the efficiency of the first use after 10 repetitions, demonstrating good stability and catalytic effect. Attached Figure Description

[0018] Figure 1 This is a photograph of the product obtained by high-temperature hydrolysis in Example 1 of the present invention. Figure 2 This is a physical image of the product obtained by high-temperature hydrolysis in Comparative Example 1 of the present invention. Figure 3 This is a photograph of the product obtained by high-temperature hydrolysis in Comparative Example 2 of the present invention. Figure 4 The infrared spectra of tin dioxide and the catalysts prepared in Example 1 and Comparative Examples 1-2 of this invention were tested. Detailed Implementation

[0019] This invention provides a method for preparing a heterogeneous, unsupported tin-based catalyst, comprising the following steps: After first mixing tin tetrachloride with an aqueous solution of an organic alcohol, a soluble aluminum salt is added, followed by a first settling period to obtain a mixed solution. The mixed solution was mixed with ammonia water for a second time and then allowed to stand for a second time. Then, it was subjected to high-temperature hydrolysis and drying in sequence to obtain a heterogeneous unsupported tin-based catalyst. The temperature for both the first and second static periods is -12 to -20°C.

[0020] In this invention, tin tetrachloride and an aqueous solution of an organic alcohol are first mixed, then a soluble aluminum salt is added, followed by a first standing period to obtain a mixed solution.

[0021] In one embodiment of the present invention, the mass concentration of the aqueous solution of the organic alcohol can be 40-60%, 45-55%, or 50%; the organic alcohol in the aqueous solution may include methanol or ethanol. By limiting the type and concentration of the aqueous solution of the organic alcohol to the above ranges, the present invention ensures good hydrolysis of tin tetrachloride subsequently.

[0022] In one embodiment of the present invention, the first mixing can be carried out in a jacketed reaction beaker; the temperature of the first mixing can be -4~0℃, -3~-1℃, or -2℃. In another embodiment of the present invention, the temperature of the first mixing can be achieved by circulating a cooling liquid through the jacket. Limiting the temperature of the first mixing to the above range in the present invention can prevent the hydrolysis of tin tetrachloride and the further formation of tin dioxide under room temperature conditions.

[0023] In one embodiment of the present invention, the first mixing can be carried out under stirring conditions; the stirring speed can be 200~300 rpm or 250 rpm. By limiting the first mixing method and stirring speed within the above range, the present invention can ensure stable stirring without eddies and form a clear and transparent homogeneous solution.

[0024] In one embodiment of the present invention, the mass ratio of tin tetrachloride to soluble aluminum salt can be 1:(0.01~0.05), 1:(0.02~0.04), or 1:0.03. In an embodiment of the present invention, the soluble aluminum salt can be aluminum chloride. The present invention limits the mass ratio of tin tetrachloride to soluble aluminum salt to the above range to utilize the ability of soluble aluminum salt to form Al(OH)3 colloids, thereby improving the stability of [Al-OHO-Sn] colloids, inhibiting the dehydration of Sn(OH)4, and improving the overall stability of the catalyst.

[0025] In one embodiment of the present invention, the soluble aluminum salt can be added in the form of an aqueous solution of soluble aluminum salt; the mass concentration of the aqueous solution of soluble aluminum salt can be 10%; the addition rate of the aqueous solution of soluble aluminum salt can be 0.2~1 mL / min, 0.4~0.8 mL / min, or 0.6 mL / min. By limiting the addition form and rate of the soluble aluminum salt to the above ranges, the present invention ensures sufficient dispersion with the tin element in the system.

[0026] In one embodiment of the present invention, after the soluble aluminum salt is added, stirring can continue; the stirring time can be 20-40 minutes, or 30 minutes; the stirring speed is the same as the stirring speed described above, and will not be repeated here. Continuing to stir after the soluble aluminum salt is added ensures that AlCl3 is completely dissolved and achieves sufficient pre-mixing with tin ions.

[0027] In this invention, the temperature of the first settling period is -12 to -20°C, preferably -14 to -18°C, more preferably -16 to -18°C; the time of the first settling period is preferably 12 to 36 hours, more preferably 20 to 30 hours, and even more preferably 24 hours. This invention limits the temperature and time of the first settling period to the ranges described above to achieve sufficient hydration of tetravalent tin-hydrated hydrogen bonds-trivalent aluminum.

[0028] In one embodiment of the present invention, the mass concentration of tin tetrachloride in the mixed solution can be 25-35%, or even 30%. Limiting the mass concentration of tin tetrachloride in the mixed solution to the above range facilitates the complete hydrolysis of tin tetrachloride.

[0029] After obtaining the mixed solution, the present invention mixes the mixed solution with ammonia water for a second time and then allows it to stand for a second time. Then, it is subjected to high-temperature hydrolysis and drying in sequence to obtain a heterogeneous unsupported tin-based catalyst.

[0030] In one embodiment of the present invention, the mass ratio of tin tetrachloride to ammonia can be 1:(0.01~0.03), 1:(0.015~0.025), or 1:0.02; the mass concentration of the ammonia can be 5~10%, or 6~8%. Limiting the concentration of ammonia and the mass ratio of tin tetrachloride to ammonia within the above ranges ensures complete hydrolysis of tin tetrachloride.

[0031] The present invention does not have any particular limitation on the second mixing method, as long as the mixed solution is thoroughly mixed with ammonia water.

[0032] In one embodiment of the present invention, the temperature of the second settling period is -12 to -20°C, preferably -14 to -18°C, and more preferably -16 to -18°C; the time of the second settling period is preferably 0.5 to 2 hours, and more preferably 1 to 1.5 hours. By limiting the temperature and time of the second settling period to the above ranges, the present invention can enhance hydration and achieve sufficient hydration of tetravalent tin-hydrated hydrogen bonds-trivalent aluminum.

[0033] In one embodiment of the present invention, the high-temperature hydrolysis can be carried out in a pressure reactor; the temperature of the high-temperature hydrolysis can be 130~190℃, 140~180℃, or 150~160℃; the time of the high-temperature hydrolysis can be 2~6h, 3~5h, or 3~4h. The present invention does not specifically limit the pressure of the pressure reactor; pressures commonly used by those skilled in the art are acceptable. The present invention limits the temperature and time of the high-temperature hydrolysis to the above-mentioned ranges, allowing for sufficient high-temperature hydrolysis of SnCl4 to achieve the conversion of Sn(OH)4.

[0034] As one embodiment of the present invention, after the high-temperature hydrolysis is completed, the reaction system obtained by the high-temperature hydrolysis can be naturally cooled to room temperature, and then centrifuged, washed and dried in sequence to obtain a heterogeneous unsupported tin-based catalyst.

[0035] In one embodiment of the present invention, the centrifugation speed can be 5000~8000 rpm or 6000~7000 rpm; the centrifugation time can be 5~15 min or 10 min. Limiting the centrifugation speed and time to the above ranges allows for better solid-liquid separation.

[0036] In one embodiment of the present invention, the solid obtained by centrifugation can be washed after centrifugation.

[0037] In one embodiment of the present invention, the washing solution used for washing can be deionized water or anhydrous methanol. The present invention does not specifically limit the number of washing cycles, as long as the pH of the washing solution obtained from the last washing is neutral.

[0038] In one embodiment of the present invention, the drying can be carried out in a desiccant or a vacuum drying oven; the drying process can be: first drying followed by a second drying; the first drying is carried out under normal pressure; the temperature of the first drying can be 40~60℃ or 50℃; the time of the first drying can be 2 hours; the second drying is carried out under vacuum conditions; the vacuum degree of the vacuum conditions can be ≤-0.08MPa; the temperature of the second drying can be 50~70℃ or 60℃; the time of the second drying can be 6~12 hours or 8~10 hours. The present invention limits the drying steps and parameters to the above ranges to completely remove physically adsorbed water and obtain catalyst powder.

[0039] This invention introduces Al element into an aqueous tin tetrachloride system (a mixture of tin tetrachloride and an aqueous solution of an organic alcohol) and performs hydration pretreatment by standing at low temperature. By limiting the low temperature, the hydrolysis pathway can be effectively controlled, forming [Al-OHO-Sn] bonds and constructing an interfacial water cluster hydrogen bond network. This can synergistically inhibit the dehydration process of Sn(OH)4, improve the stability of heterogeneous unsupported tin-based catalysts, and can be directly used for the catalytic conversion of biomass sugars, giving the heterogeneous unsupported tin-based catalysts good catalytic performance.

[0040] The present invention also provides a heterogeneous unsupported tin-based catalyst prepared by the preparation method described in the above technical solution.

[0041] This invention also provides the application of the heterogeneous unsupported tin-based catalyst described in the above technical solution in the catalytic conversion of sugars to lactose.

[0042] In an application example of the present invention, the sugar is glucose.

[0043] In one embodiment of the present invention, when the heterogeneous unsupported tin-based catalyst catalyzes the conversion of sugars to lactose, the mass ratio of the heterogeneous unsupported tin-based catalyst to the sugars can be 1:(8~12) or 1:10. Limiting the mass ratio of the heterogeneous unsupported tin-based catalyst to the sugars within the above range promotes the full conversion of sugars.

[0044] In one embodiment of the present invention, the conversion temperature can be 150~190℃ or 170℃. Limiting the conversion temperature to the above range allows for better conversion results.

[0045] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] Example 1 A method for preparing a heterogeneous, unsupported tin-based catalyst comprises the following steps: A 40% aqueous solution of tin tetrachloride and methanol was first mixed in a jacketed reaction beaker at -4°C (stirring at 300 rpm). Aluminum chloride (added as a 10% aqueous solution at a rate of 0.2 mL / min) was then added, followed by stirring at 300 rpm for 30 min. The mixture was then allowed to stand at -18°C for 24 h to obtain a mixed solution. The mass ratio of tin tetrachloride to aluminum chloride was 1:0.01, and the mass concentration of tin tetrachloride in the mixed solution was 30%. The mixed solution was mixed with ammonia (5% by mass, with a mass ratio of tin tetrachloride to ammonia of 1:0.01) for a second time, and then allowed to stand at -18°C for 1 hour. After hydrolysis at 150°C for 3 hours, it was naturally cooled to room temperature. After centrifugation at 6000 rpm for 10 minutes, the obtained solid was washed three times with deionized water until the washing liquid was neutral. Then, it was dried at 50°C under normal pressure for 2 hours, and then dried at 60°C for 6 hours under vacuum conditions of ≤-0.08 MPa to obtain a heterogeneous unsupported tin-based catalyst.

[0047] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that aluminum chloride and ammonia were not added; otherwise, they are the same as in Example 1.

[0048] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that ammonia was not added; otherwise, they are the same as Example 1.

[0049] The physical image of the product obtained by high-temperature hydrolysis in Example 1 (denoted as the Sn(OH)4 sample treated with Al synergistic ammonia water) is shown below. Figure 1 As shown, a physical image of the product obtained by high-temperature hydrolysis in Comparative Example 1 (denoted as the unhydrated Sn(OH)4 sample) is shown below. Figure 2 As shown, a physical image of the product obtained by high-temperature hydrolysis in Comparative Example 2 (denoted as the Al-doped Sn(OH)4 sample) is shown below. Figure 3 As shown.

[0050] The tin dioxide and catalysts prepared in Example 1 and Comparative Examples 1-2 were tested using an infrared spectrometer. The resulting infrared spectra are shown below. Figure 4 As shown.

[0051] from Figures 1-4 As can be seen, in Comparative Example 1, the product obtained from the high-temperature hydrolysis of untreated tin tetrachloride aqueous solution in a high-pressure reaction vessel was almost entirely converted into low-catalytic-activity tin dioxide particles due to high-temperature dehydration, and precipitated at the bottom. Figure 4Infrared spectroscopy also corroborates this, showing that its characteristic peaks are extremely similar to those of tin dioxide. In Comparative Example 2, the product obtained from the reaction of Al-doped tin tetrachloride aqueous solution without added ammonia in a high-pressure reaction vessel exhibited relatively unstable Sn(OH)4 system, resulting in partial conversion into tin dioxide with low catalytic activity. Figure 4 The infrared spectrum shows that its characteristic infrared peaks have obvious OH characteristic peaks around 3400. The product obtained from the high-temperature hydrolysis of tin tetrachloride aqueous solution pretreated with Al and ammonia in Example 1, reacted in a high-pressure reactor, exhibits a stable Sn(OH)4 system and can be dispersed as an emulsion in aqueous solution, making it suitable for use as a non-supported catalyst. Figure 4 The infrared analysis spectrum shows that the characteristic peak of its infrared compound OH is most obvious around 3400.

[0052] Application Example 1 The heterogeneous unsupported tin-based catalyst prepared in Example 1 was mixed with 1 wt% glucose solution at a mass ratio of 1:10 and then converted at 170°C for 2 h.

[0053] The product obtained by conversion in Example 1 was detected by liquid chromatography (amino column), and the conversion rate of glucose to lactic acid was over 90%.

[0054] The heterogeneous unsupported tin-based catalyst prepared in Example 1 was tested for its catalytic performance after being repeated 10 times. The catalytic performance after 10 repetitions reached 93% of the efficiency of the catalyst when it was used for the first time.

[0055] The heterogeneous, unsupported tin-based catalyst prepared by the method provided by this invention can exist stably (without transforming into tin dioxide), and can convert glucose into lactic acid with a yield of over 90%. Moreover, the catalyst can achieve 93% of the efficiency of the first use after being repeated 10 times, demonstrating good stability and catalytic effect.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a heterogeneous, unsupported tin-based catalyst, comprising the following steps: After first mixing tin tetrachloride with an aqueous solution of an organic alcohol, a soluble aluminum salt is added, followed by a first settling period to obtain a mixed solution. The mixed solution was mixed with ammonia water for a second time and then allowed to stand for a second time. Then, it was subjected to high-temperature hydrolysis and drying in sequence to obtain a heterogeneous unsupported tin-based catalyst. The temperature for both the first and second static periods is -12 to -20°C.

2. The preparation method according to claim 1, characterized in that, The mass ratio of tin tetrachloride to soluble aluminum salt is 1:(0.01~0.05).

3. The preparation method according to claim 1, characterized in that, The temperature of the first mixture is -4 to 0°C.

4. The preparation method according to claim 1, characterized in that, The mass concentration of tin tetrachloride in the mixed solution is 25-35%.

5. The preparation method according to claim 1, characterized in that, The first settling time is 12~36 hours.

6. The preparation method according to claim 1, characterized in that, The second settling time is 0.5 to 2 hours.

7. The preparation method according to claim 1, characterized in that, The mass ratio of tin tetrachloride to ammonia is 1:(0.01~0.03). The mass concentration of the ammonia water is 5-10%.

8. The preparation method according to claim 1, characterized in that, The high-temperature hydrolysis temperature is 130~190℃, and the high-temperature hydrolysis time is 2~6h.

9. The heterogeneous unsupported tin-based catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the heterogeneous unsupported tin-based catalyst of claim 9 in the catalytic conversion of sugars to lactose.

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