Solid acid catalyst, its preparation method and application

Abstract

The application discloses a solid acid catalyst and a preparation method and application thereof, and belongs to the technical field of catalyst preparation.The solid acid catalyst is prepared through two steps, including the following steps of: preparing a precursor: dissolving a nitrogen-containing compound and furfural in an H2SO4 aqueous solution, then adding potassium persulfate to perform stirring reaction, filtering and recovering solid precipitates, washing, and vacuum drying to obtain the precursor; and preparing the solid acid catalyst: dispersing the precursor into n-heptane, adding concentrated sulfuric acid, and performing stirring reaction; after the reaction is completed, the temperature is lowered to room temperature, and then the solid acid catalyst is obtained through the steps of filtering, washing, and vacuum drying.The preparation method provided by the application introduces a nitrogen-containing group in the solid acid synthesis process, enhances the stability of sulfonic acid groups of sulfonated resins, makes the sulfonic acid groups not easy to fall off, prolongs the service life of the solid acid catalyst, and the prepared solid acid catalyst has high catalytic activity and stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a solid acid catalyst, its preparation method, and its application. Background Technology

[0002] Commercial solid acid catalysts can achieve catalytic effects comparable to those of sulfuric acid. However, due to the insufficient stability of the sulfonate group in solid acid catalysts, their catalytic effect gradually decreases over time.

[0003] To enhance the stability of sulfonate groups in solid acid catalysts, and since sulfonate groups are strong electron-withdrawing groups, nitrogen-containing substances that provide electrons are incorporated during the synthesis of solid acid catalysts to enhance their stability.

[0004] The solid acid catalyst synthesized by this method has a large number of Bronsted acid sites (B acid) and Lewis acid sites (L acid), which enables it to catalyze both the esterification of acetic acid and methanol and the polymerization of lactic acid, making it of high research value. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a solid acid catalyst.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solutions, including:

[0009] Nitrogen-containing compounds and furfural are dissolved in an aqueous H2SO4 solution, and potassium persulfate is added for stirring and reaction. The solid precipitate is recovered by filtration, washed, and vacuum dried to obtain the precursor.

[0010] The precursor was dispersed in n-heptane, concentrated sulfuric acid was added, and the mixture was stirred to react. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried under vacuum to obtain a solid acid catalyst.

[0011] In a preferred embodiment of the preparation method of the solid acid catalyst of the present invention, the nitrogen-containing compound includes one or more of m-aminobenzenesulfonic acid, melamine, and ethylenediamine.

[0012] In a preferred embodiment of the preparation method of the solid acid catalyst of the present invention, the molar ratio of the nitrogen-containing compound and furfural is 1:5 to 20; and the concentration of the H2SO4 aqueous solution is 0.1 to 5 mol / L.

[0013] In a preferred embodiment of the preparation method of the solid acid catalyst of the present invention, the stirring reaction is carried out at a temperature of 90-95°C for a time of 6-24 hours.

[0014] In a preferred embodiment of the preparation method of the solid acid catalyst of the present invention, the mass ratio of sulfuric acid to precursor is 10-24:1; and the mass-volume ratio of precursor to n-heptane is 1-4 g:20 mL.

[0015] In a preferred embodiment of the preparation method of the solid acid catalyst of the present invention, the washing process involves washing the solid acid catalyst multiple times with ethyl acetate and then washing it with a large amount of water to neutralize the pH. The vacuum drying process involves a temperature of 50–90°C, a vacuum degree of 0.5–0.1 MPa, and a drying time of 6–18 h.

[0016] Another object of the present invention is to overcome the shortcomings of the prior art and provide a solid acid catalyst.

[0017] Another object of the present invention is to overcome the shortcomings of the prior art and provide an application of a solid acid catalyst, the application of which includes the preparation of polylactic acid and catalytic esterification reaction.

[0018] Another object of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing polylactic acid, comprising,

[0019] Lactic acid and the solid acid catalyst were stirred and mixed, and a prepolymerization reaction was carried out at 120-160°C and 0.01-0.05 MPa vacuum for 6-18 hours to obtain a prepolymer; then a final polymerization reaction was carried out at 170-200°C and 0.05-0.1 MPa for 6-18 hours to obtain polylactic acid.

[0020] The amount of solid acid catalyst added is 0.1% to 1%.

[0021] Another object of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing methyl acetate, comprising,

[0022] The solid acid catalyst and methanol were added to acetic acid at 70-90°C, and the mixture was stirred continuously at 200-500 rpm for 1-3 hours to carry out the esterification reaction to obtain methyl acetate.

[0023] The ratio of acetic acid, solid acid catalyst and methanol is 1-2:0.02-0.12:1.

[0024] Beneficial effects of this invention:

[0025] (1) The solid acid catalyst prepared by the present invention has high catalytic activity and stability.

[0026] (2) The preparation method provided by the present invention introduces nitrogen-containing groups in the solid acid synthesis process, which enhances the stability of sulfonate groups in sulfonated resin, making it difficult for sulfonate groups to fall off and extending the service life of solid acid catalysts. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0028] Figure 1 The infrared spectra of [AMSA-PFA], [AMSA-PFA]H2SO4, [PME-PFA]H2SO4 and [EDA-PFA]H2SO4 prepared in this invention are shown. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0032] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0033] Example 1

[0034] This embodiment provides a method for preparing a solid acid catalyst, specifically as follows:

[0035] 0.012 mol m-aminobenzenesulfonic acid (2.078 g) and 0.12 mol furfural (10 mL, i.e., the molar ratio of m-aminobenzenesulfonic acid to furfural is 1:10) were added to 20 mL of 1 mol / L H2SO4 aqueous solution and mixed well. Then, 0.3 g of potassium persulfate was added, and the mixture was stirred continuously in an oil bath at 90 °C for 12 h. The resulting solid was recovered by filtration and washed multiple times with ethanol, ethyl acetate, and water to ensure complete removal of reactants. Subsequently, it was vacuum dried at 70 °C and 0.1 MPa for 12 h to improve the purity and stability of the obtained [AMSA-PFA] precursor.

[0036] 2.5 g of [AMSA-PFA] precursor was weighed and dispersed in 20 mL of n-heptane, and then 46 g of concentrated sulfuric acid was added. The mixture was heated and stirred at 95 °C for 12 h. After the reaction was completed, the mixture was poured into a beaker containing a large amount of deionized water. After the solution temperature dropped to room temperature, it was filtered and washed several times with ethyl acetate. The solid was then washed with a large amount of water until the pH was neutral. Finally, water and ethyl acetate were removed under vacuum at 70 °C to obtain the solid acid catalyst [AMSA-PFA]H2SO4.

[0037] Example 2

[0038] The difference between this embodiment and Example 1 is that the mass of m-aminobenzenesulfonic acid is adjusted to 0.006 mol (1.039 g), that is, the molar ratio of m-aminobenzenesulfonic acid to furfural is 1:20. The rest of the preparation process is the same as in Example 1, and a solid acid catalyst is obtained.

[0039] Example 3

[0040] The difference between this embodiment and Example 1 is that the mass of m-aminobenzenesulfonic acid was adjusted to 0.024 mol (4.156 g), that is, the molar ratio of m-aminobenzenesulfonic acid to furfural was 1:5. The rest of the preparation process was the same as in Example 1, and a solid acid catalyst was obtained.

[0041] Examples 4-6

[0042] The difference between this embodiment and Examples 1-3 is that the type of nitrogen-containing compound is changed to melamine, while the rest of the preparation process is the same as in Examples 1-3, to obtain the solid acid catalyst [PME-PFA]H2SO4. Specifically, 0.012 mol, 0.006 mol, and 0.024 mol of melamine are weighed and mixed with furfural, respectively.

[0043] Examples 7-9

[0044] The difference between this embodiment and Examples 1-3 is that the nitrogen-containing compound is changed to ethylenediamine, while the rest of the preparation process is the same as in Examples 1-3, to obtain the solid acid catalyst [EDA-PFA]H2SO4. Specifically, 0.012 mol, 0.006 mol, and 0.024 mol of ethylenediamine are weighed and mixed with furfural, respectively.

[0045] Figure 1 The infrared spectra of [AMSA-PFA], [AMSA-PFA]H2SO4, [PME-PFA]H2SO4, and [EDA-PFA]H2SO4 obtained by this invention are shown. It can be seen that the method of this invention successfully prepared the target products.

[0046] The solid acid catalysts prepared in Examples 1-9 above were applied to the polymerization reaction to prepare polylactic acid and the esterification reaction to prepare methyl acetate, as follows.

[0047] Preparation of polylactic acid (PLA) (polymerization reaction): 50g of lactic acid and 0.25wt% solid acid catalyst were stirred and mixed, and prepolymerized at 140℃ and 0.05MPa vacuum for 12h; the temperature was then increased to 190℃ and the vacuum to 0.1MPa, and the final polymerization reaction was carried out for 12h to obtain PLA. The molecular weight of PLA was determined by GPC gel permeation chromatography. Parameters: The GPC chromatograph was an Agilent 1260 (USA); the separation column consisted of a guard column + two PLgel MIXED-B LS 300X7.5mm columns connected in series; the detector was a Refractive Index; the temperature was 35℃; the mobile phase was chloroform; and the flow rate was 1ml / min.

[0048] Preparation of methyl acetate (esterification reaction): 30g of acetic acid was heated to 80℃ and 2.4g of solid acid catalyst and 10g of methanol were added. The mixture was stirred continuously at 350rpm for 2h to carry out the esterification reaction. After the reaction was completed, methyl acetate and water were obtained.

[0049] Esterification product analysis: The classic reaction of acetic acid and methanol produces methyl acetate and water as the main products. Therefore, the experiment was conducted to characterize the extent of the experiment by detecting the decrease in acetic acid and the increase in methyl acetate, and to provide data support for subsequent calculations.

[0050] The gas chromatograph used was a GC-3420A manufactured by Beijing Beifen Ruili. The separation column was a capillary column with parameters of 30m * 0.32mm * 0.50μm. The detector was a flame ionization detector (FID). The initial column temperature was 80℃, the injector temperature was 220℃, and the detector temperature was 250℃. The temperature program was to hold at 80℃ for 2 min, then increase to 200℃ at a rate of 30℃ / min, and hold at 200℃ for 5 min. For experimental preparation, a mixture of methyl acetate, methanol, and acetic acid in a ratio of 15:3:1 was prepared. This mixture was analyzed by gas chromatography to determine the peak times of each component. At the start of the reaction, the volume was adjusted to 250μL using a pipette, and the sample was quickly transferred to the chromatographic chamber for gas chromatography analysis to determine its content ratio. During the reaction, samples were taken every 20 min and quickly transferred to the chromatographic chamber for gas chromatography analysis to determine the content ratio of each component. During gas chromatography analysis, rinse the syringe repeatedly at least 8 times, and take 0.6 μL of the test liquid when sampling. The total time from sampling from the three-necked flask to injection into the chromatograph should not exceed 1 minute to control the accuracy of the test.

[0051] Stability test of sulfonic acid (-SO3H) group: 30 mL of acetic acid and 1.5 g of catalyst were heated and stirred vigorously at 115 °C, and refluxed for 24 h and 48 h with an external condenser. 2.5 mL samples were taken from each sample and centrifuged for solid-liquid separation. The color change of the liquid solution was visually observed, and the sulfate content (mg / L) was determined by ion chromatography.

[0052] The test results are shown in Table 1.

[0053] Table 1

[0054]

[0055] Note: "-" in the table indicates that no stability test was performed.

[0056] As can be seen from the table above, adjusting the molar ratio of nitrogen-containing compounds to furfural has a significant impact on the performance of solid acid catalysts. This is because a low proportion of nitrogen-containing compounds leads to reduced stability of sulfonate ions, while a high proportion leads to nitrogen-containing compounds occupying the active sites of sulfonate ions. According to the results in the table above, the optimal technical effect can be obtained when the molar ratio of nitrogen-containing compounds to furfural in this invention is 1:10.

[0057] As can be seen from the table above, adjusting the type of nitrogen-containing compound has a significant impact on the performance of solid acid catalysts. This is because nitrogen-containing substances containing sulfonate not only provide electrons to stabilize sulfonate but also provide active sites for sulfonate. According to the results in the table above, the best technical effect can be obtained when the nitrogen-containing compound in this invention is m-aminobenzenesulfonic acid.

[0058] Comparative Example 1

[0059] This comparative example provides a method for preparing a solid acid catalyst, specifically as follows:

[0060] Weigh 20g of granular activated carbon that has been washed with water and dried at 115℃ to a constant weight, soak it in 120mL of 15% p-toluenesulfonic acid aqueous solution for 30h, and filter it. Dry it at 110℃ for 5h, and then cool it in a desiccator to obtain a solid catalyst.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that m-aminobenzenesulfonic acid is not added, but the rest of the preparation process is the same as in Example 1, and a solid acid catalyst is obtained.

[0063] Comparative Example 3

[0064] 0.012 mol m-aminobenzenesulfonic acid (2.078 g) and 0.12 mol furfural (10 mL, i.e., the molar ratio of m-aminobenzenesulfonic acid to furfural is 1:10) were added to 20 mL of 1 mol / L H2SO4 aqueous solution and mixed well. Then, 0.3 g of potassium persulfate was added, and the mixture was stirred continuously in an oil bath at 50 °C for 12 h. The resulting solid was recovered by filtration and washed multiple times with ethanol, ethyl acetate, and water to ensure complete removal of reactants. Subsequently, it was vacuum dried at 30 °C and 0.1 MPa for 12 h to improve the purity and stability of the obtained [AMSA-PFA] precursor.

[0065] 2.5 g of [AMSA-PFA] precursor was weighed and dispersed in 20 mL of n-heptane, and then 46 g of concentrated sulfuric acid was added. The mixture was heated and stirred at 55 °C for 12 h. After the reaction was completed, the mixture was poured into a beaker containing a large amount of deionized water. After the solution temperature dropped to room temperature, it was filtered and washed several times with ethyl acetate. The solid was then washed with a large amount of water until the pH was neutral. Finally, water and ethyl acetate were removed under vacuum at 40 °C to obtain the solid acid catalyst [AMSA-PFA]H2SO4.

[0066] Comparative Example 4

[0067] 0.012 mol m-aminobenzenesulfonic acid (2.078 g) and 0.12 mol furfural (10 mL, i.e., the molar ratio of m-aminobenzenesulfonic acid to furfural is 1:10) were added to 20 mL of 1 mol / L H2SO4 aqueous solution and mixed well. Then, 0.3 g of potassium persulfate was added, and the mixture was stirred continuously in an oil bath at 110 °C for 12 h. The resulting solid was recovered by filtration and washed multiple times with ethanol, ethyl acetate, and water to ensure complete removal of reactants. Subsequently, it was vacuum dried at 100 °C and 0.1 MPa for 12 h to improve the purity and stability of the obtained [AMSA-PFA] precursor.

[0068] Weigh 2.5g of [AMSA-PFA] precursor and disperse it in 20mL of n-heptane. Then add 46g of concentrated sulfuric acid and heat and stir at 115℃ for 12h. After the reaction is complete, pour it into a beaker containing a large amount of deionized water. After the solution temperature drops to room temperature, filter it and wash it several times with ethyl acetate. Then wash the solid with a large amount of water until the pH is neutral. Finally, remove water and ethyl acetate under vacuum at 100℃ to obtain the solid acid catalyst [AMSA-PFA]H2SO4.

[0069] The performance of the above comparative examples was tested, and the results compared with Example 1 are shown in Table 2.

[0070] Table 2

[0071] Polylactic acid molecular weight Methyl acetate yield (%) Example 1 62145 80.2 Comparative Example 1 28979 76.8 Comparative Example 2 29887 64.5 Comparative Example 3 37889 71.2 Comparative Example 4 38897 74.9

[0072] As can be seen from the table above, the preparation method provided by the present invention introduces nitrogen-containing groups during the solid acid synthesis process, which enhances the stability of sulfonate groups in sulfonated resins, making it difficult for sulfonate groups to fall off, thus extending the service life of the solid acid catalyst. The prepared solid acid catalyst has high catalytic activity.

[0073] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a solid acid catalyst, characterized in that: include, Step 1: Nitrogen-containing compounds and furfural are dissolved in an aqueous H2SO4 solution, and potassium persulfate is added for stirring and reaction. The solid precipitate is recovered by filtration, washed, and vacuum dried to obtain the precursor. Step 2: Disperse the precursor in n-heptane, add concentrated sulfuric acid, stir and react. After the reaction is complete, cool to room temperature, filter, wash, and vacuum dry to obtain a solid acid catalyst. The nitrogen-containing compound includes one or more of m-aminobenzenesulfonic acid, melamine, and ethylenediamine.

2. The method for preparing the solid acid catalyst according to claim 1, characterized in that: The molar ratio of the nitrogen-containing compound to furfural is 1:5~20; the concentration of the H2SO4 aqueous solution in step one is 0.1~5 mol / L.

3. The method for preparing the solid acid catalyst according to claim 1, characterized in that: The stirring reaction in steps one and two is carried out at a temperature of 90-95 °C for 6-24 h.

4. The method for preparing the solid acid catalyst according to claim 1, characterized in that: The mass ratio of sulfuric acid to precursor is 10~24:1; the mass-volume ratio of precursor to n-heptane is 1~4 g:20 mL.

5. The method for preparing the solid acid catalyst according to claim 1, characterized in that: In step two, the washing process involves washing the product multiple times with ethyl acetate, followed by washing with a large amount of water to bring the pH to neutral. In step one, the vacuum drying process involves a temperature of 50-90°C, a vacuum degree of 0.5-0.1 MPa, and a drying time of 6-18 hours.

6. A solid acid catalyst prepared by any one of the preparation methods described in claims 1 to 5.

7. An application of the solid acid catalyst as described in claim 6, characterized in that: The applications include the preparation of polylactic acid and methyl acetate.

8. A method for preparing polylactic acid, characterized in that: include, Lactic acid and the solid acid catalyst described in claim 6 are stirred and mixed, and a prepolymerization reaction is carried out at 120~160℃ and 0.01~0.05MPa vacuum for 6~18h to obtain a prepolymer; then a final polymerization reaction is carried out at 170~200℃ and 0.05~0.1MPa for 6~18h to obtain polylactic acid. The amount of solid acid catalyst added is 0.1~1wt%.

9. A method for preparing methyl acetate, characterized in that: include, Add the solid acid catalyst and methanol as described in claim 6 to acetic acid at 70~90℃, and carry out esterification reaction for 1~3 hours with continuous stirring at 200~500 rpm to obtain methyl acetate; The ratio of acetic acid, solid acid catalyst and methanol is 1~2:0.02~0.12:1.

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