A method for preparing an acidic solid catalyst

Abstract

This invention belongs to the field of catalyst technology, specifically relating to a method for preparing an acidic solid catalyst and its application in the catalytic production of biodiesel. Specifically, using a bromomethylated microporous polymer as a matrix, sodium 4-hydroxybenzenesulfonate or sodium 2-naphthol-6-sulfonate hydrate is selected for sulfonation to prepare a solid catalyst with an ultra-large specific surface area and a large number of strongly acidic groups. The acidic solid catalyst prepared by this invention exhibits excellent catalytic activity and recycling stability in the catalytic production of methyl oleate, and is easily recovered through filtration. Therefore, the acidic solid catalyst prepared by this invention has great potential for practical production in the field of biodiesel production.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a method for preparing an acidic solid catalyst and its application in biodiesel production. Background Technology

[0002] Biodiesel, as a renewable and green energy source, is considered a promising alternative to traditional fossil fuels in the future. Acidic catalysis is a crucial method for biodiesel production. Currently, the catalysts used in biodiesel production are mostly traditional catalysts such as concentrated sulfuric acid and sodium hydroxide. These catalysts suffer from problems such as equipment corrosion, difficult recycling, and environmental pollution, severely impacting large-scale biodiesel production. In recent years, acidic ionic liquids, as novel, green, and efficient catalysts, have been used to replace traditional catalysts in biodiesel production. However, liquid ionic liquids are difficult to recycle and cannot be reused. To address this recycling challenge, researchers have attempted to load acidic ionic liquids onto polymers to form acidic immobilized ionic liquids for biodiesel production. However, polymers have a small specific surface area, resulting in low catalyst activity. Furthermore, the protons used to exert the acidic catalytic performance of acidic immobilized ionic liquids are mainly obtained through the addition of acid. During the reaction, protons are lost as the added acid dissolves in water, leading to a decrease in activity.

[0003] The Dutch journal *Fuel Processing Technology* (2014, 118:296-301) reported an acidic ionic liquid catalyst for biodiesel production. The catalyst first reacts imidazole with sulfonyl lactone, then acidifies it with sulfuric acid to obtain the acidic ionic liquid. When this acidic ionic liquid is used to catalyze the production of biodiesel from black algae seed oil, the reaction yield reaches 97.70%. However, the liquid acidic ionic liquid is difficult to recover and cannot be reused.

[0004] The Dutch journal *Journal of Molecular Catalysis A Chemical* (2010, 332(1):152-157) reported an acidic supported ionic liquid catalyst for biodiesel production. This supported ionic liquid catalyst was prepared by supporting an ionic liquid on highly cross-linked chloromethylstyrene. A series of esterification reactions were conducted on the catalyst, and the results showed that the catalyst achieved a yield of 87.20% in biodiesel production. However, the catalyst, based on chloromethylstyrene, has a very low inherent specific surface area, resulting in low catalytic activity. Furthermore, the active protons of the supported ionic liquid are provided by an added acid, and the catalyst needs to be recovered by filtration after the catalytic reaction. The added acid dissolves in water and is lost during filtration, leading to a high risk of proton loss and poor cycle stability.

[0005] The Chinese journal *Chemical Reaction Engineering and Technology* (2009, 24(6): 503-508) reported an acidic supported ionic liquid catalyst for biodiesel production. The acidic supported ionic liquid was prepared by bonding the Brønsted acidic ionic liquid 1-methylimidazolium hydrogen sulfate ionic liquid ([Mim]HSO4) onto amorphous silica gel. A series of esterification reactions were carried out using this catalyst, and the results showed that the reaction yield could reach over 95%. However, this catalyst relies on the interaction between the imidazolium quaternary ammonium group and free HSO4. - Formation of zwitterions (-HSO4) - ...N + The catalyst uses an externally added acid to provide active protons to achieve high catalytic activity. However, this method of acid catalysis is highly unstable, as the water-soluble acid is lost during catalyst filtration and recovery, resulting in poor catalyst cycle stability. The results show that the catalytic activity of this catalyst significantly decreased after three repeated experiments.

[0006] To address the above issues, developing an acidic solid catalyst with high catalytic activity and stability that is easy to recycle is of great significance for biodiesel production. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a method for preparing an acidic solid catalyst, in order to overcome the technical defects of existing acidic catalysts used in biodiesel production.

[0008] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0009] A method for preparing an acidic solid catalyst includes the following steps: dissolving a bromomethylated self-porous polymer (PIM-Br) in an organic solvent, then adding sodium 4-hydroxybenzenesulfonate or sodium 2-naphthol-6-sulfonate hydrate to the PIM-Br solution for reaction, followed by washing, acidifying, and drying the reaction product to finally obtain an acidic solid catalyst (PIM-SO3H) based on the self-porous polymer.

[0010] The PIM-Br is composed of repeating units containing bromomethyl groups and repeating units not containing bromomethyl groups, and its structural formula is as follows:

[0011]

[0012] Where x = 0.05 - 1.

[0013] The degree of methyl bromination of the PIM-Br is 5% - 100%, where the degree of methyl bromination refers to the molar percentage of repeating units containing bromomethyl groups to all repeating units, i.e., x in the structure shown above.

[0014] The organic solvent used to dissolve PIM-Br is selected from N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide.

[0015] The concentration of the PIM-Br solution is 1 wt% to 60 wt%.

[0016] The molar amount of sodium 4-hydroxybenzenesulfonate or sodium 2-naphthol-6-sulfonate hydrate is 0.1 to 10 times the molar amount of bromomethyl in PIM-Br.

[0017] The reaction temperature of PIM-Br with sodium 4-hydroxybenzenesulfonate or sodium 2-naphthol-6-sulfonate hydrate is 0-150℃, and the reaction time is 2-48 h.

[0018] The acidification treatment refers to immersing the product in a hydrochloric acid solution.

[0019] The preparation method of PIM-Br includes the following steps: 3-methylcatechol is dissolved in a mixed solution of hydrobromic acid and glacial acetic acid, then acetone is added, and the mixture is reacted at 120 °C for 12 h to obtain a brown reaction solution; the brown reaction solution is poured into deionized water to precipitate a brown solid, which is washed repeatedly with glacial acetic acid to obtain a white product, namely TTSBI-M; TTSBI-M, tetrafluoroterephthalonitrile and anhydrous potassium carbonate are then added to N-methylpyrrolidone, dissolved, and then anhydrous toluene is added, and the mixture is reacted at 155 °C for 24 h to obtain the microporous polymer PIM-M; the above PIM-M is then mixed with N-bromosuccinimide (NBS) and azobisisobutyronitrile (AIBN) and added to chlorobenzene, and the mixture is reacted at 135 °C for 6 h to obtain a brominated microporous polymer PIM-Br with a methyl bromide degree of 5%-100%. The molar ratio of PIM-M to NBS is 1:(0.1-3), and PIM-Br with different degrees of bromination can be prepared according to different molar ratios.

[0020] The structural formula of the acidic solid catalyst is shown in a or b below.

[0021]

[0022] The significant advantages of this invention are:

[0023] This invention uses PIM-Br, a microporous polymer with an ultra-high specific surface area, as a matrix. It utilizes the high reactivity between the bromomethyl group and sodium 4-hydroxybenzenesulfonate or sodium 2-naphthol-6-sulfonate hydrate contained in PIM-Br to graft strong acidic sulfonic acid groups, thereby preparing an acidic solid catalyst. Specifically, the preparation method of the acidic solid catalyst provided by this invention has the following outstanding advantages: (1) The extremely high specific surface area inside the microporous polymer can effectively improve catalytic activity; (2) Grafting strong acidic sulfonic acid groups onto the catalyst through a chemical reaction eliminates the problem of proton loss, thus enabling the catalyst to possess both high catalytic activity and stability; (3) The catalyst is solid, making it easy to filter and recover after the reaction, thus exhibiting good recyclability; (4) By selecting microporous polymers with different degrees of methyl bromination and adjusting various conditions in the reaction process, the performance of the acidic solid catalyst can be precisely controlled, and the optimal acidic solid catalyst can be selected for biodiesel production. Attached Figure Description

[0024] Figure 1 The TTSBI-M, PIM-M, and PIM-Br synthesized in Example 1 1 1H NMR spectra. Comparison of the peak positions, peak shapes, and peak areas of the characteristic proton NMR spectra of each substance indicates that PIM-Br was successfully synthesized.

[0025] Figure 2The images show the FT-IR spectra of the acidic solid catalysts PIM-SO3H and PIM-Br synthesized in Example 1. Comparison of their infrared absorption peaks indicates that PIM-SO3H was successfully synthesized.

[0026] Figure 3 SEM images of PIM-Br and the acidic solid catalyst PIM-SO3H synthesized in Example 1 are shown. (a)(b) PIM-Br, (c)(d) PIM-SO3H. The results show that the specific surface area of ​​the synthesized acidic solid catalyst PIM-SO3H reaches 350 m². 2 g -1 . Detailed Implementation

[0027] The following describes the embodiments of the present invention clearly and completely with reference to the technical solutions, but the present invention is not limited thereto. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0028] All chemical reagents used in the embodiments of this invention are commercially available.

[0029] Example 1

[0030] 22.4 g of 3-methylcatechol was dissolved in a mixed solution of 48 mL hydrobromic acid and 40 mL glacial acetic acid, followed by the addition of 28 mL acetone. The reaction was carried out at 120 °C for 12 h to obtain a brown reaction solution. The brown reaction solution was poured into deionized water to precipitate a brown solid, which was washed repeatedly with glacial acetic acid to obtain a white product, namely TTSBI-M. Then, 11.045 g of TTSBI-M, 6.027 g of tetrafluoroterephthalonitrile, and 10.365 g of anhydrous potassium carbonate were added to 60 mL of N-methylpyrrolidone, dissolved, and then 20 mL of anhydrous toluene was added. The reaction was carried out at 155 °C for 24 h to obtain the microporous polymer PIM-M. Then, 10 g of the above-mentioned PIM-M was mixed with 43.6 g of N-bromosuccinimide (NBS) and 9.587 g of azobisisobutyronitrile (AIBN) and added to 80 mL of chlorobenzene. The mixture was reacted at 135 °C for 6 h to obtain a brominated self-porous polymer PIM-Br with a methyl bromide degree of 100%.

[0031] One g of a brominated microporous polymer (PIM-Br, bromomethyl: 1.85 mmol) with a methyl bromide degree of 100% was dissolved in 9 g of N-methylpyrrolidone to form a homogeneous solution with a concentration of 10 wt%. Then, 3.63 g of sodium 4-hydroxybenzenesulfonate (18.5 mmol) was added, and the reaction was carried out at 75 °C for 24 h. After thoroughly washing the reaction product with methanol, it was soaked in 0.5 mol / L hydrochloric acid aqueous solution at 25 °C for 12 h. Finally, the product was dried in a constant temperature drying oven at 60 °C for 12 h. The resulting acidic solid catalyst based on the microporous polymer (PIM-SO3H) was obtained. The acid value of PIM-SO3H (i.e., the content of sulfonic acid groups in the membrane) was measured to be 1.56 mmol / g.

[0032] The PIM-SO3H catalyst prepared in this embodiment was used to prepare methyl oleate via the esterification reaction of oleic acid and methanol to evaluate the performance of PIM-SO3H in biodiesel catalysis. Specifically, 2.645 g of oleic acid and 3.0 g of methanol (methanol / oleic acid molar ratio of 10:1) were mixed, and then 0.282 g of catalyst (mass concentration of 5 wt%) was added. The esterification reaction was carried out at 70 °C for 2 h. After the reaction, PIM-SO3H was recovered by filtration. The results showed that the conversion rate of methyl oleate was 97.3%, indicating that PIM-SO3H has excellent catalytic performance. Ten repeated experiments were conducted on PIM-SO3H to prepare methyl oleate. The results showed that the conversion rate of oleic acid remained unchanged, indicating that PIM-SO3H has excellent catalytic stability. Furthermore, the recovery rate of PIM-SO3H after the reaction was >99%, indicating that PIM-SO3H has good recyclability. In summary, the acidic solid catalyst prepared by this invention has great application potential in the field of biodiesel catalytic production.

[0033] Example 2

[0034] Similar to Example 1, but with the bromination degree of PIM-Br changed to 5%. 1 g of PIM-Br with a methyl bromination degree of 5% (molar amount of bromomethyl: 0.1 mmol) was dissolved in 9 g of N-methylpyrrolidone to form a homogeneous solution with a concentration of 10 wt%. Then, 1.96 mg of sodium 4-hydroxybenzenesulfonate (0.01 mmol) was added, and the reaction was carried out at 45 °C for 6 h. After thoroughly washing the reaction product with methanol, it was soaked in 0.5 mol / L hydrochloric acid aqueous solution at 25 °C for 12 h. Finally, the product was dried in a constant temperature drying oven at 60 °C for 12 h. The resulting acidic solid catalyst (PIM-SO3H) based on a microporous polymer was obtained. The acid value of PIM-SO3H was measured to be 0.2 mmol / g.

[0035] The performance of the PIM-SO3H catalyst prepared in this example for biodiesel catalytic production was tested under the same catalytic conditions as in Example 1. The results showed that the conversion rate of methyl oleate was 57.4%. Then, five repeated experiments were conducted on PIM-SO3H to prepare methyl oleate as described above. The results showed that the oleic acid conversion rate remained unchanged, indicating that PIM-SO3H has excellent catalytic stability. Furthermore, the recovery rate of PIM-SO3H after the reaction was >99%, indicating that PIM-SO3H has good recyclability.

[0036] Example 3

[0037] A similar method to Example 1 was used, except that the degree of bromination of PIM-Br was changed to 80%. 1 g of PIM-Br with a methyl bromination degree of 80% (molality of bromomethyl: 1.48 mmol) was dissolved in 9 g of N-methylpyrrolidone to form a homogeneous solution with a concentration of 10 wt%. Then, 1.452 g of sodium 4-hydroxybenzenesulfonate (7.4 mmol) was added, and the reaction was carried out at 60 °C for 12 h. After thoroughly washing the reaction product with methanol, it was soaked in a 0.5 mol / L hydrochloric acid aqueous solution at 25 °C for 12 h. Finally, the product was dried in a constant temperature drying oven at 60 °C for 12 h. The resulting acidic solid catalyst (PIM-SO3H) based on a microporous polymer was obtained. The acid value of PIM-SO3H was measured to be 0.84 mmol / g.

[0038] The PIM-SO3H catalyst prepared in this embodiment was tested for its performance in biodiesel catalytic production under the same catalytic conditions as in Example 1. The results showed that the conversion rate of methyl oleate was 85.5%. Ten repeated experiments were then conducted on PIM-SO3H to prepare methyl oleate as described above. The results showed that the oleic acid conversion rate remained constant, indicating that PIM-SO3H has excellent catalytic stability. Furthermore, the recovery rate of PIM-SO3H after the reaction was >99%, indicating that PIM-SO3H has good recyclability. In summary, the acidic solid catalyst prepared in this invention has great application potential in the field of biodiesel catalytic production.

[0039] Example 4

[0040] PIM-Br with a methyl bromide degree of 100% was prepared using the same method as in Example 1. 1 g of the methyl bromide-based microporous polymer (PIM-Br, bromomethyl: 1.85 mmol) with a methyl bromide degree of 100% was dissolved in 9 g of N-methylpyrrolidone to form a homogeneous solution with a concentration of 10 wt%. Then, 4.55 g of sodium 2-naphthol-6-sulfonate hydrate (18.5 mmol) was added, and the reaction was carried out at 75 °C for 24 h. After thoroughly washing the reaction product with methanol, it was soaked in 0.5 mol / L hydrochloric acid aqueous solution at 25 °C for 12 h. Finally, the product was dried in a constant temperature drying oven at 60 °C for 12 h. The resulting acidic solid catalyst based on the microporous polymer (PIM-SO3H) was obtained. The acid value of PIM-SO3H was measured to be 1.08 mmol / g.

[0041] The performance of the PIM-SO3H catalyst prepared in this embodiment for biodiesel catalytic production was tested under the same catalytic conditions as in Example 1. The results showed that the conversion rate of methyl oleate was 89.6%. Ten repeated experiments were then conducted on PIM-SO3H to prepare methyl oleate as described above. The results showed that the oleic acid conversion rate remained unchanged, indicating that the PIM-SO3H catalyst modified with sodium 2-naphthol-6-sulfonate hydrate also exhibits excellent catalytic stability. Furthermore, the recovery rate of PIM-SO3H after the reaction was >99%, indicating that the PIM-SO3H modified with sodium 2-naphthol-6-sulfonate hydrate also has good recyclability. In summary, the acidic solid catalyst prepared in this invention has great application potential in the field of biodiesel catalytic production.

[0042] Example 5

[0043] Similar to Example 1, but with the degree of bromination of PIM-Br changed to 80%. 1 g of PIM-Br with a methyl bromination degree of 80% (molality of bromomethyl: 1.48 mmol) was dissolved in 4 g of N-methylpyrrolidone to form a homogeneous solution with a concentration of 20 wt%. Then, 2.3 g of sodium 2-naphthol-6-sulfonate hydrate (9.3 mmol) was added, and the reaction was carried out at 60 °C for 24 h. After thoroughly washing the reaction product with methanol, it was soaked in 0.5 mol / L hydrochloric acid aqueous solution at 25 °C for 12 h. Finally, the product was dried in a constant temperature drying oven at 60 °C for 12 h. The resulting acidic solid catalyst (PIM-SO3H) based on a microporous polymer was obtained. The acid value of PIM-SO3H was measured to be 0.72 mmol / g.

[0044] The performance of the PIM-SO3H catalyst prepared in this embodiment for biodiesel catalytic production was tested under the same catalytic conditions as in Example 1. The results showed that the conversion rate of methyl oleate was 80.9%. Ten repeated experiments were then conducted on PIM-SO3H to prepare methyl oleate as described above. The results showed that the oleic acid conversion rate remained unchanged, indicating that the PIM-SO3H catalyst modified with sodium 2-naphthol-6-sulfonate hydrate has excellent catalytic stability. Furthermore, the recovery rate of PIM-SO3H after the reaction was >99%, indicating that the PIM-SO3H prepared in this embodiment has good recyclability. In summary, the acidic solid catalyst prepared in this invention has great application potential in the field of biodiesel catalytic production.

[0045] Example 6

[0046] Using a method similar to that in Example 1, except that the degree of bromination of PIM-Br was changed to 20%, the final biodiesel solid catalyst had an acid value of 0.5 mmol / g, and under the same catalytic conditions as in Example 1, the catalytic reaction yield was 66.5%. This indicates that the degree of methyl bromination of the microporous polymer affects the number of grafted strong acid groups, further influencing the acid value and catalytic performance of the biodiesel solid catalyst.

[0047] Example 7

[0048] An acidic solid catalyst was prepared using a method similar to that in Example 1, except that the organic solvent was changed to N,N-dimethylformamide. The resulting biodiesel solid catalyst had an acid value of 1.53 mmol / g, and under the same catalytic conditions as in Example 1, the catalytic reaction yield was 97.1%. This indicates that the choice of organic solvent does not affect the acid value and catalytic performance of PIM-SO3H.

[0049] Example 8

[0050] An acidic solid catalyst was prepared using a method similar to that in Example 1, except that the concentration of the PIM-Br solution was changed to 30 wt%. The resulting biodiesel solid catalyst had an acid value of 1.38 mmol / g, and under the same catalytic conditions as in Example 1, the catalytic reaction yield was 95.4%. This indicates that the concentration of the PIM-Br solution affects the number of strongly acidic groups grafted onto PIM-SO3H, further influencing the acid value and catalytic performance of PIM-SO3H.

[0051] Example 9

[0052] A novel biodiesel solid catalyst was prepared using a method similar to that in Example 4, except that the reaction temperature was changed to 85°C and the reaction time to 48 h. The resulting biodiesel solid catalyst had an acid value of 1.32 mmol / g, and under the same catalytic conditions as in Example 4, the catalytic reaction yield was 90.9%. This indicates that reaction temperature and time affect the number of grafted strong acid groups, further influencing the acid value and catalytic performance of the biodiesel solid catalyst.

[0053] The results of the above examples show that the present invention selects PIM-Br, a microporous polymer with different degrees of methyl bromide, and grafts a large number of sulfonic acid groups onto it as a matrix. By utilizing the catalytic activity of sulfonic acid groups in acid-alcohol esterification reactions, a solid catalyst with high catalytic performance is prepared for catalytic application in the biodiesel production process. This catalyst can meet the requirements of actual industrial applications and has broad application prospects.

[0054] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an acidic solid catalyst, characterized in that, Includes the following steps: The bromomethylated microporous polymer PIM-Br was dissolved in an organic solvent to form a homogeneous solution. Sodium 4-hydroxybenzenesulfonate or sodium 2-naphthol-6-sulfonate hydrate was then added to the PIM-Br solution to carry out the reaction. The reaction product was then washed, acidified, and dried to finally obtain the acidic solid catalyst PIM-SO3H based on the microporous polymer. The PIM-Br is composed of repeating units containing bromomethyl groups and repeating units without bromomethyl groups, and its structural formula is as follows: ； Where x = 0.05 - 1.

2. The method for preparing an acidic solid catalyst as described in claim 1, characterized in that, The degree of methyl bromination of the PIM-Br is 5% - 100%, where the degree of methyl bromination refers to the molar percentage of repeating units containing bromomethyl groups to all repeating units, i.e., x in the structural formula shown above.

3. The method for preparing an acidic solid catalyst as described in claim 1, characterized in that, The organic solvent used to dissolve PIM-Br is selected from N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide.

4. The method for preparing an acidic solid catalyst as described in claim 1, characterized in that, The concentration of the PIM-Br solution is 1 wt% - 60 wt%.

5. The method for preparing an acidic solid catalyst as described in claim 1, characterized in that, The molar amount of sodium 4-hydroxybenzenesulfonate or sodium 2-naphthol-6-sulfonate hydrate is 0.1 to 10 times the molar amount of bromomethyl in PIM-Br.

6. The method for preparing an acidic solid catalyst as described in claim 1, characterized in that, The reaction temperature of PIM-Br with sodium 4-hydroxybenzenesulfonate or sodium 2-naphthol-6-sulfonate hydrate is 0-150 °C, and the reaction time is 2-48 h.

7. The acidic solid catalyst prepared by the method according to any one of claims 1-6, characterized in that, The structural formula of the acidic solid catalyst is shown in a or b: ； Where x = 0.05 - 1.

8. The application of the acidic solid catalyst as described in claim 7 in the catalytic production of biodiesel.

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