A catalyst for preparing acrylic acid by lactide cracking reaction, a preparation method thereof, and a preparation method of acrylic acid

Abstract

The present invention discloses a catalyst for preparing acrylic acid by lactide cracking reaction and a preparation method thereof, and a preparation method of acrylic acid. The catalyst comprises an active component and a silica aerogel carrier, and the active component comprises a hafnium salt or a zirconium salt. The preparation method of acrylic acid comprises the following steps: using zirconium or hafnium salt supported on silica aerogel as a catalyst, iodide as an auxiliary agent, and performing a cracking reaction on lactide to prepare acrylic acid. The raw material is lactide, and there is no requirement for the optical purity of lactide. Therefore, the low-optical-purity lactide by-produced in the preparation process of polylactic acid is more preferably used. The raw material conversion rate and product selectivity are high. On the one hand, the emission of the three wastes in the polylactic acid process is reduced, making it more environmentally friendly. On the other hand, effective utilization is achieved to improve economic benefits.

Description

Technical Field

[0001] The present invention belongs to the fields of catalysts and fine chemical synthesis, and particularly relates to a catalyst for preparing bio-based acrylic acid and a preparation method of acrylic acid. Background Art

[0002] Acrylic acid and its esters, due to their unsaturated double bonds, can be used as monomers for various polymers and are extremely important chemical raw materials. Acrylic acid and its esters are applied in the fields of hygiene products, textiles, and building materials, and the market demand is extremely large.

[0003] Currently, acrylic acid is mainly prepared by two-step catalytic oxidation of propylene, which belongs to the petrochemical field and is non-renewable. With the increasing prominence of environmental protection issues, low-carbon processes have received more attention. Lactic acid, as a renewable resource, has a very mature current process and a wide range of sources. However, there are many side reactions in the current process of dehydrating lactic acid or lactic acid esters to prepare bio-based acrylic acid and its esters, and the yield is not high.

[0004] CN101811059B discloses a lactic acid ester dehydration catalyst and its preparation and application. The catalyst consists of an alkali metal dihydrogen phosphate, a grafted hydrophobic group, and silica gel, and is used for catalyzing the dehydration of lactic acid esters to prepare acrylic acid and acrylic esters. The total selectivity can reach 74%, and the total yield can reach 70%. On the one hand, lactic acid esters are used as raw materials, with high costs and poor selectivity. On the other hand, the separation of the reaction products of acrylic acid and its esters is relatively complex.

[0005] US4729978A discloses a phosphate catalyst supported on silica, titanium dioxide, or alumina, which catalyzes the dehydration of lactic acid to prepare acrylic acid at 350 °C. The highest yield of acrylic acid is only 58%. At the same time, a large amount of acetaldehyde is by-produced, and water is generated during the reaction, making the subsequent separation and purification relatively difficult and the economy relatively low. Summary of the Invention

[0006] The present invention relates to a catalyst for preparing acrylic acid by the cracking reaction of lactide, and also relates to a preparation method of bio-based acrylic acid. The raw material of this method is lactide, and zirconium or hafnium salts supported on silica aerogel are used as catalysts, and iodides are used as additives, which can efficiently prepare acrylic acid and have good economic benefits. There is no need to use high-purity lactide, which enables the effective utilization of the low-purity lactide by-produced in the preparation process of polylactic acid.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A catalyst for preparing acrylic acid by lactide cracking reaction, comprising an active component and a silica aerogel support, wherein the active component comprises a hafnium salt or a zirconium salt, and the content of the zirconium salt or hafnium salt is 0.42% - 14.8 wt%, preferably 1.96% - 6.80 wt%, based on the weight of the catalyst.

[0009] The preparation method of the catalyst according to the present invention comprises the following steps:

[0010] (1) Mix an aqueous solution of zirconium nitrate or hafnium nitrate with silica aerogel, then add ammonia water thereto, stir, dry, and calcine;

[0011] (2) Add the product obtained in step (1) to an aqueous sulfuric acid solution, stir, dry, and calcine.

[0012] In step (1) of the present invention, the concentration of the aqueous solution of zirconium nitrate or hafnium nitrate is 0.1% - 1 wt%, preferably 0.3% - 0.7 wt%.

[0013] In step (1) of the present invention, the dosage of silica aerogel is 1 / 20 - 1 / 5 of the mass of the aqueous solution of zirconium nitrate or hafnium nitrate, preferably 1 / 12 - 1 / 8.

[0014] In step (1) of the present invention, the stirring time is 15 - 120 min, preferably 30 - 60 min.

[0015] Preferably, in step (1) of the present invention, the stirring temperature is room temperature.

[0016] In step (1) of the present invention, the concentration of the ammonia water is 15% - 28 wt%, preferably 25% - 28 wt%.

[0017] In step (1) of the present invention, the molar ratio of ammonia to zirconium nitrate or hafnium nitrate in the ammonia water is 4:1 - 10:1, preferably 5:1 - 8:1.

[0018] In step (1) of the present invention, during the addition of ammonia water, stir at room temperature for 60 - 120 min, and after the stirring ends, dry to remove moisture at 80 - 100 °C.

[0019] In step (1) of the present invention, the calcination conditions are calcination at 180 - 250 °C for 1 - 3 h.

[0020] In step (2) of the present invention, the concentration of the aqueous sulfuric acid solution is 0.05% - 5 wt%, preferably 0.5% - 1 wt%.

[0021] In step (2) of the present invention, the stirring time is 15 - 120 min, preferably 30 - 60 min, and the temperature is room temperature.

[0022] In step (2) of the present invention, the molar amount of sulfuric acid is 2 - 2.5 times that of zirconium nitrate or hafnium nitrate, preferably 2.1 - 2.3 times.

[0023] In step (2) of the present invention, the drying temperature is 80 - 100 °C.

[0024] In step (2) of the present invention, the calcination conditions are calcination at 500 - 600 °C for 4 - 8 h.

[0025] A preparation method of bio - based acrylic acid, comprising the following steps: using zirconium or hafnium salt supported on silica aerogel as a catalyst, iodide as an auxiliary agent, and subjecting lactide to a cracking reaction to prepare acrylic acid.

[0026]

[0027] The silica aerogel in the catalyst of the present invention has an ultrafine particle structure, with characteristics such as small particle size and high specific surface area. As a carrier, it can greatly enhance the activity of zirconium or hafnium in the catalyst, enhance the coordination ability with the carbonyl group in lactide, transfer the entire ester group electron cloud to the carbonyl group, making the alkoxy bond more likely to break to obtain a carbocation, and then form a carbon - carbon double bond through hydrogen ion transfer, ultimately obtaining acrylic acid. In addition, the reactive distillation process is adopted, making it easier to remove low - boiling - point acrylic acid, further improving the reaction conversion rate, reducing the occurrence of side reactions, and improving selectivity.

[0028] In the present invention, the raw material is lactide, and there is no requirement for the optical purity of lactide. Therefore, low - optical - purity lactide by - produced in the preparation process of polylactic acid is more preferably used.

[0029] As a preferred scheme, in the cracking reaction of the present invention, a reactive distillation process is adopted, the reaction operating pressure is atmospheric pressure, and the solvent used in the reaction process is a high - boiling - point hydrocarbon, preferably an alkane with a boiling point > 300 °C, such as n - heptadecane, n - octadecane, or heavy diesel oil, etc.

[0030] The temperature of the cracking reaction of the present invention is 200 - 250 °C.

[0031] As a preferred scheme, in the preparation method of the bio - based acrylic acid of the present invention, the acrylic acid obtained by the reaction is absorbed with water and cooled to 20 - 30 °C to obtain an aqueous acrylic acid solution with a concentration of 30 - 60 wt%, and more preferably an aqueous acrylic acid solution with a concentration of 35 - 45 wt%.

[0032] In the cracking reaction of the present invention, the dosage of the catalyst is 0.1 wt%-5 wt% of the solvent, preferably 0.5 wt%-2 wt%.

[0033] Surprisingly, the addition of iodide can reduce the occurrence of side reactions and improve selectivity. In the present invention, the iodide is preferably potassium iodide and / or sodium iodide. The addition of iodide ions can promote the departure of carboxylate anions during the cracking process, promote the progress of the forward reaction, and improve the reaction yield.

[0034] As a preferred embodiment, the dosage of the iodide is 0.1 wt%-10 wt% of the catalyst, preferably 0.5 wt%-5 wt%.

[0035] In the cracking reaction of the present invention, based on the total amount of the bottom solvent (excluding the amounts of the catalyst and additives), the mass space velocity of the lactide feed is 0.05-0.3 h -1 .

[0036] In the present invention, the conversion rate of lactide > 99%, and the selectivity of acrylic acid > 95%. This solution enables the effective utilization of the low-purity lactide by-produced during the preparation of polylactic acid. On the one hand, it reduces the emission of the three wastes in the polylactic acid process and is more environmentally friendly. On the other hand, it realizes effective utilization and improves economic benefits. Detailed implementation manners

[0037] The present invention will be further described below through specific examples. The examples described in the present invention are only for the purpose of illustrating the present invention and do not limit the scope of the present invention.

[0038] Manufacturer and model of the analysis and characterization instrument:

[0039] Chromatography instrument: Agilent 7890A, chromatographic column model: HP-5, inner diameter: 320.00 μm, length: 30.0 m, maximum temperature: 325.0 °C. Injection port temperature: 280 °C, split ratio: 30:1. Temperature programming: First, hold at 50 °C for 2 minutes, increase the temperature to 180 °C at a rate of 10 °C / min and hold for 5 minutes, then increase the temperature to 280 °C at a rate of 20 °C / min and hold for 10 min.

[0040] The lactide is the low-purity lactide by-produced during the preparation of polylactic acid (the content of L-lactide is 70%, and the rest are D-lactide and M-lactide).

[0041] Catalyst a

[0042] Prepare 500 g of an aqueous solution of hafnium nitrate with a concentration of 0.7 wt% and add it to a 2 L reaction kettle for stirring. Slowly add 41.67 g of silica aerogel (Aerogel silica of Arigo Group, Wuzhen Technology Group). The addition amount of silica aerogel is about 1 / 12 of the mass of the above solution. Continue stirring for 60 min. Add 3.99 g of 28 wt% ammonia water to the above mixture so that the molar ratio of ammonia to hafnium nitrate is 8:1. Stir at room temperature for 120 min, then dry to remove water at 100 °C, and then calcine at 250 °C for 3 h. Slowly add the above-obtained solid to 185.19 g of an aqueous solution of sulfuric acid with a concentration of 1 wt%. The molar amount of sulfuric acid used is 2.3 times that of the hafnium salt, and then dry at 100 °C. Finally, calcine the above solid at 600 °C for 8 h to obtain a silica aerogel catalyst with a hafnium sulfate loading of 6.8 wt%.

[0043] Catalyst b

[0044] Prepare 500 g of an aqueous solution of zirconium nitrate with a concentration of 0.3 wt% and add it to a 2 L reaction kettle for stirring. Slowly add 62.5 g of silica aerogel (Aerogel silica of Arigo Group, Wuzhen Technology Group). The addition amount of silica aerogel is about 1 / 8 of the mass of the above solution. Continue stirring for 30 min. Add 1.504 g of 25 wt% ammonia water to the above mixture so that the molar ratio of ammonia to zirconium nitrate is 5:1. Stir at room temperature for 60 min, then dry to remove water at 80 °C, and then calcine at 180 °C for 1 h. Slowly add the above-obtained solid to 182.12 g of an aqueous solution of sulfuric acid with a concentration of 0.5 wt%. The molar amount of sulfuric acid used is 2.1 times that of the zirconium salt, and then dry at 80 °C. Finally, calcine the above solid at 500 °C for 4 h to obtain a silica aerogel catalyst with a zirconium sulfate loading of 1.96 wt%.

[0045] Catalyst c

[0046] Prepare 500 g of an aqueous solution of hafnium nitrate with a concentration of 0.5 wt% and add it to a 2 L reactor for stirring. Slowly add 50 g of silica aerogel (Aerogel silica from Wuzhen Technology Group Areg) to it. The addition amount of silica aerogel is about 1 / 10 of the mass of the above solution. Continue stirring for 45 min. Add 2.447 g of 26.5 wt% ammonia water to the above mixture to make the molar ratio of ammonia to hafnium nitrate 6.5:1. Stir at room temperature for 90 min, then dry to remove water at 90 °C, and then calcine at 215 °C for 2 h. Slowly add the above-obtained solid to 168.70 g of an aqueous sulfuric acid solution with a concentration of 0.75 wt%. The molar amount of sulfuric acid used is 2.2 times that of hafnium salt, and then dry at 90 °C. Finally, calcine the above solid at 550 °C for 6 h to obtain a silica aerogel catalyst with a hafnium sulfate loading of 4.16 wt%.

[0047] Comparative Example 1

[0048] Add 500 g of n-octadecane, 10 g of silica aerogel, and 0.5 g of potassium iodide to a 2 L reactor. The reaction operating pressure is atmospheric pressure. At 250 °C, dropwise add lactide at a rate of 2.5 g / min. The acrylic acid obtained from the reaction is absorbed with water and cooled to 20 °C to obtain a 35 wt% aqueous acrylic acid solution. After analyzing the raw materials and products, the yield of acrylic acid < 2%.

[0049] Comparative Example 2

[0050] Add 500 g of n-octadecane and 10 g of catalyst a to a 2 L reactor. The reaction operating pressure is atmospheric pressure. At 250 °C, dropwise add lactide at a rate of 2.5 g / min. The acrylic acid obtained from the reaction is absorbed with water and cooled to 20 °C to obtain a 35 wt% aqueous acrylic acid solution. After analyzing the raw materials and products, the conversion rate of lactide is 98.5%, and the selectivity of acrylic acid is 82.3%.

[0051] Example 1

[0052] Add 500 g of n-octadecane, 10 g of catalyst a, and 0.5 g of potassium iodide to a 2 L reactor. The reaction operating pressure is atmospheric pressure. At 250 °C, dropwise add lactide at a rate of 2.5 g / min. The acrylic acid obtained from the reaction is absorbed with water and cooled to 20 °C to obtain a 35 wt% aqueous acrylic acid solution. After analyzing the raw materials and products, the conversion rate of lactide is 99.7%, and the selectivity of acrylic acid is 98.6%.

[0053] Example 2

[0054] Add 500 g of heavy diesel oil, 10 g of catalyst b, and 0.5 g of potassium iodide into a 2-L reaction kettle. The reaction operation pressure is normal pressure. At 250 °C, dropwise add lactide at a rate of 2.5 g / min. The acrylic acid obtained from the reaction is absorbed with water and cooled to 20 °C to obtain an aqueous acrylic acid solution with a concentration of 35 wt%. After analyzing the raw materials and products, the conversion rate of lactide is 99.2%, and the selectivity of acrylic acid is 95.3%.

[0055] Example 3

[0056] Add 500 g of n-heptadecane, 2.5 g of catalyst a, and 0.0125 g of potassium iodide into a 2-L reaction kettle. The reaction operation pressure is normal pressure. At 250 °C, dropwise add lactide at a rate of 0.417 g / min. The acrylic acid obtained from the reaction is absorbed with water and cooled to 20 °C to obtain an aqueous acrylic acid solution with a concentration of 45 wt%. After analyzing the raw materials and products, the conversion rate of lactide is 99.1%, and the selectivity of acrylic acid is 96.4%.

[0057] Example 4

[0058] Add 500 g of n-octadecane, 10 g of catalyst a, and 0.5 g of sodium iodide into a 2-L reaction kettle. The reaction operation pressure is normal pressure. At 200 °C, dropwise add lactide at a rate of 1.25 g / min. The acrylic acid obtained from the reaction is absorbed with water and cooled to 30 °C to obtain an aqueous acrylic acid solution with a concentration of 35 wt%. After analyzing the raw materials and products, the conversion rate of lactide is 99.5%, and the selectivity of acrylic acid is 97.8%.

[0059] Example 5

[0060] Add 500 g of n-octadecane, 6.25 g of catalyst c, and 0.172 g of potassium iodide into a 2-L reaction kettle. The reaction operation pressure is normal pressure. At 225 °C, dropwise add lactide at a rate of 2.5 g / min. The acrylic acid obtained from the reaction is absorbed with water and cooled to 25 °C to obtain an aqueous acrylic acid solution with a concentration of 40 wt%. After analyzing the raw materials and products, the conversion rate of lactide is 99.3%, and the selectivity of acrylic acid is 97.2%.

[0061] Those skilled in the art can understand that under the teaching of this specification, some modifications or adjustments can be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing bio-based acrylic acid, comprising the following steps: In the presence of a catalyst, with iodide as an auxiliary agent, lactide undergoes a cracking reaction to prepare acrylic acid; the catalyst comprises an active component and a silica aerogel carrier, and the active component comprises a hafnium salt or a zirconium salt, and the content of the zirconium salt or hafnium salt is 0.42% - 14.8 wt%, based on the weight of the catalyst.

2. The method according to claim 1, wherein, the content of the zirconium salt or hafnium salt is 1.96% - 6.80 wt%, based on the weight of the catalyst.

3. The method according to claim 1, wherein, the method for preparing the catalyst comprises the following steps: (1) An aqueous solution of zirconium nitrate or hafnium nitrate is mixed with silica aerogel, then ammonia water is added thereto, stirred, dried, and calcined; (2) The product obtained in step (1) is added to an aqueous sulfuric acid solution, stirred, dried, and calcined.

4. The method according to claim 3, wherein, in step (1), the concentration of the aqueous solution of zirconium nitrate or hafnium nitrate is 0.1% - 1 wt%.

5. The method according to claim 3, wherein, in step (1), the concentration of the aqueous solution of zirconium nitrate or hafnium nitrate is 0.3% - 0.7 wt%.

6. The method according to claim 3, wherein, in step (1), the amount of silica aerogel used is 1 / 20 - 1 / 5 of the mass of the aqueous solution of zirconium nitrate or hafnium nitrate.

7. The method according to claim 3, wherein, in step (1), the amount of silica aerogel used is 1 / 12 - 1 / 8 of the mass of the aqueous solution of zirconium nitrate or hafnium nitrate.

8. The method according to claim 3, wherein, in step (1), the molar ratio of ammonia in the ammonia water to zirconium nitrate or hafnium nitrate is 4:1 - 10:

1.

9. The method according to claim 3, wherein, in step (1), the molar ratio of ammonia in the ammonia water to zirconium nitrate or hafnium nitrate is 5:1 - 8:

1.

10. The method according to claim 3, wherein, in step (1), the concentration of the ammonia water is 15% - 28 wt%; and / or, in step (1), the calcination condition is calcination at 180 - 250 °C for 1 - 3 h.

11. The method according to claim 3, wherein, in step (1), the concentration of the ammonia water is 25% - 28 wt%.

12. The method according to claim 3, wherein, in step (2), the concentration of the aqueous sulfuric acid solution is 0.05% - 5 wt%; the molar amount of sulfuric acid is 2 - 2.5 times that of zirconium nitrate or hafnium nitrate.

13. The method according to claim 3, wherein, in step (2), the concentration of the aqueous sulfuric acid solution is 0.5% - 1 wt%; the molar amount of sulfuric acid is 2.1 - 2.3 times that of zirconium nitrate or hafnium nitrate.

14. The method according to claim 3, wherein, In the step (2), the calcination conditions are calcination at 500 - 600 °C for 4 - 8 h.

15. According to the method described in claim 1, it is characterized in that the iodide is potassium iodide and / or sodium iodide.

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