A process for the preparation of maleic acid

Abstract

This invention relates to a method for preparing maleic acid, belonging to the field of organic chemistry. The method includes the following steps: mixing choline chloride, propylene glycol, and malonic acid to obtain a eutectic solvent; adding furfural and a titanium-silicon molecular sieve catalyst to the eutectic solvent under a microwave-ultrasound composite field atmosphere, followed by the dropwise addition of an oxidant to carry out a catalytic oxidation reaction, thereby obtaining maleic acid. Compared with existing technologies, this invention, for the first time, constructs a reaction system using a ternary eutectic solvent of choline chloride-propylene glycol-malonic acid and a titanium-silicon molecular sieve catalyst, while simultaneously enhancing the mass and heat transfer processes within the reaction system through the application of an externally applied microwave-ultrasound composite field of appropriate power, thereby improving the yield of the target product, maleic acid, and overcoming the shortcomings of existing technologies such as low product yield, providing a new technical means for the preparation of maleic acid.

Description

Technical Field

[0001] This invention relates to the field of organic chemistry, and more particularly to a method for preparing maleic acid. Background Technology

[0002] Maleic acid, also known as maleic acid, is an important unsaturated dicarboxylic acid widely used in unsaturated polyester resins, coatings, pharmaceutical intermediates, food additives, and agrochemicals, possessing extremely high industrial application value. Currently, the main industrial route for producing maleic acid is through catalytic oxidation using benzene or n-butane as raw materials. While this method is mature, it suffers from drawbacks such as reliance on petrochemical sources for raw materials, demanding reaction conditions (high temperature and pressure), high energy consumption, and potential environmental pollution.

[0003] In recent years, with the deepening of green chemistry and sustainable development concepts, the synthesis of maleic acid from biomass platform compounds has attracted widespread attention. Furfural, as an important platform molecule derived from lignocellulosic biomass, contains a furan ring and an aldehyde group in its molecular structure. Through selective oxidative ring-opening, it can be converted into maleic acid, providing a feasible pathway for the high-value utilization of biomass resources. However, the catalytic oxidation process for preparing maleic acid from furfural still faces many technical challenges, such as low product yield, further limiting its industrial-scale promotion and application. Summary of the Invention

[0004] To address the above problems, this invention provides a method for preparing maleic acid.

[0005] This invention provides a method for preparing maleic acid, such as... Figure 1 As shown, it includes the following steps: Choline chloride, propylene glycol, and malonic acid are mixed to obtain a eutectic solvent; Under a microwave-ultrasonic composite field atmosphere, furfural and titanium-silicon molecular sieve catalysts are added to the eutectic solvent, followed by the dropwise addition of an oxidant to carry out a catalytic oxidation reaction to obtain maleic acid; In the microwave-ultrasound composite field, the microwave power W1 and the ultrasonic power W2 satisfy the following relationship: 3.0≤W2 / W1≤4.5.

[0006] Furthermore, the microwave power W1 is 110W-145W; And / or, the ultrasonic power W2 is 430W-500W.

[0007] Furthermore, the microwave power W1 is 120W; And / or, the ultrasonic power W2 is 480W.

[0008] Furthermore, the molar ratio of choline chloride, propylene glycol, and malonic acid is 1:1:3.

[0009] Furthermore, by weight percentage, the added titanium-silicon molecular sieve catalyst accounts for 10%-15% of the weight of furfural.

[0010] Furthermore, in molar percentage, the added molar amount of the oxidant accounts for 500%-600% of the molar amount of furfural.

[0011] Furthermore, the furfural concentration in the reaction system is 3.5%-5.0% by weight.

[0012] Furthermore, the titanium-silicon molecular sieve catalyst includes TS-1 titanium-silicon molecular sieve; And / or, the oxidant includes hydrogen peroxide.

[0013] Furthermore, the oxidant is added over a period of 1-2 hours.

[0014] Furthermore, the operating conditions for the catalytic oxidation reaction include: a reaction temperature of 55℃-65℃, and a reaction time of 1h-1.5h after the oxidant is added.

[0015] The technical solutions provided in the embodiments of the present invention have at least the following advantages compared with the prior art: This invention provides a method for preparing maleic acid. Compared with existing technologies, this invention, for the first time, constructs a reaction system using a ternary eutectic solvent of choline chloride-propylene glycol-malonic acid and a titanium-silicon molecular sieve catalyst. Simultaneously, it utilizes an externally applied microwave-ultrasound composite field of appropriate power to synergistically enhance the mass and heat transfer processes within the reaction system, thereby improving the yield of the target product, maleic acid. This overcomes the shortcomings of existing technologies, such as low product yield, and provides a new technical means for the preparation of maleic acid. Specifically: 1. Reaction system of eutectic solvent and titanium-silicon molecular sieve catalyst The ternary eutectic solvent in this invention comprises choline chloride (hydrogen bond acceptor), propylene glycol (hydrogen bond donor), and malonic acid (bifunctional hydrogen bond donor / acceptor). On the one hand, it provides a moderately acidic environment for the reaction system, which is conducive to the protonation activation of the framework titanium active sites in the titanium-silicon molecular sieve catalyst and promotes the generation of Ti-OOH active species. On the other hand, the hydrogen bond network of the ternary eutectic solvent is conducive to the stability of active intermediates, promotes the selective oxidation of silicon molecular sieve catalyst, and improves the yield of the target product maleic acid.

[0016] 2. Synergistic enhancement of microwave-ultrasound composite field This invention constructs a microwave-ultrasound composite field using high-power ultrasound and low-power microwaves. The power ratio W2 / W1 (the value obtained by dividing the ultrasound power W2 by the microwave power W1) is controlled between 3.0 and 4.5. Within this window, the ultrasonic cavitation mechanical effect dominates, while microwave dielectric heating assists, making the energy provided by the microwave-ultrasound composite field more suitable for the above-mentioned reaction system. This not only enhances the mass and heat transfer processes within the reaction system but also improves the dispersion of the silicon molecular sieve catalyst in the ternary eutectic solvent and the heating uniformity of the external heat source on the reaction system. As a result, the oxidation pathway from furfural to maleic acid is optimized both thermodynamically and kinetically, thereby significantly improving the yield of the target product. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of a method for preparing maleic acid according to an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. Furthermore, unless otherwise specified, the process steps and parameters involved in this invention can be implemented based on the maleic acid preparation process disclosed in the prior art, or using existing equipment and conventional operating methods. For example, the microwave-ultrasound composite field can be directly achieved using commercially available mature equipment such as ultrasonic-microwave combined reaction systems, ultrasonic-microwave reactors, and microwave-ultrasound combined reaction instruments. Alternatively, the ultrasonic instrument and microwave instrument can be independently set according to preset parameters, and then simultaneously turned on to operate the reaction system to form a microwave-ultrasound composite field.

[0022] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0023] Example 1 This example provides a method for preparing maleic acid, including the following steps: Step (1): Mix choline chloride, propylene glycol and malonic acid in a molar ratio of 1:1:3 to obtain a eutectic solvent; Step (2): Under the microwave-ultrasonic composite field atmosphere, furfural and TS-1 titanium silicon molecular sieve catalyst were added to the eutectic solvent, and then 35% by mass of hydrogen peroxide oxidant was added dropwise to carry out the catalytic oxidation reaction. The reaction temperature was 60℃, the dropwise addition time of the oxidant was 1.5h, and the reaction continued for 1h after the dropwise addition was completed; maleic acid was obtained. In the microwave-ultrasound composite field, the microwave power W1 and the ultrasonic power W2 satisfy the following relationship: W2 / W1=4. Specifically, the microwave power W1 is 120W and the ultrasonic power W2 is 480W. The furfural concentration in the reaction system is 4.5% by weight. The titanium-silicon molecular sieve catalyst accounts for 13% of the weight of furfural by weight. The amount of hydrogen peroxide added accounts for 550% of the amount of furfural in terms of molar percentage.

[0024] In this example, the yield of maleic acid was 87.1%.

[0025] Example 2 This example provides a method for preparing maleic acid, including the following steps: Step (1): Same as in Example 1; Step (2): Under the microwave-ultrasonic composite field atmosphere, furfural and TS-1 titanium silicon molecular sieve catalyst were added to the eutectic solvent, and then 35% by mass of hydrogen peroxide oxidant was added dropwise to carry out the catalytic oxidation reaction. The reaction temperature was 55℃, the dropwise addition time of the oxidant was 2h, and the reaction continued for 1.5h after the dropwise addition was completed; maleic acid was obtained. In the microwave-ultrasound composite field, the microwave power W1 and the ultrasonic power W2 satisfy the following relationship: W2 / W1=3, specifically: the microwave power W1 is 145W and the ultrasonic power W2 is 435W. The furfural concentration in the reaction system is 3.5% by weight. The titanium-silicon molecular sieve catalyst is added at a weight percentage of 10% of the furfural weight. The amount of hydrogen peroxide added accounts for 500% of the amount of furfural, in molar percentage.

[0026] In this example, the yield of maleic acid was 74.9%.

[0027] Example 3 This example provides a method for preparing maleic acid, including the following steps: Step (1): Same as in Example 1; Step (2): Under the microwave-ultrasonic composite field atmosphere, furfural and TS-1 titanium silicon molecular sieve catalyst were added to the eutectic solvent, and then 35% by mass of hydrogen peroxide oxidant was added dropwise to carry out the catalytic oxidation reaction. The reaction temperature was 65℃, the dropwise addition time of the oxidant was 1.5h, and the reaction continued for 1h after the dropwise addition was completed; maleic acid was obtained. In the microwave-ultrasound composite field, the microwave power W1 and the ultrasonic power W2 satisfy the following relationship: W2 / W1=4.5. Specifically, the microwave power W1 is 110W and the ultrasonic power W2 is 495W. The furfural concentration in the reaction system is 5.0% by weight. The titanium-silicon molecular sieve catalyst accounts for 15% of the weight of furfural by weight. The amount of hydrogen peroxide added accounts for 600% of the amount of furfural, in molar percentage.

[0028] In this example, the yield of maleic acid was 76.2%.

[0029] Comparative Example 1 This example provides a method for preparing maleic acid, which differs from Example 1 only in that: (1) Replace the eutectic solvent with choline chloride and oxalic acid in a molar ratio of 1:1.

[0030] In this example, the yield of maleic acid was 54.8%.

[0031] Comparative Example 2 This example provides a method for preparing maleic acid, which differs from Example 1 only in that: (1) The microwave power W1 is 480W and the ultrasonic power W2 is 120W.

[0032] In this example, the yield of maleic acid was 65.3%.

[0033] In summary, this invention provides a method for preparing maleic acid. Compared with the prior art, this invention is the first to construct a reaction system using a ternary eutectic solvent of choline chloride-propylene glycol-malonic acid and a titanium-silicon molecular sieve catalyst. At the same time, it combines this with the application of a microwave-ultrasound composite field of appropriate power to synergistically enhance the mass and heat transfer processes within the reaction system, thereby improving the yield of the target product, maleic acid. This solves the shortcomings of the prior art, such as the low product yield, and provides a new technical means for the preparation of maleic acid.

[0034] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0035] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement 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 present 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 claimed herein.

Claims

1. A method for preparing maleic acid, characterized in that, Includes the following steps: Choline chloride, propylene glycol, and malonic acid are mixed to obtain a eutectic solvent; Under a microwave-ultrasonic composite field atmosphere, furfural and titanium-silicon molecular sieve catalysts are added to the eutectic solvent, followed by the dropwise addition of an oxidant to carry out a catalytic oxidation reaction to obtain maleic acid; In the microwave-ultrasound composite field, the microwave power W1 and the ultrasonic power W2 satisfy the following relationship: 3.0≤W2 / W1≤4.

5.

2. The method for preparing maleic acid according to claim 1, characterized in that, The microwave power W1 is 110W-145W; And / or, the ultrasonic power W2 is 430W-500W.

3. The method for preparing maleic acid according to claim 1, characterized in that, The microwave power W1 is 120W; And / or, the ultrasonic power W2 is 480W.

4. The method for preparing maleic acid according to claim 1, characterized in that, The molar ratio of choline chloride, propylene glycol, and malonic acid is 1:1:

3.

5. The method for preparing maleic acid according to claim 1, characterized in that, The titanium-silicon molecular sieve catalyst is added at a weight percentage of 10%-15% of the weight of furfural.

6. The method for preparing maleic acid according to claim 1, characterized in that, The amount of oxidant added accounts for 500%-600% of the amount of furfural, in molar percentage.

7. The method for preparing maleic acid according to claim 1, characterized in that, The furfural concentration in the reaction system is 3.5%-5.0% by weight.

8. The method for preparing maleic acid according to claim 1, characterized in that, The titanium-silicon molecular sieve catalyst includes TS-1 titanium-silicon molecular sieve; And / or, the oxidant includes hydrogen peroxide.

9. The method for preparing maleic acid according to claim 1, characterized in that, The oxidant is added over a period of 1-2 hours.

10. The method for preparing maleic acid according to claim 1, characterized in that, The operating conditions for the catalytic oxidation reaction include: a reaction temperature of 55℃-65℃, and a reaction time of 1-1.5 hours after the oxidant is added.

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