Ionic liquid catalyst for preparing methylacrolein and preparation method thereof

Abstract

The invention belongs to the technical field of catalytic materials, and particularly discloses an ionic liquid catalyst for preparing methylacrolein and a preparation method of the ionic liquid catalyst. According to the preparation method, ionic liquid (protonated morpholine hydrochloride or 1-butyl-3-methylimidazole chloride salt) and metal chloride are subjected to a reaction, metal chelating ionic liquid is obtained, and the ionic liquid catalyst is obtained. The ionic liquid catalyst disclosed by the invention is simple in synthesis operation and mild in reaction condition, and has good industrial amplification potential; compared with the traditional supported or single metal salt catalyst, the catalyst provided by the invention has the advantages that the metal ion loss or agglomeration phenomenon is not easy to occur in the use process, the service life of the catalyst is effectively prolonged, and the problem that the existing catalyst is easy to inactivate is solved; the catalyst is adjustable in active center, high in selectivity and excellent in catalytic performance.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, and in particular to an ionic liquid catalyst for preparing methacrolein and its preparation method. Background Technology

[0002] Methacrolein is an important chemical intermediate with wide applications. It is a basic chemical product that, through oxidation and esterification, yields methacrylic acid (MAA) and methyl methacrylate (MMA). MMA is commonly used as a monomer in the polymerization of polymethyl methacrylate (PMMA), which is known as "acrylic glass." Furthermore, methacrolein can be used as a modifying additive in polymer materials, significantly improving various performance characteristics of the products.

[0003] Currently, there are three main methods for preparing methacrolein: isobutylene oxidation, isobutane oxidation, and direct condensation of formaldehyde / propionaldehyde. Chinese patent applications CN117399024A, CN115260015B, CN114591156B, and CN112871182B disclose a method for preparing methacrolein by isobutylene / isobutane oxidation, but this method suffers from problems such as complex operation, harsh reaction conditions, high energy consumption, and an inability to simultaneously achieve high conversion rate and high selectivity. Existing methods for preparing methacrolein through direct condensation of formaldehyde / propionaldehyde still have other technical problems. For example, Chinese patent applications CN112638856A, CN113248359A, CN104311403A, and CN101074192A, which use direct condensation of formaldehyde / propionaldehyde to prepare methacrolein, suffer from problems such as easy catalyst deactivation and poor selectivity.

[0004] Therefore, it is crucial to develop a catalyst with a simple synthesis process, high selectivity, and stable structure for the mild catalytic aldol condensation to prepare methacrolein. Summary of the Invention

[0005] In view of this, the present invention provides an ionic liquid catalyst for the preparation of methacrolein and a method thereof, in order to solve the problems of complex operation, harsh conditions, easy deactivation of catalyst and poor selectivity in the existing preparation of methacrolein.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an ionic liquid catalyst for the preparation of methacrolein includes the following steps: The reaction of ionic liquids with metal chlorides yields metal-chelated ionic liquids, which are thus ionic liquid catalysts. The ionic liquid is protonated morpholine hydrochloride or 1-butyl-3-methylimidazolium chloride.

[0007] Preferably, the molar ratio of the ionic liquid to the metal chloride is 1:0.5~2.

[0008] Preferably, the reaction temperature is 0~10℃ and the reaction time is 5~20min.

[0009] Preferably, the metal chloride includes one or more of CuCl2, CuCl, ZnCl2, CoCl3, MnCl2, FeCl3, NiCl2, and AlCl3.

[0010] Preferably, the method for preparing the protonated morpholine hydrochloride is to react a morpholine solution with a hydrochloric acid solution to obtain the protonated morpholine hydrochloride.

[0011] Preferably, the molar ratio of morpholine in the morpholine solution to hydrogen chloride in the hydrochloric acid solution is 1:0.8~1.2; The hydrochloric acid solution has a mass fraction of 35-40%.

[0012] Preferably, the reaction temperature is 0~10℃ and the reaction time is 5~20min.

[0013] Another object of the present invention is to provide an ionic liquid catalyst prepared by the preparation method described above.

[0014] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: 1. The catalyst described in this invention has a simple synthesis operation, mild reaction conditions, no need for high-temperature calcination, high-pressure reaction or complex post-treatment, simple process flow, readily available raw materials, and good industrial scale-up potential. 2. Compared with traditional supported or single metal salt catalysts, the catalyst of this invention is less prone to metal ion loss or aggregation during use, effectively extending the service life of the catalyst and solving the problem of easy deactivation of existing catalysts. 3. The active center is tunable and highly selective. By adjusting the ratio of protonated morpholine hydrochloride / 1-butyl-3-methylimidazolium chloride to different metal chlorides, the electron cloud density and spatial structure of the metal center can be precisely controlled. 4. The catalyst of this invention has excellent catalytic performance and good selectivity for methacrolein. Detailed Implementation

[0015] This invention provides a method for preparing an ionic liquid catalyst for the preparation of methacrolein, comprising the following steps: The reaction of ionic liquids with metal chlorides yields metal-chelated ionic liquids, which are thus ionic liquid catalysts.

[0016] In this invention, the ionic liquid is protonated morpholine hydrochloride or 1-butyl-3-methylimidazolium chloride.

[0017] In this invention, the molar ratio of the ionic liquid to the metal chloride is 1:0.5~2, preferably 1:0.8~1.5, and more preferably 1:1.

[0018] In this invention, the reaction temperature is 0~10℃, specifically 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, or 9℃; the reaction time is 5~20min, specifically 6min, 8min, 10min, 12min, 14min, 15min, 16min, or 18min.

[0019] In this invention, the metal chloride includes one or more of CuCl2, CuCl, ZnCl2, CoCl3, MnCl2, FeCl3, NiCl2, and AlCl3; the metal chloride also includes the hydrate corresponding to the metal chloride.

[0020] In this invention, the protonated morpholine hydrochloride is prepared by reacting a morpholine solution with a hydrochloric acid solution to obtain the protonated morpholine hydrochloride.

[0021] In this invention, the molar ratio of morpholine in the morpholine solution to hydrogen chloride in the hydrochloric acid solution is 1:0.8~1.2, preferably 1:0.9~1.1, and more preferably 1:1.

[0022] In this invention, the mass fraction of the hydrochloric acid solution is 35-40%, specifically 36%, 36.5%, 37%, 38%, or 39%.

[0023] In this invention, the reaction temperature is 0~10℃, specifically 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, or 9℃; the reaction time is 5~20min, specifically 6min, 8min, 10min, 12min, 14min, 15min, 16min, or 18min.

[0024] The present invention also provides an ionic liquid catalyst prepared by the preparation method described above.

[0025] In this invention, the ionic liquid catalyst is used to catalyze the reaction of formaldehyde and propionaldehyde to yield methacrolein. In the classic aldol condensation reaction, two aldehyde molecules (or one aldehyde and one ketone) first generate an intermediate product containing both a hydroxyl and an aldehyde group under catalysis; this product is called a β-hydroxyaldehyde. The reaction is named after its first-step stable product.

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0027] Example 1

[0028] A certain amount of morpholine was diluted with deionized water to prepare an aqueous solution of morpholine, which was then added dropwise to a 36.5% hydrochloric acid solution. The molar ratio of morpholine to hydrogen chloride in hydrochloric acid was 1:1. The solution was stirred at 5°C for 10 min, and the water was removed by rotary evaporation to obtain protonated morpholine hydrochloride Cat-1. A certain amount of Cat-1 was dissolved in deionized water, and a certain amount of AlCl3·6H2O was dissolved in deionized water. The Cat-1 aqueous solution was added dropwise to the aluminum chloride aqueous solution, with a molar ratio of Cat-1 to aluminum chloride of 1:1. The mixture was stirred at 5°C for 10 min, and the water was removed by rotary evaporation to obtain the metal chelated ionic liquid Cat-2, which is the ionic liquid catalyst.

[0029] Using the metal chelate ionic liquid Cat-2 prepared in Example 1 as a catalyst, 3.6501 g of Cat-2, 0.8928 g of formaldehyde solution, 0.5988 g of propionaldehyde solution, and 3.336 g of deionized water were mixed (Cat-2:formaldehyde:propionaldehyde (molar ratio) = 1:1.1:1, and the mass fraction of the deionized water was 39%). After stirring in a water bath at 70°C for 30 min, the contents of propionaldehyde and methacrolein were determined by gas chromatography. The propionaldehyde conversion rate was calculated to be 82.59%, and the methacrolein selectivity was 81.32%.

[0030] Example 2

[0031] A certain amount of morpholine was diluted with deionized water to prepare an aqueous solution of morpholine, which was then added dropwise to a 36.5% hydrochloric acid solution. The molar ratio of morpholine to hydrogen chloride in the hydrochloric acid was 1:1. The solution was stirred at 5°C for 10 minutes, and the water was removed by rotary evaporation to obtain morpholine hydrochloride Cat-1. A certain amount of Cat-1 was dissolved in deionized water, and a certain amount of AlCl3·6H2O was dissolved in deionized water. The Cat-1 aqueous solution was added dropwise to the aluminum chloride aqueous solution. The molar ratio of Cat-1 to aluminum chloride was 2:1. The mixture was stirred at 5°C for 10 minutes, and the water was removed by rotary evaporation to obtain the metal chelated ionic liquid Cat-2, which is the ionic liquid catalyst.

[0032] Using the metal chelate ionic liquid Cat-2 prepared in Example 2 as a catalyst, 2.443 g of Cat-2, 0.5681 g of formaldehyde solution, 0.2994 g of propionaldehyde solution, and 2.5467 g of deionized water were mixed (Cat-2:formaldehyde:propionaldehyde (molar ratio) = 1:1.4:1, and the mass fraction of the deionized water was 43%). After stirring in a water bath at 60 °C for 40 min, the contents of propionaldehyde and methacrolein were determined by gas chromatography. The propionaldehyde conversion rate was calculated to be 78.54%, and the methacrolein selectivity was 99.92%.

[0033] It can be seen that the ionic liquid catalyst prepared by the present invention has a high propionaldehyde conversion rate and methacrolein selectivity, and a high methacrolein yield.

[0034] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0035] 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 ionic liquid catalyst for the preparation of methacrolein, characterized in that, Includes the following steps: The reaction of ionic liquids with metal chlorides yields metal-chelated ionic liquids, which are thus ionic liquid catalysts. The ionic liquid is protonated morpholine hydrochloride or 1-butyl-3-methylimidazolium chloride.

2. The method for preparing an ionic liquid catalyst for preparing methacrolein according to claim 1, characterized in that, The molar ratio of the ionic liquid to the metal chloride is 1:0.5~2.

3. The method for preparing an ionic liquid catalyst for preparing methacrolein according to claim 2, characterized in that, The reaction temperature is 0~10℃, and the reaction time is 5~20min.

4. A method for preparing an ionic liquid catalyst for preparing methacrolein according to any one of claims 1 to 3, characterized in that, The metal chlorides include one or more of CuCl2, CuCl, ZnCl2, CoCl3, MnCl2, FeCl3, NiCl2, and AlCl3.

5. The method for preparing an ionic liquid catalyst for preparing methacrolein according to claim 4, characterized in that, The method for preparing the protonated morpholine hydrochloride is to react a morpholine solution with a hydrochloric acid solution to obtain the protonated morpholine hydrochloride.

6. The method for preparing an ionic liquid catalyst for preparing methacrolein according to claim 5, characterized in that, The molar ratio of morpholine in the morpholine solution to hydrogen chloride in the hydrochloric acid solution is 1:0.8~1.2; The hydrochloric acid solution has a mass fraction of 35-40%.

7. A method for preparing an ionic liquid catalyst for preparing methacrolein according to claim 5 or 6, characterized in that, The reaction temperature is 0~10℃, and the reaction time is 5~20min.

8. The ionic liquid catalyst prepared by the preparation method according to any one of claims 1 to 7.