A catalyst coated with a self-curing ionic liquid film, and a preparation method and application thereof

Abstract

This invention discloses a catalyst coated with a self-curing ionic liquid membrane, its preparation method, and its application. The catalyst preparation process involves sulfonating polyethyleneimine to obtain a self-curing acidic ionic liquid, namely sulfonated polyethyleneimine, which is then coated onto a substrate surface to prepare the catalyst coated with the self-curing acidic ionic liquid membrane. The prepared catalyst is applied in a stirred tank reactor, a membrane reactor, and a fixed-bed reactor to catalyze the esterification reaction of oleic acid and methanol. The catalyst prepared by this invention not only has a high acid content but also a large mass transfer area and low diffusion resistance within the catalyst membrane layer, thus exhibiting good catalytic performance. When applied to membrane reactors and fixed-bed reactors, it not only realizes the continuous esterification process of oleic acid and methanol but also overcomes the problems of large bed pressure drop and flooding when conventional solid acid catalysts are applied to fixed-bed reactors. Simultaneously, it provides a novel packing material for reactive distillation that possesses both catalytic activity and improved mass transfer efficiency.

Description

Technical Field

[0001] This invention belongs to the field of membrane catalysis, specifically relating to a catalyst coated with a self-curing ionic liquid membrane, its preparation method, and its application. Technical Background

[0002] Esterification is an important type of organic reaction that can synthesize various ester compounds. It has wide applications in the synthesis of pharmaceuticals, pesticides, dyes, surfactants, fragrances, and biofuels. Esterification reactions often use acids as catalysts, including liquid acid catalysts such as sulfuric acid and methanesulfonic acid, and solid acid catalysts such as strongly acidic ion exchange resins, molecular sieves, and sulfonated carbon. Liquid acid catalysts suffer from problems such as strong corrosivity, difficulty in recycling, and the generation of large amounts of wastewater during washing and removal. Solid acid catalysts suffer from high intraparticle mass transfer resistance, low catalytic efficiency, and long reaction times. In particular, when used in fixed-bed reactors, they exhibit problems such as large bed pressure drop and susceptibility to flooding. Summary of the Invention

[0003] To address the problems existing in current esterification catalysts, the present invention aims to provide a catalyst coated with a self-curing ionic liquid membrane, its preparation method, and its applications. This invention uses high-viscosity polyethyleneimine as a raw material and 1,3-propanesulfonyl lactone as a sulfonating agent to synthesize a sulfonated polyethyleneimine ionic liquid with self-curing film-forming properties through a sulfonation reaction. This liquid is then coated onto the surface of a base membrane or filler to prepare a membrane catalyst. The prepared catalyst is then tested in a stirred tank reactor, a membrane reactor, and a fixed-bed reactor to catalyze the esterification reaction of oleic acid and methanol.

[0004] The technical solution adopted in this invention is as follows:

[0005] A method for preparing a catalyst coated with a self-curing ionic liquid film includes two steps: first, sulfonating polyethyleneimine to obtain a self-curing acidic ionic liquid, namely sulfonated polyethyleneimine; second, coating the self-curing ionic liquid onto the surface of a substrate to prepare a catalyst with a surface coated with a self-curing acidic ionic liquid film.

[0006] The specific steps for preparing the catalyst of this invention are as follows:

[0007] 1) 1,3-propanesulfonyl lactone is heated and melted, and an ethanol solution of polyethyleneimine is added dropwise. The sulfonation reaction is carried out by stirring under heating. After the reaction is completed, the mixture is cooled and filtered. The filtered solid is washed with ethanol to remove the unreacted 1,3-propanesulfonyl lactone. After drying, an acidic self-curing ionic liquid containing sulfonic acid groups is obtained.

[0008] 2) Heat the acidic self-curing ionic liquid obtained in step 1) to above 70°C to make it a viscous liquid, then coat it evenly on the substrate surface, and lower the temperature to below 50°C to allow it to self-cur on the substrate surface to form an acidic ionic liquid film, thereby obtaining a catalyst with a self-curing ionic liquid film on its surface.

[0009] Further, the molecular weight of the polyethyleneimine is 50,000-100,000, preferably 60,000-70,000, and the mass fraction of the polyethyleneimine ethanol solution is 30-70%.

[0010] Furthermore, the mass ratio of polyethyleneimine to 1,3-propanesulfonyl lactone is 1:1-5, preferably 1:3-5, the sulfonation temperature is 40-70℃, preferably 50-60℃, and the sulfonation time is 8-12h.

[0011] Furthermore, the substrate is a base membrane or a filler, the base membrane is a polypropylene membrane, a polyvinylidene fluoride membrane, or a nylon membrane, and the corresponding catalyst is a self-curing ionic liquid catalytic membrane, in which the ionic liquid loading is 30-60%; the filler is a plastic filler or a metal filler, and the corresponding catalyst is a self-curing ionic liquid catalytic membrane filler, in which the ionic liquid loading is 20-50%.

[0012] The present invention also discloses the application of the catalyst coated with a self-curing ionic liquid membrane in the catalytic esterification reaction of oleic acid, wherein the reactor for the catalytic esterification reaction is a stirred tank reactor, a membrane reactor or a fixed bed reactor.

[0013] Furthermore, when the reactor is a stirred tank, the catalytic reaction steps are as follows:

[0014] 1) Add methanol and oleic acid to the stirred tank, with a mass ratio of methanol to oleic acid of 1:0.8-1.2;

[0015] 2) Add the catalyst to the stirred tank. The mass of the catalyst is 5%-16% of the mass of oleic acid.

[0016] 3) With stirring, heat the material in the stirred tank to 60-70℃ and react for 2-4 hours;

[0017] 4) After the reaction is complete, the catalyst is filtered out and separated. The reaction solution is distilled to remove methanol and water to obtain methyl oleate product.

[0018] Furthermore, when the reactor is a membrane reactor, the catalytic reaction steps are as follows:

[0019] S1: The catalyst is a self-curing ionic liquid catalytic membrane. The membrane reactor includes the self-curing ionic liquid catalytic membrane and two reaction chambers. The self-curing ionic liquid catalytic membrane is sealed between the two reaction chambers. The liquid outlets of the two reaction chambers are connected to the liquid inlet of the storage tank through pipelines. The liquid inlets of the two reaction chambers are connected to the liquid outlet of the storage tank through pipelines via a transfer pump.

[0020] S2: Methanol and oleic acid are added to the storage tank at a mass ratio of 1:0.8-1.2. The reactants in the storage tank are heated to 60-70℃. Then, the reactants are transported to the reaction chamber of the membrane reactor by a transfer pump with a flow rate of 20-50 mL / min. The reactants undergo catalytic reaction in contact with the self-curing ionic liquid catalytic membrane. Under the action of the transfer pump, the reactants circulate and react in the system formed by the storage tank, transfer pump, reaction chamber and pipeline. The reaction time is controlled to be 4-8 hours.

[0021] S3: After the reaction is complete, the liquid in the storage tank is released, and methanol and water are removed by distillation to obtain methyl oleate product.

[0022] Furthermore, when the reactor is a fixed-bed reactor, the catalytic reaction steps are as follows:

[0023] Step 1: The catalyst is a self-curing ionic liquid catalytic membrane packing material. The catalyst is filled in a fixed bed reactor. An insulation jacket is provided on the outside of the fixed bed reactor, and hot water at 60-70°C is introduced into the insulation jacket.

[0024] Step 2: Methanol and oleic acid are mixed at a mass ratio of 1:0.8-1.2. The reaction mixture is heated to 60-70°C and then fed into the fixed-bed reactor from the bottom and overflowed from the top. The residence time of the reaction mixture in the fixed-bed reactor is controlled to be 4-8 hours.

[0025] Step 3: After the overflow material is evaporated to remove methanol and water, methyl oleate product is obtained.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) After sulfonation of high-viscosity polyethyleneimine, an ionic liquid with both acidic catalytic sites and self-curing film-forming properties can be obtained.

[0028] (2) The preparation of ionic liquid catalytic membrane by coating the base membrane with self-curing acidic ionic liquid has the following advantages: ① It can be directly applied to membrane reactor to realize the continuous production of methyl oleate; ② After the self-curing acidic ionic liquid is coated on the base membrane, the mass transfer area is increased and the mass transfer path is shortened, so that more catalytic sites are exposed on the catalyst surface, thereby overcoming the problem of large diffusion resistance in particulate solid catalysts and the problem of difficult solid-liquid separation of nano-sized powder catalysts.

[0029] (3) A self-curing ionic liquid catalytic membrane packing is prepared by coating the packing surface with a self-curing acidic ionic liquid, which has the following advantages: ① The catalytic sites are located in a very thin membrane layer on the inner and outer surfaces of the packing, which also overcomes the problem of large mass transfer resistance of conventional solid acid catalysts; ② Existing conventional solid acid catalysts are microporous particles and small particles. When conventional solid acid catalysts are applied to fixed bed reactors, there are problems such as large bed pressure drop and easy flooding. This invention can directly apply the catalytic membrane packing to the fixed bed reactor, and take advantage of the characteristics of large packing particles, large pores and large liquid holding capacity to avoid problems such as large bed pressure drop and easy flooding; ③ It can be further applied to reactive distillation, providing a new type of packing for reactive distillation that has both catalytic effect and improved mass transfer efficiency. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a membrane reactor; where: 1-feed inlet pipe, 2-PTFE plate; 3-reaction chamber; 4-ionic liquid catalytic membrane; 5-rubber gasket; 6-feed outlet pipe.

[0031] Figure 2 This is a schematic flow diagram of the reaction apparatus for the continuous catalytic esterification reaction of oleic acid and methanol using an ionic liquid catalytic membrane in Embodiment 11 of the present invention, wherein: 7-transfer pump; 8-membrane reactor; 9-storage tank.

[0032] Figure 3 These are photographs of the metal wire mesh and the wound cylindrical catalytic membrane packing material in Example 9. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] Example 1: Preparation of self-curing ionic liquid

[0035] 10 g of 1,3-propanesulfonyl lactone was added to a 50 mL round-bottom flask and heated to approximately 35 °C to melt it. 2 g of polyethyleneimine (molecular weight 70,000) was mixed with 2 g of ethanol to obtain an ethanol solution of polyethyleneimine, which was then added dropwise to the molten 10 g of 1,3-propanesulfonyl lactone. The mixture was stirred and heated to 60 °C for sulfonation reaction for 8 h. After the reaction was complete, the mixture was cooled to room temperature, filtered, and the filtrate was washed with ethanol to remove unreacted 1,3-propanesulfonyl lactone. The filtrate was then dried in an oven at 70 °C for 12 h to obtain an acidic self-curing ionic liquid containing sulfonic acid groups. The total acid content and strong acid content of the prepared self-curing ionic liquid were determined by NaOH titration and NaCl ion exchange method, respectively, and were found to be 4.83 mmol / g and 3.70 mmol / g, respectively.

[0036] Examples 2-7: Preparation of self-curing ionic liquids

[0037] The preparation process of the self-curing ionic liquids in Examples 2-7 was the same as that in Example 1, except that the following sulfonation conditions were changed: "adjusting the mass of 1,3-propanesulfonyl lactone to change the mass ratio of polyethyleneimine to 1,3-propanesulfonyl lactone", "changing the sulfonation temperature", and "changing the sulfonation time". The specific changes in the sulfonation conditions in Examples 2-7, as well as the test results of the total acid content and strong acid content of the obtained self-curing ionic liquids, are summarized in Table 1.

[0038] Table 1

[0039]

[0040] In the field of esterification reactions of oleic acid and methanol, the strength of the solid acid is positively correlated with the esterification reaction effect.

[0041] Under the sulfonation conditions examined in the examples, the present invention can prepare self-curing acidic ionic liquids with a large acid content. Among them, the self-curing ionic liquid obtained in Example 1 has a large acid content and requires a short sulfonation time. Therefore, the subsequent examples use the self-curing ionic liquid obtained in Example 1 as raw material, coat it on the surface of the base film and filler, and further prepare a catalyst coated with a self-curing acidic ionic liquid film, which is then applied to the esterification reaction of oleic acid and methanol.

[0042] Example 8: Preparation of Ionic Liquid Catalytic Membranes

[0043] A 5 cm diameter polypropylene membrane was used as the base membrane, with a pore size of 0.45 μm and a mass of 0.37 g. The self-curing ionic liquid powder prepared in Example 1 was weighed and heated to 70 °C to soften and melt it. It was then uniformly coated onto both sides of the polypropylene membrane. After standing at room temperature for 1 hour, the coated ionic liquid layer self-cured on both sides of the polypropylene membrane and covered the surface of the base membrane, thus preparing an ionic liquid catalytic membrane. The catalytic membrane was 0.5 g heavier than the base membrane, therefore the ionic liquid loading in the catalytic membrane was 57.5%.

[0044] Example 9: Preparation of Ionic Liquid Catalytic Membrane Packing Material

[0045] Using a 100-mesh metal wire mesh as the substrate, and a strip-shaped metal wire mesh with a length of 2.5 cm and a width of 3 mm, molten ionic liquid from Example 1 was uniformly coated onto both sides of the metal wire mesh using the coating method of ionic liquid in Example 8. The mesh was left to stand at room temperature for 1 hour to allow the ionic liquid to solidify, thus obtaining an ionic liquid catalytic membrane. The ionic liquid coating amount was calculated to be 0.6 g / g substrate by weighing, meaning that the ionic liquid loading in the catalytic membrane filler was 37.5%.

[0046] After the ionic liquid to be coated on the aforementioned metal wire mesh self-cures into a film at room temperature, it is wound into a cylindrical shape with a diameter of 3 mm and a height of 3 mm, which is the ionic liquid catalytic membrane filler. The bulk density of this catalytic membrane filler was measured to be 520 kg / m³. 3 Specific surface area is 2800 m² 2 / m 3 The porosity is 93%.

[0047] The photographs of the wire mesh and the wound cylindrical catalytic membrane packing in Example 9 are shown below. Figure 3 As shown.

[0048] Example 10: Application of ionic liquid catalytic membranes in a stirred tank.

[0049] The self-curing ionic liquid catalytic membrane prepared in Example 8 was cut into fragments of approximately 1 cm in size to facilitate stirring in the mixed solution within the stirred tank. 10 g of methanol and 10 g of oleic acid were added to a 100 mL stirred tank; 0.5 g of the above catalytic membrane fragments were weighed and added to the methanol and oleic acid mixture; the mixture was heated to 64 °C with stirring and maintained for 3 hours to allow the reaction to proceed; after the reaction was complete, the catalytic membrane was removed, and the liquid was evaporated to remove methanol and water, yielding methyl oleate. The yield of methyl oleate was 91.2%.

[0050] Example 11: Application of ionic liquid catalytic membranes in membrane reactors

[0051] use Figure 1The membrane reactor shown comprises two 100mm × 100mm × 30mm square PTFE plates 2. Each PTFE plate 2 has a cylindrical cavity with an inner diameter of 50mm and a depth of 20mm at its center; this cylindrical cavity is designated as the reaction chamber 3. An ionic liquid catalytic membrane 4, prepared in Example 8, is sealed between the two PTFE plates 2. The ionic liquid catalytic membrane 4 is vertically aligned with the two reaction chambers 3, and a rubber gasket 5 is installed between the ionic liquid catalytic membrane 4 and the reaction chambers 3 for sealing. (Comparison) Figure 1 As can be seen, bolt holes are provided around the PTFE plate 2, and the two PTFE plates are installed and fixed together by bolts.

[0052] according to Figure 2 The schematic diagram of the reaction device shown illustrates the setup. The membrane reactor 8 consists of two PTFE plates 2 and the ionic liquid catalytic membrane 4 between them. The left side of each of the two reaction chambers of the membrane reactor is connected to a feed inlet pipe 1, which is connected to the outlet of the storage tank 9 via a pipeline through a delivery pump 7. The right side of each of the two reaction chambers is connected to a feed outlet pipe 6, which is connected to the inlet of the storage tank 9.

[0053] 60g of methanol and 60g of oleic acid were added to a storage tank. The reactants in the storage tank were heated to 64°C. The reactants were then pumped into the reaction chamber of a membrane reactor. The reactants underwent a catalytic reaction in contact with the self-curing ionic liquid catalytic membrane. The flow rate of the pump was adjusted to 28mL / min. Under the action of the pump, the reactants circulated and reacted in the system formed by the storage tank, pump, reaction chamber, and pipelines. The reaction time was controlled to be 6 hours. After the reaction, the liquid in the storage tank was released, and methanol and water were evaporated to obtain methyl oleate. The yield of methyl oleate was 75%. Due to the limited conditions of the laboratory-scale experiment, the membrane reactor was small, and the amount of reactants in contact with the catalytic membrane was relatively small, so the experimental results were relatively poor. However, the experimental results of Example 10 verified the catalytic activity of the catalytic membrane.

[0054] Example 12 Application of ionic liquid catalytic membrane packing in a stirred tank

[0055] 10g of methanol and 10g of oleic acid were added to a 100mL stirred tank. 1.6g of the self-curing ionic liquid catalytic membrane packing material prepared in Example 9 (1g of packing material coated with 0.6g of self-curing ionic liquid membrane) was weighed and added to the mixed solution of methanol and oleic acid. The material in the tank was heated to 64°C under stirring and maintained for 3h to allow the reaction to proceed. After the reaction was completed, the catalytic membrane packing material was removed by filtration. Methanol and water were removed by evaporation of the liquid to obtain methyl oleate product. The yield of methyl oleate was 90.2%.

[0056] Example 13: Application of ionic liquid membrane packing in fixed-bed reactors

[0057] A jacketed glass column was used as a fixed-bed reactor. The glass column had an inner diameter of 1 cm and a length of 15 cm. 9.5 g of the self-curing ionic liquid catalytic membrane packing material prepared in Example 9 (1 g of packing material coated with 0.6 g of self-curing ionic liquid membrane) was packed inside the glass column. Hot water at 65°C was circulated through the jacket of the glass column. When the temperature of the packing material inside the glass column rose to 60-64°C, a mixed solution of methanol and oleic acid (methanol to oleic acid mass ratio of 1:1) heated to 64°C was pumped into the fixed-bed reactor from the bottom and overflowed from the top. The pump flow rate was adjusted to 0.03 mL / min, i.e., the mass flow rate of the material was 0.02518 g / min, ensuring a residence time of 6 hours in the fixed bed. After evaporation to remove methanol and water from the overflowing material, methyl oleate was obtained, with a yield of 95.6%.

Claims

1. A method for preparing a catalyst coated with a self-curing ionic liquid film, characterized in that... Sulfonation of polyethyleneimine yields a self-curing acidic ionic liquid, namely sulfonated polyethyleneimine, which is then coated onto the substrate surface. The specific steps are as follows: 1) 1,3-propanesulfonyl lactone is heated and melted, and an ethanol solution of polyethyleneimine is added dropwise. The sulfonation reaction is carried out by stirring under heating. After the reaction is completed, the mixture is cooled and filtered. The filtered solid is washed with ethanol to remove the unreacted 1,3-propanesulfonyl lactone. After drying, an acidic self-curing ionic liquid containing sulfonic acid groups is obtained. 2) Heat the acidic self-curing ionic liquid from step 1) to above 70°C to make it a viscous liquid, then coat it evenly on the substrate surface, and lower the temperature to below 50°C to allow it to self-cur on the substrate surface to form an acidic ionic liquid film, thereby obtaining a catalyst with a self-curing ionic liquid film on its surface. The molecular weight of the polyethyleneimine is 50,000-100,000; The mass ratio of polyethyleneimine to 1,3-propanesulfonyl lactone is 1:3-5, the sulfonation temperature is 40-70℃, and the sulfonation time is 8-12h. The substrate is a base film or a filler. The base film is a polypropylene film, a polyvinylidene fluoride film, or a nylon film; the filler is a plastic filler or a metal filler.

2. The method for preparing a catalyst coated with a self-curing ionic liquid film as described in claim 1, characterized in that... The molecular weight of the polyethyleneimine is 60,000-70,000, and the mass fraction of the polyethyleneimine ethanol solution is 30-70%.

3. The method for preparing a catalyst coated with a self-curing ionic liquid film as described in claim 1, characterized in that... The sulfonation temperature is 50-60℃.

4. The method for preparing a catalyst coated with a self-curing ionic liquid film as described in claim 1, characterized in that... When the substrate is a base membrane, the corresponding catalyst is a self-curing ionic liquid catalytic membrane, in which the ionic liquid loading is 30-60%; when the substrate is a filler, the corresponding catalyst is a self-curing ionic liquid catalytic membrane filler, in which the ionic liquid loading is 20-50%.

5. A catalyst coated with a self-curing ionic liquid membrane prepared by any one of claims 1-4.

6. The application of the catalyst coated with a self-curing ionic liquid membrane as described in claim 5 in the catalytic esterification reaction, wherein the reactor for the catalytic esterification reaction is a stirred tank reactor, a membrane reactor, or a fixed bed reactor.

7. The application as described in claim 6, characterized in that... When the reactor is a stirred tank, the catalytic reaction steps are as follows: 1) Add methanol and oleic acid to the stirred tank, with a mass ratio of methanol to oleic acid of 1:0.8-1.2; 2) Add the catalyst to the stirred tank. The mass of the catalyst is 5%-16% of the mass of oleic acid. 3) With stirring, heat the material in the stirred tank to 60-70℃ and react for 2-4 hours; 4) After the reaction is complete, the catalyst is filtered out and separated. The reaction solution is distilled to remove methanol and water to obtain methyl oleate product.

8. The application as described in claim 6, characterized in that... When the reactor is a membrane reactor, the catalytic reaction steps are as follows: S1: The substrate is a base membrane, the catalyst is a self-curing ionic liquid catalytic membrane, and the membrane reactor includes the self-curing ionic liquid catalytic membrane and two reaction chambers. The self-curing ionic liquid catalytic membrane is sealed between the two reaction chambers. The liquid outlets of the two reaction chambers are connected to the liquid inlet of the storage tank through pipelines, and the liquid inlets of the two reaction chambers are connected to the liquid outlet of the storage tank through pipelines via a delivery pump. S2: Methanol and oleic acid are added to the storage tank at a mass ratio of 1:0.8-1.

2. The reactants in the storage tank are heated to 60-70℃. Then, the reactants are transported to the reaction chamber of the membrane reactor by a transfer pump with a flow rate of 20-50 mL / min. The reactants undergo catalytic reaction in contact with the self-curing ionic liquid catalytic membrane. Under the action of the transfer pump, the reactants circulate and react in the system formed by the storage tank, transfer pump, reaction chamber and pipeline. The reaction time is controlled to be 4-8 hours. S3: After the reaction is complete, the liquid in the storage tank is released, and methanol and water are removed by distillation to obtain methyl oleate product.

9. The application as described in claim 6, characterized in that... When the reactor is a fixed-bed reactor, the catalytic reaction steps are as follows: Step 1: The substrate is a filler, and the catalyst is a self-curing ionic liquid catalytic membrane filler. The catalyst is filled in the fixed bed reactor. An insulation jacket is provided on the outside of the fixed bed reactor, and hot water at 60-70℃ is introduced into the insulation jacket. Step 2: Methanol and oleic acid are mixed at a mass ratio of 1:0.8-1.

2. The reaction mixture is heated to 60-70℃ and then fed into the fixed bed reactor from the bottom and overflowed from the top. The residence time of the reaction mixture in the fixed bed reactor is controlled to be 4-8 hours. Step 3: After the overflow material is evaporated to remove methanol and water, methyl oleate product is obtained.

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