A method for preparing levulinic acid esters

Abstract

The present application relates to the field of molecular sieve, and particularly to a preparation method of levulinic acid ester.The present application provides a preparation method of levulinic acid ester, comprising the following steps: subjecting composite molecular sieve, cellulose, acid liquor and alcohol solvent to alcoholysis reaction to obtain levulinic acid ester; the composite molecular sieve is composed of transition metal and molecular sieve, and the transition metal exists in the molecular sieve framework in monodispersed tetrahedral coordination form.The method provided by the present application uses the composite molecular sieve with transition metal compounded in the framework and the pore channel as a catalyst to prepare levulinic acid ester by alcoholysis, and has high yield.Experiments show that in the whole reaction, the cellulose alcoholysis mainly generates the corresponding solvent levulinic acid ester, and the side reaction is less; under suitable conditions, the conversion rate of cellulose can reach 100%, and the molar yield of corresponding levulinic acid ester is greater than 60%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of molecular sieve, and particularly relates to a preparation method of levulinic acid ester. BACKGROUND

[0002] It has very broad development prospects to convert renewable biomass resources into high value-added chemicals. Cellulose is the most abundant biomass biomacromolecule in nature, which is a biological polymer connected by beta-1, 4-glucosidic bonds and presents a network structure with high crystallinity. The cellulose polymer structure contains a large number of hydroxyl functional groups, and the hydrogen bond force between these hydroxyl functional groups is very strong. Meanwhile, the intramolecular and intermolecular hydrogen bond force makes it form a stubborn three-dimensional crystal network structure. Due to the stubbornness and complexity of the structure of cellulose, it is very difficult to carry out downstream conversion of cellulose, and the product distribution is relatively complex. As an alcoholysis product of cellulose in biomass raw materials, levulinic acid (ester) has been prepared on a large scale. Levulinic acid (ester) can be used to prepare many fine chemicals, such as fuels, cosmetics or food additives, and the large-scale development of its downstream applications has great contribution.

[0003] The process of preparing levulinic acid ester by alcoholysis of cellulose is complex, so it is a key problem in this field to find a high-efficiency and practical catalytic system. There are about four types of cellulose alcoholysis systems reported at present, including inorganic acid catalysis represented by sulfuric acid, metal salt catalysis, heteropoly acid catalysis and ionic liquid catalysis. However, these catalytic systems have certain defects. They all need high temperature, and the inorganic acid catalysis represented by sulfuric acid is easy to coking at high temperature and will corrode the reactor. The metal salt catalysis has many active sites, so there are many by-products and low selectivity during the alcoholysis of cellulose. The heteropoly acid and ionic liquid both have the problem of high cost, and most of the ionic liquids have toxicity.

[0004] In summary, there are technical problems such as harsh reaction conditions, low product yield and low selectivity in the process of preparing levulinic acid ester by alcoholysis of cellulose. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is to provide a preparation method of levulinic acid ester. The method provided by the present application uses a composite molecular sieve with transition metal in the framework and pore as a catalyst to prepare levulinic acid ester, and has high yield.

[0006] The present application provides a preparation method of levulinic acid ester, which comprises the following steps: carrying out alcoholysis reaction of a composite molecular sieve, cellulose, acid liquor and alcohol solvent to obtain levulinic acid ester; the composite molecular sieve is composed of transition metal and molecular sieve, and the transition metal exists in the molecular sieve framework in the form of monodisperse tetrahedral coordination.

[0007] The present application inventors creatively found that the above-mentioned composite molecular sieve is used for alcoholysis reaction of cellulose, and acetoxyester can be obtained with high yield, and stable, efficient and high-selectivity conversion of acetoxyester is realized.

[0008] The composite molecular sieve of the present application is composed of transition metal and molecular sieve, and the transition metal exists in the form of monodispersed tetrahedral coordination in the framework of the molecular sieve. The composite molecular sieve provided by the present application is a composite molecular sieve containing single-site framework-confined transition metal. The high dispersion of transition metal is realized by using the framework and pore of the molecular sieve, the active surface area of the catalyst is increased, and the conversion efficiency of the catalyst is improved. At the same time, the framework and pore of the molecular sieve can also avoid sintering of the catalyst at high temperature, and ensure the stability and good reproducibility of the catalyst. Figure 1 As shown in the following formula, Figure 1 The present application provides a preparation method of the above-mentioned composite molecular sieve. The above-mentioned composite molecular sieve is prepared according to the following steps: mixing a structure directing agent, a silicon source and water, heating to obtain an initial sol; crystallizing the initial sol, a transition metal salt and a mineralizer to obtain a solid product; and calcining the solid product to obtain the composite molecular sieve.

[0009] The present application provides a preparation method of the above-mentioned composite molecular sieve. The above-mentioned composite molecular sieve is prepared according to the following steps: mixing a structure directing agent, a silicon source and water, heating to obtain an initial sol; crystallizing the initial sol, a transition metal salt and a mineralizer to obtain a solid product; and calcining the solid product to obtain the composite molecular sieve.

[0010] The present application first mixes a structure directing agent, a silicon source and water, and heats to obtain an initial sol. The structure directing agent of the present application is selected from one or more of nitrogen-containing organic compounds containing tertiary amine centers or nitrogen-containing organic compounds containing quaternary ammonium centers. In one embodiment, the structure directing agent is specifically selected from one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide or pyridine.

[0011] The silicon source of the present application is selected from one or more of an organic silicon source and an inorganic silicon source. In one embodiment, the silicon source is selected from one or more of a silica sol, colloidal silica, aerogel silica, sodium silicate and tetraethyl orthosilicate, preferably from one or more of aerogel silica, silica sol and tetraethyl orthosilicate.

[0012] In some embodiments of the present application, the heating temperature is 40-100℃, preferably 50-80℃; the heating time is 5-20h, preferably 10-14h. In some embodiments of the present application, the mass ratio of the structure-directing agent, the silicon source and water is 10-40:20-60:20-60.

[0013] In the present application, in order to make the raw materials more uniform, the mixture of the structure-directing agent, the silicon source and water is preferably stirred. In some embodiments of the present application, the structure-directing agent, the silicon source and water are mixed, heated while stirring to obtain an initial sol; in this process, the initial sol, i.e. the molecular sieve precursor, is synthesized from the above-mentioned raw materials, i.e. the structure-directing agent, the silicon source and water; the stirring speed is 10-1500r / min, preferably 300-500r / min.

[0014] After obtaining the initial sol, the initial sol, the transition metal salt and the mineralizer are crystallized to obtain a solid product. Specifically, the initial sol is added with the transition metal salt and the mineralizer, and then transferred to a hydrothermal kettle for crystallization to grow a molecular sieve structure, thereby obtaining a solid product.

[0015] In some embodiments of the present application, the transition metal salt is selected from one or more of an iron salt, a cobalt salt, a nickel salt, a copper salt and a zinc salt; wherein the iron salt is selected from one or more of FeCl2·4H2O, FeCl3·6H2O, FeSO4·7H2O, Fe(NO3)3·9H2O and Fe2(SO4)3·9H2O; the cobalt salt is selected from one or more of CoSO4·7H2O, Co(NO3)2·6H2O, CoCl2·6H2O and CoC2O4·2H2O; the nickel salt is selected from one or more of Ni(NO3)2·6H2O, NiSO4·7H2O, NiSO4·6H2O, Ni(CH3COO)2 and NiCl2·6H2O; the copper salt is selected from one or more of Cu(NO3)2·3H2O, Cu(NO3)2·6H2O, CuSO4·5H2O, CuCl2·2H2O and Cu(CH3COO)2·H2O; and the zinc salt is selected from one or more of Zn(NO3)2·6H2O, ZnSO4·7H2O, ZnCl2 and Zn(CH3COO)2·2H2O.

[0016] In some embodiments of the present application, the mineralizer is selected from one or more of alkali metal inorganic salts or alkali metal inorganic bases. In one embodiment, the mineralizer is selected from one or more of NaOH, KOH, NaF, KF, NaCl and KCl. In one embodiment, the crystallization temperature is 30-300°C, preferably 150-200°C; the crystallization time is 3-240h, preferably 15-30h.

[0017] After obtaining the solid product, the solid product is calcined to obtain the composite molecular sieve. The obtained solid product is finally calcined to remove the structure-directing agent to obtain the composite molecular sieve. Specifically, after obtaining the solid product, the obtained solid product is preferably washed, dried, and then calcined. In some embodiments of the present application, after obtaining the solid product, the solid product is washed until the pH of the washing liquid is less than 8, then dried, and then calcined to obtain the composite molecular sieve. In one embodiment, the drying temperature is 60-120°C, preferably 80-100°C; the drying time is 5-20h, preferably 10-14h. In one embodiment, the calcination temperature is 200-800°C, preferably 500-600°C; the calcination time is 0.5-24h, preferably 1-3h.

[0018] The composite molecular sieve is obtained by introducing transition metal into the molecular sieve by one-step hydrothermal synthesis method, and the active sites are highly dispersed by the confinement effect of the molecular sieve framework, which avoids the disadvantages of the catalysts synthesized by traditional impregnation method, such as uneven structure, poor dispersibility, easy agglomeration, and small active surface area. The composite molecular sieve catalyst obtained by the present application is resistant to acid, alkali, oxygen, sulfur, water, and carbon deposition, has long service life, high reaction activity and product selectivity, and can realize stable, efficient and high-selectivity conversion of cellulose to levulinic acid ester, thereby solving the technical problems of harsh reaction conditions, low product yield and low selectivity in the process of preparing levulinic acid ester from cellulose alcoholysis in the prior art.

[0019] The application provides a preparation method of levulinic acid ester, which comprises the following steps: subjecting composite molecular sieve, cellulose, acid liquor and alcohol solvent to alcoholysis reaction to obtain levulinic acid ester; the composite molecular sieve is the composite molecular sieve or the composite molecular sieve prepared by the preparation method. In some embodiments of the application, the composite molecular sieve, cellulose and acid liquor are subjected to alcoholysis reaction in alcohol solvent to obtain levulinic acid ester; the composite molecular sieve is the composite molecular sieve or the composite molecular sieve prepared by the preparation method. In one embodiment, the composite molecular sieve, cellulose, acid liquor and alcohol solvent are subjected to alcoholysis reaction in a pressure-resistant tube under stirring to obtain levulinic acid ester; the composite molecular sieve is the composite molecular sieve or the composite molecular sieve prepared by the preparation method. In one embodiment, the acid liquor is selected from at least one of sulfuric acid and hydrochloric acid; and the alcohol solvent is selected from at least one of methanol, ethanol or butanol. By using the composite molecular sieve catalyst and acid liquor in alcohol as solvent, the preparation of levulinic acid ester from cellulose under mild reaction conditions is realized.

[0020] In some embodiments of the application, the use amount ratio of the composite molecular sieve, cellulose, acid liquor and alcohol solvent is 1000 mass parts: 50-150 mass parts: 50-150 mass parts: 5 volume parts. In one embodiment, the use amount ratio of the composite molecular sieve, cellulose, acid liquor and alcohol solvent is 1 g: 50-150 mg: 50-150 mg: 5 mL. In one embodiment, the temperature of the alcoholysis reaction is 90-150 DEG C, preferably 110-130 DEG C; and the time of the alcoholysis reaction is 4-16 h, preferably 6-12 h.

[0021] The application provides a preparation method of levulinic acid ester, which comprises the following steps: subjecting composite molecular sieve, cellulose, acid liquor and alcohol solvent to alcoholysis reaction to obtain levulinic acid ester; the composite molecular sieve is composed of transition metal and molecular sieve, and the transition metal exists in the molecular sieve framework in monodispersed tetrahedral coordination form. The method provided by the application has high yield in the preparation of levulinic acid ester by alcoholysis with the composite molecular sieve with transition metal in the framework and pore as catalyst. The application realizes the preparation of levulinic acid ester from cellulose under relatively mild conditions by using the composite molecular sieve catalyst which is simple in source, green and efficient, and thus can better meet the needs of industrial application. In addition, the process for preparing 1,5-dimethyl-2-pyrrolidone from levulinic acid (ester) is simple, the reaction equipment is simple, the operation is simple, the reaction conditions are relatively mild, the catalyst is cheap and easy to obtain, the catalyst has good stability and can be recycled, is suitable for industrial production, and has a very wide application prospect. Experiments show that in the whole reaction, the cellulose alcoholysis mainly generates the corresponding solvent levulinic acid ester, and the side reaction is less. Under suitable conditions, the conversion rate of cellulose can reach 100%, and the molar yield of the corresponding levulinic acid ester is greater than 60%. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the composite molecular sieve described in this invention;

[0023] Figure 2 The image shows the XRD pattern of the composite molecular sieve prepared in Example 1. Detailed Implementation

[0024] This invention discloses a method for preparing levulinic ester. Those skilled in the art can refer to this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to implement and apply the technology of this invention.

[0025] The present invention will be further described below with reference to the embodiments:

[0026] Example 1

[0027] 6 g of TEOS, 3.75 g of TPAOH, and 5 g of H2O were mixed and stirred at 60 °C and 300 r / min for 12 hours to prepare a zeolite precursor. Then, two aqueous solutions, one containing 178.33 mg Co(NO3)2·6H2O and the other containing 51.46 mg NaF (Co / Na = 1 / 2), were immediately added to the precursor. The mass composition of the mixture followed the formula TEOS:TPAOH:H2O = 1:0.25:11. The mixture was heated at 170 °C for 24 hours in a 50 mL PTFE-lined autoclave. The zeolite product was collected after filtration, washed with water, and vacuum dried at 80 °C. The resulting zeolite was calcined in air at 550 °C for 2 hours at a heating rate of 3 °C / min to obtain the Co-MFI catalyst. XRD analysis of the obtained catalyst was performed, and the results are shown below. Figure 2 As shown; Figure 2 The XRD pattern of the composite molecular sieve prepared in Example 1 is shown below. Figure 2 It can be seen that the Co@MFI catalyst has a high intensity MFI topological peak, and no characteristic diffraction peaks of Co3O4 and Co were found, indicating that the MFI molecular sieve framework is highly transformed and the Co particles are well embedded in the molecular sieve. Under these synthesis conditions, the composite molecular sieve Co-MFI catalyst was successfully grown into an MFI crystal structure.

[0028] Example 2

[0029] A zeolite precursor was prepared by mixing 6 g of TEOS, 3.75 g of TPAOH and 5 g of H2O under magnetic stirring at 60 °C and 300 r / min for 12 h. Then, two aqueous solutions were mixed, one containing 181.39 mg of Cu(N03)2-6H2O and the other containing 51.46 mg of NaF (Cu / Na = 1 / 2), and immediately added to the precursor. The mass composition of the mixture followed TEOS:TPAOH:H2O = 1:0.25:11. The mixture was heated in a 50 mL Teflon-lined autoclave at 170 °C for 24 h. After filtration, the zeolite product was washed with water and dried under vacuum at 80 °C. The zeolite thus obtained was calcined in air at 550 °C for 2 h with a heating rate of 3 °C / min, obtaining a Cu-MFI catalyst.

[0030] Example 3

[0031] A zeolite precursor was prepared by mixing 4.05 g of tetrapropylammonium bromide, 5.32 g of fumed silica and 5.89 g of H2O under constant temperature of 70 °C and stirring at 450 r / min for 12 h. Then, 0.59 g of CuS04-5H2O was added to the precursor, which was transferred to a hydrothermal kettle for crystallization at 170 °C for 25 h. The crystallized sample was washed until the pH was less than 8 and dried at 85 °C for 13 h. Finally, the sample was calcined at 560 °C for 2.5 h, obtaining a Cu-*BEA catalyst.

[0032] Example 4

[0033] A zeolite precursor was prepared by mixing 4.05 g of tetrapropylammonium bromide, 5.32 g of fumed silica and 5.89 g of H2O under constant temperature of 70 °C and stirring at 450 r / min for 12 h. Then, 0.66 g of CoS04-7H2O was added to the precursor, which was transferred to a hydrothermal kettle for crystallization at 170 °C for 25 h. The crystallized sample was washed until the pH was less than 8 and dried at 85 °C for 13 h. Finally, the sample was calcined at 560 °C for 2.5 h, obtaining a Co-*BEA catalyst.

[0034] Example 5

[0035] A zeolite precursor was prepared by mixing 2.39 g of pyridine, 5.32 g of sodium silicate and 4.75 g of H2O under constant temperature of 90 °C and stirring at 500 r / min for 10 h. Then, 0.11 g of CoC204-2H2O was added to the precursor, which was transferred to a hydrothermal kettle for crystallization at 200 °C for 15 h. The crystallized sample was washed until the pH was less than 8 and dried at 100 °C for 10 h. Finally, the sample was calcined at 600 °C for 1 h, obtaining a Co-CHA catalyst.

[0036] Example 6

[0037] The molecular sieve precursor was obtained by mixing 2.39 g of pyridine, 5.32 g of sodium silicate and 4.75 g of H2O, stirring at 90°C for 10 h at a rotation speed of 500 r / min; 0.09 g of CuC2O4 was added into the precursor, and then transferred into a hydrothermal kettle for crystallization at 200°C for 15 h; the crystalline sample was washed until the pH was less than 8, and then dried at 100°C for 10 h; finally, the sample was calcined at 600°C for 1 h to obtain a Cu-CHA catalyst.

[0038] Experimental examples 1-18

[0039] The composite molecular sieve catalysts prepared in examples 1-6 were evaluated for the performance of preparing acetyl propionate by alcoholysis of cellulose; 1 g of cellulose, 50 mg-150 mg of the composite molecular sieve, 50 mg-150 mg of concentrated sulfuric acid and 5 mL of an alcohol solvent were placed in a 15 mL pressure tube, the pressure tube was placed in an oil bath with magnetic stirring and heated to 110°C-130°C, and reacted for 6 h-12 h. The specific selection of materials, reaction amount and reaction results are shown in Table 1, which is a table of reaction conditions and reaction results data of different examples.

[0040] Table 1

[0041]

[0042]

[0043] As can be seen from the reaction results in Table 1, the composite molecular sieve catalyst with concentrated sulfuric acid and alcohol as a solvent can prepare acetyl propionate by one-step alcoholysis of cellulose; at the same time, the catalyst has very good catalytic effect, and the molar yield of acetyl propionate can reach more than 60%. The preferred reaction conditions of the present application are as follows: the composite molecular sieve catalyst Co-MFI is selected, and reacts with sulfuric acid at a mass ratio of 1:1, the reaction temperature is 120°C, and the reaction time is 8 h, under such reaction conditions, cellulose can be efficiently alcoholized to prepare acetyl propionate.

[0044] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical solution and inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing levulinic acid ester, comprising the steps of: carrying out an alcoholysis reaction on cellulose, a composite molecular sieve, an acid solution and an alcohol solvent to obtain levulinic acid ester; the composite molecular sieve is composed of a transition metal and a molecular sieve, and the transition metal exists in a monodispersed tetrahedral coordination form in the molecular sieve framework; the transition metal is selected from Co; the molecular sieve is one of MFI molecular sieve, CHA molecular sieve or BEA molecular sieve.

2. The production method according to claim 1, characterized by, The mass ratio of the transition metal in the composite molecular sieve is 0.01 wt% to 50 wt%.

3. The preparation method according to claim 1, characterized in that, The ratio of the cellulose, the composite molecular sieve, the acid solution and the alcohol solvent is 1000 mass parts: 50 to 150 mass parts: 50 to 100 mass parts: 5 volume parts.

4. The method of claim 1, wherein, The acid solution is selected from at least one of sulfuric acid and hydrochloric acid.

5. The preparation method according to claim 1, characterized in that, The alcohol solvent is selected from at least one of methanol, ethanol or butanol.

6. The method of claim 1, wherein, The temperature of the alcoholysis reaction is 90°C to 150°C, and the time of the alcoholysis reaction is 4 h to 16 h.

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