A Ti / Zr-Si porous molecular sieve and its preparation method and catalytic esterification method

Abstract

The present invention belongs to the technical field of organic ester preparation, and in particular to a kind of Ti / Zr-Si porous molecular sieve and its preparation method and catalytic esterification method, the preparation method comprises the following steps: (1) silicon source, titanium source, zirconium source, structure directing agent, water are mixed, and heated hydrolysis dispersion is obtained under normal pressure to obtain precursor gel I, and organic acid source is added to precursor gel I to obtain precursor gel II; (2) precursor gel II is transferred to reactor, hydrothermally reacted under autogenous pressure, and finally cooled, depressurized, filtered, dried and roasted to obtain Ti / Zr-Si porous molecular sieve. The present invention can improve the diffusion performance in molecular sieve crystal, improve the accessibility of active centers in molecular sieve crystal, and regulate the amount of Lewis acid produced by surface hydroxyl groups by introducing organic acid source in molecular sieve preparation system. Therefore, catalytic efficiency and catalytic stability when using Ti / Zr-Si porous molecular sieve catalytic esterification reaction are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic esters, and particularly relates to a heteroatom molecular sieve catalyst used in esterification reactions and a preparation method thereof. Background Art

[0002] Organic esters, including ethyl acetate, methyl oleate, and triglyceride acetate, are important chemical raw materials, and their efficient synthesis is of great significance. Typically, an organic acid reacts with an alcohol in the presence of an acid catalyst to produce an ester through a dehydration reaction. However, esterification is a reversible reaction. To increase the yield of the ester, water is often removed through azeotropic distillation or the use of a water absorbent to shift the reaction equilibrium. Furthermore, an excess of acid or alcohol can be added to the reaction system to shift the reaction toward esterification.

[0003] Commonly used catalysts for esterification reactions are primarily homogeneous catalytic materials such as sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, and metal organic compounds. Although homogeneous catalysts can catalyze esterification reactions under relatively mild conditions, they suffer from long reaction times and low production efficiency. To address these issues, heterogeneous esterification catalytic materials have garnered widespread attention. Heterogeneous esterification catalytic materials refer to catalytic systems in which both liquid and solid phases coexist during the esterification reaction. These catalytic systems can provide higher reaction efficiency and product purity, and offer the advantages of easy separation and recovery. Despite this, the activity and stability of heterogeneous esterification catalysts remain significant constraints on their industrialization. When using heterogeneous esterification catalysts, their deactivation is primarily due to corrosion by organic acids and dehydration of alcohols under acidic conditions. Therefore, heterogeneous esterification catalysts must be acid-resistant and exhibit low activity in alcohol dehydration reactions.

[0004] Heteroatom molecular sieves, such as titanium silicalite and zirconium silicalite, have unique Lewis acidity. They not only exhibit excellent activity in selective oxidation reactions, but also have certain transesterification performance. In addition, both titanium silicalite and zirconium silicalite have excellent hydrothermal stability and acid resistance. However, perhaps due to the limitations of the molecular sieve pore size or the influence of the molecular sieve's weak acidity, there are very few reports on the direct use of heteroatom molecular sieves to catalyze acid-base esterification to synthesize organic esters. Patents with application numbers 202210760318.4 and 202210762756.4 disclose that heteroatom molecular sieves such as titanium silicalite, iron silicalite, or tin silicalite can catalyze the reaction of C3-C20 straight-chain or branched fatty acids with pentaerythritol to form esters under reaction conditions of 80-300°C, reaction time of 2-24h, catalyst dosage of 0.1-2%, and atmospheric pressure. To enhance the catalytic activity of heteroatom molecular sieves in esterification reactions, acid centers such as ionic liquids and phosphotungstic acid can be loaded, but in this case, the molecular sieve primarily serves as a support. Furthermore, sulfonate catalysts immobilized on amorphous SiO2-TiO2 also exhibit good activity in esterification reactions, but the amorphous SiO2-TiO2 also serves solely as a support. While heteroatom molecular sieves exhibit some esterification performance, their pore sizes are typically below 1 nm. Therefore, during catalytic esterification reactions, their intracrystalline active centers struggle to interact with larger organic acids and alcohols, and catalytic efficiency still needs to be further improved. Summary of the Invention

[0005] The present invention aims to provide a Ti / Zr-Si porous molecular sieve, which can effectively improve the catalytic efficiency of existing molecular sieve catalysts in the process of catalyzing esterification reactions.

[0006] The first object of the present invention is to provide a method for preparing a Ti / Zr-Si porous molecular sieve, comprising the following steps:

[0007] (1) mixing a silicon source, a titanium source, a zirconium source, a structure directing agent, and water, and heating and hydrolyzing and dispersing the mixture under normal pressure to obtain a precursor gel I, and adding an organic acid source to the precursor gel I to obtain a precursor gel II;

[0008] (2) The precursor gel II is transferred to a reactor and subjected to a hydrothermal reaction under autogenous pressure, and finally cooled, depressurized, filtered, dried and calcined to obtain a Ti / Zr-Si porous molecular sieve.

[0009] Normally, the synthesis of molecular sieves is carried out under alkaline conditions. However, the present invention introduces an organic acid source in the system prepared by molecular sieve, which can produce a neutralization effect with the alkaline precursor gel I to form a precursor gel II comprising an organic carboxylic acid group, and the organic carboxylic acid group can regulate the nucleation and grain growth of molecular sieve to a certain extent, thereby affecting the integrity, morphology and the coordination state of Ti / Zr of the crystal structure of molecular sieve. When the hydrophobic groups of the organic carboxylic acid group interact to form a cluster with internal hydrophobicity and external hydrophilicity, the cluster can also act on the molecular sieve precursor or its crystallization transition state, thereby introducing secondary pores and surface hydroxyl groups in the molecular sieve crystal, improving the diffusion performance in the molecular sieve crystal, improving the accessibility of the active center in the molecular sieve crystal, and regulating the Lewis acidity produced by the surface hydroxyl groups. Therefore, in the process of preparing organic esters by catalytic esterification reaction of the Ti / Zr-Si porous molecular sieve obtained using the present technical solution, catalytic activity and stability are all higher, and the production efficiency of organic esters can be effectively improved.

[0010] Preferably, the silicon source in step (1) is selected from at least one of organic silicate, silica gel, white carbon black, and silica sol; in order to reduce the influence of heteroatoms in the silicon source on the crystallized product, a single silicon source is preferred; further preferably, it is an organic silicate, such as at least one of methyl orthosilicate, isopropyl silicate, ethyl silicate, tetraethoxysilane, and tetraethyl orthosilicate.

[0011] Preferably, the titanium source in step (1) is selected from at least one of organic titanium esters and / or inorganic titanium salts such as titanium tetrachloride, tetrabutyl titanate, tetraethyl titanate, and titanium tetrafluoride; preferably, the titanium source is at least one of tetrabutyl titanate and tetraethyl titanate.

[0012] Preferably, the zirconium source in step (1) is selected from at least one of organic zirconium compounds such as zirconium acetate, zirconium isooctanoate, zirconium n-propoxide, zirconium cyclohexane, zirconium tetra-tert-butoxide, zirconium acetylacetonate, and tetrabutyl zirconate; preferably, the zirconium source is at least one of tetrabutyl zirconate and zirconium acetylacetonate.

[0013] Furthermore, the structure directing agent in step (1) is selected from at least one of quaternary ammonium base, quaternary ammonium salt, aliphatic amine and aliphatic alcohol amine.

[0014] Specifically, the general structural formula of the quaternary ammonium hydroxide is:

[0015]

[0016] Wherein, R1, R2, R3, and R4 are each at least one C1-C4 alkyl group, wherein the C1-C4 alkyl group is selected from at least one of a C1-C4 linear alkyl group and a C3-C4 branched alkyl group. R1, R2, R3, and R4 can independently be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0017] Specifically, the general structural formula of the quaternary ammonium salt is:

[0018]

[0019] Wherein, R1, R2, R3, and R4 are each at least one C1-C4 alkyl group, and the C1-C4 alkyl group is selected from at least one of a C1-C4 linear alkyl group and a C3-C4 branched alkyl group. R1, R2, R3, and R4 can independently be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl group; and X in the quaternary ammonium salt is at least one halogen ion selected from F, Cl, Br, I, and the like.

[0020] Specifically, the aliphatic amine has the general structural formula R5(NH2)n, where n is an integer of 1 or 2. When n is 1, R5 is at least one C1-C6 alkyl group, and the C1-C6 alkyl group is selected from at least one of a C1-C6 straight-chain alkyl group and a C3-C6 branched-chain alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, isopentyl, tert-pentyl, or n-hexyl group. When n is 2, R5 is at least one C1-C6 alkylene group, and the C1-C6 alkylene group is selected from at least one of a C1-C6 straight-chain alkylene group and a C3-C6 branched-chain alkylene group, such as methylene, ethylene, n-propylene, n-butylene, n-pentylene, or n-hexylene.

[0021] Specifically, the general structural formula of the aliphatic alcohol amine is R6(ONH)n, wherein n is an integer of 1 or 2. When n is 1, R6 is at least one C1-C6 alkyl group, and the C1-C6 alkyl group is selected from at least one of a C1-C6 straight-chain alkyl group and a C3-C6 branched-chain alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, isopentyl, tert-pentyl or n-hexyl. When n is 2, R6 is at least one C1-C6 alkylene group, and the C1-C6 alkylene group is selected from at least one of a C1-C6 straight-chain alkylene group and a C3-C6 branched-chain alkylene group, such as methylene, ethylene, n-propylene, n-butylene, n-pentylene or n-hexylene.

[0022] Preferably, the structure directing agent is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride, tetrabutylammonium chloride, tripropylamine, triethylamine, diethylamine, tributylamine, and hexamethylenediamine; more preferably, it is selected from at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and hexamethylenediamine. When the alkaline source is tetraethylammonium hydroxide, triethylamine, or diethylamine, the obtained ※ Molecular sieves with BEA topology structure; when the structure directing agent is tetrapropylammonium hydroxide or tripropylamine, molecular sieves with MFI topology structure are prepared; when the structure directing agent is hexamethylenediamine, ZSM-48 molecular sieves are prepared; when the structure directing agent is tetrabutylammonium hydroxide or tributylamine, molecular sieves with MEI topology structure are prepared.

[0023] Preferably, the organic acid source includes at least one of monocarboxylic acid, dicarboxylic acid and tricarboxylic acid.

[0024] Specifically, the monocarboxylic acid is a monocarboxylic acid containing a C2-C18 group, wherein the C2-C18 group can be a linear alkyl group, an isomeric alkyl group, an alkenyl group, a polycyclic group, or an aromatic group. The monocarboxylic acid can be at least one of acetic acid, acrylic acid, methacrylic acid, n-butyric acid, n-hexanoic acid, isooctanoic acid, isononanoic acid, p-isopropylcyclohexylcarboxylic acid, benzoic acid, lauric acid, oleic acid, and the like. Preferably, the monocarboxylic organic acid is at least one of isooctanoic acid, lauric acid, and oleic acid.

[0025] Specifically, the dibasic acid is at least one of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, terephthalic acid, phthalic acid, glutamic acid, aspartic acid, etc. Preferably, the dibasic acid is at least one of adipic acid, terephthalic acid, and glutamic acid.

[0026] Specifically, the tribasic acid is at least one of citric acid, trimesic acid, and the like.

[0027] Preferably, the molar ratio of the silicon source, titanium source, zirconium source, structure directing agent, organic acid source and water in step (1) is 1: (0.0001-0.025): (0.0001-0.023): (0.05-0.39): (0.05-3): (15-200), and the silicon source, titanium source and zirconium source are calculated as SiO2, TiO2 and ZrO2, respectively.

[0028] Preferably, the conditions for heating and hydrolysis in step (1) are: temperature 40-80° C., time 0.5-24 h.

[0029] In the present invention, the temperature and time of the hydrothermal reaction in step (2) are one of the important factors affecting the crystal form, crystal size and product morphology of the hydrothermal product. Specifically, the conditions of the hydrothermal reaction in step (2) are: temperature 70-190° C., time 1-72 hours. As a further preferred embodiment, the conditions of the hydrothermal reaction in step (2) are: first reacting at 85-130° C. for 1-12 hours, then heating to 140-180° C. and reacting for 3-48 hours.

[0030] The pressure of the hydrothermal reaction system is another important factor affecting the product's crystal form and crystallization rate. The autogenous pressure of the reaction system depends on the free volume in the reactor. To improve the efficiency of the hydrothermal reaction, the total volume of the precursor gel II added in step (2) is preferably 60-85% of the reactor's capacity.

[0031] Preferably, the drying conditions in step (2) are: temperature 80-120° C., time 4-24 h.

[0032] Preferably, the calcination conditions in step (2) are: temperature 350-600° C., time 2-8 h.

[0033] The second object of the present invention is to provide a Ti / Zr-Si porous molecular sieve, which is prepared by any one of the above preparation methods.

[0034] Preferably, the Ti / Zr-Si porous molecular sieve comprises a secondary pore structure of 1 to 7 nm, and the volume of the secondary pore structure is 0.09 to 0.36 cm 3 / g. Furthermore, the Ti / Zr-Si porous molecular sieve contains a secondary pore structure of 2 to 6 nm, and the volume of the secondary pore structure is 0.13 to 0.31 cm 3 / g.

[0035] The Ti and Zr in the Ti / Zr-Si porous molecular sieve catalytic material are both located in the framework structure of the molecular sieve, which can be framework elements in the form of tetra-coordinate, penta-coordinate or hexa-coordinate, and the molar ratio of tetra-coordinate framework Ti, Zr to penta- or hexa-coordinate framework Ti, Zr is 1:(0.2~2); preferably, the molar ratio of tetra-coordinate framework Ti, Zr to penta- or hexa-coordinate framework Ti, Zr is 1:(0.4~1.2).

[0036] The framework Ti, Zr and hydroxyl groups on the molecular sieve surface together constitute the Lewis acid center of the catalytic material. Preferably, the acid amount of Lewis acid in the Ti / Zr-Si porous molecular sieve is 9.4-87.6 mmol / g; preferably, the acid amount of Lewis acid is 17.4-50.3 mmol / g.

[0037] The third object of the present invention is to propose the application of any one of the above-mentioned Ti / Zr-Si porous molecular sieves in a catalytic esterification reaction process.

[0038] Preferably, the catalytic esterification reaction is carried out using Ti / Zr-Si porous molecular sieve as catalyst at a temperature of 130-390°C, a pressure of 0.13-6 MPa, and a mass space velocity of organic acid of 0.01-80 h -1 Under the conditions of , organic acid and alcohol are introduced into a fixed bed reactor at a molar ratio of carboxyl group to hydroxyl group of 1: (0.1-20) to obtain organic ester.

[0039] Specifically, the organic acid is at least one of a monobasic acid, a dibasic acid, and a tribasic acid of C1 to C18, such as formic acid, acetic acid, acrylic acid, methacrylic acid, adipic acid, succinic acid, glutaric acid, isooctanoic acid, isononanoic acid, benzoic acid, terephthalic acid, phthalic acid, trimesic acid, lauric acid, oleic acid, citric acid, etc.

[0040] Specifically, the alcohol is at least one of C1-C18 monohydric alcohol, dihydric alcohol, trihydric alcohol and tetrahydric alcohol, such as methanol, ethanol, n-propanol, isopropanol, propylene glycol, ethylene glycol, hexylene glycol, tert-butanol, glycerol, pentaerythritol, oleyl alcohol, lauryl alcohol and the like.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention introduces an organic acid source into the system prepared by molecular sieve, which can produce a neutralization effect with the precursor gel I to form a precursor gel II containing an organic carboxylic acid group. The organic carboxylic acid group can regulate the nucleation of the molecular sieve and the growth of the grains to a certain extent, thereby affecting the integrity and morphology of the crystal structure of the molecular sieve. When the hydrophobic groups of the organic carboxylic acid group interact to form a cluster with internal hydrophobicity and external hydrophilicity, the cluster can also act on the molecular sieve precursor or its crystallization transition state, thereby introducing secondary pores and surface hydroxyl groups in the molecular sieve crystal, improving the diffusion performance in the molecular sieve crystal, improving the accessibility of the active center in the molecular sieve crystal, and regulating the Lewis acidity. In addition, the present invention further realizes the adjustment of the product morphology of the molecular sieve by adjusting the ratio of each component of the Ti / Zr-Si porous molecular sieve and the hydrothermal reaction conditions. Therefore, in the process of preparing organic esters by catalytic esterification using the Ti / Zr-Si porous molecular sieve of the invention, catalytic activity and stability are effectively improved. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the specification and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0044] The unified preparation method of the Ti / Zr-Si porous molecular sieve in the embodiment is:

[0045] (1) A silicon source, a titanium source, a zirconium source, a structure-directing agent, and deionized water are mixed under stirring conditions, and the mixture is heated and hydrolyzed and dispersed under normal pressure to obtain a clear and transparent precursor gel I. The precursor gel I is transferred to a hydrothermal crystallization reactor, and an organic acid source is added under stirring conditions to obtain a molecular sieve precursor gel II.

[0046] (2) After the hydrothermal crystallization reactor is sealed, a hydrothermal reaction is carried out under autogenous pressure, and finally the Ti / Zr-Si porous molecular sieve is obtained by cooling, depressurizing, filtering, drying and calcining.

[0047] In the examples, the unified method for preparing organic esters by esterification reaction catalyzed by Ti / Zr-Si porous molecular sieve is as follows:

[0048] The prepared Ti / Zr-Si porous molecular sieve is pressed and sieved to obtain 20-40 mesh molecular sieve particles. 2g of the pellets are weighed and loaded into the catalyst bed of a fixed-bed reactor. Under a nitrogen atmosphere, the temperature is raised and the pressure is maintained constant. A mixed reactant of an organic acid and an alcohol is then introduced according to the ratio of carboxyl groups to hydroxyl groups. The resulting reaction mass is condensed and separated into water and oil. The aqueous phase is discharged, and the oil phase is fractionated to obtain the organic ester product.

[0049] Examples 1-3

[0050] The raw materials, raw material ratios and preparation conditions for preparing Ti / Zr-Si porous molecular sieves in Examples 1-3 are detailed in Table 1 below.

[0051] Table 1

[0052]

[0053]

[0054] Examples 4-6

[0055] The raw materials, raw material ratios and preparation conditions for preparing Ti / Zr-Si porous molecular sieves in Examples 4-7 are detailed in Table 2 below.

[0056] Table 2

[0057]

[0058]

[0059] Examples 7-9

[0060] The raw materials, raw material ratios and preparation conditions for preparing Ti / Zr-Si porous molecular sieves in Examples 7-9 are detailed in Table 3 below.

[0061] Table 3

[0062]

[0063]

[0064] Comparative Example 1

[0065] The difference between Comparative Example 1 and Example 1 is that no organic acid source is added. The rest is the same as Example 1 and will not be described in detail in this section.

[0066] Comparative Example 2

[0067] The difference between Comparative Example 2 and Example 1 is that no titanium source is added. The rest is the same as Example 1 and will not be described in detail in this section.

[0068] Comparative Example 3

[0069] The difference between Comparative Example 3 and Example 1 is that no zirconium source is added, and the rest is the same as Example 1, which will not be described in detail in this section.

[0070] Performance Test 1

[0071] The Ti / Zr-Si porous molecular sieves prepared in Examples 1-9 and Comparative Examples 1-3 were subjected to the following performance tests, and the crystal structures and catalytic effects were obtained as shown in the following table. The determination methods were as follows: the acid content was analyzed by BIQ-RAD FTS3000 Fourier transform infrared spectrometer; the secondary pores and pore volumes were measured and calculated using a Micrometrics ASAP 2460 physical adsorption instrument; and the molar ratio of tetracoordinate framework Ti / Zr to penta / hexacoordinate Ti / Zr (Q4:(Q5&Q6)) was calculated by peak fitting of the corresponding characteristic peaks in the UV-Vis spectrum.

[0072]

[0073]

[0074] Table 4

[0075]

[0076] Performance Test 2

[0077] The Ti / Zr-Si porous molecular sieves after esterification reaction of Example 1 and Comparative Example 1 were recovered and subjected to cyclic catalysis under the same esterification reaction conditions. The conversion rate and selectivity of organic alcohol were measured, and the results were shown in the following table.

[0078] Table 5

[0079]

Claims

1. A method for preparing a Ti / Zr-Si porous molecular sieve, characterized in that: The following steps are involved: (1) mixing a silicon source, a titanium source, a zirconium source, a structure directing agent, and water, and heating and hydrolyzing and dispersing the mixture under normal pressure to obtain a precursor gel I, and adding an organic acid source to the precursor gel I to obtain a precursor gel II; (2) transferring the precursor gel II to a reactor, subjecting it to a hydrothermal reaction under autogenous pressure, and finally cooling, depressurizing, filtering, drying, and calcining to obtain a Ti / Zr-Si porous molecular sieve; In step (1), the molar ratio of the silicon source, titanium source, zirconium source, structure directing agent, organic acid source and water is 1: (0.0001-0.025): (0.0001-0.023): (0.05-0.39): (0.05-3): (15-200).

2. The method for preparing the Ti / Zr-Si porous molecular sieve according to claim 1, characterized in that: The organic acid source includes at least one of monocarboxylic acid, dicarboxylic acid and tricarboxylic acid.

3. The method for preparing the Ti / Zr-Si porous molecular sieve according to claim 1, characterized in that: The silicon source, titanium source and zirconium source are calculated as SiO2, TiO2 and ZrO2 respectively.

4. A Ti / Zr-Si porous molecular sieve, characterized in that: It is prepared by any one of the preparation methods of claims 1 to 3.

5. The Ti / Zr-Si porous molecular sieve according to claim 4, characterized in that: The amount of Lewis acid in the Ti / Zr-Si porous molecular sieve is 9.4 to 87.6 mmol / g.

6. The Ti / Zr-Si porous molecular sieve according to claim 4, characterized in that: The molar ratio of tetracoordinated framework Ti / Zr to penta / hexacoordinated Ti / Zr in the Ti / Zr-Si porous molecular sieve is 1:(0.2-2).

7. The Ti / Zr-Si porous molecular sieve according to claim 4, characterized in that: The Ti / Zr-Si porous molecular sieve includes a secondary pore structure of 1 to 7 nm, and the volume of the secondary pore structure of the Ti / Zr-Si porous molecular sieve is 0.09 to 0.36 cm 3 / g.

8. Use of the Ti / Zr-Si porous molecular sieve prepared by the method according to any one of claims 1 to 3 or the Ti / Zr-Si porous molecular sieve according to any one of claims 4 to 7 in catalytic esterification reactions.

9. The use according to claim 8, characterized in that The catalytic esterification reaction is to use Ti / Zr-Si porous molecular sieve as catalyst, at a temperature of 130-390°C, a pressure of 0.13-6 MPa, and a mass space velocity of organic acid of 0.01-80 h -1 Under the conditions of , organic acid and alcohol are introduced into a fixed bed reactor at a molar ratio of carboxyl group to hydroxyl group of 1: (0.1-20) to obtain organic ester.

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