Method for carrying out esterification reaction

Abstract

The invention provides a method for carrying out esterification reaction, which comprises the following steps: in a reaction system containing a catalyst, carrying out esterification reaction on a C2-C16 straight-chain or branched-chain polyhydroxy compound and (methyl) acrylic acid to generate an ester product; the catalyst is MOF containing a sulfonic acid group, the MOF containing the sulfonic acid group contains a transition metal and an organic ligand or an organic part derived from the organic ligand, the organic ligand contains an aromatic ring and has two or more coordination sites, and the transition metal and the organic ligand are assembled into a frame structure with pores. The method provided by the invention can achieve excellent catalytic efficiency and product yield, and has the advantages of stable catalyst activity, easy catalyst recovery, low corrosion to equipment, low wastewater yield and the like.

Description

Technical Field

[0001] This application relates to the field of chemical synthesis, and more specifically to a method for esterification reaction using polyhydroxy compounds and (meth)acrylic acid as raw materials. Background Technology

[0002] (Methacrylic esters), obtained from linear or branched polyhydroxy compounds and (meth)acrylic acid, are a class of (meth)acrylic esters with excellent properties, widely used in coatings, paints, printing, packaging, and protective materials. For example, one of the important properties of this type of ester is its radiation curing performance. Radiation curing technology is a highly efficient, energy-saving, environmentally friendly, and widely applicable material surface treatment technology, hailed as a new technology for 21st-century green industry. In recent years, radiation curing technology has developed rapidly, and its products are widely used in printing and packaging, furniture decoration, microelectronics, and telecommunications industries. With the rapid development of high-tech industries and increasing environmental protection requirements, the domestic radiation curing market has huge potential, providing broad prospects for the application of specialty acrylates.

[0003] (Meth)acrylates based on the aforementioned polyhydroxy compounds—especially dipropylene glycol diacrylate (DPGDA)—are considered novel photocurable monomers with excellent properties such as fast curing speed, low viscosity, strong dilution, and high transparency. They can be used to synthesize radiation-cured coatings, inks, and adhesives, and are widely used in the aforementioned fields, generating huge market demand.

[0004] Contrary to the huge market demand, existing synthesis processes for these acrylate monomers suffer from significant flaws, resulting in consistently unsatisfactory yields and costs. For example, current synthesis processes for such esters (e.g., DPGDA) initially used liquid acids as catalysts. However, liquid acids are prone to causing severe equipment corrosion, difficulties in catalyst recovery, and large wastewater volumes, and their catalytic activity needs further improvement. To address these issues, researchers in this field have invested considerable funds and manpower in research and development, such as attempting to improve the conditions of the esterification reaction process and developing novel catalysts (e.g., solid catalysts). However, these studies have failed to effectively solve the aforementioned problems and may even lead to further decreases in catalytic activity, poor catalyst stability, and poor overall process economics. These shortcomings have become a key bottleneck restricting the industrial application of these acrylates, and those skilled in the art urgently hope to develop a new technology to solve these problems. Summary of the Invention

[0005] To address the aforementioned problems, the inventors, through extensive and in-depth research, have developed a novel method that successfully solves long-standing issues in the prior art. Specifically, this application provides a method for carrying out esterification reactions, the method comprising, in a reaction system containing a catalyst, causing a C2-C16 straight-chain or branched polyhydroxy compound to undergo an esterification reaction with (meth)acrylic acid to generate an ester product; The catalyst is a metal-organic framework (MOF) containing sulfonic acid groups. The MOF contains a transition metal and an organic ligand or an organic moiety derived from the organic ligand. The organic ligand contains an aromatic ring and has two or more coordination sites. The transition metal and the organic ligand are assembled into a porous framework structure.

[0006] According to one embodiment of this application, in the catalyst, the transition metal is selected from one or more of the following: Zn, Cu, Fe, Co, Ni.

[0007] According to another embodiment of this application, in the catalyst, the organic ligand comprises a first organic ligand and a second organic ligand, wherein the first organic ligand is selected from one or more of the following: tetrakis(1-imidazolylphenyl)ethylene (TIPE), 1,1,2,2-tetrakis(4-(1H-imidazol-1-yl)phenyl)ethylene, 1,1,2,2-tetrakis(4-(1H-benzo[D]imidazol-1-yl)phenyl)ethylene, and 1,1,2,2-tetrakis(4-(1H-pyrazole-3-yl)phenyl)ethylene; and the second organic ligand is selected from one or more of the following: 5-sulfonic isophthalic acid, 2-sulfonic terephthalic acid, 3,3'-disulfonic-4,4'-biphenyl dicarboxylic acid, 4,8-disulfonic-2,6-dicarboxynaphthalene, and 5-sulfonic-1,2,4-benzenetricarboxylic acid.

[0008] According to another embodiment of this application, in the catalyst, the molar ratio of the transition metal to the first organic ligand is 3.5:1 to 1:1.5, and the molar ratio of the transition metal to the second organic ligand is 3:1 to 1:3.

[0009] According to another embodiment of this application, the content of sulfonic acid groups in the catalyst is 2.0-10.0% by weight, based on the total weight of the catalyst.

[0010] According to another embodiment of this application, the catalyst content is 2.0-10.0% by weight, based on the total weight of all materials in the reaction system excluding organic solvents.

[0011] According to another embodiment of this application, the C2-C16 straight-chain or branched polyhydroxy compound is selected from one or more of the following: ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, pentanediol, hexanediol, di(ethylene glycol), di(propylene glycol), and di(butanediol).

[0012] According to another embodiment of this application, in the reaction system, the molar ratio of the C2-C16 straight-chain or branched polyhydroxy compound to (meth)acrylic acid is from 1.0:1.2 to 1.0:4.0.

[0013] According to another embodiment of this application, the reaction system of the esterification reaction further includes a polymerization inhibitor selected from one or more of the following: p-hydroxyanisole, hydroquinone, 2-tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, p-benzoquinone, and methylhydroquinone.

[0014] According to another embodiment of this application, the content of the polymerization inhibitor is 0.1-0.8 by weight, based on the total weight of all materials in the reaction system excluding the organic solvent.

[0015] According to another embodiment of this application, the reaction system of the esterification reaction further includes an antioxidant, which is selected from one or more of the following: hypophosphite, sodium hypophosphite, sodium borohydride, lithium aluminum hydride, and diisobutylaluminum hydride.

[0016] According to another embodiment of this application, the antioxidant content is 0.2-1.0% by weight, based on the total weight of all materials in the reaction system excluding organic solvents.

[0017] According to another embodiment of this application, the reaction system of the esterification reaction further includes a first organic solvent, which is selected from one or more of the following: cyclohexane, benzene, toluene, xylene, n-heptane, and carbon tetrachloride.

[0018] According to another embodiment of this application, with the total weight of all materials in the reaction system excluding the organic solvent being 100 parts by weight, the content of the first organic solvent is 20 parts by weight to 150 parts by weight.

[0019] According to another embodiment of this application, the catalyst is prepared by a self-assembly reaction, the self-assembly reaction comprising: causing a transition metal source, a first organic ligand, a second organic ligand, a second organic solvent and an inorganic acid to undergo a self-assembly reaction together to generate the MOF containing sulfonic acid groups.

[0020] According to another embodiment of this application, the transition metal source is a nitrate, phosphate, sulfate, chloride, formate, acetate, or oxalate of the transition metal.

[0021] According to another embodiment of this application, the second organic solvent is selected from one or more of the following: dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetonitrile, dimethylacetamide, N-methylpyrrolidone, and diethylformamide.

[0022] According to another embodiment of this application, the inorganic acid is selected from one or more of the following: hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid.

[0023] According to another embodiment of this application, the esterification reaction is carried out at a temperature of 50-130°C.

[0024] According to another embodiment of this application, the self-assembly reaction is carried out at a temperature of 120-160°C for 40-60 hours.

[0025] In the detailed description section below, the method and (meth)acrylate product of this application will be further described in conjunction with the accompanying drawings. Attached Figure Description

[0026] Figure 1 The XRD pattern of the catalyst prepared in Example 1 of this application is shown; Figure 2 The gas chromatogram of DPGDA obtained by the esterification reaction in Example 2 of this application is shown. Detailed Implementation

[0027] The “range” disclosed in this document takes the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive and composable; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0028] In this application, unless otherwise stated, the numerical range "ab" is a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this document, and "0-5" is simply a shortened representation of these numerical combinations.

[0029] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0030] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0031] In this application, unless otherwise specified, the term "comprising" as used herein can be either open-ended or closed-ended. For example, "comprising" may mean that it may also include other components not listed, or it may only include the listed components.

[0032] One inventive aspect of this invention is the use of a metal-organic framework (MOF) compound containing a sulfonic acid group as a catalyst for the esterification reaction of C2-C16 straight-chain or branched polyhydroxy compounds with (meth)acrylic acid.

[0033] The MOF used in this invention is an organic-inorganic hybrid composite compound, in which metal ions and ligands with multiple coordination sites form the smallest structural unit (basic unit). Multiple such structural units are then orderly assembled along at least one of the X, Y, and Z directions of a Cartesian coordinate system to construct a porous material with a periodic porous network framework. The pore size of the channels in this framework can be on the nanometer scale (e.g., several nanometers, tens of nanometers, or hundreds of nanometers). Channels of this size can be called "nanopores," and composite compounds with such pore sizes can be called "nanoscale composite compounds" or "nanocomposite compounds." The pore size of the channels in the framework can also be on the micrometer scale (e.g., several micrometers, tens of micrometers, or hundreds of micrometers). Channels of this size can be called "micrometer channels," and composite compounds with such pore sizes can be called "micrometer-scale composite compounds" or "micrometer composite compounds." Depending on the specific assembly form of the structural units in the composite compound, the composite compound may also include both nanopores and micropores; in this case, the composite compound can also be called a "hybrid composite compound." Furthermore, in the basic unit of the aforementioned composite compounds, the transition metal can directly coordinate with each coordination site of the ligand, or the transition metal can act as a center, connecting with multiple atoms, atomic groups, or anions (e.g., carbonyl oxygen atoms, O atoms) surrounding the transition metal through ionic bonds, covalent bonds, or coordinate bonds. 2- S2- Cl - ,Br - I - CO, -OH, OH - (or H2O) to form a cluster structure, which is then, as described above, used together with ligands as components of the basic unit to form the composite compound of the present invention through ordered self-assembly. Examples of the cluster structure include a "metal-oxygen tetrahedral cluster" or "metal-oxygen octahedral cluster" in which a central metal cation is surrounded by oxygen anions, or at least one of the above "metal-oxygen tetrahedral cluster" or "metal-oxygen octahedral cluster" in which oxygen ions or oxygen atoms surrounding the metal cation (e.g., located at the vertices of the tetrahedral or octahedral cluster) are selected from S 2- Cl - ,Br - I - CO, CO2, -OH, OH - Cluster structures formed by the substitution of H2O anions or small molecules, etc.

[0034] According to one embodiment of this application, the transition metal in the MOF may be one or more selected from the following: Zn, Cu, Fe, Co, Ni; preferably zinc. The transition metal in the MOF is in the form of a cation, such as Zn. 2+ ion.

[0035] According to another embodiment of this application, the organic ligand in the MOF contains two or more coordination sites, i.e., groups / sites capable of forming coordination bonds with the transition metal. The coordination sites can be oxygen-containing groups, nitrogen-containing groups, sulfur-containing groups, or combinations thereof. For example, the coordination sites contained in the organic ligand can be carboxyl, hydroxyl, ester, lactone, amide, lactam, anhydride, amino, amine, mercapto, furanyl, thiophene, pyrrole, thiazolyl, imidazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, indoleyl, quinolinyl, acridineyl, etc. Preferably, the organic ligand contains one or more aromatic structures, such as phenyl, fused phenyl, heteroaryl, fused heteroaryl, etc.

[0036] According to a preferred embodiment of this application, the organic ligand includes a first organic ligand and a second organic ligand.

[0037] The first organic ligand is selected from one or more of the following: 1,1,2,2-tetra(4-(1H-imidazol-1-yl)phenyl)ethylene, tetra(1-imidazolphenyl)ethylene (TIPE), 1,1,2,2-tetra(4-(1H-benzo[D]imidazol-1-yl)phenyl)ethylene, 1,1,2,2-tetra(4-(1H-pyrazole-3-yl)phenyl)ethylene, etc. Preferably, the organic ligand is 1,1,2,2-tetra(4-(1H-imidazol-1-yl)phenyl)ethylene, which has the structure shown in Formula I:

[0038] Formula I

[0039] The second organic ligand is selected from one or more of the following: 5-sulfonic isophthalic acid, 2-sulfonic terephthalic acid, 3,3'-disulfonic-4,4'-biphenyl dicarboxylic acid, 4,8-disulfonic-2,6-dicarboxynaphthalene, and 5-sulfonic-1,2,4-benzenetricarboxylic acid; preferably, the second organic ligand is 5-sulfonic isophthalic acid.

[0040] According to one embodiment of this application, the molar ratio of the transition metal to the first organic ligand in the MOF is 3.5:1 to 1:1.5, preferably 3:1 to 1:1; the molar ratio of the transition metal to the second organic ligand is 3:1 to 1:3, preferably 2:1 to 1:2, more preferably 2:1 to 1:1. According to a preferred embodiment of this application, the molar ratio of the transition metal to the first organic ligand and the second organic ligand is 2:1:1.

[0041] According to another embodiment of this application, based on the total weight of the MOF containing sulfonic acid groups of the present invention, the content of sulfonic acid groups in the MOF is 2.0-10.0% by weight, for example 5.0-8.0% by weight, preferably 6.0-7.0% by weight. The sulfonic acid groups contained in the catalyst may exist entirely in the form of free sulfonic acid groups (-S(=O)2-OH), or a portion may exist in the form of sulfonates (e.g., sodium salts, potassium salts, ammonium salts, etc.).

[0042] According to one embodiment of this application, the catalyst can be prepared by a self-assembly reaction, the self-assembly reaction comprising: causing a transition metal source, a first organic ligand, a second organic ligand, a second organic solvent and an inorganic acid to undergo a self-assembly reaction together to generate the MOF containing sulfonic acid groups.

[0043] According to an exemplary embodiment of this application, the transition metal source is a nitrate, phosphate, sulfate, chloride, formate, acetate, or oxalate of the transition metal, and these metal salts may optionally contain water of crystallization. According to an exemplary preferred embodiment of this application, the transition metal salt may be zinc nitrate or zinc nitrate hexahydrate.

[0044] According to another embodiment of this application, the second organic solvent is selected from one or more of the following: dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetonitrile, dimethylacetamide, N-methylpyrrolidone, and diethylformamide. Based on 100 parts by weight of the total weight of the transition metal, organic ligand, and compound containing a sulfonic acid group, the total amount of the second organic solvent can be 1500-8000 parts by weight, preferably 1700-5000 parts by weight.

[0045] According to another embodiment of this application, the inorganic acid is selected from one or more of the following: hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid; preferably hydrochloric acid. Based on 100 parts by weight of the total weight of the transition metal, organic ligand, and compound containing a sulfonic acid group, the total amount of the inorganic acid can be 15-400 parts by weight, preferably 20-350 parts by weight. The concentration of the inorganic acid (in aqueous solution) can be 0.5-1.5 M, preferably 0.6-1.2 M, and more preferably 0.8-1.0 M.

[0046] According to another embodiment of this application, the reaction temperature of the self-assembly reaction can be 120-160°C, preferably 130-150°C, more preferably 140-150°C; the reaction duration is 40-60 hours, preferably 45-60 hours, more preferably 48-55 hours. According to another embodiment of this application, after the above self-assembly reaction is completed, the temperature of the reaction system is reduced to room temperature at a cooling rate of 2-8°C / hour, preferably 3-7°C / hour, more preferably 4-6°C / hour, thereby obtaining the MOF containing sulfonic acid groups.

[0047] According to one embodiment of this application, the MOF is in the form of crystals or crystalline powder, and its microstructure has nanopores, micropores, or a combination thereof.

[0048] According to an exemplary embodiment of this application, the MOF containing sulfonic acid groups is prepared using a zinc salt (e.g., zinc nitrate), 1,1,2,2-tetra(4-(1H-imidazol-1-yl)phenyl)ethylene and 5-sulfonic acid isophthalic acid, having the structure shown in Formula II.

[0049]

[0050] Formula II

[0051] In Equation II above, This is a simplified representation of "1,1,2,2-tetra(4-(1H-imidazol-1-yl)phenyl)ethylene", meaning that in the compound shown in Formula II, each Zn ion is simultaneously connected to two "1,1,2,2-tetra(4-(1H-imidazol-1-yl)phenyl)ethylene", one "5-sulfonic acid isophthalic acid", and one "nitrate". Furthermore, for clarity, it is not shown in Formula II above, but each organic ligand "1,1,2,2-tetra(4-(1H-imidazol-1-yl)phenyl)ethylene" contains four nitrogen atoms that can serve as coordination sites, each coordinated to a metal ion (e.g., a zinc ion).

[0052] According to one embodiment of this application, the MOF containing sulfonic acid groups prepared above can be used as a catalyst to carry out an esterification reaction to prepare the target ester product of the present invention.

[0053] According to one embodiment of this application, the esterification reaction includes, in a reaction system containing the catalyst described above, esterifying a C2-C16 straight-chain or branched polyhydroxy compound with (meth)acrylic acid; and the reaction system may further contain a polymerization inhibitor, an antioxidant, and a first organic solvent.

[0054] According to one embodiment of this application, the catalyst content in the reaction system is 2.0-10.0% by weight, preferably 3.0-9.0% by weight, and more preferably 5.0-8.0% by weight, based on the total weight of all materials in the reaction system excluding the first organic solvent.

[0055] According to another embodiment of this application, the C2-C16 straight-chain or branched polyhydroxy compound contains 2-4 hydroxyl groups, preferably 2-3 hydroxyl groups, more preferably two hydroxyl groups; the molecule contains 2-12 carbon atoms, preferably 2-10 carbon atoms, more preferably 2-8 carbon atoms. Specific examples of the C2-C16 straight-chain or branched polyhydroxy compound include one or more of the following: ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, pentanediol, hexanediol, di(ethylene glycol), di(propylene glycol), di(butanediol); preferably dipropylene glycol.

[0056] According to another embodiment of this application, the (meth)acrylic acid described in this invention is acrylic acid or methacrylic acid.

[0057] According to another embodiment of this application, in the reaction system, the molar ratio of C2-C16 straight-chain or branched polyhydroxy compound to (meth)acrylic acid is 1.0:1.2-1.0:4.0, preferably 1.0:1.5-1.0:3.5, and more preferably 1.0:2.0-1.0:3.0.

[0058] According to another embodiment of this application, in the reaction system, the polymerization inhibitor is selected from one or more of the following: p-hydroxyanisole, hydroquinone, 2-tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, p-benzoquinone, and methylhydroquinone; preferably p-hydroxyanisole. According to one embodiment of this application, based on the total weight of all materials in the reaction system excluding the first organic solvent, the content of the polymerization inhibitor is 0.1-0.8% by weight, preferably 0.2-0.7% by weight, and more preferably 0.3-0.6% by weight.

[0059] According to another embodiment of this application, in the reaction system, the antioxidant is selected from one or more of the following: hypophosphite, sodium hypophosphite, sodium borohydride, lithium aluminum hydride, and diisobutylaluminum hydride; preferably hypophosphite. According to one embodiment of this application, based on the total weight of all materials in the reaction system excluding the first organic solvent, the antioxidant content is 0.2-1.0% by weight, preferably 0.3-0.8% by weight, and more preferably 0.5-0.7% by weight.

[0060] According to another embodiment of this application, in the reaction system, the first solvent is selected from one or more of the following: cyclohexane, benzene, toluene, xylene, n-heptane, and carbon tetrachloride; preferably cyclohexane. According to one embodiment of this application, based on 100 parts by weight of the total weight of all materials in the reaction system excluding the organic solvent, the content of the first organic solvent is 20-150 parts by weight, preferably 30-120 parts by weight, and more preferably 50-100 parts by weight.

[0061] According to another embodiment of this application, the esterification reaction is carried out at a reaction temperature of 50-130°C, preferably 60-120°C, and more preferably 70-120°C. During the reaction, air can be continuously introduced into the reaction system as needed, and the air flow rate can be 20-100 ml / min, preferably 40-100 ml / min, and more preferably 50-80 ml / min.

[0062] After the esterification reaction is complete, the esterification product can be further processed, such as neutralization with alkali, washing with water, removing solvent by vacuum distillation, and filtration.

[0063] Not wishing to be limited to any particular theory, the method of the present invention can achieve one or more of the following advantages: the method of the present invention can achieve extremely excellent catalytic reaction efficiency and target ester product yield, the catalyst exhibits extremely high catalytic activity and stability, can be easily recovered and recycled after the reaction, and still maintains its excellent catalytic performance after multiple cycles, avoiding catalyst corrosion of reaction equipment and solving the problem of large wastewater volume.

[0064] The following embodiments illustrate the methods of this application in detail, with the aim of providing a better understanding of the content of this application. It should be understood that these embodiments are merely illustrative and not restrictive. Unless otherwise stated, the reagents used in the embodiments are commercially available. Unless otherwise specified, the methods and conditions used in the embodiments are conventional methods and conditions.

[0065] Example

[0066] All reagents used in the following examples were of analytical grade, so the water used was deionized water.

[0067] Unless otherwise stated, all percentages in the examples are by weight.

[0068] Example 1

[0069] In this embodiment, a MOF containing a sulfonic acid group was synthesized by: 6 g of 1,1,2,2-tetrakis(4-(1H-imidazol-1-yl)phenyl)ethylene, 3 g of 5-sulfonic acid isophthalic acid, and 6 g of Zn(NO3)2 6H₂O, 300 mL DMF, 50 mL DMSO, and 10 mL 1 M hydrochloric acid were added to a reaction vessel, and stirring was started to ensure thorough mixing. The temperature of the reaction vessel was then raised to 140 °C, and the reaction was continued at this temperature for 50 hours. After that, the reaction was stopped, and the temperature of the reaction vessel was lowered to room temperature at a rate of 5 °C / h to obtain a blocky crystalline product.

[0070] The crystal was characterized using X-ray diffraction techniques, such as... Figure 1 As shown, the peak positions and relative intensities of the XRD spectrum of the prepared product are basically consistent with those of the corresponding MOF in the database, thus confirming that a MOF containing free sulfonic acid groups has been obtained.

[0071] Example 2

[0072] In this embodiment, the sulfonic acid-containing MOF prepared in Example 1 was used as a catalyst for the esterification reaction.

[0073] 134 g of dipropylene glycol, 216 g of acrylic acid, 1 g of p-hydroxyanisole, 10 g of MOF particles, 1 g of hypophosphite, and 200 g of cyclohexane were added to a reaction vessel. The reaction vessel was sealed, and stirring was started. Air was continuously introduced into the reaction vessel at a flow rate of 50 mL / min. The temperature of the reaction vessel was raised to 120 °C. Reflux dehydration was continuously performed simultaneously with the reaction. After 10 hours of continuous reaction, when no more water was released, the reaction was stopped. The temperature of the reaction vessel was lowered to room temperature, and the solid MOF was separated from the reaction solution by centrifugation. The solution was washed successively with 20 wt% NaOH solution and deionized water. The collected organic phase was distilled under reduced pressure at 80 °C for 1 hour to remove the solvent, followed by filtration to obtain the liquid product. The product was characterized by gas chromatography, as shown in the figure. Figure 2 As shown, it was identified as the target product DPGDA. Based on the amount of dipropylene glycol added, the yield of the target product was calculated to be 95%.

[0074] Example 3

[0075] In this embodiment, the solid MOF recovered after the esterification reaction in Example 2 was used as a catalyst for the esterification reaction.

[0076] 134 g of dipropylene glycol, 216 g of acrylic acid, 1 g of p-hydroxyanisole, 10 g of MOF particles, 1 g of hypophosphite, and 200 g of cyclohexane were added to a reaction vessel. The reaction vessel was sealed, and stirring was started. Air was continuously introduced into the reaction vessel at a flow rate of 50 mL / min. The temperature of the reaction vessel was raised to 120 °C. Reflux dehydration was continuously performed simultaneously with the reaction. After 10 hours of continuous reaction, when no more water was released, the reaction was stopped. The temperature of the reaction vessel was lowered to room temperature, and the solid MOF was separated from the reaction solution by centrifugation. The solution was washed successively with 20 wt% NaOH solution and deionized water. The collected organic phase was distilled under reduced pressure at 80 °C for 1 hour to remove the solvent, followed by filtration to obtain the liquid product. Gas chromatography confirmed that it was the target product DPGDA. Based on the amount of dipropylene glycol added, the yield of the target product was calculated to be 94%.

[0077] Example 4

[0078] In this embodiment, the solid MOF recovered after the esterification reaction in Example 3 was used as a catalyst for the esterification reaction.

[0079] 134 g of dipropylene glycol, 216 g of acrylic acid, 1 g of p-hydroxyanisole, 10 g of MOF particles, 1 g of hypophosphite, and 200 g of cyclohexane were added to a reaction vessel. The reaction vessel was sealed, and stirring was started. Air was continuously introduced into the reaction vessel at a flow rate of 50 mL / min. The temperature of the reaction vessel was raised to 120 °C. Reflux dehydration was continuously performed simultaneously with the reaction. After 10 hours of continuous reaction, when no more water was released, the reaction was stopped. The temperature of the reaction vessel was lowered to room temperature, and the solid MOF was separated from the reaction solution by centrifugation. The solution was washed successively with 20 wt% NaOH solution and deionized water. The collected organic phase was distilled under reduced pressure at 80 °C for 1 hour to remove the solvent, followed by filtration to obtain the liquid product. Gas chromatography confirmed that it was the target product DPGDA. Based on the amount of dipropylene glycol added, the yield of the target product was calculated to be 92%.

[0080] Example 5

[0081] In this embodiment, the solid MOF recovered after the esterification reaction in Example 4 was used as a catalyst for the esterification reaction.

[0082] 134 g of dipropylene glycol, 216 g of acrylic acid, 1 g of p-hydroxyanisole, 10 g of MOF particles, 1 g of hypophosphite, and 200 g of cyclohexane were added to a reaction vessel. The reaction vessel was sealed, and stirring was started. Air was continuously introduced into the reaction vessel at a flow rate of 50 mL / min. The temperature of the reaction vessel was raised to 120 °C. Reflux dehydration was continuously performed simultaneously with the reaction. After 10 hours of continuous reaction, when no more water was released, the reaction was stopped. The temperature of the reaction vessel was lowered to room temperature, and the solid MOF was separated from the reaction solution by centrifugation. The solution was washed successively with 20 wt% NaOH solution and deionized water. The collected organic phase was distilled under reduced pressure at 80 °C for 1 hour to remove the solvent, followed by filtration to obtain the liquid product. Gas chromatography confirmed that it was the target product DPGDA. Based on the amount of dipropylene glycol added, the yield of the target product was calculated to be 89%.

[0083] Example 6

[0084] In this embodiment, the solid MOF recovered after the esterification reaction in Example 5 was used as a catalyst for the esterification reaction.

[0085] 134 g of dipropylene glycol, 216 g of acrylic acid, 1 g of p-hydroxyanisole, 10 g of MOF particles, 1 g of hypophosphite, and 200 g of cyclohexane were added to a reaction vessel. The reaction vessel was sealed, and stirring was started. Air was continuously introduced into the reaction vessel at a flow rate of 50 mL / min. The temperature of the reaction vessel was raised to 120 °C. Reflux dehydration was continuously performed simultaneously with the reaction. After 10 hours of continuous reaction, when no more water was released, the reaction was stopped. The temperature of the reaction vessel was lowered to room temperature, and the solid MOF was separated from the reaction solution by centrifugation. The solution was washed successively with 20 wt% NaOH solution and deionized water. The collected organic phase was distilled under reduced pressure at 80 °C for 1 hour to remove the solvent, followed by filtration to obtain the liquid product. Gas chromatography confirmed that it was the target product DPGDA. Based on the amount of dipropylene glycol added, the yield of the target product was calculated to be 86%.

[0086] As can be seen from Examples 2-6 above, the MOF catalyst of the present invention has excellent catalytic activity and stability, and can be easily separated from the esterification products and recycled. Even after repeated recycling five times, it can still achieve satisfactory catalytic reaction results.

[0087] Example 7

[0088] In this embodiment, the sulfonic acid-containing MOF prepared in Example 1 was used as a catalyst for the esterification reaction.

[0089] 134 g of dipropylene glycol, 180 g of acrylic acid, 1 g of p-hydroxyanisole, 10 g of MOF particles, 1 g of hypophosphite, and 200 g of cyclohexane were added to a reaction vessel. The reaction vessel was sealed, and stirring was started. Air was continuously introduced into the reaction vessel at a flow rate of 50 mL / min. The temperature of the reaction vessel was raised to 120 °C. Reflux dehydration was continuously performed simultaneously with the reaction. After 10 hours of continuous reaction, when no more water was released, the reaction was stopped. The temperature of the reaction vessel was lowered to room temperature, and the solid MOF was separated from the reaction solution by centrifugation. The solution was washed successively with 20 wt% NaOH solution and deionized water. The collected organic phase was distilled under reduced pressure at 80 °C for 1 hour to remove the solvent, followed by filtration to obtain the liquid product. Gas chromatography confirmed that it was the target product DPGDA. Based on the amount of dipropylene glycol added, the yield of the target product was calculated to be 93%.

[0090] Example 8

[0091] In this embodiment, the sulfonic acid-containing MOF prepared in Example 1 was used as a catalyst for the esterification reaction.

[0092] 134 g of dipropylene glycol, 144 g of acrylic acid, 1 g of p-hydroxyanisole, 10 g of MOF particles, 1 g of hypophosphite, and 200 g of cyclohexane were added to a reaction vessel. The reaction vessel was sealed, and stirring was started. Air was continuously introduced into the reaction vessel at a flow rate of 50 mL / min, and the temperature of the reaction vessel was raised to 120 °C. Reflux dehydration was continuously performed simultaneously with the reaction. After 10 hours of continuous reaction, when no more water was released, the reaction was stopped. The temperature of the reaction vessel was lowered to room temperature, and the solid MOF was separated from the reaction solution by centrifugation. The solution was washed successively with 20 wt% NaOH solution and deionized water. The collected organic phase was distilled under reduced pressure at 80 °C for 1 hour to remove the solvent, followed by filtration to obtain a liquid product. Gas chromatography confirmed that this was the target product DPGDA. Based on the amount of dipropylene glycol added, the yield of the target product was calculated to be 90%.

[0093] Example 9

[0094] In this embodiment, the sulfonic acid-containing MOF prepared in Example 1 was used as a catalyst for the esterification reaction.

[0095] 134 g of dipropylene glycol, 216 g of acrylic acid, 1 g of p-hydroxyanisole, 10 g of MOF particles, 1 g of hypophosphite, and 200 g of cyclohexane were added to a reaction vessel. The reaction vessel was sealed, and stirring was started. Air was continuously introduced into the reaction vessel at a flow rate of 50 mL / min. The temperature of the reaction vessel was raised to 100 °C. Reflux dehydration was continuously performed simultaneously with the reaction. After 10 hours of continuous reaction, when no more water was released, the reaction was stopped. The temperature of the reaction vessel was lowered to room temperature, and the solid MOF was separated from the reaction solution by centrifugation. The solution was washed successively with 20 wt% NaOH solution and deionized water. The collected organic phase was distilled under reduced pressure at 80 °C for 1 hour to remove the solvent, followed by filtration to obtain the liquid product. Gas chromatography confirmed that it was the target product DPGDA. Based on the amount of dipropylene glycol added, the yield of the target product was calculated to be 92%.

[0096] In all the above embodiments, no significant acid corrosion was caused to the reaction equipment, and very little wastewater was generated.

Claims

1. A method for carrying out an esterification reaction, the method comprising, in a reaction system containing a catalyst, causing a C2-C16 straight-chain or branched polyhydroxy compound to undergo an esterification reaction with (meth)acrylic acid to generate an ester product; The catalyst is a metal-organic framework (MOF) containing sulfonic acid groups. The MOF contains a transition metal and an organic ligand or an organic moiety derived from the organic ligand. The organic ligand contains an aromatic ring and has two or more coordination sites. The transition metal and the organic ligand are assembled into a porous framework structure.

2. The method of claim 1, wherein, In the catalyst, The transition metal is selected from one or more of the following: Zn, Cu, Fe, Co, Ni; The organic ligand comprises a first organic ligand and a second organic ligand, wherein the first organic ligand is selected from one or more of the following: tetrakis(1-imidazolylphenyl)ethylene (TIPE), 1,1,2,2-tetrakis(4-(1H-imidazol-1-yl)phenyl)ethylene, 1,1,2,2-tetrakis(4-(1H-benzo[D]imidazol-1-yl)phenyl)ethylene, and 1,1,2,2-tetrakis(4-(1H-pyrazole-3-yl)phenyl)ethylene; and the second organic ligand is selected from one or more of the following: 5-sulfonic acid isophthalic acid, 2-sulfonic acid terephthalic acid, 3,3'-disulfonic acid-4,4'-biphenyl dicarboxylic acid, 4,8-disulfonic acid-2,6-dicarboxynaphthalene, and 5-sulfonic acid-1,2,4-benzenetricarboxylic acid; The molar ratio of the transition metal to the first organic ligand is 3.5:1 to 1:1.5, and the molar ratio of the transition metal to the second organic ligand is 3:1 to 1:

3.

3. The method of claim 1, wherein, Based on the total weight of the catalyst, the content of sulfonic acid groups in the catalyst is 2.0-10.0% by weight. Based on the total weight of all materials in the reaction system excluding organic solvents, the content of catalyst is 2.0-10.0% by weight.

4. The method of claim 1, wherein, The C2-C16 straight-chain or branched polyhydroxy compound is selected from one or more of the following: ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, pentanediol, hexanediol, diethylene glycol, dipropylene glycol, and dibutanediol. In the reaction system, the molar ratio of the C2-C16 straight-chain or branched polyhydroxy compound to (meth)acrylic acid is from 1.0:1.2 to 1.0:4.

0.

5. The method of claim 1, wherein, The reaction system of the esterification reaction also includes a polymerization inhibitor, which is selected from one or more of the following: p-hydroxyanisole, hydroquinone, 2-tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, p-benzoquinone, and methylhydroquinone; Based on the total weight of all materials in the reaction system excluding organic solvents, the content of the polymerization inhibitor is 0.1-0.8% by weight.

6. The method of claim 1, wherein, The reaction system of the esterification reaction also includes an antioxidant, which is selected from one or more of the following: hypophosphite, sodium hypophosphite, sodium borohydride, lithium aluminum hydride, and diisobutylaluminum hydride. Based on the total weight of all materials in the reaction system excluding organic solvents, the content of antioxidant is 0.2-1.0 by weight.

7. The method of claim 1, wherein, The reaction system of the esterification reaction further includes a first organic solvent, which is selected from one or more of the following: cyclohexane, benzene, toluene, xylene, n-heptane, and carbon tetrachloride; Based on a total weight of 100 parts by weight of all materials in the reaction system excluding the organic solvent, the content of the first organic solvent is 20-150 parts by weight.

8. The method of any one of claims 1-3, wherein, The catalyst is prepared by a self-assembly reaction, which includes: causing a transition metal source, a first organic ligand, a second organic ligand, a second organic solvent, and an inorganic acid to undergo a self-assembly reaction together to generate the MOF containing sulfonic acid groups.

9. The method of claim 8, wherein, The transition metal source is a nitrate, phosphate, sulfate, chloride, formate, acetate, or oxalate of the transition metal; The second organic solvent is selected from one or more of the following: dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetonitrile, dimethylacetamide, N-methylpyrrolidone, and diethylformamide; The inorganic acid is selected from one or more of the following: hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid.

10. The method as claimed in claim 1 or claim 8, characterized in that, The esterification reaction is carried out at a temperature of 50-130°C; The self-assembly reaction was carried out at 120-160°C for 40-60 hours.

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