A method for preparing methyl methoxyacetate by the carbonylation of formaldehyde

Abstract

The present invention provides a method for preparing methyl methoxyacetate by the carbonylation of formaldehyde. The method comprises: (1) contacting formaldehyde with a CO-containing gas in a mixed solution system comprising a rhodium carbonyl compound, an organic solvent and an ionic liquid to carry out a carbonylation reaction; (2) contacting the obtained methoxyacetic acid with methanol to carry out an esterification reaction to form methyl methoxyacetate; the structure of the ionic liquid is shown in formula (I): wherein, in formula (I), n = 7-21, X ‑ is CH3SO3 ‑ . In the method of the present invention, an organic solvent phase containing the product and an ionic liquid phase containing the catalyst can be separately obtained by simple phase separation, the product separation step is omitted, and the catalyst can be directly recycled.

Description

Technical Field

[0001] The present invention relates to the field of petrochemical industry, and particularly to a method for preparing methyl methoxyacetate by formaldehyde carbonylation carried out in an acid-functionalized ionic liquid two-phase system. Background Art

[0002] The carbonylation of formaldehyde and its derivatives is an important research direction in C1 chemistry. This route uses formaldehyde and its derivatives derived from coal, natural gas or biomass as raw materials to produce ethylene glycol, which is one of the important alternatives to the existing ethylene glycol processes. Methyl methoxyacetate, one of the carbonylation products, is a very valuable intermediate, which can be used for the kinetic resolution of chiral amine compounds, the synthesis of vitamin B6 and sulfanilamide-5-pyrimidine, etc., as a catalyst in polymerization reactions, and can also be hydrogenated and hydrolyzed to produce ethylene glycol.

[0003] The main technical difficulties in the carbonylation reaction are slow reaction rate and low selectivity. There are two reasons for the slow reaction rate: ① lack of an efficient catalyst system, ② the CO concentration in the solution or at the reaction site is not high, and mass transfer is difficult. Due to the difficulty in developing highly active catalysts, methods such as increasing temperature and pressure and prolonging the reaction time are usually used to improve the reaction effect, while the harsh reaction conditions exacerbate the problems of many side reactions and low selectivity. Therefore, the core of the carbonylation reaction research lies in two aspects: catalyst development and reaction process intensification, and the optimization of the reaction is achieved by using a novel highly active catalyst and adjusting the reaction system. Summary of the Invention

[0004] Aiming at the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing methyl methoxyacetate by formaldehyde carbonylation carried out in an acid-functionalized ionic liquid two-phase system. This method not only has no corrosion to the reaction equipment by the catalyst, but also can directly separate the carbonylation product from the catalyst through liquid-liquid phase separation after the carbonylation reaction, and recycle the catalyst, effectively reducing the energy consumption of the separation process and saving the production cost, providing a new idea for solving the problem of complex separation in homogeneous reactions.

[0005] Traditional homogeneous methods mainly use inorganic liquid acids as catalysts, such as concentrated sulfuric acid, hydrofluoric acid, fluorosulfonic acid, etc. There are generally problems such as difficult product separation and liquid acid corrosion of the device. Although various solid acids developed (such as molecular sieves, heteropolyacids, ion exchange resins, etc.) have less corrosion and are easy to separate, their catalytic activity and recycling performance still need to be improved. In addition, immobilizing highly active catalysts can also achieve simple separation and recovery of the catalysts, but there may be phenomena such as loss of active components and decline in catalytic performance during recycling.

[0006] Ionic liquids have attracted increasing attention and been applied in some carbonylation reactions due to their many advantages that traditional solvents do not have and their application as green solvents in the synthesis of organic and polymeric substances. For example, in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate system, methyl glycolate can be synthesized using methylbenzenesulfonic acid and CF3SO3Ag as catalysts. However, in such reaction systems, there are still problems of unsatisfactory product selectivity and difficult separation and recovery of catalysts. How to effectively combine the advantages of high activity of homogeneous acid catalysts and the characteristics of easy recovery and reuse of heterogeneous catalysts to develop new catalysts, ensuring both mass transfer efficiency and easy separation and recovery of catalysts, has become the focus of carbonylation research.

[0007] According to the foregoing theoretical analysis, the present invention provides a method for preparing methyl methoxyacetate by the carbonylation of formaldehyde, which method comprises:

[0008] (1) In a mixed solution system comprising a rhodium carbonyl compound, an organic solvent and an ionic liquid, bringing formaldehyde into contact with a CO-containing gas to carry out a carbonylation reaction;

[0009] (2) Bringing the obtained methoxyacetic acid into contact with methanol to carry out an esterification reaction to form methyl methoxyacetate;

[0010] The ionic liquid has a structure as shown in formula (I):

[0011]

[0012] wherein in formula (I), n = 7-21, and X - is CH3SO3 - .

[0013] The method of the present invention is used for the carbonylation of formaldehyde to synthesize methyl methoxyacetate, and the catalytic system is non-corrosive to the reaction equipment. The present invention adopts a specific acid-functionalized ionic liquid two-phase system, and after the carbonylation reaction, the direct separation of the carbonylation product and the catalyst and the recycling of the catalyst can be realized through automatic liquid layering, effectively reducing the energy consumption of the separation process and saving the production cost.

[0014] The method of the present invention has the characteristics of high product yield, non-corrosion of the reaction equipment, easy separation and recycling of the catalyst, etc.

[0015] The method of the present invention can separately obtain an organic solvent phase containing the product and an ionic liquid phase containing the catalyst through simple phase separation, eliminating the product separation step, and the catalyst can be directly recycled. Specific Embodiments

[0016] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0017] The present invention provides a method for preparing methyl methoxyacetate by the carbonylation of formaldehyde, which method comprises:

[0018] (1) In a mixed solution system comprising a rhodium carbonyl compound, an organic solvent and an ionic liquid, bringing formaldehyde into contact with a CO-containing gas to carry out a carbonylation reaction;

[0019] (2) Bringing the obtained methoxyacetic acid into contact with methanol to carry out an esterification reaction to form methyl methoxyacetate;

[0020] The ionic liquid has a structure as shown in formula (I):

[0021]

[0022] wherein, in formula (I), n = 7-21, X - is CH3SO3 - . The method of the present invention has the characteristics of high product yield, no corrosion of reaction equipment, easy separation and recycling of the catalyst, etc.

[0023] According to a preferred embodiment of the present invention, the method comprises:

[0024] (1) In a mixed solution system comprising a rhodium carbonyl compound, an organic solvent and an ionic liquid, bringing formaldehyde into contact with a CO-containing gas to carry out a carbonylation reaction, and the reaction system is automatically separated into an upper organic phase and a lower ionic liquid phase;

[0025] (2) Bringing the obtained upper organic phase into contact with methanol to carry out an esterification reaction to form methyl methoxyacetate.

[0026] According to the method of the present invention, preferably the method further comprises: recovering the lower ionic liquid phase for use as a raw material for the ionic liquid and the rhodium carbonyl compound.

[0027] The present invention adopts a specific acid-functionalized ionic liquid two-phase system, and after the carbonylation reaction, the direct separation of the carbonylation product from the catalyst and the recycling of the catalyst can be realized through automatic liquid stratification, effectively reducing the energy consumption of the separation process and saving the production cost.

[0028] According to a more preferred embodiment of the present invention, preferably the mass fraction of the ionic liquid in the mixed solution system is 5-20 wt%. Thereby, the direct separation of the carbonylation product from the catalyst can be better realized, and at the same time, the product yield is increased.

[0029] In the present invention, ionic liquids satisfying the aforementioned structure of the present invention can all achieve the object of the present invention. Specifically, the types of ionic liquids have little influence on the results of the present invention, and can all achieve the direct separation of the carbonylation product and the catalyst, while improving the product yield.

[0030] In the present invention, the ionic liquid can be purchased or synthesized by itself. The preferred synthesis method includes: under the protection of an inert gas and under ice bath conditions, stirring and contacting polyethylene glycol monomethyl ether, triethylamine, toluene, and methylsulfonyl chloride to obtain a toluene solution of polyethylene glycol methyl sulfonate, removing the solvent to obtain polyethylene glycol methyl sulfonate, then adding an excessive amount of diethylamine, heating and reacting under pressure conditions, then adding 1,3-propane sultone and heating and stirring to react, and performing vacuum distillation to remove water and the solvent to obtain the target ionic liquid.

[0031] According to a preferred embodiment of the present invention, the synthesis method of the ionic liquid includes: placing 0.06 mol of polyethylene glycol monomethyl ether in a round bottom flask, adding 0.1 mol of triethylamine and 200 mL of toluene under nitrogen protection, dropwise adding 0.12 mol of methylsulfonyl chloride in an ice bath, stirring for 3 hours and then standing still. The upper clear liquid is the toluene solution of polyethylene glycol methyl sulfonate; adding the polyethylene glycol methyl sulfonate from which the solvent has been removed to an excessive amount of diethylamine, heating and stirring to react for 4 hours in the nitrogen atmosphere of a high-pressure reaction kettle; adding an equal amount of 1,3-propane sultone to the mixture in the previous step, heating and stirring to react at 50 °C for 4 hours, and after the reaction is completed, performing vacuum distillation to remove water and the solvent to obtain the target ionic liquid.

[0032] In the present invention, the types of rhodium carbonyl compounds have a relatively wide selection range. According to a more preferred embodiment of the present invention, the rhodium carbonyl compound is selected from one or more of rhodium(II) acetylacetonate dicarbonyl, carbonylchlorobis(triphenylphosphine)rhodium(I), hydridocarbonyltris(triphenylphosphine)rhodium(I), dichlorodirhodium tetracarbonyl, and triphenylphosphineacetylacetonatorhodium(I) carbonyl, preferably one or more of hydridocarbonyltris(triphenylphosphine)rhodium(I), rhodium(II) acetylacetonate dicarbonyl, and carbonylchlorobis(triphenylphosphine)rhodium(I). According to the present invention, hydridocarbonyltris(triphenylphosphine)rhodium(I) is preferred.

[0033] In the present invention, the types of organic solvents have a relatively wide selection range. For the present invention, it is preferred that the organic solvent is selected from one or more of benzene, toluene, ethylbenzene, xylene, sulfolane, cyclopentane, cyclohexane, and cycloheptane. According to the present invention, it is preferred that the organic solvent is selected from one or more of toluene, cyclohexane, sulfolane, and cycloheptane, and more preferably a mixture of toluene and cyclohexane and / or cycloheptane. The weight ratio of toluene to cyclohexane and / or cycloheptane is 0.3 - 3:1, preferably 0.9 - 2:1.

[0034] According to a more preferred embodiment of the present invention, the organic solvent is preferably toluene: cyclohexane = 0.3 - 3:1, preferably 0.9 - 2:1.

[0035] In the present invention, preferably, the amount of the rhodium carbonyl compound used is 0.1 mol% - 1 mol% of the feed amount of the formaldehyde monomer source substance in terms of moles.

[0036] In the present invention, the conditions for the carbonylation reaction in step (1) include: the temperature is 80 - 140 °C, the pressure is 4 - 8 MPa, and the amount of the rhodium carbonyl compound used is 0.1 - 1 mol% of the formaldehyde feed amount.

[0037] In the present invention, the conditions for the carbonylation reaction in step (1) include: the reaction time is 2 - 6 h.

[0038] In the present invention, the conditions for the esterification reaction in step (2) include: the temperature is 80 - 120 °C, and the time is 1 - 4 h.

[0039] According to the present invention, preferably, the esterification catalyst is one or more of solid acid, heteropolyacid, molecular sieve and cation exchange resin, and more preferably Amberlite resin and / or Purolite resin.

[0040] According to the preferred embodiment of the present invention, the feed amount of methanol is in excess relative to the theoretical feed molar amount of formaldehyde.

[0041] In the present invention, preferably, the CO-containing gas is CO.

[0042] According to the present invention, the formaldehyde is provided as an aqueous formaldehyde solution, and preferably the concentration of the aqueous formaldehyde solution is 40 - 60% by weight.

[0043] In the present invention, after the reaction in step (1) is completed and cooled to room temperature, the mixture becomes a liquid-liquid two-phase system. The upper layer is the organic solvent phase dissolved with the carbonylation product, and the lower layer is the ionic liquid phase loaded with rhodium carbonyl. The upper layer product can be separated from the system by simple phase separation and sent to the next esterification reaction to obtain methyl methoxyacetate product. The lower layer mixture is an ionic liquid and a catalyst, which can be recycled multiple times.

[0044] In the present invention, the rhodium carbonyl compound and the organic solvent in step (1) can be fresh rhodium carbonyl or rhodium carbonyl from the ionic liquid recovered during the reaction process. The separated ionic liquid and the ionic liquid phase of rhodium carbonyl can be directly added to step (1) for recycling.

[0045] The present invention provides a method for preparing methyl methoxyacetate by carbonylation of formaldehyde, which method comprises the following steps:

[0046] (1) Formaldehyde monomer source material and CO undergo a carbonylation reaction in a mixed solution system of acid-functionalized ionic liquid;

[0047] (2) The organic solvent phase containing the product obtained in step (1) is separated, and methanol is added to carry out an esterification reaction to produce methyl methoxyacetate;

[0048] (3) The ionic liquid phase containing the catalyst obtained in step (1) is separated, and the ionic liquid phase containing the catalyst is recycled and reused.

[0049] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited to the following description.

[0050] For those not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0051] In the present invention, the product obtained is expressed by the yield of methyl methoxyacetate, and the by-products are glycolic acid (ester) and methyl formate. The calculation method of the product yield is as follows:

[0052] Yield of methyl methoxyacetate (%) = Molar generation amount of methyl methoxyacetate / Molar amount of raw material formaldehyde × 100%.

[0053] The calculation method of the by-products in the present invention is as follows:

[0054] Yield of glycolic acid (ester) (%) = Molar generation amount of glycolic acid (ester) (theoretical value) / Molar amount of raw material formaldehyde × 100%;

[0055] Among them, the molar generation amount of glycolic acid (ester) (theoretical value) is the amount that can be converted into effective intermediates in all theoretically hydrogenation-to-ethylene glycol steps, that is, the products of glycolic acid, methyl glycolate, and organic carboxylic acids in the solvent protecting glycolic acid (ester);

[0056] Yield of methyl formate (%) = Molar amount of methyl formate / Feed amount of formaldehyde × 100%

[0057] Example 1

[0058] 1. Synthesis of ionic liquid

[0059] Under nitrogen protection, 0.06 mol of polyethylene glycol monomethyl ether, 0.1 mol of triethylamine, and 200 mL of toluene are added. 0.12 mol of methylsulfonyl chloride is added dropwise in an ice bath. After stirring for 3 hours, it is left to stand. The upper clear liquid is taken to remove the solvent toluene, and it is added to an excess of diethylamine. It is heated and stirred in a nitrogen atmosphere in a high-pressure reaction kettle for 4 hours; an equal amount of 1,3-propane sultone is added, and it is heated and stirred at 50 °C for 4 hours. After the reaction is completed, water and the solvent are removed by vacuum distillation to obtain ionic liquid I.

[0060] 2. Carbonylation reaction

[0061] Weigh 0.185 g (0.2 mmol, n CAT / HCHO = 0.2%) of rhodium hydridocarbonyltris(triphenylphosphine) in a glove box and load it into a 100 mL stainless steel high-pressure reactor. Then, successively add 4 g of ionic liquid I, 14 g of toluene, 8 g of cyclohexane, and 5.45 g (0.1 mol HCHO) of 55 wt% aqueous formaldehyde solution. Seal the reactor, displace the air in the reactor with CO three times, introduce high-pressure CO to 8 MPa, and react at 110 °C for 3 hours. After the reaction is completed, cool the reactor to room temperature. Under the protection of nitrogen, use a syringe to suck out the upper organic phase, and the lower ionic liquid phase is retained in the reactor for direct recycling.

[0062] 3. Esterification reaction

[0063] Put the upper organic phase filtered by a microporous filter membrane into another reactor, add 10 mL of methanol and 1 g of Amberlite IR 120 resin, seal the reactor, and react with stirring at 100 °C for 2 hours. After the reaction is completed, cool the reactor to room temperature, take out the liquid in the reactor, and analyze it by gas chromatography and high-performance liquid chromatography. The yields of methyl methoxyacetate and glycolic acid (ester) are shown in Table 1.

[0064] By using this method, after the carbonylation reaction, the direct separation of the organic product (upper layer) from the ionic liquid-catalyst (lower layer) can be achieved, and the direct recycling of the catalyst is realized.

[0065] Repeat the reaction steps of Example 1, where the rhodium carbonyl catalyst and the ionic liquid are left in the reactor for repeated use. The catalytic effects of repeated use are shown in Table 1. It shows that this reaction system can achieve multiple recycling of the catalyst.

[0066] Table 1 Product yields when the ionic liquid and catalyst are recycled

[0067]

[0068] Example 2

[0069] The dosage of the ionic liquid is 5 wt%; the weight ratio of the organic solvents toluene and cycloheptane is 1:1, and the carbonylation reaction conditions are 140 °C and 6 MPa;

[0070] 1. Carbonylation reaction

[0071] Weigh 0.185 g (0.2 mmol, CAT / HCHO = 0.2%) of tris(triphenylphosphine)rhodium(I) hydride carbonyl and load it into an autoclave. Then, successively add 1 g of ionic liquid I, 9 g of toluene, 9 g of cycloheptane, and 5.45 g of 55 wt% aqueous formaldehyde solution (0.1 mol HCHO). Seal the reaction kettle, displace the air in the kettle with CO, introduce high-pressure CO to 6 MPa, and react at 140 °C for 3 hours. After the reaction is completed, cool it to room temperature and take the upper organic phase.

[0072] 2. Esterification reaction

[0073] Put the upper organic phase filtered through a microporous membrane into another reaction kettle, add 10 mL of methanol and 1 g of Amberlite resin, and react at 100 °C for 2 hours. After the reaction is completed, cool it to room temperature. The yields of methyl methoxyacetate and glycolic acid (ester) are shown in Table 2.

[0074] Example 3

[0075] The dosage of ionic liquid is 20 wt%; the organic solvent is sulfolane, and the carbonylation reaction conditions are 80 °C and 8 MPa;

[0076] 1. Carbonylation reaction

[0077] Weigh 0.185 g (0.2 mmol, CAT / HCHO = 0.2%) of tris(triphenylphosphine)rhodium(I) hydride carbonyl and load it into an autoclave. Then, successively add 4 g of ionic liquid I, 16 g of sulfolane, and 5.45 g of 55% aqueous formaldehyde solution (0.1 mol HCHO). Seal the reaction kettle, displace the air in the kettle with CO, introduce high-pressure CO to 8 MPa, and react at 80 °C for 3 hours. After the reaction is completed, cool it to room temperature and take the upper organic phase.

[0078] 2. Esterification reaction

[0079] Put the upper organic phase filtered through a microporous membrane into another reaction kettle, add 10 mL of methanol and 1 g of Purolite resin, and react at 100 °C for 2 hours. After the reaction is completed, cool it to room temperature. The yields of methyl methoxyacetate and glycolic acid (ester) are shown in Table 2.

[0080] Example 4

[0081] The rhodium carbonyl used is rhodium(II) acetylacetonate dicarbonyl, and the others are the same as in Example 1.

[0082] 1. Carbonylation reaction

[0083] Weigh 0.1 g of rhodium(II) acetylacetonate (0.4 mmol, CAT / HCHO = 0.4%) and place it in an autoclave. Then, sequentially add 4 g of ionic liquid I, 14 g of toluene, 8 g of cyclohexane, and 5.45 g of 55% aqueous formaldehyde solution (0.1 mol HCHO). Seal the reaction kettle, displace the air in the kettle with CO, introduce high-pressure CO to 8 MPa, and react at 110 °C for 3 hours. After the reaction is completed, cool it to room temperature and take the upper organic phase.

[0084] 2. Esterification reaction

[0085] Put the upper organic phase filtered through a microporous membrane into another reaction kettle, add 10 mL of methanol and 1 g of Amberlite resin, and react at 100 °C for 2 hours. After the reaction is completed, cool it to room temperature. The yields of methyl methoxyacetate and glycolic acid (ester) are shown in Table 2.

[0086] Example 5

[0087] The rhodium carbonyl used is dichlorocarbonylbis(triphenylphosphine)rhodium(I), and the others are the same as in Example 1.

[0088] 1. Carbonylation reaction

[0089] Weigh 0.138 g of dichlorocarbonylbis(triphenylphosphine)rhodium(I) (0.2 mmol, CAT / HCHO = 0.2%) and place it in an autoclave. Then, sequentially add 4 g of ionic liquid I, 14 g of toluene, 8 g of cyclohexane, and 5.45 g of 55% aqueous formaldehyde solution (0.1 mol HCHO). Seal the reaction kettle, displace the air in the kettle with CO, introduce high-pressure CO to 8 MPa, and react at 110 °C for 3 hours. After the reaction is completed, cool it to room temperature and take the upper organic phase.

[0090] 2. Esterification reaction

[0091] Put the upper organic phase filtered through a microporous membrane into another reaction kettle, add 10 mL of methanol and 1 g of Amberlite resin, and react at 100 °C for 2 hours. After the reaction is completed, cool it to room temperature. The yields of methyl methoxyacetate and glycolic acid (ester) are shown in Table 2.

[0092] Example 6

[0093] The rhodium carbonyl used is hydridocarbonyltris(triphenylphosphine)rhodium(I), and the molar ratio of the catalyst to the reactant formaldehyde is 1%, and the others are the same as in Example 1.

[0094] 1. Carbonylation reaction

[0095] Weigh 0.918 g of tris(triphenylphosphine)rhodium(I) hydride carbonyl (1 mmol, CAT / HCHO = 1%) and place it into an autoclave. Then, successively add 4 g of ionic liquid I, 14 g of toluene, 8 g of cyclohexane, and 5.45 g of 55% aqueous formaldehyde solution (0.1 mol HCHO). Seal the reaction kettle, displace the air in the kettle with CO, introduce high-pressure CO to 8 MPa, and react at 110 °C for 3 hours. After the reaction is completed, cool it to room temperature and take the upper organic phase.

[0096] 2. Esterification reaction

[0097] Put the upper organic phase filtered through a microporous membrane into another reaction kettle, add 10 mL of methanol and 1 g of resin, and react at 100 °C for 2 hours. After the reaction is completed, cool it to room temperature. The yields of methyl methoxyacetate and glycolic acid (ester) are shown in Table 2.

[0098] Table 2 Product yields of the examples

[0099]

[0100] Comparative Example 1

[0101] In this comparative example, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, an ionic liquid without separation effect after reaction, was used as the catalyst.

[0102] 1. Carbonylation reaction

[0103] In a 100 mL stainless steel high-pressure reaction kettle, successively add 2 g of 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 20 mL of a mixed solvent of cyclohexane:acetic acid = 5:1 (molar ratio), and 3 g of paraformaldehyde (0.1 mol HCHO). Seal the reaction kettle, displace the air in the kettle with CO three times, introduce high-pressure CO to 8 MPa, and react at 110 °C for 3 h. After the reaction is completed, cool the reaction kettle to room temperature, take out all the reaction liquid and place it in a separating funnel, and the liquid does not separate.

[0104] 2. Esterification reaction

[0105] Put all the liquid after the carbonylation reaction into the reaction kettle, add 20 mL of methanol and 1 g of Amberlite IR 120 resin, seal the reaction kettle, and react with stirring at 100 °C for 2 h. After the reaction is completed, cool the reaction kettle to room temperature, take out the material liquid in the kettle, and analyze it by gas chromatography and high-performance liquid chromatography. The yields of methyl methoxyacetate and glycolic acid (ester) are shown in Table 3.

[0106] As can be seen from this comparative example, using the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate without post-reaction separation effect as the catalyst, the product after the carbonylation reaction does not separate into layers, and products such as glycolic acid and methoxyacetic acid and the solvent all enter the next esterification reaction together, increasing the throughput of the esterification step and subsequent distillation and other operations. In addition, after purification steps such as distillation and methanol washing, part of the methanol is mixed into the solvent (acetic acid, propionic acid, isobutyric acid), causing difficulties in the recycling of the solvent.

[0107] Comparative Example 2

[0108] In this comparative example, tris(triphenylphosphine)rhodium hydride carbonyl is directly used as the catalyst.

[0109] 1. Carbonylation reaction

[0110] In a 100 mL stainless steel high-pressure reactor, add 8.1 g of aqueous formaldehyde solution (0.1 mol HCHO) and 30 mL of a mixed solvent of cyclohexane:isobutyric acid = 5:1 (molar ratio). Quickly weigh 0.185 g of tris(triphenylphosphine)rhodium hydride carbonyl (0.2 mmol, CAT / HCHO = 0.2%) and load it into the reactor. After fully stirring and mixing evenly, seal the reactor, displace the air in the reactor with CO 3 times, introduce high-pressure CO to 8 MPa, and react at 110 °C for 3 h. After the reaction is completed, cool the reactor to room temperature, take out all the reaction liquid and place it in a separating funnel, let it stand until it separates into layers, and filter the lower dark liquid through a microporous filter membrane to obtain a light brownish-yellow carbonylation product for standby.

[0111] 2. Esterification reaction

[0112] Put the filtered lower-layer carbonylation product into the reactor, add 20 mL of methanol and 1 g of Amberlite IR 120 resin, seal the reactor, and react under stirring at 100 °C for 2 h. After the reaction is completed, cool the reactor to room temperature, take out the liquid in the reactor, and analyze it by gas chromatography and high-performance liquid chromatography. The yields of the products methyl methoxyacetate and glycolic acid (ester) are shown in Table 3.

[0113] As can be seen from this comparative example, directly using rhodium carbonyl as the catalyst can obtain a relatively high product yield, but the recycling of the catalyst cannot be achieved.

[0114] Comparative Example 3

[0115] In this comparative example, HZSM-5 molecular sieve is used as the catalyst

[0116] 1. Carbonylation reaction

[0117] In a 100 mL stainless steel high-pressure reactor, 3 g of paraformaldehyde (0.1 mol HCHO), 2 g of HZSM-5 molecular sieve, and 20 mL of a mixed solvent of sulfolane:acetic acid = 1:1 were added. After stirring well and mixing evenly, the reactor was sealed. The air in the reactor was replaced with CO three times, and then high-pressure CO was introduced to 8 MPa. The reaction was carried out at 110 °C for 3 h. After the reaction, the reactor was cooled to room temperature, and the liquid in the reactor was filtered out as the carbonylation product for standby, and the solid catalyst was recovered.

[0118] 2. Esterification reaction

[0119] The carbonylation product was put into the reactor, 20 mL of methanol and 1 g of Amberlite IR 120 resin were added. The reactor was sealed and the reaction was carried out with stirring at 100 °C for 2 h. After the reaction, the reactor was cooled to room temperature, and the liquid in the reactor was taken out and analyzed by gas chromatography and high performance liquid chromatography. The yields of the products methyl methoxyacetate and glycolic acid (ester) are shown in Table 3.

[0120] It can be seen from this comparative example that although the use of a solid acid catalyst can achieve the recovery of the catalyst, due to the limitation of mass transfer in the gas-liquid-solid three-phase reaction, the reaction efficiency is low and the product yield is not ideal.

[0121] Comparative Example 4

[0122] 1. Carbonylation reaction

[0123] 0.185 g of tris(triphenylphosphine)rhodium hydride carbonyl (CAT / HCHO = 0.2%) was weighed and loaded into a stainless steel high-pressure reactor. Subsequently, 4 g of ionic liquid quaternary ammonium salt [(C2H5)3N(CH2CH2O) n CH3] + [CH3SO3] - 15 g of toluene, 5 g of n-heptane, and 5 g of 55% formaldehyde solution were added successively. The reactor was sealed, the air in the reactor was replaced with CO three times, and then high-pressure CO was introduced to 8 MPa. The reaction was carried out at 120 °C for 3 hours. After the reaction, the reactor was cooled to room temperature.

[0124] 2. Esterification reaction

[0125] The upper organic phase filtered through a microporous membrane was put into another reactor, 10 mL of methanol and 1 g of Amberlite IR 120 resin were added. The reactor was sealed and the reaction was carried out with stirring at 100 °C for 2 hours. After the reaction, the liquid in the reactor was taken out and analyzed by gas chromatography and high performance liquid chromatography. The product yields are shown in Table 3.

[0126] As can be seen from Table 3, the yield of methyl methoxyacetate in Comparative Example 4 is lower than that in the Examples, which confirms the necessity of the presence of sulfonic acid groups in the ionic liquid phase. That is, only by using a specific acid-functionalized ionic liquid two-phase system can a high reaction yield and easy separation and recovery of the catalyst be achieved.

[0127] Product Yields of Comparative Examples in Table 3

[0128]

[0129] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention as provided, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing methyl methoxyacetate by the carbonylation of formaldehyde, characterized in that, The method comprises: (1) In a mixed solution system comprising a rhodium carbonyl compound, an organic solvent and an ionic liquid, bringing formaldehyde into contact with a CO-containing gas to carry out a carbonylation reaction; (2) Bringing the obtained methoxyacetic acid into contact with methanol to carry out an esterification reaction to form methyl methoxyacetate; The ionic liquid has a structure as shown in formula (I): Among them, in formula (I), n = 7 - 21, X - is CH3SO3 - ; The rhodium carbonyl compound is selected from one or more of rhodium acetylacetonate dicarbonyl, carbonylrhodium(III) chloride bis(triphenylphosphine), hydridocarbonyltris(triphenylphosphine)rhodium(I), dichlorodirhodium tetracarbonyl and rhodium(III) acetylacetonate carbonyltriphenylphosphine; The organic solvent is selected from one or more of benzene, toluene, ethylbenzene, xylene, sulfolane, cyclopentane, cyclohexane and cycloheptane.

2. The method according to claim 1, wherein, The method comprises: (1) In a mixed solution system comprising a rhodium carbonyl compound, an organic solvent and an ionic liquid, bringing formaldehyde into contact with a CO-containing gas to carry out a carbonylation reaction, and the reaction system is automatically separated into an upper organic phase and a lower ionic liquid phase; (2) Bringing the obtained upper organic phase into contact with methanol to carry out an esterification reaction to form methyl methoxyacetate.

3. The method according to claim 2, wherein, The method further comprises: recovering the lower ionic liquid phase for use as a raw material for the ionic liquid and the rhodium carbonyl compound.

4. The method according to claim 1 or 2, wherein, The mass fraction of the ionic liquid in the mixed solution system is 5-20 wt%.

5. The method according to claim 1 or 2, wherein The rhodium carbonyl compound is one or more of hydridocarbonyltris(triphenylphosphine)rhodium(I), rhodium acetylacetonate dicarbonyl and carbonylrhodium(III) chloride bis(triphenylphosphine).

6. The method according to claim 5, wherein, The rhodium carbonyl compound is hydridocarbonyltris(triphenylphosphine)rhodium(I).

7. The method according to claim 1 or 2, wherein The organic solvent is a mixture of toluene and cyclohexane and / or cycloheptane, and the weight ratio of toluene to cyclohexane and / or cycloheptane is 0.3-3:

1.

8. The method according to claim 7, wherein The weight ratio of toluene to cyclohexane and / or cycloheptane is 0.9-2:

1.

9. The method according to claim 1 or 2, wherein The conditions of the carbonylation reaction in step (1) include: The temperature is 80-140 °C, the pressure is 4-8 MPa, and the usage amount of the rhodium carbonyl compound is 0.1-1 mol% of the formaldehyde feed amount.

10. The method according to claim 1 or 2, wherein The conditions of the esterification reaction in step (2) include: the temperature is 80-120 °C, the time is 1-4 h, and the esterification catalyst is one or more of solid acid, heteropolyacid, molecular sieve and cation exchange resin.

11. The method according to claim 10, wherein, The esterification catalyst in step (2) is Amberlite resin and / or Purolite resin.

12. According to the method of claim 1 or 2, wherein, The CO-containing gas is CO; and / or The formaldehyde is provided as an aqueous formaldehyde solution.

13. According to the method of claim 12, wherein, The concentration of the aqueous formaldehyde solution is 40-60 wt%.

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