Preparation method of methyl acetate by taking methanol and formaldehyde as raw materials and reaction system

Abstract

The invention discloses a methyl acetate preparation method and a reaction system using methanol and formaldehyde as raw materials, the method uses methanol and formaldehyde as raw materials, a catalyst is an A-B / SiC catalyst prepared by using silicon carbide as a carrier, A is selected from Pt and Cu, and B is selected from Al2O3 and CeO2. The method can reduce the corrosion of an acid catalyst to a reactor and the dependence on acetic acid in a reactive distillation method, consumes redundant formaldehyde in the industry and the environment, and reduces the pollution to the environment. Therefore, the method has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of compound preparation, and particularly relates to a preparation method and a reaction system for methyl acetate using methanol and formaldehyde as raw materials. Background Art

[0002] Methyl acetate, also known as methyl acetate, is an important chemical raw material and is widely used in the preparation of acetic acid, ethanol and their derivatives.

[0003] At present, the preparation methods of methyl acetate include acetic acid methanol dehydration condensation, dimethyl ether carbonylation method, methanol carbonylation method, synthesis gas method, etc.

[0004] The method of dehydration condensation of acetic acid and methanol (EP473688A) uses concentrated sulfuric acid as the catalyst, which corrodes equipment and pollutes the environment. In addition, due to strong oxidizing properties and dehydration, a series of side reactions are generated, and subsequent treatment is complicated. In addition, the raw material of this method is acetic acid, and the methanol carbonylation method of Monsanto Company is required for the preparation of acetic acid. This process requires Rh or Ir noble metal catalysts, and it is also necessary to use methyl iodide with greater toxicity as an auxiliary agent.

[0005] Methanol carbonylation refers to the process of methanol and carbon monoxide reacting to produce methyl acetate (Chem. Commun., 1968, 24, 1578). The catalyst used in this method is the precious metal rhodium, and iodide is required as a promoter. However, high concentrations of iodide increase the corrosiveness of the catalyst, and excessive iodine content in the product affects the product quality. However, the rhodium / iridium-based catalyst used in methanol carbonylation production is expensive, the catalyst and product are difficult to separate, and the halogen has high requirements for equipment materials. Cheap Fe-Co cluster compounds can catalyze the direct homogeneous conversion of methanol into methyl acetate, but the reaction pressure is 27MPa, and the energy consumption is high (US4408069A). For the methanol gas phase carbonylation process without any promoter on the sulfurized CoMo / C catalyst, although the gas phase reaction efficiency is high, the conversion rate of methanol and the selectivity of the product are low (Appl. Catal. A: Gen., 1995, 133, 67).

[0006] The dimethyl ether carbonylation process refers to the preparation of methyl acetate using dimethyl ether and carbon monoxide as raw materials. This method widely uses precious metal catalysts such as Rh and Ir, but carbon deposition is serious. When activated carbon-supported nickel is used as a catalyst, the selectivity of methyl acetate is 80% and the yield is 34%, but the process must use highly toxic iodomethane as an auxiliary agent (Appl. Catal. A: Gen., 1983, 7, 361).

[0007] Recently, Wang Ye et al. reported a one-step method for preparing methyl acetate from synthesis gas. Although the method is called a one-step method, it actually includes the process of preparing methanol from synthesis gas, condensing methanol into dimethyl ether, and carbonylating dimethyl ether with carbon monoxide to prepare methyl acetate. Although the selectivity of methyl acetate in this method is about 90%, the conversion rate is less than 20% (CN108774130B) Summary of the invention

[0008] In order to overcome the shortcomings of the prior art, the present invention provides a method for preparing methyl acetate using methanol and formaldehyde as raw materials and a reaction system. The method takes into account both high raw material conversion rate and high product selectivity, can realize the one-step preparation of methyl acetate from formaldehyde and methanol, and can consume excess methanol and formaldehyde in the industry. It has the characteristics of long catalyst life, low investment, low operating energy consumption, etc. The technical solution of the present invention is as follows:

[0009] As the first aspect of the present invention, there is provided a method for preparing methyl acetate using methanol and formaldehyde as raw materials, wherein methanol and formaldehyde are used as raw materials, and the catalyst is an AB / SiC catalyst prepared with silicon carbide as a carrier, wherein A is selected from Pt and Cu, and B is selected from Al2O3 and CeO2.

[0010] Preferably, the catalyst is Cu-CeO2 / SiC.

[0011] Preferably, the reaction temperature is 200-300°C, preferably 200°C.

[0012] Preferably, the reaction pressure is 0.1-0.3 MPa, preferably 0.1 MPa.

[0013] Preferably, the ratio of methanol to formaldehyde is 1:2-1:5, preferably 1:2.

[0014] Preferably, the gas hourly space velocity is 500-2000 mL g cat h -1 , preferably 1000 mL g cat h -1 .

[0015] In an embodiment of the present invention, the following steps are included: placing a catalyst Cu-CeO2 / SiC in a constant temperature zone of a reactor, wherein the mass fractions of Cu and CeO2 in the catalyst are 5wt% and 10wt%, respectively; introducing a 5% H2 / N2 mixed gas, heating the catalyst to 300℃ / min at a heating rate of 10℃ / min, and maintaining the temperature for 30min; and the reaction conditions are as follows: a reaction temperature of 200℃, a reaction pressure of 0.1MPa, a ratio of methanol to formaldehyde of 1:2, and a gas hourly space velocity of 1000mL g cat h -1, N2 flow rate 100mL / min, methanol flow rate 6g / h, formaldehyde flow rate 150mL / min. The present invention uses a fixed bed reactor, the reaction gas enters, and the product below flows out immediately. Sampling is taken every 1 hour and detected by gas chromatography.

[0016] As a second aspect of the present invention, there is provided a reaction system, comprising a reaction chamber, wherein a catalyst is placed in the reaction chamber to catalyze the reaction of methanol and formaldehyde;

[0017] A mixing chamber to evenly mix methanol and formaldehyde;

[0018] and a vaporization chamber for vaporizing methanol;

[0019] And methanol cylinders, formaldehyde cylinders, nitrogen cylinders, H2 / N2 gas sources;

[0020] The methanol cylinder and the vaporization chamber are connected by a pipeline, and a No. 1 valve and a flow meter are set on the pipeline. The vaporization chamber and the mixing chamber are connected by a pipeline, and a No. 2 valve is set on the pipeline. The formaldehyde cylinder is connected to the mixing chamber; the upper part of the mixing chamber and the lower part of the reaction chamber are connected by a pipeline, and a No. 4 valve is set on the pipeline; a No. 7 valve is set on the pipeline connecting the H2 / N2 gas source and the reaction chamber.

[0021] Preferably, it also includes a first condensation system and a second condensation system; the top of the reaction chamber is connected to the first condensation system and the second condensation system in sequence through pipelines, and the second condensation system is connected to the product chamber.

[0022] Preferably, the second stage condensation system is connected to the mixing chamber via a recovery pipeline, and a No. 6 valve and a one-way valve are provided on the recovery pipeline to ensure the gas flow direction; the formaldehyde cylinder is connected to the recovery pipeline via a pipeline and then introduced into the mixing chamber.

[0023] Preferably, it also includes a recovery chamber, the first section condensation system is connected to the recovery chamber through a pipeline, and the condensation system and the second section condensation system are connected to the first water tank and the second water tank respectively.

[0024] Preferably, a No. 5 valve and a flow meter are provided on the passage connecting the recovery chamber to the pipeline between the methanol cylinder and the vaporization chamber.

[0025] Preferably, in the reaction chamber, the dispersion plate is a perforated plate and the catalyst bed is a two-layered one.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The method for preparing methyl acetate provided by the present invention uses methanol and formaldehyde, which are relatively cheap, as raw materials. There is no literature report on the method for preparing methyl acetate using methanol and formaldehyde as raw materials. This method can reduce the corrosiveness of the acid catalyst to the reactor and the dependence on acetic acid in the reactive distillation method, consume excess formaldehyde in industry and the environment, and reduce pollution to the environment. Therefore, this method has a wide range of application prospects.

[0028] 2. The reaction system provided by the present invention has a simple structure and is easy to scale up.

[0029] 3. The preparation method provided by the present invention has a high methanol conversion rate, which can reach 35%, and a high selectivity for methyl acetate, which can reach 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0031] Figure 1 This is a structural diagram of the reaction system provided by the present invention.

[0032] Among them, 101-reaction chamber, 102-mixing chamber, 103-recovery chamber, 104-vaporization chamber, 105-product chamber;

[0033] 201-methanol cylinder, 202-formaldehyde cylinder, 203-nitrogen cylinder, 204-H2 / N2 gas source;

[0034] 301-1 valve, 302-2 valve, 303-3 valve, 304-4 valve, 305-5 valve, 306-6 valve, 307-7 valve, 308-check valve;

[0035] 401- first section condensation system, 402- second section condensation system;

[0036] 501-the first water tank, 502-the second water tank;

[0037] 701-recovery pipeline, 702-connecting pipeline. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0040] Example 1, a method for preparing methyl acetate using methanol and formaldehyde as raw materials

[0041] based on Figure 1 A reaction system is provided for preparing methyl acetate, the reaction system comprising: a reaction chamber 101, a mixing chamber 102, a recovery chamber 103, a vaporization chamber 104 and a product chamber 105, as well as a methanol cylinder 201, a formaldehyde cylinder 202, a nitrogen cylinder 203, an H2 / N2 gas source 204, and a first-stage condensation system 401 and a second-stage condensation system 402; pressure reducing valves are respectively provided on the formaldehyde cylinder 202 and the nitrogen cylinder 203; the H2 / N2 gas source 204 is connected to the reaction chamber 101; the methanol cylinder 201 and the vaporization chamber 104 are connected to the product chamber 105; The recovery chamber 103 is connected to the methanol cylinder 201 and the vaporization chamber 104. A valve No. 5 305 and a flow meter are set on the pipeline. The vaporization chamber 104 and the mixing chamber 102 are connected by a pipeline. A valve No. 2 302 is set on the pipeline. The upper part of the mixing chamber 102 and the lower part of the reaction chamber 101 are connected by a pipeline. A valve No. 4 304 is set on the pipeline. The top of the reaction chamber 101 is connected to the first section condensation system 401, The second section condensation system 402 is then connected to the lower part of the mixing chamber 102 through the recovery pipeline 701. The recovery pipeline is provided with a No. 6 valve 306 and a one-way valve 308 to ensure the gas flow direction; the formaldehyde cylinder 202 is directly connected to the mixing chamber 102, or is connected to the recovery pipeline 701 through a pipeline, and then passes into the mixing chamber 102; a connecting pipeline 702 is provided between the pipeline connecting the formaldehyde cylinder 202 to the recovery pipeline 701 and the pipeline connecting the nitrogen cylinder 203 to the mixing chamber 102, which is used for nitrogen purging and eliminating the pipeline. The air in the nitrogen cylinder 203 is connected to the connecting pipe 702, and a valve No. 303 and a flow meter are set at one end of the nitrogen cylinder 203; the first section condensation system 401 is connected to the recovery chamber 103 through a pipe, and the second section condensation system 402 is connected to the product chamber 105 through a pipe. The first section condensation system 401 and the second section condensation system 402 are respectively connected to the first water tank 501 and the second water tank 502 for secondary condensation to improve the liquid phase collection efficiency; a valve No. 7 307 is set on the pipeline connecting the H2 / N2 gas source 204 and the reaction chamber 101.

[0042] The control process of the reaction system is:

[0043] 1. Before starting the reaction, close valve No. 2 302 and the main valve of formaldehyde cylinder 202, connect valve No. 6 306 to the environment, open valve No. 3 303 and the main valve of nitrogen cylinder 203, adjust the pressure reducing valve, and exhaust.

[0044] 2. When the reaction starts, open the H2 / N2 gas source 204 and valve 7 307, and introduce the heated H2 / N2 mixed gas into the reaction chamber 101 to increase the temperature of the reaction chamber;

[0045] Close valve No. 2 302, valve No. 303, valve No. 4 304, valve No. 5 305, open valve No. 1 301 to control methanol to enter vaporization chamber 104, after methanol is completely introduced, close valve No. 1 301, and heat the vaporization chamber for vaporization. After all vaporization is completed, open valve No. 2 302 and the main valve of formaldehyde cylinder 202, adjust the pressure reducing valve of formaldehyde cylinder and valve No. 2 302 to control the ratio of formaldehyde and methanol, and after the two are mixed in mixing chamber 102, after the temperature of reaction chamber 101 rises to about 200°C, open valve No. 4 304 for injection.

[0046] 3. In the reaction chamber, the dispersion plate adopts a perforated plate. The purpose of the bottom dispersion plate is to make the injected gas evenly fill the reaction chamber. The upper dispersion plate acts as a fixed catalyst bed. The catalyst bed is designed with two layers to maximize the yield.

[0047] 4. Tail gas treatment, using segmented condensation for recovery, the first condensation system 401 is set at 60°C to condense methanol into the recovery chamber 103, which can be reused in the vaporization chamber 104 through valve 305 No. 5. The second condensation system 402 is set at room temperature, the condensed liquid phase is methyl acetate entering the product chamber 105, and the gas phase is formaldehyde and uncondensed formic acid, which are recycled through valve 306 No. 6.

[0048] 5. The product was detected by gas chromatography SP-7820, the chromatographic column was TDX-01, the vaporization chamber temperature was 120°C, the detector temperature was 150°C, the bridge flow was 130 mA, the argon flow rate was 100 ml / min, and the correction factors of various gases were verified and used to calculate the conversion rate and selectivity.

[0049] Example 2, a method for preparing methyl acetate using methanol and formaldehyde as raw materials

[0050] 0.2g of catalyst Cu-CeO2 / SiC (Cu and CeO2 mass fractions are 5wt% and 10wt%, respectively) was placed in the constant temperature zone of the reactor. A 5% H2 / N2 mixed gas was introduced and heated to 300℃ / min at a heating rate of 10℃ / min to pretreat the catalyst and maintained for 30min. The reaction temperature was 200℃, the reaction pressure was 0.1MPa, the ratio of methanol to formaldehyde was 1:2, and the gas hourly space velocity was 1000mL g cat h -1 Under the conditions (N2 (100mL / min, mass flow meter control), methanol (6g / h, peristaltic pump control), formaldehyde (150mL / min, mass flow meter control)), sampling was performed every 1 hour and gas chromatography was used for detection. The conversion rate of methanol and the selectivity of methyl acetate were 35% and 95%, respectively.

[0051] In this embodiment, the preparation method of the catalyst Cu-CeO2 / SiC is:

[0052] 1g SiC, 187mg copper nitrate trihydrate, 250mg cerium nitrate hexahydrate, and 10mL deionized water were placed in a beaker and dried overnight, placed in a muffle furnace and calcined at 300°C for 2h, and then pretreated by heating to 300°C / min in a 5% H2 / N2 mixed gas at a heating rate of 10°C / min and maintaining for 30min to obtain Cu-CeO2 / SiC (the mass fractions of Cu and CeO2 are 5wt% and 10wt%, respectively).

[0053] The reaction formula of this method is:

[0054] CH3OH+2HCHCO=CH3COOCH3+H2O.

[0055] Since this method has not been reported in the literature, we first calculated the standard molar reaction enthalpy and standard molar reaction Gibbs function of the reaction from a thermodynamic point of view to explore the possibility of the reaction in essence. For CH3OH+2HCHCO=CH3COOCH3+H2O, since the standard molar reaction enthalpy and standard molar reaction Gibbs function of this reaction at 298K are -273 and -188 kJ / mol respectively, and the reaction Δ r C pm It is 6 J / mol (Table 1), so the temperature has little effect on the standard molar reaction enthalpy of this reaction, and it is a strongly exothermic spontaneous reaction below 700°C.

[0056] In order to reduce the carbon deposition rate, the present invention uses silicon carbide foam with good thermal conductivity, acid and alkali resistance, good stability and good mass transfer effect as a carrier to prepare AB / SiC catalyst (A: Pt, Cu, etc., B: Al2O3, CeO2) (Table 2).

[0057] Table 1 Thermodynamic function values ​​of the reaction at 25℃

[0058] Methanol formaldehyde Methyl formate water Standard molar enthalpy of formation (kJ / mol) -201 -108 -413 -241 Standard molar entropy (J / (mol K)) 239 218 324 188 Molar heat capacity at constant pressure (J / (mol K)) 43.8 35.4 86 33

[0059] Table 2 Catalytic performance of different catalysts

[0060]

[0061] The reaction mechanism of the present invention is as follows: the surface of the "metal / metal oxide" has a "metal-Lewis acid" active site, the metal transfers electrons to the oxide, making the metal positively charged, the positively charged metal adsorbs hydrogen in formaldehyde, and the oxide adsorbs oxygen in formaldehyde to form an active intermediate. Methanol then acts on the Lewis acid site in the oxide, and methyl acetate is obtained after CC coupling, dehydration and other steps.

[0062] The same principle as the present invention uses methanol and formaldehyde as raw materials, whether formaldehyde and methanol are fed together, or methanol is first oxidized to obtain formaldehyde and then fed with methanol, all fall within the protection scope of this patent.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing methyl acetate using methanol and formaldehyde as raw materials, It is characterized in that Methanol and formaldehyde are used as raw materials, and the catalyst is an AB / SiC catalyst prepared with silicon carbide as a carrier, wherein A is selected from Pt or Cu, and B is selected from Al 2 O 3 or CeO 2 .

2. The preparation method according to claim 1, It is characterized in that The catalyst is Cu-CeO 2 / SiC.

3. The preparation method according to claim 1, It is characterized in that The reaction temperature is 200-300°C.

4. The preparation method according to claim 1, It is characterized in that The reaction pressure is 0.1-0.3MPa.

5. The preparation method according to claim 1, It is characterized in that The ratio of methanol to formaldehyde is 1:2-1:

5.

6. The preparation method according to claim 1, It is characterized in that Gas hourly space velocity is 500-2000mL g cat h -1 .

7. The preparation method according to claim 1, It is characterized in that The catalyst Cu-CeO 2 / SiC is placed in the constant temperature zone of the reactor, and Cu and CeO in the catalyst 2 The mass fractions were 5wt% and 10wt% respectively; 5% H 2 / N 2 The mixed gas was heated to 300℃ / min at a heating rate of 10℃ / min to pretreat the catalyst and maintained for 30min; the reaction conditions were: reaction temperature of 200℃, reaction pressure of 0.1MPa, ratio of methanol to formaldehyde of 1:2, gas hourly space velocity of 1000mL g cat h -1 , N 2 The flow rate was 100 mL / min, the methanol flow rate was 6 g / h, the formaldehyde flow rate was 150 mL / min, sampling was performed every 1 hour, and the gas chromatography was used for detection.

8. A reaction system, It is characterized in that It includes reaction chamber, mixing chamber and vaporization chamber, as well as methanol cylinder, formaldehyde cylinder, nitrogen cylinder, H 2 / N 2 Gas source; the methanol cylinder and the vaporization chamber are connected by a pipeline, and a No. 1 valve and a flow meter are set on the pipeline; the vaporization chamber and the mixing chamber are connected by a pipeline, and a No. 2 valve is set on the pipeline; the nitrogen cylinder is connected to the pipeline between the vaporization chamber and the mixing chamber, and a No. 3 valve and a flow meter are set on the pipeline; the mixing chamber and the reaction chamber are connected by a pipeline, and a No. 4 valve is set on the pipeline; H 2 / N 2 A No. 7 valve is provided on the pipeline connecting the gas source and the reaction chamber.

9. The reaction system according to claim 8, It is characterized in that It also includes a first condensation system and a second condensation system; the top of the reaction chamber is connected to the first condensation system and the second condensation system in sequence through pipelines, and the second condensation system is connected to the product chamber; The second section of the condensation system is connected to the mixing chamber through a recovery pipeline, and a No. 6 valve and a one-way valve are set on the recovery pipeline to ensure the flow of gas.

10. The reaction system according to claim 8, It is characterized in that It also includes a recovery chamber, the first section of the condensation system is connected to the recovery chamber through a pipeline, and the condensation system and the second section of the condensation system are respectively connected to the first water tank and the second water tank; further, a No. 5 valve and a flow meter are set on the passage of the pipeline connecting the recovery chamber to the methanol cylinder and the vaporization chamber.

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