Preparation method of methyl propionate

Abstract

The invention discloses a preparation method of methyl propionate, and belongs to the technical field of methyl propionate. The preparation method of methyl propionate comprises the following steps: S1, preheating methyl acetate, formaldehyde and methanol to 350-380 DEG C, then feeding into a fixed bed reactor, and reacting at 350-400 DEG C under the action of a synthetic catalyst to obtain a reaction solution; and S2, mixing the reaction liquid obtained in the step S1 with hydrogen, feeding the mixture into a hydrogenation reactor, obtaining a product under the action of a hydrogenation catalyst, and rectifying and separating the product after the hydrogenation reaction to obtain methyl propionate. Compared with the prior art, the preparation method provided by the invention is simpler and more efficient, and the yield of methyl propionate is improved.

Description

Technical Field

[0001] The invention relates to the technical field of methyl propionate, and in particular to a method for preparing methyl propionate. Background Art

[0002] Methyl acetate is a by-product in the production of polyvinyl alcohol, and there is a problem of overcapacity. In the prior art, there is a related technology for preparing methyl propionate using methyl acetate as a raw material. However, the methyl acetate usually prepared contains a large number of by-products. In particular, the prepared methyl propionate can further react with formaldehyde to produce methyl methacrylate. The reaction formula is as follows:

[0003] CH3CH2COOCH3+HCHO→CH2=CHCH3COOCH3+H2O

[0004] How to improve the yield of methyl propionate and reduce the generation of methyl methacrylate is a technical problem that needs to be solved in the prior art. Summary of the invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, provide a method for preparing methyl propionate, and solve the technical problem of how to improve the yield of methyl propionate in the prior art.

[0006] In order to achieve the above technical purpose, the technical solution of the present invention provides a method for preparing methyl propionate, comprising the following steps:

[0007] S1, preheating methyl acetate, formaldehyde and methanol to 350-380° C. and then entering into a fixed bed reactor to react at 350-400° C. under the action of a synthesis catalyst to obtain a reaction liquid;

[0008] S2, mixing the reaction liquid obtained in step S1 with hydrogen and sending it into a hydrogenation reactor to obtain a product under the action of a hydrogenation catalyst, wherein the unreacted formaldehyde in the reaction liquid is converted into methanol, and methyl acrylate is converted into methyl propionate, and the product after the hydrogenation reaction is separated by distillation to obtain methyl propionate.

[0009] In any embodiment, in step S1, the reaction pressure in the fixed bed reactor is normal pressure to 1.0 MPa, and the feed space velocity is 0.2-2.0 h -1 .

[0010] In any embodiment, in step S1, the synthetic catalyst includes an active ingredient and a carrier for loading the active ingredient; the active ingredient includes metal Cs, and the carrier is one or more of SiO2, TiO2, Al2O3, and ZSM-5 molecular sieve; the loading amount of Cs in the synthetic catalyst is 0.1-20wt%, and more preferably 1-5wt%.

[0011] In any embodiment, the active ingredient further comprises bismuth chloride; the loading amount of the bismuth chloride is 0.1-10wt%, more preferably 0.2-1wt%.

[0012] In any embodiment, the hydrogenation catalyst includes a Cu-based hydrogenation catalyst and a Ni-based hydrogenation catalyst.

[0013] The Cu-based catalyst is a conventional commercial catalyst, the main components of which are Cu, Al and their corresponding oxides, and is used to promote the hydrogenation of formaldehyde into methanol; the Ni-based hydrogenation catalyst is also a commercial catalyst, such as HTCNi400RP1.2 and HTCNI500RP1.2 produced by Johnson Matthey, which are used to promote the conversion of methyl acrylate into methyl propionate.

[0014] In any embodiment, the mass ratio of the Cu-based hydrogenation catalyst to the Ni-based hydrogenation catalyst is 1:(0.1-10).

[0015] In any embodiment, in step S1, the molar ratio of the methyl acetate to the formaldehyde is (1-5):(1-5).

[0016] In any embodiment, in step S1, the molar ratio of the methanol to the methyl acetate is (1-5):(1-5).

[0017] In any embodiment, before step S2, the reaction solution obtained in step S1 is preheated to 80-200°C, more preferably 100-150°C.

[0018] In any embodiment, the product after the hydrogenation reaction is distilled and separated to obtain methyl propionate, which includes: cooling the product of the hydrogenation reactor in step S2 to 20-40° C., separating gas and liquid through a gas-liquid separator, and distilling and separating the obtained liquid to obtain methyl propionate.

[0019] The obtained gas mainly contains dimethyl ether, CO2 and hydrogen, among which the hydrogen can be separated by a hydrogen separation membrane and recycled to the hydrogenation step.

[0020] In any embodiment, the operating pressure of the distillation separation is -90 to -50 kPa, the tower top temperature is 45-60°C, and the tower bottom temperature is 80-90°C.

[0021] The hydrogen separation membrane may be a commercial gas separation membrane, such as a Plexane membrane.

[0022] The obtained liquid mainly contains methyl acetate, methanol, methyl propionate, water, and heavy components produced by side reactions; methyl propionate can be obtained by distillation separation.

[0023] Furthermore, the obtained liquid is first subjected to light removal treatment, the light removal tower is operated at normal pressure, the tower top temperature is 55-60°C, the reflux ratio is 1-2, and the tower bottom temperature is 80-90°C. Methyl acetate and methanol are separated from the top of the light removal tower, and this part of the azeotrope can be returned to step S1 as a raw material for the synthesis reaction; methyl propionate, water, and heavy components produced by side reactions are obtained in the tower bottom of the light removal tower, and the tower bottom materials are further distilled and separated; the distillation tower is subjected to vacuum distillation, the operating pressure is -90 to -50 kPa, the tower top temperature is 45-60°C, and the tower bottom is 80-90°C. Methyl propionate with a concentration of 80-95% can be obtained at the top of the tower, and water and heavy components are obtained in the tower bottom.

[0024] Furthermore, as required, a rectification tower can be added, and the 80-95% concentration of methyl propionate can be further refined to obtain 98-99.5% industrial grade methyl propionate.

[0025] Compared with the prior art, the beneficial effects of the present invention include: under the action of a synthetic catalyst, methyl acetate and formaldehyde react to obtain methyl acrylate; the intermediate reaction liquid composed of methyl acrylate, by-products, and unreacted raw materials is directly hydrogenated with hydrogen in a hydrogenation reactor, and under the action of a hydrogenation catalyst, methyl acrylate is hydrogenated to obtain the product methyl propionate, and at the same time, the unreacted formaldehyde in S1 reacts with hydrogen to generate methanol, which reduces the continued reaction of formaldehyde and methyl propionate, thereby increasing the yield of methyl propionate and reducing the generation of methyl methacrylate. In addition, the intermediate product is directly hydrogenated, and hydrogen reacts with formaldehyde to generate methanol, which is better separated from formaldehyde, and no water is needed, thereby reducing the discharge of sewage. DETAILED DESCRIPTION

[0026] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0028] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0029] This specific embodiment provides a method for preparing methyl propionate, comprising the following steps:

[0030] S1. Preheat methyl acetate, formaldehyde and methanol to 350-380°C and then enter a fixed bed reactor to react at 350-400°C under the action of a synthetic catalyst to obtain a reaction liquid; the reaction pressure in the fixed bed reactor is normal pressure to 1.0 MPa, and the feed space velocity is 0.2-2.0 h -1; The molar ratio of the methyl acetate to the formaldehyde is (1-5):(1-5), the formaldehyde raw material is 37-85% formaldehyde solution, paraformaldehyde, trioxymethylene, anhydrous formaldehyde gas, preferably anhydrous formaldehyde gas; In some embodiments, the synthetic catalyst comprises an active ingredient and a carrier for loading the active ingredient; The active ingredient comprises metal Cs, and the carrier is one or more of SiO2, TiO2, Al2O3, and ZSM-5 molecular sieve; The loading amount of Cs in the synthetic catalyst is 0.1-20wt%; In some embodiments, the active ingredient further comprises bismuth chloride; The loading amount of bismuth chloride is 0.1-10wt%; The molar ratio of the methanol to the methyl acetate is (1-5):(1-5); The height-to-diameter ratio of the catalyst bed is (0.5-3):1, and the catalyst bed can be one or more sections;

[0031] S2, mixing the reaction liquid obtained in step S1 with hydrogen and sending it into a hydrogenation reactor to obtain a product under the action of a hydrogenation catalyst, and separating the product after the hydrogenation reaction by distillation to obtain methyl propionate; preheating the intermediate product to 80-200° C., and then reacting it with hydrogen in a hydrogenation reactor, and separating the product after the hydrogenation reaction to obtain methyl propionate; the hydrogenation catalyst includes a Cu-based hydrogenation catalyst and a Ni-based hydrogenation catalyst.

[0032] In some embodiments, the product after the hydrogenation reaction is distilled and separated to obtain methyl propionate, comprising: cooling the product of the hydrogenation reactor in step S2 to 20-40°C, separating gas and liquid through a gas-liquid separator; the operating pressure of the distillation separation is -90--50 kPa, the tower top temperature is 45-60°C, and the tower bottom temperature is 80-90°C. The obtained gas mainly contains dimethyl ether, CO2 and hydrogen, wherein the hydrogen can be separated by a hydrogen separation membrane and reused in the hydrogenation step.

[0033] The obtained liquid mainly contains methyl acetate, methanol, methyl propionate, water and heavy components produced by side reactions; the obtained liquid is first subjected to light removal treatment, and an azeotrope of methyl acetate and methanol is separated at the top of a light removal tower, and this part of the azeotrope can be returned to step S1 as a raw material for a synthetic reaction; methyl propionate, water and heavy components produced by side reactions are obtained in the bottom of the light removal tower, and the bottom material is further subjected to rectification and separation; the operating pressure of the rectification and separation is -90 to -50 kPa, the top temperature is 45-60° C., the bottom temperature is 80-90° C., methyl propionate is obtained at the top of the distillation tower, and water and heavy components are obtained in the bottom.

[0034] The reaction formula involved in the present invention is as follows:

[0035] CH3COOCH3+HCHO→CH2=CHCOOCH3+H2O

[0036] CH2=CHCOOCH3+H2→CH3CH2COOCH3

[0037] HCHO+H2→CH3OH

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] In the present invention, reference is made to “some embodiments”, “this embodiment”, examples, etc., which describe a subset of all possible embodiments, but it can be understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0040] If similar descriptions of "first / second" appear in the application documents, the following instructions are added. In the following description, the terms "first\second\third" are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It can be understood that "first\second\third" can be interchanged in a specific order or sequence where permitted, so that the embodiments described herein can be implemented in an order other than that described herein.

[0041] In this embodiment, the term "and / or" is merely a description of the association relationship between associated objects, indicating that three relationships may exist. For example, object A and / or object B may represent three situations: object A exists alone, object A and object B exist at the same time, and object B exists alone.

[0042] In the following examples, formaldehyde is anhydrous formaldehyde obtained by decomposition of paraformaldehyde, and the catalyst bed height-to-diameter ratio is 5: 1. The synthetic catalysts used are all from the prior art.

[0043] Example 1

[0044] This embodiment provides a method for preparing methyl propionate, comprising the following steps:

[0045] S1. Preheat methyl acetate, formaldehyde and methanol to 350°C and then enter a fixed bed reactor to react at 380°C under the action of a synthetic catalyst to obtain an intermediate product; the reaction pressure in the fixed bed reactor is 0.2 MPa, and the feed space velocity is 1 h -1 ; The molar ratio of the methyl acetate to the formaldehyde is 1:1; the synthetic catalyst is SiO2 loaded with Cs; the loading amount of Cs is 1.2wt%; the molar ratio of the methanol to the methyl acetate is 1:2.

[0046] S2. The intermediate product is preheated to 120° C. and sent to a hydrogenation reactor to react with hydrogen in the hydrogenation reactor. The hydrogenation reactor is loaded with two catalysts: a Cu-based hydrogenation catalyst and a Ni-based hydrogenation catalyst. The mass ratio of the two catalysts is 1:1, and the pressure in the hydrogenation reactor is 1.1±0.1 MPa.

[0047] S3, the hydrogenated product is cooled to 30°C, the gas is separated by a gas-liquid separator, the separated gas is recovered by membrane separation to obtain hydrogen, and is reused in the S2 hydrogenation step.

[0048] The obtained liquid is first subjected to light removal treatment, and the light removal tower is operated at normal pressure, with a tower top temperature of 57±2°C, a reflux ratio of 2, and a tower bottom temperature of 88±2°C. The azeotrope of methyl acetate and methanol is separated at the top of the light removal tower, and this part of the azeotrope is returned to step S1 as a raw material for the synthesis reaction; methyl propionate, water, and heavy components produced by side reactions are obtained in the tower bottom of the light removal tower, and further distilled and separated. The distillation tower is operated under reduced pressure, with an operating pressure of -70±10kPa, a tower top temperature of 47±2°C, and a tower bottom temperature of 85±2°C. Methyl propionate is obtained at the top of the tower with a concentration in the range of 80%-95%, and impurities such as water, methanol, and heavy components are obtained in the tower bottom.

[0049] In this embodiment, the yield of the product methyl acrylate is 95.4%, and the conversion rate of methyl acetate is 20.5%.

[0050] Example 2

[0051] The difference between this embodiment and embodiment 1 is that the synthetic catalyst used in step S1 is SiO2 loaded with Cs, wherein the loading amount of Cs is 1.2 wt%.

[0052] In this embodiment, the yield of the product methyl acrylate is 93.6%, and the conversion rate of methyl acetate is 18.9%.

[0053] Example 3

[0054] The difference between this embodiment and embodiment 1 is that the synthetic catalyst used in step S1 is SiO2 loaded with Cs, wherein the loading amount of Cs is 1.5 wt%.

[0055] In this embodiment, the yield of the product methyl acrylate is 92.8%, and the conversion rate of methyl acetate is 19.2%.

[0056] Example 4

[0057] The difference between this embodiment and embodiment 1 is that the synthetic catalyst used in step S1 is SiO2 loaded with Cs and TiO2 loaded with bismuth chloride; wherein the loading amount of Cs is 1.2wt%, the loading amount of bismuth chloride on TiO2 is 0.3wt%, and the mass ratio of SiO2 to TiO2 is 1:1.

[0058] In this embodiment, the yield of the product methyl acrylate is 97.7%, and the conversion rate of methyl acetate is 28.6%.

[0059] Example 5

[0060] The difference between this embodiment and embodiment 4 is that in step S1, the molar ratio of methanol to methyl acetate is 1:1.

[0061] In this embodiment, the yield of the product methyl acrylate is 95.3%, and the conversion rate of methyl acetate is 22.4%.

[0062] Example 6

[0063] The difference between this embodiment and embodiment 4 is that the hydrogenation catalyst used in step S2 contains only Ni-based hydrogenation catalyst, and the amount used is the same as that of the hydrogenation catalyst in embodiment 4.

[0064] In this embodiment, the yield of the product methyl acrylate is 84.7%, and the conversion rate of methyl acetate is 16.3%.

[0065] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing methyl propionate, characterized in that, The following steps are involved: S1, preheating methyl acetate, formaldehyde and methanol to 350-380° C. and then entering into a fixed bed reactor to react at 350-400° C. under the action of a synthesis catalyst to obtain a reaction liquid; S2, mixing the reaction liquid obtained in step S1 with hydrogen and sending them into a hydrogenation reactor to obtain a product under the action of a hydrogenation catalyst, and separating the product after the hydrogenation reaction by rectification to obtain methyl propionate.

2. The method for preparing methyl propionate according to claim 1, characterized in that In step S1, the reaction pressure in the fixed bed reactor is normal pressure-1.0 MPa, and the feed space velocity is 0.2-2.0 h -1 .

3. The method for preparing methyl propionate according to claim 1, characterized in that In step S1, the synthetic catalyst includes an active ingredient and a carrier for loading the active ingredient; the active ingredient includes metal Cs, and the carrier is one or more of SiO2, TiO2, Al2O3, and ZSM-5 molecular sieve; the loading amount of Cs in the synthetic catalyst is 0.1-20wt%.

4. The method for preparing methyl propionate according to claim 3, characterized in that The active ingredient further comprises bismuth chloride; the loading amount of the bismuth chloride is 0.1-10 wt%.

5. The method for preparing methyl propionate according to claim 1, characterized in that In step S2, the hydrogenation catalyst includes a Cu-based hydrogenation catalyst and a Ni-based hydrogenation catalyst.

6. The method for preparing methyl propionate according to claim 1, characterized in that In step S1, the molar ratio of the methyl acetate to the formaldehyde is (1-5):(1-5).

7. The method for preparing methyl propionate according to claim 1, characterized in that In step S1, the molar ratio of the methanol to the methyl acetate is (1-5):(1-5).

8. The method for preparing methyl propionate according to claim 1, characterized in that Before step S2, the reaction solution obtained in step S1 is preheated to 80-200°C.

9. The method for preparing methyl propionate according to claim 1, characterized in that: The product after the hydrogenation reaction is distilled and separated to obtain methyl propionate, which includes: cooling the product of the hydrogenation reactor in step S2 to 20-40° C., separating gas and liquid through a gas-liquid separator, and distilling and separating the obtained liquid to obtain methyl propionate.

10. The method for preparing methyl propionate according to claim 9, characterized in that: The operating pressure of the distillation separation is -90 to -50 kPa, the tower top temperature is 45-60°C, and the tower bottom temperature is 80-90°C.