A method and apparatus for preparing dimethyl ketone

Abstract

This invention discloses a method and apparatus for preparing dimethyl ketene using a two-stage thermal decomposition coupling technology. The method includes the following steps: (1) thermally decomposing acetic acid to generate ketene; (2) absorbing the obtained ketene with isobutyric acid to generate isobutyric anhydride and acetic acid; (3) thermally decomposing the obtained isobutyric anhydride to generate dimethyl ketene. The acetic acid generated in step (2) is returned to step (1), and the isobutyric acid generated in the thermal decomposition process of step (3) is returned to step (2). This invention uses isobutyric acid to absorb ketene, realizing the conversion of isobutyric acid to isobutyric anhydride, thereby achieving full utilization of the materials in the isobutyric anhydride thermal decomposition process.

Description

Technical Field

[0001] This invention relates to the field of dimethyl ketene, and more specifically, to a method and apparatus for preparing dimethyl ketene using a two-stage thermal decomposition coupling technology. Background Technology

[0002] Dimethyl ketone (DMK) is an important intermediate in the chemical industry. Dimerizing DMK yields 2,2,4,4-tetramethyl-1,3-cyclobutanedione (TMCB). Further hydrogenation of TMCB yields the novel polyester monomer 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO), which can be used to synthesize various novel copolyesters. In particular, copolymerizing TMCB with terephthalic acid (PTA) and 1,4-cyclohexanediethanol (CHDM) produces a high-performance copolyester, which Eastman named Tritan. Compared to traditional polyethylene terephthalate-1,4-cyclohexanediethanol (PETG), Tritan typically has a glass transition temperature higher than 120°C, and its hydrolytic stability, processability, and chemical resistance are significantly improved, making it widely applicable in industries such as food, display panels, and automotive interiors. In particular, in the food industry, Tritan's safety is significantly improved due to its bisphenol A-free nature, making it widely used in the manufacture of medical bottles, hot-fill bottles, and infant drinking water bottles. However, the production technology for TMCB / CBDO is exclusively owned by Eastman, and its CBDO is not sold externally. Therefore, Eastman holds a monopoly on this grade of polyester, and exploring the efficient synthesis of TMCB is crucial to breaking Eastman's monopoly. The key to producing Tritan is obtaining polymer-grade CBDO monomer. CBDO is synthesized through the hydrogenation of TMCB; therefore, obtaining TMCB monomer is key to preparing CBDO monomer.

[0003] Chinese patents CN105732354A, CN111875481 A, and CN100439311 A all disclose a process route that uses isobutyric anhydride as a starting material, thermally decomposes it to generate DMK, and then dimers it to generate TMCB. However, during the thermal decomposition of isobutyric anhydride, for every molecule of DMK generated, one molecule of isobutyric acid is necessarily generated. Therefore, none of these processes mention the recycling of isobutyric acid.

[0004] To address this issue, Chinese patent CN112047834A discloses a method for converting isobutyric acid to isobutyric anhydride. This method uses isobutyric acid and acetic anhydride as initial raw materials, converting isobutyric acid to isobutyric anhydride through reactive distillation, followed by thermal cracking to generate TMCB. However, this process is complex, and acetic acid is inevitably produced as a byproduct. Other literature indicates that at high temperatures, a catalyst (such as MgO) can dehydrate two molecules of isobutyric acid to generate isobutyric anhydride; however, this process has a low conversion rate and poor selectivity.

[0005] Chinese patent CN112457170A avoids the thermal cracking route and uses isobutyryl chloride to dehydrochlorinate DMK. However, this process generates a large amount of saline wastewater, resulting in low economic and environmental benefits. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a green and efficient new process for preparing dimethyl ketone (TMCB), which achieves efficient preparation of TMCB by coupling the thermal cracking processes of acetic acid and isobutyric anhydride.

[0007] One objective of this invention is to provide a method for preparing dimethyl ketene, comprising the following steps:

[0008] (1) Acetic acid is thermally decomposed to produce ketene;

[0009] (2) Isobutyric acid is used to absorb the obtained ketone to generate isobutyric anhydride and acetic acid;

[0010] (3) The obtained isobutyric anhydride is thermally decomposed to generate dimethyl ketone.

[0011] In step (1), acetic acid is thermally decomposed at high temperature to produce ketene. The thermal decomposition method of acetic acid is known to those skilled in the art. More preferably,

[0012] In step (1), the thermal decomposition temperature is controlled at 600–900℃, preferably 600–800℃, and the partial pressure of acetic acid is 10–100 kPa, so as to generate ketene with high selectivity. The thermal decomposition temperature can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, etc., and the partial pressure of acetic acid can be 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, 100 kPa, etc. The residence time can be 0.2–1 s, for example 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.6 s, 0.7 s, 0.8 s, 0.9 s, 1 s, etc.

[0013] In step (1), the thermal decomposition is carried out in the presence of a catalyst, which can be a catalyst commonly used in the art, preferably triethyl phosphate; the catalyst content is 0.1 to 1 wt% of acetic acid.

[0014] In step (1), the acetic acid stream from the acetic acid thermal decomposition is partly or entirely derived from the acetic acid generated in step (2).

[0015] In step (2), isobutyric acid is used to absorb the ketene obtained in step (1) to generate isobutyric anhydride and acetic acid. More preferably,

[0016] The molar ratio of isobutyric acid to ketene is (1:0.4) to (1:0.7), preferably (1:0.5) to (1:0.6), and can be, for example, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7, etc.

[0017] The absorption temperature is 10 to 180°C, more preferably 10 to 150°C, for example, it can be 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 150°C, 180°C, etc.

[0018] The absorption residence time is 0.01 to 10 min, more preferably 0.01 to 5 min, for example, it can be 0.01 min, 0.1 min, 0.2 min, 0.3 min, 0.4 min, 0.5 min, 0.6 min, 0.7 min, 0.8 min, 0.9 min, 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.;

[0019] The generated isobutyric anhydride and acetic acid are separated by distillation, and the generated acetic acid can be returned to step (1);

[0020] The isobutyric acid in step (2) is partly derived from the isobutyric acid byproduct generated during the thermal decomposition process in step (3).

[0021] In step (3), the isobutyric anhydride obtained in step (2) is thermally decomposed to generate dimethyl ketene. The thermally decomposed product stream also includes isobutyric acid and isobutyric anhydride. More preferably,

[0022] The reaction temperature for thermal decomposition is 350–650°C, preferably 350–550°C, and more preferably 400–500°C;

[0023] The reaction pressure for thermal pyrolysis is 1 kPa to 0.3 MPa, preferably 10 kPa to 0.1 MPa;

[0024] The reaction residence time for thermal pyrolysis is 0.1–4 s, preferably 0.1–1 s;

[0025] A dilution gas is introduced during thermal pyrolysis, wherein the volume ratio of isobutyric anhydride gas to dilution gas is (1:30) to (1:0.2), preferably (1:20) to (1:0.5). The dilution gas is a gas used in thermal pyrolysis that is known to those skilled in the art.

[0026] Step (3) may also include a process of rapid cooling of the thermal decomposition products and absorption of dimethyl ketene. After multi-stage cooling, the thermal decomposition product stream containing isobutyric acid and isobutyric anhydride can be returned to step (2) together, or the isobutyric acid and isobutyric anhydride can be separated and the isobutyric acid can be returned to step (2) separately. The obtained dimethyl ketene stream undergoes an absorption process.

[0027] The endpoint temperature of the rapid cooling process is 34–150°C, preferably 34–120°C;

[0028] The solvent used in the absorption process is an organic solvent known to those skilled in the art, such as esters and ethers, specifically isoamyl acetate, etc.

[0029] The second objective of this invention is to provide an apparatus for preparing dimethyl ketene, for performing the above-described method, comprising an acetic acid thermal pyrolysis unit, an isobutyric acid absorption unit, and an isobutyric anhydride thermal pyrolysis unit connected in series.

[0030] The acetic acid thermal decomposition unit includes a decomposition furnace I for thermal decomposition of acetic acid to produce ketene. The resulting acetic acid thermal decomposition stream enters the isobutyric acid absorption unit, and the unit can also receive acetic acid streams from the isobutyric acid absorption unit.

[0031] The preferred process for acetic acid thermal decomposition is as follows: thermal decomposition temperature of 600–900℃, acetic acid partial pressure of 10–100 kPa, and triethyl phosphate content of the catalyst of 0.1–1 wt%.

[0032] The isobutyric acid absorption unit includes an absorption device and a separation device connected in sequence, wherein...

[0033] The absorption device is connected to the acetic acid pyrolysis unit for the absorption of isobutyric acid from ketene, and receives isobutyric acid and the stream flowing out of the acetic acid pyrolysis unit. It can be any equipment known to those skilled in the art, including but not limited to at least one of bubble column, spray column, and stirred tank. The absorption device can receive the stream containing isobutyric acid from the isobutyric anhydride pyrolysis unit.

[0034] The separation device is used to separate isobutyric anhydride and acetic acid generated after absorption. The acetic acid stream flowing out of the separation device is returned to the acetic acid thermal cracking unit, and the isobutyric anhydride stream flowing out enters the isobutyric anhydride thermal cracking unit. The separation device can be a distillation column, using a conventional distillation process.

[0035] The molar ratio of isobutyric acid to ketene is (1:0.4) to (1:0.7), preferably (1:0.5) to (1:0.6).

[0036] The temperature of the absorption process is 10–180°C, preferably 10–150°C; the residence time of the absorption process is 0.01–10 min, preferably 0.01–5 min.

[0037] The isobutyric anhydride thermal cracking unit includes a cracking furnace II, which receives the isobutyric anhydride stream flowing out of the separation device and is used to perform thermal cracking of isobutyric anhydride to obtain thermal cracking products containing dimethyl ketene, isobutyric acid and isobutyric anhydride.

[0038] The isobutyric anhydride pyrolysis unit also includes a rapid cooling device and an absorption device connected in sequence.

[0039] The rapid cooling device is connected to pyrolysis furnace II to receive the pyrolysis products of isobutyric anhydride and rapidly cools them. The dimethyl ketone stream flowing out of the rapid cooling device flows into the absorption unit. The stream containing isobutyric acid flowing out of the rapid cooling device returns to the isobutyric acid absorption unit. The byproduct stream flowing out of the rapid cooling device includes isobutyric acid and isobutyric anhydride, which can be returned together to the isobutyric acid absorption unit, or the isobutyric acid and isobutyric anhydride can be separated, with the isobutyric acid returned separately to the isobutyric acid absorption unit. The rapid cooling device and the absorption unit can be any equipment known to those skilled in the art.

[0040] The thermal decomposition process of isobutyric anhydride has a reaction temperature of 350–650°C, preferably 350–550°C.

[0041] The thermal decomposition reaction pressure of the isobutyric anhydride is 1 kPa to 0.3 MPa, preferably 10 kPa to 0.1 MPa.

[0042] The volume ratio between isobutyric anhydride gas and dilution gas in the isobutyric anhydride thermal decomposition process is (1:30) to (1:0.2), preferably (1:20) to (1:0.5).

[0043] The residence time of the reactants in the isobutyric anhydride thermal decomposition process is 0.1–4 s, preferably 0.1–1 s.

[0044] The final temperature of the rapid cooling device is 34–150°C, preferably 34–120°C.

[0045] The solvent in the absorption device is an organic solvent known to those skilled in the art, such as esters and ethers.

[0046] The apparatus for preparing dimethyl ketene according to the present invention may further include a vacuum system to provide a vacuum environment for other units.

[0047] This invention provides an efficient method for preparing DMK using isobutyric acid as the initial raw material. The method utilizes isobutyric acid to absorb ketene, achieving the conversion of isobutyric acid to isobutyric anhydride, thus fully utilizing the materials from the isobutyric anhydride pyrolysis process. Simultaneously, the product is fully utilized in the system, with theoretically the only byproduct being water, making the entire process green and efficient. In subsequent industrial implementation, the two pyrolysis stages involved in this invention can employ the same shared process, which can reduce production costs.

[0048] The present invention will be further illustrated by the following embodiments, but is not limited to these embodiments. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of a process for preparing dimethyl ketone according to the present invention.

[0050] Figure 1 Marker explanation:

[0051] 1-Pyrolysis Furnace I;

[0052] 2-Isobutyric acid absorption unit;

[0053] 3-Pyrolysis Furnace II;

[0054] 4-Rapid cooling device;

[0055] 5-Absorption device;

[0056] 6-Acetic acid;

[0057] 7-Isobutyric acid;

[0058] 8-Isobutyric anhydride logistics;

[0059] 9-Acetic acid logistics;

[0060] Stream of 10-isobutyric anhydride thermal decomposition products;

[0061] 11-Isobutyric acid-containing logistics;

[0062] 12-Dimethylketene logistics;

[0063] 13-dimethylketene stream after absorption;

[0064] 14-Exhaust gas;

[0065] 15-Vacuum system.

[0066] Figure 1 In the process, acetic acid 6 is fed into pyrolysis furnace I for thermal pyrolysis. The acetic acid thermal pyrolysis product stream containing ketene is fed into isobutyric acid absorption unit 2. Fresh isobutyric acid 7 flows into isobutyric acid absorption unit 2. In the absorption device of isobutyric acid absorption unit 2, isobutyric acid absorbs ketene to generate a stream containing isobutyric anhydride and acetic acid. Then, it is separated into isobutyric anhydride stream 8 and acetic acid stream 9 by a separation device. Acetic acid stream 9 is returned to pyrolysis furnace I. Isobutyric anhydride stream 8 is fed into pyrolysis furnace II for thermal pyrolysis. The isobutyric anhydride thermal pyrolysis product stream 10 is sent to rapid cooling device 4 for rapid cooling to obtain dimethyl ketene stream 12 and isobutyric acid stream 11. Dimethyl ketene stream 12 can be sent to the subsequent absorption device 5, and isobutyric acid stream 11 is returned to isobutyric acid absorption unit 2. Detailed Implementation

[0067] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0068] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0069] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0070] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0071] Example 1

[0072] This embodiment includes the following steps:

[0073] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0074] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0075] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0076] in,

[0077] Step (1) Preparation process of ketene: thermal decomposition reaction temperature 800℃, fresh acetic acid partial pressure 50kPa, residence time 1s, catalyst triethyl phosphate content 0.5wt%.

[0078] The selectivity for ketene in this process is 91.5%, and the yield of ketene is 90.1%.

[0079] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 50℃, and the residence time is 0.1min. The absorption solvent is fresh isobutyric acid, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.55.

[0080] The yield of isobutyric anhydride in this process was 95.2%.

[0081] Step (3) Isobutyric anhydride thermal decomposition process: thermal decomposition reaction temperature 400℃, reaction tube pressure 0.1MPa, wherein the partial pressure of the prepared isobutyric anhydride is 10kPa, the dilution gas is nitrogen with a partial pressure of 91kPa, the residence time is 1s, the temperature of the quenching unit after reaction is 50℃, and the absorption solvent is isoamyl acetate.

[0082] The selectivity for dimethyl ketene in this process was 90.3%, and the yield was 30.1%.

[0083] Example 2

[0084] The process flow of this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0085] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0086] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0087] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0088] in,

[0089] Step (1) Preparation process of ketene: reaction temperature 800℃, partial pressure of acetic acid obtained in the isobutyric anhydride preparation stage 50kPa, residence time 1s, catalyst triethyl phosphate content 0.5%.

[0090] The selectivity for ketene in this process is 91.5%, and the yield of ketene is 90.1%.

[0091] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 50℃, and the residence time is 0.1min. The absorption solvent is a mixed solution of isobutyric anhydride and isobutyric acid obtained by thermal decomposition of isobutyric anhydride, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.55.

[0092] The yield of isobutyric anhydride in this process was 80.1%.

[0093] Step (3) Isobutyric anhydride thermal decomposition process: reaction temperature 400℃, reaction tube pressure 0.1MPa, wherein the partial pressure of the prepared isobutyric anhydride is 10kPa, the dilution gas is nitrogen with a partial pressure of 91kPa, the residence time is 1s, the temperature of the quenching unit after the reaction is 50℃, and the absorption solvent is isoamyl acetate.

[0094] The selectivity for dimethyl ketene in this process was 90.8%, and the yield was 29.7%.

[0095] Example 3

[0096] The process flow of this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0097] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0098] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0099] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0100] in,

[0101] Step (1) Ketene preparation process: reaction temperature 660℃, partial pressure of acetic acid obtained in the isobutyric anhydride preparation stage 10kPa, residence time 0.5s, catalyst triethyl phosphate content 0.1%.

[0102] The selectivity for ketene in this process is 98.2%, and the yield of ketene is 93.7%.

[0103] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 100℃, and the residence time is 2min. The absorption solvent is a mixed solution of isobutyric anhydride and isobutyric acid obtained by thermal decomposition of isobutyric anhydride, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.6.

[0104] The yield of isobutyric anhydride in this process was 85.3%.

[0105] Step (3) Isobutyric anhydride thermal decomposition process: reaction temperature 440℃, reaction tube pressure 0.015MPa, wherein the partial pressure of the isobutyric anhydride prepared above is 10kPa, the dilution gas is nitrogen with a partial pressure of 5kPa, the residence time is 0.5s, the temperature of the quenching unit after the reaction is 34℃, and the absorption solvent is n-butyl acetate.

[0106] The selectivity for dimethyl ketene in this process was 95.4%, and the yield was 42.4%.

[0107] Example 4

[0108] The process flow of this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0109] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0110] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0111] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0112] in,

[0113] Step (1) Ketone preparation process: reaction temperature 600℃, partial pressure of acetic acid obtained in the isobutyric anhydride preparation stage 10kPa, residence time 0.3s, catalyst triethyl phosphate content 0.7%.

[0114] The selectivity for ketene in this process is 99.1%, and the yield of ketene is 78.5%.

[0115] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 120℃, and the residence time is 0.5min. The absorption solvent is a mixed solution of isobutyric anhydride and isobutyric acid obtained by thermal decomposition of isobutyric anhydride, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.5.

[0116] The yield of isobutyric anhydride in this process was 90.3%.

[0117] Step (3) Isobutyric anhydride thermal decomposition process: reaction temperature 500℃, reaction tube pressure 0.01MPa, wherein the partial pressure of the isobutyric anhydride prepared above is 5kPa, the dilution gas is nitrogen with a partial pressure of 5kPa, the residence time is 0.1s, the temperature of the quenching unit after the reaction is 100℃, and the absorption solvent is n-butyl acetate.

[0118] The selectivity for dimethyl ketene in this process was 82.1%, and the yield was 51.3%.

[0119] Example 5

[0120] The process flow of this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0121] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0122] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0123] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0124] in,

[0125] Step (1) Ketone preparation process: reaction temperature 700℃, partial pressure of acetic acid obtained in the isobutyric anhydride preparation stage 30kPa, residence time 0.4s, catalyst triethyl phosphate content 0.2%.

[0126] The selectivity for ketene in this process is 97.5%, and the yield of ketene is 93.2%.

[0127] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 90℃, and the residence time is 0.7min. The absorption solvent is a mixed solution of isobutyric anhydride and isobutyric acid obtained by thermal decomposition of isobutyric anhydride, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.51.

[0128] The yield of isobutyric anhydride in this process was 93.1%.

[0129] Step (3) Isobutyric anhydride thermal decomposition process: reaction temperature 450℃, reaction tube pressure 0.02MPa, wherein the partial pressure of the isobutyric anhydride prepared above is 5kPa, the dilution gas is nitrogen with a partial pressure of 15kPa, the residence time is 0.3s, the temperature of the quenching unit after the reaction is 50℃, and the absorption solvent is n-butyl acetate.

[0130] The selectivity for dimethyl ketene in this process was 87.3%, and the yield was 47.2%.

[0131] Example 6

[0132] The process flow of this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0133] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0134] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0135] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0136] in,

[0137] Step (1) Ketone preparation process: reaction temperature 700℃, partial pressure of acetic acid obtained in the isobutyric anhydride preparation stage 30kPa, residence time 0.4s, catalyst triethyl phosphate content 0.2%.

[0138] The selectivity for ketene in this process is 97.5%, and the yield of ketene is 95.1%.

[0139] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 70℃, and the residence time is 0.3min. The absorption solvent is a mixed solution of isobutyric anhydride and isobutyric acid obtained by thermal decomposition of isobutyric anhydride, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.7.

[0140] The yield of isobutyric anhydride in this process was 83.7%.

[0141] Step (3) Isobutyric anhydride thermal decomposition process: reaction temperature 410℃, reaction tube pressure 0.05MPa, wherein the partial pressure of the isobutyric anhydride prepared above is 20kPa, the dilution gas is nitrogen with a partial pressure of 30kPa, the residence time is 0.2s, the temperature of the quenching unit after the reaction is 40℃, and the absorption solvent is n-butyl acetate.

[0142] The selectivity for dimethyl ketene in this process was 99.1%, and the yield was 33.1%.

[0143] Example 7

[0144] The process flow of this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0145] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0146] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0147] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0148] in,

[0149] Step (1) Ketone preparation process: reaction temperature 680℃, partial pressure of acetic acid obtained in the isobutyric anhydride preparation stage 50kPa, residence time 0.3s, catalyst triethyl phosphate content 0.2%.

[0150] The selectivity for ketene in this process is 98.1%, and the yield of ketene is 96.9%.

[0151] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 80℃, and the residence time is 0.6min. The absorption solvent is a mixed solution of isobutyric anhydride and isobutyric acid obtained by thermal decomposition of isobutyric anhydride, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.51.

[0152] The yield of isobutyric anhydride in this process was 95.1%.

[0153] Step (3) Isobutyric anhydride thermal decomposition process: reaction temperature 420℃, reaction tube pressure 0.02MPa, wherein the partial pressure of the isobutyric anhydride prepared above is 10kPa, the dilution gas is nitrogen with a partial pressure of 10kPa, the residence time is 0.35s, the temperature of the quenching unit after the reaction is 50℃, and the absorption solvent is n-butyl acetate.

[0154] The selectivity for dimethyl ketene in this process was 98.4%, and the yield was 42.8%.

[0155] Example 8

[0156] The process flow of this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0157] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0158] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0159] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0160] in,

[0161] Step (1) Ketone preparation process: reaction temperature 660℃, partial pressure of acetic acid obtained in the isobutyric anhydride preparation stage 10kPa, residence time 0.3s, catalyst triethyl phosphate content 0.1%.

[0162] The selectivity for ketene in this process is 98.8%, and the yield of ketene is 97.3%.

[0163] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 80℃, and the residence time is 0.6min. The absorption solvent is a mixed solution of isobutyric anhydride and isobutyric acid obtained by thermal decomposition of isobutyric anhydride, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.52.

[0164] The yield of isobutyric anhydride in this process was 96.3%.

[0165] Step (3) Isobutyric anhydride thermal decomposition process: reaction temperature 400℃, reaction tube pressure 0.02MPa, wherein the partial pressure of the isobutyric anhydride prepared above is 10kPa, the dilution gas is nitrogen with a partial pressure of 10kPa, the residence time is 0.35s, the temperature of the quenching unit after the reaction is 80℃, and the absorption solvent is n-butyl acetate.

[0166] The selectivity for dimethyl ketene in this process was 99.5%, and the yield was 38.8%.

[0167] Example 9

[0168] The process flow of this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0169] (1) Acetic acid is thermally decomposed at high temperature to produce ketene;

[0170] (2) The ketone generated in step 1 is absorbed by isobutyric acid to generate isobutyric anhydride and acetic acid.

[0171] (3) The isobutyric anhydride generated in step 2 is thermally decomposed to produce dimethyl ketone.

[0172] in,

[0173] Step (1) Ketone preparation process: reaction temperature 660℃, partial pressure of acetic acid obtained in the isobutyric anhydride preparation stage 10kPa, residence time 0.3s, catalyst triethyl phosphate content 0.1%.

[0174] The selectivity for ketene in this process is 98.8%, and the yield of ketene is 97.3%.

[0175] Step (2) Isobutyric anhydride preparation process: The absorption process uses a bubble column, the absorption temperature is 70℃, and the residence time is 0.6min. The absorption solvent is a mixed solution of isobutyric anhydride and isobutyric acid obtained by thermal decomposition of isobutyric anhydride, and the molar ratio of isobutyric acid stream to ketene stream is 1:0.53.

[0176] The yield of isobutyric anhydride in this process was 92.8%.

[0177] Step (3) Isobutyric anhydride thermal decomposition process: reaction temperature 430℃, reaction tube pressure 0.02MPa, wherein the partial pressure of the isobutyric anhydride prepared above is 10kPa, the dilution gas is nitrogen with a partial pressure of 10kPa, the residence time is 0.4s, the temperature of the quenching unit after the reaction is 40℃, and the absorption solvent is n-butyl acetate.

[0178] The selectivity for dimethyl ketene in this process was 95.1%, and the yield was 45.7%.

Claims

1. A method for preparing dimethyl ketene, comprising the following steps: (1) Acetic acid is thermally decomposed to produce ketene; (2) Isobutyric acid is used to absorb the obtained ketone to generate isobutyric anhydride and acetic acid; (3) The obtained isobutyric anhydride is thermally decomposed to generate dimethyl ketone; Acetic acid generated in step (2) is returned to step (1); isobutyric acid generated in the thermal decomposition process of step (3) is returned to step (2).

2. The method of claim 1, wherein In step (1): The thermal decomposition temperature is 600–900℃, and the partial pressure of acetic acid is 10–100 kPa; and / or, The thermal cracking was carried out in the presence of a catalyst, with a catalyst content of 0.1–1 wt%.

3. The method of claim 1, wherein In step (2): The molar ratio of isobutyric acid to ketene is 1:0.4 to 1:0.7; and / or, The absorption temperature is 10–180℃; and / or, The absorption residence time is 0.01 to 10 min.

4. The method of claim 3, wherein In step (2): The molar ratio of isobutyric acid to ketene is 1:0.5 to 1:0.6; and / or, The absorption temperature is 10–150℃; and / or, The absorption residence time is 0.01 to 5 minutes.

5. The method of claim 1, wherein In step (2): Isobutyric anhydride and acetic acid were separated by distillation.

6. The method of claim 1, wherein In step (3): The thermal decomposition reaction temperature is 350–650 °C; and / or, The reaction pressure for thermal pyrolysis is 1 kPa to 0.3 MPa; and / or, The residence time for thermal decomposition is 0.1–4 s; A dilution gas is introduced during thermal pyrolysis, wherein the volume ratio of isobutyric anhydride to dilution gas is 1:30 to 1:0.

2.

7. The method according to claim 6, characterized in that... In step (3): The thermal decomposition reaction temperature is 350–550 °C; and / or, The reaction pressure for thermal pyrolysis is 10 kPa to 0.1 MPa; and / or, The residence time for thermal decomposition is 0.1–1 s; The volume ratio of isobutyric anhydride to diluent gas is 1:20 to 1:0.

5.

8. The method according to claim 1, characterized in that: Step (3) also includes the rapid cooling of the thermal decomposition products and the absorption of dimethyl ketene.

9. The method according to claim 8, characterized in that: The final temperature of the rapid cooling process is 34–150 °C; the solvent used in the absorption process is selected from esters and / or ethers.

10. The method according to claim 9, characterized in that: The final temperature of the rapid cooling process is 34–120°C.

11. An apparatus for preparing dimethyl ketene, for performing the method according to any one of claims 1 to 10, comprising an acetic acid thermal decomposition unit, an isobutyric acid absorption unit, and an isobutyric anhydride thermal decomposition unit connected in series; wherein the isobutyric acid absorption unit comprises an absorption device and a separation device connected in series, wherein... The absorption device employs at least one of a bubble column, a spray column, and a stirred tank; the separation device is used to separate isobutyric anhydride and acetic acid, and the acetic acid stream flowing out of the separation device is returned to the acetic acid thermal cracking unit, and the separation device employs a distillation column; the isobutyric anhydride thermal cracking unit includes a rapid cooling device and an absorption device connected in sequence, the dimethyl ketone stream flowing out of the rapid cooling device flows into the absorption device, and the stream containing isobutyric acid flowing out of the rapid cooling device is returned to the isobutyric acid absorption unit.

12. The apparatus according to claim 11, characterized in that: The acetic acid thermal pyrolysis unit includes a pyrolysis furnace I; The isobutyric anhydride thermal cracking unit includes cracking furnace II.

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