A method for preparing dimethyl ketene by cracking isobutyric anhydride

Abstract

The present invention provides a method for preparing dimethyl ketone by cracking isobutyric anhydride. In the method, isobutyric anhydride is mixed with a catalyst and then vaporized, and the mixture is introduced into a cracking furnace. Ammonia gas is introduced into the cracked product to quench the catalyst, and the product is rapidly condensed to obtain dimethyl ketone in the gas phase, while the liquid phase is mainly unreacted isobutyric anhydride and generated isobutyric acid. In the present invention, the single-pass conversion rate of isobutyric acid is ≥68%, and the selectivity of dimethyl ketone is ≥90%, thereby greatly improving the utilization rate of isobutyric anhydride.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and particularly relates to a method for preparing dimethyl ketene by cracking isobutyric anhydride. Background Art

[0002] Ketene compounds are special unsaturated ketones containing ketone groups, in which the carbonyl group of the ketone molecule is connected to another carbon atom by a double bond. Since the molecular structure of these compounds is highly unsaturated, they can undergo addition, decomposition and polymerization reactions, and can synthesize a variety of compounds. There are many methods for preparing ketenes. One is the dehalogenation method of α-acyl halide compounds. This method has many side reactions, low selectivity, long reaction time, and high cost for three waste treatment. Another method is the high-temperature cracking method of fatty acids or fatty acid anhydrides. This method has low raw material cost and fast reaction rate, so the commonly used method in industry is the high-temperature cracking method of fatty acids or fatty acid anhydrides.

[0003] Dimethyl ketone (DMK) is an important intermediate in the preparation of 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO). In industry, it is mainly obtained by cracking isobutyric anhydride. The reaction equation is shown in Formula 1.

[0004]

[0005] Eastman patents US5258556A and US5169994A disclose a method for preparing dimethyl ketone by cracking isobutyric anhydride, with a cracking temperature of 350°C-600°C, a pressure of 3KPa-70KPa, a residence time of 0.01S-8S, an isobutyric anhydride conversion rate of 60%, and a dimethyl ketone yield of about 40%. No catalyst is required during the reaction, the reaction temperature is high, and it takes time for the high-temperature reaction liquid to cool to 20°C-40°C. In this process, dimethyl ketone is prone to reverse reaction with the product isobutyric acid, thereby reducing the single-pass conversion rate of isobutyric anhydride cracking. In addition, too high a cracking temperature will also cause further cracking of dimethyl ketone to produce low-molecular byproducts and even carbon deposition.

[0006] Patent CN202010834382.3 discloses a method for preparing ketene substances by cracking carboxylic acids or organic anhydrides, using metal oxides or non-metallic oxides as catalysts, wherein the metal oxides are one or more of MgO, ZnO and TiO2, and the non-metallic oxide catalyst is SiO2 or triethyl phosphate. The reaction temperature is 450℃-750℃, the pressure is 15KPa-60KPa, the residence time is 0.1s-1s, and by adding low-carbon alkanes to the raw materials to reduce the generation of by-products, overcome the problem of carbon deposition, and improve the yield of ketene compounds. However, this method has a high reaction temperature and introduces new hydrocarbon substances into the system, which will also crack and produce carbon deposition at high temperatures.

[0007] In summary, the current industrial preparation method of dimethyl ketene mainly adopts the isobutyric anhydride cracking method, which has high reaction temperature, many by-products in the cracking process, low product yield, severe reverse reaction during the cooling process of the reaction product, and low single-pass conversion rate. Therefore, it is necessary to find a new method to reduce the cracking reaction temperature, reduce the occurrence of side reactions in the cracking process, reduce carbon deposition, and increase the yield of ketene compounds, thereby reducing the production cost of dimethyl ketene. Summary of the invention

[0008] The invention provides a method for preparing dimethyl ketone by cracking isobutyric anhydride. Specifically, a new catalyst is used to reduce the reaction temperature of the cracking of isobutyric anhydride, reduce the occurrence of side reactions during the cracking process, and increase the yield of dimethyl ketone, thereby improving the economic efficiency of the device.

[0009] In order to achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing dimethyl ketene by cracking isobutyric anhydride, the method comprising the following steps:

[0011] S1: Raw material vaporization: isobutyric anhydride and catalyst are mixed in a certain proportion, preheated in a raw material preheater, and then enter an evaporator for vaporization to obtain raw material gas;

[0012] S2: High temperature cracking: The raw gas and preheated nitrogen are mixed in a certain proportion and enter the cracking furnace for high temperature cracking to obtain cracked gas;

[0013] S3: Gas-liquid separation: Add ammonia to the cracking gas at the cracking furnace outlet and cool it quickly to separate the products.

[0014] In the present invention, the catalyst in S1 is isopentenyl pyrophosphate, and the structural formula is:

[0015]

[0016] In the present invention, the catalyst in S1 accounts for 0.001%-0.1% of the mass of isobutyric anhydride, and preferably the catalyst accounts for 0.01%-0.1% of the mass of isobutyric anhydride.

[0017] In the present invention, the preheating temperature of S1 is 80°C-180°C, preferably 120°C-180°C, the vaporization temperature is 200°C-350°C, preferably 250°C-350°C, and the pressure of the preheater and the evaporator is 10KPa-100KPa, preferably 10KPa-40KPa.

[0018] In the present invention, the temperature of the preheated nitrogen in S2 is consistent with the vaporization temperature of the raw material, which is 200°C-350°C, preferably 250°C-350°C.

[0019] In the present invention, the mass ratio of the raw gas to nitrogen in the S2 is 5:1-50:1, preferably 10:1-30:1. The cracking furnace tube temperature of the S2 is 300°C-500°C, the residence time is 0.01S-10S, preferably 0.1S-8S, and the pressure is 10KPa-100KPa, preferably 10KPa-40KPa.

[0020] In the present invention, the mass of ammonia introduced into the cracked gas in S3 is 0.00015%-0.015% of the mass of isobutyric anhydride in the raw material, preferably 0.0015%-0.015%.

[0021] In the present invention, the purpose of adding ammonia to the cracking gas is to neutralize isopentyl pyrophosphate and react it to form isopentyl pyrophosphate, thereby preventing the catalysis of dimethyl ketone and isobutyric acid from reacting inversely to form isobutyric anhydride during the cooling process of the cracking gas, thereby improving the reaction conversion rate and selectivity. The reaction equation is shown in Formula 3.

[0022]

[0023] In the present invention, the cooling temperature in S3 is 10°C-50°C, preferably 20°C-30°C, and the pressure is consistent with the cracking furnace pressure. The liquid phase after cooling mainly contains isobutyric acid, unreacted isobutyric anhydride, by-product acetone, isopentyl pyrophosphate, etc.; the gas phase after cooling contains dimethyl ketone and a small amount of CO, CO2, methane, ethane, propylene, etc.

[0024] The experimenters of the present invention found that under the catalysis of isopentenyl pyrophosphate, the isobutyric anhydride cracking conversion rate X (unit %), dimethyl ketone selectivity S (unit %) and catalyst dosage, cracking pressure, cracking temperature, cracking residence time are related, and the relationship conforms to the following formula:

[0025] Correlation factor: a = log[(T + P 1.3 )*t*x]+3

[0026] Isobutyric anhydride conversion rate: X = 1.0471a 3 -11.692a 2 +37.126a+46.22

[0027] Dimethyl ketone selectivity: S = -0.1637a 3 +1.9515a 2 -6.0244a+96.429

[0028] Where, x is the mass fraction of catalyst in isobutyric anhydride, %

[0029] P——cracking pressure, KPa

[0030] T——cracking temperature, K

[0031] t——residence time, s.

[0032] Compared with the prior art, the positive effects of the present invention are:

[0033] (1) By adopting the above method, the single-pass conversion rate of isobutyric anhydride is ≥68%, and the selectivity of dimethyl ketone is ≥90%, which greatly improves the utilization rate of isobutyric anhydride;

[0034] (2) The present invention reduces the cracking reaction temperature by adding isopentenyl pyrophosphate, reduces the generation of CO, CO2, methane, ethane, propylene, etc. during the cracking process, reduces coking and carbon generation, and improves the product yield; and reduces the partial pressure of isobutyric anhydride by adding nitrogen to the raw material, promotes the cracking of isobutyric anhydride, improves the conversion rate of isobutyric anhydride, and reduces the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a process flow chart of the present invention.

[0036] Those skilled in the art will recognize that, since the attached drawings are schematic, a set of industrial equipment requires some other equipment, such as condensers, heat exchangers, reflux tanks, tower reboilers, pumps, vacuum pumps, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, liquid level controllers, receiving tanks, storage tanks, etc. The specifications of these auxiliary equipment are not within the scope of the present invention and can be considered based on conventional chemical technology.

[0037] like Figure 1 As shown, P01 is an isobutyric anhydride feed pump, P02 is a catalyst feed pump, M01 is a static mixer, E01 is a raw material preheater, E02 is a raw material evaporator, E03 is a nitrogen preheater, E04 is a cracking furnace, and E05 is a rapid cooler.

[0038] Isobutyric anhydride (stream 1) and catalyst (stream 2) are respectively pumped to a static mixer M01 for mixing. The mixed material (stream 3) enters a raw material preheater E01 for preheating to obtain stream 4, and then enters a vaporizer E02 for vaporization. Nitrogen (stream 5) enters E03 for preheating (stream 6) and is mixed with the vaporized material to obtain stream 7. Then, the material passes through a cracking furnace E04 for cracking reaction to produce a product (stream 8). Ammonia (stream 9) is added to the cracking product (stream 8) to deactivate the catalyst. The deactivated material (stream 10) passes through a rapid condenser E05 to obtain a gas phase product (stream 12) and a liquid phase material (stream 11). DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with examples. These examples are only used to illustrate the present invention, but not to limit the scope of the present invention.

[0040] The main raw material information is as follows:

[0041] Raw material name Specification factory Isobutyric anhydride AR Xilong Chemical Industry Co., Ltd. Isopentenyl pyrophosphate -- Shanghai Fantai Biotechnology Co., Ltd. Ammonia High purity Hainan Xingdao Gas Technology Co., Ltd.

[0042] The device information is as follows:

[0043] Device Name Equipment Specifications Equipment manufacturers Cracking furnace Material 317L Keli Chemical Equipment Co., Ltd. Static mixer Material 317L Keli Chemical Equipment Co., Ltd. Heat Exchanger Material 317L Keli Chemical Equipment Co., Ltd.

[0044] The gas chromatography analysis conditions are:

[0045] Analytical instrument: Agilent 7820, capillary column (wax);

[0046] Gas phase analysis method: area normalization method;

[0047] Gas phase analysis conditions: vaporization chamber temperature was 270°C, detector temperature was 270°C, column temperature was programmed: 50°C, 5 min; 80°C, 10°C / min to 250°C, 5 min.

[0048] Example 1

[0049] Isobutyric anhydride with a flow rate of 1000g / h and isopentyl pyrophosphate catalyst with a flow rate of 0.5g / h are mixed in a static mixer and then enter the raw material preheater for preheating at a preheating temperature of 150°C. Then, they enter the vaporizer for vaporization and maintain the temperature at 300°C. The preheater and evaporator pressures are 60KPa. After that, the 300°C raw gas is mixed with 300°C nitrogen and enters the cracking furnace. The nitrogen flow rate is 100g / h, the cracking furnace temperature is 400°C, the residence time is 1S, and the pressure is 60KPa. After adding 100mg / h of ammonia to the cracking reaction gas, it enters the cooler to reduce the cracking gas temperature to 30°C. The gas phase obtains a mixture of dimethyl ethylene ketone and nitrogen, and the liquid phase is unreacted isobutyric anhydride and generated isobutyric acid.

[0050] The single-pass conversion of isobutyric anhydride was 71.35%, and the selectivity of dimethyl ketone was 94.14%.

[0051] Example 2

[0052] Isobutyric anhydride with a flow rate of 1000g / h and isopentyl pyrophosphate catalyst with a flow rate of 0.01g / h are mixed in a static mixer and then enter the raw material preheater for preheating at a preheating temperature of 180°C. Then, they enter the vaporizer for vaporization and maintain the temperature at 350°C. The preheater and evaporator pressures are 100KPa. After that, the 350°C raw gas is mixed with 350°C nitrogen and enters the cracking furnace. The nitrogen flow rate is 200g / h, the cracking furnace temperature is 500°C, the residence time is 0.01S, and the pressure is 100KPa. After adding 2mg / h of ammonia to the cracking reaction gas, it enters the cooler to reduce the cracking gas temperature to 50°C. The gas phase obtains a mixture of dimethyl ethylene ketone and nitrogen, and the liquid phase is unreacted isobutyric anhydride and generated isobutyric acid.

[0053] The single-pass conversion of isobutyric anhydride was 73.82%, and the selectivity of dimethyl ketone was 92.02%.

[0054] Example 3

[0055] Isobutyric anhydride with a flow rate of 1000g / h and isopentyl pyrophosphate catalyst with a flow rate of 1g / h are mixed in a static mixer and then enter the raw material preheater for preheating at 80°C. Then, they enter the vaporizer for vaporization and maintain the temperature at 200°C. The pressure of the preheater and the evaporator is 10KPa. After that, the 200°C raw gas is mixed with 200°C nitrogen and enters the cracking furnace. The flow rate of nitrogen is 21g / h, the temperature of the cracking furnace is 300°C, the residence time is 10S, and the pressure is 10KPa. After adding 100mg / h of ammonia to the cracking reaction gas, it enters the cooler to reduce the cracking gas temperature to 10°C. The gas phase obtains a mixture of dimethyl ketone and nitrogen, and the liquid phase is unreacted isobutyric anhydride and generated isobutyric acid.

[0056] The single-pass conversion of isobutyric anhydride was 72.34%, and the selectivity of dimethyl ketone was 95.19%.

[0057] Example 4

[0058] Isobutyric anhydride with a flow rate of 1000g / h and isopentyl pyrophosphate catalyst with a flow rate of 0.1g / h are mixed in a static mixer and then enter the raw material preheater for preheating at a preheating temperature of 120°C. Then, they enter the vaporizer for vaporization and maintain the temperature at 250°C. The pressure of the preheater and the evaporator is 40KPa. After that, the 250°C raw gas is mixed with 250°C nitrogen and enters the cracking furnace. The nitrogen flow rate is 50g / h, the cracking furnace temperature is 450°C, the residence time is 0.6S, and the pressure is 40KPa. After adding 20mg / h of ammonia to the cracking reaction gas, it enters the cooler to reduce the cracking gas temperature to 40°C. The gas phase obtains a mixture of dimethyl ketone and nitrogen, and the liquid phase is unreacted isobutyric anhydride and generated isobutyric acid.

[0059] The single-pass conversion of isobutyric anhydride was 76.53%, and the selectivity of dimethyl ketone was 92.57%.

[0060] Comparative Example 1

[0061] Compared with Example 1, no isopentenyl pyrophosphate catalyst and no ammonia gas as a catalyst quencher were added in Comparative Example 1. The single-pass conversion rate of isobutyric anhydride was only 54.16%, and the selectivity of dimethyl ketone was only 88.75%.

[0062] Comparative Example 2

[0063] Compared with Example 1, no nitrogen was added before cracking in Comparative Example 2. The single-pass conversion rate of isobutyric anhydride was 68.79%, the selectivity of dimethyl ketone was 82.54%, the carbon deposit content at the cracking furnace outlet was 1.68%, and the reaction tube was easily blocked.

[0064] Comparative Example 3

[0065] Compared with Example 1, no catalyst quencher ammonia was added in Comparative Example 3. The single-pass conversion rate of isobutyric anhydride was 55.13%, and the selectivity of dimethyl ketone was 91.37%. A large amount of dimethyl ketone reacted with isobutyric acid during the cooling process and was converted into isobutyric anhydride.

Claims

1. A method for preparing dimethyl ketene by cracking isobutyric anhydride, the method comprising the following steps: S1: Raw material vaporization: After isobutyric anhydride and catalyst are mixed, they are preheated and vaporized to obtain raw material gas; S2: High temperature cracking: the raw gas and preheated nitrogen are mixed and cracked at high temperature to obtain cracked gas; S3: Gas-liquid separation: Add ammonia to the cracked gas and then cool it quickly to separate the products; in, The catalyst in S1 is isopentenyl pyrophosphate, and its structural formula is:

2. The method according to claim 1, wherein: The catalyst in S1 accounts for 0.001%-0.1% of the mass of isobutyric anhydride.

3. The method according to claim 1, wherein: The catalyst in S1 accounts for 0.01%-0.1% of the mass of isobutyric anhydride.

4. The method according to any one of claims 1 to 3, wherein: The preheating temperature of S1 is 80°C-180°C, and the vaporization temperature is 200°C-350°C.

5. The method according to claim 4, wherein: The preheating temperature of S1 is 120°C-180°C, and the vaporization temperature is 250°C-350°C.

6. The method according to claim 1, wherein: The temperature of the preheated nitrogen in S2 is 200°C-350°C; The mass ratio of raw gas to nitrogen is 5:1-50:

1.

7. The method according to claim 6, wherein: The temperature of the preheated nitrogen in S2 is 250°C-350°C; The mass ratio of raw gas to nitrogen is 10:1-30:

1.

8. The method according to claim 1 or 6, wherein: The cracking temperature of S2 is 300°C-500°C, the residence time is 0.01S-10S, and the pressure is 10KPa-100KPa.

9. The method according to claim 8, wherein: The residence time of S2 is 0.1S-8S, and the pressure is 10KPa-40KPa.

10. The method according to claim 1, wherein: The mass of ammonia introduced into the cracked gas in S3 is 0.00015%-0.015% of the mass of isobutyric anhydride in the raw material.

11. The method according to claim 10, wherein: The mass of ammonia introduced into the cracked gas in S3 is 0.0015%-0.015% of the mass of isobutyric anhydride in the raw material.

12. The method according to claim 1 or 10, wherein: The cooling temperature in S3 is 10°C-50°C.

13. The method according to claim 12, wherein: The cooling temperature in S3 is 20°C-30°C.

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