A method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione

Abstract

The present invention provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione. Under an inert gas atmosphere, a mixed liquid of isobutyric anhydride or a mixture of isobutyric anhydride and isobutyric acid is vaporized to obtain a mixed gas, which is subjected to a high-temperature cracking reaction under the catalysis of a metal catalytic reaction system to obtain dimethylketene, and then 2,2,4,4-tetramethyl-1,3-cyclobutanedione is obtained through a dimerization reaction. In the present invention, the metal alloy material body is surface heat-treated to obtain a highly efficient metal catalytic reaction system. Under catalytic cracking conditions, the single-pass conversion rate of isobutyric anhydride or a mixture of isobutyric anhydride and isobutyric acid can reach up to 85.1%, and the selectivity of dimethylketene is as high as 95%. 2,2,4,4-Tetramethyl-1,3-cyclobutanedione is prepared from dimethylketene, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanedione is greater than 99.8%, and the dimerization yield is as high as 99.6%. The metal catalytic reaction system of the present invention has strong stability, and the stable operation time is greater than 2000 hours. The preparation process of the present invention is simple, low in cost, economically efficient and can be used for continuous industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic chemistry, and particularly relates to a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione. Background Art

[0002] As a polyester monomer, 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) can significantly improve the glass transition temperature, weather resistance and transparency of polyesters. Currently, the most representative copolyester using CBDO monomer is the commercial product Tritan copolyester of Eastman Chemical Company. Due to its characteristics such as no bisphenol A, good transparency and weather resistance, it is widely used in fields such as baby products, medical, cosmetics, and outdoors. The expansion of polyester product applications, the differential production of polyester products, and high-end special polyester products are the future development directions of the polyester industry. As a key intermediate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, its synthesis method is crucial for controlling tetramethylcyclobutanediol.

[0003] There are various methods for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione in the prior art. They are listed as follows:

[0004] The prior art CN111718252A provides a method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, including: step (a) pyrolyzing isobutyric anhydride to form a gas containing dimethylketene; step (b) introducing the gas containing dimethylketene into an ester solvent to dissolve dimethylketene in the ester solvent to form an ester solution containing dimethylketene; and step (c) allowing the ester solution containing dimethylketene to stand under an inert gas to dimerize dimethylketene to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione. This method does not use a catalyst and directly adopts a thermal pyrolysis method. Its conversion rate is between 30% and 70%, so there is mainly a problem of low single-pass conversion rate.

[0005] The prior art CN110105186B provides a method for preparing ketene compounds, including: (1) preheating a carrier gas, a lower hydrocarbon, and a carboxylic acid and / or an organic anhydride; (2) under high-temperature pyrolysis conditions, subjecting the preheated materials in step (1) to a high-temperature pyrolysis reaction; (3) separating the high-temperature pyrolysis reaction product obtained in step (2). In this method, lower hydrocarbons need to be mixed into the raw material gas. Mixing lower hydrocarbons has the following disadvantages: 1) Lower hydrocarbons may form carbon deposits on the catalyst surface due to high-temperature pyrolysis during the reaction, resulting in catalyst deactivation; 2) The products formed by the reaction of the lower hydrocarbons mixed in the raw materials cannot be recovered by economic means. It is obvious from the examples that not only is there obvious carbon deposition, but the contents of ethane, propylene, and propane in the tail gas are very low, and the economy of recycling using industrial pressure swing adsorption technology or distillation technology cannot be achieved.

[0006] The prior art US5258556A provides a method for manufacturing 2,2,4,4-tetramethylcyclobutane-1,3-diol: (1) feeding isobutyric anhydride into a pyrolysis zone, where the isobutyric anhydride is heated at a temperature of about 350 to 600 degrees; a vapor effluent containing dimethylketene, isobutyric acid, and unreacted isobutyric anhydride is produced after the reaction; (2) rapidly cooling the vapor effluent to condense isobutyric acid and isobutyric anhydride and separating the condensate from the dimethylketene vapor; (3) feeding the dimethylketene vapor into an absorption zone, where the dimethylketene vapor contacts and dissolves in a solvent containing 2,2,4,4-tetramethylcyclobutane-1,3-dione to produce an effluent containing a dimethylketene solution; (4) feeding the effluent from the absorption zone into a dimerization zone, where dimethylketene is converted into 2,2,4,4-tetramethylcyclobutane-1,3-dione. This method does not use a catalyst and directly adopts a thermal pyrolysis method. The examples show that the highest conversion rate is only 54.6%, and the single-pass conversion rate is not high.

[0007] In summary, in the prior art, the preparation of 2,2,4,4-tetramethyl-1,3-cyclobutanedione is divided into two methods: thermal pyrolysis and catalytic pyrolysis. In the prior art, the main problem with the thermal pyrolysis method is that the single-pass conversion rate of dimethylketene is not high. As a result, when the technology is implemented industrially, a large amount of unreacted raw material isobutyric anhydride needs to be separated by distillation and then returned to the reaction unit, resulting in increased distillation energy consumption and reduced economy during industrial implementation. In the catalytic pyrolysis in the prior art, there are obvious carbon deposits on the catalyst and the introduction of other impurities.

[0008] Therefore, developing a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione with a high single-pass conversion rate is an urgent problem to be solved in the art. Summary of the Invention

[0009] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione with a high single-pass conversion rate. Through the selection of a metal-catalyzed reaction system and the optimization of the method, the single-pass conversion rate and selectivity of dimethylketene are high, and the yield of 2,2,4,4-tetramethyl-1,3-cyclobutanedione prepared therefrom is high.

[0010] To achieve this purpose, the present invention adopts the following technical solutions:

[0011] The first purpose of the present invention is to provide a preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione. Under an inert gas atmosphere, a mixed liquid of isobutyric anhydride or a mixture of isobutyric anhydride and isobutyric acid is vaporized to obtain a mixed gas, which is subjected to a high-temperature cracking reaction under the catalysis of a metal-catalyzed reaction system to obtain dimethylketene, and then dimerized to obtain 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0012] The "under an inert gas atmosphere, a mixed liquid of isobutyric anhydride or a mixture of isobutyric anhydride and isobutyric acid is vaporized to obtain a mixed gas" mentioned in the present invention has the following several schemes: The first scheme is that under an inert gas atmosphere, isobutyric anhydride is vaporized to obtain a mixed gas of inert gas and isobutyric anhydride gas; the second scheme is that under an inert gas atmosphere, a mixed liquid of isobutyric anhydride and isobutyric acid is vaporized to obtain a mixed gas of inert gas, isobutyric anhydride and isobutyric acid gas.

[0013] Preferably, the metal-catalyzed reaction system includes a metal alloy material body and an alumina active layer formed on the surface of the metal alloy material body.

[0014] Preferably, the metal alloy material body is one selected from iron-chromium-aluminum alloy, iron-chromium-aluminum alloy and iron-chromium alloy, and iron-chromium-aluminum alloy and iron-nickel alloy;

[0015] More preferably, when the metal alloy material body is a mixed alloy, the mass fraction of iron-chromium-aluminum alloy in the mixed alloy is not less than 85%. The mixed alloy mentioned in the present invention refers to that the metal alloy material body is one of iron-chromium-aluminum alloy and iron-chromium alloy, and iron-chromium-aluminum alloy and iron-nickel alloy.

[0016] Among them, the mass fraction of iron-chromium-aluminum alloy in the mixed alloy can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, etc., but is not limited to the above-listed values, and other unlisted values within the above numerical range are equally applicable.

[0017] Preferably, the metal alloy material body is heat-treated at 500 - 1300 °C to form a metal catalytic reaction system with the alumina active layer on the surface;

[0018] More preferably, the temperature of the heat treatment is 800 - 1100 °C, and the time of the heat treatment is 10 - 20 h.

[0019] Among them, the temperature of the heat treatment can be 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C or 1300 °C, etc. More preferably, the temperature of the heat treatment can be 800 °C, 825 °C, 850 °C, 875 °C, 900 °C, 925 °C, 950 °C, 975 °C, 1000 °C, 1025 °C, 1050 °C, 1075 °C or 1100 °C, etc.; the time of the heat treatment can be 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h or 20 h, etc. However, it is not limited to the above-listed values, and other unlisted values within the above numerical range are equally applicable.

[0020] Preferably, the inside of the metal catalytic reaction system is a pore network structure, and the mesh number of the pore network is 20 - 500 meshes;

[0021] More preferably, the mesh number of the pore network is 50 - 150 meshes.

[0022] Among them, preferably, the mesh number of the pore network can be 20 meshes, 50 meshes, 100 meshes, 150 meshes, 200 meshes, 250 meshes, 300 meshes, 350 meshes, 400 meshes, 450 meshes or 500 meshes, etc. More preferably, the mesh number of the pore network can be 50 meshes, 60 meshes, 70 meshes, 80 meshes, 90 meshes, 100 meshes, 110 meshes, 120 meshes, 130 meshes, 140 meshes or 150 meshes, etc. However, it is not limited to the above-listed values, and other unlisted values within the above numerical range are equally applicable.

[0023] Preferably, the mixed gas is an inert gas and isobutyric anhydride gas, and the molar concentration range of isobutyric anhydride is 0.1 - 50%;

[0024] More preferably, the molar concentration range of isobutyric anhydride is 1 - 20%; Further preferably, the molar concentration range of isobutyric anhydride is 3 - 10%.

[0025] Among them, the mixed gas is an inert gas and isobutyric anhydride gas. The molar concentration range of isobutyric anhydride can be 0.1%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc.; more preferably, the molar concentration range of isobutyric anhydride can be 1%, 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5% or 20%, etc.; further preferably, the molar concentration range of butyric anhydride can be 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0026] Preferably, the mixed gas is an inert gas, isobutyric anhydride and isobutyric acid gas. The molar concentration of isobutyric anhydride is 0.1 - 50%, and the molar concentration of isobutyric acid is 0.1 - 30%.

[0027] More preferably, the molar concentration of isobutyric anhydride is 1 - 20%, and the molar concentration of isobutyric acid is 0.1 - 10%.

[0028] Further preferably, the molar concentration of isobutyric anhydride is 3 - 10%, and the molar concentration of isobutyric acid is 0.1 - 5%.

[0029] Among them, the mixed gas is an inert gas, isobutyric anhydride and isobutyric acid gas. The molar concentration of isobutyric anhydride can be 0.1%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., and the molar concentration of isobutyric acid can be 0.1%, 1%, 5%, 10%, 15%, 20%, 25% or 30%, etc.; more preferably, the molar concentration of isobutyric anhydride can be 1%, 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5% or 20%, etc., and the molar concentration of isobutyric acid can be 0.1%, 0.5%, 1%, 3%, 5%, 7.5% or 10%, etc.; further preferably, the molar concentration of isobutyric anhydride can be 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., and the molar concentration of isobutyric acid can be 0.1%, 0.25%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., but not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0030] Preferably, the temperature of the high-temperature pyrolysis reaction is 300 - 600 °C, the reaction residence time is 0.01 - 10 s, and the total pressure of the reaction system is 20 - 200 kPa.

[0031] More preferably, the temperature of the reaction is 450 - 550 °C, the reaction residence time is 0.05 - 2 s, and the total pressure of the reaction system is 20 - 150 kPa.

[0032] Among them, preferably, the temperature of the pyrolysis reaction can be 300 °C, 325 °C, 350 °C, 375 °C, 400 °C, 425 °C, 450 °C, 475 °C, 500 °C, 525 °C, 550 °C, 575 °C or 600 °C, etc., the reaction residence time can be 0.01 s, 0.05 s, 0.04 s, 0.07 s, 0.1 s, 1 s, 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s or 10 s, etc., and the total pressure of the reaction system can be 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, 100 kPa, 110 kPa, 120 kPa, 130 kPa, 140 kPa, 150 kPa, 160 kPa, 170 kPa, 180 kPa, 190 kPa or 200 kPa, etc.;

[0033] More preferably, the temperature of the reaction can be 450 °C, 460 °C, 470 °C, 475 °C, 480 °C, 490 °C, 500 °C, 510 °C, 520 °C, 530 °C, 540 °C or 550 °C, etc., the reaction residence time can be 0.05 s, 0.06 s, 0.07 s, 0.08 s, 0.09 s, 0.1 s, 0.12 s, 0.14 s, 0.16 s, 0.18 s, 0.2 s, 0.22 s, 0.24 s, 0.26 s, 0.28 s, 0.3 s, 0.32 s, 0.34 s, 0.36 s, 0.38 s, 0.4 s, 0.5 s, 0.6 s, 0.7 s, 0.8 s, 0.9 s, 1.0 s, 1.1 s, 1.2 s, 1.3 s, 1.4 s, 1.5 s, 1.6 s, 1.7 s, 1.8 s, 1.9 s or 2.0 s, etc., and the total pressure of the reaction system can be 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, 100 kPa, 110 kPa, 120 kPa, 130 kPa, 140 kPa or 150 kPa, etc.; however, it is not limited to the above-listed values, and other unlisted values within the above value range are equally applicable.

[0034] Preferably, after the pyrolysis reaction, a gas containing dimethylketene is obtained, and then dimethylketene is obtained by cooling, and the temperature of the cooling is -40 - 20 °C;

[0035] More preferably, the temperature of the cooling is -20 - 10 °C.

[0036] Among them, the temperature of the cooling can be -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C or 20°C, etc. More preferably, the temperature of the cooling can be -20°C, -17.5°C, -15°C, -12.5°C, -10°C, -7.5°C, -5°C, 0°C, 2.5°C, 5°C, 7.5°C or 10°C, etc.; however, it is not limited to the values listed above, and other unlisted values within the above numerical range are equally applicable.

[0037] Preferably, isobutyric anhydride or a mixed liquid of isobutyric anhydride and isobutyric acid is vaporized after preheating, and the temperature of the preheating is 150 - 400°C.

[0038] Among them, the temperature of the preheating can be 150°C, 175°C, 200°C, 225°C, 250°C, 275°C, 300°C, 325°C, 350°C, 375°C or 400°C, etc.; however, it is not limited to the values listed above, and other unlisted values within the above numerical range are equally applicable.

[0039] Preferably, the temperature of the dimerization reaction is 100 - 200°C, the reaction time is 0.1 - 10 h, and the pressure is 50 - 500 kPa;

[0040] More preferably, the temperature is 110 - 160°C, the reaction time is 0.5 - 5 h, and the pressure is 120 - 250 kPa.

[0041] Preferably, the dimethylketene is absorbed by an ester solvent and then undergoes a dimerization reaction, and the mass concentration of the dimethylketene in the ester solvent is 0.5 - 25%;

[0042] More preferably, the mass concentration is 0.5 - 10%.

[0043] Among them, preferably, the temperature of the dimerization reaction can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, etc.; the reaction time can be 0.1 h, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h or 10 h, etc.; the pressure can be 50 kPa, 100 kPa, 150 kPa, 200 kPa, 250 kPa, 300 kPa, 350 kPa, 400 kPa, 450 kPa or 500 kPa, etc.;

[0044] More preferably, the temperature can be 110°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C or 160°C, etc., the reaction time can be 0.5 h, 0.75 h, 1 h, 1.25 h, 1.5 h, 1.75 h, 2 h, 2.25 h, 2.5 h, 2.75 h, 3 h, 3.25 h, 3.5 h, 3.75 h, 4 h, 4.25 h, 4.5 h, 4.75 h or 5 h, etc., and the pressure can be 120 kPa, 130 kPa, 140 kPa, 150 kPa, 160 kPa, 170 kPa, 180 kPa, 190 kPa, 200 kPa, 210 kPa, 220 kPa, 230 kPa, 240 kPa or 250 kPa, etc.;

[0045] Preferably, the mass concentration of dimethylketene in the ester solvent can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, etc. More preferably, the mass concentration can be 0.5%, 0.75%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc., but not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0046] The ester solvent includes esters with 4 - 12 carbon atoms. The ester solvent can be selected from at least one or a combination of n-butyl acetate, isobutyl acetate, isobutyl isobutyrate, octyl acetate, ethyl propionate, etc.

[0047] The thermal conductivity of the metal catalytic reaction system of the present invention is not less than 10 W / (m·°C); the total pressure drop of the high-temperature cracking reaction catalyzed by the metal catalytic reaction system of the present invention is not greater than 5 kPa.

[0048] Among them, the thermal conductivity of the metal catalytic reaction system can be 10 W / (m·°C), 13 W / (m·°C), 15 W / (m·°C), 19 W / (m·°C) or 20 W / (m·°C), etc., but not limited to the values listed above. Other unlisted values within the above numerical range are equally applicable.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention provides a method for preparing 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione. A metal alloy material body is subjected to surface heat treatment to obtain a highly efficient metal catalytic reaction system. Under catalytic cracking conditions, the single - pass conversion rate of isobutyric anhydride or a mixture of isobutyric anhydride and isobutyric acid can reach up to 85.1%, and the selectivity of dimethylketene is as high as 95%. 2,2,4,4 - Tetramethyl - 1,3 - cyclobutanedione is prepared from dimethylketene, and the selectivity of 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione is greater than 99.8%, and the dimerization yield is as high as 99.6%. The metal catalytic reaction system of the present invention has strong stability, and the stable operation time is greater than 2000 hours. The preparation process of the present invention is simple, low - cost, economically efficient and can be used for continuous industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 are SEM images of the surface - treated metal catalytic reaction system provided in Example 1 and Example 2 of the present invention;

[0052] Figure 2 are XRD images of the surface - treated metal catalytic reaction system provided in Example 1 and Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0053] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0054] Example 1

[0055] This example provides a method for preparing 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione. The specific preparation method is as follows:

[0056] S1. Take the metal alloy material body as an iron - chromium - aluminum alloy, calcine it at 950 °C for 15 h to obtain a metal catalytic reaction system with an alumina active layer on the surface. As shown in the attached figure, the average mesh number of the pore network inside the metal catalytic reaction system is 100 mesh. Fill the above - mentioned metal catalytic reaction system into a reactor; Figure 1-2 As shown, the average mesh number of the pore network inside the metal catalytic reaction system is 100 mesh. Fill the above - mentioned metal catalytic reaction system into a reactor;

[0057] S2. Under a nitrogen atmosphere, use a metering pump to control the molar concentration of isobutyric anhydride feed to be 6.1%. After the two are mixed, they enter a pre - heater at 200 °C to be vaporized to obtain a mixed gas. The mixed gas enters the above - mentioned reactor for high - temperature cracking reaction. The reaction temperature is 450 °C, the reaction residence time is about 0.12 s, and the reaction pressure is 150 kPa. The gas at the reactor outlet passes through a condenser, is cooled to 4 °C and then undergoes gas - liquid separation to obtain dimethylketene. The single - pass conversion rate of isobutyric anhydride is 85.1%, and the selectivity of dimethylketene is 95%;

[0058] S3. Feed the dimethylketene prepared above into an absorption column, and introduce n-butyl acetate at a rate of 8 ml / min for absorption. The yield of dimethylketene absorbed by n-butyl acetate is 99.8%. The absorbed solution (the mass concentration of dimethylketene in n-butyl acetate is 5%) enters a reaction kettle to undergo a dimerization reaction. The reaction temperature is 140 °C, the time is 2 h, and the pressure is 200 kPa, obtaining an n-butyl acetate solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione. The conversion rate is 99.8%, and the yield is 99.6%.

[0059] In this example, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 3 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0060] Example 2

[0061] This example provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as Example 1. The difference is that in step S1, the metal alloy material body is calcined at 950 °C for 10 h, as shown in the appendix. Finally, the single-pass conversion rate of isobutyric anhydride is 84.2%, and the selectivity of dimethylketene is 94.8%. Figure 1-2 Finally, the single-pass conversion rate of isobutyric anhydride is 84.2%, and the selectivity of dimethylketene is 94.8%.

[0062] In this example, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 3 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0063] Example 3

[0064] This example provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as Example 1. The difference is that in step S1, the metal alloy material body is calcined at 800 °C for 15 h. Finally, the single-pass conversion rate of isobutyric anhydride is 84.6%, and the selectivity of dimethylketene is 94.2%.

[0065] In this example, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 4 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0066] Example 4

[0067] This embodiment provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that of Embodiment 1. The difference lies in that in step S1, the average mesh number of the pore network inside the metal catalytic reaction system is 150 meshes, and in step S2, the reaction residence time is about 0.1 s. Finally, the single-pass conversion rate of isobutyric anhydride is 83.5%, and the selectivity of dimethylketene is 92.6%.

[0068] In this embodiment, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 4 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0069] Embodiment 5

[0070] This embodiment provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that of Embodiment 1. The difference lies in that in step S1, the metal alloy material body is iron-chromium-aluminum alloy and iron-chromium alloy, and the mass fraction of the iron-chromium-aluminum alloy is 90%. Finally, the single-pass conversion rate of isobutyric anhydride is 82.3%, and the selectivity of dimethylketene is 92.1%.

[0071] In this embodiment, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 3 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0072] Embodiment 6

[0073] This embodiment provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that of Embodiment 1. The difference lies in that in step S1, the metal alloy material body is iron-chromium-aluminum alloy and iron-nickel alloy, and the mass fraction of the iron-chromium-aluminum alloy is 95%. Finally, the single-pass conversion rate of isobutyric anhydride is 80.1%, and the selectivity of dimethylketene is 90.8%.

[0074] In this embodiment, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 5 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0075] Embodiment 7

[0076] This embodiment provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that of Embodiment 1. The difference lies in that in step S2, in the high-temperature cracking reaction, the reaction residence time is 10 s. Finally, the single-pass conversion rate of isobutyric anhydride is 75.6%, and the selectivity of dimethylketene is 87.9%.

[0077] In this embodiment, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 5 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0078] Example 8

[0079] This embodiment provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as Example 1, except that in step S2, under a nitrogen atmosphere, a metering pump is used to control the molar concentration of isobutyric anhydride feed to be 9.6%, and the single-pass conversion rate of isobutyric anhydride is finally 84.2%, and the selectivity of dimethylketene is 94.8%.

[0080] In this embodiment, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 5 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0081] Example 9

[0082] This embodiment provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as Example 1, except that in step S2, under a nitrogen atmosphere, a metering pump is used to control the molar concentration of isobutyric acid to be 1.1% and the molar concentration of isobutyric anhydride to be 5%. Finally, the single-pass conversion rates of isobutyric anhydride and isobutyric acid are 82.4%, and the selectivity of dimethylketene is 93%.

[0083] In this embodiment, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 4 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0084] Example 10

[0085] This embodiment provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as Example 1, except that in step S2, under a nitrogen atmosphere, a metering pump is used to control the molar concentration of isobutyric acid to be 0.1% and the molar concentration of isobutyric anhydride to be 6%. Finally, the single-pass conversion rates of isobutyric anhydride and isobutyric acid are 83.5%, and the selectivity of dimethylketene is 94.1%.

[0086] In this embodiment, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature cracking unit system is less than 3 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0087] Example 11

[0088] This example provides a method for preparing 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione, which is basically the same as Example 1. The difference is that in step S2, for the high - temperature pyrolysis reaction, the reaction temperature is 550 °C, the reaction residence time is about 2 s, the reaction pressure is 170 kPa, and the single - pass conversion rate of isobutyric anhydride to obtain is 88.1%, and the selectivity of dimethylketene is 93.2%.

[0089] In this example, the reactor with a metal - catalyzed reaction system can be reused up to 2000 h, the pressure drop of the high - temperature pyrolysis unit system is less than 4 kPa, and the catalytic activity of the metal - catalyzed reaction system can still be maintained.

[0090] Example 12

[0091] This example provides a method for preparing 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione, which is basically the same as Example 10. The difference is that in step S3, the absorbed solution (the mass concentration of dimethylketene in n - butyl acetate is 10%) enters the reaction kettle to undergo a dimerization reaction, obtaining an n - butyl acetate solution containing 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione, with a conversion rate of 98.2% and a yield of 98.0%.

[0092] In this example, the reactor with a metal - catalyzed reaction system can be reused up to 2000 h, the pressure drop of the high - temperature pyrolysis unit system is less than 3 kPa, and the catalytic activity of the metal - catalyzed reaction system can still be maintained.

[0093] Example 13

[0094] This example provides a method for preparing 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione, which is basically the same as Example 10. The difference is that in step S3, the absorbent is isobutyl acetate at 8 ml / min, the yield of dimethylketene absorbed by isobutyl acetate is 98.5%, obtaining an isobutyl acetate solution containing 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione, with a conversion rate of 98% and a yield of 96.5%.

[0095] In this example, the reactor with a metal - catalyzed reaction system can be reused up to 2000 h, the pressure drop of the high - temperature pyrolysis unit system is less than 3 kPa, and the catalytic activity of the metal - catalyzed reaction system can still be maintained.

[0096] Example 14

[0097] This embodiment provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that of Embodiment 10. The difference is that in step S3, the absorbent is a mixed solvent of n-butyl acetate and isobutyl acetate at 8 ml / min, the yield of dimethylketene absorbed by the mixed solvent is 99.5%, and a mixed solvent solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione is obtained, with a conversion rate of 98.5% and a yield of 98%.

[0098] In this embodiment, the reactor with a metal catalytic reaction system can be reused up to 2000 h, the pressure drop of the high-temperature pyrolysis unit system is less than 3 kPa, and the catalytic activity of the metal catalytic reaction system can still be maintained.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that of Embodiment 1. The difference is that in step S1, the metal catalytic reaction system is replaced with an alumina catalyst, the pressure drop of its bed layer becomes larger, and the reaction performance becomes worse. As the reaction runs for 20 h, the pressure drop of the high-temperature pyrolysis unit system increases to 10 kPa. Finally, the single-pass conversion rate of isobutyric anhydride is 41.2%, and the selectivity of dimethylketene is 45.3%. After the reaction runs for 25 h, the single-pass conversion rate of isobutyric anhydride decreases to 20%. Therefore, the catalyst life of this comparative example is short and the stability is not high.

[0101] Comparative Example 2

[0102] This comparative example provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that of Embodiment 1. The difference is that in step S1, the metal catalytic reaction system is replaced with a silica catalyst, the pressure drop of its bed layer becomes larger, and the reaction performance becomes worse. As the reaction runs for 20 h, the pressure drop of the high-temperature pyrolysis unit system increases to 9 kPa. Finally, the single-pass conversion rate of isobutyric anhydride is 38.2%, and the selectivity of dimethylketene is 46.3%. After the reaction runs for 25 h, the single-pass conversion rate of isobutyric anhydride decreases to 8%. Therefore, the catalyst life of this comparative example is short and the stability is poor.

[0103] Comparative Example 3

[0104] This comparative example provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that of Embodiment 1. The difference is that in step S1, the metal alloy material body is not calcined at high temperature and is directly used for catalyzing the high-temperature pyrolysis reaction. The reaction performance becomes worse, and finally the single-pass conversion rate of isobutyric anhydride is 21.3%, and the selectivity of dimethylketene is 45.3%.

[0105] Comparative Example 4

[0106] This comparative example provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that in Example 1. The difference is that in step S2, the temperature of the high-temperature pyrolysis reaction is 700 °C, the single-pass conversion rate of isobutyric anhydride in the pyrolysis reaction is 50.3%, and the selectivity is 15.6%. After the device runs for 30 h, the catalyst is significantly carbon-deposited and its performance deteriorates further.

[0107] In addition, we also tried some pressures and residence times that are not within the scope of the present invention. For example, when other conditions are the same as those in Example 1 and the pressure is 300 kPa, the catalyst is significantly carbon-deposited, the single-pass conversion rate is 30.6%, and the selectivity is 34.5%; when the residence time is selected as 3 min, the single-pass conversion rate of isobutyric anhydride is 42.3%, and the selectivity is 12.0%.

[0108] Comparative Example 5

[0109] This comparative example provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that in Example 10. The difference is that in step S3, toluene at 8 ml / min is used as the absorbent, and the yield of dimethylketene absorbed by toluene is only 62.3%. An ethyl acetate solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione is obtained, with a conversion rate of 52% and a yield of 45.2%.

[0110] Comparative Example 6

[0111] This comparative example provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, which is basically the same as that in Example 10. The difference is that in step S3, the absorbed solution (the mass concentration of dimethylketene in n-butyl acetate is 20%) enters the reaction kettle to undergo a dimerization reaction, and an ethyl acetate solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione is obtained, with a conversion rate of 87% and a yield of 35%. Since the concentration of DMK in n-butyl acetate is too high, DMK undergoes polymerization, resulting in more by-products and thus a lower conversion rate of DMK.

[0112] In addition, we also tested when the concentration of DMK in n-butyl acetate is very low, about 0.2 wt%. When other conditions are the same as those in Example 1, due to the very low concentration, the process economy is poor.

[0113] The present invention provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione. By subjecting the metal alloy material body to surface heat treatment, a highly efficient metal catalytic reaction system is obtained. Under catalytic cracking conditions, the single-pass conversion rate of isobutyric anhydride or a mixture of isobutyric anhydride and isobutyric acid can reach up to 85.1%, and the selectivity of dimethylketene is as high as 95%. 2,2,4,4-Tetramethyl-1,3-cyclobutanedione is prepared from dimethylketene, with the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanedione being greater than 99.8% and the dimerization yield being as high as 99.6%. The metal catalytic reaction system of the present invention has strong stability and a stable operation time of more than 2000 hours. The preparation process of the present invention is simple, low-cost, economically efficient, and can be used for continuous industrial production.

[0114] The applicant declares that the present invention uses the above embodiments to illustrate a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione of the present invention, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods such as reaction conditions, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing 2,2,4,4 - tetramethyl - 1,3 - cyclobutanedione, characterized in that, Under an inert gas atmosphere, the mixed liquid of isobutyric anhydride or isobutyric anhydride and isobutyric acid is vaporized to obtain a mixed gas, which is subjected to a high-temperature cracking reaction under the catalysis of a metal catalytic reaction system to obtain dimethylketene, and then undergoes a dimerization reaction to obtain 2,2,4,4-tetramethyl-1,3-cyclobutanedione; Among them, the metal catalytic reaction system includes a metal alloy material body and an alumina active layer formed on the surface of the metal alloy material body; the metal alloy material body is one selected from iron-chromium-aluminum alloy, iron-chromium-aluminum alloy and iron-chromium alloy, and iron-chromium-aluminum alloy and iron-nickel alloy; the metal alloy material body is calcined at 500-1300 °C for 10-20 h to form a metal catalytic reaction system with the alumina active layer on the surface.

2. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 1, wherein The temperature of the calcination is 800-1100 °C.

3. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to any one of claims 1-2, characterized in that, The interior of the metal catalytic reaction system is a pore network structure, and the mesh number of the pore network is 20-500 meshes.

4. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 3, characterized in that, The mesh number of the pore network is 50-150 meshes.

5. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to any one of claims 1-2, characterized in that, The mixed gas is an inert gas and isobutyric anhydride gas, and the molar concentration range of isobutyric anhydride is 0.1-50%.

6. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 5, characterized in that, The molar concentration range of isobutyric anhydride is 1-20%.

7. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 6, characterized in that, The molar concentration range of isobutyric anhydride is 3-10%.

8. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to any one of claims 1-2, characterized in that, The mixed gas is an inert gas, isobutyric anhydride and isobutyric acid, the molar concentration of isobutyric anhydride is 0.1-50%, and the molar concentration of isobutyric acid is 0.1-30%.

9. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 8, characterized in that, The molar concentration of isobutyric anhydride is 1-20%, and the molar concentration of isobutyric acid is 0.1-10%.

10. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 9, characterized in that, The molar concentration of isobutyric anhydride is 3-10%, and the molar concentration of isobutyric acid is 0.1-5%.

11. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to any one of claims 1-2, characterized in that, The temperature of the high-temperature cracking reaction is 300-600 °C, the reaction residence time is 0.01-10 s, and the total pressure of the reaction system is 20-200 kPa.

12. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 11, characterized in that, The temperature of the reaction is 450-550 °C, the reaction residence time is 0.05-2 s, and the total pressure of the reaction system is 20-150 kPa.

13. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to any one of claims 1-2, characterized in that, After the high-temperature cracking reaction, a gas containing dimethylketene is obtained, and then it is cooled to -40-20 °C to obtain dimethylketene.

14. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 13, characterized in that, The temperature of the cooling is -20-10 °C.

15. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to any one of claims 1-2, characterized in that, The mixed liquid of isobutyric anhydride or isobutyric anhydride and isobutyric acid is vaporized after being preheated, and the temperature of the preheating is 150-400 °C.

16. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to any one of claims 1-2, characterized in that, The temperature of the dimerization reaction is 100-200 °C, the reaction time is 0.1-10 h, and the pressure is 50-500 kPa.

17. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 16, wherein, The temperature is 110-160 °C, the reaction time is 0.5-5 h, and the pressure is 120-250 kPa.

18. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to any one of claims 1-2, characterized in that, The dimethylketene is absorbed by an ester solvent and then undergoes a dimerization reaction. The mass concentration of dimethylketene in the ester solvent is 0.5-25%.

19. The preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione according to claim 18, characterized in that, The mass concentration of dimethylketene in the ester solvent is 0.5-10%.

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