A method for preparing tetramethylcyclobutanedione

Abstract

The application provides a method for preparing tetramethyl cyclobutanedione, which comprises the following steps: (1) absorbing a gas rich in dimethyl vinyl ketone DMK by a first absorbent to obtain a first absorption solution; (2) performing a polymerization reaction on the first absorption solution, and precipitating a solid product after cooling; (3) dissolving the solid product in a second absorbent to configure a third absorbent; (4) absorbing the gas rich in dimethyl vinyl ketone DMK by the third absorbent to obtain a second absorption solution; and (5) performing a cyclization reaction on the second absorption solution to obtain a solution containing tetramethyl cyclobutanedione TMCB. The method of the application comprises adopting an initial absorption solution to react under certain conditions to form an absorption aid; and using the aid for absorption and improving the yield of a cyclization process, which can significantly improve the concentration of DMK in the solution after absorption, and make the yield of TMCB in the cyclization process higher than 99.5%.

Description

Technical Field

[0001] This invention relates to a method for preparing tetramethylcyclobutanedione. Background Technology

[0002] Polyester is one of the most commonly used polymers in daily life, and my country is a major polyester producer. By 2022, my country's output of polyethylene terephthalate (PET) had reached over 50 million tons. However, PET needs to be used at temperatures below 80°C. To improve the heat resistance of polyester and enable it to be used at temperatures above 100°C, the most direct method is to use rigid glycol monomers for copolymerization modification. Among these, the most widely used rigid glycol monomer is 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO).

[0003] CBDO is typically obtained from dimethyl ketene (DMK) through a series of complex reactions including dimerization, hydrogenation, and isomerization. The foundation of these complex reactions is obtaining a DMK solution of a certain concentration. Currently, the industrialized method for preparing DMK involves the thermal decomposition of isobutyric anhydride to produce DMK, which is then concentrated and absorbed using ester solvents. Because DMK has low solubility in ester solvents, the absorption process requires a large amount of solvent, and the absorbed DMK solution readily undergoes carbon-carbon and carbon-oxygen double bond additions at low temperatures, resulting in an increase in impurities in the product. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a novel process for DMK absorption and cyclization, which includes reacting an initial absorption solution under certain conditions to form an absorption aid; and using the aid to absorb and improve the yield of the cyclization process. This method can significantly increase the concentration of DMK in the solution after absorption and make the TMCB yield of the cyclization process higher than 99.5%.

[0005] To achieve the aforementioned objective, the present invention provides a method for preparing tetramethylcyclobutanedione, the method comprising the following steps: (1) absorbing a gas rich in dimethyl ketene (DMK) with a first absorbent to obtain a first absorbent solution;

[0006] (2) The first absorbent solution is subjected to a polymerization reaction, and a solid product is precipitated after cooling;

[0007] (3) Dissolve the solid product in the second absorbent to prepare the third absorbent;

[0008] (4) The gas rich in dimethyl ketone (DMK) is absorbed by a third absorbent to obtain a second absorbent solution;

[0009] (5) The second absorbent solution is subjected to a cyclization reaction to obtain a solution containing tetramethylcyclobutanedione (TMCB). The method of the present invention includes reacting the initial absorbent solution under certain conditions to form an absorbent aid; and using the aid to absorb and improve the yield of the cyclization process. This method can significantly increase the concentration of DMK in the solution after absorption and make the TMCB yield of the cyclization process higher than 99.5%.

[0010] In this invention, the range of types of the first absorbent and the second absorbent in steps (1) and (3) is relatively wide. Commonly used absorbent solvents in the art can be used in this invention. For this invention, the first absorbent and the second absorbent are preferably selected from any one or more of fatty acid alkyl esters, fatty acid anhydrides, and alkanes.

[0011] In this invention, there are no special requirements for the types of fatty acid alkyl esters, fatty acid anhydrides, and alkanes. Commonly used types in the art can be used in this invention. The following description of the types of substances is exemplary, but does not limit the scope of this invention.

[0012] According to one embodiment of the present invention, the structure of the fatty acid alkyl ester is as shown in formula (I):

[0013]

[0014] Wherein, R1 is H or an alkyl group having 1-6 carbon atoms, and R2 is an alkyl group having 1-6 carbon atoms;

[0015] Preferably, the fatty acid alkyl ester is one or more selected from n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, n-butyl propionate, n-butyl butyrate, ethyl isobutyrate, propyl isobutyrate, and isobutyl isobutyrate.

[0016] According to one embodiment of the present invention, the fatty acid anhydride has the structure of formula (II):

[0017]

[0018] Among them, R3 and R4 are H, alkyl groups having 1-6 carbon atoms;

[0019] Preferably, the fatty acid anhydride is one or more of isobutyric anhydride, isobutyric acid anhydride, acetic anhydride, propionic anhydride, and isobutyric acid propionate.

[0020] According to one embodiment of the present invention, the alkane is a C6-10 alkane; preferably, the alkane is one or more selected from n-hexane, n-heptane, 2-methylheptane, and n-octane.

[0021] According to one embodiment of the present invention, the first absorbent is selected from one or more of n-hexane, isobutyl isobutyrate, and isobutyric anhydride.

[0022] According to one embodiment of the present invention, the second absorbent is selected from one or more of n-butyl acetate, n-amyl acetate, and isobutyric anhydride propionate.

[0023] In this invention, the absorption conditions in steps (1) and (4) have a wide range of options. Preferably,

[0024] The absorption conditions in steps (1) and (4) each include a temperature of -30°C to 30°C, preferably -20°C to 10°C.

[0025] According to one embodiment of the present invention, the absorption conditions in step (1) include a temperature of -15°C to 10°C.

[0026] According to one embodiment of the present invention, the absorption conditions in step (4) include a temperature of -20°C to -10°C.

[0027] In this invention, there are no special requirements for the polymerization conditions. For this invention, the polymerization reaction conditions in step (2) include: a reaction pressure of 0.1-10 MPa, preferably 0.1-5 MPa, and more preferably 0.3-1.5 MPa.

[0028] As an example, for the present invention, the polymerization reaction conditions in step (2) include: a temperature of -100℃ to 20℃, preferably -80℃ to 10℃, and more preferably -50℃ to 10℃.

[0029] As an example, for the present invention, the polymerization reaction conditions in step (2) include: a reaction time of 2-20 h, preferably 4-15 h, and more preferably 8-10 h.

[0030] In this invention, there are no special requirements for cooling conditions. According to one embodiment of this invention, in step (2), the final temperature of cooling is -50°C to 10°C, preferably -50°C to -10°C.

[0031] In this invention, the molecular weight of the solid product can be selected from a wide range. According to a preferred embodiment of this invention, the molecular weight of the solid product is 300-1500, preferably 300-1000, more preferably 600-980, such as 600, 650, 700, 750, 800, 850, 900, 950, etc.

[0032] In this invention, the concentration range of the solid product in the third absorbent solvent can be selected in a wide range, and can be specifically selected as needed. According to one embodiment of the invention, the concentration of the solid product in the third absorbent solvent is 0.1-3 wt%, preferably 0.1-1 wt%, for example 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, and 1 wt%.

[0033] The present invention does not have special requirements for the cyclization reaction conditions in step (5), and can be conventional cyclization reaction conditions. According to one embodiment of the present invention, the exemplary description includes: the cyclization pressure is 0.1-5 MPa, preferably 0.1-3 MPa, and more preferably 0.5-1 MPa.

[0034] According to one embodiment of the present invention, the exemplary description includes: the cyclization temperature is 80-180°C, preferably 100-160°C, and more preferably 100-130°C.

[0035] According to one embodiment of the present invention, the exemplary description includes: the cyclization time is 0.5-6h, preferably 1-5h, and more preferably 2-5h.

[0036] The present invention does not have any special requirements on the composition of the gas rich in dimethyl ketene. Any gas containing dimethyl ketene can be absorbed by the absorption method of the present invention. The following is an illustrative description of the embodiments of the present invention, but the present invention is not limited to this scope.

[0037] According to one embodiment of the present invention, the volume content of dimethyl ketene in the gas rich in dimethyl ketene is 5-90%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.

[0038] According to one embodiment of the present invention, preferably, the gas rich in dimethyl ketene contains 5-70% dimethyl ketene, with the remainder being an inert gas.

[0039] The present invention does not have any special requirements for the source of the gas rich in dimethyl ketene. For the present invention, it is preferred that the gas rich in dimethyl ketene is obtained by the thermal decomposition reaction of isobutyric acid and / or isobutyric anhydride, followed by multi-stage cooling to remove isobutyric acid and / or isobutyric anhydride from the system.

[0040] In this invention, there are no special requirements for the reaction conditions of the thermal pyrolysis process. The following is an illustrative description of the embodiments of this invention, but the invention is not limited to this scope.

[0041] According to one embodiment of the present invention, the reaction conditions of the thermal pyrolysis process include: a temperature of 350 to 650°C, preferably 350 to 550°C.

[0042] According to one embodiment of the present invention, the pressure is 1 kPa to 0.3 MPa, preferably 10 kPa to 0.1 MPa.

[0043] According to one embodiment of the present invention, the dwell time is 0.1 to 4 seconds, preferably 0.1 to 1 second.

[0044] According to one embodiment of the present invention, a dilution gas is introduced during pyrolysis.

[0045] In this invention, there are no special requirements for the amount and type of diluting gas used. The following is an illustrative description of the embodiments of this invention, but this invention is not limited to this scope.

[0046] According to one embodiment of the present invention, the volume ratio of isobutyric acid and / or isobutyric anhydride to dilution gas is (1:30) to (1:0.2), preferably (1:20) to (1:0.5).

[0047] According to one embodiment of the present invention, the diluting gas is selected from inert gases, preferably nitrogen.

[0048] The method of the present invention can overcome the defects of the existing technology, such as large solvent consumption and low absorption efficiency in the absorption process of dimethyl ketone (DMK), and can significantly increase the concentration of DMK in the solution after absorption.

[0049] The method of this invention achieves a TMCB yield of over 99.5% in the cyclization process. Detailed Implementation

[0050] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0051] In this invention, the structural formula of dimethyl ketone (DMK) is as follows:

[0052]

[0053] In this invention, the structural formula of tetramethylcyclobutanedione is as follows:

[0054]

[0055] The concentration of DMK in the solution is obtained by testing the substance content through chromatographic analysis. The equilibrium concentration of DMK after absorption is calculated as: mass of DMK in the solution / total mass of the absorption solution.

[0056] In this invention, the DMK-rich gas is generated as follows: Isobutyric anhydride is introduced into a vaporizer at 300°C at a rate of 1.2 mL / min. The vaporized isobutyric anhydride gas is mixed with hot nitrogen gas at a flow rate of 4.8 L / min (nitrogen preheating temperature is 300°C). The mixed gas is then introduced into a pyrolysis reactor made of quartz tube with a diameter of 15 mm and a length of 800 mm. The reactor internal temperature is 410°C. The resulting pyrolysis product is rapidly cooled to 40°C to remove isobutyric anhydride and isobutyric acid from the system, yielding a gas rich in dimethyl ketone (DMK). Online gas chromatography analysis shows that the DMK content in this gas phase is 9.53%.

[0057] Example 1

[0058] In this embodiment, absorbent solvent I is n-hexane, and absorbent solvent II is n-butyl acetate.

[0059] (1) The absorption in step (1) was carried out using 100 mL of n-hexane at 0 °C.

[0060] (2) The absorbed solution was stirred and reacted for 10 h at 0.3 MPa and 0 °C. The reacted solution was cooled to -10 °C and solid-liquid separation was performed to obtain solid product I. The molecular weight of solid product I was found to be 950 by GPC analysis.

[0061] (3) Dissolve solid product I in solvent II to prepare 0.5 wt% absorption solvent III;

[0062] (4) The gas rich in dimethyl ketone (DMK) was absorbed using 300 mL of absorption solvent III at a temperature of -10 °C. The concentration change of DMK in the absorption solvent is shown in Table 1. It can be seen that the equilibrium concentration of DMK after absorption can reach 31.98 wt%.

[0063] Table 1

[0064]

[0065] (5) The absorbent solution was then subjected to a cyclization reaction at 130°C and 1 MPa for 3 hours, and the yield of TMCB reached 99.8%.

[0066] Comparative Example 1

[0067] The comparative example uses n-butyl acetate as the absorption solvent and skips steps (1) to (3). Step (4) is performed directly using 300 mL of the absorption solvent at a temperature of -10 °C. The concentration change of DMK in the absorption solvent is shown in Table 2. It can be seen that the equilibrium concentration of DMK after absorption is 16.93 wt%.

[0068] Table 2

[0069]

[0070] The absorbent solution was subjected to a cyclization reaction at 130 °C and 1 MPa for 3 h. The yield of TMCB in this process was only 80.3%, and a large amount of β-lactone cyclized by DMK cyclization was detected in the system.

[0071] Comparative Example 2

[0072] The comparative example uses a butyl acetate solution containing 0.5 wt% tetramethylcyclobutanedione (TMCB) as the absorption solvent. Steps (1) to (3) are omitted. Step (4) is performed directly using 300 mL of the absorption solvent at a temperature of -10 °C. The concentration change of DMK in the absorption solvent is shown in Table 3. It can be seen that the equilibrium concentration of DMK after absorption is 22.31 wt%.

[0073] Table 3

[0074]

[0075] The absorbent solution was cyclized at 130°C and 1 MPa for 3 hours. The yield of TMCB in this process was only 97.1%, and trace amounts of DMK oligomers were present in the system.

[0076] Example 2

[0077] In this embodiment, absorbent solvent I is isobutyl isobutyrate, and absorbent solvent II is n-amyl acetate.

[0078] (1) 100 mL of isobutyl isobutyrate was used to carry out the absorption in step (1) at a temperature of 10 °C;

[0079] (2) The absorbed solution was stirred for 8 hours at 1.0 MPa and 10 °C. The solution was then cooled to -20 °C and subjected to solid-liquid separation to obtain solid product I. The molecular weight of solid product I was determined to be 600 by GPC analysis.

[0080] (3) Dissolve solid product I in solvent II to prepare 1.0 wt% absorption solvent III;

[0081] (4) The gas rich in dimethyl ketone (DMK) was absorbed using 300 mL of absorption solvent III at a temperature of -15 °C. The concentration change of DMK in the absorption solvent is shown in Table 4. It can be seen that the equilibrium concentration of DMK after absorption can reach 32.87 wt%.

[0082] Table 4

[0083]

[0084] (5) The absorbent solution was then subjected to a cyclization reaction at 120°C and 0.5 MPa for 2 hours, during which the TMCB yield reached 99.5%.

[0085] Example 3

[0086] In this embodiment, absorbent solvent I is isobutyric anhydride, and absorbent solvent II isobutyric propionate.

[0087] (1) The absorption of step (1) was carried out using 100 mL of isobutyric anhydride at a temperature of -15℃;

[0088] (2) The absorbed solution was stirred for 10 h at 1.5 MPa and -50 °C. The solution was maintained at -50 °C and solid-liquid separation was performed to obtain solid product I. The molecular weight of solid product I was 980 as determined by GPC analysis.

[0089] (3) Dissolve solid product I in solvent II to prepare 0.3 wt% absorption solvent III;

[0090] (4) The gas rich in dimethyl ketone (DMK) was absorbed using 300 mL of absorption solvent III at a temperature of -20 °C. The concentration change of DMK in the absorption solvent is shown in Table 5. It can be seen that the equilibrium concentration of DMK after absorption can reach 33.81 wt%.

[0091] Table 5

[0092]

[0093] (5) The absorbent solution was then subjected to a cyclization reaction at 100°C and 0.5 MPa for 5 h, and the TMCB yield reached 99.1% in this process.

[0094] Example 4

[0095] In this embodiment, absorbent solvent I is n-hexane, and absorbent solvent II is n-butyl acetate.

[0096] (1) The absorption in step (1) was carried out using 100 mL of n-hexane at 0 °C.

[0097] (2) The absorbed solution was stirred and reacted for 10 h at 4 MPa and 0 °C. The reacted solution was cooled to -10 °C and solid-liquid separation was performed to obtain solid product I. The molecular weight of solid product I was 1400 as determined by GPC analysis.

[0098] (3) Dissolve solid product I in solvent II to prepare 0.5 wt% absorption solvent III;

[0099] (4) The gas rich in dimethyl ketone (DMK) was absorbed using 300 mL of absorption solvent III at a temperature of -10 °C. The concentration change of DMK in the absorption solvent is shown in Table 6. It can be seen that the equilibrium concentration of DMK after absorption can reach 29.13 wt%.

[0100] Table 6

[0101]

[0102] (5) The absorbent solution was then subjected to a cyclization reaction at 130°C and 1 MPa for 3 hours, and the yield of TMCB reached 98.9%.

[0103] Example 5

[0104] The method of Example 1 is the same, except that in step (3), solid product I is dissolved in solvent II to prepare 0.05 wt% absorption solvent III; all other conditions are the same.

[0105] The absorption results are shown in Table 7 below, with a TMCB yield of 98.54%.

[0106] Table 7

[0107]

[0108] Example 6

[0109] The method is the same as in Example 1, except that in step (3), solid product I is dissolved in solvent II to prepare 1.2 wt% absorbent solvent III, at which point there is insoluble matter; all other conditions are the same.

[0110] The absorption results are shown in Table 8 below, with a TMCB yield of 98.19%.

[0111] Table 8

[0112]

[0113]

[0114] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A process for the preparation of tetramethylcyclobutandione, characterized in that, The method comprises the following steps: (1) absorbing the gas rich in dimethyl ethylene ketone DMK by a first absorbent to obtain a first absorption solution; (2) performing a polymerization reaction on the first absorption solution, and precipitating a solid product after cooling; (3) dissolving the solid product in a second absorbent to configure a third absorbent; (4) absorbing the gas rich in dimethyl ethylene ketone DMK by the third absorbent to obtain a second absorption solution; (5) performing a cyclization reaction on the second absorption solution to obtain a solution containing tetramethyl cyclobutanedione TMCB; The first absorbent and the second absorbent are each selected from any one or more of a fatty acid alkyl ester, a fatty acid anhydride and an alkane; The temperature of the absorption in step (1) is -15℃ to 10℃, and the absorption temperature in step (4) is -20℃ to -10℃. The polymerization reaction condition in step (2) comprises: the reaction pressure is 0.1~10MPa; the temperature is -100℃~20℃; and the reaction time is 2~20 h. The concentration of the solid product in the third absorption solvent is 0.1~3wt%. The temperature of the cyclization reaction is 100~130℃.

2. The method of claim 1, wherein, In steps (1) and (3), the structure of the fatty acid alkyl ester is as formula (I): （I）， In steps (1) and (3), 3. The method of claim 1, wherein, The fatty acid alkyl ester is one or more of n-butyl acetate, isobutyl acetate, n-pentyl acetate, isoamyl acetate, n-butyl propionate, n-butyl butyrate, ethyl isobutyrate, propyl isobutyrate and isobutyl isobutyrate; The structure of the fatty acid anhydride is as formula (II): In steps (1) and (3), (I) The fatty acid anhydride is one or more of isobutyric anhydride, isobutyric anhydride, acetic anhydride, propionic anhydride and isobutyric anhydride; 4. The method of claim 1, wherein, The alkane is a C6-10 alkane.

5. The method according to claim 4, wherein The alkane is one or more of n-hexane, n-heptane, 2-methylheptane and n-octane.

6. The method according to claim 1, wherein The second absorbent is selected from one or more of n-butyl acetate, n-pentyl acetate and isobutyric anhydride; And / or The first absorbent is selected from one or more of n-hexane, isobutyl isobutyrate and isobutyric anhydride. The polymerization reaction condition in step (2) comprises: the reaction pressure is 0.1~5MPa; and / or the temperature is -80℃~10℃; and / or the reaction time is 4~15h. The polymerization reaction condition in step (2) comprises: the reaction pressure is 0.3~1.5MPa; and / or the temperature is -50℃~10℃; and / or the reaction time is 8~10h.

7. The method of claim 1 or 2, wherein, In step (2), 8. The method of claim 1 or 2, wherein, The end temperature of the cooling is -50℃ to 10℃; 9. The method of claim 1 or 2, wherein, And / or The molecular weight of the solid product is 300~1500. In step (2), The end temperature of the cooling is -50℃ to -10℃; and / or the molecular weight of the solid product is 300~1000.

10. The method of claim 1 or 2, wherein, In step (2), the molecular weight of the solid product is 600~980. The concentration of the solid product in the third absorption solvent is 0.1~1wt%.

11. The method of claim 1 or 2, wherein, ​ 12. The method of claim 1 or 2, wherein, ​ 13. The method of claim 1 or 2, wherein, The conditions of the cyclization reaction of step (5) include: a pressure of 0.1-5 MPa; and / or a time of 0.5-6 h.

14. The method of claim 1 or 2, wherein, The conditions of the cyclization reaction of step (5) include: a pressure of 0.1-3 MPa; and / or a time of 1-5 h.

15. The method of claim 1 or 2, wherein, The conditions of the cyclization reaction of step (5) include: a pressure of 0.5-1 MPa; and / or a time of 2-5 h.

16. The method of claim 1 or 2, wherein The dimethyl vinyl ketone-rich gas is obtained by cooling the isobutyric acid and / or isobutyric anhydride thermal cracking reaction and removing isobutyric acid and / or isobutyric anhydride from the system.

17. The method of claim 1 or 2, wherein The dimethyl vinyl ketone-rich gas contains 5-90% by volume of dimethyl vinyl ketone.

18. The method of claim 1 or 2, wherein, The dimethyl vinyl ketone-rich gas contains 5-70% by weight of dimethyl vinyl ketone, and the remainder is inert gas.

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