Preparation method of 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanedione

Abstract

The invention belongs to the technical field of organic synthesis, and particularly relates to a preparation method of 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanedione. The preparation method comprises the steps that isobutyric anhydride or isobutyric anhydride and inert gas are preheated and then subjected to thermal cracking, the volume ratio of isobutyric anhydride to inert gas is 1: (500-3000), obtained mixed gas containing dimethyl ketene is condensed and then subjected to gas-liquid separation, a gas component and condensate are obtained, and the gas component contains dimethyl ketene gas; the method comprises the following steps: absorbing a gas component by adopting an absorbent, and carrying out dimerization reaction on the obtained absorption liquid containing dimethyl ketene in an inert gas atmosphere or under a vacuum condition to obtain 2, 2, 4, 4-tetramethyl-1, 3-cyclobutanedione. The volume ratio of the isobutyric anhydride to the inert gas enables the isobutyric anhydride to be fully cracked into the dimethyl ketene, and the conversion rate is high; and the content of isobutyric anhydride in the reaction liquid after dimerization is low, so that the separation and purification of the target product are facilitated.

Description

Technical Field

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

[0002] 2,2,4,4-Tetramethyl-1,3-cyclobutanediol (CBDO) is an important diol polyester monomer, mainly used for the production of high-performance polyester materials. Adding CBDO to the production of copolyesters can significantly improve the properties of the polyester, such as improving heat resistance, transparency, chemical resistance, impact strength, etc. And 2,2,4,4-tetramethyl-1,3-cyclobutanedione (TMCD) is the hydrogenation raw material of CBDO.

[0003] Currently, in the industrial implementation method, most of them are to thermally crack isobutyric anhydride (IBAN) to generate dimethylketene (DMK) and isobutyric acid (IBA), then cool down for gas-liquid separation, then spray an absorbent solution to absorb DMK gas to absorb DMK, then carry out a dimerization reaction to prepare TMCD, and then directly hydrogenate TMCD to obtain CBDO. In this preparation process, TMCD is not separated and purified, and the residual uncracked IBAN and IBA in the solution directly enter the hydrogenation system, which will affect the activity and service life of the hydrogenation catalyst.

[0004] The related technology discloses a method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, including: step (a) cracking isobutyric anhydride to form a gas containing dimethylketene; step (b) introducing the gas containing dimethylketene into an ester solvent; and step (c) standing the ester solution containing dimethylketene under an inert gas to dimerize dimethylketene to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione. This method directly thermally cracks isobutyric anhydride, and the conversion rate is between 30% and 60%, there is a problem that the conversion rate of isobutyric anhydride is not high, and the content of isobutyric anhydride in the reaction solution after dimerization is high, which is not conducive to the separation and purification of the target product 2,2,4,4-tetramethyl-1,3-cyclobutanedione. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione of the present invention has a high conversion rate of isobutyric anhydride; and the content of isobutyric anhydride in the reaction solution after dimerization is low, which is convenient for the separation and purification of the target product 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0006] The present invention provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, including the following steps:

[0007] Preheat the raw materials and then carry out thermal cracking to obtain a mixed gas containing dimethylketene; the raw materials are isobutyric anhydride, or isobutyric anhydride and an inert gas; when the raw material is isobutyric anhydride, the thermal cracking is carried out under vacuum; when the raw material is isobutyric anhydride and an inert gas, the volume ratio of isobutyric anhydride to the inert gas is 1:500 to 3000;

[0008] Condense the mixed gas containing dimethylketene, carry out gas-liquid separation on the obtained gas-liquid mixture to obtain a gas component and a condensate, and the gas component contains dimethylketene gas;

[0009] Absorb the gas component with an absorbent to obtain an absorbent solution containing dimethylketene;

[0010] Carry out a dimerization reaction on the absorbent solution containing dimethylketene in an inert gas atmosphere or under vacuum conditions to obtain 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0011] Preferably, the volume ratio of isobutyric anhydride to the inert gas is 1:500 to 1000.

[0012] Preferably, the feeding rate of isobutyric anhydride is 0 to 10 mL / min and not 0; the feeding rate of the inert gas is 0 to 10 L / min and not 0.

[0013] Preferably, the temperature of the preheating is 100 to 450 °C; the temperature of the thermal cracking is 450 to 700 °C, the pressure is -100 to 300 kPa, and the residence time is 0.1 to 0.5 s.

[0014] Preferably, the temperature of the condensation is -20 to 40 °C.

[0015] Preferably, a condenser is used for the condensation, and the condenser includes an inner tube for gas-liquid separation and a condensing tube wound outside the inner tube; the inner wall of the inner tube is provided with internal threads.

[0016] Preferably, the absorbent includes one or more of ethyl acetate, acetone, dichloromethane, n-hexane, n-butyl acetate, and 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0017] Preferably, the inert gas atmosphere includes a nitrogen atmosphere or an argon atmosphere.

[0018] Preferably, the temperature of the dimerization reaction is 45 to 150 °C, and the gauge pressure is 0 to 600 kPa.

[0019] Preferably, after the dimerization reaction, the following steps are further included: distilling the obtained reaction solution, crystallizing, separating the solid from the liquid, washing and drying the obtained solid to obtain a pure product of 2,2,4,4-tetramethyl-1,3-cyclobutanedione; the pressure of the distillation is -100 to 101.3 kPa, and the temperature is 30 to 120 °C; the volume after distillation is 0.2 times the total volume of the reaction solution.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione, including the following steps: preheating the raw material and then performing pyrolysis to obtain a mixed gas containing dimethylketene; the raw material is isobutyric anhydride, or isobutyric anhydride and an inert gas; when the raw material is isobutyric anhydride, the pyrolysis is carried out under vacuum; when the raw material is isobutyric anhydride and an inert gas, the volume ratio of isobutyric anhydride to the inert gas is 1:500 to 3000; condensing the mixed gas containing dimethylketene, separating the obtained gas-liquid mixture into a gas component and a condensate, the gas component containing dimethylketene gas; absorbing the gas component with an absorbent to obtain an absorbent solution containing dimethylketene; performing a dimerization reaction on the absorbent solution containing dimethylketene in an inert gas atmosphere or under vacuum conditions to obtain 2,2,4,4-tetramethyl-1,3-cyclobutanedione. The vacuum conditions or the volume ratio of isobutyric anhydride to the inert gas in the present invention can fully pyrolyze isobutyric anhydride into dimethylketene with a high conversion rate; moreover, the content of isobutyric anhydride in the reaction solution after dimerization is low, which is convenient for the separation and purification of the target product 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0022] Furthermore, the present invention uses a condenser with internal threads provided on the inner wall of the inner tube to effectively separate DMK from by-products, and the inert gas and jet pump circulation device enables DMK to be fully mixed with the absorbent solution, resulting in a high DMK yield. Moreover, the separated collected liquid can be recycled, greatly reducing the production cost and being applicable to industrial production. The present invention greatly shortens the dimerization time by increasing the temperature and pressure, and the solvent after distillation can be recycled. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1Internal view of the condenser (improved cyclone separator) of the isobutyric anhydride cracking device in Examples 5-6;

[0025] Figure 2 Cross-sectional view of the internal threaded tube of the improved cyclone separator;

[0026] Figure 3 Oblique view of the internal threaded tube of the improved cyclone separator. Detailed implementation manners

[0027] The present invention provides a method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, comprising the following steps:

[0028] Preheat the raw materials and then perform thermal cracking to obtain a mixed gas containing dimethylketene; the raw materials are isobutyric anhydride, or isobutyric anhydride and an inert gas; when the raw material is isobutyric anhydride, the thermal cracking is carried out under vacuum; when the raw materials are isobutyric anhydride and an inert gas, the volume ratio of isobutyric anhydride to the inert gas is 1:500-3000;

[0029] Condense the mixed gas containing dimethylketene, perform gas-liquid separation on the obtained gas-liquid mixture to obtain a gas component and a condensate, and the gas component contains dimethylketene gas;

[0030] Absorb the gas component with an absorbent to obtain an absorption liquid containing dimethylketene;

[0031] Perform a dimerization reaction on the absorption liquid containing dimethylketene in an atmosphere of an inert gas or under vacuum conditions to obtain 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0032] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0033] In the present invention, the raw materials are preheated and then subjected to thermal cracking to obtain a mixed gas containing dimethylketene; the raw materials are isobutyric anhydride, or isobutyric anhydride and an inert gas; when the raw material is isobutyric anhydride, the thermal cracking is carried out under vacuum; when the raw materials are isobutyric anhydride and an inert gas, the volume ratio of isobutyric anhydride to the inert gas is 1:500-3000.

[0034] When the raw materials are isobutyric anhydride and an inert gas, an inert gas is used, or an inert gas is used in combination with vacuum to carry out dimethylketene. When the raw material is isobutyric anhydride (without using an inert gas), dimethylketene gas is extracted by vacuum, and the mixed gas is pumped to the condenser by a vacuum pump. The dimethylketene gas enters the high-temperature and high-pressure polymerization reactor through a diaphragm vacuum pump (negative pressure at the inlet and positive pressure at the outlet) for dimerization reaction.

[0035] In the present invention, the isobutyric anhydride and the inert gas are preferably introduced into the preheating reactor using a jet atomizer or a diaphragm vacuum pump. The rotation speed of the jet pump of the jet atomizer is preferably 300 - 900 r / min, more preferably 300 - 650 r / min.

[0036] In the present invention, when the raw material is isobutyric anhydride, the feeding rate of the isobutyric anhydride is preferably 5 L / min.

[0037] When the raw materials are isobutyric anhydride and an inert gas, the volume ratio of the isobutyric anhydride to the inert gas is preferably 1:500 - 1000; the inert gas is preferably nitrogen. The feeding rate of the isobutyric anhydride (IBAN) is preferably 0 - 10 L / min and not 0, more preferably 4 - 5 mL / min; the feeding rate of the inert gas is preferably 0 - 10 L / min and not 0, more preferably 2 - 5 L / min, and specifically can be 2.5 L / min, 3 L / min, 4 L / min, or 5 L / min. The rate ratio of the isobutyric anhydride and the inert gas in the present invention can enable the isobutyric anhydride to be fully cracked into dimethylketene with a high conversion rate.

[0038] In the present invention, the preheating temperature is preferably 100 - 450 °C, more preferably 150 - 300 °C, and specifically can be 185 °C.

[0039] In the present invention, the thermal cracking temperature is preferably 450 - 700 °C, more preferably 450 - 600 °C, and specifically can be 475 °C or 500 °C. The pressure of the thermal cracking reaction is preferably -100 - 300 kPa, more preferably -70 kPa, atmospheric pressure, or 130 - 140 kPa, and specifically can be 135 kPa. The residence time is preferably 0.1 - 0.5 s, more preferably 0.13 - 0.3 s, and further preferably 0.18 - 0.2 s, and specifically can be 0.19 s. The mixed gas obtained after thermal cracking contains unreacted isobutyric anhydride (IBAN), the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA).

[0040] After obtaining the mixed gas containing dimethylketene, in the present invention, the mixed gas containing dimethylketene is condensed, and the obtained gas-liquid mixture is subjected to gas-liquid separation to obtain a gas component and a condensate. The gas component contains dimethylketene gas.

[0041] In the present invention, the condensation temperature is preferably -20 - 40 °C, more preferably 20 - 40 °C, and further preferably 35 - 40 °C; the condensation temperature in the present invention can condense other gases in the mixed gas except dimethylketene into liquids, while dimethylketene remains a gas, thereby realizing the separation of dimethylketene and impurity gases.

[0042] In the present invention, the condensation preferably uses a condenser, which is a gas-liquid separator. The condenser preferably includes an inner tube for gas-liquid separation and a condensing tube wound around the outside of the inner tube. The inner wall of the inner tube is provided with an internal thread, and the type, pitch, nominal diameter, and nominal length of the internal thread are preferably triangular thread, 20 mm, 2.5 mm, and 400 mm, respectively.

[0043] The inner tube is provided with a mixed gas inlet, a gas phase outlet, and a liquid phase outlet. The condensing tube is provided with a condensate inlet and a condensate outlet.

[0044] After obtaining the gas components, the present invention absorbs the gas components with an absorbent to obtain an absorbent solution containing dimethylketene.

[0045] In the present invention, the absorbent preferably includes one or more of ethyl acetate, acetone, dichloromethane, n-hexane, n-butyl acetate, and 2,2,4,4-tetramethyl-1,3-cyclobutanedione. The absorption preferably includes three-stage absorption, and the concentration of dimethylketene in the obtained absorbent solution decreases in sequence.

[0046] The present invention preferably uses a jet pump or a diaphragm vacuum pump to introduce the gas components into the absorbent for absorption. On the one hand, it can make dimethylketene fully mixed with the absorbent, and on the other hand, it can reduce the usage amount of inert gas.

[0047] After obtaining the absorbent solution containing dimethylketene, the present invention carries out a dimerization reaction on the absorbent solution containing dimethylketene in an inert gas atmosphere or under vacuum conditions to obtain 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0048] In the present invention, the inert gas atmosphere is preferably a nitrogen range or an argon atmosphere. The temperature of the dimerization reaction is preferably 45-150 °C, more preferably 60-120 °C, still more preferably 85-95 °C, and specifically can be 90 °C. The gauge pressure is preferably 0-600 kPa, still more preferably 90-110 kPa, and specifically can be 100 kPa. The time is preferably 36-60 h, more preferably 48 h.

[0049] In the present invention, the dimerization reaction under vacuum conditions is preferably that the polymerization reactor is in a vacuum at the beginning.

[0050] In the present invention, after the dimerization reaction, it preferably further includes: distilling the obtained reaction solution, crystallizing, performing solid-liquid separation, washing and drying the obtained solid to obtain a pure product of 2,2,4,4-tetramethyl-1,3-cyclobutanedione; the pressure of the distillation is preferably -100 to 101.3 kPa, specifically it can be -90 kPa; the temperature is preferably 30 to 120 °C, specifically it can be 70 °C; the volume after distillation is 0.2 times the total volume of the reaction solution. The present invention has no special requirements for the conditions of the crystallization, solid-liquid separation, washing and drying, and the conditions commonly used by those skilled in the art can be adopted.

[0051] The 2,2,4,4-tetramethyl-1,3-cyclobutanedione obtained by the present invention has high purity, and the distillate obtained by distillation can be recycled, reducing production costs and being suitable for industrial production.

[0052] In order to further illustrate the present invention, the preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione provided by the present invention will be described in detail below in conjunction with examples and drawings, but they cannot be understood as limiting the protection scope of the present invention.

[0053] Example 1

[0054] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min. After being preheated in a preheating reactor at 185 °C, isobutyric anhydride changes from a liquid state to a gaseous state and is introduced into a cracking reactor at 475 °C. During this process, the residence time of the cracking reaction is 0.20 s, and the reaction pressure is -70 kPa. The cracked product (containing unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) passes through a condenser. When the temperature drops to about -10 °C, other components except DMK become liquids, realizing gas-liquid separation. The liquid product is introduced into a storage tank, and the gas product is introduced into an absorption tank containing butyl acetate to obtain an ethyl acetate solution containing DMK, and the mass fractions of DMK are 22 wt%, 6 wt%, and 2 wt% respectively (the volumes of the absorption liquid are 70 mL, 250 mL, and 250 mL respectively). The total cracking reaction time is 1 h.

[0055] The single-pass conversion rate of isobutyric anhydride is 42.1%, and the selectivity of dimethylketene is 78.7%.

[0056] Example 2-1

[0057] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min. After nitrogen at a rate of 3 L / min is introduced into a preheating reactor at 185 °C for preheating, the isobutyric anhydride changes from liquid to gas and is introduced into a cracking reactor at 475 °C. During this process, the residence time of the cracking reaction is 0.28 s and the reaction pressure is atmospheric pressure. The cracked products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) pass through a condenser. When the temperature drops to about -10 °C, components other than DMK become liquid, achieving gas-liquid separation. The liquid products are introduced into a storage tank, and the gas products are introduced into an absorption tank containing butyl acetate to obtain an ethyl acetate solution containing DMK, with the mass fractions of DMK being 27 wt%, 9 wt%, and 3 wt% respectively (the volumes of the absorption liquid are 70 mL, 250 mL, and 250 mL respectively), and the total cracking reaction time is 1 h.

[0058] The single-pass conversion rate of isobutyric anhydride is 50.6%, and the selectivity of dimethylketene is 90.5%.

[0059] Example 2-2

[0060] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min. After nitrogen at a rate of 2.5 L / min is introduced into a preheating reactor at 185 °C for preheating, the isobutyric anhydride changes from liquid to gas and is introduced into a cracking reactor at 475 °C. During this process, the residence time of the cracking reaction is 0.3 s and the reaction pressure is 130 kPa. The cracked products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) pass through a condenser. When the temperature drops to about 40 °C, components other than DMK become liquid, achieving gas-liquid separation. The liquid products are introduced into a storage tank, and the gas products are introduced into an absorption tank containing ethyl acetate. The absorption tank has three stages to obtain an ethyl acetate solution containing DMK, with the mass fractions of DMK being 26 wt%, 9 wt%, and 3 wt% respectively (the volumes of the absorption liquid are 70 mL, 250 mL, and 250 mL respectively), and the total cracking reaction time is 1 h.

[0061] The single-pass conversion rate of isobutyric anhydride is 46.4%, and the selectivity of dimethylketene is 90.3%.

[0062] Example 3

[0063] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min. After being preheated in a preheating reactor at 185 °C with a nitrogen rate of 5 L / min, the isobutyric anhydride changes from liquid to gas and is introduced into a pyrolysis reactor at 475 °C. During this process, the residence time of the pyrolysis reaction is 0.20 s, and the reaction pressure is 135 kPa. The pyrolysis products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) pass through a condenser. When the temperature drops to about 40 °C, other components except DMK become liquid, achieving gas-liquid separation. The liquid products are introduced into a storage tank, and the gas products are introduced into an absorption tank containing ethyl acetate. The absorption tank has 3 stages, and an ethyl acetate solution containing DMK is obtained. The mass fractions of DMK are 29 wt%, 9 wt%, and 3 wt% respectively (the volumes of the absorption liquids are 70 mL, 250 mL, and 250 mL respectively), and the total pyrolysis reaction time is 1 h.

[0064] The single-pass conversion rate of isobutyric anhydride is 55.7%, and the selectivity of dimethylketene is 93.1%.

[0065] Example 4

[0066] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min. After being preheated in a preheating reactor at 185 °C with a nitrogen rate of 5 L / min, the isobutyric anhydride changes from liquid to gas and is introduced into a pyrolysis reactor at 500 °C. During this process, the residence time of the pyrolysis reaction is 0.19 s, and the reaction pressure is 140 kPa. The pyrolysis products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) pass through a condenser. When the temperature drops to about 40 °C, other components except DMK become liquid, achieving gas-liquid separation. The liquid products are introduced into a storage tank, and the gas products are introduced into an absorption tank containing ethyl acetate. The absorption tank has 3 stages, and an ethyl acetate solution containing DMK is obtained. The mass fractions of DMK are 33 wt%, 13 wt%, and 3 wt% respectively (the volumes of the absorption liquids are 70 mL, 250 mL, and 250 mL respectively), and the total pyrolysis reaction time is 1 h.

[0067] The single-pass conversion rate of isobutyric anhydride is 61.7%, and the selectivity of dimethylketene is 97.8%.

[0068] Example 5

[0069] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min. After nitrogen gas at a rate of 5 L / min is introduced into a preheating reactor at 185 °C for preheating, the isobutyric anhydride changes from liquid to gas and is introduced into a cracking reactor at 500 °C. During this process, the residence time of the cracking reaction is 0.19 s and the reaction pressure is 140 kPa. The cracked products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) pass through a condenser. When the temperature drops to about 40 °C, other components except DMK become liquid, achieving gas-liquid separation. The liquid products are introduced into a storage tank, and the gas products are introduced into an absorption tank containing n-butyl acetate to obtain an n-butyl acetate solution containing DMK, with the mass fractions of DMK being 40.8 wt%, 12 wt%, and 2 wt% respectively (the volumes of the absorption liquid are 70 mL, 250 mL, and 250 mL respectively), and the total cracking reaction time is 1 h.

[0070] The single-pass conversion rate of isobutyric anhydride is 63.6%, and the selectivity of dimethylketene is 98.4%.

[0071] Example 6

[0072] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min. After nitrogen gas at a rate of 5 L / min is introduced into a preheating reactor at 185 °C for preheating, the isobutyric anhydride changes from liquid to gas and is introduced into a cracking reactor at 500 °C. During this process, the residence time of the cracking reaction is 0.19 s and the reaction pressure is 140 kPa. The cracked products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) pass through a condenser. When the temperature drops to about 40 °C, other components except DMK become liquid, achieving gas-liquid separation. The liquid products are introduced into a storage tank, and the gas products are introduced into an absorption tank containing acetone to obtain an acetone solution containing DMK, with the mass fractions of DMK being 31 wt%, 13 wt%, and 4 wt% respectively (the volumes of the absorption liquid are 70 mL, 250 mL, and 250 mL respectively), and the total cracking reaction time is 1 h.

[0073] The single-pass conversion rate of isobutyric anhydride is 61.2%, and the selectivity of dimethylketene is 96.7%.

[0074] In the following Examples 7 and 8, a jet atomizer is used to fully mix the isobutyric anhydride liquid with an inert gas (nitrogen) before entering the cracking furnace, and an improved cyclone separator is used to effectively separate the product DMK from the by-products.

[0075] Figure 1It is an internal view of the condenser (improved cyclone separator) of the isobutyric anhydride cracking device. The small red and blue arrows in the figure represent the material flow directions. After cracking, dimethylketene, isobutyric acid and part of isobutyric anhydride enter this gas-liquid separator. In this device, isobutyric acid and isobutyric anhydride are condensed and enter the storage tank, while nitrogen and dimethylketene gas enter the absorption liquid. The jet pump provides negative pressure at the gas end after the gas-liquid separator to introduce the dimethylketene gas into the absorption tank. The inner wall of the inner tube of the improved cyclone separator is provided with internal threads, so that the gas entering the cyclone separator rotates in two directions, fully realizing gas-liquid separation. Figure 2 It is a sectional view of the internal thread tube. Figure 3 It is an oblique view of the internal thread tube.

[0076] Example 7

[0077] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min, the nitrogen rate is 2.5 L / min, and the jet pump rotates at 300 r / min. After being preheated in a preheating reactor at 185 °C, isobutyric anhydride changes from liquid to gas and is introduced into a cracking reactor at 500 °C. During this process, the residence time of the cracking reaction is 0.18 s, and the reaction pressure is 130 kPa. The cracked products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) pass through the condenser (improved cyclone separator). When the temperature drops to about 40 °C, other components except DMK become liquid, realizing gas-liquid separation. The liquid product is introduced into the storage tank, and the gas product is introduced into an absorption tank containing ethyl acetate. The absorption tank has 3 stages, and an ethyl acetate solution containing DMK is obtained, with the mass fractions of DMK being 34 wt%, 13 wt%, and 4 wt% respectively (the volumes of the absorption liquid are 70 mL, 250 mL, and 250 mL respectively), and the total cracking reaction time is 1 h.

[0078] The single-pass conversion rate of isobutyric anhydride is 62.8%, and the selectivity of dimethylketene is 97.9%.

[0079] Example 8

[0080] At room temperature, isobutyric anhydride (IBAN) is fed at a rate of 5 mL / min, the nitrogen rate is 5 L / min, and the jet pump rotates at 650 r / min. After being preheated in a preheating reactor at 185 °C, the isobutyric anhydride changes from liquid to gas and is introduced into a cracking reactor at 500 °C. During this process, the residence time of the cracking reaction is 0.13 s, and the reaction pressure is 120 kPa. The cracked products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by-product isobutyric acid (IBA)) pass through a condenser (improved cyclone separator). When the temperature is cooled to about 40 °C, other components except DMK become liquid, achieving gas-liquid separation. The liquid products are introduced into a storage tank, and the gas products are introduced into an absorption tank containing ethyl acetate. The absorption tank has 3 stages, and an ethyl acetate solution containing DMK is obtained, with the mass fractions of DMK being 38 wt%, 16 wt%, and 6 wt% respectively (the volumes of the absorption liquid are 70 mL, 250 mL, and 250 mL respectively), and the entire cracking reaction time is 1 h.

[0081] The single-pass conversion rate of isobutyric anhydride is 72.6%, and the selectivity of dimethylketene is 98.2%.

[0082] Example 9

[0083] After repeating Example 4 three times, the obtained DMK solution with a concentration of 33 wt% is introduced into a dimerization kettle under a nitrogen atmosphere for dimerization reaction. The temperature of the dimerization kettle is controlled at 90 °C, and the gauge pressure is 100 kPa. The DMK solution undergoes a dimerization reaction at this temperature and pressure for 48 h to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione (TMCD). Then, filtration is carried out at low temperature, and the filter cake is rinsed with an absorption liquid (ethyl acetate) refrigerated at 0 °C. The filtrate and the filter cake are analyzed by gas chromatography-mass spectrometry.

[0084] Analysis of the filter cake shows that its composition is only TMCD, and the purity of TMCD ≥ 99 wt%.

[0085] Take 2 L of the filtrate and analyze it by gas chromatography-mass spectrometry. The filtrate contains TMCD (4.5 wt%), IBAN (0.36 wt%), and other impurities (0.1 wt%). The 2 L of the filtrate is subjected to vacuum distillation. The volume of the distillation tank is 5 L, the Raschig rings are filled in the condenser, the set pressure is -90 kPa, the distillation temperature is 70 °C, and the distillation is stopped when the remaining liquid volume in the distillation tank accounts for about 0.2 times of the total liquid volume. The kettle liquid is transferred and refrigerated at low temperature. After crystallization, filtration is carried out, and analysis of the solid shows that its composition is only TMCD, and the purity of TMCD ≥ 99 wt%.

[0086] If the dimerization reaction is carried out at room temperature and normal pressure for 48 h, it is observed that the color of the absorption liquid containing dimethylketene hardly changes, indicating that a lot of dimethylketene does not dimerize.

[0087] Example 10

[0088] After repeating Example 5 three times, the obtained DMK solution with a concentration of 40.8 wt% was introduced into a dimerization reactor under a nitrogen atmosphere for dimerization reaction. The temperature of the dimerization reactor was controlled at 90 °C, and the gauge pressure was 100 kPa. The DMK solution underwent a dimerization reaction at this temperature and pressure for 48 h to form TMCD. Then, filtration was carried out at a low temperature, and the filter cake was rinsed with an absorbent solution refrigerated at 0 °C. The filtrate and the filter cake were analyzed by gas chromatography - mass spectrometry.

[0089] Analysis of the filter cake showed that its composition was only TMCD, and the purity of TMCD was ≥ 99 wt%.

[0090] 2 L of the filtrate was taken and analyzed by gas chromatography - mass spectrometry. The filtrate contained TMCD (6.1 wt%), IBAN (0.56 wt%), and other impurities (0.18 wt%). The 2 L filtrate was subjected to vacuum distillation. The volume of the distillation tank was 5 L, and Raschig rings were filled in the condenser. The set pressure was -90 kPa, and the distillation temperature was 70 °C. Distillation was stopped when the remaining liquid volume in the distillation tank accounted for about 0.2 times the total liquid volume. The kettle liquid was transferred and refrigerated at a low temperature. After crystallization, filtration was carried out. Analysis of the solid showed that its composition was only TMCD, and the purity of TMCD was ≥ 99 wt%.

[0091] Comparative Example 1

[0092] At room temperature, isobutyric anhydride (IBAN) was fed at a rate of 5 mL / min, the nitrogen rate was 2.5 L / min, and the jet pump speed was 300 r / min. After being preheated in a preheating reactor at 185 °C, the isobutyric anhydride changed from liquid to gas and was introduced into a cracking reactor at 500 °C. During this process, the residence time of the cracking reaction was 0.18 s, and the reaction pressure was 130 kPa. The cracked products (including unreacted isobutyric anhydride, the main product dimethylketene (DMK), and the by - product isobutyric acid (IBA)) passed through a condenser (here the condenser is an ordinary gas - liquid separator). When the temperature dropped to about 40 °C, other components except DMK became liquid. The liquid products were introduced into a storage tank, and the gas products were introduced into an absorption tank containing ethyl acetate. The absorption tank had three stages, and an ethyl acetate solution containing DMK was obtained. The mass fractions of DMK in it were 29 wt%, 9 wt%, and 2 wt% (the volumes of the absorbent solutions were 70 mL, 250 mL, and 250 mL respectively), and the total cracking reaction time was 1 h.

[0093] In this comparative example, an ordinary gas - liquid separator was used. Compared with Example 7, the DMK yield decreased, and the mass fraction of DMK in the obtained ethyl acetate solution containing DMK decreased significantly.

[0094] Preparation method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione in an embodiment, comprising: Step (a): Under a vacuum or an inert gas atmosphere, isobutyric anhydride vaporized by a preheater cracks at a high temperature to generate a gas containing dimethylketene; Step (b): Using an inert gas and a jet pump circulation device to introduce the gas containing dimethylketene into an absorption liquid; Step (c): In a vacuum or an inert gas atmosphere, dimerize dimethylketene to generate 2,2,4,4-tetramethyl-1,3-cyclobutanedione; Step (d): Distill the collected liquid containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, and crystallize at a low temperature with a small amount of the collected liquid remaining; Step (e): Separate and dry to obtain solid 2,2,4,4-tetramethyl-1,3-cyclobutanedione. In the synthesis method of the present invention, the dependence of the reaction on inert gas is reduced during high-temperature cracking. The inert gas and the jet pump circulation device enable DMK to be fully mixed with the absorption liquid, and the atomizer enables the isobutyric anhydride liquid and the inert gas to be fully mixed before entering the cracking furnace; the improved gas-liquid separator enables the product DMK to be effectively separated from by-products. Dimethylketene dimerizes to generate 2,2,4,4-tetramethyl-1,3-cyclobutanedione under high pressure and an inert gas atmosphere, greatly shortening the reaction time, and the separated collected liquid can be recycled, reducing the production cost to a greater extent and being applicable to industrial production.

[0095] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments according to the embodiments of the present invention without creative labor, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, characterized in that: The following steps are involved: Preheating the raw material and then performing thermal cracking to obtain a mixed gas containing dimethyl ketene; the raw material is isobutyric anhydride, or isobutyric anhydride and an inert gas; when the raw material is isobutyric anhydride, the thermal cracking is performed under vacuum; when the raw material is isobutyric anhydride and an inert gas, the volume ratio of the isobutyric anhydride to the inert gas is 1:500-3000; Condensing the mixed gas containing dimethyl ketene, and performing gas-liquid separation on the obtained gas-liquid mixture to obtain a gas component and a condensate, wherein the gas component contains dimethyl ketene gas; The gas component is absorbed by an absorbent to obtain an absorption liquid containing dimethyl ketene; The absorption liquid containing dimethyl ketene is subjected to a dimerization reaction in an inert gas atmosphere or under vacuum conditions to obtain 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

2. The preparation method according to claim 1, characterized in that: The volume ratio of the isobutyric anhydride to the inert gas is 1:500-1000.

3. The preparation method according to claim 2, characterized in that: The feed rate of the isobutyric anhydride is 0 to 10 mL / min, and is not 0; the feed rate of the inert gas is 0 to 10 L / min, and is not 0.

4. The preparation method according to claim 1, characterized in that: The preheating temperature is 100-450°C; the thermal cracking temperature is 450-700°C, the pressure is -100-300 kPa, and the residence time is 0.1-0.5 s.

5. The preparation method according to claim 1, characterized in that: The condensation temperature is -20 to 40°C.

6. The preparation method according to claim 1 or 5, characterized in that: The condensation uses a condenser, which includes an inner tube for gas-liquid separation and a condenser tube wound around the outer side of the inner tube; the inner wall of the inner tube is provided with an internal thread.

7. The preparation method according to claim 1, characterized in that: The absorbent includes one or more of ethyl acetate, acetone, dichloromethane, n-hexane, n-butyl acetate and 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

8. The preparation method according to claim 1, characterized in that: The inert gas atmosphere includes a nitrogen atmosphere or an argon atmosphere.

9. The preparation method according to claim 1 or 8, characterized in that: The temperature of the dimerization reaction is 45-150° C., and the gauge pressure is 0-600 kPa.

10. The preparation method according to claim 1, characterized in that: After the dimerization reaction, the method further comprises: distilling the obtained reaction liquid, crystallizing, and separating the solid from the liquid, washing and drying the obtained solid to obtain a pure product of 2,2,4,4-tetramethyl-1,3-cyclobutanedione; the distillation pressure is -100 to 101.3 kPa, and the temperature is 30 to 120° C.; and the volume after the distillation is 0.2 times the total volume of the reaction liquid.

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