TWI698423B - Method of synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutadione - Google Patents

Abstract

Method of synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutadione is provided, which includes step (a) pyrolizing isobutyric anhydride to form dimethylketene-containing gas, step (b) bubbling the dimethylketene-containing gas into ester solvent, and dissolving dimethylketene in the ester solvent to form dimethylketene-containing solution, and step (c) putting the dimethylketene-containing solution under inert gas to dimerize the dimethylketene for forming 2,2,4,4-tetramethyl- 1,3-cyclobutadione.

Description

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

This disclosure relates to a synthesis method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

2,2,4,4-Tetra methyl-1,3-cyclobutadione (2,2,4,4-Tetra methyl-1,3-cyclobutadione, TMCD) is 2,2,4,4-tetra Hydrogenation raw material for methyl-1,3-cyclobutanediol (2,2,4,4-Tetramethyl-1,3-cyclobutanediol, CBDO). CBDO is a special diol intermediate with high rigidity, toughness, heat resistance, and hydrolysis resistance, which can increase the glass transition temperature of polyester. TMCD is mainly produced from the dimerization of dimethylketene (DMK), and the preparation methods of DMK mainly include the chlorine method, isobutyric anhydride (Isobutyric anhydride, IBAN) thermal cracking method, and isobutyric acid (Isobutyric acid). , IBA) 3 methods such as catalytic dehydration. The chlorination method produces a large amount of salts during the synthesis of TMCD, and the subsequent processing procedures are quite complicated, which is not suitable for mass production. The IBA catalyst dehydration method produces a large amount of by-products in the catalyst reaction process, and the product selectivity is low. The current industrial implementation method is to produce IBA and DMK through thermal cracking of IBAN, firstly cool down for gas-liquid separation, then spray the gas containing DMK with the absorption liquid to absorb DMK, then proceed to dimerization of DMK to prepare TMCD, and finally directly hydrogenate TMCD (TMCD not separated and purified) to form CBDO.

The current TMCD synthesis method has the following problems: (1) The equipment and operating procedures are complicated by spraying the absorbing liquid to dissolve DMK in the gas containing DMK; (2) After spraying the absorbing liquid, the dissolved DMK concentration in the absorbing liquid is low (about 12~20wt%); and (3) TMCD is not isolated and purified. The cracking impurity, IBAN, and IBA remain in the solution. Direct entry into the hydrogenation system will affect the activity and life of the hydrogenation catalyst.

In summary, a new method is needed to collect the DMK generated by cracking IBAN and dimerize the DMK to form TMCD to overcome the above problems.

An embodiment of the present disclosure provides 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) pass the gas containing dimethyl ketone into the ester solvent, so that the ester solvent dissolves the dimethyl ketone to form an ester solution containing dimethyl ketone; and step (c) in the inert gas The ester solution containing dimethyl ketone is allowed to stand still to dimerize the dimethyl ketene to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

In some embodiments, before passing the dimethyl ketone-containing gas into the ester solvent in step (b), it further includes cooling the dimethyl ketone-containing gas to between 30°C and 40°C.

In some embodiments, in the step of passing the dimethyl ketone-containing gas into the ester solvent in step (b), the temperature of the ester solvent is between 0°C and 10°C.

In some embodiments, step (c) standing the ester solution containing dimethyl ketone under inert gas to dimerize dimethyl ketene to form 2,2,4,4-tetramethyl-1, The temperature of 3-cyclobutanedione is between 20°C and 50°C.

In some embodiments, the ester solvent includes C _4-12 esters.

In some embodiments, after step (c), it further includes step (d) lowering the temperature of the dimethyl ketene-containing ester solution to a temperature between 0°C and 5°C to precipitate 2,2,4,4-tetramethyl -1,3-cyclobutanedione.

In some embodiments, after step (d), it further includes step (e) heating the ester solution containing dimethyl ketone to a temperature between 70°C and 80°C to dimerize the remaining dimethyl ketene to form 2 ,2,4,4-Tetramethyl-1,3-cyclobutanedione.

In some embodiments, step (f) is further included after step (e) to recover the ester solution by distillation.

In some embodiments, the recovered ester solution can be used as the ester solvent in step (b).

In some embodiments, the recovered ester solution includes 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

An embodiment of the present disclosure provides a synthesis method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione. First, proceed to step (a) cracking isobutyric anhydride to form a gas containing dimethyl ketene, and the reaction is as follows:

In step (a), the gas containing isobutyric anhydride can be preheated to a temperature between 280°C and 350°C, and then the gas containing isobutyric anhydride can be heated to a temperature between 400°C and 500°C to thermally crack the isobutyric anhydride to form Dimethyl ketene and isobutyric acid. The pressure of the thermal cracking can be between 60 Torr and 120 Torr, the thermal cracking time can be between 0.01 second and 1 second, and the conversion rate of isobutyric anhydride can be between 30% and 70%. In one embodiment, pure isobutyric anhydride gas may be used for the thermal cracking reaction. In another embodiment, a carrier gas such as argon or nitrogen can be mixed with isobutyric anhydride gas before pyrolysis. Therefore, the molar ratio of carrier gas to isobutyric anhydride can be between 50:50 and 0:100 between. It is understandable that the above-mentioned process parameters of thermal cracking isobutyric anhydride are only used as examples and are not limited to this disclosure. For example, a catalyst can be used to perform the above cracking reaction to reduce the cracking temperature.

Then step (b) can be carried out, the gas containing dimethyl ketone is bubbled into the ester solvent, so that the ester solvent dissolves (absorbs) the dimethyl ketone to form an ester solution containing dimethyl ketone . In one embodiment, before the gas containing dimethyl ketone is passed into the ester solvent in step (b), the temperature of the gas containing dimethyl ketone may be lowered to between 30°C and 40°C, so that the gas containing two The gas of methyl ketone forms a gas-liquid mixture. In the gas-liquid mixture, the liquid mainly contains unreacted isobutyric anhydride and by-product isobutyric acid, and the gas is mainly dimethyl ketene. After gas-liquid separation of the gas-liquid mixture, the gas containing dimethyl ketone is passed into the ester solvent, and bubbles are generated to fully contact the ester solvent. Step (b) can be continued until the concentration of dimethyl ketene in the ester solvent reaches 30 wt% to 58 wt%. For example, step (b) can last from 60 minutes to 240 minutes. In some embodiments, the temperature of the ester solvent is between 0°C and 10°C. If the temperature of the ester solvent is too low, higher refrigeration power is required. If the temperature of the ester solvent is too high, the proportion of dimethyl ketene that can be dissolved in the ester solvent is too low, and the ester solvent used in step (b) needs to be increased. The conventional method of collecting dimethyl ketone is generally to spray high temperature esters (between 100°C and 150°C) solvent onto the gas containing dimethyl ketone to form esters containing dimethyl ketone Solution (the concentration of dimethyl ketone is less than 10wt%). Compared with the conventional method, the concentration of dimethyl ketene in the ester solution containing dimethyl ketone obtained in step (b) can be between 30 wt% and 58 wt%, which can greatly reduce the absorption of dimethyl ketone. The amount of ketene ester solvent. In some embodiments, the ester solvent includes C _4-12 esters. For example, the boiling point of the ester solvent is preferably higher than 100°C to avoid loss due to large amounts of pumping out during the vacuum process. The ester solvent suitable for the embodiments of the present disclosure may be isobutyl isobutyrate, ethyl propionate, octyl acetate, other suitable ester solvents, or a combination of the above.

由於此二聚反應為放熱反應，在少量反應時可由室溫冷卻，但在大量反應時需採用冷卻裝置以避免此步驟之反應溫度過高。在一實施例中，步驟(c)的溫度需控制在介於20℃至50℃之間。若溫度過低，則反應過慢，需要增加反應時間。若溫度過高，則會產生聚酯或聚酮的寡聚物，降低二聚產物的純度與收率。在一實施例中，二聚反應的時間介於2小時至50小時之間。若二聚反應時間過短，則二聚產物產率較低，導致收率降低。若二聚反應時間過長，則後續量產時所需之槽體體積過大，不利成本及操作。此外，步驟(c)需置於惰性氣體如氮氣或氬氣下，因為二甲基乙烯酮對空氣中的氧具有高活性。由於酯類溶劑對2,2,4,4-四甲基-1,3-環丁二酮的溶解度較低，因此步驟(c)中形成的2,2,4,4-四甲基-1,3-環丁二酮會自酯類溶劑析出。待步驟(c)的反應結束後，可過濾收集2,2,4,4-四甲基-1,3-環丁二酮的固體，並以酯類溶劑沖洗固體以得高純度的2,2,4,4-四甲基-1,3-環丁二酮(＞99wt%)。 Then proceed to step (c), stand the dimethyl ketene-containing ester solution obtained in step (b) under an inert gas to dimerize dimethyl ketene to form 2,2,4,4-tetramethyl -1,3-cyclobutanedione. The above dimerization reaction is as follows:

Since this dimerization reaction is an exothermic reaction, it can be cooled at room temperature in a small amount of reaction, but a cooling device must be used in a large amount of reaction to avoid excessively high reaction temperature in this step. In one embodiment, the temperature of step (c) needs to be controlled between 20°C and 50°C. If the temperature is too low, the reaction is too slow and the reaction time needs to be increased. If the temperature is too high, oligomers of polyester or polyketone will be produced, reducing the purity and yield of the dimerization product. In one embodiment, the dimerization reaction time is between 2 hours and 50 hours. If the dimerization reaction time is too short, the yield of the dimerization product is lower, resulting in a lower yield. If the dimerization reaction time is too long, the tank volume required for subsequent mass production will be too large, which is unfavorable for cost and operation. In addition, step (c) needs to be placed under an inert gas such as nitrogen or argon because dimethyl ketene has high activity to oxygen in the air. Due to the low solubility of ester solvents to 2,2,4,4-tetramethyl-1,3-cyclobutanedione, the 2,2,4,4-tetramethyl-formed in step (c) 1,3-cyclobutanedione will precipitate from ester solvents. After the reaction of step (c) is completed, the solid of 2,2,4,4-tetramethyl-1,3-cyclobutanedione can be collected by filtration, and the solid can be washed with an ester solvent to obtain high purity 2, 2,4,4-Tetramethyl-1,3-cyclobutanedione (>99wt%).

In some embodiments, after step (c), it further includes step (d) lowering the temperature of the dimethyl ketene-containing ester solution to a temperature between 0°C and 5°C to precipitate 2,2,4,4-tetramethyl Base-1,3-cyclobutanedione. Similarly, the solid of 2,2,4,4-tetramethyl-1,3-cyclobutanedione can be collected by filtration, and the solid can be washed with an ester solvent to obtain high-purity 2,2,4,4-tetra Methyl-1,3-cyclobutanedione (>99wt%). The main purpose of step (d) is to reduce the 2,2,4,4-tetramethyl-1,3-cyclobutanedione dissolved in the ester solution containing dimethylketene. After step (d), the 2,2,4,4-tetramethyl-1,3-cyclobutanedione contained in the ester solution is between 4wt% and 12wt%, and dimethylketene Between 2wt% to 5wt%.

In some embodiments, after step (d), it further includes step (e) heating the ester solution containing dimethyl ketone to a temperature between 70° C. and 80° C. to make the dimethyl ketene remaining in the ester solution Dimerize to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione. In one embodiment, the heating time of step (e) is between 60 minutes and 180 minutes. The main purpose of step (e) is to consume the residual dimethyl ketene in the ester solution containing dimethyl ketone, so as to prevent the dimethyl ketene from adhering to the distillation device (such as distillation tube or distillation) of step (e). Tower). Dimethyl ketene attached to the distillation device will continue to undergo polymerization reaction, and polymer will be produced and attached to the surface of the filling of the distillation device, which may cause the distillation tower to block and cause danger. In one embodiment, the ester solution containing dimethyl ketene heated in step (e) contains the aforementioned rinse solid (2,2,4,4-tetramethyl-1,3-cyclobutanedione). The resulting lotion.

In some embodiments, step (f) is further included after step (e) to recover the ester solution by distillation. For example, distillation may be vacuum distillation, the temperature is between 55°C and 100°C (for example, between 80°C and 95°C), and the pressure is between 20torr and 80torr, such as 50torr To 65torr. After step (f), most of the IBAN and other impurities in the ester solution can be removed. The distilled liquid is mainly ester solvent (between 88wt% and 99wt%) and a small amount of 2,2,4,4- Tetramethyl-1,3-cyclobutanedione (between 1wt% and 12wt%).

In some embodiments, the ester solution recovered in step (e) can be used as an ester solvent to dissolve (absorb) the gas containing dimethyl ketone in step (b). On the other hand, the ester solution recovered in step (e) can also be used to wash the filter cake of 2,2,4,4-tetramethyl-1,3-cyclobutanedione to remove impurities.

In summary, in the embodiment of the present disclosure, the gas containing dimethyl ketone is passed into the ester solvent, so that the ester solvent dissolves the dimethyl ketone to form an ester solution containing a high concentration of dimethyl ketone. In addition, the ester solution containing dimethyl ketene is allowed to stand under inert gas to dimerize dimethyl ketene to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione. This method can produce high-purity 2,2,4,4-tetramethyl-1,3-cyclobutanedione in large quantities, which is beneficial for subsequent applications. For example, 2,2,4,4-tetramethyl-1,3-cyclobutanedione can be hydrogenated to form 2,2,4,4-tetramethyl-1,3-cyclobutanediol, and then Take this alcohol and other acids to form polyester.

To make the above and other objects of the present disclosure, features, and advantages can be more fully understood by referring include the preferred embodiments and accompanying figures, described in detail below: Example

Example 1 Isobutyric anhydride (IBAN, 4.17 ml/min) and nitrogen (200 ml/min) were mixed in a mixing tank at 150° C. to form a mixed gas with an IBAN concentration of 75 mol%. After the mixed gas is introduced into a preheating reactor at 325°C for preheating, it is introduced into a cracking reactor at 475°C to crack IBAN at a reaction pressure of 110 torr. The gas residence time of the above cracking reaction was 0.14 seconds, and the total reaction time was 1 hour. The conversion rate of IBAN was 62.9%, and the selectivity of dimethyl ketene (DMK) was 97.2%. The cracked products (containing unreacted IBAN, main product DMK, and by-product isobutyric acid (IBA)) quickly pass through the condenser, and are cooled to between 30°C and 40°C to form a gas-liquid mixture. The liquid in the gas-liquid mixture is mainly unreacted IBAN and by-product IBA, and the gas is mainly DMK. The cooled gas-liquid mixture is separated by a separation device, and then the gas product is introduced into the (bubble) absorption bottle (total 2 bottles) isobutyl isobutyrate (IBIB, the first bottle 60g, the second bottle) at 0°C 250g) For 60 minutes, allow IBIB to absorb DMK in the gas product to form a DMK solution with a concentration of 31wt% and 11wt%, respectively.

Example 2 IBAN (4.17 ml/min) and nitrogen (100 ml/min) were mixed in a mixing tank at 150° C. to form a mixed gas with an IBAN concentration of 87 mol%. After the mixed gas is introduced into a preheating reactor at 325°C for preheating, it is introduced into a cracking reactor at 475°C to crack IBAN at a reaction pressure of 110 torr. The gas residence time of the above cracking reaction was 0.16 seconds, and the total reaction time was 1 hour. The IBAN conversion rate was 63.0%, and the DMK selectivity rate was 98.3%. The cracked product (containing unreacted IBAN, main product DMK, and by-product IBA) quickly passes through the condenser and is cooled to between 30°C and 40°C to form a gas-liquid mixture. The liquid in the gas-liquid mixture is mainly unreacted IBAN and by-product IBA, and the gas is mainly DMK. The cooled gas-liquid mixture is separated by a separation device, and then the gas product is introduced into the IBIB (the first bottle 60g, the second bottle 250g) in the (bubble) absorption bottle (2 bottles in total) at 0°C for 60 minutes to make the IBIB The DMK in the gas product is absorbed to form DMK solutions with a concentration of 34wt% and 11wt%, respectively.

Example 3 IBAN (4.17ml/min) was introduced into a mixing tank at 150°C to form a gas with an IBAN concentration of 100mol%. After the gas is introduced into the preheating reactor at 325°C for preheating, it is introduced into the cracking reactor at 475°C, and the IBAN is cracked at a reaction pressure of 110 torr. The gas residence time of the above cracking reaction was 0.18 seconds, and the total reaction time was 1 hour. The IBAN conversion rate was 59.4%, and the DMK selectivity rate was 98.4%. The cracked product (containing unreacted IBAN, main product DMK, and by-product IBA) quickly passes through the condenser and is cooled to between 30°C and 40°C to form a gas-liquid mixture. The liquid in the gas-liquid mixture is mainly unreacted IBAN and by-product IBA, and the gas is mainly DMK. The cooled gas-liquid mixture is separated by a separation device, and then the gas product is introduced into the (bubble) absorption bottle (2 bottles in total) at 0℃ IBIB (the first bottle 60g, the second bottle 250g) for 60 minutes to make the IBIB The DMK in the gas product is absorbed to form DMK solutions with concentrations of 43wt% and 5wt%, respectively.

Example 4 IBAN (4.17ml/min) was introduced into a mixing tank at 150°C to form a gas with an IBAN concentration of 100mol%. After the gas is introduced into the preheating reactor at 325°C for preheating, it is introduced into the cracking reactor at 460°C, and the IBAN is cracked at a reaction pressure of 110 torr. The gas residence time of the above cracking reaction is 0.19 seconds, and the total reaction time is 2 hours. The IBAN conversion rate is 55.3%, and the DMK selectivity rate is 97.7%. The cracked product (containing unreacted IBAN, main product DMK, and by-product IBA) quickly passes through the condenser and is cooled to between 30°C and 40°C to form a gas-liquid mixture. The liquid in the gas-liquid mixture is mainly unreacted IBAN and by-product IBA, and the gas is mainly DMK. The cooled gas-liquid mixture is separated by a separation device, and then the gas product is introduced into the (bubble) absorption bottle (2 bottles in total) at 0℃ IBIB (60g for the first bottle, 60g for the second bottle) for 60 minutes to make the IBIB The DMK in the gas product is absorbed to form DMK solutions with a concentration of 55wt% and 30wt%, respectively.

Example 5 IBAN (4.17ml/min) was passed into a mixing tank at 150°C to form a gas with an IBAN concentration of 100wt%. After the gas is introduced into a preheating reactor at 325°C for preheating, it is introduced into a cracking reactor at 450°C, and the IBAN is cracked at a reaction pressure of 110 torr. The gas residence time of the above cracking reaction was 0.19 seconds, and the total reaction time was 2 hours. The IBAN conversion rate was 52.2%, and the DMK selectivity rate was 94.9%. The cracked product (containing unreacted IBAN, main product DMK, and by-product IBA) quickly passes through the condenser and is cooled to between 30°C and 40°C to form a gas-liquid mixture. The liquid in the gas-liquid mixture is mainly unreacted IBAN and by-product IBA, and the gas is mainly DMK. The cooled gas-liquid mixture is separated by a separation device, and then the gas product is introduced into the (bubble) absorption bottle (2 bottles in total) at 5℃ IBIB (80g for the first bottle, 80g for the second bottle) for 120 minutes to make the IBIB The DMK in the gas product is absorbed to form DMK solutions with a concentration of 45wt% and 32wt%, respectively.

Example 6 After repeating Example 4 four times, a DMK solution with a concentration of 55 wt% was placed in a dimerization tank under a nitrogen atmosphere to perform dimerization. The weight of IBIB in the DMK solution is 240 g, and the TMCD content is 308 g. The temperature of the dimerization tank is controlled to 25°C, and the DMK solution undergoes an exothermic dimerization reaction at this temperature for 48 hours to form TMCD. After filtering, the filtrate and filter cake were analyzed by gas chromatograph. The filtrate contains TMCD (8.1wt%), IBAN (1.16wt%), and trace lysis impurities. The filter cake was sampled to form a solution with a concentration of 8wt%. After analysis, it was found that the filter cake contained about 0.15wt% of IBAN. Take 475g of fresh IBIB solution as washing liquid (washing liquid/TMCD=1.5), wash the crude TMCD product twice at 25°C, and analyze the washing liquid and purified TMCD solid by gas chromatography. The concentration of IBAN in the lotion is 0.21wt%. Take the purified TMCD solid to prepare a solution with a concentration of 8wt%. After analysis, it can be seen that there is no IBAN in the purified TMCD solid and the purity of TMCD is ³99wt%.

Example 7 IBAN thermal cracking was performed according to the conditions of Example 3. The reaction time was extended to 2 hours, and the IBIB of the first absorption bottle was 60g. After the reaction, the DMK solution with a concentration of 58 wt% was placed in a dimerization tank under a nitrogen atmosphere for dimerization reaction. The weight of IBIB in the DMK solution is 60 g, and the TMCD content is 84 g. The temperature of the dimerization tank is controlled to 25°C, and the DMK solution undergoes an exothermic dimerization reaction at this temperature for 48 hours to form TMCD. After filtering, the filtrate and filter cake were analyzed by gas chromatograph. The filtrate contains TMCD (9wt%), IBAN (1.6wt%), and trace lysis impurities. The filter cake was sampled to form a solution with a concentration of 8wt%. After analysis, it was found that the filter cake contained about 0.16wt% of IBAN. Take 75g of fresh IBIB solution as washing liquid (washing liquid/TMCD=0.9), wash the crude TMCD product twice at 25°C, and analyze the washing liquid and purified TMCD solid by gas chromatography. The concentration of IBAN in the lotion is 0.27wt%. Take the purified TMCD solid to prepare a solution with a concentration of 8wt%. After analysis, it can be seen that there is no IBAN in the purified TMCD solid and the purity of TMCD is ³99wt%.

Example 8 After repeating Example 5, the DMK solutions in the two absorption bottles were mixed to form a DMK solution with a concentration of 39% by weight, and placed in a dimerization tank under a nitrogen atmosphere for dimerization. The dimerization tank is not temperature controlled, and the DMK solution undergoes an exothermic dimerization reaction for 5 hours to form TMCD. After filtering, the filtrate and filter cake were analyzed by gas chromatograph. Take a fresh IBIB solution and wash the crude TMCD product twice at 25°C to obtain a high-purity TMCD solid (code 5hr-TMCD). The filtrate contains TMCD (12.3wt%), IBAN (1.3wt%), DMK (4.5wt%), and trace lysis impurities. The filtrate was divided into two parts, respectively placed in a nitrogen atmosphere at 25°C and 70°C for two hours, and then cooled to 5°C to precipitate solids. Take the fresh IBIB solution and wash the solids twice at 25°C to obtain high-purity TMCD solids (code 7hr-TMCD-RT, 7hr-TMCD-70°C). The solids numbered 5hr-TMCD, 7hr-TMCD-RT, and 7hr-TMCD-70°C were prepared into 10wt% solutions with ethyl acetate respectively, and the solution penetration was tested with UV-VIS spectrometer. The transmittance of solutions numbered 5hr-TMCD and 7hr-TMCD-RT to 620nm light is the same as that of pure ethyl acetate solvent, both are 100%. The penetration of the solution of 7hr-TMCD-70℃ to 620nm light is only 99.8%, indicating that the dimerization temperature is too high (such as 70℃) to easily produce polyester or polyketone oligomers.

Example 9 A mixture solution of 2000 g of the filtrate after DMK dimerization to form TMCD and the filtrate after washing the TMCD filter cake was taken and analyzed by a gas chromatograph. The mixed solution contains TMCD (12.3wt%), IBIB (84.9wt%), IBAN (1.6wt%), and other impurities (1.2wt%). Take the above mixed solution and distill under reduced pressure. The distillation tube is 1.5 meters high and 5 cm in diameter. The tube is filled with Raschig rings. The set pressure is 29 torr and the distillation temperature is 80°C. After 50 minutes of distillation, 195g of the overhead distillate was collected for analysis. The composition of the distillate was TMCD (2.9wt%) and IBIB (97.1wt%), without IBAN. Adjust the pressure to 50 torr and the distillation temperature at 90°C. After 200 minutes of distillation, 263g of the top distillate was collected for analysis. The composition of the distillate was TMCD (5.5wt%) and IBIB (94.5wt%), without IBAN.

Example 10 A mixture solution of 2000 g of the filtrate after DMK dimerization to form TMCD and the filtrate after washing the TMCD filter cake was taken and analyzed by gas chromatography. The mixed solution contains TMCD (11.6wt%), IBIB (87.7wt%), IBAN (0.6wt%), and other impurities (0.1wt%). Take the above mixed solution for vacuum distillation. The distillation tube is 1.5 meters high and 5 cm in diameter. The tube is filled with Raschig rings. The set pressure is 65 torr and the distillation temperature is 95°C. After 220 minutes of distillation, 1503g of the overhead distillate was collected for analysis. The composition of the distillate was TMCD (6.9wt%) and IBIB (93.1wt%) without IBAN.

Take the filtrate after DMK dimerization to form TMCD, and another mixed solution of 1600 g of the filtrate after washing the TMCD filter cake, and analyze it with a gas chromatograph. The other mixed solution contains TMCD (9.9wt%), IBIB (88.82wt%), IBAN (1.04wt%), and other impurities (0.24wt%). After placing another mixed solution at the bottom of the aforementioned distillation tower (including the bottoms of the aforementioned vacuum distillation), adjust the pressure to 60 torr, the distillation temperature of 95°C, and collect 1597 g of the overhead distillate after 170 minutes of distillation for analysis. The effluent composition was TMCD (7.6wt%), IBIB (92.4wt%), and IBAN (0.008wt%).

Comparative Example 1 (DMK absorption at 25°C) Isobutyric anhydride (IBAN, 4.17 ml/min) and nitrogen (200 ml/min) were mixed in a mixing tank at 150°C to form a mixed gas with an IBAN concentration of 75 mol%. After the mixed gas is introduced into a preheating reactor at 325°C for preheating, it is introduced into a cracking reactor at 460°C, and the IBAN is cracked at a reaction pressure of 110 torr. The residence time of the reaction gas from the above cracking was 0.14 seconds, and the total reaction time was 1 hour. The conversion rate of IBAN was 33.2% and the selectivity of dimethyl ketene (DMK) was 96.1%. The cracked products (containing unreacted IBAN, main product DMK, and by-product isobutyric acid (IBA)) quickly pass through the condenser, and are cooled to between 30°C and 40°C to form a gas-liquid mixture. The liquid in the gas-liquid mixture is mainly unreacted IBAN and by-product IBA, and the gas is mainly DMK. The cooled gas-liquid mixture is separated by a separation device, and then the gas product is introduced into the (bubble) absorption bottle (total 2 bottles) of IBIB (the first bottle 60g, the second bottle 250g) at 25°C for 60 minutes to make the IBIB The DMK in the gas product is absorbed to form a DMK solution with a concentration of 0.2wt% and 6.0wt%, respectively. It can be seen from the above that too high temperature of IBIB will greatly reduce its DMK absorption effect.

Although this disclosure has been disclosed in several preferred embodiments as described above, it is not intended to limit the disclosure. Anyone with ordinary knowledge in the relevant technical field can make any changes without departing from the spirit and scope of this disclosure. Therefore, the scope of protection of this disclosure shall be subject to the scope of the attached patent application.

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Claims (9)

A method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione, comprising: step (a) cracking isobutyric anhydride to form a gas containing dimethyl ketene; step (b ) Pass the dimethyl ketone-containing gas into an ester solvent to dissolve the dimethyl ketone in the ester solvent to form an ester solution containing dimethyl ketone; and step (c) in an inert gas Next, let the ester solution containing dimethyl ketene dimerize to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione, wherein in step (b ) In the step of passing the gas containing dimethyl ketone into the ester solvent, the temperature of the ester solvent is between 0°C and 10°C. The method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione as described in item 1 of the scope of the patent application, wherein in step (b) the gas containing dimethylketene Before passing the ester solvent, it further includes cooling the dimethyl ketone-containing gas to between 30°C and 40°C. The synthesis method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione as described in item 1 of the scope of patent application, wherein step (c) is to stand the dimethyl-containing compound under inert gas The ester solution of ketene dimerizes dimethyl ketene to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione at a temperature between 20°C and 50°C. The method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione as described in item 1 of the scope of patent application, wherein the ester solvent includes C _4-12 esters. The method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione as described in item 1 of the scope of the patent application, wherein after step (c), it further includes step (d) cooling the containing The ester solution of dimethyl ketene is between 0°C and 5°C to precipitate 2,2,4,4-tetramethyl -1,3-cyclobutanedione. The method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione as described in item 5 of the scope of patent application, wherein step (d) further includes step (e) heating the containing The ester solution of dimethyl ketone is between 70°C and 80°C to dimerize the remaining dimethyl ketene to form 2,2,4,4-tetramethyl-1,3-cyclobutanedione. As described in item 6 of the scope of patent application, the synthesis method of 2,2,4,4-tetramethyl-1,3-cyclobutanedione, wherein after step (e), it further includes step (f) distillation and recovery of the Ester solution. The method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione as described in item 7 of the scope of patent application, wherein the recovered ester solution can be used as the ester in step (b) Solvent. For example, the method for synthesizing 2,2,4,4-tetramethyl-1,3-cyclobutanedione described in item 7 or item 8 of the scope of patent application, wherein the recovered ester solution includes 2,2, 4,4-Tetramethyl-1,3-cyclobutanedione.