A method for treating mixed gas produced in a process for synthesizing 3,3',4,4'-diphenyl ether dianhydride

Abstract

This invention belongs to the field of resource recycling technology and provides a method for treating the mixed gas generated during the synthesis of 3,3',4,4'-diphenyl ether dianhydride. The method first condenses the mixed gas of monomethylamine and dimethylamine. Due to their different boiling points (monomethylamine boiling point -6.3℃, dimethylamine boiling point 6.1℃), most of the dimethylamine gas is condensed, yielding a dimethylamine liquid, which is sold as a byproduct. The condensed monomethylamine-dimethylamine gas is then absorbed by water, absorbing the remaining dimethylamine and a portion of the monomethylamine, resulting in a monomethylamine-dimethylamine solution and monomethylamine gas. The obtained monomethylamine gas is then subjected to acid absorption, converting the monomethylamine into monomethylamine hydrochloride, thus recovering the monomethylamine. The method provided by this invention is simple to operate and can separate monomethylamine and dimethylamine, recovering the monomethylamine as monomethylamine hydrochloride.

Description

Technical Field

[0001] This invention relates to the field of chemical reaction technology, and in particular to a method for treating the mixed gas generated during the synthesis of 3,3',4,4'-diphenyl ether dianhydride. Background Technology

[0002] 3,3',4,4'-Diphenyl ether dianhydride is an important monomer for synthesizing polyimides. It can introduce flexible ether bonds into the polyimide backbone, giving polyimides excellent thermal processing properties and high insulation properties, enabling their wide application in aerospace, electromechanical, and electronic fields. With the development of digitalization, intelligence, and touchscreen technology, the use of polyimides as high-end electronic materials for displays is rapidly increasing.

[0003] Using 4-nitro-N-methylphthalimide as the main raw material to produce 3,3',4,4'-diphenyl ether dianhydride is currently one of the main methods for synthesizing 3,3',4,4'-diphenyl ether dianhydride. During the synthesis of 3,3',4,4'-diphenyl ether dianhydride, the intermediate oxobis-(N-methylphthalimide) is generated. The hydrolysis of oxobis-(N-methylphthalimide) produces a large amount of monomethylamine gas. Simultaneously, due to the residual small amount of N,N-dimethylformamide (DMF) in oxobis-(N-methylphthalimide), dimethylamine gas is also generated during hydrolysis. Therefore, the hydrolysis process produces a mixture of monomethylamine and dimethylamine gases.

[0004] Currently, the main methods for treating mixtures of monomethylamine and dimethylamine include biodegradation, chemical oxidation, and physical adsorption. Biodegradation and chemical oxidation destroy or degrade the monomethylamine and dimethylamine in the mixture, making them unusable. While physical adsorption does not destroy the structure of the monomethylamine or dimethylamine in the mixture, re-desorption is required for reuse, making the process complex. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method for treating the mixed gas generated during the synthesis of 3,3',4,4'-diphenyl ether dianhydride. The treatment method of the present invention is simple to operate and can recover dimethylamine and monomethylamine separately, with the monomethylamine being recovered in the form of monomethylamine hydrochloride.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for treating a mixed gas generated during the synthesis of 3,3',4,4'-diphenyl ether dianhydride, wherein the mixed gas comprises monomethylamine and dimethylamine, and includes the following steps:

[0008] The mixed gas is condensed to obtain monomethylamine-dimethylamine gas and dimethylamine liquid;

[0009] The monomethylamine-dimethylamine gas was absorbed by water to obtain a monomethylamine-dimethylamine solution and monomethylamine gas.

[0010] The monomethylamine gas was subjected to acid absorption to obtain an aqueous solution of monomethylamine hydrochloride;

[0011] The aqueous solution of monomethylamine hydrochloride was adjusted to acidity and then subjected to vacuum distillation to obtain monomethylamine hydrochloride.

[0012] The reagent used for acid absorption includes hydrochloric acid.

[0013] Preferably, the condensation temperature is 0 to -5°C.

[0014] Preferably, the monomethylamine-dimethylamine solution is a saturated monomethylamine-dimethylamine solution; the pH value of the saturated monomethylamine-dimethylamine solution is 12-13.

[0015] Preferably, the hydrochloric acid has a mass concentration of 5-20%.

[0016] Preferably, the methylamine hydrochloride aqueous solution is a saturated methylamine hydrochloride aqueous solution, and the pH value of the saturated methylamine hydrochloride aqueous solution is 7-9.

[0017] Preferably, the acidic pH value is 2 to 5.

[0018] Preferably, the vacuum degree of the reduced pressure distillation is -0.05MPa to -0.09MPa, and the temperature is 40℃ to 70℃.

[0019] Preferably, the amount of water distilled under reduced pressure is 50 wt% to 70 wt% of an aqueous solution of methylamine hydrochloride.

[0020] Preferably, after the vacuum distillation, the process further includes cooling and centrifuging the obtained vacuum distillate concentrate; the temperature of the cooling and centrifugation is 20-30°C.

[0021] Preferably, it further includes:

[0022] The monomethylamine-dimethylamine solution was distilled to obtain recovered monomethylamine-dimethylamine gas.

[0023] The parameters for condensing and absorbing the recovered monomethylamine-dimethylamine gas during gas recycling and distillation include: pH value of 12-12.5, vacuum degree of -0.05MPa--0.09MPa, temperature of 40-70℃, and the mass of the distilled water being 50%-70% of the total mass.

[0024] This invention provides a method for treating a mixed gas generated during the synthesis of 3,3',4,4'-diphenyl ether dianhydride, wherein the mixed gas comprises monomethylamine and dimethylamine, and includes the following steps: condensing the mixed gas to obtain monomethylamine-dimethylamine gas and dimethylamine liquid; absorbing the monomethylamine-dimethylamine gas with water to obtain a monomethylamine-dimethylamine solution and monomethylamine gas; absorbing the monomethylamine gas with acid to obtain a monomethylamine hydrochloride aqueous solution; adjusting the monomethylamine hydrochloride aqueous solution to acidity and performing vacuum distillation to obtain monomethylamine hydrochloride; the reagent used for acid absorption includes hydrochloric acid. This invention condenses the mixed gas, using the difference in boiling points (monomethylamine boiling point -6.3℃, dimethylamine boiling point 6.1℃), to condense most of the dimethylamine, obtaining dimethylamine liquid, which is sold as a byproduct. The obtained monomethylamine-dimethylamine gas is absorbed by water, which absorbs the condensed residual dimethylamine and a portion of the monomethylamine, yielding a monomethylamine-dimethylamine solution and monomethylamine gas. The obtained monomethylamine gas is then subjected to acid absorption, converting the monomethylamine into monomethylamine hydrochloride, thus recovering the monomethylamine. The processing method provided by this invention is simple to operate and can separate monomethylamine and dimethylamine, recovering the monomethylamine as monomethylamine hydrochloride. Attached Figure Description

[0025] Figure 1 A schematic diagram of the system structure used in the processing method provided by this invention. Detailed Implementation

[0026] This invention provides a method for treating a mixed gas generated during the synthesis of 3,3',4,4'-diphenyl ether dianhydride, wherein the mixed gas comprises monomethylamine and dimethylamine, and includes the following steps:

[0027] The mixed gas is condensed to obtain monomethylamine-dimethylamine gas and dimethylamine liquid;

[0028] The monomethylamine-dimethylamine gas was absorbed by water to obtain a monomethylamine-dimethylamine solution and monomethylamine gas.

[0029] The monomethylamine gas was subjected to acid absorption to obtain an aqueous solution of monomethylamine hydrochloride;

[0030] The aqueous solution of monomethylamine hydrochloride was adjusted to acidity and then subjected to vacuum distillation to obtain monomethylamine hydrochloride.

[0031] The reagent used for acid absorption includes hydrochloric acid.

[0032] Unless otherwise specified, all raw materials used in this invention are preferably commercially available products.

[0033] The present invention condenses the mixed gas to obtain monomethylamine-dimethylamine gas and dimethylamine liquid.

[0034] In this invention, the mixed gas comprises monomethylamine and dimethylamine; the volume ratio of monomethylamine to dimethylamine in the mixed gas is preferably 10 to 13:1.

[0035] In this invention, the condensation temperature is preferably 0 to -5°C.

[0036] In this invention, the condensation is preferably carried out in a condenser.

[0037] In this invention, the condensation utilizes the different boiling points of monomethylamine and dimethylamine in the mixed gas to separate monomethylamine and dimethylamine.

[0038] After obtaining monomethylamine-dimethylamine gas, the present invention absorbs the monomethylamine-dimethylamine gas with water to obtain a monomethylamine-dimethylamine solution and monomethylamine gas.

[0039] In this invention, the reagent for water absorption preferably includes water. In this invention, the water absorption is preferably carried out in an absorption tower.

[0040] In this invention, the monomethylamine-dimethylamine solution is preferably a saturated monomethylamine hydrochloride aqueous solution, that is, the monomethylamine-dimethylamine gas is absorbed by water until the obtained monomethylamine-dimethylamine solution is preferably a saturated monomethylamine hydrochloride aqueous solution, and then further processing is performed; the pH value of the saturated monomethylamine hydrochloride aqueous solution is preferably 7 to 9.

[0041] After obtaining the monomethylamine-dimethylamine solution, the present invention preferably further includes: distilling the monomethylamine-dimethylamine solution to obtain recovered monomethylamine-dimethylamine gas; and circulating the recovered monomethylamine-dimethylamine gas for condensation and water absorption. In the present invention, the parameters of the distilled water preferably include: a pH value of 12–12.5; a vacuum degree of -0.05 MPa to -0.09 MPa, more preferably -0.06 MPa to -0.08 MPa, and more preferably -0.07 MPa; a temperature of 40–70°C, more preferably 50–60°C; and a mass of distilled water of 50%–70% of the total mass, more preferably 60%.

[0042] In this invention, the water absorption can completely absorb the dimethylamine gas in the monomethylamine-dimethylamine gas and absorb a portion of the monomethylamine.

[0043] After obtaining monomethylamine gas, the present invention performs acid absorption on the monomethylamine gas to obtain an aqueous solution of monomethylamine hydrochloride.

[0044] In this invention, the reagent for acid absorption includes hydrochloric acid, and the mass concentration of the hydrochloric acid is preferably 5-20%.

[0045] In this invention, the methylamine hydrochloride aqueous solution is preferably a saturated methylamine hydrochloride aqueous solution, that is, when the methylamine hydrochloride aqueous solution is preferably a saturated methylamine hydrochloride aqueous solution, subsequent operations are performed; the pH value of the saturated methylamine hydrochloride aqueous solution is preferably 7 to 9.

[0046] In this invention, the acid absorption is preferably carried out in an absorption tower.

[0047] In this invention, during the acid absorption process, the chemical formula of the conversion of monomethylamine to monomethylamine hydrochloride is shown below:

[0048]

[0049] In this invention, the acid absorption is capable of converting monomethylamine into monomethylamine hydrochloride.

[0050] After obtaining an aqueous solution of monomethylamine hydrochloride, the present invention adjusts the aqueous solution of monomethylamine hydrochloride to acidity and performs vacuum distillation to obtain monomethylamine hydrochloride.

[0051] In this invention, the pH value of the acid is preferably 2 to 5.

[0052] In this invention, the vacuum degree of the vacuum distillation is preferably -0.05 MPa to -0.09 MPa, more preferably -0.06 MPa to -0.08 MPa; the temperature is preferably 40℃ to 70℃, more preferably 50℃ to 60℃. In this invention, the vacuum distillation is preferably carried out in an evaporating kettle.

[0053] In this invention, the amount of distilled water from vacuum distillation is preferably 50 wt% to 70 wt% of an aqueous solution of methylamine hydrochloride. In this invention, the distilled water from vacuum distillation is preferably used as a raw material for preparing an acid absorption reagent.

[0054] Following the vacuum distillation, the present invention preferably further includes cooling and centrifuging the obtained vacuum distillate concentrate. In the present invention, the temperature for cooling and centrifugation is preferably 20–30°C.

[0055] The processing method provided by the present invention is preferably in Figure 1 This is carried out in the system shown.

[0056] The following detailed description, in conjunction with embodiments, of the method for treating the mixed gas generated during the synthesis of 3,3',4,4'-diphenyl ether dianhydride provided by the present invention, should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] The mixed gas of monomethylamine and dimethylamine produced during the hydrolysis of oxobis-(N-methylphthalimide) (with a volume ratio of monomethylamine to dimethylamine of 13:1) is first condensed in a -5℃ condenser, condensing most of the dimethylamine into liquid dimethylamine. The monomethylamine and uncondensed dimethylamine are then introduced into a 300L primary absorption tower as monomethylamine-dimethylamine gas. 150kg of water is added to the primary absorption tower to obtain a monomethylamine-dimethylamine solution and monomethylamine gas. When the pH of the monomethylamine-dimethylamine solution in the primary absorption tower reaches 12, i.e., the monomethylamine-dimethylamine solution becomes saturated, water is distilled off (the parameters for water distillation include: pH value of 12, vacuum degree of -0.07MPa, temperature of 50℃, and mass of distilled water of 105kg). Monomethylamine and dimethylamine are distilled off and recycled back into the condenser and the primary absorption tower.

[0059] The obtained monomethylamine gas is fed into a 500L secondary absorption tower. 300kg of 15wt% hydrochloric acid water is added to the secondary absorption tower to obtain a monomethylamine hydrochloride aqueous solution. When the pH value of the monomethylamine hydrochloride aqueous solution is 8.0, it becomes a saturated monomethylamine hydrochloride aqueous solution.

[0060] 330 kg of saturated monomethylamine hydrochloride aqueous solution was pumped into a 500 L evaporator, and 30 wt% industrial hydrochloric acid was added dropwise until the pH value reached 3.0. Vacuum distillation was then carried out under reduced pressure, with the vacuum degree controlled at -0.06 MPa to -0.08 MPa and the temperature at 50℃ to 60℃. The amount of water distilled off was 210 kg. The resulting concentrated distillate was cooled to 25℃ and centrifuged to obtain 65 kg of monomethylamine hydrochloride, with a monomethylamine hydrochloride content of 99.2%.

[0061] Example 2

[0062] The mixed gas of monomethylamine and dimethylamine produced during the hydrolysis of oxobis-(N-methylphthalimide) (with a volume ratio of monomethylamine to dimethylamine of 13:1) is first condensed in a -5℃ condenser, condensing most of the dimethylamine into liquid dimethylamine. The monomethylamine and uncondensed dimethylamine are then introduced into a 300L primary absorption tower as monomethylamine-dimethylamine gas. 150kg of water is added to the primary absorption tower to obtain a monomethylamine-dimethylamine solution and monomethylamine gas. When the pH of the monomethylamine-dimethylamine solution in the primary absorption tower reaches 12, i.e., the monomethylamine-dimethylamine solution becomes saturated, water is distilled off (the parameters for water distillation include: pH value of 12, vacuum degree of -0.065MPa, temperature of 55℃, and mass of distilled water of 100kg) to distill off monomethylamine and dimethylamine. The distilled off monomethylamine and dimethylamine are then recycled back into the condenser and the primary absorption tower.

[0063] The obtained monomethylamine gas is fed into a 500L secondary absorption tower. 300kg of 10wt% hydrochloric acid water is added to the secondary absorption tower to obtain a monomethylamine hydrochloride aqueous solution. When the pH value of the monomethylamine hydrochloride aqueous solution reaches 7.5, it becomes a saturated monomethylamine hydrochloride aqueous solution.

[0064] 320 kg of saturated monomethylamine hydrochloride aqueous solution was pumped into a 500 L evaporator, and 30 wt% industrial hydrochloric acid was added dropwise until the pH value reached 3.5. Vacuum distillation was then carried out under reduced pressure, with the vacuum degree controlled at -0.06 MPa to -0.08 MPa and the temperature at 50℃ to 60℃. The amount of water distilled was 195 kg. The resulting concentrated distillate was cooled to 25℃ and centrifuged to obtain 43 kg of monomethylamine hydrochloride, with a monomethylamine hydrochloride content of 99.1%.

[0065] Example 3

[0066] The mixed gas of monomethylamine and dimethylamine produced during the hydrolysis of oxobis-(N-methylphthalimide) (with a volume ratio of monomethylamine to dimethylamine of 13:1) is first condensed in a -5℃ condenser, condensing most of the dimethylamine into liquid dimethylamine. The monomethylamine and the uncondensed dimethylamine are then introduced into a 300L primary absorption tower as monomethylamine-dimethylamine gas. 150kg of water is added to the primary absorption tower to obtain a monomethylamine-dimethylamine solution and monomethylamine gas. When the pH of the monomethylamine-dimethylamine solution in the primary absorption tower reaches 12, i.e., the monomethylamine-dimethylamine solution becomes saturated, water is distilled off (the parameters for water distillation include: pH value of 12, vacuum degree of -0.06MPa, temperature of 60℃, and mass of distilled water of 102kg), distilling off monomethylamine and dimethylamine. The distilled off monomethylamine and dimethylamine are then recycled back into the condenser and the primary absorption tower.

[0067] The obtained monomethylamine gas is fed into a 500L secondary absorption tower. 300kg of 20wt% hydrochloric acid water is added to the secondary absorption tower to obtain a monomethylamine hydrochloride aqueous solution. When the pH value of the monomethylamine hydrochloride aqueous solution reaches 8.0, it becomes a saturated monomethylamine hydrochloride aqueous solution.

[0068] 345 kg of saturated monomethylamine hydrochloride aqueous solution was pumped into a 500 L evaporator, and 30 wt% industrial hydrochloric acid was added dropwise until the pH value reached 3.0. Vacuum distillation was then carried out under reduced pressure, with the vacuum degree controlled at -0.06 MPa to -0.08 MPa and the temperature at 50℃ to 60℃. 220 kg of water was distilled off. The resulting concentrated distillate was cooled to 25℃ and centrifuged to obtain 87 kg of monomethylamine hydrochloride, with a mass content of 99.1%.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating a mixed gas produced in a process for synthesizing 3,3',4,4'-diphenyl ether dianhydride, the mixed gas comprising monomethylamine and dimethylamine, characterized by, Includes the following steps: The mixed gas is condensed to obtain a mixed gas of monomethylamine and dimethylamine and a liquid dimethylamine; The mixed gas of monomethylamine and dimethylamine is absorbed by water to obtain a solution containing monomethylamine and dimethylamine and monomethylamine gas; The monomethylamine gas was subjected to acid absorption to obtain an aqueous solution of monomethylamine hydrochloride; The aqueous solution of monomethylamine hydrochloride was adjusted to acidity and then subjected to vacuum distillation to obtain monomethylamine hydrochloride. The reagent used for acid absorption includes hydrochloric acid.

2. The treatment method according to claim 1, characterized in that, The condensation temperature is 0~-5℃.

3. The treatment method of claim 1, wherein The solution containing monomethylamine and dimethylamine is a saturated solution of monomethylamine and dimethylamine; the pH value of the saturated solution of monomethylamine and dimethylamine is 12-13.

4. The treatment method of claim 1, wherein The mass concentration of the hydrochloric acid is 5-20%.

5. The treatment method according to claim 1 or 4, characterized in that, The methylamine hydrochloride aqueous solution is a saturated methylamine hydrochloride aqueous solution, and the pH value of the saturated methylamine hydrochloride aqueous solution is 7-9.

6. The treatment method of claim 1, wherein The acidic pH value is 2-5.

7. The treatment method of claim 1, wherein The vacuum degree of the vacuum distillation is -0.05MPa to -0.09MPa, and the temperature is 40℃ to 70℃.

8. The processing method according to claim 1 or 7, characterized in that, The amount of water distilled under reduced pressure is 50 wt% to 70 wt% of the aqueous solution of methylamine hydrochloride.

9. The processing method according to claim 1 or 7, characterized in that, After vacuum distillation, the process further includes cooling and centrifuging the obtained vacuum distillate concentrate; the temperature of the cooling and centrifugation is 20~30℃.

10. The processing method according to claim 1, characterized in that, Also includes: The solution containing monomethylamine and dimethylamine is subjected to distillation to obtain a mixed gas containing recovered monomethylamine and dimethylamine; The mixed gas containing the recovered monomethylamine and dimethylamine is recycled for condensation and water absorption; The parameters of the distilled water include: pH value of 12~12.5, vacuum degree of -0.05MPa~-0.09MPa, temperature of 40~70℃, and the mass of the distilled water is 50%~70% of the total mass.

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