Acetonitrile continuous negative pressure distillation extraction process

Abstract

The invention belongs to the field of acetonitrile distillation and extraction processes, and particularly relates to an acetonitrile continuous negative pressure distillation and extraction process which comprises the following steps: S1, mixing an alkaline adsorbent with acid-containing acetonitrile waste liquid, uniformly stirring at 200-300rpm, reacting for 0.5-1 hour, centrifugally separating, filtering and collecting filtrate; s2, filtering the filtrate in the step S1 through a ceramic membrane, then introducing the filtrate into a dehydration tower, carrying out negative pressure rectification separation, removing ammonium sulfate and water, collecting a tower top gas phase, condensing into a liquid phase, and passing through a pervaporation membrane; and S3, adding the liquid phase treated by the pervaporation membrane in the step S2 and ethylene glycol into a negative pressure extractive distillation tower for extraction, collecting a tower top gas phase, condensing and liquefying to obtain acetonitrile, and performing molecular sieve dehydration and heat pump distillation on a tower bottom liquid phase to obtain ethylene glycol. Through multi-stage cooperation of alkaline adsorption, membrane-negative pressure rectification and extractive rectification, the purity and energy efficiency of acetonitrile recovery are remarkably improved, and the method is especially suitable for purification of high-acidity and high-moisture crude acetonitrile.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of distillation extraction, in particular to a continuous negative pressure distillation extraction process of acetonitrile. BACKGROUND

[0002] In the production process of acetonitrile, the crude acetonitrile synthesized by "glacial acetic acid + liquid ammonia" contains 52% acetonitrile, 47% water, 1% ammonium sulfate, and a small amount of acetone, propionitrile, tar, etc.; in order to obtain pure acetonitrile with a content of more than 99%, the crude acetonitrile synthesized needs to be purified. The current purification methods include extractive distillation, membrane separation technology, etc.

[0003] After searching, the patent with publication number CN105968028A discloses a continuous negative pressure distillation extraction process of acetonitrile, which preheats the synthesized crude acetonitrile to 70-80℃ and then sends it into a dehydration tower for rectification separation, the acetonitrile with a content of more than 70% obtained at the top of the tower is sent into an extractive rectification tower, and 0.2% water-containing ethylene glycol is added into the extractive rectification tower to extract and remove water from the acetonitrile for purification; the 99% acetonitrile obtained at the top of the extractive rectification tower is condensed by the external condenser of the extractive rectification tower and then stored in an acetonitrile receiving tank for product storage, which has the advantages of saving energy, saving cost, stable process, easy operation, and high purity. The patent CN114213282A discloses a recycling method of acid-containing acetonitrile waste solvent, which neutralizes the acid in the acid-containing acetonitrile waste solvent by using tri-n-butylamine, which does not produce water in the process, does not need multiple rectifications, and can obtain high-purity and quality-qualified acetonitrile without acid by only one rectification, which is simpler and easier to operate, saves a large amount of energy, saves the recycling cost, improves the utilization rate of acetonitrile, greatly shortens the processing time, and saves a large amount of manpower and material resources.

[0004] However, the existing purification process of acid-containing acetonitrile waste liquid has relatively complex process steps, low purity of acetonitrile, and strong corrosiveness to the extractive distillation tower and other equipment. SUMMARY

[0005] The present application aims to provide a continuous negative pressure distillation extraction process of acetonitrile, which significantly improves the purity and energy efficiency of acetonitrile recovery through multi-stage cooperation of basic adsorption, membrane, negative pressure rectification, and extractive rectification, and is especially suitable for the purification of high-acidity and high-moisture crude acetonitrile.

[0006] The technical problem of the present application is solved by using the following technical solution.

[0007] On the one hand, the present application provides a continuous negative pressure distillation extraction process of acetonitrile, which includes the following steps: S1, mixing a basic adsorbent with acid-containing acetonitrile waste liquid, stirring uniformly at 200-300 rpm, and then reacting for 0.5-1 h, centrifugal separation, filtration, and collecting the filtrate; S2, filtering the filtrate of step S1 through a ceramic membrane, then passing the filtrate into a dehydration tower, and removing ammonium sulfate and water by negative pressure rectification separation, collecting the gas phase at the top of the tower, and condensing into liquid phase, and then passing through a pervaporation membrane; S3, adding the liquid phase after pervaporation membrane treatment in step S2 and ethylene glycol into a negative pressure extractive rectification tower for extraction, collecting the gas phase at the top of the tower and condensing into liquid, to obtain acetonitrile, and the liquid phase at the bottom of the tower is subjected to molecular sieve dehydration and heat pump rectification to obtain ethylene glycol. The ratio of the circulation amount of ethylene glycol to the backflow amount in the negative pressure extractive rectification tower is 3:1.

[0008] In some embodiments of the present application, in step S1, the basic adsorbent comprises 3A molecular sieves and supported tri-n-butylamine, and the basic adsorbent is prepared as follows: The 3A molecular sieves are mixed with a 5-10% NaOH solution, stirred uniformly, and then allowed to stand, filtered, and the 3A molecular sieves are collected; the 3A molecular sieves are added to tri-n-butylamine, stirred uniformly, to obtain the basic adsorbent.

[0009] In some embodiments of the present application, the mass ratio of the 3A molecular sieves to tri-n-butylamine is (1-2):1.

[0010] In some embodiments of the present application, the mass ratio of the basic adsorbent to the acid-containing acetonitrile waste liquid is (1:10)-(1:5).

[0011] In some embodiments of the present application, in step S1, the centrifugal separation is performed at a speed of 3000 rpm for 10 min.

[0012] In some embodiments of the present application, in step S2, the pore size of the ceramic membrane is 0.5 um, and the pressure in the dehydration tower is 40-50 kPa.

[0013] In some embodiments of the present application, in step S3, the pressure in the negative pressure extractive rectification tower is 10-15 kPa; when the gas phase at the top of the tower is collected, the gas phase fraction below 76℃ is removed, and the gas phase fraction at 80-81℃ is collected.

[0014] Compared with the prior art, the present application has the following beneficial effects: The acid acetonitrile waste liquid is first subjected to acid-base neutralization and adsorption cooperative treatment: the basic adsorbent adopts a composite structure of 3A molecular sieve loaded with tri-n-butylamine, and the molecular sieve forms strong alkaline sites after NaOH activation, which can efficiently neutralize the acidic components in the waste liquid, and the organic phase characteristics of tri-n-butylamine can selectively adsorb organic impurities, which are complementary to the micropore adsorption of the molecular sieve, and the comprehensive removal rate is more than 95%; and the basic adsorbent provided by the present application will not produce excess water during acid-base neutralization, and under the action of the basic adsorbent, the acidic substances in the liquid are removed, reducing the corrosion of the acidic substances on the subsequent equipment, and the basic adsorption treatment of S1 protects the ceramic membrane and the rectifying column of S2, avoiding acid corrosion and fouling, and prolonging the service life of the equipment.

[0015] Step S2 first adopts a 0.5 μm ceramic membrane for pretreatment, which can intercept solid particles ≥0.8 μm, protecting the subsequent rectifying equipment, and then operates at a negative pressure of 40-50 kPa in the dehydration tower, so that the boiling point of acetonitrile is reduced to about 60℃, significantly reducing energy consumption (30% energy saving compared with normal pressure); the gas phase discharged from the dehydration tower is condensed and then passed through a pervaporation membrane, which preferentially permeates acetonitrile molecules based on the dissolution-diffusion mechanism, further reducing the water content of acetonitrile and improving the processing efficiency of the subsequent negative pressure extractive rectifying column and the purity of acetonitrile; ceramic membrane pre-filtration ensures that the flux of the pervaporation membrane is stable at 15-20 L / (m²·h), and the intermediate product produced by the pervaporation membrane reduces the load of the subsequent extractive rectifying column by 40%.

[0016] In step S3, in the negative pressure extractive rectifying column, ethylene glycol forms a hydrogen bond complex with acetonitrile to change the relative volatility, so that the acetonitrile-water separation factor is increased from 1.2 to 2.5, and the boiling point of acetonitrile is reduced to 80-81℃ under a negative pressure of 10-15 kPa, and the fraction collection interval is accurately controlled (±0.5℃).

[0017] The negative pressure system of the present application has a comprehensive energy saving of more than 40%, and the heat pump rectification reduces the energy consumption of ethylene glycol recovery by 60%, so that the final acetonitrile purity is ≥99.5%, the water content is ≤100 ppm, the metal ion content is ≤10 ppb, and the ethylene glycol recovery purity is ≥99.8%, meeting the recycling standard.

[0018] Environmental friendliness: closed loop design reduces wastewater discharge by 80%, no organic solvent discharge, basic adsorbent can be reused 5-8 times, and solid waste is reduced by 70%. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to specific embodiments.

[0021] The acetonitrile continuous negative pressure distillation extraction process provided by the embodiment of the present application comprises the following steps: S1, mixing the basic adsorbent with the acid-containing acetonitrile waste liquid, stirring uniformly at 200-300 rpm, and then reacting for 0.5-1 h, centrifugal separation, the centrifugal separation speed is 3000 rpm, and the time is 10 min; then filtering, and collecting the filtrate; the mass ratio of the basic adsorbent to the acid-containing acetonitrile waste liquid is (1:10)-(1:5).

[0022] S2, filtering the filtrate of step S1 through a ceramic membrane, then passing the filtrate into a dehydration tower, and performing negative pressure rectification separation to remove ammonium sulfate and water, collecting the gas phase at the top of the tower, and condensing into a liquid phase, and then treating through a pervaporation membrane (polyvinyl alcohol / polyacrylonitrile); the pore size of the ceramic membrane is 0.5 um, and the pressure in the dehydration tower is 40-50 kPa.

[0023] S3, adding the liquid phase treated through the pervaporation membrane in step S2 and ethylene glycol into a negative pressure extraction rectification tower for extraction, collecting the gas phase at the top of the tower and condensing and liquefying, so as to obtain acetonitrile, and subjecting the liquid phase at the bottom of the tower to molecular sieve dehydration and heat pump rectification, so as to obtain ethylene glycol. In the negative pressure extraction rectification tower, the pressure is 10-15 kPa; when the gas phase at the top of the tower is collected, the gas phase fraction below 76 ℃ is removed, and the gas phase fraction at 80-81 ℃ is collected.

[0024] In the embodiment of the present application, in step S1, the basic adsorbent comprises 3A molecular sieve and supported tri-n-butylamine, and the basic adsorbent is prepared by the following method: Mixing 3A molecular sieve with 5-10% NaOH solution, stirring uniformly, standing, filtering, and collecting 3A molecular sieve; adding the 3A molecular sieve into tri-n-butylamine, and stirring uniformly, so as to obtain the basic adsorbent. The mass ratio of the 3A molecular sieve to the tri-n-butylamine is (1-2):1.

[0025] It should be noted that the 3A molecular sieve used in the embodiment of the present application is produced by Zibo Green Chemical Co., Ltd.

[0026] The features and performances of the present application will be further described in detail below in combination with embodiments.

[0027] Embodiment one An acetonitrile continuous negative pressure distillation extraction process comprises the following steps: S1. The alkaline adsorbent and the acid-containing acetonitrile waste liquid are mixed at a mass ratio of 1:10. After stirring at 200 rpm until homogeneous, the mixture is reacted for 0.5 h. Then, it is centrifuged at 3000 rpm for 10 min. Finally, the mixture is filtered and the filtrate is collected.

[0028] S2, after filtering the filtrate from step S1 using a ceramic membrane with a pore size of 0.5 μm, the filtrate is then passed into a dehydration tower. The vacuum pump is turned on to stabilize the absolute pressure in the dehydration tower at 50 kPa. The filtrate is then separated by negative pressure distillation to remove ammonium sulfate and water. The gas phase at the top of the tower is collected, condensed into a liquid phase, and then passed through a pervaporation membrane.

[0029] In step S3, the liquid phase obtained from the pervaporation membrane treatment in step S2, along with ethylene glycol, is added to a negative pressure extractive distillation column for extraction. The overhead vapor phase is collected and condensed to obtain acetonitrile. The bottom liquid phase is dehydrated using a molecular sieve and then distilled using a heat pump to obtain ethylene glycol. The pressure inside the negative pressure extractive distillation column is maintained at 10 kPa. When collecting the overhead vapor phase, the vapor fraction below 76°C is removed, and the vapor fraction at 80-81°C is collected. The ratio of ethylene glycol circulation rate to reflux rate is 3:1.

[0030] Example 2 An acetonitrile continuous negative pressure distillation extraction process includes the following steps: S1. The alkaline adsorbent and the acid-containing acetonitrile waste liquid are mixed at a mass ratio of 1:12.5. The mixture is stirred at 200 rpm and reacted for 1 hour. Then, it is centrifuged at 3000 rpm for 10 minutes. Finally, it is filtered and the filtrate is collected.

[0031] S2, after filtering the filtrate from step S1 using a ceramic membrane with a pore size of 0.5 μm, the filtrate is then passed into a dehydration tower. The vacuum pump is turned on to stabilize the absolute pressure in the dehydration tower at 50 kPa. The filtrate is then separated by negative pressure distillation to remove ammonium sulfate and water. The gas phase at the top of the tower is collected, condensed into a liquid phase, and then passed through a pervaporation membrane.

[0032] In step S3, the liquid phase obtained from the pervaporation membrane treatment in step S2, along with ethylene glycol, is added to a negative pressure extractive distillation column for extraction. The overhead vapor phase is collected and condensed to obtain acetonitrile. The bottom liquid phase is dehydrated using a molecular sieve and then distilled using a heat pump to obtain ethylene glycol. The pressure inside the negative pressure extractive distillation column is maintained at 10 kPa. When collecting the overhead vapor phase, the vapor fraction below 76°C is removed, and the vapor fraction at 80-81°C is collected. The ratio of ethylene glycol circulation rate to reflux rate is 3:1.

[0033] Example 3 An acetonitrile continuous negative pressure distillation extraction process includes the following steps: S1, the basic adsorbent and the waste liquid containing acid acetonitrile were mixed in a mass ratio of 1:15, and then stirred at 200 rpm for 1 h. Then, the mixture was centrifuged at 3000 rpm for 10 min. Then, the filtrate was collected by filtration.

[0034] S2, the filtrate of step S1 was filtered by a ceramic membrane with a pore size of 0.5 um. Then, the filtrate was introduced into a dehydration column, and a vacuum pump was started. The absolute pressure in the dehydration column was stabilized at 50 kPa. Then, the negative pressure rectification separation was carried out to remove ammonium sulfate and water. The gas phase at the top of the column was collected and condensed into liquid phase. Then, the liquid phase was treated by a pervaporation membrane.

[0035] S3, the liquid phase treated by the pervaporation membrane in step S2 and ethylene glycol were introduced into a negative pressure extraction rectification column for extraction. The gas phase at the top of the column was collected and condensed into liquid phase, which was acetonitrile. The liquid phase at the bottom of the column was dehydrated by a molecular sieve and subjected to heat pump rectification to obtain ethylene glycol. The pressure in the negative pressure extraction rectification column was maintained at 10 kPa. When the gas phase at the top of the column was collected, the gas phase fraction below 76℃ was removed, and the gas phase fraction between 80-81℃ was collected.

[0036] In examples 1-3, the basic adsorbent was prepared as follows: 3A molecular sieve was mixed with 5% NaOH solution, stirred uniformly, and then filtered to collect 3A molecular sieve. The 3A molecular sieve was added to tri-n-butylamine, and the mixture was stirred uniformly to obtain the basic adsorbent. The mass ratio of 3A molecular sieve to tri-n-butylamine was 1:1. The ratio of the circulating amount of ethylene glycol to the backflow amount was 3:1.

[0037] Comparative example 1 The difference between example 1 and comparative example 1 is that tri-n-butylamine is used instead of the basic adsorbent in step S1. The other steps and parameters are the same as those in example 1.

[0038] Comparative example 2 The difference between example 1 and comparative example 2 is that 3A molecular sieve is used instead of the basic adsorbent in step S1. The other steps and parameters are the same as those in example 1.

[0039] Detection test The acetonitrile obtained in examples 1-3 and comparative examples 1 and 2 was used as the detection object, and the purity and water content of the acetonitrile were detected by gas chromatography. The results are shown in Table 1. The chromatographic column was Elite-624 (30 m x 0.53 mm x 3.0 um), and the detection limit was 0.025 ug / mL.

[0040] The residual amount of tri-n-butylamine in each acetonitrile was detected by gas chromatography, and the results are shown in Table 1; wherein, the chromatographic column is CP-Volamide special column (KOH treatment is used to eliminate the interference of silanol group); the detector is nitrogen phosphorus detector (NPD); the programmed temperature is 40℃ for 2 min, and then increased to 150℃ at the rate of 10℃ / min.

[0041] Table 1

[0042] As shown in the data in Table 1, the purity of acetonitrile purified by the present application can reach more than 99.9%, the water content is less, and tri-n-butylamine is not detected; while in the comparative examples 1 and 2, the purity of acetonitrile is relatively low.

[0043] In summary, the negative pressure distillation extraction process provided by the embodiments of the present application can save energy by more than 40% in the negative pressure system, and the energy consumption of ethylene glycol recovery is reduced by 60% by heat pump rectification. The purity of acetonitrile is ≥99.5%, the water content is ≤100ppm, the metal ion is ≤10ppb, the purity of ethylene glycol recovery is ≥99.8%, which meets the recycling standard.

[0044] The above-described embodiments are part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

Claims

1. A continuous negative pressure distillation and extraction process for acetonitrile, characterized in that, Includes the following steps: S1. Mix the alkaline adsorbent with the acidic acetonitrile waste liquid, stir at 200-300 rpm until homogeneous, react for 0.5-1 h, centrifuge, filter, and collect the filtrate. S2, after filtering the filtrate from step S1 through a ceramic membrane, the filtrate is then passed into a dehydration tower for negative pressure distillation to remove ammonium sulfate and water. The gas phase at the top of the tower is collected, condensed into a liquid phase, and then passed through a pervaporation membrane. S3, the liquid phase after pervaporation membrane treatment in step S2 and ethylene glycol are added to a negative pressure extractive distillation column for extraction. The gas phase at the top of the column is collected and condensed to obtain acetonitrile. The liquid phase at the bottom of the column is dehydrated by molecular sieve and distilled by heat pump to obtain ethylene glycol.

2. The acetonitrile continuous negative pressure distillation and extraction process according to claim 1, characterized in that, In step S1, the alkaline adsorbent comprises 3A molecular sieve and supported tri-n-butylamine, and the alkaline adsorbent is prepared by the following method: Mix 3A molecular sieve with 5-10% NaOH solution, stir until homogeneous, let stand, filter, and collect 3A molecular sieve; add 3A molecular sieve to tri-n-butylamine, stir until homogeneous, and the alkaline adsorbent is obtained.

3. The acetonitrile continuous negative pressure distillation and extraction process according to claim 2, characterized in that, The mass ratio of the 3A molecular sieve to tri-n-butylamine is (1-2):

1.

4. The acetonitrile continuous negative pressure distillation and extraction process according to claim 1, characterized in that, The mass ratio of the alkaline adsorbent to the acidic acetonitrile waste liquid is (1:10) to (1:5).

5. The acetonitrile continuous negative pressure distillation and extraction process according to claim 1, characterized in that, In step S1, the centrifugation speed is 3000 rpm and the time is 10 min.

6. The acetonitrile continuous negative pressure distillation and extraction process according to claim 1, characterized in that, In step S2, the pore size of the ceramic membrane is 0.5 μm, and the pressure in the dehydration tower is 40-50 kPa.

7. The preparation method of the acetonitrile continuous negative pressure distillation and extraction process according to claim 6, characterized in that, In step S3, the pressure in the negative pressure extraction distillation column is 10-15 kPa; when collecting the gas phase at the top of the column, the gas phase fraction before 76°C is removed, and the gas phase fraction at 80-81°C is collected.

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