A method and device for regenerating solvent in a 1,3-butadiene extraction process using acetonitrile

Abstract

The present application belongs to the technical field of ethylene cracking C4 fraction separation, and relates to a 1,3-butadiene extraction process solvent regeneration method and device based on acetonitrile. The method comprises the following steps: extracting a circulating acetonitrile solvent into the middle part of a light-removing column, obtaining an azeotrope containing organic matters at the top of the column, and obtaining the light-removed acetonitrile solvent at the bottom of the column; the light-removed acetonitrile solvent is sent into a heavy-removing column to obtain a heavy-removing column top regenerated solvent and a heavy component product at the bottom of the column, and the heavy-removing column top regenerated solvent is returned to an extraction system. The present application has the following beneficial effects: the light-removing column top organic matter waste liquid discharge device is used to inhibit the circulation accumulation of organic matters such as alcohols and ketones in the entire butadiene extraction device at the cost of a small amount of acetonitrile loss. A new circulating acetonitrile solvent is extracted for regeneration, and negative pressure operation is avoided. The continuous regeneration mode or the intermittent regeneration mode can be selected, the device operation cost is reduced, and the economic benefit of the newly added solvent regeneration system is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of ethylene cracking C4 fraction separation technology, specifically, it relates to a solvent regeneration method and apparatus for acetonitrile-based 1,3-butadiene extraction process. Background Technology

[0002] Acetonitrile is recycled as an extractant in the butadiene extraction unit. Actual operation shows that during continuous production, the recycled acetonitrile solvent accumulates large amounts of alcohols, ketones, butadiene dimers, and polymers. This compositional change degrades the solvent's extraction performance; in severe cases, solvent foaming causes flooding in the extraction system, while simultaneously accelerating polymerization, generating polymers that clog the trays, making normal production impossible. Therefore, the recycled acetonitrile solvent needs continuous regeneration to maintain quality and ensure stable unit operation.

[0003] In the existing process, acetonitrile solvent regeneration involves taking approximately 1% of the circulating solvent from the solvent storage tank and feeding it into an alkyne washing tower to remove dimers. This solvent, along with wash water from other washing towers, then passes through a solvent recovery tower to remove other impurities. The top of the solvent recovery tower yields approximately 78% regenerated solvent, which is returned to the extraction system. However, due to the high water content of the regenerated solvent returned to the extraction system and the limited dehydration capacity of the extraction system, the amount of solvent regeneration is limited to maintain a stable solvent concentration. Researchers have proposed using negative pressure operation to increase solvent concentration, but impurities such as alcohols and ketones in the circulating solvent still cannot be removed. Because organic compounds such as alcohols and ketones, as well as heavy components such as butadiene polymers, cannot be effectively removed from the solvent, their accumulation affects the extraction effect. Therefore, during unit maintenance, some or all of the solvent needs to be replaced with fresh solvent, which is costly and results in a significant waste of acetonitrile. The large quantities of expired acetonitrile hazardous waste cannot be disposed of arbitrarily. How to safely and effectively handle the replaced expired acetonitrile poses a challenge for butadiene unit producers. Therefore, it is necessary to improve the existing continuous acetonitrile regeneration method to solve the problems existing in the current solvent regeneration process. Summary of the Invention

[0004] The purpose of this invention is to solve the aforementioned problems existing in the prior art. This invention provides a method and apparatus for solvent regeneration in an acetonitrile-based 1,3-butadiene extraction device. A stream of circulating acetonitrile solvent is extracted for regeneration, removing impurities such as alcohols, ketones, and butadiene polymers, thus purifying the circulating acetonitrile solvent. This solves the problems of low quality, limited regeneration capacity, and inability to remove large amounts of impurities in a timely manner in existing solvent regeneration methods, improving solvent quality and extending the device's production cycle. It eliminates the need for periodic solvent replacement, saving production costs and bringing certain economic benefits.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for solvent regeneration in an acetonitrile-based 1,3-butadiene extraction process, comprising the following steps: circulating acetonitrile solvent enters the middle section of a light-light component removal column, an azeotrope containing organic matter is obtained at the top of the column, and a light-light component removal acetonitrile solvent is obtained at the bottom of the column; the light-light component removal acetonitrile solvent is sent to a heavy-weight component removal column to obtain a regenerated solvent at the top of the heavy-weight component removal column and a heavy component product at the bottom of the heavy-weight component removal column; the regenerated solvent at the top of the heavy-weight component removal column is returned to the extraction system.

[0006] In this invention, circulating acetonitrile solvent enters the middle of the light component removal tower. By adjusting the parameters of the light component removal tower, organic substances such as C4, acetone, methanol, ethanol, and isopropanol in the feedstock form an azeotrope with water and a small amount of acetonitrile, which is distilled off from the top of the tower and sent to the waste liquid system. The solvent at the bottom of the tower is sent to the heavy component removal tower, where dimers, polymers, and a small amount of acetonitrile are discharged from the bottom of the heavy component removal tower and sent to the waste liquid system. The regenerated solvent at the top of the heavy component removal tower is returned to the extraction system.

[0007] The solvent regeneration method of the present invention can be used as a supplement to existing solvent regeneration methods.

[0008] According to the present invention, preferably, the circulating acetonitrile solvent contains 85-95 wt% acetonitrile, 1-5 wt% light component impurities, 0.2-2 wt% heavy component impurities, and the remainder is water.

[0009] According to the present invention, preferably, the light component impurity is C4 and an oxygen-containing compound, including methanol, ethanol, isopropanol, acetone, etc.; the heavy component impurity is a butadiene polymer.

[0010] According to the present invention, preferably, the content of light component impurities in the regeneration solvent at the top of the de-heavy component tower is not higher than 0.1 wt%, the content of heavy component impurities is not higher than 0.1 wt%, and the total loss of acetonitrile is less than 3 wt% of the extracted acetonitrile.

[0011] According to the present invention, preferably, the number of trays in the light-light-removal tower is 40-90, the reboiler temperature is 80-150°C, the top pressure is 0.01-0.5 MPaG, and the reflux ratio is 15-50;

[0012] According to the present invention, preferably, the number of trays in the light-light removal tower is 50-80, the bottom temperature is 80-130°C, the top pressure is 0.01-0.4 MPaG, and the reflux ratio is 20-40.

[0013] The number of trays in the deweight removal tower is 6 to 20, the bottom temperature is 85 to 155°C, and the top pressure is 0.01 to 0.3 MPaG.

[0014] According to the present invention, preferably, the number of trays in the deweight removal tower is 10 to 17, the bottom temperature is 95 to 135°C, and the top pressure is 0.01 to 0.1 MPaG.

[0015] According to the present invention, preferably, the solvent regeneration method is a continuous regeneration method or an intermittent regeneration method.

[0016] A second aspect of the present invention is a solvent regeneration apparatus for an acetonitrile-based 1,3-butadiene extraction process, the apparatus comprising: a light-weight removal tower and a heavy-weight removal tower;

[0017] The light component removal tower is equipped with a circulating acetonitrile solvent feed line in the middle, a light component removal tower top discharge line at the top of the tower, and a light component removal tower bottom discharge line at the bottom of the tower. The light component removal tower bottom discharge line is connected to the heavy component removal tower. The heavy component removal tower is equipped with a heavy component removal tower top discharge line and a heavy component removal tower bottom discharge line. The heavy component removal tower top discharge line is connected to the extraction system.

[0018] The beneficial effects of this invention are as follows:

[0019] The organic waste liquid discharge device at the top of the light-weight solvent removal tower, at the cost of a small amount of acetonitrile, inhibits the circulation and accumulation of organic substances such as alcohols and ketones throughout the butadiene extraction unit. A new stream of circulating acetonitrile solvent is drawn for regeneration, avoiding negative pressure operation. Both continuous and intermittent regeneration methods can be selected, reducing operating costs and significantly improving the economic efficiency of the new solvent regeneration system.

[0020] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0021] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0022] Figure 1 A flowchart of the solvent regeneration method of the acetonitrile-based 1,3-butadiene extraction apparatus of the present invention is shown.

[0023] Explanation of reference numerals in the attached figures:

[0024] 1-Acetonitrile solvent feed, 2-Light weight removal tower, 3-Light weight removal tower top condenser, 4-Light weight removal tower top reflux tank, 5-Light weight removal tower top reflux pump, 6-Light weight removal tower top waste liquid, 7-Light weight removal tower reboiler, 8-Light weight removal tower reboiler solvent / heavy weight removal tower feed, 9-Heavy weight removal tower, 10-Regenerated solvent cooler, 11-Regenerated solvent, 12-Heavy weight removal tower reboiler, 13-Heavy weight removal tower reboiler heavy components. Detailed Implementation

[0025] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0026] Example

[0027] A 160,000-ton / year acetonitrile-based 1,3-butadiene extraction unit has an initial acetonitrile solvent charge of 600 tons and a circulating solvent charge of approximately 332 tons / hour. After four years of operation, the circulating solvent composition is as follows: acetonitrile 91.19 wt%, water 5.31 wt%, light component impurities such as alcohols and ketones totaling 3.03 wt%, and heavy component impurities such as butadiene polymers 0.47 wt%.

[0028] A 3-ton / hour circulating solvent is drawn out for regeneration.

[0029] The light-weight removal tower has 75 trays, feed on the 30th tray, reboiler temperature of 87℃, top pressure of 0.01MPaG, and reflux ratio of 28.

[0030] The deweight removal tower has 13 trays, feeds from the top, has a bottom temperature of 118℃, a pressure of 0.01MPaG, and no reflux.

[0031] The composition of the regenerated acetonitrile solvent is as follows: organic compounds such as alcohols and ketones not exceeding 0.06 wt%, and butadiene polymer not exceeding 0.1 wt%.

[0032] Choose the intermittent regeneration method, regenerate once a year, and the regeneration cycle is 7 to 14 days.

[0033] The main logistics components are shown in Table 1.

[0034] Table 1 (all compositions are in wt%)

[0035]

[0036] As shown in the table above, after regeneration, 2.83 t / h of regenerated solvent with an acetonitrile content of 94.5 wt% was obtained from a circulating solvent with an acetonitrile content of 91.2 wt% at a capacity of 3 t / h. The total acetonitrile loss was 2.24 wt%, while the alcohol and ketone content decreased from 3.03 wt% to 0.06 wt%, and the polymer content decreased from 0.47 wt% to 0.1 wt%. C4, acetone, methanol, ethanol, and isopropanol in the feed were discharged from the top waste liquid of the light component removal tower, which contained 38.22 wt% acetonitrile, and returned to the waste liquid system. Butadiene dimer and polymers were discharged from the bottom heavy component of the heavy component removal tower, which contained 9.51 wt% acetonitrile, and returned to the waste liquid system. The increased acetonitrile content solved the problem of limited solvent regeneration capacity, maintained stable solvent concentration in the system, and enabled timely removal of solvent impurities even when their content was high.

[0037] The estimated operating costs are shown in Table 2.

[0038] Table 2

[0039]

[0040] As shown in the table above, based on the existing pricing system of 0.16 yuan / t for circulating water, 140 yuan / t for low-pressure steam, and 15,000 yuan / t for acetonitrile, the estimated operating cost of this unit is roughly: 1352.78 yuan per hour and 478.01 yuan per ton of regenerated acetonitrile.

[0041] The initial acetonitrile solvent capacity is 600 tons, with intermittent regeneration once a year, a regeneration cycle of 200 hours, and a cost of 1.082 million yuan over 4 years. Under the existing process, after 4 years of operation, the solvent needs to be completely replaced with fresh solvent, costing 9 million yuan. This invention will save approximately 7.918 million yuan over 4 years, demonstrating considerable economic benefits.

[0042] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A solvent regeneration method for an acetonitrile-based 1,3-butadiene extraction process, characterized in that, The process includes the following steps: A fresh stream of circulating acetonitrile solvent is drawn off for regeneration. This circulating acetonitrile solvent enters the middle section of the light component removal column, where an azeotrope containing organic matter is obtained at the top, and the acetonitrile solvent after light component removal is obtained at the bottom. The acetonitrile solvent after light component removal is then fed into a heavy component removal column, yielding a regenerated solvent at the top of the heavy component removal column and a heavy component product at the bottom. The regenerated solvent at the top of the heavy component removal column is returned to the extraction system. The circulating acetonitrile solvent contains 85-95 wt% acetonitrile, 1-5 wt% light component impurities, 0.2-2 wt% heavy component impurities, and the remainder is water. The light component impurities are C4 atoms and oxygen-containing compounds. The heavy component impurities are butadiene polymers. The light-light-removal tower has 40-90 trays, a reboiler temperature of 80-150 ℃, a top pressure of 0.01-0.5 MPaG, and a reflux ratio of 15-50. The number of trays in the deweight removal tower is 6 to 20, the bottom temperature is 85 to 155 ℃, and the top pressure is 0.01 to 0.3 MPaG.

2. The solvent regeneration method for the acetonitrile-based 1,3-butadiene extraction process according to claim 1, wherein, The content of light component impurities in the regenerated solvent at the top of the deweighting tower is no higher than 0.1 wt%, the content of heavy component impurities is no higher than 0.1 wt%, and the total loss of acetonitrile is less than 3 wt% of the extracted acetonitrile.

3. The solvent regeneration method for the acetonitrile-based 1,3-butadiene extraction process according to claim 1, wherein, The light-light removal tower has 50-80 trays, a reboiler temperature of 80-130 ℃, a top pressure of 0.01-0.4 MPaG, and a reflux ratio of 20-40.

4. The solvent regeneration method for the acetonitrile-based 1,3-butadiene extraction process according to claim 1, wherein, The number of trays in the deweight removal tower is 10~17, the bottom temperature is 95~135 ℃, and the top pressure is 0.01~0.1 MPaG.

5. The solvent regeneration method for the acetonitrile-based 1,3-butadiene extraction process according to claim 1, wherein, The solvent regeneration method can be either continuous regeneration or intermittent regeneration.

6. The solvent regeneration method for the acetonitrile-based 1,3-butadiene extraction process according to claim 1, wherein, The regeneration method employs a solvent regeneration device for the acetonitrile-based 1,3-butadiene extraction process, which includes a light-weight removal tower and a heavy-weight removal tower. The light component removal tower is equipped with a circulating acetonitrile solvent feed line in the middle, a light component removal tower top discharge line at the top of the tower, and a light component removal tower bottom discharge line at the bottom of the tower. The light component removal tower bottom discharge line is connected to the heavy component removal tower. The heavy component removal tower is equipped with a heavy component removal tower top discharge line and a heavy component removal tower bottom discharge line. The heavy component removal tower top discharge line is connected to the extraction system.

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