A kind of hindered amine high-efficiency composite desulfurization solvent and preparation method thereof

Abstract

The present application discloses a sterically hindered amine efficient composite desulfurization solvent and a preparation method thereof, which relates to the technical field of desulfurization agents. The solvent comprises the following raw materials in parts by weight: 25-45 parts of N-methyldiethanolamine, 27.5-49.5 parts of sterically hindered amine, 10-20 parts of stabilizer, 1-2 parts of corrosion inhibitor, 1-3 parts of defoamer, 0.03-0.07 parts of desulfurization accelerator, and 0.1-0.5 parts of antioxidant; the sterically hindered amine raw materials include: intermediate 4-carboxylic acid chloride benzo-15-crown ether- 5, 1,4-diamine, anhydrous ethanol, pyridine; the raw materials of the 4-carboxylic acid chloride benzo-15-crown ether-5 include: 4-carboxybenzo-15-crown ether-5, thionyl chloride, pyridine; the preparation method is as follows: N-methyldiethanolamine, sterically hindered amine and stabilizer are put into a mixing tank according to weight parts for mixing and stirring, and then corrosion inhibitor, defoamer, desulfurization accelerator, antioxidant are added, and the circulating pump is used for 40-60min of circulation reflux to obtain the composite desulfurization solvent. The composite desulfurization solvent provided in this application can effectively improve the desulfurization performance.

Description

Technical Field

[0001] The present application relates to the field of desulfurization agent technology, and in particular to a hindered amine high-efficiency composite desulfurization solvent and a preparation method thereof. Background Art

[0002] The desulfurization process of refinery dry gas, circulating hydrogen and liquefied gas generally adopts mature amine solution absorption process. The typical amine system process of refinery enterprises is: the raw gas rich in acidic gas first enters the absorption tower and contacts with the fresh MDEA solution in countercurrent, the purified gas produced at the top of the tower enters the next process, the rich absorption liquid at the bottom of the tower enters the amine regeneration tower, the acidic gas produced at the top of the tower enters the sulfur recovery process, and the regenerated amine liquid returns to the absorption tower for recycling. Among them, the amine desulfurizer is the main factor that determines the desulfurization effect.

[0003] Hindered amine desulfurizer is a composite high-efficiency desulfurizer based on the formula of N-methyldiethanolamine with the addition of certain sterically hindered amines and defoamers, corrosion inhibitors, stabilizers and additives that promote the absorption of organic sulfur. The sterically hindered amine has a special steric hindrance effect, which makes the activity of the amine group higher than that of conventional alcohol amines, and the dissociation constant is also larger. The rate of absorbing hydrogen sulfide is faster than MDEA. Under the steric hindrance effect, the reaction with carbon dioxide is inhibited, and the selective absorption effect of hydrogen sulfide is enhanced. Under the same conditions, the desulfurization rate and selectivity are better than MDEA.

[0004] However, the current composite desulfurizers generally have operational problems such as low solution concentration, degradation in solution, high content of corrosion products, and lax control of regeneration conditions. In the face of the increasing requirements for energy saving and consumption reduction, it is crucial to improve the selectivity of amine liquid, especially the selectivity of amine liquid under acidic gas conditions with a high carbon-sulfur ratio, to absorb more H2S and less CO2. Summary of the invention

[0005] In order to improve the selectivity of composite desulfurization agent absorption, the present application provides a hindered amine high-efficiency composite desulfurization solvent and a preparation method thereof.

[0006] The present application provides a hindered amine high-efficiency composite desulfurization solvent, which adopts the following technical solution:

[0007] A hindered amine high-efficiency composite desulfurization solvent and a preparation method thereof, comprising the following raw materials in parts by weight: 25-45 parts of N-methyldiethanolamine, 27.5-49.5 parts of sterically hindered amine, 10-20 parts of stabilizer, 1-2 parts of corrosion inhibitor, 1-3 parts of defoamer, 0.03-0.07 parts of desulfurization accelerator, and 0.1-0.5 parts of antioxidant;

[0008] The structural formula of the sterically hindered amine is as follows:

[0009]

[0010] Preferably, the sterically hindered amine is composed of the following raw materials: intermediate 4-carboxylic acid chloride benzo-15-crown ether-5, 1,4-butanediamine, anhydrous ethanol, pyridine;

[0011] The structural formula of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 is as follows:

[0012]

[0013] Preferably, the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 is composed of the following raw materials: 4-carboxybenzo-15-crown ether-5, thionyl chloride, and pyridine; the molar ratio of the 4-carboxybenzo-15-crown ether-5 to thionyl chloride is 1:1-1.3.

[0014] Preferably, the molar ratio of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 to 1,4-butanediamine is 2-2.5:1.

[0015] Preferably, the corrosion inhibitor is one of molybdate, tungstate, polyphosphate and zinc salt.

[0016] Preferably, the stabilizer is one of diethylethanolamine, N-aminoethylpiperazine, 4-methylmorpholine, and N,N-bis(2-hydroxyethyl)piperazine.

[0017] Preferably, the mass ratio of the N-methyldiethanolamine to the sterically hindered amine is 1.1-1.2.

[0018] The present application provides a method for preparing a hindered amine high-efficiency composite desulfurization solvent, which adopts the following technical scheme:

[0019] A method for preparing a hindered amine high-efficiency composite desulfurization solvent comprises the following steps:

[0020] N-methyldiethanolamine, sterically hindered amine and stabilizer are added into a mixing tank according to weight proportions and mixed and stirred evenly, and then corrosion inhibitor, defoamer, desulfurization accelerator and antioxidant are added, and the mixture is circulated and refluxed for 40-60 minutes by a circulating pump to obtain the composite desulfurization solvent.

[0021] Preferably, the method for preparing the sterically hindered amine comprises the following steps:

[0022] The intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 and diaminobutane are added into a reaction kettle respectively, and an appropriate amount of anhydrous ethanol is added as a solvent; after reacting at a reaction temperature of 100-120°C for 2-3 hours, the heating is stopped, and the reaction liquid is cooled naturally, and the reaction liquid is taken out; the reaction liquid is poured into a three-necked flask, a certain amount of pyridine is added, and reflux reaction is carried out at a certain temperature for 0.5-1.5 hours; after the reaction is completed, the reaction is filtered, and the filtrate is distilled to remove excess solvent and unreacted diaminobutane, 4-carboxylic acid chloride benzo-15-crown ether-5, etc., to obtain a sterically hindered amine product.

[0023] Preferably, the preparation method of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 comprises the following steps:

[0024] The temperature of 4-carboxybenzo-15-crown-5 is lowered to about 0°C by using an ice-water bath, and thionyl chloride is slowly added dropwise to control the temperature of the reaction solution below 20°C. Under this condition, the reaction raw materials are added dropwise; after the addition is completed, it is stirred at room temperature for 2-4 hours, left overnight, and an appropriate amount of pyridine is slowly added. After reflux reaction for 3-5 hours, the reaction is terminated, and the excess reactant is distilled off. After cooling, it is poured into ice water and allowed to stand for stratification, and then vacuum distillation is performed to collect the intermediate 4-carboxylic acid chloride benzo-15-crown-5.

[0025] By adopting the above technical scheme, 4-carboxybenzo-15-crown-5 is reacted with thionyl chloride to obtain an intermediate 4-carboxylic acid chloride benzo-15-crown-5, and the intermediate 4-carboxylic acid chloride benzo-15-crown-5 is reacted with 1,4-butanediamine to obtain a sterically hindered amine. The reaction process is as follows:

[0026] In summary, the present application includes at least one of the following beneficial technical effects:

[0027] 1. The composite desulfurization solvent prepared by compounding the sterically hindered amine and MDEA provided in the present application has a high desulfurization rate and desulfurization selectivity;

[0028] 2. The composite desulfurization solvent provided in this application effectively improves the load processing capacity of the device without expanding the capacity of the device, with a small amount of amine liquid circulation, low energy consumption, and obvious energy-saving effect. DETAILED DESCRIPTION

[0029] The present application is further described in detail below with reference to the embodiments.

[0030] Preparation Example

[0031] The 4-carboxybenzo-15-crown ether-5 used in this preparation example was purchased from Shanghai Mairui Biochemical Technology Co., Ltd., and the structural formula is:

[0032]

[0033] Preparation Example 1

[0034] S1. 100g of 4-carboxybenzo-15-crown-5 was cooled to about 0°C by ice-water bath, 38g of thionyl chloride was slowly added dropwise, the temperature of the reaction solution was controlled below 20°C, and the reaction raw materials were added dropwise under this condition; after the addition was completed, it was stirred at room temperature and a stirring speed of 500rpm for 2h, left overnight, 25.5g of pyridine was slowly added, and the reaction was terminated after reflux reaction for 3h, the excess reactant was distilled out, and after cooling, it was poured into ice water and allowed to stand for stratification, followed by vacuum distillation to collect the intermediate 4-carboxylic acid chloride benzo-15-crown-5;

[0035] S2. Add 264.7g of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 and 35.3g of diaminobutane into the reactor respectively, and add 380mL of anhydrous ethanol as a solvent; after reacting for 2h at a reaction temperature of 100°C and a stirring speed of 120rpm, stop heating, wait for the reaction liquid to cool naturally, and take out the reaction liquid; pour the reaction liquid into a three-necked flask, add 63.3g of pyridine, and reflux at a certain temperature for 0.5h; filter after the reaction, and distill the filtrate to remove excess solvent and unreacted diaminobutane, 4-carboxylic acid chloride benzo-15-crown ether-5, etc., to obtain a sterically hindered amine product.

[0036] Preparation Example 2

[0037] S1. 100g of 4-carboxybenzo-15-crown-5 was cooled to about 0°C by ice-water bath, and 45.7g of thionyl chloride was slowly added dropwise, and the temperature of the reaction solution was controlled to be below 20°C. Under this condition, the reaction raw materials were added dropwise; after the addition was completed, the mixture was stirred at room temperature and a stirring speed of 550rpm for 3h, and then allowed to stand overnight. 25.5g of pyridine was slowly added, and the reaction was terminated after reflux reaction for 3.5h. The excess reactant was distilled off, and after cooling, it was poured into ice water and allowed to stand for stratification, and then vacuum distillation was performed to collect the intermediate 4-carboxylic acid chloride benzo-15-crown-5;

[0038] S2. Add 264.7g of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 and 35.3g of diaminobutane into the reactor respectively, and add 380mL of anhydrous ethanol as a solvent; after reacting for 2h at a reaction temperature of 100°C and a stirring speed of 120rpm, stop heating, wait for the reaction liquid to cool naturally, and take out the reaction liquid; pour the reaction liquid into a three-necked flask, add 63.3g of pyridine, and reflux at a certain temperature for 0.5h; filter after the reaction, and distill the filtrate to remove excess solvent and unreacted diaminobutane, 4-carboxylic acid chloride benzo-15-crown ether-5, etc., to obtain a sterically hindered amine product.

[0039] Preparation Example 3

[0040] S1. 100g of 4-carboxybenzo-15-crown-5 was cooled to about 0°C by ice-water bath, and 49.5g of thionyl chloride was slowly added dropwise, and the temperature of the reaction solution was controlled to be below 20°C. Under this condition, the reaction raw materials were added dropwise; after the addition was completed, the mixture was stirred at room temperature and a stirring speed of 600rpm for 4h, and allowed to stand overnight. 25.5g of pyridine was slowly added, and the reaction was terminated after reflux reaction for 5h. The excess reactant was distilled off, and the mixture was poured into ice water after cooling and allowed to stand for stratification, and then vacuum distillation was performed to collect the intermediate 4-carboxylic acid chloride benzo-15-crown-5;

[0041] S2. Add 264.7g of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 and 35.3g of diaminobutane into the reactor respectively, and add 380mL of anhydrous ethanol as a solvent; after reacting for 2h at a reaction temperature of 100°C and a stirring speed of 120rpm, stop heating, wait for the reaction liquid to cool naturally, and take out the reaction liquid; pour the reaction liquid into a three-necked flask, add 63.3g of pyridine, and reflux at a certain temperature for 0.5h; filter after the reaction, and distill the filtrate to remove excess solvent and unreacted diaminobutane, 4-carboxylic acid chloride benzo-15-crown ether-5, etc., to obtain a sterically hindered amine product.

[0042] Preparation Example 4

[0043] S1. 100g of 4-carboxybenzo-15-crown-5 was cooled to about 0°C by ice-water bath, 38g of thionyl chloride was slowly added dropwise, the temperature of the reaction solution was controlled below 20°C, and the reaction raw materials were added dropwise under this condition; after the addition was completed, it was stirred at room temperature and a stirring speed of 500rpm for 2h, left overnight, 25.5g of pyridine was slowly added, and the reaction was terminated after reflux reaction for 3h, the excess reactant was distilled out, and after cooling, it was poured into ice water and allowed to stand for stratification, followed by vacuum distillation to collect the intermediate 4-carboxylic acid chloride benzo-15-crown-5;

[0044] S2. Add 304.4g of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 and 35.3g of diaminobutane into the reactor respectively, and add 410mL of anhydrous ethanol as a solvent; after reacting for 2.5h at a reaction temperature of 110°C and a stirring speed of 140rpm, stop heating, wait for the reaction liquid to cool naturally, and take out the reaction liquid; pour the reaction liquid into a three-necked flask, add 63.3g of pyridine, and reflux at a certain temperature for 1h; filter after the reaction, and distill the filtrate to remove excess solvent and unreacted diaminobutane, 4-carboxylic acid chloride benzo-15-crown ether-5, etc., to obtain a sterically hindered amine product.

[0045] Preparation Example 5

[0046] S1. 100g of 4-carboxybenzo-15-crown-5 was cooled to about 0°C by ice-water bath, 38g of thionyl chloride was slowly added dropwise, the temperature of the reaction solution was controlled below 20°C, and the reaction raw materials were added dropwise under this condition; after the addition was completed, it was stirred at room temperature and a stirring speed of 500rpm for 2h, left overnight, 25.5g of pyridine was slowly added, and the reaction was terminated after reflux reaction for 3h, the excess reactant was distilled out, and after cooling, it was poured into ice water and allowed to stand for stratification, followed by vacuum distillation to collect the intermediate 4-carboxylic acid chloride benzo-15-crown-5;

[0047] S2. 330.8g of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 and 35.3g of diaminobutane were added into the reactor respectively, and 450mL of anhydrous ethanol was added as a solvent; after reacting for 3h at a reaction temperature of 120°C and a stirring speed of 160rpm, the heating was stopped, and the reaction liquid was allowed to cool naturally, and the reaction liquid was taken out; the reaction liquid was poured into a three-necked flask, 63.3g of pyridine was added, and the reaction was refluxed at a certain temperature for 1.5h; after the reaction was completed, the reaction was filtered, and the filtrate was distilled to remove excess solvent and unreacted diaminobutane, 4-carboxylic acid chloride benzo-15-crown ether-5, etc., to obtain a sterically hindered amine product. Example Example 1

[0048] In this example, 25 g of N-methyldiethanolamine, 27.5 g of the sterically hindered amine prepared in Preparation Example 1, 10 g of diethylethanolamine as a stabilizer, 1 g of molybdate as a corrosion inhibitor, 1 g of tertiary amine silicone oil as a defoamer, 0.03 g of 2,4,6-tris(dimethylaminomethyl)phenol as a desulfurization accelerator, and 0.1 g of N-methyldiethanolamine as an antioxidant were weighed;

[0049] N-methyldiethanolamine, sterically hindered amine and stabilizer are put into a mixing tank for uniform mixing and stirring, and then corrosion inhibitor, defoamer, desulfurization accelerator and antioxidant are added, and the mixture is circulated and refluxed for 40 minutes by a circulating pump to obtain the composite desulfurization solvent. Example 2

[0050] In this example, 35 g of N-methyldiethanolamine, 38.5 g of the sterically hindered amine prepared in Preparation Example 1, 15 g of diethylethanolamine as a stabilizer, 1.5 g of molybdate as a corrosion inhibitor, 2 g of tertiary amine silicone oil as a defoamer, 0.05 g of 2,4,6-tris(dimethylaminomethyl)phenol as a desulfurization accelerator, and 0.3 g of N-methyldiethanolamine as an antioxidant were weighed;

[0051] N-methyldiethanolamine, sterically hindered amine and stabilizer are put into a mixing tank and mixed and stirred evenly, and then corrosion inhibitor, defoamer, desulfurization accelerator and antioxidant are added, and the mixture is circulated and refluxed for 50 minutes by a circulating pump to obtain the composite desulfurization solvent. Example 3

[0052] In this example, 45 g of N-methyldiethanolamine, 49.5 g of the sterically hindered amine prepared in Preparation Example 1, 20 g of diethylethanolamine as a stabilizer, 2 g of molybdate as a corrosion inhibitor, 3 g of tertiary amino silicone oil as a defoamer, 0.07 g of 2,4,6-tris(dimethylaminomethyl)phenol as a desulfurization accelerator, and 0.5 g of N-methyldiethanolamine as an antioxidant were weighed;

[0053] N-methyldiethanolamine, sterically hindered amine and stabilizer are put into a mixing tank for uniform mixing and stirring, and then corrosion inhibitor, defoamer, desulfurization accelerator and antioxidant are added, and the mixture is circulated and refluxed for 60 minutes by a circulating pump to obtain the composite desulfurization solvent. Example 4

[0054] The difference between Example 4 and Example 1 is that the mass of N-methyldiethanolamine used in Example 4 is 25 g; the mass of the sterically hindered amine prepared in Preparation Example 1 is 28.75 g. Example 5

[0055] The difference between Example 5 and Example 1 is that the mass of N-methyldiethanolamine used in Example 5 is 25 g; the mass of the sterically hindered amine prepared in Preparation Example 1 is 30 g. Example 6

[0056] The difference between Example 6 and Example 1 is that the mass of N-methyldiethanolamine used in Example 6 is 25 g; the mass of the sterically hindered amine prepared in Preparation Example 1 is 25 g. Example 7

[0057] The difference between Example 7 and Example 1 is that the mass of N-methyldiethanolamine used in Example 7 is 25 g; the mass of the sterically hindered amine prepared in Preparation Example 1 is 32.5 g. Example 8

[0058] The difference between Example 8 and Example 1 is that the sterically hindered amine used in Example 8 comes from Preparation Example 2, with a mass of 27.5 g. Example 9

[0059] The difference between Example 9 and Example 1 is that the sterically hindered amine used in Example 9 comes from Preparation Example 3, with a mass of 27.5 g. Example 10

[0060] The difference between Example 10 and Example 1 is that the sterically hindered amine used in Example 10 comes from Preparation Example 4, with a mass of 27.5 g. Embodiment 11

[0061] The difference between Example 11 and Example 1 is that the sterically hindered amine used in Example 11 comes from Preparation Example 5, with a mass of 27.5 g. Comparative Example

[0062] Comparative Example 1

[0063] The difference between Comparative Example 1 and Example 1 is that no sterically hindered amine is added in Comparative Example 1.

[0064] 1. The composite desulfurization solvents prepared in Examples 1-11 and Comparative Example 1 were put into a low-pressure 8KPAG desulfurization system for a cyclic use period of more than 5,000 hours. Samples were taken every 10 hours to measure the removal effect of the sulfiding agent. The results are shown in Table 1.

[0065] The specific test results are as follows:

[0066] Table 1 Performance test results

[0067] Detection object Desulfurization selectivity S Desulfurization rate / % Example 1 12 78 Example 2 14 81 Example 3 13 80 Example 4 15 85 Example 5 13 82 Example 6 8 70 Example 7 9 73 Example 8 12 79 Example 9 12 78 Example 10 13 79 Embodiment 11 13 79 Comparative Example 1 5 45

[0068] It can be seen from the test results in Table 1 that the composite desulfurization solvent provided in the present application has high desulfurization selectivity and desulfurization rate. It can be seen from the test results of Examples 1, 4, 5, 6 and 7 that the preferred mass ratio of N-methyldiethanolamine to sterically hindered amine in the present application is 1.1-1.2.

[0069] From the test results of the sterically hindered amine not added in Comparative Example 1, it can be seen that the sterically hindered amine provided in the present application, after being compounded with N-methyldiethanolamine, has a desulfurization rate increased by 33% and a selectivity S increased by 7 under the same conditions.

[0070] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A hindered amine high-efficiency composite desulfurization solvent, characterized in that: The invention comprises the following raw materials in parts by weight: 25-45 parts of N-methyldiethanolamine, 27.5-49.5 parts of sterically hindered amine, 10-20 parts of stabilizer, 1-2 parts of corrosion inhibitor, 1-3 parts of defoamer, 0.03-0.07 parts of desulfurization accelerator, and 0.1-0.5 parts of antioxidant; The structural formula of the sterically hindered amine is as follows: ； The sterically hindered amine is prepared from the following raw materials: intermediate 4-carboxylic acid chloride benzo-15-crown ether-5, 1,4-butanediamine, anhydrous ethanol, and pyridine; The structural formula of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 is as follows: ； The intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 is prepared from the following raw materials: 4-carboxybenzo-15-crown ether-5, thionyl chloride, and pyridine; the molar ratio of the 4-carboxybenzo-15-crown ether-5 to the thionyl chloride is 1:1-1.

3.

2. The hindered amine high-efficiency composite desulfurization solvent according to claim 1, characterized in that: The molar ratio of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 to 1,4-butanediamine is 2-2.5:

1.

3. The hindered amine high-efficiency composite desulfurization solvent according to claim 1, characterized in that: The corrosion inhibitor is one of molybdate, tungstate, polyphosphate and zinc salt.

4. The hindered amine high-efficiency composite desulfurization solvent according to claim 1, characterized in that: The stabilizer is one of diethylethanolamine, N-aminoethylpiperazine, 4-methylmorpholine and N,N-di(2-hydroxyethyl)piperazine.

5. The method for preparing a hindered amine high-efficiency composite desulfurization solvent according to any one of claims 1 to 4, characterized in that: The following steps are involved: N-methyldiethanolamine, sterically hindered amine and stabilizer are added into a mixing tank according to weight proportions and mixed and stirred evenly, and then corrosion inhibitor, defoamer, desulfurization accelerator and antioxidant are added, and the mixture is circulated and refluxed for 40-60 minutes by a circulating pump to obtain the composite desulfurization solvent.

6. The method for preparing a hindered amine high-efficiency composite desulfurization solvent according to claim 5, characterized in that: The method for preparing the sterically hindered amine comprises the following steps: The intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 and diaminobutane are added into a reaction kettle respectively, and an appropriate amount of anhydrous ethanol is added as a solvent; after reacting at a reaction temperature of 100-120°C for 2-3 hours, the heating is stopped, and the reaction liquid is cooled naturally, and the reaction liquid is taken out; the reaction liquid is poured into a three-necked flask, a certain amount of pyridine is added, and reflux reaction is carried out at a certain temperature for 0.5-1.5 hours; after the reaction is completed, the reaction is filtered, and the filtrate is distilled to remove excess solvent and unreacted diaminobutane, 4-carboxylic acid chloride benzo-15-crown ether-5, etc., to obtain a sterically hindered amine product.

7. The method for preparing a hindered amine high-efficiency composite desulfurization solvent according to claim 6, characterized in that: The preparation method of the intermediate 4-carboxylic acid chloride benzo-15-crown ether-5 comprises the following steps: The temperature of 4-carboxybenzo-15-crown-5 is lowered to about 0°C by using an ice-water bath, and thionyl chloride is slowly added dropwise to control the temperature of the reaction solution below 20°C. Under this condition, the reaction raw materials are added dropwise; after the addition is completed, it is stirred at room temperature for 2-4 hours, left overnight, and an appropriate amount of pyridine is slowly added. After reflux reaction for 3-5 hours, the reaction is terminated, and the excess reactant is distilled off. After cooling, it is poured into ice water and allowed to stand for stratification, and then vacuum distillation is performed to collect the intermediate 4-carboxylic acid chloride benzo-15-crown-5.

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