JP5235082B2 - Chlorination method and detection method of reaction end point - Google Patents

Description

  The present invention relates to a chlorination method for converting an organic carboxylic acid into an acid chloride, for example, and relates to a method for detecting the reaction end point.

  As a conventional method known as a method for producing an acid chloride by phosgenating an organic carboxylic acid with phosgene gas, for example, a calculated amount of phosgene gas is introduced into the charged carboxylic acid, and the exhaust gas is analyzed by gas chromatography or the like. And the method of detecting unreacted phosgene gas and detecting the end point of reaction is known (refer to patent documents 1 and patent documents 2).

In addition, in the production of bischloroformate by phosgenating an organic dihydroxy compound with phosgene gas, one that detects the end point of the reaction by measuring the pH of the reaction solution is known (see Patent Document 3 and Patent Document 4). . Alternatively, the product precipitation is detected to detect the reaction end point (see Patent Document 3), the method of measuring the reaction heat in the same phosgenation reaction and detecting the reaction end point (see Patent Document 5), etc. Has been reported.
JP 56-103131 A U.S. Pat. No. 4,298,301 JP-A-62-26251 JP-A-2-69444 U.S. Pat. No. 4,814,420

  Each of the above-mentioned methods has drawbacks such as many errors, troublesome detection of the phenomenon, and troublesome separation of the reaction mixture, and it is difficult to say that it is a simple method. It is unsuitable.

  Accordingly, an object of the present invention is to provide a production method and a method for detecting a reaction end point that can easily detect the end point of a reaction in phosgenation by a reliable method, do not introduce an excessive phosgene gas, and can easily process the process.

In order to solve the above-mentioned problems, a chlorination method according to the present invention is a chlorination method in which phosgene gas is introduced into a reaction vessel in which an exhaust phosgene condenser, an exhaust gas separator, and a hydrogen chloride gas absorption tower are connected to each other through an exhaust gas pipe. The phosgene gas is introduced into the reaction vessel, the by-product gas is sucked in and the pressure in the reaction vessel is maintained at a pressure lower than the atmospheric pressure, and the pressure in the reaction vessel is detected. The introduction of phosgene into the reaction vessel is stopped at the time when the pressure drops to 0.25.

  Further, the method for detecting the reaction end point of phosgenation according to the present invention is a method for detecting the reaction end point of the chlorination method in which phosgene gas is introduced into the reaction tank, wherein phosgene gas is introduced into the reaction tank and the by-product gas is sucked. The pressure in the reaction vessel is maintained at a pressure reduced from 0.2 kPa to 1.0 kPa from atmospheric pressure, the pressure in the reaction vessel is detected, and the chlorination method is performed when the atmospheric pressure in the reaction vessel rapidly decreases. The reaction end point of

  In the present invention, for example, when an organic carboxylic acid is used, the introduction of phosgene can be stopped at an addition amount of phosgene close to the theoretical amount with respect to the organic carboxylic acid, and the reaction can be managed by a rapid decrease in pressure. Process control is reliable and process automation is easy.

  The organic carboxylic acid in the present invention is an unsaturated fatty acid, a saturated fatty acid or an aromatic carboxylic acid, for example, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid, There are phthalic acid, terephthalic acid, acrylic acid, succinic acid and maleic acid. In the present invention, in accordance with a known method for reacting an organic carboxylic acid and phosgene gas, the organic carboxylic acid is charged into the reaction vessel in the presence of a catalyst without solvent or using a solvent, and phosgene gas is introduced to phosgene. Turn into.

  As the solvent, conventionally known solvents can be used, and examples thereof include hydrocarbons such as benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, ether, tetrahydrofuran, carboxylic acid chloride and the like. The use of a solvent has the advantage that the product is less likely to be colored, but there are disadvantages such as the need for solvent recovery equipment, the time required for phosgenation by diluting the reaction system, and a decrease in productivity. Therefore, it is efficient to introduce the raw organic carboxylic acid and catalyst into the reaction vessel and introduce phosgene gas while stirring in the absence of solvent. As the catalyst, known catalysts can be used, but lower fatty acid amides such as dimethylformamide or imidazole are economical and preferable, and it is sufficient to add 1.5% by weight or less based on the organic carboxylic acid.

  The reaction temperature is usually 20 ° C. to 120 ° C., and when the temperature is 120 ° C. or higher, a decrease in yield due to the side reaction is conspicuous, and when it is 20 ° C. or lower, the reaction rate becomes slow and impractical. C. to 50.degree. C. is desirable. The introduction rate of phosgene gas does not affect the reaction even if it fluctuates somewhat, but it is desirable to introduce the phosgene gas into the reaction vessel at a substantially constant rate in order to allow the reaction to proceed stably. It is desirable to introduce it slowly at a low temperature, for example, for 10 hours or more from the standpoint of preventing coloring and preventing side reactions.

  For example, at the beginning of the reaction, the amount of phosgene gas introduced per hour can be increased, and at the end of the reaction when 80% of the planned introduction amount has been introduced into the reaction vessel, the introduction of phosgene can be reduced to increase the production efficiency of the apparatus. . However, when changing the introduction rate of phosgene, it is necessary to carry out at a substantially constant rate within a range in which the degree of decompression in the reaction tank is not affected as much as possible, for example, so as not to cause a change of 1 kPa or more per minute. The pressure in the reaction tank is exhausted from an exhaust gas pipe communicating with the reaction tank and is 0.2 kPa or more from atmospheric pressure, preferably 0.2 kPa to 1.0 kPa, more preferably 0.2 kPa to 0.5 kPa. Retained. When the degree of decompression is 0.2 kPa or less from atmospheric pressure, phosgene gas tends to leak out of the reaction vessel. Further, when the pressure is 1.0 kPa or more, not only the power for maintaining the degree of decompression increases, but also the difference from the decrease in the atmospheric pressure at the end of the reaction decreases, so that more precise operation is required.

  It is desirable to keep the pressure in the reaction tank at a reduced pressure before introducing phosgene gas. In this case, the introduction of phosgene is started by maintaining the pressure at 2 kPa to 4 kPa from the atmospheric pressure for the subsequent pressure management in the reaction tank. Convenient. Phosgene reacts with the organic carboxylic acid to generate hydrogen chloride gas and carbon dioxide gas, but is exhausted from the exhaust gas pipe and maintained at a predetermined degree of reduced pressure. When the organic carboxylic acid in the reaction tank is exhausted, no gas is generated in the reaction system, so that the pressure in the reaction tank drops suddenly, for example, from 0.5 kPa to 1 kPa or more per minute. At this time, the introduction of phosgene gas is stopped immediately.

  Even if the valve of the phosgene gas introduction pipe is closed in order to stop the introduction of the phosgene gas, the phosgene gas remains in the valve, the phosgene introduction pipe to the reaction tank, etc., so these are introduced into the reaction tank. However, when dimethylformamide is used as a catalyst, dimethylformamide and phosgene react with each other to form a Beersmeier reagent, which is insoluble in organic carboxylic acid chloride, so that some of this phosgene gas is introduced excessively. However, there is no substantial problem, and the insoluble beer smear reagent can be recovered and reused. Although the degree of pressure drop at the end of phosgenation varies depending on the exhaust gas suction capability, it is usually a variation of about 0.5 kPa to 1.5 kPa and can be sufficiently detected.

  As the reaction vessel, a glass-lined reactor equipped with a commonly used stirrer and cooling jacket can be used, and phosgene gas is desirably introduced at a position below the liquid level of the organic carboxylic acid at the bottom of the reaction vessel. An exhaust gas pipe is installed in the upper part of the reaction tank, and is connected to an abatement equipment such as an exhaust phosgene condenser, an exhaust gas separator, and a hydrogen chloride gas absorption tower. The pressure sensor in the reaction tank can be installed anywhere in the system as long as effective sensitivity can be obtained for measuring the pressure in the reaction tank. It is desirable to provide it after the hydrogen gas absorption tower.

  After completion of the reaction, the organic carboxylic acid chloride can be separated as necessary in the same manner as the phosgenation of a conventionally known organic carboxylic acid. For example, when a solvent is used, the solvent can be removed by distillation or the like to obtain a crude organic carboxylic acid chloride.

EXAMPLES Next, an Example is given and this invention is demonstrated still in detail.
(Example 1) 6200 liters of butyric acid (d = 0.959, 6008 kg, 68 kmoles) in an 8.0 cubic meter reactor equipped with a glass lining having a pressure sensor in the reactor in the exhaust gas system , And 40 liters of dimethylformamide (d = 0.9445, 37.8 kg, 0.517 mol, 0.9 mol%) as catalyst. The internal temperature of the reaction vessel was kept at 40 ± 0.5 ° C., and the inside of the reaction vessel was kept at a reduced pressure of 0.5 kPa from atmospheric pressure. Thereafter, phosgene gas was introduced into the reaction vessel at 55 cubic meters / hour in about 26 hours. Meanwhile, the inside of the reaction vessel was kept 0.5 kPa lower than the atmospheric pressure. Since the pressure in the reaction vessel rapidly decreased from atmospheric pressure to 1.8 kPa per minute near the reaction end point expected from the expected introduction amount of phosgene gas, the valve of the phosgene introduction pipe was automatically closed. Residual phosgene gas such as a phosgene introduction tube was introduced into the reaction vessel. The total amount of phosgene gas introduced was 4900 liters (70.6 kmol: 1.038 mol ratio).

  The composition of the reaction solution after the reaction was as follows. Hydrogen chloride content: 0.13% by weight, phosgene content: not detected, dimethylformamide content: 0.21% by weight, propionic anhydride content: 0.11% by weight, hue: tan, purity: butyric acid 99.71% by weight of chloride, yield from butyric acid: 97.43%

  (Example 2) Using a 7.5 cubic meter reactor, 5030 liters of propionic acid (d = 0.993, 5988 kg, 80.0 kmole), 61 liters of dimethylformamide (1.16 mol%), The reaction was carried out according to Example 1 with an internal temperature of 35 ± 0.5 ° C. and a phosgene gas introduction rate of 66 cubic meters / hour, which required about 26 hours in the reaction vessel. Near the end point of the reaction expected from the expected amount of phosgene gas introduced, the pressure in the reaction vessel suddenly dropped from atmospheric pressure by 1.6 kPa per minute, and the valve of the phosgene introduction pipe was automatically closed. The total amount of phosgene gas introduced was 4912 liters (7033 Kg: 71.1 kmol).

  The composition of the reaction solution after the reaction was as follows. Hydrogen chloride content: 0.23% by weight, phosgene content: not detected, dimethylformamide content 10.65% by weight, propionic acid content: 0% by weight, propionic anhydride content: 0.78% by weight, Hue: yellowish brown, purity: 98.2% by weight of propionic acid chloride, 97.7% yield from propionic acid

Claims (7)

In a chlorination method in which phosgene gas is introduced into a reaction tank in which an exhaust phosgene condenser, an exhaust gas separator, and a hydrogen chloride gas absorption tower are connected to the upper part through an exhaust gas pipe, phosgene gas is introduced into the reaction tank and a by-product gas is sucked in. The pressure in the reaction tank is maintained at a pressure lower than the atmospheric pressure, and the pressure in the reaction tank is detected. When the atmospheric pressure in the reaction tank rapidly decreases, phosgene is introduced into the reaction tank. A chlorination method characterized by stopping.   The chlorination method according to claim 1, wherein phosgene gas is introduced into the reaction vessel at a substantially constant rate.   The chlorination method according to claim 1 or 2, wherein the introduction of phosgene is stopped when the rate of pressure decrease in the reaction tank becomes 0.5 kPa or more per minute.   The chlorination method according to any one of claims 1 to 3, wherein the pressure in the reaction vessel is reduced from atmospheric pressure to 0.2 kPa to 1.0 kPa.   The chlorination method according to any one of claims 1 to 4, wherein the chlorination method is a method of converting an organic carboxylic acid into an acid chloride.   In the method of detecting the reaction end point of the chlorination method in which phosgene gas is introduced into the reaction vessel, phosgene gas is introduced into the reaction vessel, the gas produced as a by-product is sucked, and the pressure in the reaction vessel is changed from 0.2 kPa to 1 at atmospheric pressure. A method of detecting the reaction end point of the chlorination method when the pressure in the reaction vessel is detected while maintaining the pressure reduced to 0.0 kPa, and the atmospheric pressure in the reaction vessel is rapidly reduced.   The method for detecting the reaction end point of the chlorination method according to claim 6, wherein phosgene gas is introduced into the reaction vessel at a substantially constant rate.