JPS6115856B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing monochloroacetone by chlorination of acetone, and particularly to a method for industrially advantageously producing high-purity monochloroacetone with a low content of polychlorinated compounds. Monochloroacetone is a compound useful as a synthetic raw material for dyes, pigments, pesticides, insecticides, etc. It has been known for a long time that this compound can be obtained by introducing chlorine gas into acetone, but it is difficult to control due to sudden reactions, progress of side reactions (polychlorination and condensation), especially 1. It has been difficult to safely and efficiently produce high-purity monochloroacetone due to drawbacks such as the tendency to generate by-products such as impurities that are difficult to separate and purify from the target product, such as dichloroacetone and mesityl oxide. A gas phase chlorination method was also attempted, but there were difficulties in controlling the reaction. The invention described in Japanese Patent Publication No. 50-37650 is a method for producing high-purity monochloroacetone by limiting the reaction conditions of liquid phase chlorination and in combination with specific separation operations to overcome the drawbacks of the prior art described above. provided. However, in order to do this, it was necessary to keep the reaction rate of acetone extremely low, and to use a complicated method of neutralizing the reaction mixture, separating the liquid-liquid phase, and then distilling the organic layer. A low reaction rate due to a low chlorine/acetone molar ratio and limited residence time was effective in suppressing by-products of higher chlorides, but it led to a decrease in production efficiency. Furthermore, since hydrogen chloride, which is a by-product from the chlorination of acetone, is present in the system, if the reaction solution is distilled and separated without being neutralized, an acid-catalyzed condensation reaction will occur. In order to prevent this, the invention requires immediate neutralization of hydrogen chloride dissolved in the reaction product. This made it possible to avoid sudden reactions and condensation of acetone, but the separation and purification process became quite complicated, and the by-product hydrogen chloride could not be recovered as a valuable product. When propylene is oxidized to produce acetone in the presence of palladium chloride and copper chloride catalysts, a chloroacetone mixture is produced as a by-product, and this also includes monochloroacetone. However, since 1,1-dichloroacetone, which has very close boiling points, coexists, it is difficult to separate it by normal methods, as is the case with chlorination of acetone. Several techniques have been proposed for the separation of monochloroacetone from such mixtures (Japanese Patent Application Laid-Open No. 1989-1999).
124012, 50-37714, and 52-125105). Distillation in the presence of water increases the boiling point difference of 0.3°C between monochloroacetone and 1,1-dichloroacetone to about 2°C, so it is possible to separate them by precise distillation, but it requires a large reflux ratio and a high distillation tower. do.
In this way, 1,1-dichloroacetone is extremely difficult to separate from monochloroacetone, so when monochloroacetone is produced by chlorinating acetone, it is harmful to product quality and unnecessary polychlorinated by-products are produced. Life must be suppressed as much as possible. The ketone (particularly preferred for 2-butanone) is introduced into the reaction chamber together with chlorine in the gas phase, and as soon as the gas phase chlorination reaction takes place, the reaction product is cooled and liquefied, and the cooled product is sent to the rectification column. A method is known in which by-product hydrogen chloride is distilled off to obtain monochloroketone in high yield (US Pat. No. 2,120,392). This method is similar to the invention described in Japanese Patent Publication No. 1983-37650 mentioned above in that the reaction is carried out in a short time and separation is carried out immediately thereafter, but the reaction is carried out in the gas phase and is cooled immediately after the reaction. The difference is that monochloroketone and by-product hydrogen chloride are separated from the liquid by a rectification column rather than by neutralization and liquid separation. In this method, the reaction that takes place in the gas phase must be controlled at an appropriate temperature and residence time, but there is no description of set values or specific methods of control, and it is not possible to carry out monochlorination of acetone. The characteristics, response rate, etc. are unknown. In principle, the reaction is carried out by introducing equimolar amounts of ketone and chlorine in the gas phase, but one may be in excess.The unreacted portion is evaporated in the rectification column, and the ketone cooled and liquefied in the top condenser is transferred to the storage tank. accumulates in This technology teaches that by-product hydrogen chloride is recovered by distillation, but what is fed into the rectification column for hydrogen chloride recovery is the product of a gas phase reaction, and by this method monochloroketone production method As with all technologies, there are both reactors and separation and purification equipment. As a result of studying the method for producing high-purity monochloroacetone, for which there was no fully satisfactory method due to various difficulties, the present inventor discovered a method for producing high-purity monochloroacetone that involved absorption of chlorine into liquid acetone, chlorination reaction, and production. By simultaneously separating the monochloroacetone, by-product hydrogen chloride, and unreacted acetone in a distillation column, we have discovered a method for efficiently obtaining high-purity monochloroacetone using extremely simple equipment and operations. That is, the present invention is a method for producing monochloroacetone by reacting acetone with chlorine, in which chlorine is continuously introduced into a distillation column in which acetone is refluxed from the upper part of the column, and chlorine is removed from an excess amount of liquid acetone stream. The chlorine is absorbed and the chlorination reaction is carried out by contacting with chlorine, hydrogen chloride as a by-product is continuously removed from the top of the column, and the monochloroacetone produced is distilled and separated from unreacted acetone, while chlorine and hydrogen chloride are removed. This is a method for producing monochloroacetone, which is characterized in that monochloroacetone is introduced into the lower part of a distillation column where substantially no monochloroacetone exists. In this invention, unlike all of the production techniques related to monochloroacetone production described above, the reaction and separation and purification are performed simultaneously in a single distillation apparatus in parallel. The distillation equipment consists of well-known components such as the main body of the distillation column, such as a packed column or tray column, as well as a heater such as a reboiler, a tower top condenser, piping for feeding and refluxing raw materials, and removing target products and by-products. has been done. An embodiment in which the method of the present invention using a distillation apparatus is carried out in a continuous manner will be described. A distillation column capable of distilling and separating acetone and monochloroacetone is used. Acetone is normally charged continuously from near the top of the tower and heated in a reboiler. Acetone distilled from the top of the column is liquefied in a condenser and completely refluxed to the top of the column. Usually, chlorine is continuously introduced into the middle stage of a distillation column, and as it rises through the column, it comes into contact with and is absorbed by the reflux liquid from the top of the column and liquid acetone flowing down as a feed liquid, causing a chlorination reaction. Even if the amount of acetone charged is equivalent to the amount of chlorine, there is acetone that refluxes at the top of the column, so the amount of acetone that comes into contact with the chlorine is in large excess. This is an advantageous condition for chlorine absorption and monochlorination reaction. Hydrogen chloride, a by-product of the chlorination reaction, is extremely volatile, so it is immediately expelled from the liquid and rises in the column in the gas phase. The heat of reaction is removed as the heat of vaporization of the excess acetone, so it is advantageous not only in gas phase reactions with low specific heat, but also in the ease of heat removal for temperature control compared to normal liquid phase reactions. . Acetone vaporized by heating and reaction heat in the bottom reboiler is distilled out from the top of the tower along with hydrogen chloride.
In the condenser, only acetone is liquefied and refluxed, while hydrogen chloride is continuously removed in gaseous form. The monochloroacetone produced is much less volatile than acetone, so it can be easily separated by distillation within the column. In other words, the flow of liquid that flows down the tower while coming into contact with the gas phase is almost exclusively acetone at the top of the tower, and the concentration of monochloroacetone gradually increases as it goes down the reaction section, and then suddenly below the chlorine introduction section. . Chlorine consumed in the reaction between highly volatile hydrogen chloride and excess acetone suddenly decreases below the chlorine introduction section, so there is virtually no chlorine present at the bottom of the tower where monochloroacetone is concentrated. become. That is, the area where chlorine exists and the chlorination reaction occurs is limited to the upper part of the tower where acetone is present in excess water, and monochloroacetone is kept at a low concentration there, so that monochloroacetone is further chlorinated and becomes 1 - The chance of producing polychlorides such as 1- or 1,3-dichloroacetone as a by-product is reduced. Also, the absence of hydrogen chloride in the lower part of the column prevents loss of monochloroacetone due to acid-catalyzed condensation. The presence of hydrogen chloride generated by the reaction in the upper part of the column is unavoidable, but since the distilled state is maintained, hydrogen chloride is hardly dissolved in the liquid phase, and it is not possible to carry out the acid-catalyzed condensation of acetone and monochloroacetone. The chances of it happening are small. At the bottom of the tower, acetone is virtually gone, and the liquid mainly consisting of monochloroacetone is heated by the reboiler, so by removing monochloroacetone from the reboiler or the bottom of the tower, the amount of polychlorides and acid-catalyzed condensates can be reduced. A small amount of high purity monochloroacetone can be easily obtained. A distillation section sufficient to at least drive out dissolved chlorine and hydrogen chloride is required between the chlorine introduction point and the bottom of the column where the heating section is located, but this does not require a large number of distillation stages. That is, even if the rectification section below the chlorine introduction section is small, the object of the present invention of producing monochloroacetone with less polychloride can be achieved. However, it is more preferable to extract monochloroacetone in a state where there is substantially no acetone at the bottom of the column as in the embodiment described above. To this end, a rectification section sufficient to distill and separate unreacted acetone and monochloroacetone is provided below the chlorine introduction section. In this way, unreacted acetone in the liquid flowing down from the chlorine introduction section is also recovered in the gas phase and eventually refluxed from the top of the column, so that the amount of acetone charged can be reduced by that amount. If the distillation capacity is such that acetone can be substantially cut off at the bottom of the column, it is sufficient to charge the equivalent molar amount of acetone to chlorine, so the position of chlorine introduction is usually determined based on this. On the other hand, the required number of stages above the chlorine introduction position is determined with the aim of ensuring that acetone absorbs the introduced chlorine and does not release it into the off-gas. This invention can be practiced not only by a continuous method but also by a semi-batch method. In this case, acetone is first charged into an evaporator, heated, and then completely refluxed from the top of the distillation column. Chlorine is continuously introduced from the middle stage and below at such a rate that the acetone stream refluxing from the top of the column is in excess of chlorine, and the reaction is caused to occur. As in the continuous method, absorption of chlorine, chlorination reaction, and removal of by-product hydrogen chloride as non-condensable gas at the top of the column are carried out continuously. The produced monochloroacetone is separated by distillation from unreacted acetone, led to the lower part of the distillation column, and accumulated in the evaporator. Since almost no chlorine and hydrogen chloride are present slightly below the chlorine introduction section, there is little chance of polychlorination or acid-catalyzed condensation even if monochloroacetone is heated in the evaporator in a semi-batch operation for a longer time than in a continuous process. When the desired amount of monochloroacetone has accumulated in the evaporator, the introduction of chlorine is stopped to complete the reaction.
Even at the end of chlorine introduction, it is necessary to maintain a state in which an excess amount of acetone is refluxing in the upper part of the column. If batch distillation is subsequently performed, high purity monochloroacetone with less unreacted acetone fraction and dichloroacetone can be obtained. In this way, the present invention introduces chlorine directly into the distillation column, and causes an absorption reaction by bringing it into contact with a liquid acetone stream in excess of the molar amount produced by refluxing from the top of the column (refluxing and charging in the case of a continuous method). . Even though the distillation conditions were such that acetone vaporized, chlorine was still absorbed, making it possible to use a reactive distillation method. The invention can normally be carried out under normal pressure, ie overhead atmospheric pressure. If necessary, the pressure can be increased or decreased. When the pressure is reduced, the reaction distillation temperature is lowered, but the reaction can be carried out without a catalyst even if the temperature is lowered to, for example, about 30°C. If the pressure is too high, there is a risk that side reactions such as acid-catalyzed condensation will proceed more easily due to the influence of temperature rise and increase in hydrogen chloride solubility. Therefore, the reaction is carried out at a value that does not cause any problems, for example, 4 atm or less. In order to suppress the polychlorination reaction and produce monochloroacetone with high purity, it is advantageous to carry out chlorination in a state where the acetone/monochloroacetone ratio is large, but conventional technology does not allow for liquid-phase or gas-phase reactions. After a short reaction time, the reaction was immediately stopped by neutralization or cooling condensation, and a high selectivity was obtained at the cost of a low reaction rate. The present invention provides overhead reflux of acetone by distillation, removal of hydrogen chloride, and derivation of monochloroacetone from the reaction zone to the lower part of the column.
By carrying out absorption and reaction simultaneously, the overall acetone reaction rate was extremely high, but the acetone/monochloroacetone ratio was maintained at a high level in the areas where the chlorination reaction occurred, and monochloroacetone was successfully produced selectively. In addition to reaction-related effects such as prevention of polychlorination and acid-catalyzed condensation, the present invention has many advantages. That is, in the present invention, since the reaction and separation are carried out in the same distillation column, the present invention is simpler in terms of equipment and operation than the conventional method for producing monochloroacetone. By-product hydrogen chloride can be recovered as a useful product without any problems in heat removal or other reaction control. All of these effects are achieved by introducing chlorine directly into the distillation column, refluxing acetone at the top of the column, separating monochloroacetone and unreacted acetone by distillation within the column, and removing hydrogen chloride into the gas phase. This is unique to the present invention. Example 1 A column consisting of a reactive distillation zone made of glass tubes with a diameter of 35 mm and a height of 500 mm randomly filled with Raschig rings of 5 mmφ x 10 mm L, and a distillation zone below the reactive distillation zone with a column diameter of 35 mm, a plate interval of 50 mm, and an actual number of plates of 20. Using a vacuum cleaner, chlorine was introduced from the bottom of the reaction distillation zone at a rate of 1.4/hr while acetone was completely refluxed at normal pressure, and acetone was charged from the top of the column at a rate of 3.7 g/hr. After 10 hours of operation, monochloroacetone is extracted from the gas phase at the bottom of the distillation tower.
A product containing 96.2% 1,1-dichloroacetone, 2.1% acetone, and 0.5% acetone could be extracted. Example 2 300 g of acetone was charged into a device consisting of a reactive distillation zone made up of a glass tube with a diameter of 35 mm and a height of 500 mm randomly filled with Raschig rings of 5 mmφ x 10 mm L, and a glass three-necked flask evaporator with an internal volume of 1, and heated. While refluxing the acetone,
Chlorine was introduced from the bottom of the reactive distillation zone at a rate of 1.4/hr. Samples were taken from the evaporator over time and analyzed using gas chromatography. The acetone conversion rate and monochloroacetone selectivity (ratio of monochloroacetone/monochloroacetone + dichloroacetone) are shown in Table 1. According to the method of the present invention, even if the overall acetone conversion rate is high, monochloroacetone It was found that the selection rate did not deteriorate.

[Table] Comparative example 500g of acetone was added to a reactor equipped with a four-necked separable flask equipped with a stirrer, a thermometer, a chlorine inlet tube, and a condenser, and chlorine was added under total reflux.
After blowing at a rate of 28.5/hr for 5.5 hours, the reaction solution was analyzed by gas chromatography, and the monochloroacetone selectivity was 87% at an acetone conversion rate of 60%.

Claims (1)

[Claims] 1 In the method of producing monochloroacetone by reacting acetone with chlorine, chlorine is continuously introduced into the middle part of the distillation column where acetone is completely refluxed from the top of the column, and the chlorine is brought into contact with an excess amount of acetone stream. The chlorination reaction is carried out by continuously removing the by-product hydrogen chloride from the top of the column, and the monochloroacetone produced is distilled and separated from unreacted acetone. A method for producing monochloroacetono, which is characterized by introducing it to the lower part.