Method for producing carbon tetrachloride

Abstract

To efficiently increase a production ratio of carbon tetrachloride when methyl chloride is reacted with chlorine to produce higher chlorinated methanes consisting of methylene chloride, chloroform, and carbon tetrachloride.SOLUTION: In a method for producing higher chlorinated methanes, chlorination reaction is carried out in such a manner that at least a part of chloroform contained in highly chlorinated methanes is separated and circulated and supplied to the reaction system of the highly chlorinated methanes, while the methylene chloride contained in the higher chlorinated methanes is circulated and supplied to the reaction system in an amount ranging from 0 to 100 mass% relative to chloroform being circulated and supplied to the reaction system.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing carbon tetrachloride. Specifically, the present invention relates to a method for producing the above-mentioned carbon tetrachloride by reacting methyl chloride with chlorine to produce higher-order chlorinated methanes composed of methylene chloride, chloroform, and carbon tetrachloride.

Background Art

[0002] A method of producing higher-order chlorinated methanes composed of methylene chloride, chloroform, and carbon tetrachloride by reacting methyl chloride with chlorine for chlorination has been implemented. So far, among the above-mentioned chlorinated methanes, methylene chloride and chloroform have been particularly useful as raw materials for producing solvents, fluorocarbons, fluororesins, etc. Therefore, in the production of the above-mentioned higher-order chlorinated methanes, the operating conditions are such that the yields of these methylene chloride and chloroform are as high as possible. In other words, the production amount of carbon tetrachloride, which is the final chlorinated product, is often suppressed to a low level. For this purpose, for example, in Patent Document 1, in order to increase the yield of chloroform, a part of methylene chloride is separated from the higher-order chlorinated methanes obtained by the chlorination reaction, and the methylene chloride is supplied to and reacted with the chlorination reaction to enhance the chlorination of the methylene chloride to chloroform. A method has been proposed. In this method, the production ratio that increases is solely the above-mentioned chloroform, and the production ratio of carbon tetrachloride does not increase significantly.

[0003] However, in recent years, among the above-mentioned higher-order chlorinated methanes, the usefulness of carbon tetrachloride has been rapidly increasing. Specifically, carbon tetrachloride has been attracting increasing attention as a raw material for hydrofluorocarbon (HFC)-based blowing agents (e.g., HFC-245fa, HFC-236fa, HFC-365mfc, etc.), hydrochlorofluorolefin (HCFO)-based blowing agents (e.g., HCFO-1233zd, etc.), and hydrofluoroolefin (HFO)-based blowing agents (e.g., HFO-1336mzz, etc.). New blowing agents such as HCFO-1233zd and HFO-1336mzz can solve the two major problems of ozone layer depletion and global warming, which have been eagerly awaited in the production of rigid urethane foam, in the context of international discussions on global warming prevention measures.

[0004] As characteristics of these blowing agents, since they contain a double bond in the main chain of carbon, their lifespan in the atmosphere is short and their impact on global warming is very small. Also, since the thermal conductivity of the gas is as low as that of conventional chlorofluorocarbons, an improvement in the heat insulation performance of heat insulation materials using them can be expected. Furthermore, regarding refrigerants and aerosol propellants that have conventionally used chlorofluorocarbons, substances having a double bond in the main chain such as HFO-1234yf and HFO-1234ze have also been developed and put into practical use. The amount of carbon tetrachloride used as a raw material for these substances is also increasing, and the demand for it is growing. In addition, an increase in the use of carbon tetrachloride as a pharmaceutical intermediate and an agricultural chemical intermediate is also expected. Therefore, reflecting these trends, in the production of higher-order chlorinated methanes, there is an increasing demand to operate under conditions that further increase the production amount of the above-mentioned carbon tetrachloride.

[0005] In response to this demand, for example, in Patent Document 2, in the chlorination reaction of methyl chloride, while supplying methyl chloride and methylene chloride contained in the overhead stream discharged from the chlorination reactor to the chlorination reactor, partial chlorides other than the target carbon tetrachloride, namely, methyl chloride, methylene chloride, and chloroform, are also separated from the reaction product and directly supplied to the chlorination reactor to continue the operation, and an attempt has been made to increase the production amount of carbon tetrachloride (〔0033〕and 〔Figure 1〕).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] According to the method of the above Patent Document 2, chloroform, which is a chlorination precursor of carbon tetrachloride, is circulated and supplied to the chlorination reactor, and this is subjected to further chlorination. Therefore, in order to increase the production ratio of carbon tetrachloride, the reaction conditions are somewhat advantageous. However, a large amount of methylene chloride is also contained in the partially chlorinated product that is circulated and supplied, and when the amount of methylene chloride in the reaction system increases due to this, the production amount of chloroform, which is the next chlorinated product, will also increase significantly. For this reason, the production ratio of carbon tetrachloride does not increase sufficiently, and further improvement has been desired.

Means for Solving the Problems

[0008] In view of the above problems, the present inventors have been intensively studying to develop an efficient method for increasing the yield of carbon tetrachloride in the production of higher-order chlorinated methanes. As a result, in a mode where the circulation supply of methylene chloride contained in the higher-order chlorinated methanes to the reaction system is suppressed, at least a part of the chloroform contained in the higher-order chlorinated methanes is circulated and supplied, and it has been found that the above problems are solved, and the present invention has been completed.

[0009] That is, the present invention is a method for reacting methyl chloride and chlorine to produce higher-order chlorinated methanes composed of methylene chloride, chloroform, and carbon tetrachloride, at least a part of the chloroform contained in the higher-order chlorinated methanes is separated and circulated and supplied to the reaction system of the higher-order chlorinated methanes, and on the other hand, By allowing methylene chloride contained in the higher-order chlorinated methanes to be circulated and supplied only in an amount of 0 to 100% by mass with respect to chloroform circulated and supplied to the reaction system, the production ratio of carbon tetrachloride contained in the higher-order chlorinated methanes is increased. A method for producing carbon tetrachloride, characterized by the above.

Advantages of the Invention

[0010] According to the present invention, in the production of higher-order chlorinated methanes by reacting methyl chloride with chlorine, the yield of carbon tetrachloride can be favorably increased.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0012] In the present invention, carbon tetrachloride is produced by reacting methyl chloride as a raw material with chlorine (hereinafter, the reaction with chlorine is also referred to as a "chlorination reaction"). In this method, the raw material methyl chloride can be produced relatively stably by the reaction of hydrogen chloride and methanol, and those obtained in this way are most commonly used. Further, as the methyl chloride as the raw material, it is common to use part or all of the methyl chloride recovered from the reaction product with chlorine together with the above methyl chloride.

[0013] In the present invention, as the chlorination method, known methods such as a photochlorination method, a thermal chlorination method, or a liquid-phase chlorination method carried out in a liquid phase in the presence of a catalyst can be used. Among these, it is preferable to use a liquid-phase chlorination method because it is easy to control the reaction temperature in the reaction system, the formation of a partial high-temperature region is suppressed, and the generation of impurities such as multimers is suppressed. The liquid-phase chlorination method is particularly suitable because it can increase the reaction rate between methyl chloride and chlorine and can increase the production ratio of methylene chloride and further carbon tetrachloride, which is the target product in the present invention.

[0014] In the present invention, the conditions under which methyl chloride can maintain a liquid phase vary depending on the reaction temperature, but usually, a pressure of 0.8 MPaG or more, preferably a pressure of 1 to 3 MPaG can be set.

[0015] Also, generally, the above reaction temperature is preferably 60 to 150 °C, more preferably 80 to 130 °C.

[0016] In the method of the present invention, the supply amount of chlorine to the chlorination reaction is such that since the raw material to be chlorinated is not only methyl chloride but also partial chlorides of chloroform and methylene chloride are added by circulation supply as described later, considering the added amount of these partial chlorides, the value of Cl2 / X represented by the following formula Cl2 / X Cl2: number of moles of chlorine X: number of moles of methyl chloride + (2 / 3 × number of moles of methylene chloride) + (1 / 3 × number of moles of chloroform) is preferably an amount such that the value is 0.3 to 1.5, more preferably 0.6 to 1.3.

[0017] In the present invention, a known radical generator can be used for the chlorination reaction. Exemplary typical radical generators include (a) compounds in which an azo group is bonded to the carbon at the α-position of a nitrile, azobisnitriles represented by αα'-azobisisobutyronitrile, or (b) peroxides such as benzoyl peroxide, lauryl peroxide, and cumyl peroxide.

[0018] The above radical generator is preferably used in a chlorinated hydrocarbon at a ratio of 1 ppm or more, preferably 10 to 3000 ppm.

[0019] The greatest feature of the present invention is that in the above chlorination reaction, at least a part of the chloroform contained in the obtained higher-order chlorinated methanes is separated and circulated and supplied to the reaction system of the higher-order chlorinated methanes. On the other hand, the methylene chloride contained in the higher-order chlorinated methanes is circulated and supplied to the reaction system in an amount of only 0 to 100% by mass with respect to the chloroform circulated and supplied to the reaction system. That is, if the reaction is continued under such conditions, the chlorinated product circulated and supplied is mainly chloroform, which is a chlorination precursor of carbon tetrachloride, and the production reaction of the carbon tetrachloride in the whole chlorination reaction is effectively amplified. As a result, the yield of carbon tetrachloride can be increased.

[0020] Specifically, in the reaction product obtained by reacting methyl chloride with chlorine, in the composition of the remaining higher-order chlorinated methanes excluding the content (15 to 30% by mass) of unreacted methyl chloride, the content of carbon tetrachloride is usually about 5 to 12% by mass. By carrying out this by the method of the present invention, it is possible to increase the content ratio of the above carbon tetrachloride to 14% by mass or more in many cases, and up to 15 to 35% by mass depending on conditions. More preferably, the content ratio of the above carbon tetrachloride is 1.1 times by mass or more, more preferably 1.2 to 2 times by mass, compared with the reaction result in which such partial chlorinated product is not circulated and supplied at the same chlorine supply amount (the same value of Cl2 / X). At this time, it is also possible and useful to maintain the content ratio of chloroform so as not to decrease to 1.1 times by mass or less, more preferably 1.2 times by mass or less, with respect to the content of carbon tetrachloride.

[0021] When only methylene chloride is circulated and supplied to the reaction system as in Patent Document 1, the content ratio of chloroform can be increased to about 55% by mass, but the ratio of carbon tetrachloride decreases to at most about 10% by mass. From this, the superiority of the method for producing carbon tetrachloride of the present invention is also clear.

[0022] Here, the circulating supply amount of chloroform contained in the higher-order chlorinated methanes is not limited as long as at least a part of it is concerned, and it may be appropriately determined according to the desired production ratio of carbon tetrachloride. Specifically, in the reaction system of the higher-order chlorinated methanes, it is preferably supplied so as to be in the range of 0.02 to 0.50 mol, more preferably 0.1 to 0.3 mol, per 1 mol of methyl chloride. It is preferable to circulate and supply 5 to 80 mol%, more preferably 20 to 60 mol%, of the chloroform contained in the chloroform contained in the reaction product of the chlorination reaction.

[0023] On the other hand, it is required that methylene chloride is circulated and supplied only in an amount of 0 to 100% by mass, more preferably 20 to 90% by mass, based on the chloroform circulated and supplied to the reaction system. That is, when the circulating supply amount of methylene chloride exceeds the above range, the production ratio of carbon tetrachloride decreases to a value that cannot be satisfied. The circulating supply amount of the methylene chloride is generally an amount that circulates and supplies 0 to 70% by mass, more preferably 20 to 55% by mass, of the methylene chloride contained in the reaction product of the chlorination reaction.

[0024] In the present invention, in order to circulate and supply at least a part of the chloroform contained in the higher-order chlorinated methanes obtained by the chlorination reaction in this way, it is preferably carried out by the following purification steps. That is, 1) A step of distilling off hydrogen chloride and methyl chloride from the higher-order chlorinated methanes 2) A step of dehydrating the residue obtained by distilling off hydrogen chloride and methyl chloride in the step 1) as necessary, and then supplying it to a methylene chloride rectification column to separate methylene chloride as a distillate 3) A step of supplying the bottom liquid of the methylene chloride rectification column obtained in the step 2) to a chloroform rectification column to separate chloroform as a distillate This is implemented by passing through, and the chloroform separated as the distillate of the chloroform rectification column in the above step 3) is circulated and supplied to the reaction system of the higher-order chlorinated methanes. Hereinafter, this production method will be described using the process diagrams of FIGS. 1 and 2 showing representative embodiments. It should be noted that although the reflux sections are not shown in these diagrams, usually, each rectification column is provided with a reflux section. That is, the extraction of chlorinated methanes from the top of each rectification column is carried out as the distillate from the liquid phase of the above reflux section.

[0025] In the process diagram of FIG. 1, into the chlorination reactor 1, methyl chloride 7 and chlorine 8 are added, and further partial chlorides such as methyl chloride and chloroform circulated and supplied from lines 105 and 111 described later are also added, and the chlorination reaction raw materials are supplied from line 101. As a result, in the chlorination reactor 1, the sequential chlorination reaction of methyl chloride proceeds, and higher-order chlorinated methanes composed of methylene chloride, chloroform, and carbon tetrachloride are generated. The separation of each higher-order chlorinated methane from the reaction product containing such higher-order chlorinated methanes is preferably carried out by performing a rectification operation after previously separating and removing hydrogen chloride and methyl chloride. The removal of such hydrogen chloride and methyl chloride can be carried out using known rectification columns respectively. Starting from the removal of such hydrogen chloride and methyl chloride, the rectification of higher-order chlorinated methanes sequentially carried out hereinafter is preferably carried out sequentially using the pressure in the reactor.

[0026] The reaction product is supplied from the chlorination reactor 1 to the hydrogen chloride separation column 2 through line 102. In the hydrogen chloride separation column 2, hydrogen chloride is preferably rectification-separated while controlling the top temperature to -60 to 10°C under a pressure lower than the pressure of the reactor from which the reaction product is obtained and at a pressure of 0.2 to 2 MPaG. The number of trays of the rectification column is selected from 30 to 300, more preferably 40 to 250, and these may be provided separately in a plurality of columns. The reflux ratio is generally selected from 0.2 to 3.0, more preferably 0.4 to 2.0.

[0027] Hydrogen chloride 9 is distilled and removed from the top of the hydrogen chloride separation column 2 through line 103, and chlorinated methanes are supplied from the bottom of the column to the methyl chloride rectification column 3 through line 104. It is preferable that methyl chloride is rectification-separated under a pressure lower than that of the hydrogen chloride separation column and while controlling the top temperature to 5 to 60°C under a pressure of 0.2 to 1.5 MPaG. The number of trays, reflux ratio, etc. of the rectification column at this time may be adopted from the same conditions as those described for the hydrogen chloride separation column 2.

[0028] Methyl chloride is distilled and removed from the top of the methyl chloride rectification column 3. This rectification is preferably carried out under conditions where the concentration of methyl chloride in the distillate is sufficiently purified to 99.9% by mass or more. For example, it is preferable to carry out rectification separation while controlling the top temperature to 5 to 60°C under a pressure lower than that of the hydrogen chloride separation column 2 and under a pressure of 0.2 to 1.5 MPaG. The separated methyl chloride is circulated and supplied to the chlorination reactor 1 through line 105 and is used again as a raw material for the chlorination reaction, which is favorable for maintaining the production ratios of methylene chloride and chloroform at a certain high level.

[0029] On the other hand, higher-order chlorinated methanes are supplied as the bottom liquid of the methyl chloride rectification column 3 to the methylene chloride rectification column 5 through line 106. In such a methylene chloride rectification column 5, methylene chloride is distilled and removed from the top. This rectification is preferably carried out under conditions where the concentration of methylene chloride in the distillate is sufficiently purified to 99.9% by mass or more, more preferably 99.95% by mass or more. These rectification conditions can be adjusted by controlling the number of trays, reflux ratio, etc. of the rectification column. The number of trays, reflux ratio, etc. of the rectification column at this time may be adopted from the same conditions as those described for the hydrogen chloride separation column 2. Specifically, the distillation of methylene chloride is preferably carried out while controlling the top temperature to 40 to 75°C under a pressure of 0 to 0.2 MPaG.

[0030] The distillate of the separated methylene chloride 10 is entirely withdrawn from the system through line 109 in the process diagram of FIG. 1. However, in some cases, a part of it may be circulated and supplied to the chlorination reactor 1 and used again as a raw material for the chlorination reaction. This mode is good for maintaining the production ratio of chloroform at a certain high level. In the present invention, however, the amount of the circulated supply needs to be within the range of 0 to 100% by mass with respect to the chloroform circulated and supplied to the reaction system as described above.

[0031] In addition, the higher-order chlorinated methanes, which are the residue remaining after the distillation of hydrogen chloride and methyl chloride and obtained as the bottom liquid of the methyl chloride rectification column 3, are supplied to the methylene chloride rectification column 5 after being provided with a methylene chloride rough separation column 4 for separating the rough form of methylene chloride contained in the higher-order chlorinated methanes in the middle of line 106 as shown in FIG. 2. It is also a preferable mode to supply the bottom liquid roughly separated here to the methylene chloride rectification column 5. Specifically, the rough separation of methylene chloride in this methylene chloride rough separation column 4 is preferably carried out by rectification separation while controlling the top temperature at 40 to 88°C under a pressure of 0 to 0.2 MPaG. In this case, the number of stages of the rectification column, the reflux ratio, etc. are preferably set to the conditions for obtaining the concentration of the methylene chloride. Note that by this rough separation, it is preferable to distill off 10 to 70% by mass, and more preferably 15 to 55% by mass, of the methylene chloride contained in the higher-order chlorinated methanes.

[0032] Due to the rough separation by the methylene chloride rough separation column 4, part of the roughly separated methylene chloride is preferably circulated and supplied to the reaction system (chlorination reactor 1) of the higher-order chlorinated methanes through line 107 and used again as a raw material for the chlorination reaction from the viewpoint of improving the efficiency of the chlorination reaction. However, when a part of the methylene chloride is also circulated and supplied from another line as part of the distillate from the above-mentioned methylene chloride rectification column 5, etc., it is necessary to keep the total amount of these within the range of 0 to 100% by mass with respect to the chloroform circulated and supplied to the reaction system.

[0033] As the bottom liquid of the methylene chloride rectification column 5, a mixed liquid of chloroform and carbon tetrachloride is supplied to the chloroform rectification column 6 through line 110. In this chloroform rectification column 6, chloroform is distilled off and removed from the top of the column. This rectification is preferably carried out under the condition that the chloroform concentration is sufficiently purified to 99.9 mass% or more, more preferably 99.95 mass% or more. This rectification condition is preferably to carry out rectification separation while controlling the top temperature at 60 to 100 °C under a pressure of 0 to 0.2 MPaG. In this case, the number of trays, reflux ratio, etc. of the distillation column are preferably set under the condition of obtaining the above-mentioned chloroform concentration. Also, the distillation of chloroform from the chloroform rectification column 6 may, in some cases, be obtained not as the distillate from the top of the column as described above, but by side-cutting from the rectification column to obtain a liquid with a slightly lower chloroform concentration.

[0034] A part of the distillate of the separated chloroform 11 is taken out of the system if necessary, and then circulated and supplied to the chlorination reactor 1 through line 111, and is used again as a raw material for the chlorination reaction. As described above, circulating and supplying at least a part of the chloroform contained in the higher-order chlorinated methanes to the reaction system of the higher-order chlorinated methanes through this line 111 is the greatest feature of the present invention, whereby the production ratio of carbon tetrachloride is significantly increased. In addition, for the amount of chloroform circulated and supplied to the reaction system, in the embodiment provided with the methylene chloride rough separation column 4 as shown in FIG. 2, the amount of chloroform contained in the rough methylene chloride circulated and supplied to the reaction system through line 107 is also added.

[0035] By undergoing the above purification process, purified carbon tetrachloride 12 is withdrawn from the bottom of the chloroform rectification column 6 through line 113 in a high yield. Since the obtained carbon tetrachloride 12 may contain a small amount of high-boiling impurities, it is preferably purified by subjecting it to a carbon tetrachloride rectification column, distilling off the purified carbon tetrachloride from the top of the column, and discharging the high-boiling impurities as the bottom liquid. In the above carbon tetrachloride 12, when the removal of low-boiling impurities is not sufficient, it is preferable to sufficiently remove the low-boiling impurities prior to distilling off the purified carbon tetrachloride from the top of the carbon tetrachloride rectification column. By performing such a purification treatment, it is usually possible to obtain purified carbon tetrachloride having a concentration of 99.8% by mass or more, more preferably 99.9% by mass or more.

Example

[0036] Hereinafter, in order to more specifically explain the method of the present invention, examples implemented according to the attached drawings showing typical embodiments of the method of the present invention are shown, but the present invention is not limited to such attached drawings.

[0037] In the following examples and comparative examples, the concentrations of each chlorinated methane consisting of methyl chloride, methylene chloride, chloroform, and carbon tetrachloride were measured using a gas chromatograph (GC2014-FID) manufactured by Shimadzu Corporation equipped with a low-polarity capillary column "InertCap5" [manufactured by GL Sciences Inc.] having a length of 30 meters (chemically bonded with 5% diphenyl - 95% dimethylpolysiloxane). Each measured value was shown as the average value of the results obtained by arbitrarily sampling each object three times after the production of higher-order chlorinated methanes by the chlorination reaction had stabilized.

[0038] Example 1 The present invention was implemented according to the process diagram shown in FIG. 1.

[0039] That is, methyl chloride 7, chlorine 8, the methyl chloride fraction distilled by the methyl chloride rectification column 3 circulated from line 105, and the chloroform fraction distilled by the chloroform rectification column 6 circulated from line 111 were mixed in the chlorination reactor 1 so as to have a pressure of 2.7 MPaG and supplied from line 101. Azobisisobutyronitrile was supplied to this chlorination reactor 1 as a radical generator at a concentration of 100 ppm in the chlorinated hydrocarbon, and the chlorination reaction of methyl chloride in the liquid phase state was carried out at an average reaction temperature of 105°C.

[0040] The reaction product was led to the hydrogen chloride separation column 2 through line 102 and rectified under the conditions of a top temperature of -40°C and a pressure of 0.8 MPaG. By this rectification, hydrogen chloride 9 was distilled out and discharged out of the system through line 103.

[0041] On the other hand, the chlorinated methanes after removing hydrogen chloride withdrawn from the bottom of the hydrogen chloride separation column 2 were led to the methyl chloride rectification column 3 through line 104, and rectification for separating methyl chloride was carried out under the conditions of a top temperature of 40°C and a pressure of 0.8 MPaG. By this rectification, the methyl chloride fraction distilled out to line 105 was circulated to the chlorination reactor 1 through line 105 so as to have a supply amount that achieves the raw material composition of the chlorination reaction shown in Table 1 described later, and was used for the chlorination reaction again. The concentration of the methyl chloride fraction distilled out to this line 105 was 99.9% by mass.

[0042] On the other hand, the higher-order chlorinated methanes withdrawn from the bottom of the methyl chloride rectification column 3 were led to the methylene chloride rectification column 5 through line 106, and rectified under the conditions of a top temperature of 50°C and a pressure of 0.05 MPaG, and methylene chloride 10 with a concentration of 99.9% by mass was obtained as a product.

[0043] On the other hand, the mixed solution of chloroform and carbon tetrachloride withdrawn from the bottom of the methylene chloride rectification column 5 was led to the chloroform rectification column 6 through line 110 and rectified under the conditions of a column top temperature of 60°C and a pressure of 0.05 MPaG. By this rectification, a part of the chloroform fraction distilled out through line 112 was taken out of the system as a product of 99.9 mass% chloroform. The remainder was circulated through line 110 to the chlorination reactor 1 so as to achieve a feed rate that would achieve the raw material composition for the chlorination reaction shown in Table 1 described later, and was again subjected to the chlorination reaction.

[0044] In the above liquid-phase chlorination reaction, the raw material composition supplied from line 101 to the chlorination reactor 1 was in the state shown in Table 1 below, including the methyl chloride fraction circulated and supplied from line 105 and the chloroform fraction circulated and supplied from line 111.

[0045]

Table 1

[0046] In this raw material composition, when converting the supply amount of chloroform circulated from line 111, it was an amount that became 0.25 mol per 1 mol of methyl chloride. Note that neither the methyl chloride fraction circulated from line 105 nor the chloroform fraction circulated from line 111 substantially contained methylene chloride. Therefore, the supply amount of methylene chloride with respect to the chloroform supplied to the chlorination reactor 1 was 0 mass%.

[0047] Also, calculated from the amounts of methyl chloride and chloroform supplied to the chlorination reactor 1 above Cl2 / X Cl2: number of moles of chlorine X: number of moles of methyl chloride + (number of moles of methylene chloride × 2 / 3) + (number of moles of chloroform × 1 / 3) the value of was 0.98.

[0048] In the related chlorination reaction, the amount of unreacted methyl chloride contained in the reaction product generated in the chlorination reactor 1 was 19.2% by mass in terms of the amount of methyl chloride discharged from the methyl chloride rectification column 3 to line 105. Then, based on the amount of methylene chloride discharged from the methylene chloride rectification column 5 to line 109, the amount of chloroform discharged from the chloroform rectification column 6 to line 112, and the amount of carbon tetrachloride taken out from line 113, the composition of the remaining higher-order chlorinated methanes excluding the content of the unreacted methyl chloride was determined. As shown in Table 2 below, it was found that methylene chloride was 42.6% by mass, chloroform was 35.1% by mass, and carbon tetrachloride was 22.3% by mass, confirming that the production ratio of carbon tetrachloride was high.

[0049]

Table 2

[0050] Comparative Example 1 Figure 3 is a process diagram showing a conventional method for producing higher-order chlorinated methanes in which, in the process diagram shown in FIG. 1, there is no line 111 for circulating and supplying the chloroform fraction flowing out from the chloroform rectification column 6 to the chlorination reactor 1. Using the production apparatus of the process shown in FIG. 3, in Example 1, the chloroform fraction flowing out from the chloroform rectification column 6 was not circulated and supplied to the chlorination reactor 1, the raw material composition supplied from line 101 to the chlorination reactor 1 was changed as shown in Table 3, and the chlorination reaction was carried out in the same manner as in Example 1 except that the supply amount Cl2 / X of the chloroform fraction circulated to the chlorination reactor 1 was changed to 0.91 to produce carbon tetrachloride.

[0051]

Table 3

[0052] In the related chlorination reaction, the amount of unreacted methyl chloride contained in the reaction product generated in the chlorination reactor 1 was 23.2% by mass in terms of the amount of methyl chloride discharged from the methyl chloride rectification column 3 to line 105. Then, the composition of the remaining higher-order chlorinated methanes excluding the content of the unreacted methyl chloride was determined based on the compositions of line 109, line 112, and line 113 in the same manner as in Example 1. As shown in Table 4 below, methylene chloride was 47.6% by mass, chloroform was 41.7% by mass, and carbon tetrachloride was 10.7% by mass, and the production ratio of carbon tetrachloride was significantly reduced compared to Example 1.

[0053]

Table 4

[0054] Examples 2 - 3 In Example 1, the chlorination reaction was carried out in the same manner as in Example 1 except that the amount of chlorine supplied to the chlorination reactor 1 and the supply amount of the chloroform fraction circulated to the chlorination reactor 1 from line 111 were changed so that Cl2 / X became 0.95 (Example 2) and 0.85 (Example 3) to produce carbon tetrachloride.

[0055] In the above liquid-phase chlorination reaction, the raw material composition supplied from line 101 to the chlorination reactor 1 was in the state shown in Table 5 below, including the methyl chloride fraction circulated and supplied from line 105 and the chloroform fraction circulated and supplied from line 111.

[0056]

Table 5

[0057] In the related chlorination reaction, the amount of each unreacted methyl chloride contained in the reaction product generated in the chlorination reactor 1, when converted from the amount of methyl chloride discharged from the methyl chloride rectification column 3 to line 105, was 20.4% by mass in Example 2 and 27.0% by mass in Example 3. Then, the composition of the remaining higher-order chlorinated methanes excluding the content of these unreacted methyl chlorides was determined based on the compositions of line 109, line 112, and line 113 in the same manner as in Example 1, and the results are shown in Table 6 below. In any of the Cl2 / X values, the yield of carbon tetrachloride was high due to the high amount of carbon tetrachloride generated in the chlorinated reactant.

[0058]

Table 6

[0059] Example 4 The present invention was implemented according to the process diagram shown in FIG. 2. That is, in the process shown in FIG. 2, before supplying the higher-order chlorinated methanes obtained as the bottom liquid of the methyl chloride rectification column 3 to the methylene chloride rectification column 5 (in the middle of line 106), a methylene chloride rough separation column 4 for first separating the rough form of methylene chloride contained in the higher-order chlorinated methanes was provided. Here, the rectification of the methylene chloride rough separation column 4 was carried out under the conditions of a column top temperature of 51°C and a pressure of 0.04 MPaG. By this rectification, the rough methylene chloride distilled out to line 107 contained 51% by mass of methylene chloride and 49% by mass of chloroform. This rough methylene chloride was circulated and supplied to the chlorination reactor 1 through the above line 101. The circulation supply amount of this methylene chloride was an amount reaching 45% by mass of the methylene chloride contained in the higher-order chlorinated methanes.

[0060] In addition, the chlorination reaction in the chlorination reactor 1 and the purification of the reaction product up to the methyl chloride rectification column 3 were carried out in the same manner as in Example 1.

[0061] In the above liquid-phase chlorination reaction, the raw material composition supplied from line 101 to the chlorination reactor 1 was in the state shown in Table 7 below, including the methyl chloride fraction recycled from line 105, the crude methylene chloride fraction recycled from line 107, and the chloroform fraction recycled from line 111. Also, the supply amount Cl2 / X of the chloroform fraction recycled to the chlorination reactor 1 was 1.08.

[0062] [Table 7]

[0063] In the above raw material composition, when converting the supply amount of chloroform recycled by line 111 and line 107, it was an amount that became 0.28 mol per 1 mol of methyl chloride. Also, in the above raw material composition, methylene chloride recycled from line 107 was contained at 44.0 mass% with respect to the recycled supply amount of chloroform.

[0064] In such a chlorination reaction, the amount of unreacted methyl chloride contained in the reaction product generated in the chlorination reactor 1 was 16.6 mass% when converted from the amount of methyl chloride discharged from the methyl chloride rectification column 3 to line 105. Then, when determining the composition of the remaining higher-order chlorinated methanes excluding the content of the above unreacted methyl chloride, based on the compositions of line 107, line 109, line 112, and line 113 in the same manner as in Example 1, as shown in Table 8 below, methylene chloride was 22.6 mass%, chloroform was 46.5 mass%, and carbon tetrachloride was 30.9 mass%. It was confirmed that the production ratio of carbon tetrachloride was further increased compared to Example 1.

[0065] [Table 8]

[0066] Examples 5 - 6, Comparative Example 2 In Example 4, the chlorination reaction was carried out in the same manner as in Example 4, except that the amount of chlorine supplied to the chlorination reactor 1 and the supply amounts of the higher-order chlorinated methanes circulated to the chlorination reactor 1 from lines 107 and 111 were changed so that Cl2 / X became 1.00 (Example 5), 0.91 (Example 6), and 0.77 (Comparative Example 2), to produce carbon tetrachloride.

[0067] In these chlorination reactions, when the composition of the higher-order chlorinated methanes contained in the reaction product generated in the chlorination reactor 1 was determined based on the compositions of lines 109, 112, and 113 in the same manner as in Example 4, it changed as shown in Table 9 below.

[0068] [Table 9]

[0069] In the above chlorination reaction, in Feedstock Composition 6, methylene chloride circulated from line 107 was contained in an amount of 68.7% by mass in Example 5, 71.2% by mass in Example 6, and 610.6% in Comparative Example 2, relative to the circulation supply amount of chloroform.

[0070] In such a chlorination reaction, the amount of unreacted methyl chloride contained in the reaction product generated in the chlorination reactor 1, when converted from the amount of methyl chloride discharged from the methyl chloride rectification column 3 to line 105, was 19.7% by mass in Example 5, 22.1% by mass in Example 6, and 28.1% by mass in Comparative Example 2. Then, when the composition of the remaining higher-order chlorinated methanes excluding the content of the unreacted methyl chloride was determined based on the compositions of lines 107, 109, 112, and 113 in the same manner as in Example 1, the results were as shown in Table 10 below. In any of the Cl2 / X values, the yield of carbon tetrachloride was high due to the high amount of carbon tetrachloride generated in the above chlorination reactant.

[0071] [Table 10]

Explanation of Symbols

[0072] 1; Chlorination Reactor 2; Hydrogen Chloride Separation Tower 3; Methyl Chloride Rectification Tower 4; Methylene Chloride Crude Separation Tower 5; Methylene Chloride Rectification Tower 6; Chloroform Rectification Tower 7; Methyl Chloride 8; Chlorine 9; Hydrogen Chloride 10; Methylene Chloride 11; Chloroform 12; Carbon Tetrachloride 101,102,103,104,105,106,107,108,109,110,111,112,113; Line

Claims

1. A method for producing higher chlorinated methanes consisting of methylene chloride, chloroform, and carbon tetrachloride by reacting methyl chloride with chlorine, wherein at least a part of the chloroform contained in the higher chlorinated methanes is separated and circulated and supplied to the reaction system of the higher chlorinated methanes, while the methylene chloride contained in the higher chlorinated methanes is circulated and supplied in an amount of 0 to 100% by mass based on the chloroform circulated and supplied to the reaction system, thereby increasing the production ratio of carbon tetrachloride contained in the higher chlorinated methanes. A method for producing carbon tetrachloride, characterized by the above.

2. At least partial separation of chloroform from higher chlorinated methanes is carried out through the following purification steps 1) A step of distilling off hydrogen chloride and methyl chloride from the higher chlorinated methanes 2) A step of dehydrating the distillation residue of hydrogen chloride and methyl chloride obtained in the step 1) as necessary, and then supplying it to a methylene chloride rectification column to separate methylene chloride as a distillate 3) A step of supplying the bottom liquid of the methylene chloride rectification column obtained in the step 2) to a chloroform rectification column to separate chloroform as a distillate The method for producing carbon tetrachloride according to claim 1, wherein the chloroform separated as a distillate of the chloroform rectification column in the step 3) is circulated and supplied to the reaction system of the higher chlorinated methanes.

3. The method for producing carbon tetrachloride according to claim 2, wherein the methylene chloride separated as a distillate of the methylene chloride rectification column in the step 2) is circulated and supplied to the reaction system of the higher chlorinated methanes.

4. Before supplying the distillation residue of hydrogen chloride and methyl chloride obtained in the step 1) to the methylene chloride rectification column in the step 2), it is supplied to a methylene chloride rough separation column for first separating the crude form of methylene chloride contained in the higher chlorinated methanes, and the bottom liquid of the methylene chloride rough separation column is supplied to the above methylene chloride rectification column. The method for producing carbon tetrachloride according to claim 2 or claim 3.

5. The method for producing carbon tetrachloride according to claim 4, wherein the methylene chloride first separated as a distillate of the methylene chloride rough separation column is circulated and supplied to the reaction system of the higher chlorinated methanes.

6. In the reaction system of higher chlorinated methanes, the circulation supply amount of chloroform is an amount of 0.02 to 0.50 mol per 1 mol of methyl chloride. The method for producing carbon tetrachloride according to claim 1.

7. In the reaction system of higher chlorinated methanes, the molar ratio of chlorine (Cl ２ / X) is in the range of 0.3 to 1.5 with respect to the total amount (X) of methyl chloride, methylene chloride and chloroform supplied in circulation, and the method for producing carbon tetrachloride according to claim 1.

Images