JP2710262B2 - Method for producing chlorinated methane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing chlorinated methane.

[0002]

2. Description of the Related Art It is known to chlorinate methyl chloride to produce higher chlorinated methane such as methylene chloride, chloroform and carbon tetrachloride. In such a chlorination reaction, a reaction mixture containing higher chlorinated methane, hydrogen chloride and unreacted methyl chloride is obtained. Then, in order to separate and purify the desired higher chlorinated methane from the reaction mixture, the reaction mixture was rectified to first separate hydrogen chloride, and then similarly rectified to separate unreacted methyl chloride, The obtained high order chlorinated methane is separated in order from the compound having the lowest boiling point. In this separation and purification method, it is known that the removed unreacted methyl chloride is re-supplied to the reaction step of the chlorination reaction in order to increase the reaction rate of methyl chloride.

[0003]

By the way, in the above chlorination reaction of methyl chloride, phosgene is by-produced by oxidative decomposition of methyl chloride or higher chlorinated methane.
Here, the boiling point of phosgene is somewhat higher than that of methyl chloride but much lower than that of the higher chlorinated methane. Therefore, this phosgene is contained in the unreacted methyl chloride separated in the separation and purification process of the reaction mixture. If chlorinated methane is produced by re-supplying unreacted methyl chloride to the reaction step between methyl chloride and chlorine as described above, this phosgene accumulates in the reaction system as the reaction proceeds. I do. as a result,
When the production of chlorinated methane lasts for a long time, the ratio of phosgene in the raw material methyl chloride increases, and there has been a problem that the chlorination reaction cannot be performed efficiently. Due to such problems, after the chlorination reaction is performed for a certain period, the accumulated phosgene is extracted together with methyl chloride in a methyl chloride rectification column and removed by alkali washing or the like, but the operation is extremely complicated. In addition, when the amount of impurities in the raw materials fluctuates greatly with the lapse of the reaction time, the supply amounts of methyl chloride and chlorine to be supplied to the reaction step and the supply ratio must be changed accordingly. It was troublesome in terms of control.

[0004] In view of such a background, the present invention provides a method for producing chlorinated methane efficiently in a method for producing chlorinated methane in which unreacted methyl chloride is re-supplied to a reaction step between methyl chloride and chlorine. With the goal.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, after contacting unreacted methyl chloride separated from the reaction mixture with zeolite, the methyl chloride and chlorine It has been found that the above object can be achieved by re-supplying to the reaction step, and the present invention has been provided.

That is, according to the present invention, methyl chloride is reacted with chlorine to obtain a reaction mixture containing the objective higher chlorinated methane, hydrogen chloride and unreacted methyl chloride. A method for producing chlorinated methane, comprising separating a reacted methyl chloride by rectification, bringing the separated unreacted methyl chloride into contact with a zeolite, and then re-supplying it to a reaction step between methyl chloride and chlorine. .

In the present invention, as a method for reacting methyl chloride with chlorine, a method known as a chlorination reaction for producing high-order chlorinated methane can be employed without any limitation. In particular, a method in which methyl chloride and chlorine are reacted in the presence of a radical initiator and in a liquid phase state of methyl chloride is preferable. By such a chlorination reaction, a reaction mixture containing higher chlorinated methane composed of methylene chloride, chloroform and carbon tetrachloride, hydrogen chloride and unreacted methyl chloride is obtained. The reaction mixture also contains phosgene by-produced by oxidative decomposition of methyl chloride or higher chlorinated methane as an impurity.

In the present invention, hydrogen chloride and unreacted methyl chloride are separated from the above reaction mixture by rectification in order to purify the high-order chlorinated methane. As the rectification method, a known method can be employed without any particular limitation. Usually, the above reaction mixture is first supplied to a hydrogen chloride rectification column to separate hydrogen chloride, and then a mixture of the obtained higher chlorinated methane and unreacted methyl chloride is supplied to a methyl chloride rectification column. To separate unreacted methyl chloride. Further, the obtained higher chlorinated methane comprising methylene chloride, chloroform and carbon tetrachloride is further rectified and separated in order from compounds having lower boiling points. In such a separation and purification process, phosgene contained as the impurity is contained in unreacted methyl chloride due to its boiling point. Therefore, when this unreacted methyl chloride is re-supplied to the reaction step of the chlorination reaction in order to increase the reaction rate of methyl chloride,
As described above, there is a problem that phosgene accumulates in the reaction system. In the present invention, the separated unreacted methyl chloride may be re-supplied in its entirety to the reaction step, or may be partially re-supplied to the reaction step, and the remainder may be returned to the methyl chloride rectification column. It may be supplied or taken out of the reaction system.

The most important feature of the present invention resides in that unreacted methyl chloride separated from the reaction mixture is brought into contact with zeolite and then re-supplied to a reaction step between methyl chloride and chlorine. By doing so, phosgene contained in unreacted methyl chloride is adsorbed and removed by the zeolite, and does not accumulate in the reaction system.

The zeolite used in the present invention is:
There is no particular limitation, and the general formula M _{2 / n} O.Al ₂ O
_{3 · xSiO 2 · yH 2 O} (M is Na, K, Ca, an element selected from Ba, n is the valence) known crystalline aluminosilicate represented by the widely used. Among them, those having an average pore diameter of 3 to 13 angstroms are preferred. In particular, synthetic zeolites are preferred. The filling amount of zeolite in the adsorption layer is not particularly limited, but it is preferable that 1 to 50 g of zeolite is charged per 1 g of unreacted methyl chloride supplied to the adsorption layer in one minute.

In the present invention, the adsorption of phosgene by the zeolite needs to be performed at a site after unreacted methyl chloride is separated from the reaction mixture. That is, the adsorption of phosgene to the zeolite is preferably performed as the amount of phosgene occupying in the mixture brought into contact with the zeolite increases. Therefore, even if the adsorption treatment with zeolite is performed in a place other than the above-mentioned place where the concentration of phosgene is low, sufficient removal cannot be performed. Further, the contact form of the unreacted methyl chloride with the zeolite may be a gaseous state immediately after being discharged from the rectification column, or may be a liquid state in which the gaseous phase is condensed. . The liquid phase is preferred in that the volume of the zeolite adsorption layer can be small.

The method of contacting the unreacted methyl chloride with the zeolite is not particularly limited, and the zeolite may be brought into contact with either the fixed bed or the fluidized bed as the adsorption layer. Preferably, a fixed layer is used. Further, the temperature and the pressure at the time of contacting are not limited at all, but are preferably 32 to 55 ° C. and 6 to 20 kg.
/ Cm ² gauge pressure is preferred.

In the present invention, the zeolite can be used repeatedly by performing desorption regeneration even if the chlorination reaction is carried out for a long time and its adsorption capacity is reduced. The method of desorbing and regenerating zeolite is not particularly limited, and a known regenerating method can be employed. Preferably, regeneration is performed by a heating regeneration method using an inert gas at 160 to 250 ° C.

In the production of chlorinated methane, water may be mixed into the reaction system as impurities such as methyl chloride or chlorine as a raw material. In that case, such a production method causes a problem of corroding the reactor and the piping. According to the method for producing chlorinated methane of the present invention, the contaminated water can be adsorbed on zeolite at the same time as phosgene and removed, which is preferable.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a schematic diagram of a method for producing chlorinated methane according to a typical embodiment of the present invention. In FIG. 1, methyl chloride and chlorine are supplied to a reactor 1 from a pipe 2 and a pipe 3, respectively. Then, in the reactor 1, methylene chloride,
Higher-order chlorinated methane consisting of chloroform and carbon tetrachloride,
A reaction mixture containing hydrogen chloride and unreacted methyl chloride is formed. The reaction mixture contains a small amount of phosgene by-produced. Then, the reaction mixture is first supplied to the hydrogen chloride rectification column 5 through the pipe 4 and rectified to separate hydrogen chloride from the top of the column. Next, a mixture containing higher chlorinated methane, unreacted methyl chloride, and a small amount of phosgene discharged from the bottom of the hydrogen chloride rectification column 5 is supplied to the methyl chloride rectification column 7 through a pipe 6. Is done. Then, the mixture is rectified in the methyl chloride rectification column 7, and unreacted methyl chloride is separated from the top of the column. At this time,
The phosgene contained in the mixture is contained in the separated unreacted methyl chloride because its boiling point is somewhat higher than that of methyl chloride but much lower than that of high-order chlorinated methane. The high-order chlorinated methane discharged from the bottom of the methyl chloride rectification column 7 is then supplied to the methylene chloride rectification column 8 and further to the chloroform rectification column 9 and separated into components in ascending order of boiling point. Is done.

On the other hand, the gas phase of unreacted methyl chloride discharged from the top of the methyl chloride rectification column 7 is sent to a cooler 11 through a pipe 10 to be liquefied, and then the zeolite-filled adsorbent layer 12 is liquefied. Supplied to Then, by passing through the adsorption layer 12, impurities such as phosgene are adsorbed by the zeolite and removed. The unreacted methyl chloride purified by the contact with the zeolite is then re-supplied to the reactor 1 through the pipe 13 and used again as a raw material for the chlorination reaction. At this time, a part of the unreacted methyl chloride is supplied to the pipe 14 or the pipe 1.
According to 5, it may be re-supplied to the methyl chloride rectification column 7 or taken out of the reaction system.

[0018]

According to the present invention, in a method for producing chlorinated methane in which unreacted methyl chloride is re-supplied to a reaction step between methyl chloride and chlorine, phosgene produced as a by-product can be removed by a simple operation. The problem that the phosgene accumulates in the reaction system can be solved. Further, even when water is mixed in the reaction system, the water can be removed, and corrosion of the reaction device and the like can be prevented. Moreover, the zeolite having the phosgene or the like adsorbed thereon can be repeatedly used by desorbing and regenerating, and is extremely efficient.

[0019]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples below, but the present invention is not limited to these examples.

Example 1 Chlorinated methane was produced by the production process shown in FIG. The supply of methyl chloride and chlorine to the reactor 1 via the pipes 2 and 3 was such that the molar ratio of chlorine / methyl chloride was 1.698. In addition, the adsorption layer 12
Was provided with a fixed layer filled with 1100 kg of molecular sieve 5A (trade name, manufactured by Union Carbide Co., Ltd.). The unreacted methyl chloride separated in the methyl chloride purification tower 7 was supplied to the adsorption layer 12 at a rate of 71 kg / min. The temperature in the adsorption layer 12 was 32 ° C., and the pressure was 13 kg / cm ² gauge.
50% of the separated unreacted methyl chloride was supplied to the methyl chloride purification tower 7 via a pipe 14, and the rest was supplied again to the reactor 1 via a pipe 13.

100 hours after the start of production, the adsorbent layer 12
When the composition of the unreacted methyl chloride before supply was measured, the unreacted methyl chloride contained 900 mg of phosgene.
ppm and water were contained at 56 ppm. On the other hand, unreacted methyl chloride discharged from the adsorption layer 12 contained only 82 ppm of phosgene and 8 ppm of water.

Comparative Example 1 Chlorinated methane was produced in the same manner as in Example 1, except that anhydrous calcium chloride was used instead of the molecular sieve 5A used to fill the adsorption layer 12. 48 hours after the start of the production, the composition of the unreacted methyl chloride discharged from the adsorption layer 12 was measured.
The unreacted methyl chloride contained 2.6% by weight of phosgene, water or $ 62 ppm (amount before supply to the adsorption layer 12: 11%).
3 ppm). Therefore, in the methyl chloride rectification column, phosgene accumulated in the above reaction system was extracted together with methyl chloride and removed by alkali washing or the like, and then the subsequent production was continued.

Example 2 In Example 1, the supply of methyl chloride and chlorine to the reactor 1 was carried out at a molar ratio of chlorine / methyl chloride of 1.3.
A chlorinated methane was produced in the same manner as in Example 1, except that the chlorinated methane was 75. The amount of unreacted methyl chloride supplied to the adsorption layer 12 was 141 kg / min. 100 hours after the start of the production, the composition of unreacted methyl chloride before being supplied to the adsorption layer 12 was measured. The unreacted methyl chloride contained 357 ppm of phosgene and 23 ppm of water.
ppm. On the other hand, the unreacted methyl chloride discharged from the adsorption layer 12 contains 36% of phosgene.
ppm, water contained only 3 ppm.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a method for producing chlorinated methane according to a typical embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Reactor 2 Pipe which supplies methyl chloride 3 Pipe which supplies chlorine 4 Pipe which connects a reactor and a hydrogen chloride rectification tower 5 Hydrogen chloride rectification tower 6 Connects a hydrogen chloride rectification tower and a methyl chloride rectification tower Pipe 7 Methyl chloride rectification tower 8 Methylene chloride rectification tower 9 Chloroform rectification tower 10 Pipe for discharging unreacted methyl chloride from methyl chloride rectification tower 11 Cooler 12 Adsorption layer filled with zeolite 13 Unreacted methyl chloride Pipe for re-supplying to the reactor 14 Pipe for re-supplying unreacted methyl chloride to the methyl chloride rectification column 15 Pipe for taking out unreacted methyl chloride out of the reaction system

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C07C 19/041 7106-4H C07C 19/041

Claims (1)

(57) [Claims] (1) reacting methyl chloride with chlorine,
Obtaining a reaction mixture containing the objective higher chlorinated methane, hydrogen chloride and unreacted methyl chloride, separating hydrogen chloride and unreacted methyl chloride from the reaction mixture by rectification, and separating the separated unreacted methyl chloride into zeolite Chlorinated methane, which is supplied again to a reaction step between methyl chloride and chlorine after contacting with chlorinated methane.