DE2137499A1 - PROCESS FOR THE PRODUCTION OF CHLORINE METHANES BY THERMAL CHLORINATION - Google Patents

Description

FARBVrERKEHOECHSTAKTIENGESELLSCILiFT 2137499

formerly Master Lucius & Brüning

File number: - HOE 71 / F 186

Date: July 23, 1971 - DPh.HS / sch

Process for the production of chloromethanes by thermal chlorination -

The invention is a process for the production of Chloromethanes by thermal chlorination.

It is known that methane or gas mixtures of methane and chloromethanes with chlorine in a volume ratio of 10 to 4: 1 and shaping in a loop reactor or a walled chamber at 400 ⁰ C for reaction. If dichloromethane is to be produced, the reactor outgassing is cooled, the unconverted methane and the monochloromethane are separated off and returned to form a mixture with the chlorine. If carbon tetrachloride is to be produced, the reactor outgassing is mixed again and repeatedly with chlorine after sufficient cooling and chlorinated further in downstream reactors; there is no return. Methane is also reacted with excess chlorine and at a higher temperature, but tetrachlorethylene is formed at the same time, and the excess chlorine is used up in a post-reaction with methane.

To improve the temperature control, it has been proposed to add carbon tetrachloride or a lot of hydrogen chloride in the circulating gas to leave.

In all the processes used for the thermal chlorination of Methane, the pressure in the reactor is limited to 4 ata and the chlorine content of the gas in the first reactor is limited to approx. 10 to 20% by volume. The low chlorine content requires preheating of the gas, which is achieved by heat exchange between the hot reactor gas and incoming single gas mixture is reached. A low chlorine content and thus high circulating gas ballast, for example, must be accepted

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to increase the dichloromethane yield.

For the details of the processes mentioned, reference is made to Ullmann Encyklopadie der technischen Chemie, 3rd Edition, Volume 5, 1954, Pages 400-413.

Attempts have also been made to use methane in series U-tubes, which are tempered in a resting molten salt, by injecting chlorine into each U-tube, to be chlorinated, A hollow cylindrical reactor with a radial temperature gradient was also proposed. Furthermore, a fluidized bed was created for the thermal methane chlorination proposed.

Technically useful embodiments of these processes are so far not known. Of course, all reactor proposals have one goal in common, the temperature control of the strong to control exothermic chlorination reaction.

All known thermal chlorination processes have the disadvantage that monochloromethane is used in the undiluted state Cannot be chlorinated because significant chlorine levels cause disruptive decomposition with strong soot formation.

A process for the preparation of chloromethanes by thermal chlorination has now been found, which is characterized is that chlorine with CH Cl with η = 1 to 4 and m = 4 - η and.

η m

optionally inert gas and / or hydrogen chloride is mixed in gaseous form under pressure of 2 to 25 ata in such a proportion that the volume fraction of chlorine in the total gas mixture is 10% to 50% and based on the sum of the volume fractions of the chlorinable components is at least 14 % that this is Reaktoreingasgemisch flowing around in a slender tube at a flow rate of at least 3 m / s by means of the pipe 270 to 400 ° C warm heat transfer medium, whose highest and lowest temperature indistinguishable within the circulation at 40 ⁰ C, warming up and to the reaction, brings, with a gas temperature peak of 330 ° C to 600 ° C

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maintained and that the gas mixture leaving the reactor a processing and separation plant.

Slender pipes with widths between approx. 20 and 100 ram, which are at least 6 m long with a width of 20 mm and at least 60 m with a width of 100 mm, have proven to be particularly useful
proven.

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. INSPECTED

? - 7137499

In the processing and separation plant, the chlorination resulting products and the inert gas introduced with the reaction components are separated from the reactor exhaust gas and the remaining mixture in the same or a different chlorination reactor reinstated.

Also, several chlorination each represented by - are introduced ^L Chlorzumischung, carried out in the same reactor or in different reactors which are connected in series, in the inventive manner, without, however, between the chlorination steps, cooling it tint 270 ° C and working up or Separation plant are required.

The basic idea of this process invention lies in the safe control of the gas temperature by creating suitable heat transfer conditions as well as the limitation of the temperature-dependent reaction rate to an area that is safe with regard to explosive decomposition, and it is based on the knowledge that the reaction rates in the chlorination reactions depend on the chlorine concentration in the gas mixture in each case depend to a different extent on the concentrations of the chlorinable components present in the gas mixture, on the gas pressure, on the average guest temperature, on the boundary layer temperature, on the surface activated - e.g. by soot, graphite or coke - and on the degree of activation of the surface covered and that, surprisingly, despite of the known rapid course of the reaction, the gas temperature caused by the released heat of reaction and heat dissipation through the correct choice of heat exchange conditions (flow guidance, flow speeds, temperatures, exchange area) in a Raforreactor can be controlled within desired limits even with such chlorine concentrations and in such pressure ranges that cannot be achieved in known processes, so the process according to the invention offers a number of advantages over the

209886/1347

known method results. Surprisingly, it was also found that, for the first time, there are also gas mixtures that contain little or no amounts of methane, hydrogen chloride and inert gas contain and preferably consist mainly of monochloromethane, can be chlorinated soot-free, which offers additional advantages except for those caused by higher chlorine concentration and higher pressure.

In the known method occurs because of inadequate temperature control excessive formation of soot occurs if the gas contains more volume fractions of monochloromethane than methane. In the inventive In this process, soot occurs only in traces, even with the chlorination of pure monochloromethane. The amount of filterable, high carbon solid is less than 1.5.

—4
10 parts by weight per part by weight of chlorine reacted. Tarry products are found only to about 10 ~ parts by weight per part by weight of chlorine. The deposition of coke and pyro ^ segraphite on *

the pipe inner wall is less than 10 parts by weight per Part by weight of chlorine. The pyrolysis graphite occurs in a very dense form, which hardly affects the heat exchange unfavorably.

For example, a reactor gas mixture in which the sum of the volume fractions of methane, hydrogen chloride and inert gas is less than 15 % is particularly advantageous.

The reactor exhaust gas, which is poor in methane and inert gas, is preferably present its decomposition in the separation plant by single or multi-stage condensation to more than 90 wt.% liquefied.

In particular, the hydrogen chloride is derived from the liquefied mixture separated and reacted in a methanol esterification plant with methanol to monochloroethane.

It is best to use only monochloromethane from the methanol esterification to be used for the chlorination, so that a composite is formed; Apart from chlorine and methanol, no other raw material is added will.

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The mixture formation, in particular of the monochloromethane with the chlorine, is preferably only 5 to 5% Mixture at the respective gas pressure.

Chlorine is preferably only 5 to 50 ° C above the dew point of the

It can be advantageous to carry out the chlorination reaction in several parallel tubes combined to form tube bundles. On the outside of the tube, the heat transfer medium can be completely or partially evaporated in order to facilitate the heat exchange to design.

The liquid heat transfer medium can be used in many different ways come into use. It is easiest to lead the liquid in countercurrent to the gas flow over the entire length of the reactor. This liquid is expediently allowed to flow so rapidly that the temperature changes over the length of the reactor are only a few Degrees. In this case, the liquid can easily flow in cocurrent instead of countercurrent.

With regard to heat recovery, for example, it can be useful to have several liquid circuits with different temperature levels to be installed in sections over the length of the reactor.

For the purpose of start-up, the circuit of heat transfer fluid heated electrically or by combustion heat. If the reactor is heated to 270 to 320 ° C in this way, so the gas mixture can be fed in immediately. The gas mixture reacts immediately. An accumulation of an explosive gas mixture at ignition temperature is therefore excluded.

It has also been found that the chlorination is strongly catalyzed when the walls of the reactor are covered with a carbon layer. The formation of this layer is undermined the process conditions according to the invention in the course of some Days by itself. During this formation time, the space-time load can be steadily increased.

The reactor as the main part of the device for carrying out: the The method according to the invention is used as a single tube or as

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213

Tube bundle and constructed in such a way that the heat exchange is possible is largely guaranteed over the entire reaction path. Because v / o the heat exchange is not sufficient, it comes to Overheating of the Vfand, the consequence of which is the deposition of coke. Increased Coke deposition also occurs at shadow spots in the flow in crevices, misaligned pipe connections and extensions so that constructively such places largely avoided will.

4 m long pipes have already proven to be useful, the end flanges of which, if necessary for several pipes, Tightly screwed together and involved as much as possible in the heat exchange of the heat exchange fluid flowing in the cladding tube or are prevented from overheating by other measures, e.g. air cooling, and those with a Align excess salt of at most 2 mm.

The device for carrying out the method according to the invention consists of the tubular reactor constructed as a heat exchanger and the gas mixer, as well as the soot filter, a gas drying system, optionally the gradual liquefaction, and from the separating rectification ai. In the case of partial chlorination there is a return of the unreacted and separated single gas components. As far as the monochloromethane not through partial Chlorination of methane is produced, it comes from - preferably - a methane oil esterification plant. The latter becomes the Hydrogen chloride fed from the top of the first rectification column for processing the totally liquefied reactor exhaust gas.

With the methods identified as above, a comparison achieved numerous surprising advantages in addition to the known processes:

It is due to the suppressed backmixing and due to the timing of the chlorination and subsequent reactions higher yields of the desired partially chlorinated methanes achieved.

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The space-time performance reaches many times over, because with increasing Chlorine concentration and, with increasing pressure, the rate of reaction is increased because the amount of ballast is smaller and because the chlorine conversion is accelerated catalytically at the pipe wall will. After exceeding a gas temperature of 300 C, at least 98% of the amount of chlorine that is used at 300 ° C is still present, implemented.

The entire production plant is at high chlorine content and pressure much smaller and, as a result, cheaper.

The energy expenditure is lower.

Commissioning is easier, less dangerous and faster. There is no need to heat the reactor using a gas flame.

The small-volume tubular reactor can because of the favorable dimensions (very slim pipes!) can be made pressure-resistant and explosion-proof without significant additional effort.

Since the components of the gas to be mixed are not preheated takes place and the mixer and the connection line to the reactor are preferably kept at a low temperature, which is a few degrees above the dew point of the mixture, does not apply Risk of mixer fire.

The main part of the heat of reaction released is in the reactor designed as a heat exchanger under very good heat exchange conditions, i.e. with a relatively small exchange area, discharged, so that a large part of the apparatus usually required for removing the heat of reaction is dispensed with.

By means of the fast-flowing or evaporating according to the invention Heat transfer medium can easily transfer the heat of reaction to consumers, e.g. sump boilers of the rectification columns will.

Including the possibilities of chlorinated mixtures in easier Way to re-chlorinate one or more times

209888/1347 BAD ORIGINAL

ren and undesired chlorination products in any mixture composition - returned to the chlorination reactor, can with the inventive method for the first time a End product range of all chloromethanes in almost any combination of quantities can be selected, e.g. in the case of methylene chloride production, in the worst case, "an inevitable amount of approx. 3% by weight higher chlorinated chloroethanes have to be accepted. In the case of exclusive carbon tetrachloride production Methane can be done with two additional doses of chlorine; chlorine and methane are practically completely converted so that - as with the conventional methane stage chlorination - a gas recirculation not applicable.

The high-performance and energetically expensive circulating gas fan previously required for the gas recirculation can be used in the case of the Process can be replaced by a much smaller fan because of the lower amount of circulating gas and the higher pressure;

For the first time, the process according to the invention permits pure monochloromethane to chlorinate. This results in the following additional ones, in particular for the preferred production of dichloromethane or special advantages:

The reactor exhaust gas can be totally condensed through moderate cooling. The hydrogen chloride is separated off from the condensate and the chloromethanes are separated by rectification under pressure. The separated hydrogen chloride is used directly in the methanol esterification plant, in which it is reacted with methanol to form monochloromethane. Compared to the methane base according to CH ₄ + 2 CIo ** CH ₂ Cl ₂ + 2 HCl, the pure methanol base according to

CH ₃ Cl + Cl ₂ = CH ₂ CL ₂ + HCl · HCl + CH ₃ OH = CH ₃ Cl + H ₃ O

-only uses half the amount of chlorine and does not generate hydrochloric acid, their credit value only. would cover a fraction of the chlorine costs.

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The circulating gas fan is completely eliminated.

With this procedure, the achievable yield of dichloromethane is significantly higher than, for example, with the loop reactor: it can easily amount to 97% by weight based on the sum of the chlorination products.

According to the invention, the chlorine content can even be above the lower explosion limit. Such a high chlorine content would not be justifiable in the voluminous loop reactors, for example, and cannot otherwise be controlled, since excessively high temperatures and consequently decomposition products such as C ₂ CIg and carbon deposits would occur.

As a result of the possibility of using monochloromethane according to the invention Chlorinating very high chlorine concentrations is also the yield of trichloromethane that can be achieved with one chlorination step higher than with the loop reactor.

The space-time performance achieved by the method according to the invention at a gas pressure at the reactor inlet of 8 ata and at a gas inlet temperature of 50 C approx. 12 t CHgCl ^ / h / m reactor volume. The performance of the known loop reactor is. on the other hand, at a reaction pressure of 4 ata and a gas inlet

entry temperature of 200 ⁰ C with the greatest possible monochloromethane con-

concentration approx. 0.05 t CHLClg / h / m reactor volume.

For the production of dichloromethane from monochloromethane are the preferred process conditions:

Pressure at reactor inlet: 6 to 15 ata

Temperature of the gas mixture

behind the mixer: 20 to 80

Chlorine content of the single gas: 15 to 30 vol.%

Heat transfer medium temperature: 320 to 360 ° C

Heating of the heat transfer medium while flowing through the reactor: 3 to 15 ° C

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Maximum gas temperature: Inner pipe width :, Residence time in the reactor: Pressure at the reactor outlet:

360 to 480 ° C 20 to 80 mm 1 to 6 seconds 5 to 13 ata

The method according to the invention is illustrated in FIGS. 1-13 and explained in more detail in the following examples:

FIGS. 1-3 show the temperature profile during the chlorination for 3 different operating states A, B and C of pure methane in a 25 mm wide tubular reactor. The temperature is plotted over the length of the reactor »

FIGS. 4-6 show the concentration profile during the chlorination for 3 different operating states A, B and C of pure methane in a 25 mm wide tubular reactor. The concentration is plotted over the length of the reactor,

Figures 7-9 show the respective chlorine flow rates in Reactor with three different operating states A, B and C.

FIG. 10 shows a schematic representation of a chlorination plant for carrying out the method according to the invention subsequent processing and separation plant.

FIG. 11 shows the operating state described in Example 3 the temperature profile that occurs during the chlorination of pure monochloromethane in a 24 mm wide tubular reactor «,

Figure 12 shows the contents of di, tri- and carbon tetrachloride in Outgassing when using monochloromethane.

Figure 13 shows that when preparing dichloromethane from monochloromethane significantly less trichloromethane is obtained than with optimal operation of the loop reactor during production of dichloromethane.

209886/1347

example 1

Methane and chlorine are mixed and fed into a reaction tube made of pure nickel at a mixed temperature of 28 ° C. The reaction tube is a total of 12 m long and 24 mm wide. The first 8.2 jn are jacketed and are mixed in countercurrent to the single gas temperature controlled with fast flowing liquid heat transfer medium (mixture of isomeric dibenzylbenzenes).

For example, for 3 different operating states A, B and C, the chlorination output is shown in each case by the temperature, concentration and chlorine quantity profiles plotted over the length of the reactor (FIGS. 1 to 9). The analytically determined concentrations are shown as mole bridges m / m (i = 0 for 1 for CH ₃ Cl, 2 for CH ₂ Cl ₂ , 3 for CHCl ₃ , 4 for CCl ₄ ).

The operating states are indicated by the following reaction pressures, Single gas flows and temperatures of the heat transfer medium given:

209886/1347

CD CO CT>

Operating condition

Reaction pressure

ata

4.2

Methane use

raol / s

0.16238

0.15567

0.20511

Use of chlorine

mol / s

0.04736 0.04702

0.05665

Heat transfer media

Inlet temperature

304

299

294

Outlet temperatu

306

301

292

CO

CO

AH

Example 2

In a methanol esterification (1), Figure ΙΟ, 2211 kg / h of methanol are reacted with 3286 kg / h of HCl in monochloromethane. The monochloromethane coming from the methanol esterification (1) is dried in (2) and mixed with 5371 kg / h of chlorine in the gas mixer (3). The input gas, consisting of 13 976 kg / h CH ₃ Cl, 300 kg / h HCl and 5371 kg / h Cl ₂ has a temperature of 33 ° C and is fed into the reactor (4) via line (19) at 5 atmospheres. directed. The reactor exhaust gas at 340 ° passes through line (2O) into the gas cooler (5) is cooled here to 150 ° C. and then into the gas cooler (5) through line (21)

forwarded ο

the gas cooler (6> f via line (22) it is at 50 C a soot filter (7) in which 0.2 kg / h soot are separated and from there via line (23) to a gas dryer (8) (H ₂ SO ₄ , 96%) supplied. via line (24) the dried off gas enters the gas liquefaction plant (9) composed of capacitors (107, cooler (11) (-45 ⁰ C) and the absorption column (12). the from the capacitors ( 10) running condensate is passed through a cooler (11) and fed at the top of an absorption column (12). The residual gas is passed via line (25) into the absorption column (12). This is via pump (26) and line (27} Liquefied exhaust gas leaving the absorption column is conveyed into the first rectification column (13). In this column (13), 3139 kg / h of hydrogen chloride are separated off and passed via line (28) into the methanol esterification (1). In the second rectification column (14) the Unreacted monochloromethane is separated off and gel via line (29) into the gas mixer (3) expires. In the other rectifying columns 15, 16 and 17, the residual mixture is broken down into di- (5260 kg / h) tri- (611 kg / h) and carbon tetrachloride (40 kg / h). Reactor (4) and gas cooler (5) have a common or separate circuit (18) of the heat transfer medium ("diphyl" -eutectic mixture of diphenyl and diphenyl oxide). The sump boilers of the rectification columns or other consumers can be coupled to the diphyl circuit (18) (not shown). 45 kg / h of offgas leave the absorption column (12) via line (31). The exhaust gas mainly consists of nitrogen (nitrogen content of technically pure chlorine). Via line (30) is the

hardly volatile residue (3 kg / h), mainly C ₂ C1 ₆₎ of

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der'Rektisierungskolonne 17 withdrawn.

Example 3

A 816 kg CHoCl / h at 52 ° C. and flow into a mixer (3)

«J

7.8 ata and 385 kg Cl ₂ / h at 56 ° C. and 9.8 ata.

The gas mixture generated in this way flows through a 5 m long pipe, the hot water is heated to 50 C in the heat exchanger (4). At the inlet of the heat exchanger (4) the gas pressure is 7.0 ata, am Output 6.0 ata. It consists of 21 sections, each 3 m long, which are arranged in 7 levels of 3 sections each with the help of 6 elbows are arranged. The sections and elbows each contain 7 tubes made of pure nickel with a clear width of 24 mm and a wall thickness of 3 mm. the 7 tubes are arranged in hexagonal symmetry parallel at the same distance from each other with the help of 2 tube sheets, which correspond accordingly are drilled and welded. The nickel tubes are close to the flanges of the tube sheet with 125 mm wide cladding tubes Surrounded by heat-resistant steel. While the nickel flanges the sections and bends are screwed flush and tightly together with respect to the individual nickel tubes, are the cladding tubes also connected in series, with the help of suitable pipe bends. The gas flows through the nickel tubes and through the cladding tubes of the top 5 floors in the opposite direction to the gas the heat transfer medium (= mixture of isomeric dibenzylbenzenes). Through the Cladding tubes of the lower 2 floors flows in cocurrent cooling water.

The nickel flanges are not like that in the main reaction area Cladding tubes are thermally insulated, but air-cooled. The heat transfer fluid is circulated by a centrifugal pump

promoted, which circulates approx. 50 m / h at 5 atmospheric pressure. The oil temperature at the entrance (at the end of the 5th floor from above) is 328 ° C, at the exit (at the beginning of the 1st floor) 335 ° C. These temperatures are constant at - 0.5 ° C through control with the heat consumer.

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The gas temperatures in the center of the axis of the nickel tubes are plotted in FIG. 11 as a function of the length of the nickel tube passed. You are stationary.

The cooling water is regulated so that the gas having a temperature of 60 ⁰ C leaving the heat exchanger (4). It only contains 0.02% by volume of unconverted chlorine gas.

In the case of this example, the heat exchanger (4) takes over at the same time the functions of the cooler (5) and (6) shown in Figure 10.

The 60 C hot gas flow passes through 2 parallel-connected bag fil-

2
ter (7) each 0.6 m surface (10 cm 0, ISO cm high) made of thick polytetrafluoroethylene material. In the filters the soot becomes completely with a pressure drop of 325 mm water column and one

-5

Trapped amount of 4 x 10 g soot / g of chlorine fed in. The soot is removed from the filters via bottom slides. Specifically, it is so heavy that it is deposited on the bottom of the filter vessel without any particular hatred.
The analysis of the outgassing is in vol.%:

HCl 26

52
20th
2.2 0.2 0.02 Inerts (N ₃ ) '0.03

The chlorine conversion is better than 99.9%.

When starting the heat transfer fluid with an electric Heater heated to 320 ° C. Then the monochloromethane stream employed.

The chlorine content of the gas and also the pressure, the flow rate and the temperature of the heat transfer medium varies, the use of monochloromethane results in the contents of the reactor exhaust gas plotted in FIG. 12 of di-, tri- and carbon tetrachloride. From the curves entered the yield of trichloromethane shown in FIG. 13 results. For comparison, 2 working points of the loop

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CH ₃ Cl 4th CH ₂ ^C1 2 CHCI3 CCl ^C1 2

reactor registered, namely for methane use with monochloromethane recirculation and for maximum possible monochloromethane admixture.

The achievable chlorine conversion increases with the regulated temperature of the heat transfer fluid and with the initial chlorine concentration. For example, with an input gas of 27 vol.% Cl ₀ plus 73 vol.% CH _Q C1 and a temperature of the heat transfer fluid of 340 C 99.99%, at 335 ° C 99.9%, at 330 ° C 99.5 %. According to the invention, it is always possible to achieve such a low residual chlorine content that no special measures are required for separating off residual chlorine.

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Claims (10)

Patent claims: (1. \ Process for the production of chloromethanes by thermal ^ - Chlorination, characterized in that chlorine with CH Cl with η = 1 to 4 and m = 4-η and optionally inert gas and / or mixes hydrogen chloride in gaseous form under pressure of 2 up to 25 ata in such a proportion that the volume fraction of the chlorine in the total gas mixture 10% to 50% and the sum of the proportions by volume of the chlorinable components based on at least 14% is that this reactor gas mixture is in a slim tube at a flow rate at least 3 m / s by means of a heat transfer medium with a temperature of 270 to 400 ° C flowing around the pipe, whose highest and lowest temperature within the circulation differ by no more than 40 ° C, warms up and for Bringing reaction, maintaining a gas temperature peak of 330 ° C. to 600 ° C. and leaving the reactor Gas mixture feeds a processing and separation plant. 2. The method according to claim 1, characterized in that one in a processing and separation plant in the chlorination resulting products and that with the reactive components introduced inert gas is separated from the reactor exhaust gas and the remaining mixture is reused in the same or a different chlorination reactor. 3. The method according to claim 1, characterized in that several chlorination steps, each initiated by adding chlorine be carried out in the same reactor or in different reactors in succession, without any between the chlorination steps cooling below 270 ° C processing or separation system are required. cooling steps' cooling to below 270 C and a work-up 4. Process according to claims 1-3, characterized in that the sum of the volume fractions in the reactor gas mixture Methane, hydrogen chloride and inert gas is less than 15%. 209886/1347 5. The method according to claim 4, characterized in that the reactor exhaust gas through before its decomposition in the separation plant One or more stage condensation to more than 90 wt.% Liquefied will. 6. The method according to claim 5, characterized in that from separated from the liquefied mixture (s) of hydrogen chloride and in a methanol esterification plant with methanol to form monochloromethane is implemented. 7. The method according to claim 6, characterized in that the monochloromethane produced in the methanol esterification plant in the Chlorination reactor is used and that apart from chlorine and methanol, no further raw material is fed to the process. 8. The method according to claims 1 to 7, characterized in that the mixture is prepared at temperatures below 100 ⁰ C. 9. Process according to Claims 1 to 8, characterized in that the chlorination reaction takes place in several parallel tube bundles combined pipes is carried out. 10. The method according to claims 1-9, characterized in that the heat transfer medium is completely or partially evaporated on the outside of the tube. 6/1347 IO Blank page