JPS601289B2 - Continuous production method for O- and P-chlorotoluene - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Very little is known about the results of tests on o- and p-chlorotoluene on an industrial scale.

It is known that o- and p-chlorotoleso can be prepared by the reaction of toluene and chlorine, and various catalysts for this nuclear chlorination reaction, such as iron halides, have also been described. Further addition of sulfur or inorganic and organic sulfur compounds
It serves to influence the o- and p-isomer ratio obtained during the chlorination of toluene. o-chlorotoluene in chlorination mixture
To increase the content, various metals such as Ti, T1
, Sn, Zr and W chlorides have also been used as catalysts. It is also known to chlorinate toluene in countercurrent flow, as well as chlorination at elevated temperatures (up to 150° C.) and in the presence of an aqueous phase.

All industrial processes known hitherto are essentially based on the application of discontinuous chlorination processes.

Namely, Hou 戊n-Weyl, Methoden der
CXganSchenChem, BdV/3 (19
62) According to 658, for example, toluene is mixed with chlorine for 15 to 2
During chlorination at 500 °C, a mixture of o- and p-chlorotoluene is obtained with a starting yield of about 76%. In this case, the crude product is preferably converted into a highly concentrated aqueous caustic soda solution (43%).
, which optionally makes it possible to dispense with separate drying of the chlorinated mixture before the subsequent fractional distillation (which would otherwise be necessary in industrial fractionation equipment to avoid corrosion). Furthermore, it is necessary to incubate the crude product under pressure with an alkaline solution in order to remove the chlorine bound to the side chains. Furthermore, according to BIOSFmaI Report No. 1145, the density is 1.06 at 30qo discontinuously.
However, this requires a reaction time of about 5 feed hours for 4 to 5 tons of feedstock.

After the chlorination reaction is complete, the reaction mixture is blown out with air to significantly remove dissolved hydrogen chloride. Moreover, in order to reduce the content of chlorine bound to the side chains, it is necessary to heat the crude product to 120 q0 with caustic soda solution in an autoclave for 2 hours before the fractional distillation of the isomers to chlorotoluene. However, this avoids resinification and corrosion damage of the product during distillation. In the case of continuously carried out toluene chlorination processes, the formation of side-chain chlorinated by-products also cannot be prevented (German Patent Application No. 154).
(See No. 3020).

The state of the art shows that an economically advantageous work-up of crude chlorotoluene to the pure isomer o- and p-chlorotoluene produced by known methods is suitable for the removal of hydrogen chloride from the crude chlorination mixture. The application of washing-and purification operations and the application of washing under pressure with an alkaline solution to remove side-chain bound chlorine cannot be achieved on an industrial scale. Thus, for example, isomer separation by fractional distillation can only be carried out in a carpenter's manner in the case of a crude chlorinated mixture prepurified in the above-mentioned manner; The initial distillate, which decomposes into a p-chlorotoluene-rich fraction from which the solid can be finally isolated, cannot be used again for chlorination. Uiiman
n,EmyklopadiederTechnSche
According to the description in nChemS, 3rd edition, volume 5, page 468, it is stated that it is difficult to separate isomers of chlorotoluene on an industrial scale.

The inventors have surprisingly discovered that toluene and chlorine in the presence of a catalyst form a by-product - the presence of which interferes with the subsequent work-up of the crude chlorination mixture to pure isomer chlorotoluene and its removal. The chlorinated mixture can be reacted continuously to chlortoluene without the formation of additional washing-and purification operations and/or boiling under pressure with aqueous alkaline hydroxide. I discovered that.

Therefore, the subject of the present invention is a method for continuously producing o- and p-chlorotoluene by nuclear chlorination of toluene with chlorine in the presence of a catalyst, in which toluene and chlorine are combined in a molar ratio of chlorine to toluene of 0.4. ~1. 5 at 0.6 to 0.9
The reaction is carried out at a temperature of from 70°C to 70°C, preferably from 15 to 40°C, in the presence of at least one catalyst and with vigorous mixing in a reaction chamber in cocurrent flow, and after the reaction is completed, the chlorinated mixture is distilled to remove hydrogen chloride and unreacted toluene. The above production method is characterized in that the bottom product obtained by distillation is immediately separated into isomers o- and p-chlorotoluene. The catalyst used is a nuclear chlorination catalyst commonly used in the chlorination of toluene.

Catalysts are likewise used which serve to influence the isomer ratio of the chlorotoluene formed during the chlorination reaction. Combinations of these catalysts may also be used. Thus, for example, metal halides are used. In particular iron halides and especially iron chloride are used. These can be added, for example, directly to the reaction mixture or already mixed into the toluene. In order to further increase the p-isomer content, for example, sulfur or sulfur compounds can be used, sulfur chlorides being preferred as cocatalysts, especially in combination with iron chloride catalysts. When using catalysts in combination, the components can be added individually or in mixtures. The amount of catalyst and cocatalyst used in the process according to the invention is generally from about 5 to about 100 ppm, preferably from 10 to 40 ppm, especially from 15 to 30 ppm, based on the toluene used.

The o-/p-chlorotoluene ratios achievable according to the present invention can vary within a conventional range, for example from about 2:1 to about 1:1. A particularly preferred variant of the process according to the invention consists in producing the iron chloride catalyst directly in the reaction mixture in situ, in particular in the reaction chamber, continuously as consumed from the iron and the components of the reaction mixture. This can be achieved in a simple manner by the presence of metallic iron in the reaction mixture, for example by the use of iron walls in the reactor forming the reaction castle and/or the use of iron packings, in particular in the reaction mixture. It can be carried out under the condition that the moisture content is kept at very low values, which makes it possible to avoid corrosion and too high iron chloride formations, which can be a hindrance during the work-up of the chlorinated mixture. According to the present invention, the required low water content in the reaction mixture is reduced to the extent that other moisture factors are present, and the water content of toluene used in the chlorination can be reduced up to 0.0.
Not more than 3% by weight, preferably 0.001 to 0.0
25 and especially by keeping 0.01 to 0.02% by weight. Technical toluene generally contains varying amounts of moisture, generally about 0.05 to 0.07% by weight, and the solubility of water in toluene is already present in the temperature range according to the invention of the chlorination reaction. Because of the low water content required by the invention and which further increases as the temperature increases, it is advantageous to dry the toluene appropriately before use in the chlorination.

Such drying can be carried out, for example, with dehydrating salts or, in particular, with dry hydrogen chloride gas, such as is obtained as a by-product in the chlorination reaction. In the case of continuous toluene chlorination, the hydrogen chloride obtained continuously according to the invention during the work-up of the chlorination mixture is used directly for toluene drying, the toluene and the dry hydrogen chloride gas preferably being co-flowed. Strong contact is made with each other and dry toluene, the water content of which corresponds to the requirements according to the invention, is obtained. In this case, any water present in the crude toluene together with hydrogen chloride forms hydrochloric acid, which is separated off or separated off with excess hydrogen chloride gas. The latter can then be converted into salable concentrated technical hydrochloric acid, for example by adiabatic absorption with water.
The drying of the toluene and the separation of the crude reaction mixture free of hydrogen chloride and unreacted toluene are optionally also carried out batchwise.

However, in both cases preference is given to carrying out the process steps described above sequentially. The process according to the invention may be explained, for example, on the basis of a diagram as follows: crude toluene is
via line 1 to a toluene dryer 2, into which dry hydrogen chloride gas (which may be loaded with toluene vapor) flows via line 3; Hydrogen chloride binds the water optionally contained in the crude toluene.

Dry toluene (its moisture content max. 0.0) is added via conduit 4.
3 wt. and the chlorine is metered in at the same time in the gaseous state, resulting in intensive mixing of the reaction mixture. In the chlorinator, toluene and chlorine react in the temperature range according to the invention in the presence of the catalyst used, in particular iron chloride (m) and optionally a cocatalyst, with the formation of crude chlorotoluene and hydrogen chloride, with the chlorine actually reacting. Since the reaction is quantitative, the reaction mixture does not contain any free chlorine as soon as the reaction mixture is removed. The heat of reaction can be removed by appropriate cooling in the chlorinator and/or by evaporation of the toluene.

Reaction temperatures above 70 qo are possible as well, but do not offer any benefits.

This is because such temperatures can promote the formation of undesirable by-products. Temperatures below 5° C. are also conceivable, but then the reaction rate is very low.

The catalyst and/or cocatalyst are optionally metered into the chlorinator via line 7.

In a preferred embodiment of the process according to the invention using iron chloride as catalyst, the catalyst is not metered in as is, but is produced continuously in situ from the iron and the components of the reaction mixture directly in the chlorinator. . The iron required for this is charged, for example, in the form of Raschig rings or iron wire spirals or in the form of thin steel sheets at a slackening/filling rate in a chlorinator, in which it is gradually
eC3 and continuously provide the necessary nuclear chlorination catalyst. The iron content, as absorbed by the reaction mixture under the production of iron chloride, for example from iron Raschig rings charged in a chlorinator, can amount to, for example, about 15 to 20 ppm.
The iron content can optionally be supplemented by addition of a cocatalyst, for example S2C. The sulfur content in the reaction mixture obtained from S2CI2 can be, for example, about 15 to 20 ppm. In the simplest case, the chlorinator 5 can consist of a flow tube with a cooling device.

However, in industrial installations it is preferable to use double jacket reactors which resemble columns. Suitable corrosion-resistant materials in the chlorinator include in particular standard chains such as St 35 or boiler plate H.
I can be used. In this case, it is often advantageous to coat the walls of the reactor in certain areas of the iron filling with other corrosion-resistant materials. Since effective removal of the heat of reaction is important for maintaining the reaction temperature according to the invention, the required residence time of the reaction mixture in the chlorinator can be significantly influenced by the type of heat removal. In the case of industrial chlorination with jacket cooling, the residence time is, for example, up to 1 hour in the 10th reactor, in particular from 8 to 1 hour. After the reaction is completed, the crude chlorinated mixture and the generated hydrogen chloride gas are passed through a conduit 8 to a distillation column 9.
is reached, in which the toluene remaining unchlorinated in the column is distilled off via the top 10 together with the HC oil gas, and in the bottom the crude chlorotoluene containing any by-products and dissolved catalyst components is distilled off. is removed via line volume 8 and fed to vacuum column 12. The top product from the distillation column 9 is condensed in a condenser 13, optionally in various stages, and some of the toluene is returned to the distillation section 9 via line 14 or toluene is dried together with the HC cogas via line 3. Vessel 2
, where the HC sour gas is used in the manner described to dry the crude toluene, then passes via conduit 15 to absorber 16 and is converted to salable hydrochloric acid 18 by adiabatic absorption with water 17 . The gaseous water/toluene mixture leaving the absorption column 16 via the top is condensed in a heat exchanger 19, the condensed component is separated in a separator 20 and the separated toluene is transferred to a toluene dryer 2, the water is absorbed Return to container 16. In the vacuum column 12 the isomeric chlorotoluene mixture is isolated from the bottom product of the distillation column 9, the high-boiling and solid residues being taken off as bottom product via line 21;
The p-chlorotoluene is optionally liquefied in a condenser 22 and/or optionally also intermediately condensed and introduced into a vacuum fractionation column 23 from the bottom of which p-chlorotoluene 2
4 and at the top via a condenser 25 o-chlorotoluene 26 can be taken off. Separation and complete purification of p-chlorotoluene can also be carried out by crystallization. The pressure at which the chlorination reaction according to the invention is carried out is not critical per se.

However, atmospheric pressure is particularly preferred. Higher or lower pressures are possible, but generally do not provide benefits. Advantageously, the pressure is selected such that at the reaction temperature maintained, chlorine is present in gaseous form. As already mentioned above, the chlorine in the chlorination mixture used according to the invention reacts virtually quantitatively.

In this case, the yield of monochlorotoluene is significantly higher relative to the chlorine used. If the chlorine:toluene molar ratio and/or the reaction temperature are respectively selected within the ranges below according to the invention, virtually no dichlorotoluene will be formed and an almost theoretical amount of monochlorotoluene will be produced relative to the chlorine used. is generated. Moreover, surprisingly low amounts of catalyst are required according to the present method. Therefore, the present invention provides for the first time excellent quality o- and p-
- makes it possible to produce chlorotoluene industrially in a surprisingly simple manner and continuously with very good yields. The high economy and the undoubtedly significant industrial inventiveness of the continuous process according to the invention are due inter alia to the purification steps required before separation of the crude chlorination mixture in the known process, such as the removal of any unreacted chlorine. , washing out hydrogen chloride, removing unstable side chain chlorine by boiling with alkaline IJ liquid, drying the crude product with a solid desiccant before fractional distillation, and in some cases necessary for corrosion reasons. It is clear that the selection of materials for the chlorinator, which is costly (e.g., Nucleically chlorinated monochlorotoluene is used partly as a solvent and partly as a starting material or intermediate for the production of, for example, plant protection agents.

Example chlorination, corresponding to the schematic diagram, height approximately &m and diameter approximately 1
．． Industrial chlorination equipment with a 4 m cylindrical reactor 5, which is filled with an approximately 5-force cylindrical steel hollow body (approximately 35 ribs long, 35 sides small and 1 side thick) toluene and chlorine gases are continuously fed into the reactor and the crude reaction product leaves the reactor via line 8 in proportion to the feed of starting product.

Toluene (water content <0.03% by weight) 13.6 in the reactor
6 tons/day, 286 gallons of chlorine gas/day and S2C〆2 approx. 7
Feed 0 females/day. The temperature in the reactor is approximately 303°. The amount of chlorine supplied was about 8 stoichiometrically required.
It is 0%. The residence time of the reaction mixture in the reactor is approximately 1 hour. The liquid crude reaction product which can be discharged from the reactor is 17.7 kg/day of unreacted toluene and 15.7 kg/day of crude chlorotoluene. From enemy/day, and furthermore HC〆286
Gade/day is generated.

Chlortoluene, a compound capable of removing hydrogen chloride and reactive toluene, has the following composition (in weight percent): o-chlorotoluene 49. Town weight % m - chlorotoluene <0. awt% P-chlorotoluene 48. Weight% of penzyl chloride
0% by weight dichlorotoluene
2. Analytical measurements of the weight percentage of the product were carried out by gas chromatography, and yield measurements were carried out by weighing.

The overall yield of o- and p-chlorotoluene is greater than 97% of theory, based on the reacted toluene.

The supplied chlorine reacts practically quantitatively.

[Brief explanation of the drawing]

The drawings systematically illustrate the method of the invention.

Claims (1)

[Claims] 1. A method for continuously producing o- and p-chlorotoluene by chlorinating toluene with chlorine in the presence of a catalyst,
Toluene and chlorine are mixed in a chlorine to toluene molar ratio of 0.4 to 1.0, preferably 0.6 to 0.9, at a temperature of 5 to 70°C, preferably 15 to 40°C, in the presence of at least one catalyst. After the end of the reaction, the chlorinated mixture is distilled to remove hydrogen chloride and unreacted toluene, and the bottom product obtained by distillation is immediately converted to the isomeric o- and p-chloride. The above manufacturing method is characterized by separation into toluene. 2. Catalyst: 5 to 100 ppm based on toluene used
The method according to claim 1, preferably used in an amount of 15 to 30 ppm. 3. The manufacturing method according to claim 1 or 2, which uses iron chloride as a catalyst. 4. The manufacturing method according to claim 1 or 2, which uses iron chloride and sulfur chloride as catalysts. 5. A process according to any of claims 1 to 4, wherein iron chloride is produced in the reaction zone during chlorination. 6. According to claims 1 to 5, the water content of the toluene does not exceed a maximum of 0.03% by weight, preferably 0.001 to 0.025% by weight, especially 0.01 to 0.02% by weight. Any manufacturing method described. 7. The manufacturing method according to any one of claims 1 to 6, wherein gaseous hydrogen chloride produced during chlorination is used for drying toluene. 8. The production method according to any one of claims 1 to 7, in which unreacted toluene is returned to chlorination. 9 Claim 1 in which the chlorination is carried out under atmospheric pressure
The manufacturing method according to any one of Items 8 to 8.