JPS5825648B2 - Teikiyutankasuisonoen sokahouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the chlorination of lower hydrocarbons and/or partially halogenated lower hydrocarbons, and particularly to chlorination using chlorine obtained by diaphragm electrolysis as a raw material.

It is widely practiced to produce chlorinated hydrocarbons by chlorinating lower hydrocarbons and/or partially halogenated lower hydrocarbons such as methane, methyl chloride, ethane, ethylene, and propylene with chlorine.

Chlorination includes thermal chlorination, photochlorination, addition chlorination in the presence of a catalyst, and oxychlorination, and oxychlorination uses hydrogen chloride as a chlorinating agent.

Selective production of low chlorinated products when chlorinating lower hydrocarbons and/or partially halogenated lower hydrocarbons using chlorine as a chlorinating agent, especially when producing lower chlorinated lower hydrocarbons using lower hydrocarbons as raw materials. For this purpose, hydrocarbons are usually supplied in a considerable excess of the stoichiometric amount relative to chlorine.

As a result, the reaction rate of hydrocarbons in one pass naturally decreases, so in order to increase the utilization rate of hydrocarbons, a method is adopted in which unreacted hydrocarbons are recycled.

At this time, some of the unreacted hydrocarbons are purged out of the system, but this is to avoid a reduction in the reaction rate and the risk of explosion due to the accumulation of inert contained in the raw material in the system. It is controlled by the amount of inert contained, especially by the oxygen concentration.

On the other hand, conventionally most of the chlorine was obtained by mercury electrolysis.

However, mercury electrolysis has become difficult to use due to pollution problems, and is being replaced by diaphragm electrolysis.

Furthermore, an ion exchange membrane electrolysis method has also been developed in which the amount of sodium chloride in sodium hydroxide is smaller than that of the diaphragm electrolysis method.

Chlorine obtained by this diaphragm electrolysis or ion exchange membrane electrolysis contains a large amount of oxygen compared to conventional mercury electrolysis.

The concentration of oxygen in chlorine obtained by mercury electrolysis is approximately 0.1
The amount of chlorine contained is approximately 0.2% by volume, but chlorine obtained by diaphragm electrolysis or ion exchange membrane electrolysis contains approximately 0.5 to 5% by volume, usually approximately 2% by volume.

This is thought to be due to the influence of the pH of the salt water during electrolysis, the material of the electrodes, and the structure of the electrolytic cell.

When chlorinating lower hydrocarbons using chlorine with a high oxygen content, the oxygen gas concentration in the recycled lower hydrocarbons increases, and the purge amount must be increased to maintain the same oxygen concentration as before. , this is a large loss of lower hydrocarbons.

For example, the oxygen concentration in chlorine by conventional mercury electrolysis is approximately 0.
．． 2% by volume, but in diaphragm electrolysis, it is approximately 2% by volume, so the purge amount of lower hydrocarbons must be approximately 10 times the conventional amount.

Therefore, a large amount of lower hydrocarbons must be disposed of, resulting in a large loss of raw materials.

Possible countermeasures to this problem include liquefying chlorine to remove oxygen and using it as chlorine with low oxygen content, and separating purge gas by cryogenic separation to recover unreacted hydrocarbons. At present, it is difficult to adopt the method due to the high cost of liquefied bone, and the high equipment cost of the cryogenic separation method.

The present inventor has researched and considered various methods for avoiding the accumulation of oxygen contained in chlorine in the chlorination of lower hydrocarbons and/or partially halogenated hydrocarbons.

As a result, it was found that the most economical method is to directly treat the reaction gas discharged from the chlorination process, which contains less than 5% by volume of oxygen, especially about 1 to 4% by volume, to remove oxygen. Ta.

Oxychlorination is known as this direct treatment method, but
This method has conventionally been applied as a method for producing chlorinated hydrocarbons in an oxygen concentration range of 10 to 20% by volume.

The present inventor has determined that the oxychlorination reaction is carried out at an oxygen concentration of 1 to 4% by volume.
The present invention was achieved by confirming that the method can be applied even in the low concentration region.

That is, the present invention involves a chlorination reaction including substitutional chlorination using lower hydrocarbons and/or partially halogenated lower hydrocarbons and chlorine with an oxygen content of 5% by volume or less obtained by diaphragm electrolysis or ion exchange membrane electrolysis as raw materials. In a method for producing a chlorinated hydrocarbon, (1) the lower hydrocarbon and/or the partially chlorinated hydrocarbon, the chlorine, and the recycled gas are subjected to a chlorination reaction including substitution chlorination in the first reaction step. (2) separating the chlorinated hydrocarbons from the first-stage reaction gas discharged from the first-stage reaction step, or performing the first reaction without introducing oxygen into the first-stage reaction gas; (3) performing an oxychlorination reaction in the presence of a catalyst in the second reaction step; (4) a second reaction gas discharged from the second reaction step; Separates most of the chlorinated hydrocarbons and hydrogen chloride from
This method of chlorinating hydrocarbons is characterized in that the recycled gas containing remaining unreacted lower hydrocarbons and/or partially halogenated hydrocarbons as main components is sent to the first reaction step.

According to the present invention, since the oxygen in the inert is consumed in the second stage oxychlorination step, the amount of oxygen in the system can always be kept below a certain amount.

Therefore, the amount of purge can be reduced and the loss of raw materials can be reduced.

FIG. 1 shows an example of a process diagram of the present invention when methane is used as the lower hydrocarbon.

In the first reaction step A, thermal chlorination or photochlorination is performed using methane a, chlorine gas containing 5% by volume or less of oxygen, and recycled gas i as raw materials.

The second stage reaction gas CK is CH) cc14 x ( such as methyl chloride, methylene chloride, chloroform, carbon tetrachloride, etc.
Chlorinated methane, hydrogen chloride, oxygen and small amounts of unreacted chlorine and by-products are present.

Oxychlorination is carried out in the first reaction step B without introducing oxygen into the first reaction step C.

Since the purpose of oxychlorination is to remove oxygen from the system, oxygen is not particularly supplied from outside the system.

The reaction produces methane chloride using hydrogen chloride, oxygen and unreacted methane, methyl chloride or methylene chloride.

The first stage reaction gas d is then introduced into the absorption tower C and brought into contact with water g.

Hydrochloric acid f is taken out from the lower part of the absorption column C, and a reaction gas mixture e from which most of the hydrogen chloride has been removed is taken out from the upper part.

This reaction gas mixture is separated by a separator into a chlorinated methane mixture and a recycle gas i mainly composed of methane and containing oxygen, and the recycle gas i is sent to the first reaction step A.

As described above, the main focus of the present invention is to perform oxychlorination at a low oxygen concentration following thermal chlorination or photochlorination to consume oxygen and reduce the concentration of oxygen circulating within the system. be.

Therefore, no oxygen other than the oxygen contained in chlorine is introduced into the system.

In the chlorination of hydrocarbons, it is known that the utilization rate of chlorine is increased by conventionally performing oxychlorination following thermal chlorination and using hydrogen chloride produced by the thermal chlorination as a chlorinating agent.

However, in this case, oxygen was always introduced before oxychlorination, and oxychlorination was carried out under a high oxygen concentration.

In the present invention, although a small amount of hydrogen chloride is consumed in the oxychlorination reaction, most of the hydrogen chloride is recovered with hydrochloric acid.

The oxychlorination reaction in the present invention is carried out in the presence of hydrogen chloride.

Therefore, the thermal chlorination or photochlorination in the first reaction step must include a substitution reaction.

That is, chlorination requires a reaction that produces chlorinated hydrocarbons and hydrogen chloride, and a portion of this hydrogen chloride is used as a chlorine agent for oxychlorination in the second reaction step.

Therefore, in the first stage chlorination reaction, a chlorination reaction producing hydrogen chloride, that is, a combination reaction of substitutional chlorination or reactions resulting in substitutional chlorination is performed.

The latter is a combination of two reactions, for example, when chlorine is added to ethylene to produce EDC, and EDC is decomposed to produce vinyl chloride and hydrogen chloride, and as a result, it is considered to be a chlorination reaction of ethylene. It is something that can be done.

Of course, not only the substitutional chlorination reaction but also a combination of two chlorination reactions can be carried out, such as when the substitutional chlorination reaction and the addition chlorination reaction are carried out simultaneously or sequentially.

Further, as the substitutional chlorination reaction, thermal chlorination is most preferable in terms of yield, equipment scale, operating conditions, cost, etc.

The raw material lower hydrocarbons may be aliphatic, alicyclic, aromatic, etc. hydrocarbons that can be normally chlorinated by thermal chlorination, photochlorination or oxychlorination, but preferably,
Aliphatic hydrocarbons having 6 or less carbon atoms, particularly aliphatic hydrocarbons having 3 or less carbon atoms, are suitable.

For example, saturated or unsaturated aliphatic hydrocarbons such as methane, ethane, propane, ethylene, propylene.

Furthermore, it can also be applied to the chlorination of partially halogenated lower hydrocarbons as raw materials, particularly aliphatic hydrocarbons having 3 or less carbon atoms containing 1 or 2 chlorines.

For example, methyl chloride, ethyl chloride, etc. can be used as raw materials, and these can also be used in combination with non-halogenated lower hydrocarbons.

Furthermore, the present invention is most suitable for carrying out chlorination while circulating a relatively large amount of unreacted lower hydrocarbons. It can be most advantageously used in the manufacturing method.

Oxychlorination is carried out in the second reaction step.

This oxychlorine reaction is carried out under low oxygen concentrations and produces small amounts of chlorinated hydrocarbons.

The oxygen concentration in the first stage reaction gas introduced into the oxychlorination step is 10% by volume or less, particularly usually 5% by volume or less.

The reaction temperature is 200-600°C, especially 250-500°C,
The reaction is carried out in a fluidized bed type or fixed bed type catalytic reaction apparatus with a contact time of 0.1 to 20 seconds, particularly 1 to 10 seconds.

Since the oxychlorination reaction in the present invention has a low oxygen concentration, the heat of reaction is small, so operation in an adiabatic system is also possible, and a fixed bed type catalytic reaction apparatus is preferable from the viewpoint of operation and handling.

Various oxychlorination catalysts can be used as catalysts.
For example, metal chlorides such as copper chloride, iron chloride, zinc chloride, or combinations thereof, or combinations thereof with alkali metal chlorides or alkaline earth metal chlorides can be used.

In particular, a combination of copper chloride and an alkali metal chloride is preferred.

These catalysts can be used with or without being supported on a carrier.

When supporting on a carrier, various carriers can be used, but in particular, silica-based carriers with a surface area of 10rrl/gr or more,
Alumina-based or silica-alumina-based supports are preferred.

In the oxychlorination step, the conversion rate of oxygen is preferably 20% or more, particularly preferably 40% or more.

By selecting conditions such as the type of catalyst and carrier and the reaction temperature, it is possible to achieve a conversion rate of 70% or more.

Oxygen can be effectively removed.

Note that it is possible to remove some or all of the chlorinated hydrocarbons before introducing the first reaction gas into the second reaction step, but the chlorinated hydrocarbons may be removed as a diluent or Since it can be used as a part of the raw material, there will be no major hindrance to the reaction even if it is not particularly removed.

In the second stage reaction gas discharged from the second stage reaction process,
Contains chlorinated hydrocarbons, hydrogen chloride, unreacted lower hydrocarbons and small amounts of chlorine, oxygen and by-products.

Most of the chlorinated hydrocarbons and hydrogen chloride are separated from this reaction gas, and the recycled gas containing unreacted lower hydrocarbons as a main component is recycled to the first reaction step.

Further, part or all of the recycled gas is purged as necessary, but the amount of purging or the number of times of purging can be significantly reduced compared to the case where the second reaction step is not incorporated.

EXAMPLES Hereinafter, examples in which it was confirmed that the oxychlorination reaction proceeded sufficiently under low oxygen concentration will be described, and the present invention will be specifically explained.

Furthermore, the present invention is not limited only to these examples.

・Example 1 The oxychlorination reaction under low oxygen concentration was tested.

, the results are shown below. This test confirmed that in the presence of large amounts of hydrocarbons and hydrogen chloride, a sufficient oxychlorination reaction occurred with less than 5% by volume of oxygen.

A quartz reaction tube with an inner diameter of 25 mm was filled with 50 cc of a catalyst in which approximately 20% by weight of CuC12-KCI (Cu/to = 1.0 molar ratio) was supported on a γ-alumina carrier (5 mmφ helet) with a surface area of 80 m/gr. The mixture was heated externally in an electric furnace while passing N2 gas through it, and when a predetermined concentration was reached, the reaction gas was switched to, and the oxygen conversion rate was analyzed by gas chromatography.

Example 2 In the presence of the catalyst used in Example 1, a gas having the composition shown in the table below was passed at a reaction temperature of 350°C and a contact time of 3.6 seconds to cause a reaction. Even after 350 hours, the oxygen conversion rate was 70. ~90%
Met.

In addition, a quartz reaction tube (inner diameter 25 m1φ) was filled with 100 IrLl of catalyst supported on a commercially available silica-alumina carrier at a ratio of CuCl2:KC1=1=1 (molar ratio) of about 20% by weight, and heated to a predetermined temperature in an electric furnace. After heating, a gas having the composition shown below was passed through the reactor for a contact time of 4 seconds, and the oxygen conversion rate was analyzed by gas chromatography.

The results are shown below.

Example 3 Chlorination of methane was carried out according to the flow shown in FIG.

The first reaction step is thermal chlorination of methane in an open column reactor.
In the second reaction step, the fixed bed reactor packed with the catalyst used in Example 1 was used.

The reaction temperature of the first reactor is 400°C, and the second reactor is 380°C.
℃, contact time 4 seconds.

The amount and composition of gas at each stage is shown below.

In addition, in order to purge the recycled gas and maintain the oxygen concentration in the recycled gas at approximately 2.5%, it takes 101:/hr in the present invention, and 55 liters without the oxychlorination step.
/hr needed to be purged.

[Brief explanation of drawings]

Fig. 1 shows an example of the chlorination method of the present invention on a 70-sheet.After the raw material hydrocarbon a, chlorine gas and recycled gas i are subjected to a chlorination reaction in the first reaction step, the reaction mixture gas C is The oxychlorination reaction is carried out in the first stage reactor B.

Claims (1)

[Scope of Claims] 1. A chlorination reaction including substitutional chlorination using lower hydrocarbons and/or partially halogenated hydrocarbons and chlorine with an oxygen content of 5% by volume or less obtained by diaphragm electrolysis or ion exchange membrane electrolysis as raw materials. In a chlorination method for producing chlorinated hydrocarbons, (1) the lower hydrocarbons and/or partially halogenated hydrocarbons, the chlorine and the recycle gas are subjected to a chlorination reaction including substitution chlorination in the first reaction step. (2) separating chlorinated hydrocarbons from the first stage reaction gas discharged from the first stage reaction step, or without separating the chlorinated hydrocarbons, and without introducing oxygen into the first stage reaction gas; (3) performing an oxychlorination reaction in the presence of a catalyst in the second reaction step; (4) a second reaction discharged from the second reaction step; Separates most of the chlorinated hydrocarbons and hydrogen chloride from the gas,
A method for chlorinating lower hydrocarbons, which comprises sending a recycled gas containing remaining unreacted lower hydrocarbons and/or partially halogenated hydrocarbons to a first reaction step.