JPS6252729B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides 1,1,2-trichloroethane (hereinafter referred to as
vinylidene chloride (hereinafter referred to as VDM) than vinylidene chloride (hereinafter referred to as VDM)
It relates to a method of manufacturing (referred to as
This invention relates to an industrially advantageous method for producing VDM by dehydrochlorinating TCE in an alkaline aqueous solution.

VDM is an extremely useful substance as an intermediate raw material for methyl chloroform, which is used as an organic solvent, and as a raw material for vinylidene chloride resin. Industrially, TCE is first produced using ethylene or vinyl chloride and chlorine as raw materials, and then VDM is produced by contacting it with an alkali such as milk of lime to perform a dehydrochlorination reaction. This dehydrochlorination reaction is generally carried out with an alkali, and other methods have been proposed, such as thermal decomposition or catalytic decomposition in the gas phase, but both have low VDM selectivity and are not practical. In the method considered to be most suitable for selectively obtaining VDM, that is, the method of dehydrochlorination using an aqueous calcium hydroxide solution, the released hydrogen chloride is converted into chloride, which is a neutralized product with calcium hydroxide. Since it is discharged as calcium, it not only causes a loss of chlorine content, but there is also concern that it may cause pollution problems due to its release into the environment.

A method using a caustic soda solution as an alkali instead of calcium hydroxide has been proposed (for example, German Published Patent Application No. 2225512). However, to date, the method using caustic soda has not been practically adopted. One of the reasons for this is that when a caustic soda solution is used, particularly when a concentrated caustic soda solution is used, the generated VDM further undergoes a dehydrochlorination reaction to form monochloroacetylene (hereinafter referred to as MCA). This MCA has the risk of spontaneous combustion, and it is necessary to prevent its formation as much as possible in the process.

Taking the above points into consideration, the present inventors conducted intensive research on a method for dehydrochlorinating TCE with an alkaline aqueous solution to obtain VDM, and in particular on a method of dehydrochlorinating using a caustic alkaline aqueous solution.
The present invention was completed based on the finding that the MCA production reaction in the dehydrochlorination reaction of TCE can be effectively suppressed by using an aqueous caustic alkali solution containing an alkali halide. This was generated in an aqueous system where alkali halides were present.
This is presumed to be because the dissolution of VDM is reduced and it can be quickly discharged from the system after the reaction, and as a result, VDM is further inhibited from causing a dehydrochlorination reaction with caustic alkali and producing MCA. be done. Therefore, it is desirable that the content of the alkali halide in the caustic alkali aqueous solution be at or near the saturated solubility.

The most suitable alkali halide-containing aqueous caustic alkali solution in the present invention is particularly an electrolytically generated solution obtained by electrolyzing a saline solution using a diaphragm method.

The saline electrolyte for the diaphragm method usually uses sodium hydroxide.
120-130g/, sodium chloride 160-170g/
To obtain caustic soda from this, the electrolytic solution is evaporated and concentrated to precipitate sodium chloride, resulting in a concentrated caustic soda solution, which requires extremely high production costs. Therefore, the electrolytic solution is cheaper and industrially advantageous than using purified caustic soda and separated common salt. Moreover, the advantage of this electrolytic solution is that in addition to suppressing the formation of MCA during dehydrochloric acid reaction, when using TCE to purify the sodium chloride-containing solution after dehydrochloric acid and use it for electrolytic reaction,
The purpose is that the liquid can be purified easily and economically.
In other words, in the aqueous solution after the dehydrochloric acid reaction, sodium chloride exists at a concentration close to the saturated solubility, so the solubility of TCE and the generated VDM becomes extremely low, and it is necessary to purify the aqueous solution containing sodium chloride after the reaction. For example, when purifying dissolved organic chlorides by steam distillation, the amount to be distilled out is small, the operation is easy, the amount of energy used is small, and the purification is economical. It lies in what we can supply.

Conditions for the dehydrochlorination reaction in the present invention, e.g.
The molar ratio of TCE and caustic alkali, reaction temperature, reaction operation, etc. are the same as in the conventional method using an aqueous caustic alkali solution.

As described above, the method of the present invention can advantageously produce VDM while suppressing the generation of MCA, and the method using a diaphragm method saline electrolyte can effectively utilize the salt produced by the dehydrochlorination reaction. Compared to the conventional dehydrochlorination method using an aqueous calcium hydroxide solution,
It is an extremely useful process.

Example Ratschchilling packed tower (10mm diameter, 300mm height)
125 g of caustic soda and 160 g of sodium chloride were added to a 1 liter glass reactor connected to the top of the reactor.
500ml of diaphragm saline electrolyte containing g/1,1,
300 g of 2-trichloroethane was charged, and while the reaction temperature was maintained at 75°C and a small amount of nitrogen gas was supplied to the top of the reactor, the diaphragm electrolyte was mixed at 623 ml/Hr., 1,1 while stirring at 400 rpm. , 2-trichloroethane was continuously supplied at a rate of 388 g/Hr.
A time reaction was performed. The liquid level in the reactor was kept constant by an overflow pipe provided in the reactor, and unreacted trichloroethane was obtained as an overflow liquid at a rate of 146 g/Hr., and an aqueous solution containing common salt was obtained at a rate of 675 mL/Hr. In addition, vinylidene chloride distilled through a packed column at the top of the reactor was collected at a rate of about 160 g/hr. by cooling and collection. During this period, the exhaust gas, which was mainly composed of nitrogen gas, was cooled and analyzed, and it was found that the amount of monochloroacetylene discharged along with the gas was extremely small at 1 to 2 mg/Hr.
The overflowing aqueous solution was cloudy because it contained a trace amount of organic matter, but as a result of distilling off 3% of the total by heating, the remainder became clear and colorless. When this liquid was analyzed, organic chlorides such as trichloroethane and vinylidene chloride were not detected, and 7 g of caustic soda/
The solubility of sodium chloride was 300g/, which is close to the saturated solubility.

Claims (1)

[Claims] 1. When producing vinylidene chloride by contacting 1,1,2-trichloroethane with an alkaline aqueous solution to perform a dehydrochlorination reaction, a caustic alkali aqueous solution containing an alkali halide is used as the alkaline aqueous solution in the dehydrochlorination reaction. A method for producing vinylidene chloride, characterized in that it is used from the beginning.