JPH07330327A - Production of ammonium chloride - Google Patents

Abstract

PURPOSE:To provide a method for producing ammonium chloride by which a response to the total abolition of chlorofluorocarbons that are targets of regulation can be made and the ammonium chloride of good quality can be produced without any danger such as a fire, e.g. ignition or explosion by cooling a solution for crystallizing the ammonium chloride in direct contact with a refrigerant such as 1,1,1,2-tetrafluoroethane or 1,1,2,2-tetrafluoroethane in the ammonium chloride-soda process. CONSTITUTION:In a process for producing ammonium chloride by which the ammonium chloride and sodium hydrogencarbonate are alternately and cyclically crystallized with sodium ammonium chloride and carbon dioxide in an aqueous medium, a solution for crystallizing the ammonium chloride is cooled by direct contact with a refrigerant such as 1,1,1,2-tetrafluoroethane. The refrigerant is introduced as fine liquid droplets thereinto by using a suitable nozzle from the vicinity of the lower base of a crystallization vessel filled with the solution for crystallizing the ammonium chloride. Thereby, crystals having 500-1000mum grain diameter are obtained in cooling the solution at 0-15 deg.C under about 2.4kg/ cm<2>G internal pressure of the crystallization vessel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ammonium chloride, and more particularly to a method for producing ammonium chloride by the so-called ammonium chloride soda method, in which ammonium chloride and sodium hydrogen carbonate are produced alternately.

[0002]

2. Description of the Related Art The sodium chloride soda method is a method in which sodium chloride, carbon dioxide, and ammonia are used as raw materials, and sodium hydrogencarbonate and ammonium chloride are alternately and cyclically precipitated from an aqueous solution. Specifically, carbon dioxide gas is introduced into the separated mother liquor of ammonium chloride to precipitate sodium hydrogen carbonate, and ammonia and sodium chloride are added to the separated mother liquor to precipitate ammonium chloride. The mother liquor after separating the precipitated ammonium chloride is circulated and used in the first step.

In the ammonium chloride precipitation step, for example, ammonia is first added to a sodium hydrogen carbonate separation mother liquor, and then cooled to precipitate a part of ammonium chloride, and the precipitated ammonium chloride is separated or not separated. Then, a method of further precipitating ammonium chloride by adding sodium chloride and utilizing the decrease in the solubility of ammonium chloride is adopted. Alternatively, a method in which ammonia and sodium chloride are added to a mother liquor for separating sodium hydrogen carbonate and cooled to precipitate ammonium chloride is also adopted.

In any of the methods, the sodium chloride precipitation step includes a step of cooling the aqueous solution in which sodium chloride is to be precipitated. Hereinafter, in the present specification, a liquid for cooling to precipitate ammonium chloride crystals,
It is called an ammonium chloride depositing liquid.

As a means for cooling the ammonium chloride depositing liquid, a part of the ammonium chloride depositing liquid is taken out and cooled by a cooler to a supersaturated state just before crystals are deposited, and returned to the original depositing liquid storage tank. There is a method of precipitating a supersaturated ammonium chloride as crystals.
In this method, crystals often precipitate in the cooler, causing clogging, so usually several similar coolers are prepared and switched in a relatively short time to clean the clogging. Therefore, it is not always satisfactory in terms of operation and equipment.

As a means for removing the drawbacks of the above method and cooling the ammonium chloride depositing liquid by an easy means and operation, the indirect cooling is abolished and the ammonium chloride depositing liquid is directly contacted with a refrigerant to prepare a solution of 0-15. A method of cooling to a temperature of about C is known (see Japanese Patent Publication No. 54-42840). Since the refrigerant used here is in direct contact with the ammonium chloride-deposited liquid, it is necessary that it does not substantially react with ammonium chloride and other components contained in the aqueous solution. As such substances, liquefied refrigerants such as dichlorodifluoromethane, trichlorofluoromethane, chlorodifluoromethane, propane, n-butane and i-butane are mentioned in the above-mentioned known examples.

In practice, it is not preferable to use a refrigerant having a high vapor pressure or a risk of fire such as ignition or explosion in a used state. Therefore, dichlorodifluoromethane is used among these refrigerants.

[0008]

However, in recent years, the relationship between ozone layer depletion and chlorofluorocarbon has become a global problem. In particular, chlorofluorocarbons such as trichlorofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, and chloropentafluoroethane, in which carbon is bonded only to chlorine and fluorine, are chemically stable and therefore decompose. It is difficult to do so, and it is said that chlorine generated by decomposing for the first time in the stratosphere will destroy the ozone layer, and it is expected that the use will be totally abolished in 1995.

The present invention is a method for producing sodium chloride by directly contacting a cooling medium with an ammonium chloride depositing liquid to cool the liquid, and using a cooling medium which has a small influence on the environment instead of chlorofluorocarbon. , For the purpose of producing ammonium chloride.

[0010]

The present invention provides a method for producing ammonium chloride by alternately and cyclically precipitating ammonium chloride and sodium hydrogen carbonate in an aqueous medium using sodium chloride ammonia and carbon dioxide. , Cooling the ammonium chloride deposition liquid with 1,1,1,2-tetrafluoroethane or 1,1,1
The present invention provides a method for producing ammonium chloride, which is characterized by carrying out direct contact with 2,2-tetrafluoroethane.

1,1,1,2-Tetrafluoroethane and 1,1,2,2-tetrafluoroethane do not react with the ammonium chloride depositing liquid and the components such as ammonium chloride, and are safe without ignition. Compound and has little effect on the ozone layer. Of the substances known as alternatives to chlorofluorocarbons, they are the most excellent refrigerants for direct contact with the ammonium chloride-deposited liquid for cooling, in terms of vapor pressure and other factors.

When 1,1,1,2-tetrafluoroethane and 1,1,2,2-tetrafluoroethane are compared, 1,1,1,2-tetrafluoroethane has a vapor pressure higher than that of 1,1,1,2-tetrafluoroethane. It is preferable as a refrigerant for the ammonium chloride-deposited liquid because it is low. The following explanation is 1,1,1,2-
Do this for tetrafluoroethane: 1,1,2,2
The same is true for tetrafluoroethane.

The temperature at which the ammonium chloride depositing liquid is cooled can be appropriately changed depending on the amount of ammonium chloride deposited and the size of the ammonium chloride particles to be obtained. For example, the internal pressure of the deposition apparatus is 2.4 kg / cm ² G
By cooling to 0 to 15 ° C., ammonium chloride crystals having a particle diameter of 500 to 1000 μm can be precipitated. When the temperature of the ammonium chloride-deposited liquid exceeds 15 ° C., the partial pressure of ammonia and carbon dioxide gas becomes high, and the precipitation of ammonium carbonate tends to occur when the refrigerant is liquefied, which is not preferable.

As a method for bringing 1,1,1,2-tetrafluoroethane into contact with the ammonium chloride depositing liquid,
At normal temperature and pressure, gaseous 1,1,1,2-tetrafluoroethane is liquefied, and fine particles are added to the ammonium chloride precipitation aqueous solution from near the bottom of the precipitation tank filled with ammonium chloride precipitation liquid using an appropriate nozzle. The method of introducing the droplets is preferable. The droplets of 1,1,1,2-tetrafluoroethane are vaporized while rising in the ammonium chloride depositing liquid, and at this time, the heat of vaporization is taken from the ammonium chloride depositing liquid to achieve the purpose of cooling. It The precipitated ammonium chloride crystals can be appropriately separated from the solution by a known method.

The vaporized 1,1,1,2-tetrafluoroethane is taken out, for example, from above the ammonium chloride deposition tank, other gas components such as ammonia are removed if necessary, liquefied again, and chlorinated by direct cooling. It is preferably recycled for the precipitation of ammonium.

As the ammonium chloride depositing liquid, one obtained by the same process as the conventional ammonium chloride soda method can be used. The precipitated ammonium chloride is appropriately separated by a known method, and the remaining mother liquor is recycled and used in the sodium hydrogen carbonate precipitation step.

When the method of the present invention is introduced into the manufacturing process which has adopted the conventional direct cooling with dichlorodifluoromethane, there is almost no change in the conventional direct cooling equipment and manufacturing conditions. It can be carried out efficiently and easily.

Further, when the method of the present invention is introduced into a manufacturing process which employs indirect cooling by an external cooler, the steps of the conventional ammonium chloride soda method are not essentially changed, Precipitation of ammonium chloride by cooling can be carried out efficiently and easily without the use of complicated devices and operations as in the past, and inevitably increases with the increase in the size of the precipitation tank as has been done conventionally. There is no need for a cooler, and it is sufficient to simply introduce an appropriate amount of refrigerant, which has the advantage of being considerably simpler in terms of equipment and operation than the conventional indirect cooling method.

[0019]

【Example】

Example Ammonium chloride precipitating liquid obtained by adding ammonia and sodium chloride to a mother liquor obtained by separating precipitated sodium hydrogen carbonate obtained by carrying out the sodium chloride soda method (ammonium chloride 18% by weight, sodium chloride 8 % Aqueous solution containing 30% by weight of ammonium carbonate and 1.5% by weight of ammonium hydroxide and having a temperature of 30 ° C.) (200 ml) is introduced into the precipitation tank,
Liquefied as a refrigerant from the bottom of the precipitation tank under stirring 1,1,
1,2-Tetrafluoroethane was introduced at a rate of 200 g / min for 1 minute, vaporized in the tank and cooled.
The temperature in the tank was about 10 ° C., and 12.5 g of ammonium chloride was obtained as crystals.

Comparative Example Ammonium chloride deposition liquid (temperature 30
(° C) 200 ml was introduced into the precipitation tank, and 2 g of liquefied dichlorodifluoromethane as a refrigerant was stirred from the bottom of the precipitation tank under stirring.
It was introduced at a rate of 00 g / min for 1 minute, vaporized in the tank and cooled. The temperature in the tank was about 10 ° C., and 12.5 g of ammonium chloride was obtained as crystals.

The shape of ammonium chloride cooled and deposited by the sodium chloride soda method is an important quality depending on its application. When comparing the ammonium chlorides obtained in the Examples and Comparative Examples, no significant difference was observed in the crystal shape, and it was found that the present invention provides good ammonium chloride having the same quality as conventional ones. .

[0022]

EFFECTS OF THE INVENTION According to the present invention, it is possible to deal with the complete abolition of specified CFCs that are subject to regulation, there is no risk of fire or explosion such as ignition, and there is no need for special high pressure, and ammonium chloride of good quality Can be manufactured. When introducing the production method of the present invention into a conventional production process that employs direct cooling using dichlorodifluoromethane, which is a specific flon, without changing the conventional equipment,
It can be carried out efficiently and easily. Even when it is introduced into a manufacturing process that employs indirect cooling, it can be easily implemented by only changing the part of the cooling equipment without essentially changing the conventional steps.

Front page continued (72) Inventor Hiroo Mori 10th Goi coast, Ichihara City, Chiba Prefecture Asahi Glass Co., Ltd. Chiba factory (72) Inventor Masatomo Abe 10th Goi coast, Ichihara city, Chiba Asahi Glass Co., Ltd. Chiba factory

Claims (1)

[Claims] 1. A method for producing ammonium chloride by alternately and cyclically precipitating ammonium chloride and sodium hydrogen carbonate in an aqueous medium using sodium chloride ammonia and carbon dioxide, wherein the ammonium chloride depositing liquid is cooled. Is carried out by directly contacting this with 1,1,1,2-tetrafluoroethane or 1,1,2,2-tetrafluoroethane.