JPS5826027A - Washing method for anhydrous sodium carbonate crystal - Google Patents

Abstract

PURPOSE:To wash anhydrous sodium carbonate crystals without causing a yield reduction due to the transition of the crystal surfaces to hydrate, dissolution and washing loss by washing the crystals with an aqueous NaOH soln. under specified conditions. CONSTITUTION:When anhydrous sodium carbonate crystals are washed, the crystals are washed with an aqueous NaOH soln. while maintaining the washing conditions in the region X of the diagram. The x-axis of the diagram shows the NaOH concn. of the washing soln., and the y-axis shows the washing temp. The washing temp. is the surface temp. of said crystals in the strict sense, yet when the crystals are manufactured by a reaction in an aqueous soln. and washed immediately after the manufacture, the washing temp. is considered to be approximately equal to the temp. of the aqueous NaOH soln. as the washing soln. Under washing conditions in the region Y sodium carbonate monohydrate may be formed on the surfaces of the anhydrous sodium carbonate crystals.

Description

[Detailed description of the invention] The present invention relates to a method for cleaning anhydrous soda crystals.

Anhydrous sodium carbonate crystals are produced by various methods, but in many cases it is desired to remove impurities or solutions attached to the crystal surface.

Normally, washing with water and drying is considered, but this method has the following drawbacks.

One is that by washing with water, the surface of anhydrous soda carbonate transforms into a hydrated salt of sodium carbonate (usually monohydrate).

The other is that the surface of the anhydrous soda crystals dissolves and is washed away.
This results in a decrease in the yield of anhydrous carbonate sorter crystals.

The present inventors have made repeated efforts to overcome the above-mentioned drawbacks, and have succeeded in solving this problem by washing with a caustic soda aqueous solution under specific conditions. It has been discovered that the object of the present invention can be fully achieved by cleaning the wafer with a caustic soda aqueous solution so as to maintain the area X in FIG.

Anhydrous soda carbonate is conventionally produced by converting ash into monohydrate and thermally decomposing it, or by methods such as JP-A-55-7530, JP-A-55-10025, JP-A-55. A method using an aqueous solution reaction disclosed in No.-11475 etc. can be considered. In the case of the former method, usually 5TD
Anhydrous sodium carbonate crystals are obtained by thermally decomposing carbon dioxide monohydrate in a dryer called a Steam-Tubed Dryer (Steam-Tubed Dryer). When separating from the product, it is possible to adjust the impurity concentration in the product by adjusting the impurity concentration in the mother liquor or washing with water, but in the latter case, the conditions for precipitating the anhydrous sodium carbonate salt Because of this, the concentration of nac1 in the mother liquor was limited, and when washed with water, it instantly solidified in the separator due to a water utilization reaction, making it impossible to obtain an anhydrous cake.

Therefore, as a result of extensive research, the Ministry of the Invention has developed the present invention as a method that does not cause the above-mentioned phenomenon, and the gist thereof is to wash with a caustic soda aqueous solution under specific conditions.

When drying anhydrous sodium carbonate crystals, it is necessary to wash them with an aqueous caustic soda solution while maintaining the anhydrous carbonate crystals in the seismic region X in FIG.

FIG. 1 is a diagram showing the conditions for carrying out the method of the present invention, in which the horizontal axis shows the concentration of caustic soda, which is a cleaning liquid;
The vertical axis indicates the cleaning temperature. Strictly speaking, the washing temperature here refers to the optical surface temperature of the anhydrous sodium carbonate crystal, but in the case where the anhydrous soda crystal has just been produced by the latter method mentioned above, the washing temperature is This can be approximately considered to be the temperature of the caustic soda aqueous solution, which is the cleaning liquid.

If the cleaning conditions are maintained in the region Y in FIG. 1, sodium carbonate monohydrate may be generated on the surface of the anhydrous sodium carbonate crystals. Therefore, the cleaning conditions should be maintained in the region X in FIG. is necessary.

Although the present invention requires maintenance of the above-mentioned cleaning conditions, a thin film of aqueous caustic soda solution, which is the cleaning liquid, is formed on the surface of the anhydrous soda crystal after cleaning, and there is a possibility that caustic soda may remain as an impurity. There is. When such caustic soda cannot be tolerated as an impurity, it is preferable to dry the anhydrous soda crystals coated with the above caustic soda aqueous solution with carbon dioxide gas or a gas containing carbon dioxide gas.

In the case of this drying as well, it is necessary to maintain the temperature of the caustic soda adhering to the anhydrous soda crystal surface within the range X in FIG. 1.

That is, when the adhering mother liquor is in region , and precipitates and adheres to the surface as anhydrous sodium carbonate crystals.

As the drying and reaction proceed, the amount of caustic soda ζ on the surface of the anhydrous sodium carbonate crystals rapidly decreases, so the drying temperature must be increased accordingly to maintain region X. However, it is not practical to change the drying temperature as the drying progresses, and in actual industrial implementation, the temperature of the gas containing carbon dioxide gas or charcoal alcohol/gas is set at 103°C (areas and areas Y are separated). (intersection with the vertical axis of the slide) or more.

According to the method of the present invention described above, since the caustic soda aqueous solution that is the cleaning liquid can be reused, it does not have an adverse effect on the yield of anhydrous sodium carbonate crystals, and the carbon dioxide or carbon dioxide gas used for drying Since industrial combustion gas from which sulfur dioxide gas has been removed can be used as the gas containing sulfur dioxide (slightly heated if necessary), it is clear that this is a very industrially effective method.

It goes without saying that the caustic soda aqueous solution used may contain some impurities depending on the desired product purity.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example: Baking soda obtained by the ammonium chloride soda method, 49% aqueous caustic soda solution, and salt were reacted in a reaction vessel at 105°C and 1 atm to form anhydrous sodium carbonate crystals, 115 wt% NaC, and NazOO.
A slurry consisting of 14.6% mother liquor was obtained. The crystals were separated by filtration, and 0.6% of common salt was found to be attached to the surface of the anhydrous soda crystals.

Next, the crystals were washed with a 30% caustic soda aqueous solution at 90°C while being maintained at 98°C, and then dried with carbon dioxide gas at 109°C.

The part of the caustic soda that adhered to the surface completely changes to anhydrous sodium carbonate, and there is no carbonate monohydrate), and this solidly integrates with the original anhydrous carbonate soda, and this part peels off. It did not turn into powder. In addition, there was substantially no common salt impurity on the surface.

Comparative Example When an anhydrous sodium carbonate crystal containing salt obtained in the same manner as in the example was washed with an 11% aqueous sodium hydroxide solution at 90°C, a portion of the crystal surface converted to sodium carbonate monohydrate and immediately. The particles solidified together and became block-shaped.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the conditions of caustic soda aqueous solution concentration and cleaning temperature for implementing the method of the present invention, and region X is the region showing the conditions for implementing the present invention. Agents 1) Akira Agent Ryo Hagiwara

Claims (1)

[Claims] (A method for cleaning anhydrous soda carbonate crystals, which is characterized in that when cleaning 11% sodium hydroxide crystals, the anhydrous sodium carbonate crystals are washed with a caustic soda water bath solution so as to maintain the area X in the k:1 diagram (2) ) The method for cleaning anhydrous soda crystals according to claim (1), which comprises drying in carbon dioxide gas or an atmosphere containing carbon dioxide gas after cleaning.