JPH0617221B2 - Crystal growth method of sodium bicarbonate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sodium bicarbonate crystal growth method characterized by adding sodium tartrate or a derivative thereof to a mother liquor when precipitating sodium bicarbonate from an aqueous solution. It is a thing.

[Prior Art] Crystals that precipitate during the production of sodium bicarbonate from high-purity caustic soda or sodium carbonate and carbon dioxide gas are likely to become fine needle-like particles, which may cause clogging in the filtration process, poor drainage, and dryness. This causes various problems such as a decrease in yield due to scattering of fine powder in the process, thermal decomposition of sodium bicarbonate due to increase in drying temperature, formation of crystal lumps, and scale adhesion. In addition, as a result, the product sodium bicarbonate has a small particle size and is easy to congeal, and there are problems in quality such as a large amount of water and sodium carbonate, and there are problems such as scattering of fine powder, poor fluidity, and congealing during use. Contains.

As attempts to increase the grain size, attempts have been made to lengthen the crystal growth time, add crystal seeds, change the carbon dioxide gas concentration, etc., but none of them have reached a definitive solution. . In addition, a method of adding a habit modifier is also known (for example, Japanese Patent Publication No. 48-17160).
Issue). However, for example, when using a polyacrylate as described in JP-B-48-17160,
When the obtained sodium bicarbonate is used, for example, under acidic conditions, there is a problem that the polyacrylic acid salt remaining in the product floats up as a water-insoluble substance.

[Problems to be Solved by the Invention] The present invention was found as a result of research to provide an effective habit modifier for obtaining sodium bicarbonate having large crystals and a shape close to a cube from an aqueous solution. Is.

Further, it is an object of the present invention to provide a habit modifier which does not cause any problem in subsequent use even if a trace amount of habit modifier remains in the product.

[Means for Solving Problems] The present inventors have found that sodium tartrate or a derivative thereof is effective in achieving the above-mentioned object, and completed the present invention. Thus, the present invention Evaporates, cools,
A method for growing a sodium bicarbonate crystal is characterized in that a small amount of sodium tartrate or a derivative thereof is added to a mother liquor when a sodium bicarbonate crystal is precipitated from an aqueous solution by a method such as precipitation by reaction.

Although the range of the amount of sodium tartrate or its derivative to be used varies depending on the substance used, it is usually effective over a wide range from 1 ppm to 50,000 ppm, and the obtained crystal form and particle size distribution continuously change depending on the concentration. It is preferable to set the upper limit to about 5000 ppm in consideration of mixing and product cost. Also, even if it is present in an amount of more than 5000 ppm, the shape of the cube remains almost unchanged.

As the concentration of sodium tartrate decreases, the resulting crystals become elongated. And the concentration of sodium tartrate
At 500 ppm, the aspect ratio of the crystal (the ratio of the height of the columnar crystal to the effective diameter of the cross section of the column) is 10 to 20, and at 100 ppm it is 50 to 100 (where the effective diameter is the same area as the cross section of the column. The diameter of the circle. Therefore, the lower limit of the sodium tartrate concentration is about 500 ppm, although it depends on the application.

It is also possible to obtain a relatively fine crystal of sodium bicarbonate by the method of the present invention, and use this as a seed crystal, and preferably perform crystal growth from an aqueous solution free of sodium tartrate.

By doing so, the obtained sodium bicarbonate crystal having a large particle size has very few impurities, which is particularly suitable for obtaining a high-purity product.

In addition, since the habit crystallization effect of sodium tartrate or its derivative is not disturbed by coexisting chlorine ions, ammonium ions, etc., the method of the present invention can be used in the sodium bicarbonate production process of the ammoniacal soda method. Of course, other methods for precipitating sodium bicarbonate crystals from an aqueous solution include evaporation, cooling, and reaction, and they have been found to be applicable.

Examples of the present invention will be shown below, but the invention is not limited thereto.

Example 1 1 g of sodium tartrate was dissolved in 200 ml of a saturated sodium bicarbonate solution at 60 ° C., and the mixture was cooled to 10 ° C. at a rate of 10 ° C./hour to obtain a cubic crystal of about 300 μm. On the other hand, when sodium tartrate was not added, only fine needle-like crystals of about 60 μ × 10 μ were obtained.

Example 2 0.5 g of ammonium tartrate was added to 200 ml of 15% caustic soda solution.
Is dissolved and carbon dioxide is blown in while maintaining the temperature at 70 ° C.
When the bicarbonate was sufficiently advanced, the carbon dioxide gas was still blown in, and the mixture was cooled to 10 ° C at a rate of 10 ° C / hour. The obtained crystals contained many columnar crystals of 500 μ × 300 μ and many crystals of about 300 μ cubic, and the crystals grew remarkably as compared with the case where ammonium tartrate was not added.

Example 3 A caustic soda solution containing 1000 ppm of sodium tartrate was prepared, and bicarbonate was blown into the caustic soda solution, followed by slow cooling to obtain crystals. The obtained crystals were columnar crystals of 500μ × 100μ and showed remarkable growth as compared with the case where sodium tartrate was not added.

Claims (2)

[Claims] 1. A method for growing sodium bicarbonate crystals, which comprises adding a small amount of sodium tartrate or a derivative thereof to a mother liquor when precipitating sodium bicarbonate crystals from an aqueous solution by a method such as evaporation, cooling and precipitation by reaction. 2. The crystal growth method of sodium bicarbonate according to claim 1, wherein 1 to 50,000 ppm of sodium tartrate or its derivative is added to the aqueous solution.