反应详情

In this preferred embodiment of the process according to the invention, use is advantageously made of the sodium carbonate hydrate obtained by means of an operating procedure comprising an impregnation of anhydrous sodium carbonate with water and a drying of the product resulting from the impregnation at a temperature above the transition temperature of sodium carbonate heptahydrate to sodium carbonate monohydrate and lower than the boiling temperature of water. The sodium carbonate employed in this operating procedure may comprise dense soda, light soda or a mixture of dense soda and light soda. Light soda, of apparent density substantially between 550 and 650 kg/m3 is preferred. In the operating procedure just described the anhydrous sodium carbonate is used in the form of a powder. The latter advantageously consists of particles whose diameter does not exceed 200 μm and is preferably smaller than 100 μm, for example between 5 and 50 μm. The quantity of water used in the stage of impregnation of the anhydrous sodium carbonate must be at least equal to the theoretical quantity needed to form sodium carbonate monohydrate by hydration of anhydrous sodium carbonate. In general, it is recommended to use a quantity of water which is greater than the abovementioned theoretical quantity. It is preferred to use a volume quantity of water greater than 0.08 and preferably at least 0.1 times the voluble quantity of anhydrous sodium carbonate. Although the invention does not impose any upper limit on the quantity of water employed, there is no advantage in exaggerating the excess of water, in order not to overburden the cost and the duration of the subsequent drying. In general there is no advantage in employing a volume quantity of water greater than 5 times the volume quantity of anhydrous sodium carbonate used. The volume quantities of water of between 0.1 and 2 times the volume quantity of anhydrous sodium carbonate are especially recommended, those between 0.3 and 1.5 being preferred. An aging period must be provided between the beginning of the impregnation and the drying. The purpose of this aging period is to allow all the anhydrous sodium carbonate to be impregnated with the impregnating water and consequently depends on the particle size of the anhydrous sodium carbonate powder. It can vary from a few minutes (for example between 5 and 20 minutes) to a number of hours (for example between 15 and 30 hours). The drying must be performed at a temperature above the temperature of transition of sodium carbonate heptahydrate to sodium carbonate monohydrate. Its purpose is to form sodium carbonate monohydrate and to remove the moisture which impregnates it. A drying temperature not exceeding 60° C. is advantageously chosen, temperatures of between 38 and 50° C. being suitable. The drying time depends on the quantity of water used in the impregnation stage and on the drying temperature.

1. customobtained by means of an operating procedure
2. customa drying of the product