WO1992002455A1

WO1992002455A1 - Process for obtaining of sodium and potassium bicarbonates by dry route

Info

Publication number: WO1992002455A1
Application number: PCT/BR1990/000007
Authority: WO
Inventors: Manuel Monteiro Orestes
Original assignee: Bicarbon Industrial E Comercial
Priority date: 1990-08-06
Filing date: 1990-08-06
Publication date: 1992-02-20

Abstract

Process for obtaining of sodium/potassium bicarbonates by dry route comprising the phases of reacting one mol of sodium or potassium carbonate and n mols of water (n = 1, 2 or 3) at a temperature range of 10° to 50 °C; reacting the obtaining n-hydrate with one mol CO2 gas in a closed vessel at a temperature range of 15° to 45 °C and drying the obtained product by using any process that allows the maintenance of a temperature below 80 °C, such as lyophilization, rotary dryer, 'flash' dryer, and ash dryer.

Description

PROCESS FOR OBTAINING OF SODIUM AND POTASSIUM BICARBONATES BY DRY ROUTE

TECHNICAL FIELD

This invention relates to a process for producing sodium bicarbonate or potassium bicarbonate by dry route, by using reactants in the solid state, without adding any solvent.

BACKGROUND ART

Several processes for obtaining sodium bicarbonate or potassium bicarbonate by wet route, from different raw materials have been described in the prior-art. In the last fourty years about two thousand references related to wet route processes have been mentioned in the "Chemical Abstracts". This means that such a process has already been disseminated sufficiently, and some attempts for its improvements concern to the simplification of steps, adjusts in energy consumption and yields improvements.

For all that, the basic problems of this process exist, and technicians and experts in the art have been challenged. The problems can be summarized as follows:

(a) Independently of the sodium/potassium raw materials used (carbonate, sulphate, sulphite, and others) a dissolution into water with heat liberation occurs, and cooling the obtained solution is necessary which means spenditure of energy.

(b) It is necessary to burble carbon dioxide gas(pure or mixtures) through the solution (a), which requests very accurate reactor designs, in order to avoid loss of reactants from the liquid, before reacting it completely.

(c) The obtaining product consists always of an heterogeneous mixture of solid bicarbonate and aqueous solution of the same, which needs to be separated by filtration or centrifugation.

(d) The mother liquor from the previous step should be concentrated in order to recover any residual product, through a new filtration or separation means. (e) A serious problem of contamination of the end-product appears, caused by the several steps mentioned, and the need for purification is always necessary.

(f) As a consequence of the above referred problems, a large energy spenditure and a decrease in the final yield which is not higher than 85%, occurs.

It is obvious the importance in finding out other processes, that can avoid, at least, some of the problems described.

Although the direct treatment of sodium carbonate or potassium carbonate with water and CO , without the use of any solvent, is Known as theoretically possible, up to now it was not effectivelly put into practice, since the theoretical conditions have not been possible to be reproduced.

DISCLOSURE OF THE INVENTION

The present invention consists of preparing sodium bicarbonate or potassium bicarbonate from crystal sodium carbonate or crystal potassium carbonate having no more than three molecules of water, which reacts with CO gas in a temperature between 152 and 45°-C Conversion of Na CO into

Na H CO or K CO into KH CO in only one step is carried out. .

Then, yields higher than 95% are obtained.

The reaction in each case is the following:

Na CO . n H O + CO *■ 2 NaH CO . (n-l)H 0

_- . _- .

K CO. . n H O + CO. ■- 2 KH CO. . (n-l)H.O

2 3 2 2 3 2 were n = 1, 2 or 3.

The production of NaHCO or KHCO in such condition is followed by heat liberation. The exothermic heat of reaction produced in the reaction has to be cooled in order to maintain the temperature within the limits referred to above.

As it is usual for processes of this type, in which crystallization water compounds are used, the thermal balance is critical since an excessive heating can decompose the hydrate followed by loss of one of the reactants. The same occurs with the end-product, since the reaction:

2 Na H CO *■ Na CO + H O + CO or 2 K H CO 3. ► K2. CO3. + H2O + C02 occurs at temperatures above 80°.C, with increasing velocity of reaction depending on the temperature.

This new process here disclosed eliminates several disadvantages of traditional processes described in the prior-art, since carbonate solution and water are not used. Thus, by-products are not produced in the reaction. As a consequence, another advantage of the process of this invention is that, since by-products are not formed, the use of raw-materials is maximized (with better final yield) and energy consumption is considerably reduced, once filtration and centrifugation are not necessary to be used and humidity to be dryed is very low.

To achieve optimal conditions to obtain a complete carbonation process, which can envolve an eventual phase of hydration of sodium carbonate or potassium carbonate, (in order not to incorporate more than three molecules of water) one of the features of the invention here described is to react n-hydrate and CO , both carried out in an encapsuled reactor provided with serpentine where refrigerant liquid flows, in such a way to maintain the temperature in the first phase between 15°. and 45SC; at the end, a new eventual phase for drying can occur, and the excess of water should be eliminated in the crystal product; this is carried out in a temperature below 80°-C by using suitable processes which control such temperature like lyophilization or by using rotary dryer, flash dryer or tray dryer, in such a way to allow a distribution in a thin layer.

Example 1 A 20001 vessel was charged with 500 Kg (4.6 Kmols) of anidrous Na CO and is slowly added 84 Kg water (4.6 Kmols) with intense agitation, at a range of temperature between 102 to 50^eC, by using a suitable refrigeration. After closing the vessel, 203Kg (4.6 Kmols) of CO gas is supplied and an intense agitation is provided, at a temperature of 20^eC which is maintained during 6 hours. The end-product is dryed in a rotary dryer, and 93% yield is obtained.

Example 2 In a manner similar to that of Example 1, in the same vessel type, 500 g (4.6 Kmols) of anidrous Na CO , 168 Kg (9.2 Kmols) water and 203 Kg (4.6 Kmols) CO were charged to the vessel. The temperature is maintained at 25 C and dryness is provided by means of flash dryer; 95% yield is obtained.

Example 3 The same reactants of previous examples are used, except that 252 Kg (13.8 Kmols) of water is added, at a temperature of 452C and the obtained product is dryed in a air current at 80^eC; 97% yield is obtained.

Example 4 A 500 1 vessel was charged with 138 Kg (1 mol) of anidrous potassium carbonate (K CO ) , and is slowly added 18 Kg (1 mol) water and intense agitation is provided, at a range of temperature of 152 to 452C which is maintained during the reaction, by suitable refrigeration. After closing the vessel, 44 Kg (1 mol) CO gas is supplied and an intense agitation is maintained, at a range of temperature of 20² to 302C, during 6 hours. The end-product obtained is dryed in a rotary dryer, and 93% yield is obtained. Example 5 In a manner similar to that of Example 4, in the same vessel, the same reactant amounts are charged, except that water added is 36 Kg (2 mols) and temperature is maintained at 252C. Dryness is carried out in a flash dryer; 95% yield is obtained.

Example 6 The same reactants and vessel of Examples 4 and 5 are used, except that 54 Kg (3 mols) of water is added at the temperature of 452C. The drying process is carried out in tray air current at 80^eC; 97% yield is obtained.

Claims

1. Process for obtaining sodium bicarbonate by dry route, characterized by a main phase of reacting a n- hydrate, comprising one mol of sodium carbonate and n mols of water, being n an integral number, (n= 1, 2 or 3), and one mol of CO gas, in a range of temperature of 152 to 45^eC and that,in the case of sodium carbonate does net present conditions for suitable hydration to the process, an eventual hydration phase is provided, which is carried out before the mεάn phase and at a temperature between 10^s and 50^SC, both phases being carried out in a closed encapsulated vessel with serpentine through which refrigeration liquid flows, and by the fact that an eventual phase of drying the obtained product be' provided, by using any process which allows to maintain the temperature below 202C, comprising lyophylization, rotary dryer process, flash dryer process or tray dryers.

2. Process for obtaining potassium bicarbonate by dry route, characterized by a main phase of reacting a n- hydrate, comprising one mol of potassium carbonate and n mols of water, being n an integral number, (n= 1, 2 and 3), and one mol of

CO gas, in a range of temperature of 152 to 452C and that, in the case of potassium carbonate does not present conditions for suitable hydration to the process, an eventual hydration phase is provided, which is carried out before the main phase and at a temperature between 102 and 50²C, both phases being carried out in a closed encapsulated vessel with serpentine through which refrigeration liquid flows, and by the fact that an eventual phase of drying the obtained product be provided, by using any process which allows to maintain the temperature below 20²C, comprising lyophylization, rotary dryer process, flash dryer process or tray dryers.