US2241613A - Manufacture of nitrates - Google Patents

Description

May 13, 19"-1-1` H, PAULING 2,241,613

MANUFAGTURE oF NIfTRATEs Filed March 10, 1938 Hafrrrlg Paul/ng Patented May 13, 1941 2,2%!613 MANUFACTURE OF NITRATES Harry Pauling, Berlin, Germany application March 10, 193s, :serial No. 195,152 In Czechoslovakia. March i27, 1937 Claims.

It is known to manufacture the nitrates of alkalies, alkaline earths and ammonia by reacting the chlorides with nitric acid and removing the resulting hydrochloric acid from the reacting mixture by distillation. In order to prevent the decomposition of the nitric acid by the hydrochloric acid, that is to say, the formation of nitrosyl chloride and chlorine, it has already been proposed to carry out the reaction in vacuo, and for the distillation of the hydrochloric acid with simultaneous evaporation of the water, to pass superheated steam into the reaction mixture. This method of evaporating the salt liquor requires very considerable quantities of steam, whereby not only is the resulting hydrochloric acid very considerably diluted, but also reaction apparatus of large dimensions is necessary.

In accordance with the invention, the difliculties of the known processes are overcome by the fact that the conversion of the chlorides by means of nitric acid is not effected as heretofore at the lowest possible temperature but at the highest possible temperature, and furthermore steam at atmospheric pressure is introduced, in so far as it is not produced by evaporation of the nitrate liquor which is likewise carried out at atmospheric pressure. 'Ihe present process employs in this case nitric acid in excess, so that after completion of the reaction, chlorine ions are no longer present in the reaction mixture and consequently the evaporation of the nitrate liquor containing nitric acid can take place in apparatus made of ordinary materials. As, furthermore,

according to the present process, strong nitric acid may be employed, the hydrochloric acid is obtained directly in the commercial concentration of about 33%.

In accordance with theinvention, the reaction takes place in a counter-now. device comprising two stages, for example in a column which is combined with an evaporator. To the upper stage water is supplied, if desired together with a part of the chlorides to be converted, and to the lower stage are supplied aqueous nitric acid, mother liquor resulting from the separation of the nitrate, and the chloride, in so far as the latter is not already supplied to the upper stage. From the lower stage of the counter-flow device, the reaction mixture passes for evaporation under atmospheric pressure into an evaporator, from which on the one hand the vapour mixture generated is passed into the lower stage of the counter-flow device, and on the other hand the nitrate liquor is passed into a crystalliser for the separation of the nitrate.

It is also possible, however, to pass the nitrate liquor first into the crystalliser, because it is already very strongly satura-ted. The principal part of the sodium nitrate is separated out in the crystalliser. From the crystalliser the liquor passes into the evaporator, the vapours of which are led into the lower stage of the counter-flow device, while the evaporated liquor is returned to the crystalliser.

A further improvement in the method of Working is secured by providing between the lower part of the counterflow device, on the one hand, and the evaporator on the other, a second, smaller additional counter-flow device, for example a column, through which are passed the vapours coming from the evaporator and if desired steam supplied from outside, before these enter the lower part of the counter-How device. The liquor passes from the lower part of the counter-flow device first through the additional column and only then, according to the method of working, either into the crystalliser or into the evaporator. This additional counter-flow device makes it possible to employ a very considerable excess of nitric acid, which excess however, does not enter the crystalliser or evaporator because it is evaporated in the additional column and thus enters the counter-flow device. In this way the nitric acid content is kept low in accordance with the quantity of steam and the conditions of equilibrium between the steam and the nitric acid Vapour, so that crystallisation does not require to be repeated.

A ow diagram illustrating the processes disclosed herein is illustrated in the drawing.

The two part counter-flow device shown consists of an upper part a, and a lower part b. Each of these parts is in itself a counter-how device and is provided either with a charging device, bell bottoms or the like installations. Water is supplied to the upper part a through a conduit c, if desired with a part of the chloride to be converted, and to the lower part b are supplied, through a conduit d, the aqueous nitric acid, the circulating mother liquor` and the residual part of the chloride which has not yet been supplied to the upper part a; in addition water may also be supplied at this place. From the lower part b of the counter-flow device, the liquor ows through a conduit e into an auxiliary small counter-now device j and thence through a conduit g` into an evaporator h and from the latter through a conduit i into a crystalliser k. The liquor may also be led through a conduit l first into the crystalliser 1c and thence through a conduit m into the evaporator h, and after evaporation returned again to the crystalliser. The mother liquor produced in the crystalliser is returned through conduits s and d to the stage b of the counter-flow device and the salt is removed from the crystalliser through an outlet t.

From the evaporator h, the vapours pass through a conduit n into the auxiliary counternow device f, into which steam may also be introduced through a conduit o. From the auxiliary counter-flow device f, the vapours are passed through a conduit p into the stage b of the main counter-now device.

The crystalliser may be made of the known silicon cast iron or of V2A sheet metal, because chlorine ions are no longer present in the liquor, while the evaporator is preferably made of silicon cast iron vessels, which nowadays can be supplied for the evaporation of liquids containing nitric acid, up to the largest dimensions required industrially.

The hydrochloric acid escapes from the counter-now device through a conduit q into a condenser r which is cooled to as low a temperature as possible.

Since the heating of the liquids within the counter-now device causes dilution through condensing water, they may be heated indirectly, before they enter the counter-now device, at a suitable point outside the counter-flow device by means of the vapours generated during the process. rIhis step, however, does not make any difference in the heat requirement of the process, but merely results in the fact that a larger quantity or water may be supplied to the upper part of the device, while further below the addition of water should be correspondingly reduced.

The process according to the invention is based on the following facts: In the lower part b of the counter-now device, the nitric acid mainly reacts with the chloride to form nitrate and free hydrochloric acid, the hydrochloric acid being converted to a considerable extent into vapour on account of its volatility. In addition to this reaction, however, a secondary reaction takes place to a very considerable extent according to the following equation, namely the so-called aqua regia reaction:

This reaction becomes very prominent, both with increasing temperature and also with the concentration of the reaction components, to such an extent in comparison with the nitrate formation that heretofore it has deterred all investigators from following up the reaction, which has been regarded as unserviceable.

The inventor has, however, found that the aqua regia reaction is a reversible reaction, and that if the reaction products are passed through a relatively weak mixture of the components taking part or even only through pure water, the nitrosyl chloride and the chlorine in the water again form quantitatively nitric acid and hydrochloric acid, and that surprisingly, this reaction proceeds all the more rapidly and all the more completely, the higher the temperature, providaafiil ed only the concentration proportions are suitably selected and suicient time is allowed for the reaction proceeding in the reverse direction.

The process may also be carried out by employing chlorides of the alkalies, of ammonia and of the alkaline earths alone or in admixture.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. A method for the production of nitrates and hydrochloric acid from chlorides capable of metathetical reaction with nitric acid which comprises treating such chlorides at boiling temperature and at atmospheric pressure in a countercurrent reaction zone with an excess of strong nitric acid to form a nitrate liquor and a gasvapor mixture containing substantial quantities of nitrosyl chloride and chlorine, reacting the gasvapor mixture containing substantial quantities of nitrosyl chloride and chlorine eiiluent from said reaction zone at elevated temperatures under atmospheric pressure with water in countercurrent in a second treatment zone beyond that in which nitric acid is introduced to the process, whereby substantially all of the nitrosyl chloride and chlorine are converted into aqueous nitric acid which is returned to the reaction zone and gaseous hydrochloric acid which is ejected as such from said zone, and condensing the said hydrochloric acid.

2. A process asset forth in claim 1 in which the nitrate liquor is heated in an evaporating zone and the vapor formed in the evaporating zone is passed into the reaction zone countercurrent to the reactants therein.

3. A process as set forth in claim 1 in which the nitrate liquor substantially free from hydrochloric acid is passed into a third zone in countercurrent to steam supplied to said third zone from an external source, and the steam and acid vapors formed in said third zone are passed into the reaction zone in countercurrent to the reactants therein.

4. A process as set forth in claim l in which the nitrate liquor substantially free from hydrochloric acid is passed into a third zone in countercurrent to steam supplied to said third zone from an external source, the steam and acid vapors formed in said third zone are passedr into the reaction zone in countercurrent to the reactants therein, heating the nitrate liquor in an evaporating Zone, passing vapors formed in said evaporating Zone into the said third zone countercurrent to the fiow of liquor therein, subjecting the concentrated liquor formed in the evaporating zone to crystallization for the recovery of nitrates therefrom, and returning the mother liquor from said crystallization to the reaction zone.

5. A process as set forth in claim 1 in which part of the chloride used as a reactant is supplied with water to the Zone in which the nitrosyl chloride rand chlorine are converted into aqueous nitricacid and gaseous hydrochloric acid, and the remainder of the chloride is supplied with aqueous nitric acid in the reaction zone.

HARRY PAULING.

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