DE2635649A1 - PROCESS FOR PRODUCING AMMONIUM THIOSULPHATE - Google Patents

Description

HOECHST AKTIENGESELLSCHAFT **

File number: HOE 76 / f I85

Date: August 5, 1970 Dr.MD/hs

Process for the production of ammonium thiosulphate

The invention relates to a process for the production of ammonium thiosulfate, optionally mixed with ammonium sulfite, from ammonia, sulfur dioxide, water and sulfur.

A number are already available for the production of ammonium thiosulfate of procedures known.

US Pat. No. 2,219,258 describes a two-step process for the production of crystallized ammonium thiosulfate, in the case of the sulfur dioxide and ammonia in the first reaction stage be converted into ammonium sulfite in aqueous "solution. In the second reaction stage, the aqueous ammonium sulfite solution is used reacted with sulfur to form a 30% strength ammonium thiosulfate solution. This solution is made by adding ammonia Ammon. Umthiosulfat completely crystallized and separated '. The remaining ammonia solution goes back into the process. A disadvantage of this method is the proportionate low concentration of about 30% ammonium thiosulfate with

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Speaking of a lower space-time yield of crystallized ammonium thiosulfate. This also results in a further disadvantage of the process, the necessity of that which remains during the crystallization ^ pi.moniaklosung a large part of the ammonia back to remove, as for the quantitative crystallization of the ammonium thiosulphate a significantly higher ammonia concentration is necessary than for the reaction with sulfur dioxide. Farther the high heat of dissolution of the ammonia in the aqueous, approximately 30% ammonium thiosulphate solution is not taken into account, which leads to strong cooling of the crystallization process forces. Strong salt incrustations occur on the cooling surfaces.

From German patent specification 857 490 it is known to convert ammonium sulfite-containing solutions with stoichiometric amounts of sulfur or a slight excess of sulfur at temperatures of 80 ^° C. and above in the presence of free ammonia to form ammonium thiosulfate. During the reaction, the temperature is increased, for example, to about 110 to 130 ^° C. in order to achieve quantitative conversion. After the reaction has ended, part of the dissolved ammonium sulfate is separated off as a solid, anhydrous salt by cooling and / or evaporative crystallization and / or by salting out, for example with ammonia, and the mother liquor is returned to the process.

The disadvantage of this process, however, is that very long reaction times have to be accepted for the quantitative conversion of the ammonium sulfite with the stoichiometric amount of sulfur, despite the increase in temperature up to a final value of about 110 to 130 ^{° C.} Under certain circumstances, the increase in temperature even requires the use of higher pressures. However, quantitative conversion is necessary, since otherwise the ammonium thiosulfate produced is contaminated by sulfite and sulfur. The process allows only moderate space-time yields.

From the German patent document 1 263 721 is a continuous, two-step process for the production of ammonium thiosulfate from

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Ammonia, sulfur dioxide, water and sulfur are known in which the conversion of ammonia, sulfur dioxide and water to ammonium sulfite takes place in the first reaction stage in the presence of a large excess of elemental sulfur, the formed Ammonium sulfite for the most part in the first stage converted into ammonium thiosulfate, and that the implementation of the remaining Ammonium sulfite in the second stage again takes place in the presence of a large excess of elemental sulfur. * will

All known processes have in common that ammonia and sulfur dioxide are used as gases. The raw materials ammonia and sulfur dioxide, which are supplied in liquid form, must first be converted into the gases used in an upstream, energy-consuming process step. In addition, because ammonium thiosulphate is easily decomposable, it must be ensured that an excess of ammonia must be maintained in all process stages. In addition, especially when roasting gases containing sulfur dioxide are used, exhaust air problems always arise. Above all, however, the known methods are characterized by relatively low throughputs. For example, in German patent 1 2 63 721, a throughput of a maximum of 42.6 kg / h and m ³ reaction volume calculated for 100% ammonium thiosulfate is still considered advantageous compared to older processes. ^{Finally, the proposed reaction temperature of up to 130 °} C. in some known processes for increasing the reaction rate is also disadvantageous, since this results in partial decomposition of the solutions and formation of precipitates and the formation of the troublesome ammonium sulfate can take place according to the following equation:

(NH ₄ ) 30 -. + 2NH ₄ HSO-. 5 »2 (NH ₄ )" SO ,. fS + HX>

However, even low sulfate contents, in excess of about 0.5% by weight, are undesirable because they prevent the crystallization of ammonium thiosulf ats affect.

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It has now been found that ammonium thiosulfate from ammonia, sulfur dioxide, Water and sulfur can advantageously be produced if more than 50% by weight of the ammonia and sulfur dioxide required are introduced as liquefied gases into the reaction mixture and maintained at a temperature of 60 to 115 ° C during the reaction will. A temperature range from 70 to 95 ° C. is particularly preferred for the reaction.

The use of ammonia and sulfur dioxide in a predominant amount as liquid gases does not make it, as at present necessary to maintain an excess of ammonia, or a very slow reaction and high reaction temperatures of more than 100 ⁰ C respected. The process is carried out continuously in a single-stage or multi-stage reaction.

A two-stage process in which the reaction volume of the second stage is about 10 times the volume of the first stage has proven to be particularly versatile and economical. The process according to the invention is shown schematically in the figure. The starting products are then introduced into the reaction vessel (1) with a total volume of 2 m ^3. Water of reaction or any ammonium thiosulfate solution to be concentrated is introduced via line (2), liquid ammonia is introduced via lines (3) and (3a), liquid sulfur dioxide via lines (4) and (4a) and via line (5) liquid sulfur introduced. The liquid gases ammonia and sulfur dioxide are metered in via a perforated diaphragm with a pressure regulator and distributed in the reaction solution via perforated distributor pipes (3d) and (4b). These distribution pipes are about 60 cm long and have about 600 bores, each 3 mm in diameter.

If no liquid sulfur is available, it is advisable to all the required lump sulfur in unscrushed form in the post-reaction vessel (9) with a total volume of about

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18 m ^{3 to be added} continuously or discontinuously. In the vessel (9) it is also possible to replenish ammonia via line (3) and sulfur via line (5a).

The reaction solution is passed through the heat exchanger by means of the circulating pump (7) (6) returned to the reactor (1). The liquefied gases can also be fed individually or both into the circulation line (20) the line pieces (3b) and (4) are introduced after the circulation pump (7) through a single-substance or two-substance nozzle.

The solution passes from the reaction vessel (1) via the line (15) into the post-reaction vessel (9). The finished ammonium thiosulphate solution is drawn off through the filter (11) via the line (10), optionally treated with activated charcoal, filtered and fed to a crystallization stage. In practical implementation of the process according to the invention, it has proven to be advantageous, in the post-reaction vessel (9) with a small excess of sulfur, up to about 10% by weight, as this allows continuous monitoring of complete implementation becomes superfluous to ammonium thiosulfate. An occasional optical Monitoring for sulfur still contained in the reaction solution, for example via a sight glass, is sufficient to start the process safe to lead.

Of course, the excess sulfur can be removed from the concentrated ammonium thiosulphate solution can also be removed in other ways, e.g. by means of a hydrocyclone.

Occasionally it is necessary to make ammonium thiosulfate, which contains certain amounts of ammonium sulphite. Such salt mixtures are used as fixing agents for photographic purposes. Such a mixture can also be used in a simple manner the process according to the invention are produced, only care must then be taken that in the post-reaction vessel (9) a

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there is a stoichiometric deficit of sulfur, which corresponds exactly to the desired ammonium sulfite content.

As a rule, in the process described, the gases used are completely converted, so that it is not necessary to wash out sulfur dioxide or ammonia from the exhaust air. ^{In the event that temperatures above 110 °} C. occur as a result of incorrect operation of the system, the pH value is above 9.0 or the circulation pump (7) fails, the unconverted reaction gases can be protected with a tear disk (21) Line (16) are passed into the washing vessel (12) which is provided with a jet washer (13). Water is introduced into the washing stage via line (8) and - if it is necessary to maintain an acidic or alkaline reaction - ammonia via line (3c) or sulfur dioxide via line (4c). The washing solution is circulated through the line (18) by means of the circulating pump (14) and returned to the reaction vessel (1) via the line (18a).

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Examples example 1

8,000 kg of 61% strength by weight ammonium thiosulphate solution and 580% of water were fed into the reaction vessel (1) with a capacity of 1.5 m ^{3 per hour.} The liquid gases ammonia and sulfur dioxide were fed in via a cylindrical tube each with 600 bores, each 3 mm in diameter and 60 cm in length. The ammonia pressure was reduced from 9 bar to 5.1 bar and the sulfur dioxide pressure from 7 to 3.0 bar. The amount of liquid gas was limited by a screen with a diameter of 6.0 mm. The pH value of the circulated through the cooler solution turned to 6.9 to 7.3 and the temperature was maintained between 70 and 90 ⁰ C. A precipitate of ammonium sulfite in the temporarily supersaturated solution did not interfere with the course of the reaction in any way.

The solution or suspension flowing in from the overflow (15), the post-reaction vessel (9) with a useful volume of about 16m ^{3, was reacted with excess lump sulfur to form ammonium thiosulphate.} 800 kg of unbroken lump sulfur per hour were fed discontinuously to the post-reaction vessel (9). A small amount of ammonia was metered in via line (3) to achieve the stoichiometric conversion. The overflowing from the vessel (9) in an amount of 11,600 kg contained 72% by weight ammonium thiosulfate and was treated with activated charcoal in a further vessel, filtered and the. Crystallization fed. *Solution

The space-time yield was 200 kg of ammonium thiosulfate per m ³ and hour.

Example 2

Under otherwise the same conditions as described in Example 1, instead of lump sulfur was continuously 300 kg per hour

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liquid sulfur via line (5) into the reactor (1) and 500 kg likewise liquid sulfur via line (5a) into the Vessel (9) fed. The resulting 72% strength by weight ammonium thiosulfate solution was also satisfactory and contained less than 0.5 wt% sulfate.

Example 3

1900 liters of water, 400 kg of liquid sulfur and liquid ammonia were fed into the reaction vessel (1) every hour under a pressure reduced from 8 to 4.1 bar and liquid sulfur dioxide under a pressure reduced from 7 to 2.3 bar. The orifice plates for the liquid gases had a diameter of 6.0 mm. The pH value of the circulated through the cooler solution turned to 6.9 to 7.9, and the temperature was maintained at 70 to 90 ⁰ C. In the post-regeneration vessel (9), 160 kg of liquid sulfur per hour were continuously added to the solution overflowing from the reactor (1). If required, a small amount of ammonia was added. The solution overflowing from the vessel (9) in an amount of 4,100 kg / h contained 61% by weight of ammonium thiosulfate and was treated with activated charcoal and filtered.

Example 4

Under otherwise the same conditions as described in Example 3, the liquid sulfur dioxide was not in the reactor (1) but via line (4) into the circulation line behind the pump (7) fed in by means of a nozzle with a diameter of 7 mm. The reaction solution had one in the circulation line after the cooler (6) pH 6.1. The solution in the reactor (1) showed a pH of 8.5.

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Example 5

In the reactor (1) were every hour 2,050 1 of water, liquid ammonia under pressure from 9 to 4.3 tar reduced and liquid Sulfur dioxide under pressure reduced from 7 to 2.4 bar fed in. The pH of the circulating solution was between 7.3 and 8.0 and the temperature was kept at 70 to 85 ° C. From The ammonium sulfite solution overflowing the reactor (1) corresponded to a concentration of 55% by weight. In the post-reaction vessel (9) were every hour continuously fed 560 kg lump sulfur. The solution running out of the vessel (9) contained 760 g of ammonium thiosulfate and 95 g of ammonium sulfite per liter and activated charcoal was added and filtered.

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Claims (7)

- yf'- HOE 76 / f 185 Claims Process for the production of ammonium thiosulphate from ammonia, sulfur dioxide, water and sulfur, characterized in that,
that more than 50% by weight of the required ammonia and sulfur dioxide are introduced into the reaction mixture as liquid gases and a temperature of 60 to 115 ° C. during the reaction
is maintained. 2. The method of claim 1, dadurch'gekennzeichnet that the reaction is carried out at a temperature of 70 to 95 ⁰ C. 3. Process according to Claims 1 and 2, characterized in that liquid sulfur is used. 4. Process according to Claims 1 to 3, characterized in that the liquid gases enter the reaction solution through perforated tubes to be introduced. 5. Process according to Claims 1 to 4, characterized in that the process is carried out in two stages and the sulfur only is added in the second stage in the form of lump sulfur. 6- Process according to Claims 1 to 5, characterized in that the sulfur is added in a slight stoichiometric excess. 7. Process according to Claims 1 to 5, characterized in that the sulfur is added in a stoichiometric deficit
which creates a mixture of ammonium thiosulphate and ammonium sulphite. 709886/0483 ) ORIGINAL INSPECTED