DE2635649B2 - Process for the production of ammonium thiosulfate ' - Google Patents

Description

The invention relates to a process for the production of ammonium thiosulfate, if appropriate in a mixture with ammonium sulfite, from ammonia, sulfur dioxide, water and sulfur.

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

In US Pat. No. 22 19 258, a two-step process for the production of crystallized Ammonium thiosulfate described, in which in the first reaction stage sulfur dioxide and ammonia in aqueous solution to be converted to ammonium sulfite. In the second reaction stage, the aqueous Ammonium sulfite solution reacted with sulfur to form a 30% ammonium thiosulfate solution. The ammonium thiosulphate is completely crystallized out and separated off from this solution by adding ammonia. The remaining ammonia solution goes back into the process. There is a disadvantage to this method in the relatively low concentration of about 30% ammonium thiosulfate with accordingly lower space-time yield of crystallized ammonium thiosulfate. This also results in another Disadvantage of the process is the need to use the ammonia solution remaining during crystallization to remove a large part of the ammonia again, since a significantly higher ammonia concentration is necessary for the quantitative crystallization of the ammonium thiosulfate than for the reaction with Sulfur dioxide. Furthermore, the high heat of dissolution of ammonia in the aqueous, about 30% Ammonium thiosulphate solution not taken into account, which forces the crystallization process to cool down too much. Strong salt incrustations occur on the cooling surfaces.

From German patent 8 57 490 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 up to about 110 to 13O ⁰ C,! To achieve in a quantitative reaction. After the implementation has been completed, a TUI des

ίο dissolved ammonium thiosulfate by cooling and / or evaporative crystallization and / or by salting out, for example with ammonia, as a solid, deposited anhydrous salt and returned the mother liquor to the process

The disadvantage of this process, however, is that very long reaction times are accepted for the quantitative conversion of the ammonium sulfite with the stoichiometric amount of sulfur, despite an increase in the temperature to a final value of about 110 to 130 ^{° C.}

must be μ. The Increase in temperature even the application of higher pressures. However, quantitative turnover is required otherwise the ammonium thiosulphate produced is contaminated with sulphite and sulfur. That

Process allows only moderate space-time yields.

From the German patent 12 63 721 a continuous, two-stage process for the production of ammonium thiosulfate from ammonia, sulfur dioxide, water and sulfur is known, in which the Conversion of ammonia, sulfur dioxide and water to ammonium sulfile in the first reaction stage in The presence of a large excess of elemental sulfur occurs, with the ammonium sulfite formed already in the first stage for the most part in

Ammonium thiosulfate is transferred, and that the Implementation of the remaining ammonium sulfite in the

second stage again in the presence of a large one

Excess of elemental sulfur takes place. All known methods have in common that

■ »o Ammonia and sulfur dioxide are used as gases will. The raw materials ammonia and sulfur dioxide supplied in liquid form must be used initially in an upstream, energy-consuming process step in the the gases are converted. In addition, it is because of the readily decomposable nature of ammonium thiosulphate it must be ensured that an excess of ammonia must be observed in all process stages. In addition, especially when sulfur dioxide containing roasting gases are used, there are always exhaust air problems. Above all, however, the known methods are characterized by relatively low throughputs. So z. B. in German Patent 12 63 721, a throughput of a maximum of 42.6 kg / h and m ³ reaction volume calculated on 100% ammonium thiosulfate is still considered advantageous compared to older processes. ^{Finally, the reaction temperature of up to 130 °} C. proposed in some known processes to increase 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 ) ₂ SO ₃ + 2 NH ₄ HSO ₁ - 2 (NH ₄ J ₂ SO ^ SIH ₂ O

Even low sulfate contents, which exceed about 0.5% by weight, are undesirable because they cause the

Impair the crystallization of the ammonium thiosulphate.

It has now been found that ammonium thiosulfate is made up of ammonia, sulfur dioxide, water and sulfur a temperature of 60 to 115 ° C can be advantageously produced if more than 50 wt .-% of the required ammonia and sulfur dioxide are introduced into the reaction mixture as liquid gases. 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. Schematise'- ¹ , the method according to the invention is shown in the figure. Thereafter, in the reaction vessel (1) m with a total volume of 2 ³ the starting products are introduced via the line (2) water of reaction, or may be concentrated ammonium thiosulfate solution introduced via the lines (3) and (3a) are liquid ammonia, via the lines ( 4) and (4a) are liquid sulfur dioxide and liquid sulfur is introduced via line (5). 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 (3c /,) 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, then it is advisable to add all of the required lump sulfur in reduced form to the post-reaction vessel (9) with a total volume of about 18 m ^3, continuously or discontinuously Additional metering of ammonia via line (3) and sulfur via line (5a, J) take place.

By means of the circulating pump (7), the reaction solution through the heat exchanger (6) into the reactor (1) wire is returned, the liquefied gases can also individually or both in the circulation (20) via conduit pieces (3b) and (4) after the circulating pump (7 ) 5 (1 can be introduced through a single-fluid or two-fluid nozzle.

The solution passes from the reaction vessel (1) via line (15) into the post-reaction vessel (9). The finished ammonium thiosulphate solution is drawn off through the filter (II) via line (10), optionally treated with activated charcoal, filtered and fed to a crystallization stage. In the practical implementation of the process according to the invention, it has proven to be advantageous to work with a slight excess of sulfur, approximately up to 10% by weight, in the post-reaction vessel (9), since this enables continuous monitoring complete conversion to ammonium thiosulphate becomes superfluous. Line occasional optical monitoring for sulfur still contained in the h5 reaction solution, for example via a sight glass , in order to conduct the process safely.

Of course, the excess sulfur can be extracted from the finished, concentrated ammonium thiosulfate solution also in other ways z. B. be removed by means of a hydrocyclone.

Occasionally it is necessary to produce ammonium thiosulphate, which is certain quantities of ammonium sulphite contains Salt mixtures of this type are used as fixing agents for photographic purposes Such a mixture can also be produced in a simple manner by the method according to the invention but then care must be taken to ensure that a stoichiometric There is a deficit of sulfur, which corresponds exactly to the desired ammonium sulfite content

In general, the gases used be fully implemented so that a leaching of sulfur dioxide or ammonia from the exhaust air is not required In the event, however, that occur due to a wrong operation of the system temperatures above 110 ⁰ C, the pH in the process described is above 9.0 or the heating pump (7) fails, the unreacted reaction gases can be passed through the line (16) secured with a tear disk (21) into the washing vessel (12), which is provided with a jet washer (13) In the washing stage, water is passed in 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 introduced through line ( 18) is circulated by means of the circulating pump (14) and returned to the reaction vessel (1) via the line (18a ''')

Examples Example I.

In the reaction vessel (1) with an effective volume of 1.5 m ³ per hour of 8000 kg 61 wt .-% hydrochloric Animoniumthiosulfatlösung and 580 1 of water fed, the supply of the liquefied ammonia, and sulfur dioxide was carried over a respective cylindrical, with 600 holes each of 3 60 cm long tube with a diameter of 60 cm. 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 73, and the temperature was maintained between 70 and 90 ⁰ C. A precipitate of ammonium sulfide in the temporarily supersaturated solution did not interfere with the course of the reaction in any way.

The solution or suspension flowing into the overflow (15), the post-reaction vessel (9) with a useful capacity of about 16 m ^{J was converted 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 added via line (3) to achieve the stoehiometric conversion. The solution 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 sent to crystallization

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

Example 2

Under otherwise the same conditions as described in Example I, 300 kg of liquid sulfur per hour was continuously fed into the reactor (I) via line (S) and 500 kg of liquid sulfur, likewise from the line (5a), into the vessel (9). fed in. The resulting 72% strength by weight ammonium thiosulphate solution was also satisfactory and contained less than 0.5% by weight sulphate.

Example 3

1400 liters of water, 400 kg of liquid sulfur and liquid ammonia under a pressure reduced from 8 to 4.1 bar and liquid sulfur dioxide under a pressure reduced from 7 to 2J bar were fed into the reaction vessel (1) every hour a diameter of 6.0 mm. The pH value of the circulated through the cooler solution turned on b, 9 to 7.9, and the temperature was maintained at 70 to 90 C. In the post-reaction vessel (9) , 160 kg of liquid sulfur per hour were continuously added to the solution overflowing from the reactor (I). If necessary, a small amount of ammonia was added. The solution overflowing from the vessel (9) in an amount of 4100 kg / h contained 61% by weight 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 fed into the reactor (1) but into the circulation line behind the pump (7) via line (4) by means of a nozzle with a diameter of 7 mm. In the circulation line after the cooler (6) the reaction solution had a pH value of B1. The solution in the reactor (I) showed a pH value of 8. ^r >.

Example 5

r ~> In the reactor (1) were every hour 2030 l of water, liquid ammonia under a pressure reduced from 9 to 4.3 bar and liquid sulfur dioxide unier a pressure reduced from 7 to 2.4 bar. The pH of the circulating solution was between 7.3

_> o and 8.0. the temperature was kept at 70 to 85 "C. The ammonium sulfite solution overflowing from the reactor (I) corresponded to a concentration of 55 Geu.'in. In the post-reaction vessel (9) were continuous for hours 5b0 kg of lump sulfur supplied. The ones from the

:> Vessel (9) running solution contained 760 g ammonium thiosilfate and 95 g ammonium sulfil per liter and activated charcoal was added and the mixture was filtered.

For this 1 sheet of drawings

Claims (7)

Patent claims: 1. Process for the production of ammonium thiosulfate from ammonia, sulfur dioxide, water and Sulfur, at a temperature of 60 to 115 ° C, characterized in that more than 50 wt .-% of the required ammonia and sulfur dioxide as liquid gases in the reaction mixture to be introduced. 2. The method according to claim 1, characterized in that the reaction at a temperature of 70 to 95 ° C is carried out. 3. The method according to claims 1 to 2, characterized in that the liquid gases through perforated tubes are introduced into the reaction solution. 4. Process according to Claims 1 and 2, characterized in that liquid sulfur is used will. 5. Process according to Claims 1 to 3, characterized in that the process is in two stages is carried out and the sulfur only in the second stage in the form of lump sulfur is admitted. 6. The method according to claims 1 to 5, characterized in that the sulfur in a low stoichiometric excess is added. 7. Process according to Claims 1 to 5, characterized in that the sulfur is added in a stoichiometric deficit.