DE2362923A1 - Ammonium thiocyanate prodn - from carbon disulphide and ammonia - Google Patents

Abstract

is prepd. from CS2 and NH3 by reacting CS2 with an at least equiv. quantity of (NH4)2S (in an aq. soln.) to produce (NH4)2CS3, and subjecting the latter to thermolysis to split of H2S and to produce NH4SCN. The yield is practically quantitative. The reaction mixt. is not very aggressive so that most of the apparatus can be made from iron. The process is rapid.

Description

The synthetic production of Ammo.niumrhodanid from Carbon disulfide and ammonia proceed depending on how the reaction is carried out via the intermediates ammonium dithiocarb-

amate and ammonium trithiocarbonate to the end products ammonium rhodanide and hydrogen sulfide.

This reaction has been carried out because of the volatility of the starting materials and the instability of the intermediate products under elevated pressure in closed pressure vessels, which is due to the high increase in pressure by the

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hydrogen sulfide evolved during the reaction was necessary, due to a large excess of ammonia water to bind the hydrogen sulfide as sulfur ammonium and thus make it water-soluble.

A disadvantage of this procedure is that the starting materials carbon disulfide and ammonia water are present in two different, mutually insoluble liquid phases, so that the reaction initially only takes place at the phase interfaces. As a result, the reaction speed remains low and the reaction time is greatly extended. Only as the reaction progresses do the water-soluble intermediate products form, as a result of which the various liquid phases merge into a single aqueous phase.
From this point on, the implementation will continue in
relatively short time.

Another disadvantage is that this pressure reaction because of
of the strong pressure increases at the beginning of the reaction only in
individual batches and can be carried out on a limited scale and therefore a continuous operation is very difficult.

The end product of this pressure reaction is an aqueous one
Solution of ammonium rhodanide and sulfur ammonium. The latter must go through an additional process from the
Reaction mixture are boiled and can be obtained as an aqueous solution or by a further process in
a sulfhydrate can be reacted, whereby ammonia is recovered.

Recently, two processes have become known, according to which the reaction with carbon disulfide and ammonia

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is carried out continuously and without pressure or with a slight excess pressure in reaction towers. _

According to US-PS 2,850,356 a reaction tower is used, filled with conventional packing such as Raschig rings is. The reaction between carbon disulfide and ammonia is carried out in the presence of an aqueous ammonium thiocyanate solution 20 to 50 wt.% NH ^ SCN carried out by a portion of the generated Ammonium rhodanide solution is recycled. The end product is ammonium thiocyanate solution and gaseous hydrogen sulfide.

In another known continuous mode of operation, the reaction in a tubular reactor in the presence of a special activated carbon and with a large excess of carbon disulfide carried out. The end products are an aqueous solution of ammonium thiocyanate and hydrogen sulfide gas with a high content of excess carbon disulfide, which is in an additional washing plant with a suitable Absorbing oil is removed and reclaimed.

Both methods have the same equipment implementation in operation the disadvantage that the entire system is made of high quality because of the high aggressiveness of the ammonium rhodanide Stainless steel must exist in order to keep the corrosion at an economically acceptable level. This problem as well the disadvantage of the expensive activated charcoal to be repeatedly added is avoided according to the invention.

The inventive method for the production of ammonium rhodanide on the basis of carbon disulfide and ammonia is characterized in that an aqueous solution of Sulfur ammonium, which contains sulfur ammonium in at least an equivalent amount, based on carbon disulfide,

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is reacted with carbon disulfide to form the intermediate product ammonium trithiocarbonate and then this is converted into ammonium thiocyanate with thermal elimination of hydrogen sulfide.

The method according to the invention can be carried out on a batch basis. However, it is preferably continuous carried out.

The new process is based on the fact that the reaction time can be shortened considerably if the reaction is not direct with the starting materials carbon disulfide and ammonia, but with the intermediate product ammonium trithiocarbonate is started. This intermediate can be relatively easily prepared from ammonium sulfide and carbon disulfide, and it is an essential feature of this invention that the reaction is started and continued in the presence of at least equivalent amounts of ammonium sulphide, so that the introduced carbon disulfide is instantly dissolved to form ammonium trithiocarbonate. Thereby lying the reactants in dissolved form and in a uniform phase. The application is particularly advantageous an excess of ammonium sulphide. The ammonium trithiocarbonate is then in the decomposition zone in ammonium thiocyanate with elimination of hydrogen sulfide converted. While the ammonium thiocyanate is drawn off as an aqueous solution at the end of the reaction, a part forms of the evolved hydrogen sulfide with the introduced ammonia again sulfur ammonium, which continues in this way eni is regenerated.

The overall reaction therefore proceeds according to the following reaction equations:

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(1) (HH ₄ ) ₂ S + CS _{2 3}

(2) (NH ₄ ) ₂ CS ₃ - »NH ₄ SCN + 2 H ₂ S.

(3) H ₂ S + 2 IiH,> (NH ₄ ) ₂ S

The sum equation therefore results for the overall reaction:

(4) CS ₂ + 2 NH ₃ ^ NH ₄ SCN + H _£ S

i.e. the reaction is carried out with the theoretical starting amounts, and that for the formation of the intermediate product The required ammonium sulphide is only a necessary reactant within the reaction zone and becomes there continually from the ammonia introduced and the hydrogen sulfide evolved during the decomposition of the intermediate product regenerated. The excess hydrogen sulfide escapes in a gaseous state after a washing process.

If the process is carried out continuously, this is expedient Cchulfurammonium in the reaction mixture by introduced Ammonia gas and hydrogen sulfide gas formed during the reaction are continuously regenerated.

The reaction using a column, in particular a bubble-cap tray column, is particularly advantageous in carried out continuously in several stages.

The ammonium trithiocarbonate is preferably decomposed at a temperature higher than the formation temperature of the trithiocarbonate within the range of 50

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For the technical implementation of the process, the reaction is broken down into individual stages, e.g. in three zones of a Reaction tower expire. A combined bubble-cap tray column is particularly suitable for this purpose, although ' other column constructions are applicable.

The inventive reaction procedure for the preparation of IIH ^ SCIi is described below and based on the in the Drawing reproduced schematic representation explained.

The column K is divided into three zones. The lower zone

1 is used to rearrange the ammonium trithio carbonate in ammonium rhodanide with elimination of hydrogen sulfide at temperatures between 50 and 9O ³ C, preferably 70 to 80 ⁰ C, and contains two heating registers 4, 5 in the lower part for heating the reaction solution to the required temperature without any other internals. A pressure of 1 to is favorable

2 m water column, corresponding to the sum of the immersion seals of the bubble cap column and the external immersion seal 9 in the hydrogen sulfide discharge.

The aqueous ammonium thiocyanate solution formed is drawn off at the bottom of the column for further processing via a level vessel, while the hydrogen sulfide evolved escapes into the upper zones. In the middle zone 2, on the one hand, the formation of ammonium trithiocarbonate takes place from the once provided sulfur ammonium and the supplied carbon disulfide and, on the other hand, the formation of sulfur ammonium from the hydrogen sulfide developed in zone 1 and the introduced ammonia. The introduction of the raw materials in a molar ratio of 1 CS ₂ : 2 NH takes place via a circulatory system outside of this part of the column, around a.

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To achieve intensive mixing and circulation of the reactants. For this purpose, the reaction mixture is drawn off from the sump of the lower tray of zone 2 through a pipeline and fed to a gas jet pump 7. Upstream of this pump, the carbon disulfide is introduced in liquid form into the suction line. The gas jet pump 7 is operated by means of ammonia gas under the tension-wise pressure of the liquid ammonia and thus the required ammonia is introduced via the jet nozzle. At the same time, it causes intensive mixing of all reaction participants. Since this reaction is exothermic, is installed advantageously in the pressure line of the gas jet pump, a heat exchanger 8, which enables an optimal reaction in the temperature range of 30 to 50 ⁰ C, preferably 4O C ^3. The pressure line is then returned to the upper floor of zone 2 so that the circuit is closed.

The upper zone 3 of the column is used to introduce the necessary fully demineralized solution water at a temperature of about 10 to 20 ⁰ C at the top of the column, which is also used to scrub the ammonia and carbon disulfide gases entrained from the lower zones from the excess hydrogen sulfide gas. The number of plates in this zone is to be dimensioned so that pure hydrogen sulfide escapes at the top of the column and is discharged via an immersion seal 9 for further use.

For this process, the proposed bubble tray column has the advantage that the immersion seals of the individual Bell bottom from top to bottom a slight increase in pressure arises, which counteracts the decomposition of the ammonium trithiocarbonate in the starting materials and the rearrangement favored towards ammonium rhodanide.

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The most important feature of this process is the presence of ammonium sulphide in at least an equivalent amount, preferably in excess, in the middle zone 2 of the column, which is continuously regenerated and due to the rapid formation of the intermediate product ammonium trithiocarbonate leads to a sharp reduction in the reaction time.

The yields are practically theoretical. Another great advantage of this method is the low level of aggressiveness this reaction mixture, which makes it possible to carry out most of the combined bubble cap column in iron, as the years of experience have proven. Only the lower part of the column with the heating registers, in which the remaining part of the hydrogen sulfide and ammonia is boiled off must be made of high quality stainless steel, although in this phase of the process pure aluminum is also resistant if there is a risk of contact corrosion is avoided.

In a modification of the method also Alkalirhodanide, especially potassium and sodium thiocyanate may be prepared _/ in an analogous manner, 1 mole of NH, is replaced by 1 mole of the corresponding alkali metal hydroxides.

The following example serves to further explain the invention.

example

The bubble tray column is before the start of the reaction in the upper part, as far as it includes zone 3, until the overflow individual floors are filled with fully demineralized water.

In the middle part of Zone 2, for example, 200 kg of sulfur

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L INSPECT

ammonium solution with 89.4 kg (NH ^) ₂ S submitted. This sulfur ammonium can also be produced by starting the reaction with 100% excess ammonia. For this purpose, zone 2 is also filled with deionized water up to the overflow of the individual floors and then the reaction is set in motion at room temperature by gradually adding, for example, 100 kg carbon disulfide and introducing 89.4 kg ammonia via the gas jet pump. A gradual increase in temperature to about 40 to 50 ^° C. and, at the same time, a red coloration of the reaction mixture due to the formation of ammonium trithiocarbonate occurs. As soon as this reaction mixture consists of a uniform aqueous phase of ammonium trithiocarbonate and sulfur ammonium, the reaction is carried out continuously by _{adding carbon disulfide and ammonia in a ratio of 1 CS 2} : 2 IiH ₃ Temperature range from 70 to 80 ⁰ C in zone 1 and from 30 to 50 ⁰ C in zone 2 continued. The end products are 1000 kg / h of ammonium thiocyanate as a 30 to 5C aqueous solution, which corresponds to a theoretical yield, and 580 m / h of hydrogen sulfide gas.

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Claims (4)

Claims / Tl method for the production of ammonium rhodanide on the Based on carbon disulfide and ammonia, thereby characterized in that an aqueous solution of ammonium sulfur, the ammonium sulfur in at least equivalent Amount, based on carbon disulfide contains, with carbon disulfide to form the intermediate product Ammonium trithiocarbonate is reacted and this then with thermal elimination of hydrogen sulfide is converted into ammonium rhodanide. 2. The method according to claim 1, characterized that when the process is carried out continuously the sulfur ammonium in the reaction mixture by ammonia gas introduced and formed during the reaction Hydrogen sulfide gas is continuously regenerated. 3. The method according to claim 2, characterized in that the reaction using a Column, in particular a bubble cap column, is carried out continuously in several stages. 4. The method according to claim 1 to 3 »characterized in that the decomposition of the ammonium trithiocarbonate at a temperature higher than the formation temperature of the trithiocarbonate within the range from 50 to 9Ö> C is carried out. 509825/0 629