DE1767465C - Process for the production of anhydrous hydrogen fluoride - Google Patents

Description

The invention relates to a method which the Ge * o winniing of anhydrous hydrofluoric acid permitted.

Numerous technical processes deliver gaseous mixtures, in soft form residues or impurities Fluorine compounds are located. These fluorine compounds are often in the form of hydrofluoric acid, Siliciumteirafluorid or as mixtures of these compounds.

Various methods have been proposed to remove the fluorine compounds from these gaseous mixtures. Most of these processes rely on scrubbing these gases. Certain processes lead to more or less concentrated solutions of fluorosilicic acid. Others use ammonia and solutions of ammonium luoride are obtained after the silica has been separated off by filtration. Regardless of their origin, the Ammoriiumfluoridlösungen can be usually subjected to heating to a temperature of between 60 and 200 ⁰ C. After the ammonia has been removed, anhydrous ammonium dichloride or a practically anhydrous mixture which is very rich in bifluoride is obtained.

It is known to obtain hydrofluoric acid from a gas mixture of ammonia and hydrofluoric acid. The gas mixture is passed over a catalyst at elevated temperatures, which splits the ammonia into hydrogen and nitrogen, but changes the hydrogen fluoride gas. From the newly emerged. Gas mixture can be obtained in a simple manner using known process steps to obtain hydrofluoric acid. The starting gas mixtures are obtained by thermal decomposition of animonium fluoride salts, in particular from ammonium bifluonuene. According to this known process, o'.c separated gases for recovery are combined again to form ammonia in a very laborious process step and cannot be recycled to the Pro, ··.:. (Again.

It was also requested that the fluorine contained in the fluorides in the form of hydrofluoric acid to win. For example, it has been proposed .. ·. '., Anhydrous ammonium bifluoride at about 190 ° C. n> it concentrated sulfuric acid to decompose. In this way it is possible to get up to 98% of the iSifluoiid emha! Ii_nc.i To obtain fluorine in the form of anhydrous hydrofluoric acid; the ammonium is then in the form \ on Ammonium sulfate. The recovery of the By the way, ammonia in the form of a poorly usable salt is not the only disadvantage of this Extraction process, because the process is very special because of the aggressive nature of the medium Required equipment and due to the inevitable and well-known corrosion phenomena becomes very costly. These disadvantages mean that the industrial application of a cycle is not is possible.

It has now been found a method that the treatment of ammonium bifluoride to obtain anhydrous hydrofluoric acid allows to use without sulfuric acid and which therefore only marginally Has difficulties with regard to possible signs of corrosion.

The invention is based on the property of numerous metals, such as in particular bismuth, cobalt, copper, Manganese, zinc, magnesium, iron, nickel, germanium, tin, thorium, titanium, aluminum, indium, zircon Chromium, uranium, and vanadium, complex ammonium fluorides or metal-ammonium double fluorides too form, hereinafter called Ammoniumfluometallatc, which are thermally decomposable and the separated Recovery of the metal fluoride and ammonium fluoride with a view to their reuse allow.

The invention relates to a process for the recovery of anhydrous hydrogen fluoride Ammonium bifluoride, which is characterized in that ammonium bifluoride is used in a first stage or a product containing ammonium bifluoride with one capable of forming ammonium fluorometallates capable metal fluoride converts at a temperature which is between the melting temperature of the lowest melting reaction participant and the Decomposition temperature of the fluometalate formed, wins the resulting hydrogen fluoride and in a second stage at a temperature that is higher than the temperature of the first stage first stage formed ammonium fluoinetallal with the formation of Ammoniumfliiorid and the used Thermally decomposed metal fluoride. The metal fluoride obtained in the second stage is again in the first stage returned.

According to a first embodiment of the method according to the invention, a simple metal fluoride is used Fluoride of a metal is used, preferably

of bismuth, germanium, kobali, copper, manganese, Zinc, magnesium, iron, nickel, tin, thorium, titanium, aluminum, indium, zircon, chromium, vanadium or uranium.

According to another embodiment, the fluoride used is a double fluoride of ammonium and of a metal, especially aluminum, iron. Zircon, Indium, chromium, vanadium and uranium, the lowest possible double fluorides, have a lower coordination number than the double fluoride produced in the first stage of the process according to the invention.

In the case of a trivalent metal M, the playing reactions can be represented as follows:

First embodiment

3 NH ₄ F -HF I- MF ₃ -> (NH ₄ J ₃ MF, - | 3 HF

(gaseous) (ΝΙΙΛ, ΜΙΥ- - - -> MF ₃ ; 3 NlI ₄ F (gaseous)

Second embodiment
: NH ₁ F · HF + NH ₄ MF ₄ -> (NH ₄ J ₃ MF, + 2 HF

(gaseous)

(NH ₄ ) ₃ MF _e ■ -> NH ₄ MF ₄ I 2 NH ₄ F

(gaseous)

In either case, there is no difficulty in separating the products obtained because of any reaction leads to a gas and a non-gaseous fluoride and the reactants used themselves are not gaseous.

In both cases, the reaction of the second stage of the process also results in the used Metal fluoride and the amount of ammonium fluoride recovered, which was contained in the bifluoride used in the first stage.

The first-stage reaction can be carried out until it is completely converted to double fluoride and hydrofluoric acid. However, there are cases in which one wishes to stay 100 ° / ₀ by weight degree of conversion. In addition to the double fluoride formed by the reaction, the solid obtained then contains a residue of unreacted metal fluoride and ammonium bifluoride. These remaining starting products are recovered as such or in the form of their decomposition products at the end of the second stage.

The metal fluoride is used in an amount at least equal to the stoichiometric amount to be treated bifluoride is appropriate amount.

The temperature used in the first stage depends on the type of metal fluoride used. A temperature between 125 and 200 ^° C. is preferably used, although it is possible to work at an elevated temperature.

However, it is preferred to work at a relatively low temperature, in particular at a temperature close to the melting point of the chloride used. It thus avoids the contamination of the recovered hydrofluoric acid by Ammoniumfiuorid that certain by decomposition Doppcllluoride may be formed of 200 ⁰ C.

It can be advantageous to work under a pressure above atmospheric pressure in order to achieve the decomposition to slow down the fluonietallates formed and to permit the application of a relatively elevated temperature which affects the kinetics of cleavage promotes of gaseous hydrogen fluoride without the disadvantages of premature elimination of Enter ammonium fluoride.

The one used to decompose the fluomelallate The temperature depends strictly on the metal used. The fluometalates that can be used in accordance with the invention / replace each other at a rate which depends on the selected temperature, and one becomes for each of these compounds use such a heating temperature at which the decomposition rate is optimal is. The selected temperature is generally significantly higher than that for the formation of the fluometalates

ίο elimination of hydrofluoric acid applied Temperature.

It can be seen that the described process according to the invention can advantageously be used in a circuit for obtaining fluorine-containing products from gaseous mixtures. Such a cycle comprises the washing of the case with the aid of an ammoniacal solution according to known methods, the heating of these solutions to remove solid ammonium bifluoride and an amount of gaseous ammonia corresponding to that absorbed by the fluorine-containing products during the wash, then the treatment of the Bifluoride according to the method of the invention.

It is clearly evident that in such a circuit the originally contained in the gas mixture, recoverable fluorine compounds in the form of anhydrous hydrofluoric acid without this extraction causing the consumption of ammonia or any other reagent.

The following examples illustrate the process of the invention.

example 1

An ammonium fluoride solution was assumed, which was obtained by washing out the from a superphosphate plant derived gases containing hydrofluoric acid and silicon tetrafluoride had been.

The gaseous products from the decomposition of ammonium hexalflioaluminate from an earlier process step were added to this solution. This solution was ^{heated to 180 °} C., molten ammonium fluoride and gaseous ammonia being obtained. The solid bifluoride was mixed with an anhydrous aluminum fluoride in excess of the stoichiometric amount. The mix was placed in a sealed reactor which was vented and placed in a continuously heated oil bath. When the temperature of the reactor reached 147 ^° C., the elimination of gaseous hydrogen fluoride was observed, the rate of which increased rapidly with increasing temperature. The removal of HF was ensured with the aid of a stream of nitrogen and the reaction vessel was kept under a slight excess pressure (90 mm Hg above atmospheric pressure). After 1V _{for 2} hours under these temperature and Driickbedingiiiif.cn more than 90 ⁰ were / released ₀ of hydrofluoric acid and won. The presence of ammonia could not be determined in the acid obtained.

The remaining solid, which mainly referred from Ammoniumfluoaluminat, including ammonium cryolite, aluminum fluoride and non-degraded Ammonium existed, was then heated to 45O ⁰ C. The freely grazing gas mixture, which consists essentially of ammonium fluoride, accompanied by gaseous decomposition products of ammonium

niiluorid existed, was in the Armnoniumliuoridlösung returned. The solid formed in this hot stage was veri with a further portion of bifluoride iiischi.

That during the transfer of the ammonium chloride solution Gaseous gases released in bifluoride Ammonia was used to treat another portion of gas and thus to form another portion Ammonium fluid solution used.

In this way, ils became anhydrous hydrofluoric molar acid obtained practically without the consumption of additional reagents.

Example 2

In a Rcaktionsgefäß from Monei-Muall a very intimate mixture of the following ingredients was prepared in the cold: 10 g of ammonium bifluoride, erhalien Jurch evaporating a Ammoniumtluoridlösung by known Verfahrer, and 10 g of anhydrous Aluniiniumfuiorid AII _11, by thermal decomposition of the former in a. Ammoniunikryolilhs formed in the process stage had been obtained. The amount of AlF ₁₁ exceeded the stoichiometric amount by 32 "I ₁₁ .

After that (ionically homogeneous. Wind .; that The reaction vessel is closed and subjected to a stranded wire in an oil bath. By initiating An overpressure of at least 50 mm Hg was ensured in the reaction vessel with nitrogen.

At 180 ^° C., the elimination of hydrogen fluoride began. The reaction took its course at constant temperature with increasing speed, which reached its maximum value after 32 minutes at a conversion of 45%.

The temperature was throughout the Versuelis maintained, which ended after 2 hours with a recovery of 97.1% at Hl ·.

The yield was already more after 75 minutes than 95%.

The analysis showed the complete absence of ammonia in the recovered hydrofluoric acid.

The residue from the process was in the form of a fairly hard sintered cake. By stripping to 450 "C, on the one hand, the reduced amount of AIF _{11 and} , on the other hand, the amount of gaseous ammonium chloride that corresponded to the replaced bifluid. Heide products could be used again in a new cycle.

B e i s ρ i c 1 3

19.327 g ZrF ₄ were admixed with ¹ g 9.S Aninioniumlluorid intimately mixed, so that a IOO% excess of ZrF ₄ existed W.

The rcakiionsicilnchmer were in the foregoing Example described device brought.

The nitrogen supply used for the removal of III set a relative overpressure of 55 mm Hg in the Uuaktinnsgefäß.

From a temperature of 9 ° C. onwards, the Absp.iliiing occurred of lluoi hydrogen on. At forlschreiiender The rate of reaction rose rapidly as the temperature increased.

The reaction proceeded according to the following reaction equation:

γ ^ _: ^ \ ^ \\ ρ HF (NU ) Z'F '3 HF

^ ¹ '' _h * _{mo | zcn} "' _fcs , ^{4 3} " gaseous

After 10 minutes, at a temperature of 123 ^° C., the yield at 111 "was 38.5%. After 20 minutes, at 136" C, it reached 71.0% and after 35 minutes at 150 ° C., 92 "/ ". The experiment was finally ended at Ki5 'C, which was reached after 92 minutes. The conversion finally achieved in the reaction was 97.4%.

No ammonia was found in the recovered product.

The residue turned out to be a porous, fragile mass. Determination of the degree of conversion in both reactions using the weight loss gave a yield of 98.8 "/" which is significant considering the difficulty contemplates complete recovery of the solid.

F.rhiizen by the solid residue to 450 C 19.2SOg ZrF ₄ were the / m reuse ge suitable is recovered.

Example 4

This attempt is based on the following reactions:

2NH ₁ F-HF, NH ₄ AIF ₄ ■> (NH ₄ ) _{: i} AIF _e I 2 HF up to temperature 190 "C;

(NH ₁ I ₁₁ AII - ",., - NH ₄ AlF ₄ I 2 NH ₁ I- up to temperature 300" C.

9,152 g were Animoniumhifluorid (F AIF ₁₁ · 1.057 NH ₄₎ vcrmischt intimately with 11,011g Ammoniumtctrafhioraluminat the analytically bcstimmten exact formula. This powdery, egg-shaped mixture was placed in a reactor which, with the aid of a thermostatic filter

Oil bath was heated from the outside. The temperature of the oil bath was set at 175 ° C. The split off Hydrogen fluoride was taken up in water at the exit of the reactor.

The experiment lasted 2 hours and 10 minutes.

The yield of the reaction was 92% of III · ". Fs a solid residue of 17.2OK g was obtained which contained 15.07 g of ammonium cryolite. This solid The residue was placed in an electrically heated iron reactor. After 45miniligcm frictions up to

At a final temperature of 275 ° C., a weight loss of S.02 g was observed, which _{corresponded to the splitting off of NII 3} and III. 9.19 g of an Fcst substance corresponding to the formula All · "; · 1.07 NH ₄ F remained. This product can be used again in the first reaction. The gases evolved are recovered by condensation in the form of ammonium fluoride, J; | _{S can} also be used again.

If you use zirconium compounds in this process, the following reactions take place:

2NII ₁ II
(NH ₁ ) ^ room

II NII _-1 ZrF ₅

(NH ₄ ) _{: i} ZrF ₇ I 2 111 "
NH ₄ ZrF., | 2 NH ₄ F

Claims (3)

Patent claims: 1. Method of obtaining anhydrous I luorwasserMoff from ammonium bifluoride, thereby characterized in that one in a first stage ammonium or an ammonium bifluoride containing product with one capable of forming ammonium fluorometallates Metal !! uoride at a temperature between the melting temperature of the lowest melting point Reaction thermometer and the decomposition temperature of the fluometalate formed converts, wins the resulting hydrogen fluoride and in one / wide level at one compared to the tempe- '5 Temperature of the first stage increased temperature the formed ammonium fluorometallate with the formation of Ammonium fluoride and the metal fluoride used thermally splits and the metal fluoride released in the second stage in the first stage returns. 2. The method according to claim 1, characterized in that the metal fluoride is a fluoride of Bismuth, germanium, cobalt, copper, manganese, zinc, magnesium, iron, nickel, tin, thorium, * 5 Titanium, aluminum, indium. Zircon, chrome, vanadium or uranium is used. 3. The method according to claim 1 or 2, characterized in that the metal fluoride is a double fluoride of ammonium and a metal, namely aluminum, iron, zircon, indium, uranium, chromium, Vanadium, is used, its coordination number is lower than that of the double fluoride obtained in the first stage. 35