FI59076C - FRAMEWORK FOR THE FUELING OF FLUOROUS FREON AND FORMATION OF AMMONIUM FLUOROUSES AND AMMONIUM BIFLUORIDES - Google Patents

Description

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_. (44) Date of issue. - __ Q, P * tmt * OCh r «glst« ntyr * lMn An * ek * n utlatd och utl.skrffMn publkarad 27.02.81 (32) (33) (31) Pyydatty atuolkaut— B «gird prlorltat (71) Kemira Oy, Malminkatu 30, 00100 Helsinki 10, Finland-Finland (FI) - (72) Arie van der Meer, Helsinki, Lauri Armas Lepomaa, Espoo,

The present invention relates to a process for the preparation of fluorinated amine fluoride. The present invention relates to a process for the preparation of fluorinated ammonium fluoride and ammonium bifluoride to a process for the preparation of hydrogenated ammonium fluoride and ammonium bifluoride. an aqueous solution of magnesium fluoride and ammonium bifluoride by steam stripping at an elevated temperature with excess concentrated sulfuric acid to evaporate the hydrogen fluoride to the desired concentration.

Austrian Patent No. 236,340 discloses a process for the production of hydrogen fluoride by distilling HF from a mixture of ammonium fluoride and sulfuric acid in a distillation column with 15 theoretical bases. A good temperature of 135-170 ° C is required for good yield. Due to the corrosive conditions, only impregnated graphite can be used in the heat exchanger, which as a single material can withstand a maximum pressure of 600 kPa and a temperature of 165 ° C. Therefore, very expensive and large heat exchangers must be used for good HF yield. The recovery of hydrogen fluoride necessary to obtain anhydrous hydrogen fluoride at the top of the column also requires an additional supply of energy to the bottom of the column.

It has also been proposed to strip hydrogen fluoride with an inert gas from a mixture of aqueous ammonium fluoride and ammonium bifluoride and sulfuric acid (U.S. Patent 3,455,650). In this case, however, the inert gas follows 2,59076 of stripping hydrogen fluoride, interferes with the condensation of hydrogen fluoride, and must be separated from the latter at a later stage, which causes HF losses and requires exhaust gas treatment.

Also known is a two-step process (British Patent 1,060,519) in which solid ammonium fluoride-ammonium bifluoride is mixed with concentrated sulfuric acid at 150 ° C to release most of the hydrogen fluoride, after which steam is fed to the mixture and depressurized to release residual hydrogen from the mixture. is, first, that the aqueous solution of ammonium fluoride and ammonium bifluoride obtained from the ammonization of fluorosilicic acid I 2 SiF 2 must first be evaporated to dryness to obtain solid ammonium fluoride-ammonium bifluoride, and secondly, a reduced pressure must be applied in the evaporation step.

It is an object of the present invention to provide an even simpler and more economical process for the preparation of hydrogen fluoride from an aqueous solution of ammonium fluoride and ammonium bifluoride by distillation with excess concentrated sulfuric acid to produce hydrogen fluoride at the desired concentration.

The main features of the invention appear from the appended claim 1.

According to the present invention, the aqueous solution of ammonium fluoride and ammonium bifluoride is not evaporated to dryness, but the aqueous solution is used as such and mixed with sulfuric acid. Also, the mixture is not indirectly heated by pressurized steam, but the steam is introduced directly into the mixture to heat it. The hydrogen fluoride released in the stripping is then passed through a drying zone of the column where it is contacted with concentrated sulfuric acid to produce the desired concentrated hydrogen fluoride, whereby the sulfuric acid obtained from the drying is returned to the stripping section of the column.

The invention is described in more detail below with reference to the accompanying drawings, in which Figure 1 shows a schematic elevational view of a stripping column for applying the process of the invention, Figure 2 shows the dependence of boiling temperature and to the liquid vapor equilibrium of the distillable acid mixture.

Here, the concentration of free sulfuric acid means the amount of I 2 SO 4 in excess of the amount required to form ammonium bisulfate, calculated from the sum of water and free sulfuric acid in solution: (H 2 SO 4 / d 2 SC 2 + H 2 O).

In Fig. 1, the separation column is indicated by reference numeral 1 and the drying zone thereon by reference numeral 2. A mixture 3 of an aqueous solution of ammonium fluoride and ammonium bifluoride and a first portion 8 of sulfuric acid 8 is fed between the separation zone 1 and the drying zone 2. The acid used is = 93% by weight of sulfuric acid and its second part 7 is fed to the upper end of the drying zone 2. At the same time, steam 6 is fed to the lower end of the separation zone, which strips the mixture from the feed 3 to the hydrogen fluoride separation column 1. The liberated hydrogen fluoride gas flows to the drying zone 2 where it encounters a second portion 7 of 93% by weight sulfuric acid.

Thus, a hydrogen fluoride gas 4 of the desired concentration is obtained from the top of the column, which is passed to a condenser 9, where the hydrogen fluoride gas liquefies. The resulting hydrogen fluoride can be anhydrous without hydrogen fluoride recovery.

Thus, the condenser may be smaller in size and less steam is needed at the bottom of the column.

The base product of the column is about 30-60% by weight of sulfuric acid 5 with about 10-50% by weight of ammonium bisulfate. The dilute hot sulfuric acid solution 5 is cooled and can be used, for example, for the preparation of phosphoric acid.

At least enough sulfuric acid must be fed to the separation column 1 that the ammonia contained in an aqueous ammonium fluoride-bifluoride solution of more than 50% by weight is bound to ammonium bisulphate. This releases hydrogen fluoride and can be stripped with steam.

The invention is described in more detail below by means of examples.

Example 1 A 22.7% HjSiFg solution obtained by concentrating 2850 kg of phosphoric acid is ammonized by feeding 180 kg of reflux ammonia from the evaporator into the solution with 19 kg of water vapor and 316 kg of ammonia from the vaporizer. 2966 kg of the filtrate are obtained in a SiO2 separation and 380 kg of a precipitate are washed 1: 1 with water. The wash filtrate is combined with the main filtrate, which becomes a total of 3335 kg. This is concentrated by evaporation to give 1365 kg of evaporation product with an F / N ratio of 1.467 and an I 2 O content of 38%. 2300 kg of water with a NH 2 content of 0.2% and an F content of 0.06% condense from the evaporated gas in the water separation device when 510 kg of steam enters the bottom of the water separation column.

The evaporation product is fed to the column shown in Figure 1 together with 2187 kg of 93% by weight of sulfuric acid and at the same time 3103 kg of 93% by weight of sulfuric acid are fed to the drying zone 2. The column is heated by steam alone, which is fed to the bottom of column 6 at 500 kg. Hydrogen fluoride gas 4 is obtained from column 2 practically anhydrous. Hydrogen fluoride gas liquefier 9 gives 504 kg of hydrogen fluoride (93% yield) with 0.2% water. 6651 kg of basic acid 5 with 47% by weight of free sulfuric acid, 0.5% by weight of hydrogen fluoride and 31.7% by weight of ammonium bisulfate are obtained.

Example 2 1479 kg of evaporation product are fed to the column shown in Fig. 1 together with 1500 kg of 93% by weight of sulfuric acid and at the same time 2964 kg of 93% by weight of sulfuric acid are fed to the drying zone 2. The column is heated by steam alone, which is fed to the bottom of column 6, 387 kg. 75% of hydrogen fluoride gas is obtained from column 2. Hydrogen fluoride gas liquefier 9 gives 766 kg of hydrogen fluoride (92% yield)? with 25% water.

5546 kg of basic acid 5 with 39% by weight of sulfuric acid, 0.9% by weight of hydrogen fluoride and 41.7% by weight of ammonium bisulfate are obtained.