SU402378A1 - METHOD OF CLEANING GASES CONTAINING FLUORINE CONNECTIONS - Google Patents

Description

one

The invention relates to the field of purification of gases containing fluorine compounds, in particular by the absorption of these compounds in aqueous ammonium fluoride solution.

A known method of purification of gases containing fluorine compounds (for example, waste gases of superphosphate production, containing predominantly silicon tetrafluoride) by absorption of these compounds with an aqueous solution of ammonium fluoride.

As a result of absorption, a solution of ammonium fluoride is obtained, which is treated with ammonia, a silica gel is separated into a precipitate, which is then separated as a marketable product (white soot). A part of the ammonium fluoride solution remaining after the separation of the silica gel is returned to the gas absorption stage, and a part is vaporized, a mixture of normal and acidic ammonium fluoride is precipitated.

A significant disadvantage of this method is its unsuitability for the purification of weakly concentrated gases containing predominantly hydrogen fluoride, for example, gases obtained by hydrothermal processing of phosphates and containing not more than 2 g / m of fluorine.

According to the proposed method, a silica gel is introduced into the ammonium fluoride solution supplied to the absorption. When using circulating solutions of ammonium fluoride, already containing silica gel, the latter can be omitted. When irrigating weakly concentrated (fluoride) gases containing hydrogen fluoride with ammonium fluoride solution containing silica gel in an amount of the order of 1 weight. hours 1.5 weight. am dissolved ammonium fluoride, sorption is accompanied by the reaction

4HF + SiO, + 2NH, F - (NH,), SiFe + H, O

The resulting solution of ammonium silicofluoride, having a temperature of about 70 ° C,

treated with ammonia, precipitated fresh portions of silica gel. Of the total amount of silica gel precipitated in the sediment, about 80% is returned to the CYCL at the absorption stage, and about 20% is recovered from the solution as a marketable product ("white soot"). The solution remaining after the separation of the silica gel is fed to the pack, with the aim of separating the mixture of ACID and normal ammonium fluoride.

A low-quality silica gel can also be introduced into the ammonium fluoride solution supplied to the absorption stage, and the entire gel formed by neutralization with ammonia can be

case is taken out of cycle as a marketable product.

Example 1. 5000 m of gas containing 2 g / m of fluorine, preferably in the form of hydrogen fluoride, are passed through an absorption column irrigated with an ammonium fluoride solution containing a silica gel in suspension. In total, 99.5 kg of a 10% ammonium fluoride solution containing 6.3 kg of silicon dioxide in the solid phase is fed to the reaction with gas.

iB, absorption results in the formation of 141 kg of a 20% ammonium fluorofluoride solution containing 7 kg of silicon dioxide. This solution is neutralized with ammonia. 43 kg of a solution of ammonium fluoride obtained after neutralization with 6.3 kg of silica (in the form of suspended in a solution of silica gel), return to the stage of absorption. The remaining part of the ammonium fluoride solution, after separation of the silica acid from the gel, is evaporated in vacuo at 140-150 ° C, 16.5 kg of a mixture of normal and acidic ammonium fluoride are precipitated.

Example 2. 5000 kg of gas containing 2 g / m of fluorine, mainly in the form of hydrogen fluoride, is passed through an absorption column, irrigated with 98.5 kg of a 10% aqueous solution of ammonium fluoride. 6.3 kg of silica gel (waste acidic silica gel, infusor earth, etc.) are introduced into the irrigating solution at the absorption stage. As a result of absorption, 114 kg of a 20% ammonium fluorofluoride solution are obtained, which are fed to neutralization with ammonia. After neutralization from the resulting sodium fluoride solution, 7 kg of silica gel (white carbon black) are separated; 43 kg of the remaining 20% sodium fluoride solution is returned to the absorption step. The remainder of the solution was fed to an overpack, yielding 16.5 kg of a mixture of fluorides.

Subject invention

The method of purification of gases containing fluorine compounds by absorption of these compounds with an aqueous solution of ammonium fluoride, characterized in that, in order to purify slightly concentrated gases containing predominantly hydrogen fluoride, silica gel is introduced into the ammonium fluoride solution in an amount of about 1 wt. hours 1.5 weight. including dissolved ammonium fluoride.