DE2135086A1 - METHOD OF REMOVING MERCURY FROM GASES - Google Patents

Description

Badische Anilin- & Soda.-Iatrik AG 2135086

Our reference: O.Z. 27 6Ö4 Ki / AR 6700 Ludwigshafen, 13. 7 · '1.971

Process for removing mercury from gases

Chloralkali electrolysis produces chlorine, alkyl hydroxide and hydrogen in equivalent amounts. In the diaphragm process, the hydrogen is released at the iron cathode; in the amalgam process, it is created in the secondary cell, in which the alkali amalgam from the primary cell is broken down into mercury, alkali hydroxide and hydrogen with water on a catalyst ^{at temperatures of 60 to 120 ° C.} According to the temperature of the lye in the secondary cell, the escaping hydrogen is saturated with water and mercury vapor. Most of the time, this hydrogen is cooled directly or indirectly with cooling water. Compared to the previously common central cooling in a collective cooler, nowadays mostly individual cooling is preferred directly behind the secondary cell, so that the condensed mercury can be immediately returned to the mercury cycle of the cell. In the seasonal variations of the cooling water temperature of usually 5 to 25 ⁰ C then reaches hydrogen Tempera doors of about 10 to 30 ⁰ C. The amount of water and mercury vapor then corresponds to: as the partial pressures of water and mercury at the temperature concerned, here about 5 to 30 mg of mercury per m of hydrogen.

The electrolyte hydrogen is very pure, mostly over $ 99.9, but "the relatively high content of Queokeilberg makes it useless for many purposes, e.g. for the hydrogenation of fats for human nutrition, and for all those hydrogenations in which " \ the catalyst is often poisoned by traces of mercury. Discharging the hydrogen into the environment is also not permitted with the listed mercury levels for reasons of air pollution control. For these reasons and also for economic considerations, the greatest possible removal and recovery of the mercury is desirable.

222/71 '-2- ·,

209885/1075

O.Z. 27,604

Various methods are known for the fine purification of hydrogen. A residual content of up to 20 / Ug / m hydrogen can be achieved, for example, by deep-freezing to -40 to -5O ⁰ G. '

In addition to the purification of the hydrogen by absorptive means, e.g. with activated charcoal, that with iodine, sodium sulfide, sodium hydrosulfide, -polysulfide or metals, such as copper, are impregnated, it is also known to reduce the mercury content of hydrogen by a dry cleaning by washing with solutions that contain active chlorine, e.g. Chlorinated water or brine containing chlorine (F.I.A.T. Final Report No. 732). Subsequent washing with water and sodium hydroxide solution is then necessary to remove entrained chlorine, To retain chloride and mercury chloride. In the GDR patent no. 70 566 it is stated that the sprinkling with chlorine-containing thin brine has a mercury content of 5000 / ug / m Get hydrogen. This content can be achieved by post-treatment with SOg-containing water or an aqueous solution of sodium sulfite, sodium hydrogen sulfite or sodium disulfite Reduce to an optimal value of 20 to 50 / ug / m. In contrast, it has been found through experiments that. aich in a filling body trickle tower or in a spray tower the Fiat Report 732 by treating the hydrogen with chlorine Brine can achieve a mercury content down to 2.0 / Ug / m hydrogen; However, values below 20 / Ug / m could cannot be achieved. In the English patent no. 1 207 215, in which a process of withdrawing a receipt for gases from the ventilation basin of chlorine lines with the aid of brine containing chlorine is described

the lowest values given are 35 / ug mercury per m gas. The disadvantage of the chemical processes described is that 'a desired reduction in the mercury content under 4yug / m is not possible.

The object of the present invention was to remove the quenching of gases, for example hydrogen, which is obtained in the chloralkali electrolysis by the amalgam process, by chemical means by treatment with aqueous solutions containing active chlorine in such a way that the mercury can be largely removed . _y -3-

2098 * 6 / 1075-

- / - '^ O.Z. 27 604

It has been found that this problem can be solved by that the gas in one or more successive layers of aqueous solutions containing active chlorine in finely divided Form is introduced and the active chlorine-containing solution is evenly distributed over the cross section of the layer and is supplied to the layer as directly as possible above the point of introduction for the gas.

The method according to the invention is described below with reference to the figures 1 and 2 explained in more detail.

Hydrogen from the secondary cells of a chlor-alkali electrolysis is cooled directly or indirectly and, according to FIG. 1, enters a tower 2 from below at 1, in which a frit base 3 is installed is. A chlorine-containing aqueous solution flows through line 4 to, is distributed via a device 5 and flows through line 6 depleted in chlorine and enriched in mercury again. The hydrogen is finely distributed through the frit base, the chlorine-containing solution flows through and leaves the tower 2 through line 7. The hydrogen can then be fed in in a known manner washed with water and then with sodium hydroxide solution and finally dried.

Instead of the frit bottom, sieve bottoms, bell bottoms can also be used or the like can be arranged. Of course it is possible to arrange several such distributor devices in a column one above the other, the chlorine-containing aqueous solution at the top floor over a distribution, over downpipes and further distributions are made from floor to floor and drawn off above the lowest floor.

In one possible embodiment, the line 4 is flowing in aqueous solution electrolyte from the cell system, which after the reaction the electrolyte return of the cell system again is fed. ■. .

-A-

2098 85/107 5

- / - . OZ 27.604

According to a preferred embodiment, as shown in FIG. 2, a brine is used with the help of a pump 1Q in the circuit, in the "at 11 Pure brine, optionally acid or alkali for pH adjustment at 12 and chlorine at 13. The brine then arrives through line 14 into the absorption tower 15, which through line 16 is charged with hydrogen containing mercury. 17 is a distribution device such as a porous plate for the hydrogen. The distribution devices for the brine are shown in the figure . not illustrated. The purified hydrogen is drawn off at 18, the used brine at 19. The one depleted in chlorine Brine reaches the template 20, ^ from which via an overflow 21 a partial amount flows off into the electrolyte line of the cell system, which corresponds to the amount of pure brine added at 11.

> ■ ■: ■ ■ · '

With the help of the method according to the invention, the mercury. almost completely removed from the hydrogen, which can be recovered from the aqueous solution using known methods

•can. . . ■ '.

It has proven to be useful to adjust the pH of the brine in to maintain a pH range from 2 to 7, preferably from 3 to 6, because this is where the best results are achieved.

Eejspiel

In a glass tube with a diameter of 450 mm, -in its lower end a glass frit G-II is installed at room temperature "Hydrogen in an amount of 170 m / hour and an Hg content of'800 / üg Hg / m initiated. A Overflow a liquid level (with hydrogen throughput üTull) of 360 mm complied with. Immediately above the frit, sodium chloride solution with a concentration of 200 g / l and a content of 50 mg / l chlorine at a pH around 5 added. After flowing through the frit and the liquid layer, the hydrogen is in a trickle tower Caustic soda 'washed and with the help of a recording UV absorption device analyzed, resulting in an Hg content of less than 4 / Ug / m hydrogen.

209865/107 5

Claims (1)

- f- O. ζ. 27 604 Claim A process for removing mercury from gases, for example from hydrogen obtained in the chloralkali electrolysis by the amalgam process, by treating the gas with aqueous solutions containing active chlorine, characterized in that the gas is finely divided into one or more successive layers of aqueous solutions containing active chlorine is introduced and the active chlorine-containing solution is evenly distributed over the cross section of the layer and is supplied to the layer as directly as possible above the point of introduction for the gas. Badische Anilin- & Soda-Fabrik AG Zelohn, - 209896/1075 ς. R e r s e. i t e