| 摘要 |
<p>In a cyclic process for recovering CO2 from gases by successive absorption in, and desorption from, an aqueous solution having a pH greater than 7, e.g. alkali metal carbonate, containing arsenite as described in Specification 798,856, wherein absorption is decreased by the presence of arsenate, part of the solution is withdrawn from the process and the arsenate is heated in the presence of a reducing agent to above 150 DEG C., e.g. 250-280 DEG C., to convert arsenate to arsenite, which is returned to the process. Reducing agents are formaldehyde, acetaldehyde, methyl, or ethyl, alcohol, formic, oxalic, or tartaric, acid or salts thereof, hydrazine or salts thereof, potassium hydrosulphite, arsenic, antimony, bismuth, a sulphide, hydrocyanic acid, or potassium cyanide, or ferrocyanide. The heating may be effected in an autoclave lined with noble metal, e.g. silver, with stirring, and CO2 should be present, either added as such, or due to the presence of bicarbonate in the solution. Before heating, the solution may be concentrated, or the arsenate may be extracted, e.g. by crystallising, or precipitating as magnesium ammonium arsenate, and heated separately. Also the reducing agent may be added to the solution, which is evaporated to dryness, and the residue heated and redissolved.</p> |
