AQUEOUS ABSORBENTS FOR STACK GAS DESULFURIZATION BY ABSORPTION/STRIPPING.

Several alternative aqueous absorbents were experimentally evaluated for use in absorption/stripping processes for flue gas desulfurization. The pH behavior of sodium citrate, basic aluminum sulfate, ethylenediamine, and adipate buffers was measured and modeled. SO//2 vapor pressure was measured at 25 to 168 degree C over solutions with sodium citrate, glyoxylic acid, and basic aluminum sulfate. Solution stability at 100 to 180 degree C was studied with sodium citrate. The rate of SO//2 reaction with glyoxylic acid was deduced from measurements of the reverse reactions. Sodium citrate is not an attractive absorbent. With absorption of 3000 ppm SO//2 at 55 degree C the actual steam requirements would be about 41 kg/kg SO//2. Disproportionation and other side-reactions in sodium citrate buffer can be avoided by operating below 130 degree C. Glyoxylic acid is also an unattractive alternative because rate data indicate that liquid holdup requirements and mass transfer requirements in the absorber would be prohibitive. Basic aluminum sulfate may be attractive if used in absorption below 45 degree C. Solubility of basic aluminum salts limits operation to a pH less than 3. 5.