NITROGEN-OXIDES ABSORPTION INTO SODIUM-HYDROXIDE SOLUTIONS IN A PACKED-COLUMN - EFFECT OF NAOH CONCENTRATION

Experiments have been conducted to evaluate the effect of sodium hydroxide (NaOH) concentration upon the absorption rate of nitrogen oxides (NO(x)) and packed column performance. The absorption process was carried out at atmospheric pressure and 298 K, using NaOH concentrations between zero and 19% w/w, NO/NO2 ratio of 0.5 and NO(x) concentrations between 150 and 10 000 ppm in an air mixture. The performance of the column was enhanced by the presence of increasing hydroxyl ion (up to 2% NaOH) relative to the absorption into water; however, at higher concentrations it was found to be independent of NaOH concentration. The absorption rate of NO(x) into NaOH solution was similar to that into water, suggesting there is no direct reaction between NO(x) species and OH- ions, and thus in both cases the absorption process was controlled by the hydrolysis of the main transporting species. Column absorption efficiencies up to 92% and 87% were obtained during NO(x) absorption into NaOH and water, respectively.