| OCR Text |
Show 1990 AFRC Int'l Symposium Gas phase NO Interface Reaction zone I I ~ I I Figure 18 Main body of aqueous phase Cl 2 + H , Cl HOCl Reaction planes at gas-liquid interface (after Danckwerts) established, the true rate of progression for the NO removal in the system becomes the rate at which NO is absorbed into the aqueous phase. One may think of this as the reaction zone of Figure #18 moving to the left until it merges with the interfacial plane. Therefore, as quickly as the NO molecules cross the interfacial barrier, C12, aq is readily available for reaction. C12, aq availability is contingent upon its presence in the gas phase and subsequent absorption. C12,aq levels are maintained via parallel absorption and condensation of C12, g. If C12, aq were somehow produced extraneously in the bulk liquid, then the condition of diffusion through a two-film system would have to be met and the velocity of NO removal would be lessened somewhat. Evidence of this reaction/mass transfer path may be found in analyses of the experimental data using water and HCl solutions (Figures #7 & #8) utilizing data on C12 hydrolysis equilibrium as a function of pH (Figure #14). For the water scrubber system, NO removal reaches an equilibrium after sufficient C12 has been absorbed, dissociated and as modified the pH (by the dissociation product H+) such that C1 2, aq has become the predominant chlorine species in solution. As the partial pressure of C12 was increased in the water scrubber trials, more chlorine was absorbed and subsequently, more aqueous chlorine became available for reaction with NO at the interface. Similar removal efficiency is achieved in the HCl scrubbing system more rapidly because the pH condition necessary for the dominance of C1 2, aq as a hydrolysis product existed from the onset of the experiment. As may be predicted from the hydrolysis equilibria, larger concentrations of HCl may force the hydrolysis product more towards C13-. This condition, as previously mentioned, would reduce the removal efficiency of NO. The experiment using a dilute NaCl scrubber (~ 1M), theoretically, should have yield similar results to that found using a water scrubber. However, as may be seen by a comparison of Figures #7 and #10, the NaCl scrubber proved to be less efficient than the water scrubber. The cause for this was due to surface agents found as contaminants on the NaCl crystals used in -15- |
