Enhanced wet air oxidation: Synergistic rate acceleration upon effluent recirculation

Wet air oxidation (WAO) reactions of cellobiose, phenol, and syringic acid were carried out under mild conditions (155 degrees C; 0.93 MPa O-2; solubl e catalyst, Na-5[PV2Mo10O40]) Initial oxidation rates were rapid but decrea sed to small values as less reactive oxidation products accumulated. Recalc itrant oxidation products were consumed more rapidly, however, if additiona l cellobiose or phenol was added, a procedure equivalent to recirculation o f WAO-reactor effluent. A half-fraction, factorial investigation was used t o correlate rate enhancement with individual experimental variables: using a two-level design, effluents from the WAO of cellobiose were combined with unreacted cellobiose and WAO resumed. The effluents were degraded more rap idly than could be accounted for by residence time alone. Correlations iden tified by the factorial investigation were consistent with oxidation of rec alcitrant compounds by highly reactive intermediates generated during the i nitially rapid radical-chain autoxidation of unreacted cellobiose.