SONOCHEMICAL DEGRADATION OF P-NITROPHENOL IN A PARALLEL-PLATE NEAR-FIELD ACOUSTICAL PROCESSOR

The sonochemical degradation of p-nitrophenol (p-NP) in a near-field a coustical processor (NAP) is investigated. The pseudo-first-order rate constant, k, for p-NP degradation increases proportionally from 1.00 x 10(-4) to 7.94 x 10(-4) s(-1) with increasing power-to-volume ratio (i.e., power density) over the range of 0.98-7.27 W/cm(3). An increase in the power-to-area ratio (i.e., sound intensity) results in an incr ease in k up to a maximum value of 8.60 x 10(-4) s(-1) at a sound inte nsity of 1.2 W/cm(2). A mathematical model for a continuous-flow loop reactor configuration is required in order to extract k from the exper imentally observed rate constant, K-obs, which is a function of the re lative volumes of reactor and reservoir. The nature of the cavitating gas (Ar, O-2) is found to influence the overall degradation rate and t he resulting product distribution. The rate constant for p-NP degradat ion in the presence of pure O-2, k(o)2, = 5.19 x 10(-4) s(-1) , is low er than in the presence of pure Ar, k(Ar) = 7.94 x 10(-4) s(-1). A 4:1 (v/v) Ar/O-2 mixture yields the highest degradation rate, kAr/O-2 = 1 .20 x 10(-3) s(-1). Results of these experiments demonstrate the poten tial application of large-scale, high-power ultrasound to the remediat ion of hazardous compounds present at low concentrations. The NAP is a parallel-plate reactor that allows for a lower sound intensity but a higher acoustical power per unit volume than conventional probe-type r eactors.