Investigation and comparison of catalytic decomposition rates of aqueous phenol in three-phase fluidized bed reactor

Abstract

A batch three-phase fluidized-bed reactor (TPFBER) with an effective total volume of 235 mL was used to investigate the decomposition of dilute aqueous phenol. Comparison of the phenol decomposition rates under different conditions: employing only ozone (O[subscript 3], only TiO[subscript 2] photocatalyst on silica beads, only metal catalyst (Ni or Co) on mesoporous carbon beads, and ozone together with one of the mentioned catalysts, were carried out. The gas and liquid flow rate were kept constant at 1 L/min and the catalyst loading was 5 g per batch. The experimental results in the decomposition of 2 L of 10 ppm phenol solution revealed that using TiO[subscript 2] without ozone gave the worst result (initial reaction rate constant k = 0.0066 min-1). However, when combined with ozone that generated from air, the result was better (k = 0.0492 min-1). In the case of using only ozone for decomposition, the efficiency of ozone generated from pure oxygen (k = 0.1263 min-1) was higher than generated from air (k = 0.0236 min-1). Meanwhile in the case of using metallic catalyst with ozone generated from air, co-metalic catalyst (k = 0.1944 min-1) had higher efficiency than ni-metallic catalyst (k = 0.1713 min-1). Using ni-metallic catalyst with ozone generated from pure oxygen could provide the even better result. The rate constant would increase from 0.1713 to 0.2158 min-1 and complete degradation of phenol can be essentially achieved within 10 min. It was expected that using co-metallic catalyst with ozone generated from pure oxygen should enhance the rate constant at a similar level. Some intermediate products such as hydroquinone (HQ) and catechol (CC) were also detected but they were eventually decomposed down to very low concentrations.