Dechlorination of p-chlorophenol on a Pd/Fe catalyst in a magnetically stabilized fluidized bed; Implications for sludge and liquid remediation

Abstract

p-Chlorophenol is dechlorinated using a Pd/Fe bimetallic micro-size catalyst in a magnetically stabilized fluidized bed (MSFB) reactor. The catalyst is used in both powder form ( d c =7 μm) and entrapped in alginate beads ( d b =2.0 mm). The dechlorination reaction is performed in aqueous solution containing p-chlorophenol with and without the presence of soil particles (20% w/w). Several important operating parameters involved in this complex chemical process are studied: Pd/Fe weight ratio, the extent of palladization or the ratio of Pd (Fe) interface area to the amount of chlorine to be removed, system pH, and dissolved O 2. Important process resistances including formation of Fe(OH) 2, Fe(OH) 3, and hydrogen gas bubbles, which are dependent on the mentioned operating parameters, are identified for accurate representation of the overall reaction kinetics. Pseudo first-order kinetics ( k=3.81±0.08 m 3/kg min) with first order deactivation of catalyst ( k d=0.12 1/min) are found to excellently represent dechlorination chemical reaction. Once the chemical kinetics were defined, the active Pd/Fe catalyst was entrapped in alginate beads for use in a magnetically stabilized fluidized bed. Diffusion constraints ( D e =8.0×10 -10 m 2/s) through the bead material (1.5% alginate +98.5% H 2O) are not severe and are reported as being approximately 85–90% of the diffusivity measured in water (Shishido et al., Chem. Engng. Res. Design: Trans. Inst. Chem. Eng. 73(6), 719–725, 1995; Oyaas et al., 1995a Biotechnol. Bioengng 47, 492–500). It can be further moderated by decreasing the size of the beads and by using a nano size Pd/Fe catalyst particles (Wang and Zhang, 1997). Overall, the Pd/Fe bimetallic catalyst has been shown to effectively dechlorinate p-chlorophenol both as a powder and entrapped in 2 mm alginate beads. Integration of the catalyst entrapped in the beads with the MSFB introduces a novel method for the treatment of difficult to handle materials, and toxic compounds. The MSFB and alginate beads are shown to be an excellent engineering platform which can be implemented in a variety of catalytic and non-catalytic liquid-solid reaction processes.