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

p-Chlorophenol is dechlorinated using a Pd/Fe bimetallic micro-size catalys t in a magnetically stabilized fluidized bed (MSFB) reactor. The catalyst i s used in both powder form (d(c) = 7 mu m) and entrapped in alginate beads (d(b) = 2.0 mm). The dechlorination reaction is performed in aqueous soluti on containing p-chlorophenol with and without the presence of soil particle s (20% w/w). Several important operating parameters involved in this comple x chemical process are studied: Pd/Fe weight ratio, the extent of palladiza tion 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 inclu ding formation of Fe(OH)(2), Fe(OH)(3), and hydrogen gas bubbles, which are dependent on the mentioned operating parameters, are identified for accura te representation of the overall reaction kinetics. Pseudo first-order kine tics (k = 3.81 +/- 0.08 m(3)/kg min) with first order deactivation of catal yst (k(d) = 0.12 1/min) are found to excellently represent dechlorination c hemical reaction. Once the chemical kinetics were defined, the active Pd/Fe catalyst was entrapped in alginate beads for use in a magnetically stabili zed fluidized bed. Diffusion constraints (D-e = 8.0 x 10(-10) m(2)/s) throu gh the bead material (1.5% alginate + 98.5% H2O) are not severe and are rep orted as being approximately 85-90% of the diffusivity measured in water (S hishido et al., Chem. Engng. Res. Design: Trans. Inst. Chem. Eng. 73(6), 71 9-725, 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 nan o size Pd/Fe catalyst particles (Wang and Zhang, 1997). Overall, the Pd/Fe bimetallic catalyst has been shown to effectively dechlorinate p-chlorophen ol both as a powder and entrapped in 2 mm alginate beads. Integration of th e catalyst entrapped in the beads with the MSFB introduces a novel method f or 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. (C) 1999 Elsevier Science Ltd. All rights reserv ed.