Complete dechlorination of pentachlorophenol using palladized bacterial cellulose in a rotating catalyst contact reactor

A rotating catalyst contact reactor (RCCR) was developed which consisted of palladized bacterial cellulose immobilized on acrylic discs for hydrodechlorination of pentachlorophenol (PCP). More than 99% of 40 mg L−1 PCP was dechlorinated to phenol in the presence of hydrogen in batch mode at initial pH values of 5.5 and 6.5 within 2 h of reaction with stoichiometric release of free chloride. The rate of PCP dechlorination was found to be independent of rotational speed of discs. PCP (40 mg L−1) hydrodechlorination experiments were also conducted using RCCR in continuous flow mode at hydraulic retention times of 1 and 2 h. The average outlet PCP concentrations revealed that liquid phase in RCCR closely resembled that of a continuous flow complete mix reactor (CFMR). Approximately 12 and 11 L of 40 mg L−1 PCP (pH 6.5) could be treated in RCCR with 99 and 80% efficiencies in batch and continuous flow modes, respectively without any appreciable loss of the catalytic activity. These results suggested reusability of palladized bacterial cellulose which in turn is expected to substantially reduce the cost of treatment process. Thus RCCR seems to have high potential for treatment of ground water contaminated with chlorinated organic compounds. Dried palladized bacterial cellulose has been used as a material for electrodes in a fuel cell. However, its application as a hydrodechlorination catalyst in a reactor operating under room temperature and atmospheric pressure has not been reported to the best of our knowledge. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analyses suggested the irreversible deposition of palladium (Pd0) particles on the bacterial cellulose fibrils.

Graphical abstractThe figure shows the schematic diagram of RCCR (rotating catalyst contact reactor) used for treating pentachlorophenol (PCP). Palladized bacterial cellulose immobilized on the surface of the rotating acrylic discs in RCCR interacts with molecular hydrogen to generate palladium hydride (Pd-H) which in turn reductively dehalogenates sorbed PCP to the hydrocarbon product, phenol with the stoichiometric release of free chloride ions. Phenol may be further degraded to produce ring cleavage products.Figure optionsDownload full-size imageDownload as PowerPoint slide