Catalytic Hydrogel Membrane Reactor for Treatment of Aqueous Contaminants

Heterogeneous hydrogenation catalysis is a promising approach for treating oxidized contaminants in drinking water, but scale-up has been limited by the challenge of immobilization of the catalyst while maintaining efficient mass transport and reaction kinetics. We describe a new process that addresses this issue: the catalytic hydrogel membrane (CHM) reactor. The CHM consists of a gas-permeable hollow-fiber membrane coated with an alginate-based hydrogel containing catalyst nanoparticles. The CHM benefits from counter-diffusional transport within the hydrogel, where H₂ diffuses from the interior of the membrane and contaminant species (e.g., NO₂^-, O₂) diffuse from the bulk aqueous solution. The reduction of O₂ and NO₂^- were investigated using CHMs with varying palladium catalyst densities, and mass transport of reactive species in the catalytic hydrogel was characterized using microsensors. The thickness of the "reactive zone" within the hydrogel affected the reaction rate and byproduct selectivity, and it was dependent on catalyst density. In a continuously mixed flow reactor test using groundwater, the CHM activity was stable for a 3 day period. Outcomes of this study illustrate the potential of the CHM as a scalable process in the treatment of aqueous contaminants.