Nitrite removal from water by catalytic hydrogenation in a Pd-CNTs/Al₂O₃hollow fiber membrane reactor

Abstract

BACKGROUND Nitrite contaminants in groundwater endanger public health since they may cause many diseases such as blue baby syndrome, cancer and hypertension. In this work, novel Pd‐CNTs/Al2O3 catalytic hollow fiber membranes for aqueous nitrite hydrogenation reduction were fabricated by the deposition of carbon nanotubes (CNTs) and Pd nanoparticles inside porous Al2O3 hollow fibers. A hollow fiber membrane reactor was assembled for nitrite removal from water by catalytic hydrogenation reduction. RESULTS Experimental results indicated that the nitrite hydrogenation rate was highly dependent on hydrogen dissolution in water and adsorption on the catalyst. The nitrite removal increased with increasing H2 partial pressure to balance the nitrite solution, but the influence became very marginal as it approached 1.0 atm. The oxygen in the gas feed lowered the nitrite removal due to the reaction with dissolved hydrogen over the Pd‐catalyst. Compared with the conventional diffusion operation of the membrane reactor, the ‘flow‐through’ operation resulted in higher nitrite removals due to the intensified mass transfer rate. CONCLUSION The nitrites in water can be completely removed using the Pd‐CNTs/Al2O3 membrane reactor with flow‐through operation. The denitrification should be operated at around 25°C for large reaction kinetics, which is determined by both the temperature and the hydrogen solubility in water. © 2015 Society of Chemical Industry

H2-Based Membrane Catalyst-Film Reactor (H2-MCfR) Loaded with Palladium for Removing Oxidized Contaminants in Water

“…The MCfR derives from its biological counterpart, the membrane biofilm reactor (MBfR). , The microbial biofilm of the MBfR is replaced by an abiotic catalyst film. Compared to other water-treatment technologies using membranes loaded with precious-metal catalysts, − the distinctive feature of the H 2 -MCfR lies in the versatile functions of the membrane: a robust catalyst-anchoring substratum and a controllable H 2 -delivering medium; H 2 gas in the lumen diffuses through the wall of nonporous hollow-fiber membranes in a bubble-free form that allows efficient and accurate delivery of H 2 to the catalysts on a demand determined by the counter-directional diffusion of the contaminant to the catalyst. On demand, bubble-free delivery avoids mass transfer limitation from gaseous H 2 diffusion, minimizes H 2 discharge to the liquid, and prevents gas stripping of volatile compounds.…”

Electrified Membranes for Water Treatment Applications

“…As discussed above, the NO 3 RR in conventional electrochemical cells suffers from mass transport limitations. ,, While improvements in catalytic materials are required to enhance the kinetics of nitrate reduction to nitrite, the overall observed reaction kinetics can be augmented via mass transport enhancements using EMs. As observed with catalytic membranes, nanoconfinement and improved catalyst dispersion on high-surface-area supports can enhance transport of reactants to active sites (Figure B,C). − , EMs serving as porous flow-through electrodes can enhance mass transport rates by over an order of magnitude relative to traditional parallel-plate electrochemical cells, achieving reactant conversion with residence times on the order of seconds …”

“…While few examples of NO 3 RR using EMs have been reported, several examples of catalytic membranes for heterogeneous reduction of NO 3 – with H 2 have been described in the literature, with most studies employing supported Pd-based bimetallic catalysts on ceramic membranes. − As with the NO 3 RR, the reaction kinetics of catalytic NO 3 – reduction by H 2 typically are controlled by mass transport limitations. Significant enhancements in nitrate conversion rate as well as selectivity to N 2 have been achieved using flow-through catalytic membranes compared to stirred-tank/diffusion operating modes or fluidized bed reactors, with 80–100% nitrate conversion reported (Figure C). − , Catalytic activity also was found to increase with transmembrane flow rate and reduction of the pore size . These enhancements have been attributed to intensification of intraporous mass transport with increased flow rate, ,− concentration polarization effects, and increase in solvent viscosity related to low ionic and hydrogen diffusivities under nanoconfinement …”

“…Significant enhancements in nitrate conversion rate as well as selectivity to N 2 have been achieved using flow-through catalytic membranes compared to stirredtank/diffusion operating modes or fluidized bed reactors, with 80−100% nitrate conversion reported (Figure 4C). [180][181][182]188 Catalytic activity also was found to increase with transmembrane flow rate and reduction of the pore size. 186 These enhancements have been attributed to intensification of intraporous mass transport with increased flow rate, 182,188−190 concentration polarization effects, and increase in solvent viscosity related to low ionic and hydrogen diffusivities under nanoconfinement.…”

“…As observed with catalytic membranes, nanoconfinement and improved catalyst dispersion on high-surface-area supports can enhance transport of reactants to active sites (Figure 4B,C). [180][181][182]188 EMs serving as porous flow-through electrodes can enhance mass transport rates by over an order of magnitude relative to traditional parallel-plate electrochemical cells, achieving reactant conversion with residence times on the order of seconds. 59 In addition to improving NO 3 RR activity, EMs also may provide an additional knob for controlling the reaction selectivity.…”