Catalytic Denitrification in a Trickle Bed Reactor: Ion Exchange Waste Brine Treatment

Abstract

Catalytic reduction of nitrate in ion exchange (IX) waste brine for reuse is a promising option for reducing IX costs and environmental impacts. A recycling trickle bed reactor (TBR) was designed and optimized using 0.5 percent by weight (wt%) palladium–0.05 wt% indium catalysts supported on US mesh size 12 × 14 or 12 × 30 activated carbon particles. Various liquid superficial velocities (Ur) and hydrogen gas superficial velocities (Ug‐H2) were evaluated to assess performance in different flow regimes; catalyst activity increased with Ug‐H2 at all Ur for both catalysts and was greatest for the 12 × 30 catalyst at the lowest Ur (8.9 m/h). The 12 × 30 catalyst demonstrated up to 100% higher catalytic activity and 280% higher mass transfer rate compared with the 12 × 14 catalyst. Optimal TBR performance was achieved with both catalysts in the trickle flow regime. The results indicate that the TBR is a promising step forward, and continued improvements are possible to overcome remaining mass transfer limitations.

Catalytic Nitrate Removal in a Trickle Bed Reactor: Direct Drinking Water Treatment

“…This value is approximately three to 15 times greater than the catalytic activities reported previously for continuous‐flow reactors (Table 3). Also, it compares favorably with the activity (17.4 ± 0.04 mg NO 3 – /min‐g Pd) reported in a companion paper (Bergquist et al 2017), where a similarly designed TBR with Pd‐In/AC catalysts was used for NO 3 – treatment of IX waste brine. However, the TBR activity is only ~18% of the activity obtained for the same catalyst in the batch reactor, indicating H 2 mass transfer limitations in the TBR.…”

“…The different locations of the mapped flow regimes suggest that the flow regime boundaries are not specific to a fixed range of Re L or Re G and that the optimal regime(s) for apparent catalytic activity can change with values of Re L and Re G . Comparison of the results in this study with those in Bergquist et al (2017) suggests that the optimal flow regime(s) may also change with the catalyst support, possibly because of differences in grain geometry or wettability.…”

“…The results suggest that TBR performance was optimized for the conditions tested near the boundary between pulse and bubble flow. However, most commercial TBRs are operated at the boundary of trickle and pulse flow to optimize mass transfer and overall performance (Ranade et al 2011, Satterfield 1975); optimal performance was identified at this boundary in the aforementioned companion paper that used a TBR for IX waste brine treatment (Bergquist et al 2017). While the liquid Reynolds numbers (Re L = 6.7–17.5) in this work are similar to previous studies, the gas Reynolds numbers (Re G = 0.003–0.129) are much smaller because of the low superficial gas velocities tested (Figure 6).…”

“…In the TBR companion study in which NO 3 – was treated in an IX waste brine (Bergquist et al 2017), catalytic activity was stable during 90 days of NO 3 – reduction. A possible reason is that the 10 wt% brine solution inhibits biological growth, and biological products (e.g., extracellular polymeric substances) are responsible for fouling Pd and In sites.…”

Treating Water by Degrading Oxyanions Using Metallic Nanostructures

“…Werth and co-workers have worked on developing Pd–In catalyst-based trickle-bed flow reactors (TBR) for nitrate treatment of drinking water and IX waste brine. ,, Gas and liquid flow rates, catalyst metal loading, and catalyst pellet size were varied to optimize TBR performance. Catalytic activity in the flow reactor was ∼18% that of the same catalyst tested in batch mode, which was attributed to H 2 mass transfer limitations.…”