Selective Hydrogenation of Furfural in a Proton Exchange Membrane Reactor Using Hybrid Pd/Pd Black on Alumina

Invited for this month’s cover picture are the groups of Dr. Peter Pintauro (Vanderbilt University, Tennessee, USA), Dr. Levi Thompson (University of Delaware, Delaware, USA), and Dr. William Tarpeh (Stanford University, California, USA). The cover picture shows the controlled variation of furfural hydrogenation product speciation based on varying cathode formulations of hybrid Pd black and Pd on alumina support. Read the full text of the article at 10.1002/celc.201901314.“The performance of different cathode compositions is evaluated at different current densities (which varies with hydrogen production) in terms of production rate, faradaic efficiency, and selectivity. To isolate the influences of the electrocatalyst in the hybrid catalyst, the performance of electrocatalyst Pd black is evaluated separately. These four variations of the hybrid cathode are investigated to test the hypothesis that the addition of the metal loaded on metal oxide to the electrocatalyst enhances the production rate for hydrogenated products compared to electrodes with only an electrocatalyst…“ Learn more about the story behind the research featured on the front cover in this issue’s Cover Profile. Read the corresponding Article at 10.1002/celc.201901314.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152714/1/celc201901737.pd

Understanding the Catalytic Active Sites of Crystalline CoSbxOy for Electrochemical Chlorine Evolution

The chlorine evolution reaction (CER) is a key reaction in electrochemical oxidation (EO) of water treatment. Conventional anodes based on platinum group metals can be prohibitively expensive, which hinders further application of EO systems. Crystalline cobalt antimonate (CoSbxOy) was recently identified as a promising alternative to conventional anodes due to its high catalytic activity and stability in acidic media. However, its catalytic sites and reaction mechanism have not yet been elucidated. This study sheds light on the catalytically active sites in crystalline CoSbxOy anodes by using scanning electrochemical microscopy to compare the CER catalytic activities of a series of anode samples with different bulk Sb/Co ratios (from 1.43 to 2.80). The results showed that Sb sites served as more active catalytic sites than the Co sites. The varied Sb/Co ratios were also linked with slightly different electronic states of each element, leading to different CER selectivities in 30 mM chloride solutions under 10 mA cm–2 current density. The high activity of Sb sites toward the CER highlighted the significance of the electronic polarization that changed the oxidation states of Co and Sb

A US perspective on closing the carbon cycle to defossilize difficult-to-electrify segments of our economy

Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets

ATR–SEIRAS Method to Measure Interfacial pH during Electrocatalytic Nitrate Reduction on Cu

This study reports the accuracy and applications of an attenuated total reflectance–surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) technique to indirectly measure the interfacial pH of the electrolyte using the ratio of phosphate species within 10 nm of the electrocatalyst surface. This technique can be used in situ to study aqueous electrochemical reactions with a calibration range from pH 1–13, time resolution down to 4 s, and an average 95% confidence interval of 14% that varies depending on the pH region (acidic, neutral, or basic). The method is applied in this study to electrochemical nitrate reduction at a copper cathode to demonstrate its capabilities, but is broadly applicable to any aqueous electrochemical reaction (such as hydrogen evolution, carbon dioxide reduction, or oxygen evolution) and the electrocatalyst may be any SEIRAS-active thin film (e.g., silver, gold, or copper). The time-resolved results show a dramatic increase in the interfacial pH from pH 2–7 in the first minute of operation during both constant current and pulsed current experiments where the bulk pH is unchanged. Attempts to control the pH polarization at the surface by altering the electrochemical operating conditions—lowering the current or increasing the pulse frequency—showed no significant change, demonstrating the challenge of controlling the interfacial pH

Front Cover: Selective Hydrogenation of Furfural in a Proton Exchange Membrane Reactor Using Hybrid Pd/Pd Black on Alumina (ChemElectroChem 22/2019)

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152753/1/celc201901738.pd

Evaluating ion exchange for nitrogen recovery from source-separated urine in Nairobi, Kenya

Rapid population growth in developing world urban centers outpaces provision of essential services such as excreta collection and treatment. Separate collection of urine and feces and decentralized treatment can potentially serve more households at lower energy and cost than conventional waterborne sewers and treatment plants. We conducted a technical validation and preliminary economic modeling to evaluate ion exchange columns, one technical option for recovering nitrogen from urine in Nairobi, Kenya. This technology could be combined with phosphorus recovery and a disinfection step to allow local discharge of the treated urine. Performance, as measured by adsorption density (4.02–4.21 mmol N/g resin) and regeneration efficiency (>90%) of the adsorbent, was consistent over ten adsorption-regeneration cycles and with columns ten times larger than lab-scale (65 L/d vs. 6.5 L/d). Effluent absorbance and electrical conductivity were identified as indicators of urine and ammonia breakthrough, respectively; both parameters are lower cost and easier to measure on-line than ammonium concentrations. Urine storage containers should be closed to avoid changes in urine composition, including loss of ammonia (and thus potential revenue). Treatment of urine by ion exchange is 40% less expensive than disposal without treatment and urine-derived ammonium sulfate was produced well below market costs of commercial fertilizers. Keywords: Adsorption, Fertilizer, Nutrient recovery, Nitrogen, Sanitation, Urin

Comparing Ion Exchange Adsorbents for Nitrogen Recovery from Source-Separated Urine

Separate collection of urine, which is only 1% of wastewater volume but contains the majority of nitrogen humans excrete, can potentially reduce the costs and energy input of wastewater treatment and facilitate recovery of nitrogen for beneficial use. Ion exchange was investigated for recovery of nitrogen as ammonium from urine for use as a fertilizer or disinfectant. Cation adsorption curves for four adsorbents (clinoptilolite, biochar, Dowex 50, and Dowex Mac 3) were compared in pure salt solutions, synthetic urine, and real stored urine. Competition from sodium and potassium present in synthetic and real urine did not significantly decrease ammonium adsorption for any of the adsorbents. Dowex 50 and Dowex Mac 3 showed nearly 100% regeneration efficiencies. Estimated ion exchange reactor volumes to capture the nitrogen for 1 week from a four-person household were lowest for Dowex Mac 3 (5 L) and highest for biochar (19 L). Although Dowex Mac 3 had the highest adsorption capacity, material costs ($/g N removed) were lower for clinoptilolite and biochar because of their substantially lower unit cost

Life-Cycle Cost and Environmental Assessment of Decentralized Nitrogen Recovery Using Ion Exchange from Source-Separated Urine through Spatial Modeling

Nitrogen standards for discharge of wastewater effluent into aquatic bodies are becoming more stringent, requiring some treatment plants to reduce effluent nitrogen concentrations. This study aimed to assess, from a life-cycle perspective, an innovative decentralized approach to nitrogen recovery: ion exchange of source-separated urine. We modeled an approach in which nitrogen from urine at individual buildings is sorbed onto resins, then transported by truck to regeneration and fertilizer production facilities. To provide insight into impacts from transportation, we enhanced the traditional economic and environmental assessment approach by combining spatial analysis, system-scale evaluation, and detailed last-mile logistics modeling using the city of San Francisco as an illustrative case study. The major contributor to energy intensity and greenhouse gas (GHG) emissions was the production of sulfuric acid to regenerate resins, rather than transportation. Energy and GHG emissions were not significantly sensitive to the number of regeneration facilities. Cost, however, increased with decentralization as rental costs per unit area are higher for smaller areas. The metrics assessed (unit energy, GHG emissions, and cost) were not significantly influenced by facility location in this high-density urban area. We determined that this decentralized approach has lower cost, unit energy, and GHG emissions than centralized nitrogen management via nitrification-denitrification if fertilizer production offsets are taken into account

Long-term Robustness and Failure Mechanisms of Electrochemical Stripping for Wastewater Ammonia Recovery

Nitrogen in wastewater has negative environmental, human health, and economic impacts but can be recovered to reduce costs and environmental impacts of wastewater treatment and chemical production. To recover ammonia/ammonium (TAN) from urine, we operated electrochemical stripping (ECS) for over a month, achieving 83.4% TAN removal and 73.0% TAN recovery. With two reactors, we recovered sixteen 500 mL batches (8 L total) of ammonium sulfate approaching commercial fertilizer concentrations and often having greater than 95% purity. While evaluating operation and maintenance needs, we identified pH, full-cell voltage, product volume, and water flux into the product as informative process monitoring parameters that can be inexpensively and rapidly measured. Characterization of fouled cation exchange and omniphobic membranes informs cleaning and reactor modifications to reduce fouling with organics and calcium/magnesium salts. To evaluate the impact of urine collection and storage on ECS, we conducted experiments with urine at different levels of dilution with flush water, extents of divalent cation precipitation, and degrees of hydrolysis. ECS effectively treated urine under all conditions, but minimizing flush water and ensuring storage until complete hydrolysis would enable energy-efficient TAN recovery. A preliminary cost assessment indicated that ECS-derived ammonium sulfate from urine was competitive with other nitrogen treatment technologies and commercially available fertilizer. Our experimental results and cost analysis motivate a multi-faceted approach to improving ECS’s technical and economic viability by extending component lifetimes, decreasing component costs, and reducing energy consumption through material, reactor, and process engineering. In sum, we demonstrated urine treatment as a foothold for electrochemical nutrient recovery from wastewater while supporting applicability of ECS to seven other wastewaters with widely varying characteristics. Our findings will facilitate scale-up and deployment of electrochemical nutrient recovery technologies, enabling a circular nitrogen economy that fosters sanitation provision, efficient chemical production, and water resource protection

Electrochemical Stripping to Recover Nitrogen from Source-Separated Urine

Recovering nitrogen from separately collected urine can potentially reduce costs and energy of wastewater nitrogen removal and fertilizer production. Through benchtop experiments, we demonstrate the recovery of nitrogen from urine as ammonium sulfate using electrochemical stripping, a combination of electrodialysis and membrane stripping. Nitrogen was selectively recovered with 93% efficiency in batch experiments with real urine and required 30.6 MJ kg N^–1 in continuous-flow experiments (slightly less than conventional ammonia stripping). The effects of solution chemistry on nitrogen flux, electrolytic reactions, and reactions with electro-generated oxidants were evaluated using synthetic urine solutions. Fates of urine-relevant trace organic contaminants, including electrochemical oxidation and reaction with electro-generated chlorine, were investigated with a suite of common pharmaceuticals. Trace organics (<0.1 μg L^–1) and elements (<30 μg L^–1) were not detected at appreciable levels in the ammonium sulfate fertilizer product. This novel approach holds promise for selective recovery of nitrogen from concentrated liquid waste streams such as source-separated urine