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Electrochemical CO2 reduction has promise as a technology that could help society reach carbon neutrality while producing valuable fuels and chemicals. Herein, the electrochemical synthesis of methyl formate, a product not observed in aqueous CO2 electrolysis, has been analyzed by a rigorous technoeconomic model to evaluate its commercial viability. Methyl formate synthesis has been demonstrated with high faradaic efficiency through the electroreduction of CO2 in methanol. Four competing approaches were analyzed: (1) electroreduction of captured CO2 in a dual CH3OH/H2O electrolyzer, (2) direct electroreduction of flue gas CO2 in a dual CH3OH/H2O electrolyzer, (3) electroreduction of captured CO2 in a CH3OH/CH3OH electrolyzer, and (4) electroreduction of captured CO2 in a H2O/H2O electrolyzer with a downstream CH3OH reactor. Sensitivity analyses, cost contour plots, and comparison plots were generated. The dual methanol/water electrolysis approach was the most cost competitive, with a levelized cost of methyl formate below the present market price. The all-methanol electrolysis route was more expensive due to increased methanol consumption and greater distillation costs. Methyl formate production through aqueous CO2 electrolysis to formic acid with a secondary esterification reaction was by far the most expensive approach, primarily due to the energy-intensive nature of distilling formic acid from water.

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Scandium (Sc) has great potential for use in aerospace and clean energy applications, but its supply is currently limited by a lack of commercially viable deposits and the environmental burden of its production. In this work, a biosorption-based flow-through process was developed for extraction of Sc from low-grade feedstocks. A microbe-encapsulated silica gel (MESG) biosorbent was synthesized through sol–gel encapsulation of Arthrobacter nicotianae, a bacterium that selectively adsorbs Sc. Microscopic imaging revealed a high cell loading and macroporous structure, which enabled rapid mass transport and adsorption/desorption of metal ions. The biosorbent displayed high Sc selectivity against lanthanides and major base metals, with the exception of Fe­(III). Following pH adjustment to remove Fe­(III) from an acid leachate prepared from lignite coal, a packed-bed column loaded with the MESG biosorbent exhibited near-complete Sc separation from lanthanides; the column eluate had a Sc enrichment factor of 10.9, with Sc constituting 96.4% of the total rare earth elements. The MESG biosorbent exhibited no significant degradation with regard to both adsorption capacity and physical structure after 10 adsorption/desorption cycles. Overall, our results suggest that the MESG biosorbent offers an effective and green alternative to conventional liquid–liquid extraction for Sc recovery.

Exploiting renewable energy sources to drive CO2 reduction electrochemically into value-added products has gained tremendous attention towards reducing the greenhouse effect. Upstream processes for capturing and purifying the CO2 raise the overall cost of the electrolysis system. Direct reduction of flue gas into value-added C2+ products has attained much consideration in recent years. However, the sensitivity of the cathode catalyst performance in the presence of flue gas contaminants, particularly O2, and strong competition from the hydrogen evolution reaction in aqueous electrolyte are major challenges for such an approach. Herein, the influence of flue gas contaminants on electrochemical reduction of CO2 in acidic nonaqueous methanol to a methyl formate product has been investigated on a Pb-catalyzed electrode in conjunction with aqueous anolyte for the promotion of a sustainable water oxidation half-reaction. The presence of 4% O2, 0.05% SO2, and 0.05% NO is shown to have minimal effect on the total faradaic efficiency of CO2 reduction products. CO2 concentration-dependent measurements reveal declining CO2 reduction faradaic efficiencies corresponding to the decrease in partial pressure, which is attributed to CO2 mass transfer limitations to the electrode surface. XPS analysis displays the relative stability of the Pb working electrode before and after the electrochemical operation during exposure to flue gas components, which further highlights the promising tolerance of this system for direct flue gas conversion. Figure 1

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ACKOWLEDGEMNTSFirst, I would like to thank my wife, Emily, for motivating and supporting me through this work. She continuously pushed me towards completing this accomplishment, without which I may not have finished.Dr. Berson's advice on everything involving this project, from advice about CFD, supercomputer help, and writing. His help has furthered the work and myself as a researcher and human being. Javad Hashemi's knowledge of the erratic nature of CFD and his willingness to help in anything that I needed.iv ABSTRACT A comparison between mean age theory and conventional residence time distributions over a range of quantified mixing levels was conducted using computational fluid dynamics (CFD). The system was a stirred tubular reactor. The model was validated by comparing computationally derived RTD curves with experimentally obtained RTD curves, with quantified differences less than 3%. Mixing was quantified using the Tanksin-Series model. Mixing levels were set by varying flow rate and impeller rpm. Mean age distributions at the outlet, where experimental RTD's were measured, were very narrow for all levels of mixing studied. RTD's showed expected characteristics; a wider distribution and long decay for high mixing cases and a narrow distribution centered around the mean time for cases approaching plug flow. Mean age distributions remained substantially narrower than RTD's. RTD's and mean age distributions were measured at several locations along the length of the reactor to determine changes in characteristics of each along the reactor. RTD's and mean age distributions exhibited a narrowing along the length of the reactor, indicating a transition from well-mixed characteristics near the v entrance to plug flow behavior near the exit. Differences in the mean age and mean residence time at the outlet increased from 7% at low mixing to 30% at high mixing.Ultimately, this study showed mean age distributions are not comparable to RTD curves over a range of mixing levels. Mean age theory can provide age of material throughout an entire system volume, while RTD's provide a distribution only at a single measurable location.vi