Electronic and structural properties of the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulonyl)imide are studied using density functional theory (DFT) methods in addition to infrared and UV-vis spectroscopy. The DFT methods were conducted for both gas phase and solution phase using the integral equation formalism polarizable continuum model, while optical absorption experiments were conducted using neat and dilute methanol solutions. Three energetically similar conformers were obtained for each of the gas phase and solution phase DFT calculations. These multiple configurations were considered when analyzing the molecular interactions between the ion pair and for a molecular-level interpretation of the experimental IR and UV-vis spectroscopy data. Excitation energies of low-lying singlet excited states of the conformers were calculated with time-dependent DFT and experimentally with UV-vis absorption spectra. Difference density plots and excited-state calculations in the gas phase are found to be in good agreement with the experimental findings, while the implicit solvation model calculations adversely impacted the accuracy of the predicted spectra.
Wastewater sludge management is a significant challenge for small-scale, urban wastewater treatment plants (WWTPs). Common management strategies stabilize sludge for land disposal by microbial action or heat. Such approaches require large footprint processing facilities or high energy costs. A new approach considers sludge to be a fuel which can be used on-site to produce electricity. Electrical power generation fueled by sludge may serve to reduce the volume of hazardous waste requiring land disposal and create economic value for WWTP operators. To date, no detailed system designs or techno-economic analyses have been found for small scale sludge fueled power plants. Fortunately, a literature base exists describing the fundamentals of applying thermochemical conversion (TCC) technologies to sewage sludge. Thermochemical conversion of sludge is established for large WWTPs, however large system design techniques may not be applicable to small systems.To determine the feasibility of small scale power generation fueled by sludge, this work evaluates several thermochemical conversion technologies from the perspective of small urban WWTPs. Literature review suggests wet oxidation, direct combustion, pyrolysis, and gasification as candidate front-end TCC technologies for on-site generation. Air and steam blown gasification are found to be the only TCC technologies appropriate for sludge. Electrical power generation processes based on both air and steam blown gasification are designed around effective waste heat recovery for sludge drying. The systems are optimized and simulated for net electrical output in ASPEN Plus R . Air blown gasification is found to be superior. Sensitivity analyses are conducted to determine the effect of fuel chemical composition on net electrical output. A technical analysis follows which determines that such a system can be built using currently available technologies. Finally, an economic analysis concludes that a gasification based power system can be economically viable for WWTPs with raw sewage flows of 0.115 m 3 /s, or about 2.2 million gallons per day.
An optical diagnostic technique to determine the order and concentration of lithium polysulfides in lithium-sulfur (Li-S) battery electrolytes has been developed. One of the major challenges of lithium-sulfur batteries is the problem of polysulfide shuttling between the electrodes, which leads to self-discharge and loss of active material. Here we present an optical diagnostic for quantitative in situ measurements of lithium polysulfides using attenuated total reflection Fourier transform infrared (FT-IR) spectroscopy. Simulated infrared spectra of lithium polysulfide molecules were generated using computational quantum chemistry routines implemented in Gaussian 09. The theoretical spectra served as a starting point for experimental characterization of lithium polysulfide solutions synthesized by the direct reaction of lithium sulfide and sulfur. Attenuated total reflection FT-IR spectroscopy was used to measure absorption spectra. The lower limit of detection with this technique is 0.05 M. Measured spectra revealed trends with respect to polysulfide order and concentration, consistent with theoretical predictions, which were used to develop a set of equations relating the order and concentration of lithium polysulfides in a sample to the position and area of a characteristic infrared absorption band. The diagnostic routine can measure the order and concentration to within 5% and 0.1 M, respectively.
An understanding of the impact of coating irregularities on beginning of life polymer electrolyte fuel cell (PEMFC) performance is essential to develop and establish manufacturing tolerances for its components. Coating irregularities occurring in the fuel cell electrode can either possess acceptable process variations or potentially harmful defects. A segmented fuel cell (SFC) is employed to understand how 100% catalyst reduction irregularities ranging from 0.125 to 1 cm2 in the cathode electrode of a 50 cm2 sized cell impact spatial and total cell performance at dry and wet humidification conditions. By analyzing the data in a differential format the local performance effects of irregularity sizes down to 0.25 cm2 were detected in the current distribution of the cell. Slight total cell performance impacts, due to irregularity sizes of 0.5 and 1 cm2, were observed under dry operation and high current densities.
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