Doctor of Philosophy, University of Akron, 2022, Polymer Science

Photoelectrochemical (PEC) conversion of biomass (e.g., lignin) to hydrogen, a carbon-negative emission technology, is characterized by four key processes: (i) photo-generated electron-hole pairs, (ii) electron transport from the anode to the cathode, (iii) hydrogen generation at the cathode and (iv) biomass oxidation by photogenerated holes in the valence band. Overall performance of the photoelectrochemical cell is governed by step (i), electron-hole generation, followed by step (iv), charge transfer at the semiconductor/electrolyte interface. This dissertation will discuss the development of an in situ infrared spectroscopic (IR) approach to study charge dynamics during PEC reactions. Accumulated photogenerated electrons on the semiconductor surface in PEC reactions exhibit a structureless, and featureless spectrum centered around 2000 cm-1. The intensity and rate of the IR profile of photogenerated electrons at this wavenumber correlates to the charge transport in the PEC process, qualitatively characterizing the efficiency of the catalyst. Electron accumulation can also be observed under dark conditions with negative voltage bias. Adsorbed water on the semiconductor surface serves as a hole scavenger and shields the catalyst surface from oxygen, preventing electron-hole recombination, while simultaneously promoting the formation of a double layer of electrons and protons on the semiconductor surface. The effect of voltage on the performance of the PEC cell is investigated through the analysis of the IR profile (i.e., relative concentration) of photogenerated electrons. The results of charge dynamics shed a light on the PEC mechanism and provide a scientific basis for devising novel approaches to enhance the PEC efficiency. The observations of the dynamics of accumulated electrons and water coverage in PEC reactions revealed the applicability of the in situ IR approach to electro-swing CO2 capture in liquid monoethanolamine (MEA). CO2 reacts with amines (open full item for complete abstract)

Committee: Steven S.C. Chuang (Advisor); Toshikazu Miyoshi (Committee Member); Zhenmeng Peng (Committee Member); Mesfin Tsige (Committee Member); Yu Zhu (Committee Member) Subjects: Alternative Energy; Analytical Chemistry; Polymers

Master of Science in Environmental Science, Youngstown State University, 2008, Department of Geological and Environmental Sciences

Adsorption is considered one of the more promising technologies for capturing CO2 from flue gases. This research shows an efficient chemical adsorption method capable of capturing carbon dioxide under moist conditions from flue gases of coal-fired power plants. Carbon dioxide was chemically adsorbed by the reaction K2CO3*1.5H2O + CO2 ↔ 2KHCO3 + 0.5H2O + heat. Moisture however, plays a significant role in the chemical adsorption process, which readily facilitates the adsorption process. Moisture usually contained as high as 8-17% in flue gases, badly affects the capacity of conventional adsorbents such as zeolites, but the present technology has no concern with moisture; water is rather necessary in principle as shown in the equation above. Carbon dioxide uptake occurred at a temperature of 60°C and the entrapped carbon dioxide was released by the decomposition of potassium bicarbonate to shift the reaction in the reverse direction. The decomposition occurred at high enough temperatures of 150°C to ensure complete regeneration of the sorbent. For the purpose of this research, emphasis was placed more on the adsorption process. When compared to other processes such as the conventional amine process, it provided an efficient, low utility cost and energy-conservative effect. The activated carbon was prepared by 20% by weight of K2CO3 and samples used during the experimental runs were dried at 60°C for the 26-hour runs and at 25°C and 125°C for the air-dried and oven-dried samples respectively for the 48-hour runs. The samples all got to the saturation point after 6 hours of exposure to carbon dioxide and gave adsorption capacities in the range of 2.5 to 3.5mol CO2/mol K2CO3 for all experimental runs performed in this research.

Committee: Douglas Price PhD (Committee Chair); Felicia Armstrong PhD (Committee Member); Jeffrey Dick PhD (Committee Member); Alan Jacobs PhD (Committee Member) Subjects: Chemical Engineering; Chemistry; Energy; Engineering; Environmental Engineering; Environmental Science

Master of Science in Engineering, University of Akron, 2010, Chemical Engineering

Coal-fired power plants contribute 31.7% of the total CO2 emissions in the U.S. Therefore, it is necessary to develop technology that can be utilized by these plants to capture these emissions. One of the most researched technologies for removing the CO2 is absorption/stripping with monoethanolamine (MEA). Studies showed that absorption/stripping with MEA removed 90 vol% CO2 from the power plant flue gas, costing as little as $33/ton CO2 avoided. However, much research was done to further reduce capital and operating costs. Some studies showed that oxidative degradation of MEA was a significant cost, and explored the reaction mechanisms, engineering concerns, and economics associated. In addition, other technologies for CO2 capture using MEA were suggested. One technology would utilize a fluidized bed reactor, incorporating MEA-impregnated porous supports (solid sorbents). For these sorbents, amorphous silica (silica) is an attractive support due to low cost and high surface area. Characterization of the extent of MEA impregnation into the silica would be a valuable tool for silica/MEA ratio optimization. In this study, the oxidative degradation of MEA is presented. Four additives at various concentrations were proposed to reduce the rate of oxidative degradation, which was performed at 100 °C for 18 h. This study also presents the characterization of the extent of tetraethylenepentamine (TEPA) impregnation into silica. Benzene adsorption was performed on silica, silica/TEPA-65/35 wt%, and silica/TEPA-48/46 wt% at 40, 70, and 120 °C under 150 cc/min Ar and 5.5 vol% benzene. Results of the studies concluded that for the oxidative degradation of MEA, water reduced the average change in intensity of 1663 cm-1 and 1597 cm-1 the most, followed by ethyleneglycol. This indicated the greatest reductions in the oxidative degradation rate of MEA. Concentrations as low as 20-35 wt% water may be used instead of the 60-70% used in industry for the CO2 capture solution. Results (open full item for complete abstract)

Committee: Dr. Steven Chuang (Advisor) Subjects: Engineering

MS, University of Cincinnati, 2013, Engineering and Applied Science: Chemical Engineering

Chemical and phase equilibria for aqueous monoethanolamine and piperazine carbon dioxide absorption solutions were modeled using the electrolyte-NRTL activity model. Binary interaction parameters were estimated using differential evolution, and a statistically significant improvement was noted in the ability to calculate total system pressure of the solutions. Calculation of partial pressures was met with mixed success; piperazine vapor-liquid equilibrium (VLE) experimental data showed excellent agreement with calculated values, while monoethanolamine VLE experimental data showed non-trivial systemic deviations from calculated values. Equilibrium compositions were determined using a paired free energy minimization and simultaneous equations approach developed in this work; this paired approach is shown to calculate chemical and phase equlibria more quickly than traditional free energy minimization in the context of this work. Estimation of parameters for single amine systems followed by simultaneous estimation of parameters from all pertinent amine systems has been shown to effectively narrow the parameter search space and results in parameter estimates with narrow confidence intervals. Parameter estimates were obtained using data from multiple literature sources, and verified using separate data sets and additional data from the regressed data sets that was withheld from the parameter search to test the predictive capability of estimated values. Parameter estimation was performed without the use of any data that requires a complex experimental apparatus; instead computationally intensive methods were used to replace experimentally intensive methods. Despite the relative simplicity of the data used, model calculations were reasonable for monoethanolamine and excellent for piperazine.

Committee: Stephen Thiel Ph.D. (Committee Chair); Carlos Co Ph.D. (Committee Member); Junhang Dong Ph.D. (Committee Member) Subjects: Chemical Engineering