Matching Items (27)
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- All Subjects: chemical engineering
- Creators: Torres, Cesar
Description
Polymers have played a pivotal role in building modern society. Polymers can be classified as synthetic and natural polymers. Accumulation of both synthetic and natural polymer waste leads to environmental pollution. This dissertation aims at developing one-pot bioprocesses for a breakdown of natural polymers like cellulose, and hemicellulose and synthetic polymers like polyethylene terephthalate (PET). First, a one-pot process was developed for hemicellulose breakdown. A signal peptide library of native SEC pathway signal peptides was developed for efficient secretion of endoxylanse enzyme. Furthermore, in situ, the process was successfully created for hemicellulose to xylose with the highest reported xylose titer of 7.1 g/L. In addition, E. coli: B. subtilis coculture bioprocess was developed to produce succinate, ethanol, and lactate from hemicellulose in one pot process.
Second, a one-pot process was developed for cellulose breakdown. In vitro enzyme assays were used to select SEC pathway signal peptides for endoglucanase and glucosidase secretion. Then, the breakdown of carboxymethyl cellulose (CMC), a cellulose derivative, was conducted in in situ conditions. U-13C fingerprinting study showed carbon enrichment from CMC when cultures were cofed with CMC and [U-13C] glucose. Further, Whatman filter paper sheets showed a change in shape in recombinant cocultures. SEM images showed continuous orientation in the case of two enzymes confirmed by fast Fourier transform (FFT), suggesting higher crystallinity of residues. Similarly, in microcrystalline cellulose breakdown in in situ conditions, a 72% reduction of avicel cellulose was achieved in a one pot bioprocess. SEM images revealed valleys and crevices on residues of coculture compared to smoother surfaces in monoculture residues pressing the importance of the synergistic activity of enzymes.
Finally, one pot deconstruction process was developed for synthetic polymer PET. First, the PET hydrolase secretion strain was developed by selecting a signal peptide library. The first bis(2-hydroxyethyl) terephthalate (BHET) consolidated bioprocess was developed, which produced a terephthalic acid titer of 7.4 g/L. PET breakdown was successfully demonstrated in in vitro conditions with a TPA titer of 4 g/L. Furthermore, PET breakdown was successfully demonstrated in in situ conditions. Consolidated bioprocesses can be an invaluable approach to waste utilization and making cost-effective processes.
ContributorsMhatre, Apurv (Author) / Varman, Arul (Thesis advisor) / Nielsen, David (Committee member) / Misra, Rajeev (Committee member) / Nannenga, Brent (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2023
Description
Lithium-ion batteries are widely used for high energy storage systems and most of the commercially manufactured lithium-ion batteries use liquid electrolytes and
polymeric separators. However, these electrolytes and polymeric separators pose safety
issues under high temperatures and in the event of short circuit which may lead to
thermal runaway and cause fire. The application of fire-retardant high salt concentrated
electrolytes can be used to address the safety issues that arises in the use of liquid
electrolytes, but these electrolytes have high viscosity and low wettability when used on
polymeric separators which are commercially used in lithium-ion batteries. To address
this issue, zeolite powder has been synthesized and separators were prepared by coating
on the electrode using scalable blade coating method. Zeolite separators have higher
wettability and electrolyte uptake compared to polymeric separators such as
polypropylene (PP) due to their intra-particle micropores. The zeolite separators also
have higher porosity compared to PP separators resulting in higher electrolyte uptake and
better electrochemical performance of the lithium-ion batteries. Zeolite separators have
been prepared using spherical-silicalite and plate-silicalite to analyze the effect of
morphology of the particles on the electrochemical performance of the cells. The platesilicalite separators have higher capacity retention during long-term cycling at low Crates and better capacity performance at high C-rates compared to spherical-silicalite.
Therefore plate-silicalite is very promising for the development of high-performance safe
lithium-ion batteries.
ContributorsLINGAM MURALI, DHEERAJ RAM (Author) / Lin, Jerry (Thesis advisor) / Muhich, Christopher (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2022
Description
Factors affecting biofilm development, specifically the materials of the pipe, were investigated. Two laboratory scale bioreactor systems were constructed to study biofilm formations: a pipe loop bioreactor with continuous flow at 10.1 liters per minute (LPM), and a tank bioreactor under stagnant conditions with a minimal flow of 0.0095 LPM. The continuous flow bioreactors were constructed using cross-linked polyethylene (PEX), copper, and galvanized steel pipes. The tank bioreactors consisted of glass chambers containing coupons made from the pipe materials, as well as glass microscope slides. Municipality tap water was used in the experimentation, with no nutrients added. Legionella pneumophila was spiked into all the pipe loop bioreactors, and only in one tank bioreactor. Detection of heterotrophic bacteria, coliforms and Legionella using tryptic soy agar (TSA), Brilliance, and buffered yeast charcoal extract (BYCE), respectively. Over ten weeks, biofilms were developed on PEX, copper, and steel, in the pipe loop bioreactors and the tank bioreactors. Heterotrophic bacteria were detected in all systems; however, no coliforms were detected, and Legionella pneumophila was only detected on a coupon in the copper pipe loop bioreactor, as measured by bacterial concentration on test materials. In the tank bioreactors, biofilms developed the most rapidly on PEX, followed by galvanized steel, and finally copper. Out of the four materials, copper had the lowest bacterial growth, which can be ascribed to the bactericidal impact of copper ions on the bacterial cells attaching to the copper surface. After biofilm aging, higher bacterial colonization on copper and accumulation of dead bacterial layer on the surface may act as a protective barrier against copper ions. Bacterial densities in the biofilm reached a high concentration of 1.40 x 105 CFU/cm2 on the PEX pipe loop bioreactor, and 1.05 x 104 CFU/cm2in the PEX coupon in the tank bioreactors. Comparing the turbulent conditions in the pipe loop bioreactors to the stagnant conditions in the tank bioreactor, showed that biofilms formed more rapidly under stagnant conditions, but in larger quantities under turbulent conditions.
ContributorsGreenberg, Samuel Gabe (Author) / Abbaszadegan, Morteza (Thesis advisor) / Alum, Absar (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2021
Description
Corrosion is one of the key failure modes for stainless steel (SS) piping assets handling water resources managed by utility companies. During downtime, the costs start to incur as the field engineer procures its replacement parts. The parts may or may not be in stock depending on how old, complex, and common the part model is. As a result, water utility companies and its resilience to operate amid part failure are a strong function of the supply chain for replacement piping. Metal additive manufacturing (AM) has been widely recognized for its ability to (a) deliver small production scales, (b) address complex part geometries, (c) offer large elemental metal and alloy selections, (d) provide superior material properties. The key motive is to harvest the short lead time of metal AM to explore its use for replacement parts for legacy piping assets in utility-scale water management facilities. In this paper, the goal was to demonstrate 3D printing of stainless steel (SS) 316L parts using selective laser melting (SLM) technology. The corrosion resistance of 3D printed SS 316L was investigated using (a) Chronoamperometry (b) Cyclic Potentiodynamic Polarization (CPP) and Electrochemical Impedance Spectroscopy (EIS) and its improved resistance from wrought (conventional) part was also studied. Then the weldability of 3D printed SS 316L to wrought SS 316L was illustrated and finally, the mechanical strength of the weld and the effect of corrosion on weld strength was investigated using uniaxial tensile testing. The results show that 3D printed part compared to the wrought part has a) lower mass loss before and after corrosion, (b) higher pitting potential, and (c) higher charge transfer resistance. The tensile testing of welded dog bone specimens indicates that the 3D printed parts despite being less ductile were observed to have higher weld strength compared to the wrought part. On this basis, metal AM holds great value to be explored further for replacement piping parts owing to their better corrosion resistance and mechanical performance.
ContributorsSampath, Venkata Krishnan (Author) / Azeredo, Bruno (Thesis advisor) / Torres, Cesar (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2021
Description
Optimizing cathodes for microbial fuel cells is important to maximize energy harvested from wastewater. Cathodes were made by modifying a recipe from previous literature and testing the current of the cathode using linear sweep voltammetry. The cathodes contained an Fe-N-C catalyst combined with a Polytetrafluoroethylene binder. Optimizing the power resulting from the microbial fuel cells will help MFCs be an alternative energy source to fossil fuels. The new cathodes did improve in current production from −16 𝐴/𝑚 to −37 𝐴/𝑚 at -0.4 V. When fitted using a Butler-Volmer model, the cathode linear-sweep voltammograms did not follow the expected exponential trend. These results show a need for more research on the cathodes and the Butler-Volmer model, and they also show that the cathode is ready for further and longer application in a microbial fuel cell.
ContributorsRussell, Andrea Christine (Author) / Torres, Cesar (Thesis director) / Young, Michelle (Committee member) / School of Sustainable Engineering & Built Envirnmt (Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
Electrolytes play a critical role in electrochemical devices and applications, and therefore design and development of electrolytes with tailored properties are much desired to accommodate variety of operation requirements. Extreme temperatures are considered as one of the challenging environmental conditions, especially for devices rely on liquid state electrolytes, rendering failure of operations once the electrolyte systems undergo phase transitions. This work focuses on development of low-temperature iodide-containing liquid electrolyte systems, specifically designed for the molecular electronic transducer (MET) sensors in space applications. Utilizing ionic liquids, molecular liquids, and salts, multiple low-temperature liquid electrolytes were designed with enhancements in thermal, transport, and electrochemical properties. Effects of intermolecular interactions were further investigated, revealing correlations between optimization of microscopic dynamics and improvements of macroscopic characteristics. As a result, three low-temperature electrolyte systems were reported utilizing ethylammonium/water, gamma-butyrolactone/propylene carbonate, and butyronitrile as solvent with ionic liquid, 1-butyl-3-methylimidazolium iodide, and lithium iodide salt. Consequently, the liquidus range of these systems have been extended to -108 ˚C, -120 ˚C, and -152 ˚C, respectively, marking the lowest liquidus temperature of liquid electrolytes to the author’s best knowledge. Moreover, transport properties of designed systems were characterized from 25 to -75 ˚C. Effects of selected cosolvent/solvent on evolutions of transport properties were observed, revealing interplay between two governing mechanisms, ion disassociation and ion mobility, and their dominance at different temperatures. Experimental spectroscopy characterization techniques validated the hypothesized intermolecular interactions between solvent-cation and solvent-anion, complimented by computational simulation results on the complex dynamics between constituent ions and molecules. To support MET sensing technology, the essential iodide/triiodide redox were investigated in developed electrolytes. Effects of different molecular solvents on electrochemical kinetics were elucidated, and steady performances were validated under a properly controlled electrochemical window. Optimized electrolytes were tested in the MET sensor prototypes and showcased adequate functionality from calibration. The MET sensor prototype has also successfully detected real-time earthquake with low noise floor during long term testing at ASU seismology facility. The presented work demonstrates a facile design strategy for task-specific electrolyte development, which is anticipated to be further expanded to high temperatures for broader applications in the future.
ContributorsLin, Wendy Jessica (Author) / Dai, Lenore L (Thesis advisor) / Wiegart, Yu-chen Karen (Committee member) / Emady, Heather (Committee member) / Lind Thomas, MaryLaura (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2022
Description
Energy can be harvested from wastewater using microbial fuel cells (MFC). In order to increase power generation, MFCs can be scaled-up. The MFCs are designed with two air cathodes and two anode electrodes. The limiting electrode for power generation is the cathode and in order to maximize power, the cathodes were made out of a C-N-Fe catalyst and a polytetrafluoroethylene binder which had a higher current production at -3.2 mA/cm2 than previous carbon felt cathodes at -0.15 mA/cm2 at a potential of -0.29 V. Commercial microbial fuel cells from Aquacycl were tested for their power production while operating with simulated blackwater achieved an average of 5.67 mW per cell. The small MFC with the C-N-Fe catalyst and one cathode was able to generate 8.7 mW. Imitating the Aquacycl cells, the new MFC was a scaled-up version of the small MFC where the cathode surface area increased from 81 cm2 to 200 cm2. While the MFC was operating with simulated blackwater, the peak power produced was 14.8 mW, more than the smaller MFC, but only increasing in the scaled-up MFC by 1.7 when the surface area of the cathode increased by 2.46. Further long-term application can be done, as well as operating multiple MFCs in series to generate more power and improve the design.
ContributorsRussell, Andrea (Author) / Torres, Cesar (Thesis advisor) / Garcia Segura, Sergio (Committee member) / Fraser, Matthew (Committee member) / Arizona State University (Publisher)
Created2022