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Thermodynamic Framework and Applications on the Use of Water and Green Solvents for Plastics Upcycling
No full textThe benefits of plastics are undeniable; however, their widespread use and inherent chemical resistance ultimately leads to significant environmental impacts. Plastic waste is an ever-growing problem; with less than 9% of plastic being recycled, and the remaining plastic representing an estimated $7.2 billion and 3.4 EJ of embodied energy lost to landfills. As plastics persist in the environment and landfills for hundreds of years after disposal, their “end-of-life” does not equal “end-of-impact”. To meet our climate goals and reduce the burden of plastics manufacturing on our environment, a significant and rapid change to our recycling system is needed. Unfortunately, improved plastics recycling faces many challenges. Mechanical recycling, the current standard, is ineffective for most plastics as it often results in irreversible molecular weight loss which in turn degrades mechanical properties. Additionally, unknown additive composition limits the re-use of mechanical recyclate in many applications. Thus, chemical depolymerization or additive separation methods are needed for highly contaminated, colored, and mixed-plastic resins. While chemical recycling methods can often address multiple waste streams, it is energy intensive to produce small molecules of inherently lower value than plastic feed and combustion of the preferred fuel product leads to greenhouse gas emissions that can otherwise be avoided if the waste plastic is retained in its polymer form. Versatile technologies which use sustainable process conditions, are responsive to complex waste streams, preserve polymer properties and can purify waste plastics from additives or separate blended materials, can overcome the barriers of other technologies for plastics circularity. A robust circular plastics economy will require combining the principles of mechanical and chemical recycling to effectively separate complex plastic blends and additives. This thesis aims to develop novel and sustainable processes through the following objectives: 1) advance current understanding of water solubility and swelling behavior of polymers and additives through the development of a robust thermodynamic framework and 2) demonstrate how thermodynamics can aid in the development of sustainable plastics processing. The studies presented here attempt to uncover the usefulness of green solvents for polymer circularity through a thermodynamic lens
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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MOLECULAR PATHWAY ANALYSIS OF BIOCRUDE FORMATION IN HYDROTHERMAL LIQUEFACTION
No full textHydrothermal liquefaction (HTL) is a process utilized to convert high water content feedstocks into a usable biocrude oil at temperatures between 250 – 350 °C and pressures in excess of 100 bar. Despite HTL’s prevalence as a research topic since the turn of the century, the majority of research until recently focused on improving oil yields from single-source algal feeds. In recent years, the focus has shifted towards waste-based feedstocks to address feedstock availability and prohibitive cost issues plaguing early HTL research. Food, yard, and wood wastes from municipal solid waste (MSW) account for 223 million tons of waste annually. These energy-dense waste feeds have the potential to produce spatially distributed and usable biocrude oil across the United States. Despite research interest in this area, hydrothermal liquefaction has yet to realize commercialization due to insufficient biocrude yields and a lack of fundamental understanding regarding heteroatom distribution and subsequent removal. Due to the complexity of waste feedstocks as well as the severe reaction conditions, the chemistry of waste HTL is poorly understood and colloquially referred to as a black-box process. To uncover the governing chemical pathways towards biocrude production from waste, experimental research coupled with advanced analytical chemistry techniques is required. Mass spectrometry (MS) is an analytical technique used to measure the mass-to-charge ratio (m/z) of individual molecules. The most common MS technique is gas chromatography mass spectrometry (GC-MS), which measures the volatile portion of a sample (boiling point ≤ 325 °C). In typical bio-oil samples from waste HTL, less than 40% of the biocrude can be analyzed using GC-MS. In addition to GC-MS, further high-resolution mass spectrometry techniques are available with increased resolution and the ability to distinguish between mass-to-charge ratio changes on the order of parts per billion. One such technique, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) allows for this ppb resolution due to the use of a superconducting magnet at strengths of 9 – 21 Tesla. In this work, a detailed chemical understanding and pathway analysis is developed to describe the effect of feedstock composition and catalysts on biocrude formation and heteroatom distributions. HTL chemical pathways are experimentally assessed through batch reactions and subsequent mass spectrometry analysis and further confirmed using density functional theory and kinetic model simulations. Research included in this thesis utilizes analytical and computational chemistry to determine the effects of feedstock composition, catalysts, and pretreatment conditions on resultant hydrothermal liquefaction molecular pathways. Enhanced chemical knowledge of biocrude formation pathways was then applied to determine sub-mechanisms for real-world waste feedstocks
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Evaluation of Electrochemical Storage Systems for Higher Efficiency and Energy Density
No full textLack of energy storage is a key issue in the development of renewable energy sources. Most renewables, especially solar and wind, when used alone, cannot sustain a reliably constant power output over an extended period of time. These sources generally generate variable amounts of power intermittently, therefore, an efficient electrical energy storage (EES) method is required to better temporally balance power generation to power consumption.
One of the more promising methods of electrical energy storage is the unitized regenerative fuel cell (UFRC.) UFRCs are fuel cells that can operate in a charge-discharge cycle, similar to a battery, to store and then to subsequently release power. Power is stored by means of electrolysis while the products of this electrolysis reaction can be recombined as in a normal fuel cell to release the stored power. A major advantage of UFRCs over batteries is that storage capacity can be decoupled from cell power, thus reducing the potential cost and weight of the cell unit. Here we investigate UFRCs based on hydrogen-halogen systems, specifically hydrogen-bromine, which has potential for improved electrode reaction kinetics and hence cheaper catalysts and higher efficiency and energy density. A mathematical model has been developed to analyze this system and determine cell behavior and cycle efficiency under various conditions.
The conventional H2-Br2 URFCs, however also so far have utilized Pt catalysts and Nafion membranes. Consequently, a goal of this work was to explore alternate schemes and materials for the H2-Br2 URFC. Thus, three generations of test cells have been created. The first two cells were designed to use a molten bromide salt, ionic liquid or anion exchange membrane as the ion exchange electrolyte with the liquids supported on a porous membrane. This type of system provides the potential to reduce the amount of precious metal catalyst required, or possibly eliminate it altogether. Each cell showed improvement over the previous generation, although the results are preliminary. The final set of results are promising for anion exchange membranes on a cost basis compared Nafion.
Another promising energy storage solution involves liquid methanol as an intermediate or as a hydrogen carrier. An alternative to storing high-pressure hydrogen is to produce it on-board/on-site on demand via a methanol electrocatalytic reformer (eCRef), a PEM electrolyzer in which methanol-water coelectrolysis takes place. Methanol handling, storage, and transportation is much easier than that for hydrogen. The hydrogen produced via methanol eCref may then be used in any number of applications, including for energy storage and generation in a standard H2-O2 PEM fuel cell. The mathematical modeling and analysis for an eCref is very similar to that of the HBr URFC. In this work, a comprehensive model for the coelectrolysis of methanol and water into hydrogen is created and compared with experimental data. The performance of the methanol electrolyzer coupled with a H2-O2 fuel cell is then compared for efficiency to that of a direct methanol fuel cell data and was found to be superior. The results suggest that an efficient and small paired eCRef-fuel cell system is potentially be a cheaper and more viable alternative to the standard direct methanol fuel cell.
Both the H2-Br2 URFC and the methanol eCref in combination with a H2-O2 fuel cell have significant potential to provide higher energy efficiency and energy density for EES purposes
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Characterization of Biomass Materials for Understanding the Processing
No full textVibrational and thermal behavior of several important systems were studied. The first study was a measurement of the infrared vibrational spectra of glucose and two important glucose dimers (cellobiose and maltose) as a function of temperature. The purpose of his study was to measure shifts in vibrational band positions to gain insight into carbohydrate reactivity. The second study was on hydrothermally treated coffee waste biomass. Here, collaborators at University of Campinas (UNICAMP, Brazil) treated coffee waste biomass in a flow-through subcritical water hydrolysis reactor. The purpose of the M.S. study on coffee waste was to understand the chemical changes that occurred to the residual solids during hydrolysis treatment. Vibrational spectroscopy and thermal analysis techniques were used. The third and final study was to understand the chemical composition of the solid product resulting from co-solvent enhanced lignin fractionation (CELF) of several biomass feeds. Collaborators at University of California Riverside (UCR) recently developed the CELF process. The purpose of the M.S. study on the CELF solid product was to understand its composition to help guide the CELF reactor design and determine applications for the CELF solids. Taken together, the 3 studies are integrated into a cohesive whole that demonstrates the use of spectroscopic and thermal techniques for characterizing biomass and understanding its composition at the molecular level
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