Developing strategies for polymer redesign and recycling using reaction pathway analysi

The current lack of sustainability of and the limited portfolio of recycling processes for synthetic polymers have posed serious threats to the environment. Approximately 90% of plastics are produced via fossil fuels, and over 150 million tonnes of plastics have been discarded in the ocean. Annual production of plastics is expected to reach over 1 billion tons in 2050, but the current manufacturing, consumption, and disposal schemes of fossil-based polymers follow an unsustainable framework. Using reaction pathway analysis, we are pursuing a portfolio of strategies for redesign and recycling of polymers for sustainability. Please click Additional Files below to see the full abstract

Challenges and progresses made on the microkinetic description of lignin liquefaction: Application of group contribution methods

In this presentation a comprehensive microkinetic modelling framework and experimental tools are used to describe product yield and composition of direct lignin liquefaction processes with and without solvents (See Figure 1). With the framework proposed we aim to develop a unified theory and models capable of describing both dry (pyrolysis) and wet (hydrothermal and solvolysis) lignin liquefaction processes. An important phenomenon that has been shown to occur during lignin pyrolysis (as well as cellulose) is the formation of a liquid intermediate phase, and subsequent ejection of heavy products (\u3e~250 Da) as aerosols from this intermediate. In our presentation we will focus on the nature of lignin pyrolysis liquid intermediate through analysis of phase change equilibria temperatures for relevant lignin fragments, using group contribution methods. Specifically, estimation of boiling (Tb) and melting (Tm) points of lignin fragments was done using ARTIST software (Dortmund Data Bank Software & Separation Technology, GmbH). In total, 50 different lignin fragments were drawn, and their boiling and melting temperatures were calculated. The 50 fragments include monomers, dimers, trimers and tetrameters, with a variety of H, G and S units and inter-unit linkages. Figure 2 shows the calculated phase-change equilibria temperatures plotted against the number of aromatic units in a given lignin fragment. The dotted line at 400 °C is included as the approximate temperature at which both rupture of aliphatic linkages and conversion of short aromatic ring substituents occurs, but is less than the temperature for rearrangement of polycyclic structures. The collection of lignin fragments, such that Tm \u3c 400 \u3c Tb, make up the set of molecules that can exist as a liquid intermediate during pyrolysis, and are therefore the ones that have potential to be ejected as aerosols. The average lignin fragment in this range has 2.50 (± 0.11, standard error) aromatic units, molecular weight of 414 (± 20) Da, melting point of 292 (± 13) °C, and boiling point of 573 (± 19) °C. Relying solely on this analysis, one would expect these to be characteristics of an average molecule ejected as a liquid-phase aerosol during pyrolysis of lignin. Based on the quantification of phase equilibria temperatures, this liquid state can contain dimers and trimers, but typically not tetrameters or larger (they will preferentially depolymerize), or monomers (they will vaporize). It is these dimer and trimer products that should make up the majority of the heavy liquid products collected as aerosols. In order to validate this model, comparison was made with previously published work from Pecha, et al. (Ind. Eng. Chem. Res., 56, 2017, 9079-9089) and Bai, et al. (Fuel, 128, 2014, 170-179), who analyzed lignin pyrolysis oil with FT-ICR-MS. There is good agreement between the weights of species detected experimentally in these studies and those determined in this work based on group contribution calculations. Please click Additional Files below to see the full abstract

Glass transition and alpha-relaxation dynamics of thin films of labeled polystyrene

The glass transition temperature and relaxation dynamics of the segmental motions of thin films of polystyrene labeled with a dye, 4-[N-ethyl-N-(hydroxyethyl)]amino-4-nitraozobenzene (Disperse Red 1, DR1) are investigated using dielectric measurements. The dielectric relaxation strength of the DR1-labeled polystyrene is approximately 65 times larger than that of the unlabeled polystyrene above the glass transition, while there is almost no difference between them below the glass transition. The glass transition temperature of the DR1-labeled polystyrene can be determined as a crossover temperature at which the temperature coefficient of the electric capacitance changes from the value of the glassy state to that of the liquid state. The glass transition temperature of the DR1-labeled polystyrene decreases with decreasing film thickness in a reasonably similar manner to that of the unlabeled polystyrene thin films. The dielectric relaxation spectrum of the DR1-labeled polystyrene is also investigated. As thickness decreases, the $\alpha$-relaxation time becomes smaller and the distribution of the $\alpha$-relaxation times becomes broader. These results show that thin films of DR1-labeled polystyrene are a suitable system for investigating confinement effects of the glass transition dynamics using dielectric relaxation spectroscopy.Comment: 10 pages, 11 figures, 2 Table

Coal/Polymer Coprocessing with Efficient Use of Hydrogen.

The objective of the current research is to investigate the feasibility of coprocessing coal with waste polymers, with particular interest in employing the polymers as an alternate hydrogen source for coal upgrading and simultaneously recovering high valued fuels and chemicals from plastic waste. A chemical modeling approach was employed in which real and model feedstocks were used to identify the underlying reaction pathways, kinetics, and mechanisms controlling coal liquefaction in the presence of plastics and catalysts. Simple model systems were employed to facilitate product analysis and obtain information about the intrinsic reactivity. When reacted in binary mixtures, the conversion of tetradecane, a model compound of polyethylene, increased while the selectivities to primary products of 4-(naphthylmethyl) bibenzyl were enhanced. Experiments in the last six months in which the relative concentrations of the components were varied revealed that the effect was indeed a chemical one and not simply a result of dilution. An experimental protocol was developed to conduct experiments at elevated pressures more representative of coal liquefaction conditions. Preliminary experiments with real feedstocks allowed the extrinsic factors (i.e., diffusion limitations, solvent effects) to be identified. The combination of these two sets of experiments will ultimately be used to carry out process optimization and formulate strategies for catalyst development

Learning, memory and learning modulation in healthy aging and a model of amyloid pathology

Learning does not occur as an isolated event and experiences may act upon associated or subsequent memories. Strong novel events occurring around a weak learning experience can enhance the memory persistence of the latter through the behavioural tagging and capture (BTC) mechanism (Moncada and Viola, 2007). Additionally, contextual learning that is initially dependent on N-methyl-D-aspartate receptors (NMDAR) can be become independent of NMDAR after previous acquisition of a similar task (Finnie et al., 2018, Tayler et al., 2011). To date, neither the BTC mechanism nor the switch in the receptors involved in learning after prior experience have been studied in middle-aged mice or the knock-in AppNL-G-F/NL-G-F mouse model of Alzheimer’s disease. Additionally, if any impairment of the switch is seen, we ask if improving temporal memory association (Cai et al., 2016) could rescue this function. To study BTC, littermate AppNL-G-F/NL-G-F and wildtype (WT) mice were trained at 6 months in a daily behavioural paradigm, the appetitive delayed-matching-to-place (ADMP) task, to assess task acquisition, short-term memory, long-term memory, and memory modulation through novelty (i.e. BTC). These mice were then retrained at 12 months in the ADMP task to assess the impact of aging. These studies showed that BTC was impaired in AppNL-G-F/NL-G-F mice, and this occurred prior to any other deficits in learning and memory. By middle-age, spatial learning and memory were impaired in the ADMP task. To study the switch in learning mechanism occurring with prior contextual learning, male and female 3–4-month-old WT mice, 12-month-old WT mice, and 3–4-month-old AppNL-G-F/NL-G-F mice received 2 contextual fear conditionings in distinct contexts. Systemic injections of an NMDAR antagonist or saline were applied before conditioning to determine if the learning required NMDARs. Results showed that when the holding and transport cues were mis-matched between 2 learnings, the second learning remained NMDAR-dependent. Even with matched holding and transport cues, the switch in receptor mechanism in the second learning was not seen in middle-aged mice or in young AppNL-G-F/NL-G-F mice. Reducing the delay between the two conditionings rescued the switch for the middle-aged mice. While reducing the delay between recall of the first memory and the second conditioning rescued the switch in AppNL-G-F/NL-G-F mice. In conclusion, the work described in this thesis provides evidence for impairments in learning modulation in both a model of amyloid pathology and in healthy middle-aged mice. These findings may be important to help identify and target early signs of ageing- or disease-related cognitive decline

Fast pyrolysis of glucose‐based carbohydrates with added NaCl part 1: Experiments and development of a mechanistic model

Sodium ions, one of the natural inorganic constituents in lignocellulosic biomass, significantly alter pyrolysis behavior and resulting chemical speciation. Here, experiments were conducted using a micropyrolyzer to investigate the catalytic effects of NaCl on fast pyrolysis of glucose‐based carbohydrates (glucose, cellobiose, maltohexaose, and cellulose), and on a major product of cellulose pyrolysis, levoglucosan (LVG). A mechanistic model that addressed the significant catalytic effects of NaCl on the product distribution was developed. The model incorporated interactions of Na+ with cellulosic chains and low molecular weight species, reactions mediated by Na+ including dehydration, cyclic/Grob fragmentation, ring‐opening/closing, isomerization, and char formation, and a degradation network of LVG in the presence of Na+. Rate coefficients of elementary steps were specified based on Arrhenius parameters. The mechanistic model for cellulose included 768 reactions of 222 species, which included 252 reactions of 150 species comprising the mechanistic model of glucose decomposition in the presence of NaCl

Fast pyrolysis of glucose‐based carbohydrates with added NaCl part 2: Validation and evaluation of the mechanistic model

A mechanistic model considering the significant catalytic effects of Na+ on fast pyrolysis of glucose‐based carbohydrates was developed in Part 1 of this study. A computational framework based on continuous distribution kinetics and mass action kinetics was constructed to solve the mechanistic model. Agreement between model yields of various pyrolysis products with experimental data from fast pyrolysis of glucose‐based carbohydrates dosed with NaCl ranging from 0–0.34 mmol/g at 500 °C validated the model and demonstrated the robustness and extendibility of the mechanistic model. The model was able to capture the yields of major and minor products as well as their trends across NaCl concentrations. Modeling results showed that Na+ accelerated the rate of decomposition and reduced the time for complete thermoconversion of carbohydrates. The sharp reduction in the yield of levoglucosan (LVG) from fast pyrolysis of cellulose in the presence of NaCl was mainly caused by reduced decomposition of cellulose chains via end‐chain initiation and depropagation due to Na+ favoring competing dehydration reactions. Analysis of the contributions of reaction pathways showed that the decomposition of LVG made a minor contribution to its yield reduction and contributed less than 0.5% to the final yield of glycolaldehyde from fast pyrolysis of glucose‐based carbohydrates in the presence of NaCl

A Robust Strategy for Sustainable Organic Chemicals Utilizing Bioprivileged Molecules

Biobased chemicals will inevitably be an important part of a sustainable organic chemical industry. Current efforts in biobased chemicals are largely driven by opportunistic chemical product targets requiring complete technology development from feedstock to final product for a specific molecule. To enhance the development of biobased chemicals, it is important to create strategies that can be more systematic and can leverage advancements across multiple final products. Discussed here is the concept of bioprivileged molecules, which are chemical intermediates that have the potential to be efficiently converted into a range of product molecules that can both directly replace existing petrochemicals and are novel molecules that impart enhanced performance properties in end‐use applications

Flash Cracking Reactor for Waste Plastic Processing

Conversion of waste plastic to energy is a growing problem that is especially acute in space exploration applications. Moreover, utilization of heavy hydrocarbon resources (wastes, waxes, etc.) as fuels and chemicals will be a growing need in the future. Existing technologies require a trade-off between product selectivity and feedstock conversion. The objective of this work was to maintain high plastic-to-fuel conversion without sacrificing the liquid yield. The developed technology accomplishes this goal with a combined understanding of thermodynamics, reaction rates, and mass transport to achieve high feed conversion without sacrificing product selectivity. The innovation requires a reaction vessel, hydrocarbon feed, gas feed, and pressure and temperature control equipment. Depending on the feedstock and desired product distribution, catalyst can be added. The reactor is heated to the desired tempera ture, pressurized to the desired pressure, and subject to a sweep flow at the optimized superficial velocity. Software developed under this project can be used to determine optimal values for these parameters. Product is vaporized, transferred to a receiver, and cooled to a liquid - a form suitable for long-term storage as a fuel or chemical. An important NASA application is the use of solar energy to convert waste plastic into a form that can be utilized during periods of low solar energy flux. Unlike previous work in this field, this innovation uses thermodynamic, mass transport, and reaction parameters to tune product distribution of pyrolysis cracking. Previous work in this field has used some of these variables, but never all in conjunction for process optimization. This method is useful for municipal waste incinerator operators and gas-to-liquids companies

Impairment in novelty-promoted memory via behavioral tagging and capture before apparent memory loss in a knock-in model of Alzheimer’s disease

Alzheimer’s disease (AD) is associated with cognitive impairments and age-dependent memory deficits which have been studied using genetic models of AD. Whether the processes for modulating memory persistence are more vulnerable to the influence of amyloid pathology than the encoding and consolidation of the memory remains unclear. Here, we investigated whether early amyloid pathology would affect peri-learning novelty in promoting memory, through a process called behavioral tagging and capture (BTC). App(NL-G-F/NL-G-F) mice and wild-type littermates were trained in an appetitive delayed matching-to-place (ADMP) task which allows for the assessment of peri-learning novelty in facilitating memory. The results show that novelty enabled intermediate-term memory in wild-type mice, but not in App(NL-G-F/NL-G-F) mice in adulthood. This effect preceded spatial memory impairment in the ADMP task seen in middle age. Other memory tests in the Barnes maze, Y-maze, novel object or location recognition tasks remained intact. Together, memory modulation through BTC is impaired before apparent deficits in learning and memory. Relevant biological mechanisms underlying BTC and the implication in AD are discussed