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Pyrolysis and pyrolysis-catalysis of waste plastics and waste tires to produce high value fuels and chemicals
Get PDFThis research focuses on the pyrolysis of waste plastic, waste tire, and 1:1 mixtures of tire and plastics using a fixed-bed reactor with the aim of determining the influence of co-pyrolysis on the yield and composition of the product oils and gases. The liquid oil produced from the pyrolysis of tires and polystyrene (PS) was mostly composed of aromatic compounds, such as BTEX, refers to benzene, toluene, ethylbenzene and xylenes; and PAHs refers to for example, naphthalene, anthracene, phenanthrene, pyrene and fluorene and their derivatives. The liquid oil formed from the pyrolysis of high density polyethylene (HDPE) and low density polyethylene (LDPE) was mostly waxes of high molecular weight consisting of aliphatic compounds, composed of a series of alkanes, alkenes, and alkadienes. Polypropylene (PP) produced more alicyclic compounds, such as methyl-cyclohexane. Polyethylene terephthalate (PET) pyrolysis oil consisted of compounds such as xylene and styrene but was mainly composed of oxygenated compounds, such as benzoic acid. Co-pyrolysis of 1:1 mixtures of tires and individual plastics involved interaction, resulting in significantly higher yields of gas than expected for all the plastic mixtures. The oil produced from the co-pyrolysis of the tire with polyalkene plastics showed interaction between the polymer pyrolysis products, resulting in higher yields of aliphatic compounds and lower yields for BTEX, PAHs, alicyclic, and aromatic compounds.
The study also investigated the pyrolysis-catalysis of waste plastic, waste tire, and a 1:1 mixture of the two materials using a two-stage fixed-bed reactor. ZSM-5 is used as a catalyst to investigate the influence on product distribution and composition of gases and oils. The results showed that pyrolysis-catalysis of tire over ZSM-5 reduced oil yield from 54.83 wt.% in thermal pyrolysis to 37.30 wt.% in pyrolysis-catalysis, with an increase in gas yield from 8.69 wt.% in thermal pyrolysis to 24.65 wt.% in pyrolysis-catalysis. Pyrolysis-catalysis of HDPE, LDPE, PP, and PS, also showed increased gas yields, mainly consisting of hydrocarbons (C1-C4), while decreasing oil production. PS produced the lowest gas yield, while PET produced the highest, with CO and CO2 being the main gases generated. The pyrolysis of individual tire and plastic over ZSM-5 produced valuable chemicals such as benzene, toluene, ethyl benzene, xylenes, and styrene. The efficiency of ZSM-5 to minimize the heavy aliphatic fraction was high, on the other hand, the ZSM-5 with low deactivation by coke deposition and a high selectivity to produce light olefins.
The co-pyrolysis-catalysis of the tire and plastics with the ZSM-5 catalyst showed interaction between the tire and plastics which changed the composition of the product oils and gases over what would be expected from mere addition. Plastics co-pyrolysed with tire and the presence of ZSM-5 catalyst promoted the high production of the aromatic content, particularly BTEX compounds at the expense of aliphatic content. Tire/HDPE, Tire/LDPE, and Tire/PP mixtures showed a reduction in aliphatic and heavy molecular weight compounds when co-pyrolysed with tires, and the presence of a ZSM-5 catalyst increased the production of aromatic content, particularly BTEX compounds. Tire/PS mixture produced aromatic compounds, and the addition of the ZSM-5 catalyst increased aromatics at the expense of styrene. Tire/PET mixture produced BTEX and aromatic (refers to benzene derivatives, biphenyls, limonene, terphenyl, and indene compounds) due to the selectively of ZSM-5 that promotes the decarboxylation of the oxygenated compounds, and it gave high gas yields of mainly CO and hydrocarbons.
The pyrolysis-catalysis of waste plastic, waste tire, and 1:1 mixtures of tire and plastics was conducted over the MCM-41/ZSM-5 catalyst layer to determine the influence of two catalysts in series on oil and gas composition. The MCM-41 with a higher pore size was followed by ZSM-5 with a smaller pore size. The pyrolysis-catalysis process optimizes the conversion of plastic pyrolysis products to low molecular weight hydrocarbon fuels and chemicals. The production of gases during catalytic pyrolysis increases at the expense of oil yields, with oil yields of 39.50, 57.25, 53.50, 58.50, 77.00, and 36.75 wt.% for Tire, HDPE, LDPE, PP, PS, and PET, respectively. The highest hydrocarbon gases were produced from the tire and plastics while PET produced the highest gas yield with more CO and CO2. Applying the two stages MCM-41/ZSM-5 has the advantage in the cracking of HDPE, LDPE, and PP. The primary products can pass through the large pores of MCM-41, then followed by ZSM-5 with (strong acidic sites and small pores) that promote the formation of light aromatic hydrocarbons and increased the production of BTEX.
The co-pyrolysis of tire/plastic mixtures over MCM-41/ZSM-5 catalyst in series showed an increase in gas yields compared to the individual tire and plastics results. The major influence of the co-pyrolysis was the reduction of paraffin and olefin compounds. According to literature, the high cracking of long chain polyolefins and the interaction between hydrocarbon radicals produced from tire rubber and the radicals produced from the thermal decomposition of PE and PP caused the reduction of both aliphatic and alicyclic contents in the mixtures of Tire/HDPE, Tire/LDPE, and Tire/PP. Tire/PET showed negative values of interaction for the oxygenated compounds
DNA and RNA Dynamics: Probing Conformational Shifts with Single-Molecule FRET
No full textNucleic acids, which contain the essential code for life, are not static structures and a full understanding of their thermodynamic and kinetic properties is vital to understanding their biological functions. Ensemble measurements can give some insight into the impact of environmental variation on these systems but to extract precise kinetic and thermodynamic properties a single molecule approach is required. Single molecule Förster Resonance Energy Transfer (smFRET) was therefore employed to quantify the structure of two key nucleic acid systems. First the opening and closing dynamics of DNA hairpins were studied. These hairpins, formed of a doubled stranded stem and a single stranded loop appear in a range of biological processes and are used in bionanotechnological applications. pH, ionic strength, molecular crowding and temperature were all seen to be regulators of hairpin conformation. The impact of varying the loop composition and length was also investigated, showing changes to dynamics. The hairpin’s temperature dependence was exploited to extract entropic and enthalpic contributions to closing and entropic factors were seen to play a role in the loop length variation observed. Similar approaches were then applied to the SARS-CoV-2 RNA frameshifting element. A key feature of SARS-CoV-2 and many other viruses is -1 programmed ribosomal frameshifting. Essential for replication, it relies on the presence of a slippery sequence and stimulatory RNA secondary structure. This work demonstrates multiple strategies to doubly-label the SARS-Cov-2 RNA frameshifting element with a FRET pair, and evaluates the molecule’s conformation in solution, to reveal that the molecule exists in several environment-sensitive conformations, suggesting flexibility beyond the predicted structures. Overall, this work provides insights into the environmental sensitivity of nucleic acid structures, with direct implications for both fundamental biophysics and bionanotechnological applications. Therefore, contributing to the design of efficient synthetic nucleic acid systems and enhancing understanding of a potential anti-viral target
Tuna fisheries in Oman: recent trends and insights from molecular diet studies
No full textThe intensive harvesting of sardines has raised major concerns among Omani artisanal fishers regarding the future of tuna fisheries. As tuna serve as a vital economic resource and play a crucial ecological role in the marine ecosystem, this thesis investigates the dietary composition and prey diversity of two commercially significant species, yellowfin (Thunnus albacares) and longtail tuna (Thunnus tonggol), in Omani waters using morphological analysis and DNA metabarcoding techniques. The analysis of diet composition revealed that fish constitute the predominant prey group for both tuna species, while cephalopods and crustaceans represent important secondary contributors to dietary components. DNA metabarcoding significantly enhanced prey identification, overcoming the limitations of visual stomach content analysis by detecting a broader range of species and improving taxonomic resolution. A total of 40 prey species from 23 families were identified within tuna stomach samples, comprising 16 fish, 12 crustaceans, and 12 cephalopods. Despite expectations that sardines (Sardinella longiceps) would dominate the diet, carangids (jacks and trevallies) and squids were the most frequently detected prey groups. The study found genetically seasonal variations in prey community composition, with secondary prey (prey of prey) playing a role. Secondary prey influenced species composition changes, reflecting trophic interactions and prey availability rather than prey diversity. In contrast, the analysis of prey diversity revealed diversity was significantly higher in Seeb compared to Ash Sharqiyah, likely due to regional differences in habitat productivity and prey availability. Seasonally, dietary diversity was lower in winter than in spring, suggesting potential fluctuations in prey availability driven by oceanographic and climatic conditions. Metabarcoding also detected cases of secondary predation—that is, the presence of prey DNA originating from the digestive contents of the prey consumed by the predator, rather than from direct predation. This distinction is essential for accurately interpreting trophic interactions and avoiding misidentification of actual predator-prey relationships. Importantly, secondary predation should not be confused with the consumption of prey of secondary importance, which refers to prey species that are directly consumed but contribute minimally to the overall diet. Despite these complexities, the integrated methodologies confirmed that both yellowfin and longtail tuna are opportunistic predators, capable of adjusting their diets based on prey availability. The substantial presence of forage fish supports the broader ecological understanding that Oman’s upwelling-driven marine environment sustains a diverse and abundant small pelagic community, forming a critical prey base for top predators. These findings have important implications for fisheries management, particularly in light of increasing fishing pressures and environmental changes
Understanding clonal dynamics in normal and malignant haematopoietic stem cells
Get PDFEver since their discovery, haematopoietic stem cells (HSCs) have become the paradigm for understanding somatic stem cell systems. Throughout my doctoral research, I explored questions in HSC clonal dynamics by high-throughout in vitro and in vivo single-cell assays, state-of-the-art computational analysis and powerful mouse models of myeloid malignancies.
In Chapter 3, I dissected clonal evolution, functional and molecular profiles of single HSCs residing within the marrow of different bones. Phylogenetic analysis demonstrated that HSCs stay embedded their seeded location from embryogenesis. At the same time, single-cell molecular and in vivo transplantation analysis revealed that biological HSC properties are largely dictated by the tissue they reside in, thereby challenging some of the classical views on HSC migration and impact of anatomical location.
To continue in Chapter 4, I conveyed the power of somatic mutations to study preleukaemic competition dynamics. Leveraging on HSC ex vivo expansion and split cultures, a novel in vitro model of clonal competition unveiled the TET2-super competitor clones. These were highly efficient at impairing the growth of their wild-type counterparts. These findings imply that supercompetitive behaviour could be one of the fundamental mechanisms driving clone expansion in myeloid cancers.
Given the multifaceted nature of cancer, in chapter 5 I profiled the synergy between JAK2 and TET2 mutations and IP-10, a key inflammatory molecule. By generating an allelic series of MPN mouse models, we found that, albeit mildly, loss of IP-10 rescued the severe red cell phenotype driven by JAK2 V617F, and partially restored erythroid development. The paramount importance of dissecting the role of different inflammatory cytokines is therefore reinforced by this study.
In summary, this doctoral research has shed new light on HSC clonal dynamics, clonal competition and the bone marrow microenvironment in health and disease, hopefully accelerating the burgeoning HSC biology field
Investigating axonal transport in Charcot-Marie-Tooth disease Type 2A using a human embryonic stem cell model
No full textCharcot-Marie-Tooth (CMT) disease is one of the most common forms of inherited peripheral neuropathy and has many different subtypes. One such subtype is sensory and motor neuropathy CMT Type 2A (CMT2A), for which no treatments currently exist. CMT2A is caused by mutations in Mitofusin 2 (MFN2), and it is unknown how these mutations drive disease. Hence, I set out to create the first human embryonic stem cell (hESC) model of CMT2A to investigate the impact of a CMT2A-causing mutation in a disease-relevant cell type.
I generated a panel of CMT2A hESC clones by introducing the disease-causing heterozygous R94Q mutation into Mitofusin 2 via CRISPR-Cas9 editing. The clone panel was subsequently differentiated into a disease-relevant cell type: limb-innervating motor neurons. The introduction of the CMT2A-causing mutation had no effect on differentiation. Limb-innervating motor neurons containing the disease-causing mutation displayed a mitochondrial trafficking defect characterised by a reduction in the number of motile mitochondria and the motile dynamics. The reduction in motile mitochondria could be rescued via small molecule inhibition of the deacetylase HDAC6. Furthermore, using protein over-expression and co-immunoprecipitation, I also show that MFN2 containing the R94Q mutation interacts more strongly with the trafficking cargo adapter protein TRAK1, leading to TRAK1 having a reduced interaction with the axonal motor protein kinesin.
Overall, I have successfully created hESCs containing a CMT2A-causing mutation that can be differentiated into limb-innervating neurons, providing a new in vitro platform for CMT2A research. Additionally, results here contribute to evidence that axonal transport deficits are a common CMT2 hallmark. This work provides a new hypothesis for CMT2A pathophysiology and is a foundation for the further study of axonal transport machinery and its functionality in CMT2A
The role of surface topology on reactive wetting of SAC305 solder on Ag substrates
Get PDFPhysical removal of material via grit paper is the most common method of preparing surfaces for soldering. Most researchers have shown that increased roughness improves solder spreading; however, what isn't fully known is which exact feature or features create the positive outcome. This research was primarily focused on enhancing SAC305 solder interconnects to silver(Ag) via surface modification.
Ag substrates were roughened using grit paper (P120-P1000). Except for P1000, all surfaces had a final area of 2.23 +/- 0.25 mm^2, indicating minimal correlation between surface roughness and solder spreading.
A femtosecond laser was used to create parallel and hatched Ag substrates with various hatch distances and angles. The final spreading area for all the solder samples for all parallel substrates was 2.5 +/- 1 mm^2, showing no correlation between the final spreading area and hatch spacing. In contrast, altering the hatch angle resulted in minimal improvement of the mean final spreading area, of 3 +/- 1 mm^2. The exception was the 90-degree cross-hatched sample with a final spreading area equivalent to the parallel surfaces. The optimal hatch angle was 115 degrees, cross-hatched with a final solder spreading area of 3.2 mm^2. Laser-textured substrates were shown to have some control over the molten solder flow direction and morphology. This may allow improved joints and greater control of joint placement.
Otsu and Multi-Otsu methods were applied to SEM images to analyse solder/Ag interfaces. These methods identified interfaces but struggled to differentiate Ag and Cu due to minimal atomic number differences. BSE imaging provided a topological map, isolating the harder intermetallic compounds of Ag3Sn and Cu6Sn5 within the solder matrix. However, there was some uncertainty, leading to manual image adjustments that made analysis subjective and time-consuming.
A Mask R-CNN model, developed using Detectron2 on hot-stage microscopy images of SAC305 solder on Ag substrates. The model achieved 99% accuracy and an average precision of 76.25
Non-Precious Catalysts Based on Porous Media for Polymer Electrolyte Membrane Fuel Cells (PEMFCs)
No full textOxygen reduction reaction (ORR) is the key process in many electrochemical technologies, such as fuel cells and metal-air batteries. However, the ORR is kinetically sluggish, necessitating the use of an electrocatalyst. Currently, platinum-based catalysts are the state-of-the-art catalyst for the ORR and are widely used in fuel cell technologies. However, platinum is classed as a critical raw material due to its scarcity, putting supply chains at risk and potentially limiting the widespread adoption. Recently, transition-metal coordinated nitrogen doped carbon (M-N-C) materials have emerged as promising alternatives, offering activity from earth-abundant elements and tunability through structure and composition. In this work, we explore combining transition metal and nitrogen in a porous carbon structure of varying surface area and morphology. We develop catalysts that offer both high efficiency and durability. The catalysts were synthesised using a simple pyrolysis and were tested using various advanced techniques such as XRD, XPS, BET, SEM, TEM. A central contribution of this work is the application of time-resolved spectroscopies to ORR electrocatalysts. Using transient absorption spectroscopy (TAS) and terahertz spectroscopy, we directly observe charge-carrier dynamics in M-N-C materials. TAS reveals long-lived trapped states localised at metal-Nₓ sites, providing the first spectroscopic evidence that these centres act as charge-trapping sites which facilitate electron transfer during ORR. This dynamic perspective bridges structural characterisation with catalytic function, establishing a mechanistic understanding of electronic behaviour of these catalysts. Overall, this work advances both material design and fundamental understanding of non-precious ORR catalysts, demonstrating ultrafast optical spectroscopy can guide the rational development of next-generation electrocatalysts
Characterising Bias and Noise in Interferometric Synthetic Aperture Radar Time Series
No full textNatural and anthropogenic hazards associated with the deformation of the Earth’s surface pose substantial risks to societal health and safety. One of the most effective methods for categorising and monitoring these hazards is through the measurement of deformation over time. Although various methods, such as levelling surveys and GPS monitoring, can be employed to achieve this, only Interferometric Synthetic Aperture Radar (InSAR) utilising space-borne (or aerial) platforms like Sentinel-1 is capable of monitoring the majority of the Earth’s solid surface on a regular basis.
The substantial volume of SAR data generated by missions like ESA’s Sentinel-1 satellite enables near-real-time deformation monitoring through time series InSAR. While this approach has proven highly successful in the field of geodesy, several challenges persist. This thesis addresses key challenges, primarily focusing on phase noise estimation, coherence reliability, change detection, and phase bias effects.
Reliable deformation measurements depend on accurately estimating the phase noise of pixels in InSAR time series data. Coherence estimation can be improved by using groups of pixels with similar scattering characteristics, referred to as sibling ensembles. Many methods use amplitude similarity for sibling selection, raising questions about whether incorporating phase would improve coherence estimates. I test and optimise a method known as Similar Time series Interferometric Phase, or STIP, which integrates phase information into ensemble selection.
To ensure sibling ensembles continue sharing the same scattering characteristics and produce accurate coherence is important for long time series. I use the shared scattering characteristics between nearby pixels to develop a novel change detection methodology with a focus on high-resolution InSAR data.
Finally, I investigate phase bias, which affects short-term multilooked interferograms and can introduce deformation measurement errors. By analysing closure phase, a key marker of phase bias, for both C-band and L-band InSAR across different land cover types, I gain insights into the underlying scattering mechanisms. My findings show that the observed, consistently positive closure phase bias can be successfully reproduced in a simulation framework by using a temporally inconsistent and asymmetric phase noise signal. I also characterise how the mean closure phase increases with the number of looks before converging an a stable plateau, and develop a mathematical model to describe this convergence. This behaviour is understood to be a consequence of the process of multilooking suppressing the interference cross-terms between scatterers, which in turn reveals the underlying systematic bias.
This thesis presents methods and insights that enhance the accuracy and reliability of time series InSAR, particularly for long-term deformation monitoring and change detection. This leads to improved usefulness of deformation monitoring for the health and safety of society, both in relation to natural and anthropogenic hazards
Animal Speech and Perceptions of Threat in Human-Animal Narratives from Kipling (1894) to Kivirähk (2007)
No full textThis thesis argues that non-human animal speech in fiction can be used to promote a range of conflicting agendas in relation to social and interspecies hierarchies. In Chapter One, I analyse Rudyard Kipling’s Jungle Books and Kenneth Grahame’s Wind in the Willows to demonstrate how animal speech can be used in fiction to celebrate colonial and class-based hierarchies. Contrastingly, in Chapter Two, I argue that Andrus Kivirähk’s The Man Who Spoke Snakish and Salman Rushdie’s Haroun and the Sea of Stories present more-than-human speech and language as a form of resistance against colonialist oppression of humans, of non-humans and of language. In Chapter Three, I argue that Barbara Gowdy’s The White Bone and Timothy Findley’s Not Wanted on the Voyage use animal speech and language to challenge anthropocentric and heteropatriarchal narratives. In this final chapter, I also interrogate the relationship between narratives of extinction and conservation, both in these texts and in current postcolonial debates.
As well as literary animal studies, this research contributes to the study of linguistic animacy by examining the relationship between animacy and anthropomorphism in literary narratives. It also contributes to the interdisciplinary field of extinction studies, analysing the relationship between biological and linguistic extinction in the texts under discussion and engaging with contemporary debates in the study of language extinction and linguistic oppression. I also contribute to the field of biosemiotics, by interrogating the potential of biotranslation to function as a tool for constructing non-human narratives
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