Overcoming water-gas-shift equilibrium via chemical looping

PhD ThesisThis thesis is focused on overcoming the equilibrium limitation of the water-gas-shift reaction (WGS), a common way to produce hydrogen, via chemical looping using iron-containing perovskite materials. The WGS reaction is separated into reduction and oxidation half-cycle by using an oxygen carrier material (OCM) to act as an intermediate via chemical looping, therefore, water is the only impurity in the hydrogen product stream. WGS conversions are thermodynamically limited to a maximum of 50 % by equilibrium constant using a metal with two oxidation states, metal or metal oxide, during steady state operation at 817 ▫C (equal amount to oxygen is removed/replaced from the material during reduction/oxidation half-cycle). Here we show that this limitation can be overcome by using a material that is able to produce hydrogen without undergoing phase transitions and with high structural stability via chemical looping in a counter-current flow fixed bed reactor. Initial experiments were performed to select a perovskite material from the La-Sr-Fe series that remain single crystal structure and capable of achieving high redox reactivity at 820 ▫C where the WGS equilibrium constant is close to unity. La0.6Sr0.4Fe3-δ (LSF641) was selected for further investigation as it was able to overcome WGS equilibrium limitation and was showing 80 % conversions for both half-cycles during steady-state which was the highest among other materials in the series. As water and CO were fed separately in opposite directions, an oxidation state profile of the bed was established during steady state. This oxidation state profile was determined by combining theoretical thermodynamic data with lattice parameters obtained from synchrotron in-situ x-ray diffraction (XRD). WGS conversions were further improved by using shorter redox duration. The stability of LSF641 was investigated by performing longterm redox cycling and it was showing constant conversions over 270 redox cycles. In addition, composite materials consisting of perovskite material and iron oxide were investigated to improve the overall OCM oxygen capacity. La0.7Sr0.3Fe3-δ perovskite with 11 wt.% iron oxide was able to produce hydrogen 15 times higher than iron oxide alone at the 200th cycles. Different phases were found after the reduction in CO as shown in XRD experiments, in particular La2-ySryFeO4-δ was found with the highest intensity in in-situ XRD experiment during the reduction in hydrogen, suggests that this phase is partly responsible for the increase in hydrogen production. The increase in hydrogen production was also related to the increase of porosity which was determined by using micro computed-tomography imaging to inspect the change in morphology of the OCM. The OCM porosity increased from 0.8 % to 5.6 % and 13% at 70th and 140th cycle, respectively

Tracking the evolution of a single composite particle during redox cycling for application in H-2 production

Composite materials consisting of metal and metal oxide phases are being researched intensively for various energy conversion applications where they are often expected to operate under redox conditions at elevated temperature. Understanding of the dynamics of composite evolution during redox cycling is still very limited, yet critical to maximising performance and increasing durability. Here we track the microstructural evolution of a single composite particle over 200 redox cycles for hydrogen production by chemical looping, using multi-length scale X-ray computed tomography. We show that redox cycling triggers a centrifugal redispersion of the metal phase and a centripetal clustering of porosity, both seemingly driven by the asymmetric nature of oxygen exchange in composites. Initially, the particle develops a large amount of internal porosity which boosts activity, but on the long term this facilitates structural and compositional reorganisation and eventually degradation. These results provide valuable insight into redox-driven microstructural changes and also for the design of new composite materials with enhanced durability

Is 'oil pulling' a 'snake oil'? : a clinical trial

The traditional Ayurveda practice of ‘oil pulling’ has become a recent phenomenon and concerns about its efficacy have been raised. Objectives: (1) to determine awareness about the practice of ‘oil pulling’ among a group of young adults, and to determine variations in awareness with respect to socio-demographic factors, oral health behaviours (oral hygiene and dental attendance) and use of natural health products; (2) to determine the effectiveness of ‘oil pulling’ and conventional oral hygiene practice compared to the use of conventional oral hygiene practice alone in terms of oral hygiene and (3) to determine the effectiveness of ‘oil pulling’ and conventional oral hygiene practice compared to the use of conventional oral hygiene practice alone in terms of gingival health. Methods: Group members recruited seventy-four young adults to participate in a clinical trial over a two-month period comparing the effectiveness of (a) ‘oil pulling’ and conventional oral hygiene methods (toothbrush and toothpaste) versus (b) conventional oral hygiene methods alone. Oral hygiene was assessed using the Plaque Index - PI (Silness and Löe, 1964) and the proportion of sites with visible plaque (PVP). Gingival health was assessed using the Gingival Index – GI (Silness and Löe,1963) and the proportion of sites with gingival bleeding (PGB). Participants were block randomized in groups of four to a cross over clinical trial and assessments were conducted at one-month and two-months. Results: Approximately a quarter (28.4%, 21) of participants was aware of the practice of ‘oil pulling’. Awareness of the practice was associated with reported use of natural dental/oral health products (p0.05). There were observed significant differences in gingival health among both the test and control groups from baseline to one-month (p0.05). No significant differences were observed in oral health parameters from one-month to two-month among neither the test nor control groups (p>0.05). Conclusion: Awareness of the practice of ‘oil pulling’ is relatively common and is associated with use of natural dental/oral health products. Findings from the clinical trial failed to support the adjunct use of ‘oil pulling’ in addition to conventional oral hygiene practices.published_or_final_versio

Evidence-Based Point-of-Care Diagnostics: Current Status and Emerging Technologies

Point-of-care (POC) diagnostics brings tests nearer to the site of patient care. The turnaround time is short, and minimal manual interference enables quick clinical management decisions. Growth in POC diagnostics is being continuously fueled by the global burden of cardiovascular and infectious diseases. Early diagnosis and rapid initiation of treatment are crucial in the management of such patients. This review provides the rationale for the use of POC tests in acute coronary syndrome, heart failure, human immunodeficiency virus, and tuberculosis. We also consider emerging technologies that are based on advanced nanomaterials and microfluidics, improved assay sensitivity, miniaturization in device design, reduced costs, and high-throughput multiplex detection, all of which may shape the future development of POC diagnostics

Overcoming chemical equilibrium limitations using a thermodynamically reversible chemical reactor

All real processes, be they chemical, mechanical or electrical, are thermodynamically irreversible and therefore suffer from thermodynamic losses. Here, we report the design and operation of a chemical reactor capable of approaching thermodynamically reversible operation. The reactor was employed for hydrogen production via the water–gas shift reaction, an important route to ‘green’ hydrogen. The reactor avoids mixing reactant gases by transferring oxygen from the (oxidizing) water stream to the (reducing) carbon monoxide stream via a solid-state oxygen reservoir consisting of a perovskite phase (La0.6Sr0.4FeO3-δ). This reservoir is able to remain close to equilibrium with the reacting gas streams because of its variable degree of non-stoichiometry and thus develops a ‘chemical memory’ that we employ to approach reversibility. We demonstrate this memory using operando, spatially resolved, real-time, high-resolution X-ray powder diffraction on a working reactor. The design leads to a reactor unconstrained by overall chemical equilibrium limitations, which can produce essentially pure hydrogen and carbon dioxide as separate product streams