Experimental investigation of the temperature distribution in a microwave-induced plasma reactor

It is urgent to reduce CO2 emissions to mitigate the impacts of climate change. The development of advanced conversion technologies integrated with plasma torches provides a path for the optimisation of clean energy recovery from biomass and wastes, thus substituting fossil fuels utilization. This article presents the temperature characterisation within a laboratory-scale microwave-induced plasma reactor operated with air, H2O and CO2 as the plasma working gases. The benefits associated with the plasma torch are highlighted and include rapid responses of the plasma and the temperature profile within the reactor to changing operating conditions. The average temperature near the side wall in the laboratory-scale reactor is proportional to the applied microwave power, ranging from 550 °C at 2 kW to 850 °C at 5 kW, while significantly higher temperatures are locally present within the plasma plume. The described system demonstrates promising conditions that are ideal for effective energy recovery from biomass and wastes into clean fuel gas

Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures

A sound understanding of any sorption system requires an accurate determination of the enthalpy of adsorption. This is a fundamental thermodynamic quantity that can be determined from experimental sorption data and its correct calculation is extremely important for heat management in adsorptive gas storage applications. It is especially relevant for hydrogen storage, where porous adsorptive storage is regarded as a competing alternative to more mature storage methods such as liquid hydrogen and compressed gas. Among the most common methods to calculate isosteric enthalpies in the literature are the virial equation and the Clausius-Clapeyron equation. Both methods have drawbacks, for example, the arbitrary number of terms in the virial equation and the assumption of ideal gas behaviour in the Clausius-Clapeyron equation. Although some researchers have calculated isosteric enthalpies of adsorption using excess amounts adsorbed, it is arguably more relevant to applications and may also be more thermodynamically consistent to use absolute amounts adsorbed, since the Gibbs excess is a partition, not a thermodynamic phase. In this paper the isosteric enthalpies of adsorption are calculated using the virial, Clausius-Clapeyron and Clapeyron equations from hydrogen sorption data for two materials-activated carbon AX-21 and metal-organic framework MIL-101. It is shown for these two example materials that the Clausius-Clapeyron equation can only be used at low coverage, since hydrogen's behaviour deviates from ideal at high pressures. The use of the virial equation for isosteric enthalpies is shown to require care, since it is highly dependent on selecting an appropriate number of parameters. A systematic study on the use of different parameters for the virial was performed and it was shown that, for the AX-21 case, the Clausius-Clapeyron seems to give better approximations to the exact isosteric enthalpies calculated using the Clapeyron equation than the virial equation with 10 variable parameters

Fuel Gas Storage:The Challenge of Methane

Methane usage, as part of the overall energy mix, has been gradually increasing in the last few decades and the exploration and production of shale gas reserves indicates that this trend is likely to continue. Upcoming energy demand, due to population and economic growth around the world will put a severe strain on the conversion of primary energy, a reason why shale gas is predicted to be intensely explored in coming years. Shale gas, despite health and environmental concerns, is expected to create a million jobs and add £1 trillion to the European Union economy. State-of-the-art methane storage is either as a compressed gas (usually at 25 MPa) or as a liquid (as Liquefied Natural Gas, LNG, with densities of ~450 kg m-3 at -162 °C), with the overall aim of increasing the volumetric density of the methane. Both technologies, however, incur large energy penalties due to the operational constraints of attaining high pressures and/or extremely low temperatures. The advances made in gas sorption in porous materials in recent decades suggest that this technology can be a competitive alternative to current state-of-the-art methods. This is due to considerable interactions between methane and optimally tailored porous structures, even at room temperature, which enhance the density of the gas on the surface of the solid structure. A rigorous experimental programme for prospective adsorbent materials for methane storage was carried out and the results analysed, with a view to directly comparing adsorptive storage technologies with other competing alternatives. The materials analysed were the high-surface area metal-organic frameworks MIL-101 and Cu-BTC and the activated carbon AX-21. The adsorbed methane densities obtained in some of these materials, even at room temperatures and mild operating pressures, indicate that there is definite scope for high-surface area materials to be used as alternatives to achieve high volumetric energy density and even compete with LNG technologies in terms of high methane densities per unit volume

Porous silica-pillared MXenes with controllable interlayer distances for long-life Na-ion batteries

MXenes are a recently discovered class of two-dimensional materials that have shown great potential as electrodes in electrochemical energy storage devices. Despite their promise in this area, MXenes can still suffer limitations in the form of restricted ion accessibility between the closely spaced multistacked MXene layers, causing low capacities and poor cycle life. Pillaring, a strategy where a secondary species is inserted between layers, has been used to increase interlayer spacings in clays with great success, but has had limited application in MXenes. We report a new amine-assisted pillaring methodology that successfully intercalates silica-based pillars between Ti3C2 layers. Using this technique, the interlayer spacing can be controlled with the choice of amine and calcination temperature, up to a maximum of 3.2 nm, the largest interlayer spacing reported for an MXene. Another effect of the pillaring is a dramatic increase in surface area, achieving BET surface areas of 235 m2 g-1, a sixty-fold increase over the unpillared material and the highest reported for MXenes using an intercalation-based method. The intercalation mechanism was revealed by different characterisation techniques, allowing the surface chemistry to be optimised for the pillaring process. The porous MXene was tested for Na-ion battery applications, and showed superior capacity, rate capability and remarkable stability compared with non-pillared materials, retaining 98.5% capacity between the 50th and 100th cycles. These results demonstrate the applicability and promise of pillaring techniques applied to MXenes, providing a new approach to optimising their properties for a range of applications. Porous MXenes are very promising materials for a range of applications including energy storage, conversion, catalysis and gas separations

Fuel Gas Storage:The Challenge of Hydrogen

Among today’s societal challenges, arguably some of the most important are the safe, sustainable and affordable supply of clean water, food and energy. Energy is certainly a crucial challenge as demand is likely to increase greatly, due to the economic development of poorer nations and an increase in world population. This will put enormous pressure on the future exploration and production of energy sources. Perhaps an even more important aspect are current and predicted environmental problems associated with fossil fuels, the most notorious being climate change, which demands that we decarbonise our economies or risk catastrophic consequences. A solution for this problem would be to use a clean, sustainable energy system; one which converts, transports and uses energy safely, with no harmful emissions to the atmosphere and at an affordable cost.This clean and sustainable energy system would almost certainly require a great share in conversion of energy from renewable energy sources, and probably a clean energy vector, along with electricity, to decarbonise the transport sector and to balance supply and demand in the electric grid. Hydrogen is the one of the best alternatives for a clean and sustainable energy vector as it presents obvious advantages, among those the fact that it has the highest energy per unit mass of any chemical fuel, can be efficiently used in a fuel cell with no emissions, and can be produced, stored, distributed and used through a variety of different sustainable pathways.One of the biggest problems with hydrogen energy is its storage. Hydrogen is a very low density gas and methods of increasing its density, usually compression at 35 or 70 MPa or liquefaction at 20 K, carry high materials and energy penalties. Some proposed alternatives include chemical storage, which consists of reacting hydrogen with another element and storing it as a hydride or using highly porous materials to enhance the density of hydrogen on its surface. Adsorptive storage of hydrogen can be an attractive solution to the storage problem, as it can store equal amounts of hydrogen in the same volume at much milder conditions of pressure and temperature. Experiments on different adsorbent materials, including the metal-organic framework MIL-101 and activated carbons AX-21 and TE7, were done to identify and possibly tailor optimal materials for hydrogen storage. The results were analysed taking into account a number of different requirements for a hydrogen storage system, including capacity of the material, gravimetric and volumetric density, optimal operating conditions for storage, thermal management of the system and optimum kinetics and diffusion in adsorbent systems. These results were analysed in a systems approach context and used as input into the design of an improved adsorbent storage system

iCLAP: Shape Recognition by Combining Proprioception and Touch Sensing

The work presented in this paper was partially supported by the Engineering and Physical Sciences Council (EPSRC) Grant (Ref: EP/N020421/1) and the King’s-China Scholarship Council Ph.D. scholarship

Divergence-Free Motion Estimation

International audienceThis paper describes an innovative approach to estimate motion from image observations of divergence-free flows. Unlike most state-of-the-art methods, which only minimize the divergence of the motion field, our approach utilizes the vorticity-velocity formalism in order to construct a motion field in the subspace of divergence free functions. A 4DVAR-like image assimilation method is used to generate an estimate of the vorticity field given image observations. Given that vorticity estimate, the motion is obtained solving the Poisson equation. Results are illustrated on synthetic image observations and compared to those obtained with state-of-the-art methods, in order to quantify the improvements brought by the presented approach. The method is then applied to ocean satellite data to demonstrate its performance on the real images