119,271 research outputs found
Comparative energetic assessment of methanol production from COâ‚‚: chemical versus electrochemical process
Emerging emission-to-liquid (eTL) technologies that produce liquid fuels from COâ‚‚ are a possible solution for both the global issues of greenhouse gas emissions and fossil fuel depletion. Among those technologies, COâ‚‚ hydrogenation and high-temperature COâ‚‚ electrolysis are two promising options suitable for large-scale applications. In this study, two COâ‚‚ -to-methanol conversion processes, i.e., production of methanol by COâ‚‚ hydrogenation and production of methanol based on high-temperature COâ‚‚ electrolysis, are simulated using Aspen HYSYS. With Aspen Energy Analyzer, heat exchanger networks are optimized and minimal energy requirements are determined for the two different processes. The two processes are compared in terms of energy requirement and climate impact. It is found that the methanol production based on COâ‚‚ electrolysis has an energy efficiency of 41%, almost double that of the COâ‚‚ hydrogenation process provided that the required hydrogen is sourced from water electrolysis. The hydrogenation process produces more COâ‚‚ when fossil fuel energy sources are used, but can result in more negative COâ‚‚ emissions with renewable energies. The study reveals that both of the eTL processes can outperform the conventional fossil-fuel-based methanol production process in climate impacts as long as the renewable energy sources are implemented
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The interplay between thermodynamics and kinetics in the solid-state synthesis of layered oxides.
In the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase. Understanding the competition between thermodynamics and kinetics is a fundamental step towards the rational synthesis of target materials. Here, we use in situ synchrotron X-ray diffraction to investigate the multistage crystallization pathways of the important two-layer (P2) sodium oxides Na0.67MO2 (M = Co, Mn). We observe a series of fast non-equilibrium phase transformations through metastable three-layer O3, O3' and P3 phases before formation of the equilibrium two-layer P2 polymorph. We present a theoretical framework to rationalize the observed phase progression, demonstrating that even though P2 is the equilibrium phase, compositionally unconstrained reactions between powder precursors favour the formation of non-equilibrium three-layered intermediates. These insights can guide the choice of precursors and parameters employed in the solid-state synthesis of ceramic materials, and constitutes a step forward in unravelling the complex interplay between thermodynamics and kinetics during materials synthesis
Launching the Grand Challenges for Ocean Conservation
The ten most pressing Grand Challenges in Oceans Conservation were identified at the Oceans Big Think and described in a detailed working document:A Blue Revolution for Oceans: Reengineering Aquaculture for SustainabilityEnding and Recovering from Marine DebrisTransparency and Traceability from Sea to Shore: Ending OverfishingProtecting Critical Ocean Habitats: New Tools for Marine ProtectionEngineering Ecological Resilience in Near Shore and Coastal AreasReducing the Ecological Footprint of Fishing through Smarter GearArresting the Alien Invasion: Combating Invasive SpeciesCombatting the Effects of Ocean AcidificationEnding Marine Wildlife TraffickingReviving Dead Zones: Combating Ocean Deoxygenation and Nutrient Runof
Assessment of the suitability of different cassava varieties for gari and fufu flour production in Liberia
Open Access Article; Published online: 15 Feb 2020Different cassava varieties are available in Liberia, but there is little knowledge of their product suitability. Hence, the need to assess the potentials of these varieties to produce gari and fufu flour. The two products from ten improved and two local cassava varieties were characterized based on their yield and chemical, pasting and functional properties using standard methods. The results showed that TMS 96/0097 (gari 27.54%) and Butter cassava (fufu flour 27.35%) have the highest percentage yields. The starch content was higher in gari produced from TMS98/0505 (92.00%) and lower from TMS95/0289 (82.62%); the fufu flour starch content was higher in TMS98/0505 (90.59%) and lower in Bassa girl (84.75%). Gari and fufu flour produced from TMS96/0097 (507.38 RUV) and TMS00/0357 (506.04 RVU) had the highest final viscosity, and the products from TMS95/0289 (338.46 RVU and 336.80 RVU) had the least. The highest swelling power was found in gari (12.74%) and fufu flour (13.55%) produced from TMS92/0057 and the lowest in TMS91/0416 gari (8.23%) and TMS01/1235 fufu flour (8.31%). All the samples may form a paste below the boiling point of water (100°C) at < 7 min. However, cassava varieties and the interactions between varieties and locations had a significant (P < 0.05) effect on the properties of the products: Chemical (except ash content), pasting (except pasting temperature) and functional. Therefore, all the varieties may be suitable for gari and fufu flour production based on the quality preferred by the consumers
Intensive thermodynamic parameters in nonequilibrium systems
Considering a broad class of steady-state nonequilibrium systems for which
some additive quantities are conserved by the dynamics, we introduce from a
statistical approach intensive thermodynamic parameters (ITPs) conjugated to
the conserved quantities. This definition does not require any detailed balance
relation to be fulfilled. Rather, the system has to satisfy a general
additivity property, which holds in most of the models usually considered in
the literature, including those described by a matrix product ansatz with
finite matrices. The main property of these ITPs is to take equal values in two
subsystems, making them a powerful tool to describe nonequilibrium phase
coexistence, as illustrated on different models. We finally discuss the issue
of the equalization of ITPs when two different systems are put into contact.
This issue is closely related to the possibility of measuring the ITPs using a
small auxiliary system, in the same way as temperature is measured with a
thermometer, and points at one of the major difficulties of nonequilibrium
statistical mechanics. In addition, an efficient alternative determination,
based on the measure of fluctuations, is also proposed and illustrated.Comment: 17 pages, 5 figures; final version, with minor change
Mathematics and explanation in astronomy and astrophysics
The purpose of this paper is to expound and clarify the mathematics and
explanations commonly employed in certain notable areas of astronomy and
astrophysics. The first section concentrates upon the mathematics employed to
represent and understand stellar structure and evolution. The second section
analyses two different explanations for the structure of spiral galaxies
Molecular Chemical Engines: Pseudo-Static Processes and the Mechanism of Energy Transduction
We propose a simple theoretical model for a molecular chemical engine that
catalyzes a chemical reaction and converts the free energy released by the
reaction into mechanical work. Binding and unbinding processes of reactant and
product molecules to and from the engine are explicitly taken into account. The
work delivered by the engine is calculated analytically for infinitely slow
(``pseudo-static'') processes, which can be reversible (quasi-static) or
irreversible, controlled by an external agent. It is shown that the work larger
than the maximum value limited by the second law of thermodynamics can be
obtained in a single cycle of operation by chance, although the statistical
average of the work never exceeds this limit and the maximum work is delivered
if the process is reversible. The mechanism of the energy transductionis also
discussed.Comment: 8 pages, 3 figues, submitted to J. Phys. Soc. Jp
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