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Sonochemistry involves the chemical and physical processes that take place under the action of ultrasound in solution. These processes are mainly due to cavitation, which involves the formation and implosion of gas microbubbles in liquids subjected to ultrasonic waves. As these microbubbles collapse, they release enormous amounts of energy, in the form of intense local heat, comparable to the temperature at the surface of the sun (~ 5000 K), high pressure (≤1000 atm), shock waves and acoustic microcurrents. Each cavitation bubble can be compared to a microreactor capable of initiating chemical reactions without external input of heat, reagents or catalysts. This article presents an overview of the main current applications of sonochemistry in organic chemistry.
In the current energy context, hydrogen production is a subject of debate. It appears to be a very good alternative to fossil fuels, however, its production remains for economic reasons, mainly derived from steam reforming of fossil fuels. This steam reforming technique, even if it is the most profitable, leads to gray hydrogen which at best can become blue after decarbonization. It is therefore necessary to find an alternative to produce green hydrogen at a reasonable cost (competitive with that of gray hydrogen) and among the possible technologies, water electrolysis appears at the forefront and represents a promising alternative.
Biomass burnings are becoming increasingly common and their recurrence both in France, with a record number of fires in the summer of 2022, and worldwide, with fires in Australia in 2019-2020 and in California (USA) in 2021-2022, make them a priority subject for study. Biomass fires contribute to the air quality deterioration through the emission of fine particles, the production of ozone and secondary aerosols, and accelerate climate change through the production of greenhouse gases (GHGs). All the species emitted during combustion are highly various within the smoke plume and are sources of chemical reactions during transport of the plume in the troposphere and lower stratosphere.
While often described by a single one-step reaction, combustion is actually a much more complex process. A deep understanding of this complexity requires the use of detailed kinetic models describing each reaction step, from the fuel reactant down to water and carbon dioxide. Such kinetic models, tested and validated against experimental data obtained in controlled conditions, are mandatory to develop cleaner, safer and more efficient technologies. Oxidation mechanisms of fossil fuels and biofuels are thus discussed and their specificities highlighted. The formation pathways of main pollutants (nitrogen oxides, soot precursors and unburned hydrocarbons) are also presented.
In addition to the technical and economic problems of green hydrogen production and use, storage is a major problem that must be solved to envisage the development of the Hydrogen Technology. Low-temperature liquid storage and high-pressure gas storage are the main techniques. However, they operate under extreme conditions of temperature (20 K in liquid phase) and pressure (70 MPa in gas phase), and economic and safety problems are inherent. An alternative technique at moderate pressure and temperature must be envisaged. Solid-state storage, by absorption via hydride materials or by adsorption in porous materials, is a promising option. Nevertheless, progresses in fundamental research are necessary to better understand the potential of this technique.
The study of new molecules requires the knowledge of the physico-chemical properties of these molecules and by-products. In order to purify the products and assess the energy consumption of industrial processes, it is necessary to know the thermodynamic properties of these molecules and the phase equilibria of their mixtures. In the article the main predictive thermodynamic models based on ab initio calculation are reported. We present different methodologies for the determination of thermochemical properties in gas phase, and review the main COSMO-like approaches that can predict excess properties and phase equilibria.
This paper follows a first one devoted to the basic principles of terahertz electromagnetism and to components and systems for the terahertz technology. This second paper lists and explains applications of the terahertz technology including instrumentation, security, sensors for industry, biology and medicine, environment, telecoms… The authors’ opinion on the future of terahertz technology serves as a conclusion to the paper.
Electrolyte solutions are ubiquitous in the chemical industry. The modeling of unit operations involving electrolytes requires the use of specific thermodynamic models taking into account the interactions between ions. The objective of this article is to present the formalism specific to electrolyte systems, and the main models used to determine the thermodynamic properties of electrolyte solutions, the composition of different chemical species, and phase equilibria.
The understanding of interstellar chemistry and thus that of the origin of the molecules observed as well as their interaction with the grain, radiation and the energetic particles is achieved through complex chemical models which take into account several thousands of coupled reactions simulating known or postulated reactions according to observations and various environments. The computational chemistry therefore allows for understanding how the interstellar molecular matter evolves chemically under the influence of interactions between gases, grains, photons and energetic particles (cosmic rays).
Solving equations that govern the macroscopic world is done analytically, or continuously. At the quantum scale, solving the Schrödinger’s equation can be done analytically only for the hydrogen atom, and other cations possessing only one electron. The molecular scale can be represented in a discrete way by depicting atoms as interacting particles evolving in a forcefield. Between these atomic and macroscopic scales, put in another way, between the discrete and the continuous, lies the mesoscopic scale. In this article, are exposed the theoretical basis that are requested for a better understanding of the mesoscopic scale, the principal methods, and concrete examples.
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