Air separation

Résumé

An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases. The most common method for air separation is fractional distillation. Cryogenic air separation units (ASUs) are built to provide nitrogen or oxygen and often co-produce argon. Other methods such as membrane, pressure swing adsorption (PSA) and vacuum pressure swing adsorption (VPSA) are commercially used to separate a single component from ordinary air. High purity oxygen, nitrogen, and argon, used for semiconductor device fabrication, require cryogenic distillation. Similarly, the only viable source of the rare gases neon, krypton, xenon is the distillation of air using at least two distillation columns. Helium is also recovered in advanced air separation processes Cryogenic distillation process Pure gases can be separated from air by first cooling it until it liquefies, then selectively distilling the compo

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https://en.wikipedia.org/wiki/Air_separation

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Thermo-economic analysis and modeling of oxyfuel processes

Within the goal of reducing the atmospheric CO2 emissions, CO2 capture and storage (CCS) is regarded as a promising option. For CO2 capture different concepts are investigated; post-combustion, pre-combustion and oxyfuel-combustion (pure O2 oxidation). Here the oxy-fuel combustion is studied in detail. Compared to the other CO2 capture concepts the CO2 separation from the exhaust gas containing mainly H2O and CO2 is easier to perform, however an air separation unit is required. The objective is study the oxyfuel process in detail by developing a thermo-economic model to assess the performance and make a comparison of the competitiveness of different CO2 capture concepts.

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Influence of hydrophobic/hydrophilic surfaces on gas-liquid membrane separation

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Demonstrating and Unraveling a Controlled Nanometer-Scale Expansion of the Vacancy Defects in Graphene by CO2

Kumar Varoon Agrawal, Kuang-Jung Hsu, Mojtaba Rezaei, Luis Francisco Villalobos Vazquez de la Parra

A controlled manipulation of graphene edges and vacancies is desired for molecular separation, sensing and electronics applications. Unfortunately, available etching methods always lead to vacancy nucleation making it challenging to control etching. Herein, we report CO2-led controlled etching down to 2-3 angstrom per minute while completely avoiding vacancy nucleation. This makes CO2 a unique etchant for decoupling pore nucleation and expansion. We show that CO2 expands the steric-hindrance-free edges with an activation energy of 2.71 eV, corresponding to the energy barrier for the dissociative chemisorption of CO2. We demonstrate the presence of an additional configurational energy barrier for nanometer-sized vacancies resulting in a significantly slower rate of expansion. Finally, CO2 etching is applied to map the location of the intrinsic vacancies in the polycrystalline graphene film where we show that the intrinsic vacancy defects manifest mainly as grain boundary defects where intragrain defects from oxidative etching constitute a minor population.

WILEY-V C H VERLAG GMBH2022

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