An atomistic explanation of the ethanol-water azeotrope

Autor(es)

Carravetta, Vincenzo ; de Abreu Gomes, Anderson Herbert ; Teixeira Marinho, Ricardo dos Reis ; Ohrwall, Gunnar ; Agren, Hans ; Bjorneholm, Olle ; de Brito, Arnaldo Naves

• Tipo de documento: Artigo Científico
• Fonte: Physical Chemistry Chemical Physics; v. 24, n. 42, p. 9-pg., 2022-10-14.

Resumo

Ethanol and water form an azeotropic mixture at an ethanol molecular percentage of similar to 91% (similar to 96% by volume), which prohibits ethanol from being further purified via distillation. Aqueous solutions at different concentrations in ethanol have been studied both experimentally and theoretically. We performed cylindrical micro-jet photoelectron spectroscopy, excited by synchrotron radiation, 70 eV above C1s ionization threshold, providing optimal atomic-scale surface-probing. Large model systems have been employed to simulate, by molecular dynamics, slabs of the aqueous solutions and obtain an atomistic description of both bulk and surface regions. We show how the azeotropic behaviour results from an unexpected concentration-dependence of the surface composition. While ethanol strongly dominates the surface and water is almost completely depleted from the surface for most mixing ratios, the different intermolecular bonding patterns of the two components cause water to penetrate to the surface region at high ethanol concentrations. The addition of surface water increases its relative vapour pressure, giving rise to the azeotropic behaviour. (AU)

• Processo FAPESP: 17/11986-5 - Geração e Armazenamento de Novas Energias: trazendo desenvolvimento tecnológico para o país
• Beneficiário: Ana Flávia Nogueira
• Modalidade de apoio: Auxílio à Pesquisa - Programa Centros de Pesquisa em Engenharia