Avaliação dos processos de desativação e de troca-iônica em zeólitas por microcalorimetria de adsorção

Abstract

Zeolites are aluminosilicates with a well-defined crystalline structure, typically composed of aluminum, oxygen, and silicon. Their structure features a network of regular pores, giving zeolites unique adsorption and ion exchange properties. The adsorption/desorption processes in zeolites, primarily used in chemical industries, can lead to their deactivation, which refers to the reduction of their adsorption capacity. Ion exchange is a reversible process where ions present in a solid are replaced by ions of another species in a liquid solution. Zeolites are commonly used in this process due to their structure and ability to selectively adsorb and release ions. In this study, a Tian-Calvet microcalorimeter coupled with a manometric system was used to evaluate CO2 adsorption isotherms and enthalpy on both fresh and aged commercial zeolites, as well as to study the adsorbent-adsorbate interaction after ion exchange. The experimental setup was designed to control gas dosing, enabling simultaneous measurement of isotherms and CO2 adsorption heat at 298 K. The technique was also applied to assess intraparticle mass transfer by fitting microcalorimetric peaks to a deterministic mathematical model. Water vapor isotherms were measured using an Intelligent Gravimetric Analyzer (IGA) to evaluate sample porosity after ion exchange. N2 isotherms at 77 K and CO2 isotherms at 273 K were measured using an Autosorb-IQ3 instrument to determine textural characteristics. The results showed that the microcalorimeter output data are sensitive to the hydrothermal degradation experienced by the zeolites. The water vapor isotherms indicated that the ion exchange process reduced sample porosity. Furthermore, the mathematical model, based on mass and energy differential balances, allowed for the estimation of intraparticle mass transfer parameters.