TGA investigation of water and ethanol adsorption over LTA zeolites

In absolute ethanol production, LTA zeolites (3A and 4A) are industrially used because of their selectivity and affinity to water. Despite the numerous studies performed on these materials, a lack of data is encountered, particularly at the gaseous phase. This study contributes to the understanding and elucidation of the behavior of water and ethanol adsorbed separately over 3A, 4A and 5A zeolites. Using TGA measurements in dynamic mode, this study focuses on the investigation of temperature effect (T = 20-45 degrees C) on the adsorption kinetics of water and ethanol. The comparison of the adsorption properties of the three zeolites shows a particular behavior of the 3A, which is characterized by both the higher water uptake and the specific affinity reflected by the initial adsorption rate and the diffusion coefficient. Based on some previous studies, which point out that ethanol may be adsorbed on 3A, this investigation shows the role of water traces in the "ethanol" uptake. The comparison of the water and ethanol kinetics at various temperatures leads to estimate the optimal selectivity temperature. On the other hand, the modeling study using four kinetic models highlights the good fitting of pseudo-first order from which the adsorption activation energies are deduced.