Application of Design of Experiments to the Alkaline Treatment in Mordenite Zeolite: Influence on Si/Al Ratio

Abstract

This paper presents the application of Design of Experiments (DOE) to an alkaline treatment in mordenite zeolite, in order to identify the optimum settings of the variables (temperature and concentration of NaOH) that promote greater desilication. Samples of commercial mordenite with Si / Al ratio = 9 have been treated with aqueuos NaOH solution of various concentration (0,1;0,5;1,0) and temperature (30,50,70°C). Statistical analysis was carried out based on a 22 factorial design with center point replicates. Seven experiments were executed and the data of Si/Al ratio obtained. The resulting samples were characterized by x-ray difraction (XRD) and energy dispersive x-ray (EDX), to identify the structures and crystalline phases, and to determine the percentages of silicon and aluminum, respectively. In all samples, a decrease in the Si / Al ratio was observed, keeping the crystalline structure. The treatment was most effective, especially, at high temperature and NaOH concentration (experiment 4). DOE was shown to be a powerful techinique for the study of the variables, allowing determining which variables and value ranges have more influence on response, enabling optimization.

Recent Progress in Synthesis and Application of Nanosized and Hierarchical Mordenite—A Short Review

“…The reason is the aggressive action of the solution, leading to rapid amorphization of the zeolite structure as a result of its destruction [57]. Most commonly, mordenite was alkaline treated with aqueous solutions of NaOH with a concentration of 0.05-2.5 M (pH~10) in a temperature range from RT to 90 • C with duration from 10 min to 2 h [58][59][60]. The resulting formation of mesopores is due to surface hydrolysis and dissolution of the crystals, most likely in places with accumulations of crystal defects.…”