Principal Features of Tetrapropylammonium Hydroxide Removal Kinetics from Silicalite-1 in Quasi-isothermal Heating Regimes

Abstract

We study the time dependence of tetrapropylammonium hydroxide (TPAOH) removal from unconsolidated silicalite-1 crystal layers. The changes in the as-synthesized silicalite-1 crystals caused by TPAOH removal were investigated by thermogravimetric (TG) measurements using oxidative and nonoxidative gaseous agent. TG experiments were carried out under quasi-isothermal conditions that consisted of fast heating the sample to various temperatures Tmax and keeping at those temperatures. The shape of the TG curves confirmed the key role of the mobilization reaction that controls the percolation of the mobile products of TPAOH through the zeolite channel system. Another key finding was the existence of clearly defined deviations between the TG curves for air and those for N2. On the basis of these results, we proposed a simplified kinetic model that accounts for the principal features of quasi-isothermal TPAOH removal from silicalite-1. Our model approximates the TG arrangement with a continuous stirred tank reactor, a combined effect of mobilization reaction and bond–site percolation on a diamond lattice, and also possible kinetic steps involved during transport of TPAOH decomposition products from silicalite-1 crystals into the main gas stream. Based on the analysis of the TG curves, we estimated the activation energy (Ea) of the mobilization reaction from the point of deviation as 164 kJ/mol.