(410d) Hydrophobic Zeolites of High Tolerance to Reactions in Hot Liquid Water

HY zeolites hydrophobized by functionalization with organosilanes are much more stable in hot liquid water than the corresponding untreated zeolites. Silylation of the external surface of the zeolite crystals increases hydrophobicity without reducing the density of acid sites. This hydrophobization with organosilanes makes the zeolites able to stabilize water/oil emulsions and catalyze reactions of importance in biofuel upgrading, i.e., alcohol dehydration and alkylation of m-cresol and 2-propanol in the liquid phase, at high temperatures.  Moreover, the hydrophobization reduces the high susceptibility of HY zeolite to hot liquid water.  While at 200°C the crystalline structure of an untreated HY zeolite collapses in a few hours in contact with a liquid medium, the functionalized hydrophobic zeolites keep their structure practically unaltered. Detailed XRD, SEM, HRTEM, and BET analysis indicate that even after reaction under severe conditions, the hydrophobic zeolites retain their crystallinity, surface area, microporosity, and acid density.  It is proposed that by anchoring hydrophobic functionalities on the external surface, the diffusion of water into the zeolite is hindered, thus preventing the collapse of the framework during the reaction in liquid hot water. At moderate temperatures (e.g. 100-200°C) water vapor does not cause any significant degradation of the zeolite structure, but liquid water does.  Therefore, the role of the hydrophobic barrier is to prevent the contact of the zeolite with the liquid water, preventing the extensive hydrolysis accelerated by solvation and rapid ion mobility, which readily occurs with a conventional hydrophilic zeolite.