Influence of MEL Zeolite Synthesis Conditions on the Physicochemical and Catalytic Properties in the Oligomerization Reaction of Butylenes

The influence of MEL zeolite synthesis conditions on the set of physicochemical properties and catalytic activity of the zeolites in the oligomerization reaction of butylenes has been studied. The number of synthesis stages and the concentration of tetrabutylammonium hydroxide template in the reaction mixture have been used as the variable parameters for the synthesis of MEL zeolites. It has been found that the use of two-stage crystallization comprising the low-temperature stage at 90°C and the high-temperature stage at 170°C promotes a decrease in the size of MEL zeolite crystals and provides a more complete involvement of the source materials in the crystallization process. The interval of template concentration in the reaction mixture in which the pure phase of zeolite MEL free of zeolite MFI can be obtained has been determined. It has been shown that during the two-stage crystallization of the reaction mixture with a template/SiO2 molar ratio of 0.2, MEL zeolite is formed with crystals of 200–300 nm in size, whose surface is depleted in aluminum. It has been found that the nanocrystalline zeolite MEL exhibits high resistance to deactivation in the oligomerization reaction of butylenes due to a decrease in the number of acid sites on the outer surface of nanocrystals. No significant differences in the product distribution have been revealed for the oligomerization of butylenes on zeolites of the MEL and MFI structural types possessing identical physicochemical properties.