Synthesis of zeolite L crystals with different shapes

Zeolite L crystals were synthesized hydrothermally from aqueous mixtures of potassium hydroxide, metallic aluminum, and colloidal silica. The influence of hydrothermal conditions and the addition of triethanolamine (N(C2H4OH)(3); H(3)tea) upon the formation and shape of the resulting zeolite L crystals was examined. When the mixtures of KOH:Al:SiO2:H2O = 2.2 or 2.5:1.0:4.5:80 were hydrothermally treated at 130 or 175 degrees C, the zeolite L crystals had a columnar shape. Decrease in the added amount of KOH facilitated crystal growth in the axial direction, whereas a decrease in hydrothermal temperature inhibited it. For the synthesis using H(3)tea, a silica-rich starting composition of KOH:Al:SiO2:H2O:H(3)tea = 10:1.0:15:250:x and a hydrothermal temperature of 120 degrees C was used. When no H(3)tea was added, the obtained zeolite L crystals had an indistinct shape. H(3)tea addition at x = 2 led to the formation of zeolite L crystals with a well-defined, clam-like shape. The formation of the well-defined shape is due to the coordination of H(3)tea to aluminate ions. The starting composition has some influence on the formation of the clam-like shape. The zeolite L crystal morphologies obtained in this study ranged from stick-like shapes to clam-like ones. The length-to-diameter ratios ranged from 0.2 to 5.8.