Synthesis of ZSM-58 crystals with improved morphology

摘要

Methods are provided for synthesizing ZSM-58 crystals with an improved morphology and/or an improved size distribution. By controlling the conditions during synthesis of the ZSM-58 crystals, crystals of a useful size with a narrow size distribution can be generated. Additionally, by controlling the ratio of water content to silica content in the synthesis mixture, it has unexpectedly been found that ZSM-58 crystals can be formed with an improved morphology. The improved morphology can result in ZSM-58 crystals with a more uniform size across the various dimensions of the crystal, which allows for more uniform diffusion within the crystal. This is in contrast to conventionally synthesized crystals, where the size of the crystal can vary along different axes of the crystals.

主权项

1. A method for synthesizing a DDR framework type zeolite, comprising:
forming a reaction mixture capable of forming crystalline DDR framework type material, the mixture comprising water, a silicon oxide, an alkali or alkaline earth hydroxide, and a methyltropinium salt structure directing agent, the mixture having a molar ratio of water to silicon oxide of about 12 to about 25, a molar ratio of hydroxide to silicon oxide of about 0.01 to about 1.0, a molar ratio of alkali and alkaline earth metal to silicon oxide of about 0.01 to about 1.0, a molar ratio of structure directing agent to silicon oxide of about 0.01 to about 1.0, and at least about 0.05 wt % of seeds relative to the weight of silicon oxide in the mixture; and recovering DDR framework type crystals having an axis ratio of 1.1 or less, the axis ratio being a ratio of a vertex-to-vertex distance and an edge-to-edge distance, a depth dimension being less than the vertex-to-vertex distance and the edge-to-edge distance.