Formation process of organic template-free chabazite zeolite membrane and its separation performance of water-rich mixtures

The growth process of chabazite seed crystal transformed into chabazite zeolite membrane in an organic template-free and fluoride-containing synthesis gel was investigated in details. The characterization results showed that the formation process of organic template-free chabazite zeolite membrane included the processes of seed crystal dissolution and chabazite crystal reconstruction. In the first process of seed dissolution into amorphous, the secondary building units (D6Rs) of CHA framework were completely destroyed except for the presence of a small number of 4Rs. While the amorphous contained many primary building units (TO4) as the nucleation sites in the second process of chabazite crystal reconstruction, which nucleated rapidly again under the promotion of fluorine anion. With the further prolongation of crystallization time, the regenerated secondary structural units connected together to reconstruct the framework structure of chabazite zeolite, and gradually grew into a continuous and dense membrane layer with the cross-linking growth of chabazite zeolite. In addition, chabazite zeolite membrane exhibited high permeation flux and excellent long-term hydrothermal stability for the separation of water-rich mixtures. For 50 wt% EtOH/H2O and 50 wt% IPA/H2O binary mixtures at 348 K, the stable permeation fluxes of the membranes were as high as 13.50 kg m−2 h−1 and 14.80 kg m−2 h−1, respectively.