Influence of the hydrothermal synthetic parameters on the pervaporative separation performances of CHA-type zeolite membranes

The hydrothermal synthesis of intermediate-silica CHA-type zeolite membranes from the precursor mixtures containing single K+ alkali cations was studied in detail under different conditions, including the influencing factors of silica source, the crystallization temperature, water concentration and gel alkalinity of the initial gels. Additionally, CHA-type zeolite membranes were also prepared tentatively by the inter-zeolitic transformation method. The pervaporation (PV) measurements on these resulting CHA-type membranes for the dehydration of alcohol aqueous solutions were performed to investigate the quality of these membranes. As a result of these pervaporative studies, the optimal synthetic recipe was formulated with an optimized crystallization temperature spanning from 130 to 150 °C. The PV data showed that the separation performances of CHA membranes obtained were strongly dependent on the type of silica source employed with Ludox HS-30 being the optimal silica source. Furthermore, synthetic temperature had a strong influence on the morphology of the resultant CHA membranes. Under the optimized synthetic condition, the total permeation flux and separation factor of a representative membrane were 2.20 kg/m2 h and 3900, respectively, for the separation of 10 wt.% H2O/EtOH mixtures at 75 °C. The CHA membranes were characterized by X-ray diffraction, field emission-scanning electron microscopy and energy dispersive X-ray spectroscopy.

The morphology of CHA-type zeolite membranes was strongly dependent on the synthetic temperature. They could be successfully prepared from the synthetic media only containing K+ cations.Figure optionsDownload as PowerPoint slideHighlights
► CHA membrane can be prepared with K+ cation but without organic SDA or Sr2+ cation.
► Synthetic temperature has a strong effect on morphology and separation performance.
► There exist an optimal alkalinity and dilution degree of the starting gels.
► Inter-zeolitic transformation is ineffective for the preparation of CHA membrane.