A thin
and well-intergrown zeolite T membrane with high CO2 permeability
and selectivity was rapidly prepared on seeded tubular supports by
the two-step varying-temperature hydrothermal synthesis process (two-step
method). The influence of synthesis parameters such as synthesis temperature
and crystallization time during the two-step durations on crystals
growth and separation performance was investigated systematically.
The X-ray diffraction (XRD), scanning electron microscopy (SEM), and
gas permeation measurements were used to characterize the as-synthesized
membranes. Compared with the conventional hydrothermal synthesis at
a constant temperature (one-step method), the two-step method is more
effective to synthesize a thin and continuous zeolite membrane layer
in short time, which fully covered the support surface. Membrane synthesis
temperature during the two-step durations could seriously influence
the crystal growth and CO2 separation properties. It was
found that a lower temperature favored nucleation, while a higher
crystallization temperature promoted crystallization during the two-step
method, thus improving zeolite T crystal growth and membrane separation
properties. The membranes prepared by the two-step method under the
optimized conditions exhibited good reproducibility, high CO2 permeance, and relatively high permselectivity for the separation
of CO2 from CH4 or N2 gas mixtures.
For example, CO2 permeance and CO2/CH4 selectivity of the membranes reached 6.2 × 10–8 mol m–2 s–1 Pa–1 and 80 for the equimolar CO2/CH4 binary gaseous
mixtures at 35 °C, respectively.
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