Development of practically available up-scaled high-silica CHA-type zeolite membranes for industrial purpose in dehydration of N-methyl pyrrolidone solution

This is the report on the first practically available calcined high-silica zeolite membranes in an industrial scale synthesized using an organic structure directing agent for an application of dehydration of N-methyl pyrrolidone [NMP] solution by pervaporation (PV). A manufacturing method for high-silica CHA-type tubular membrane (Si/Al = 8) with 40 cm long was developed for industrial purpose. Furthermore, mass-production with high reproducibility came to be possible for commercialization. The potential membrane performance in PV was measured systematically at the wide range of conditions in temperatures of 90–130 °C and feed compositions of water concentration in the feed of 1–50 wt.%. The permeation flux of 36 kg m−2 h−1 and 2.5 × 10−6 mol m−2 s−1 Pa−1 for water permeance with separation factor (α) of 1100 were observed at 130 °C in a feed mixture of water (50 wt.%)/NMP (50 wt.%). A practical dehydration test was performed for a batch of 44 kg hydrous NMP (H2O 30 wt.%/NMP 70 wt.%) using a practical membrane module containing 31 pieces of tubular membranes with a membrane area of 0.4 m2. The product of anhydrous NMP with 99.5 wt.% could be obtained at 110 °C by PV for 400 min. These results demonstrate that the synthesized high-silica CHA-type membranes can be applied to dehydration of hydrous NMP solution at wide range of water contents in the feed. The water diffusivities were determined based on the Maxwell–Stefan equations with the PV experimental results in the water–NMP system. The reduction was observed in water diffusivity of 1 order of magnitude with decreasing of water contents from the pure water to water (1 wt.%)/NMP (99 wt.%) in the feed. The synthesized high-silica CHA-type zeolite membranes exhibited the crystallographic orientation of [1 1 1]r axis. Observations by scanning electron microscopy (SEM) and X-ray diffractometor (XRD) analysis on the synthesized samples as a function of time suggested that the growth mechanism of evolutional selection was operated in the membrane formation. This mechanism should contribute to the closed-packed polycrystalline membrane with sufficient permselective properties to practical PV applications.