Comparative study of seeding methods; dip-coating, rubbing and EPD, in SAPO-34 thin film fabrication

Abstract

Seeding methods; including rubbing, dip-coating and electro-phoretic deposition (EPD) were comparatively implemented for silicoalumino phosphate-34 (SAPO-34) thin film fabrication via secondary growth. The size of surface particles and thicknesses of fabricated layers were characterized by Scanning Electron Microscopy. The so-called properties were analyzed and modified to achieve a fairly defect free surface coverage and thin layers with finest particles. One-step dip-coating method provided well-distributed seeds on the support surface with a very poor coverage. Rubbing and EPD methods preferentially provided defect free and uniform surface coverage, however the grown particles from EPD method were bigger than those from rubbing method. It was revealed that in situ (no seeding) crystallization and one-step dip-coating method failed to produce defect free qualified membranes whereas EPD and rubbing methods caused continuous and defect free SAPO-34 membrane layers. To control synthesis parameters in the secondary growth crystallization, two important parameters were studied; crystallization time at three levels of 12, 24 and 48h and crystallization temperature at three levels of 458, 473, and 488K were simultaneously examined with the aforesaid seeding methods. Significant effects of crystallization temperature and time were observed on the formed layer qualities. The fabricated membrane by rubbing method during 24h crystallization time at 473K temperature was tested under equimolar gas mixture of hydrogen–methane at 293K with pressure drops ranging from 1 to 6bar. At one bar pressure drop, H2 was enriched up to 84.2mol% in the permeate side with the permeance of 6×10−8mol/(m2sPa).