Tubular MFI zeolite membranes made by secondary (seeded) growth

Zeolite MFI membranes with thickness 15-20 mum were grown on the surface of macroporous a-alumina and stainless steel support tubes (pore size 200 and 500 nm, respectively) by the secondary (seeded) growth technique. The tubu lar supports were dipped vertically in an aqueous suspension of colloidal s ilicalite-1 seed crystals (particle size 100 nm) and withdrawn at a speed o f 1-2 cm/h to allow for uniform formation of seed layers on the outer (for stainless steel) or inner (for alpha -alumina) cylindrical surface of the s upport tubes. The seeded tubes were treated hydrothermally with clear solut ions of different composition and the resulting MFI membranes were characte rized by SEM and permeation of butane isomers. For the best preparations, b inary n-butane/isobutane ratios at 22 degreesC were as high as 28 and 53 fo r stainless steel and or-alumina tubes, respectively, while the n-butane pe rmeation flux varied in the range 0.8-3.8 mmol m(-2) s(-1). The effect of t emperature and feed partial pressure on permeation flux was also studied fo r binary mixtures of butane isomers and was found similar to that of planar membranes developed previously on or-alumina support disks by the same syn thesis procedure. (C) 2001 Elsevier Science B.V. All rights reserved.