Preparation of thin supported MFI membranes by in situ nucleation and secondary growth

Tubular MFI zeolite membranes have been prepared in two steps with a modifi cation of the secondary growth method. The first synthetic step is only dev oted to the in situ nucleation of the molecular sieve, directly on the surf ace of the tubular ceramic UF support. and the bulk of the membrane is then grown on it under different conditions. The right choice of the synthetic parameters (composition of the synthetic clear solutions, temperature) enab les one to obtain membranes with high gas permeability and sustained select ivity. The preliminary gas transport results and the morphology are compare d with the ones from a membrane obtained in one step: permeability increase s by almost one order of magnitude. SEM observations indicate the presence of a very thin (1-2 mum) MFI zeolite layer on the tubular support. The meth od illustrated in this work is an easy way to skip the deposition of pre-fo rmed nano-sized crystals on tubular supports before the secondary growth of the MFI membrane. (C) 2001 Elsevier Science B.V. All rights reserved.