Rapid thermal processing and separation performance of columnar MFI membranes on porous stainless steel tubes

Abstract

Continuous MFI-type zeolite membranes were fabricated on porous stainless steel tube supports by secondary (seeded) growth. The physical attachment of zeolite seed particles was initiated through sonication assistance on unmodified supports. Despite a sparse seed layer, a single hydrothermal growth step reliably led to c-/h0h-out-of-plane-oriented pure-silica MFI membranes. Rapid thermal processing was applied to as-synthesized membranes, extending the findings of a previous report on controlling the density of grain boundary defects. The RTP-treated membranes showed an improved separation factor of 29 for p-/o-xylene with a maximum p-xylene permeance of 6.6 × 10⁻⁸ mol m⁻² s⁻¹Pa⁻¹, while conventionally (slowly) calcined counterparts had a maximum separation factor and p-xylene permeance of 3–4 and 2.7–4.5 × 10⁻⁸ mol m⁻² s⁻¹Pa⁻¹, respectively. The membranes also showed insensitivity to temperature for n-/i-butane separation performance (separation factor ca. 15 and n-butane permeance ca. 1.3 × 10⁻⁷ mol m⁻² s⁻¹Pa⁻¹), while conventionally calcined ones exhibited a significant decrease in the separation factor with temperature. Pervaporation measurements from a dilute aqueous feed that exploited the hydrophobicity of RTP-treated membranes revealed their potential use in bioalcohol recovery processes from fermentation broths, specifically for ethanol (total flux and separation factor of 1.2 kg m⁻² h⁻¹ and 43, respectively) and n-butanol (total flux and separation factor of 0.11 kg m⁻² h⁻¹ and 21, respectively) extraction from the aqueous phase.