Composite-alumina-carbon molecular sieve membranes prepared from novolac resin and boehmite. Part I: Preparation, characterization and gas permeation studies

Abstract

Supported composite alumina-carbon molecular sieve membranes (c-CMSM) were prepared from in house prepared novolac phenolic resin loaded with boehmite nanoparticles in a single dipping-drying-carbonization step. A porous a-alumina tube support was dipped into a N-methyl-2-pyrrolidone solution containing polymerized novolac resin loaded with boehmite, subsequently dried at 100 o C and carbonized at 500 o C under nitrogen environment. The structure, morphology and performance of the membranes were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), carbon dioxide adsorption and permeation of N2, O2, He, H2 and CO2. SEM showed carbon membranes with a thin and very uniform layer with a thickness of ca. 3 m CO2 adsorption isotherms indicated that the produced carbon membranes presented a micro-porous structure. The c-CMSM exhibited good gas separation properties. The permselectivity surpass the Robeson upper bound for polymeric membranes, especially regarding ideal permselectivities of pairs H2/N2 = 117, and He/O2 = 49. Aging effects were observed after membrane exposure to ambient air.However with a thermal treatment under nitrogen atmosphere the permeance of nitrogen increases.

Composite-alumina-carbon molecular sieve membranes prepared from novolac resin and boehmite. Part II: Effect of the carbonization temperature on the gas permeation properties

“…The novolac resin (phenol formaldehyde resin) used as polymeric precursor was synthesized by the acid-catalyzed phenol-formaldehyde condensation [62] as described elsewhere [57]. Briefly, phenol and oxalic acid were placed in a flask fitted with stirrer and a reflux condenser, when the solution reached 80 o C formaldehyde was added drop-wise, the resin was washed with hot water and further dried.…”

“…c-CMSMs were also prepared using novolac phenolic resin and boehmite nanoparticles in a single dipping-dryingcarbonization step on top of a a-Al2O3 tubular membrane support; the decrease in performance of the Al-CMSM due to air exposure (aging by adsorption of water), and the changes in the transport properties of the membranes with different activation temperatures for removing water present in the pores were studied using pure gas permeation [57].…”

Recent Advances on Carbon Molecular Sieve Membranes (CMSMs) and Reactors

“…Xiao et al [49] reported the preparation of c-CMSMs from Ag + SPAEK; they observed that the silver doped CMSMs exhibited higher CO 2 /CH 4 selectivities (it was attributed to the greater interconnection among the ultramicropores formed by the migration of silver) and permeabilities. Composite alumina-CMSM using phenolic resins resol [40,50], novolac [37,51] and composite alumina-Ag CMSM [52] were for the first time reported by Pacheco Tanaka and Llosa Tanco et al…”

“…D.A. Pacheco Tanaka, M. Llosa Tanco et al reported for the first time the preparation of a 7 cm long, 1 cm diameter-supported composite alumina-CMSM from low cost polymer precursors phenolic resins (resol [40,50,52] and novolac [37,51]) on alumina tubes (200 nm pore size) in one dip-dry-carbonization cycle. When only phenolic resin was used during the preparation, the membranes were unselective (presence of defects) because the precursor penetrated excessively in the pores of the alumina support; consequently, additional dip-dry-carbonization cycles were necessary to obtain membranes without defects.…”

“…The water molecules will adsorb on the surface and will pass through the membrane by adsorption diffusion mechanism; the pores will be blocked with water and the permeation of less absorbable molecules will be reduced. The structure of CMSMs prepared from polymers containing oxygen groups (such as phenol-formaldehyde [37,51,91], resorcinol-formaldehyde [92,93], sulfonated oxide (SPPO) [94]) carbonized at below 873.15 K still contains oxygen functional groups. In addition, during the carbonization process, the polymer precursor decomposes; gases are released leaving pores with highly reactive carbons.…”