Mixed Matrix Carbon Molecular Sieve and Alumina (CMS-Al2O3) Membranes

Abstract

This work shows mixed matrix inorganic membranes prepared by the vacuum-assisted impregnation method, where phenolic resin precursors filled the pore of α-alumina substrates. Upon carbonisation, the phenolic resin decomposed into several fragments derived from the backbone of the resin matrix. The final stages of decomposition (>650 °C) led to a formation of carbon molecular sieve (CMS) structures, reaching the lowest average pore sizes of ~5 Å at carbonisation temperatures of 700 °C. The combination of vacuum-assisted impregnation and carbonisation led to the formation of mixed matrix of CMS and α-alumina particles (CMS-Al2O3) in a single membrane. These membranes were tested for pervaporative desalination and gave very high water fluxes of up to 25 kg m−2 h−1 for seawater (NaCl 3.5 wt%) at 75 °C. Salt rejection was also very high varying between 93–99% depending on temperature and feed salt concentration. Interestingly, the water fluxes remained almost constant and were not affected as feed salt concentration increased from 0.3, 1 and 3.5 wt%.

Vacuum-assisted tailoring of pore structures of phenolic resin derived carbon membranes

“…These results suggest that upon the formation of the resin film like the CM0 membrane, the vacuum has then 13 drawn the phenolic polymers further into the porous substrate. Song and co-workers [22] also reported impregnation of porous substrates by a wet vacuum-assisted method, though their work lead to deep impregnation as phenolic resin sols permeated through the porous alumina support. In this work, a dry vacuum-assisted method was applied once resin thin films were formed, with a minor degree of resin impregnation into the porous substrate.…”

“…This has been shown by Pacheco Tanaka and co-workers [30][31][32][33] by coating novolac and resol phenolic resins, or by mixing alpha-alumina with novolac. A very recent development involves the preparation of carbon-alumina mixed matrix membranes, where the phenolic resin was incorporated into the porous structure of an alumina substrate by a vacuum impregnation, showing that the vacuum time played an important role in the structural formation of the mixed matrix membranes [22]. Phenolic resins have several advantages for the preparation of CMS membranes such as better control of its crosslinking density, molecular weight and pore size by sol-gel chemistry and carbonization process [34][35][36][37].…”

“…Subsequently, a variety of precursor materials were used to prepare carbon membranes, including derivatives of polyimides [12,13], polyfurfuryl alcohol (PFFA) [14], phenolic resins [15][16][17][18], polyacylonitrile [19], and polymers of intrinsic microporosity (PIM) [20]. Carbon membranes have been extensively developed for gas separation, though also investigated for liquid separation including oil/water [21], desalination [22], de-colorization of coke furnace wastewater [23], pervaporation of azeotropic benzene-cyclohexane mixtures [24], oil and water separation [25] and separation of chromium (VI) in ultrafiltration of water solutions [26] as representative examples. An advantage of carbon membranes is related to the good stability conferred by carbon structures.…”

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

“…Recently, a paper was published by Song et al [62] showing a new concept on the preparation of inorganic mixed matrix membrane. These authors incorporated phenolic resin into the pores of alumina substrate using a vacuum-assisted method.…”

Fine ultra-micropore control using the intrinsic viscosity of precursors for high performance carbon molecular sieve membranes

“…Therefore, the characteristics of polymer precursor and carbonisation process affect the structure and performance of CMS membranes. There is an array of polymers that have been employed for the preparation of CMS membranes including phenolic resin [1][2][3][4][5][6][7], polyimide (PI) [8][9][10][11][12][13][14][15][16][17], polyfurfuryl alcohol [18,19], poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) [20] and poly (phthalazinone ether sulfone ketone) (PPESK) [21]. In addition, carbon templates such as triblock copolymers [22] and surfactant hexyltriethylammonium bromide (C6) [23] have been embedded and carbonised in silica films as molecular sieve structures for desalination and gas separation.…”