Organic “template” approach to molecular sieving silica membranes

Raman, N.K.; Brinker, C. Jeffrey

doi:10.1016/0376-7388(95)00067-m

Cited by 226 publications

(118 citation statements)

References 7 publications

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“…This is more evident in Figure 5.9C which shows a silica impregnation thickness of ~3.3 to ~5 µm. The impregnated silica structures into the -Al 2 O 3 porous substrate is a departure from the conventional methods of silica membranes by either CTP or RTP with substrates containing interlayers, where previous works resulted in the formation of thin-films with thicknesses of < 0.5 µm [56][57][58]. Apart from dispensing with costs associated with interlayer preparation, the RTP interlayer-free method in this work produced membranes in less than 3 hours with only 2 dipping-calcination cycles.…”

Section: Membrane Performancementioning

confidence: 83%

High performance ES40-derived silica membranes for desalination

Wang¹

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Access to potable water has become one of the top 10 global problems facing our contemporary society. Desalination of vast amounts of seawater is a promising measure to ameliorate this stress.Numerous thermal and membrane processes have been employed to desalt seawater, of which reverse osmosis (RO) using polymeric membranes is the most mature technology and has been regarded as the benchmark in current desalination technologies. However, due to the high pressure requirement for RO operation, other membrane processes, such as membrane distillation and pervaporation have been developed as the alternatives to further reduce the energy cost.Furthermore, due to the lack of chemical/thermal stability and high tendency to scaling and fouling of polymeric membranes, novel inorganic membranes, in particular silica derived membranes, are emerging as potential candidates for desalination. The majority of published works on silica membranes utilizes tetraethyl orthosilicate (TEOS) as the silica precursor and interlayers are generally required to reduce the roughness of the porous substrates, followed by 4 to 6 thin-film coatings and calcinations with heating rates of 1-2 º C min -1 to form defect free silica membranes, which consume 10-14 days with extra cost. Therefore, the major target of this research is to produce interlayer-free silica membranes fabricated by rapid thermal processing (RTP) for desalination application.Ethyl silicate 40 (ES40) is used as precursor to prepare silica membranes in this work owing to their superior thermal stability as compared to the TEOS analogous product. Firstly, the sol-gel processing of ES40 was investigated in this thesis. At different temperatures and H 2 O/Si ratios, ES40 underwent various degrees of phase separation behaviour and sol-gel reactions. It was found that the hydrolysis and condensation reactions decreased with decreasing reaction temperature.Dense silica structures were obtained using low H 2 O/Si ratios, whereas higher porosity was produced from a phase-separated sol-gel system with high H 2 O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, leading to stronger silica matrices which were more resistant to densification.The second part of this work is focused on improvement of the hydrostability of ES40-derived silica membrane materials by adjusting the reactant ratios of sol-gel synthesis process, as the low resistance of silica membranes to water vapor attack, which induce enlargement of the pore size followed by failure in salt rejection, can be detrimental to desalination performance. Investigations were carried out on the effects of reactant ratios on the microstructure of the silica matrices and their hydrothermal stability under harsh conditions (550 °C, 75 mol% vapour). The most hydrothermally stable matrix was obtained by decreasing the ethanol ratio whilst increasing water II and acid ratios. The improved hydrothermal stability was attributed to the further transition of silanol to siloxa...

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Section: Membrane Performancementioning

confidence: 83%

High performance ES40-derived silica membranes for desalination

Wang¹

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“…Raman et al [90] deposited a hybrid organic-inorganic sol, prepared by co-polymerization of TEOS and methyltriethoxysilane (MTES) on a porous alumina support. The calcined silica membrane was further modified by derivatization of the pore surfaces with monomeric TEOS to allow monolayer by monolayer "fine tuning" of pore size.…”

Section: Silica Membranesmentioning

confidence: 99%

A Review of Carbon Dioxide Selective Membranes: A Topical Report

Shekhawat¹,

Luebke²,

Pennline³

2003

101

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The atmospheric concentration of anthropogenic carbon dioxide (CO 2 ) has been increasing since the start of industrialization in the mid 19th century, and the rate is increasing. It is highly unlikely that fossil fuel combustion, the main contributor to anthropogenic CO 2 , will be replaced in the foreseeable future. Therefore, CO 2 capture and storage offer a new set of options for reducing greenhouse gas emissions, in addition to the current strategies of improving energy efficiency and increasing the use of renewable energy resources. Carbon dioxide selective membranes provide a viable energy-saving alternative for CO 2 separation, since membranes do not require any phase transformation. This review examines various CO 2 selective membranes for the separation of CO 2 and N 2 , CO 2 and CH 4 , and CO 2 and H 2 from flue or fuel gas. This review attempts to summarize recent significant advances reported in the literature about various CO 2 selective membranes, their stability, the effect of different parameters on the performance of the membrane, the structure and permeation properties relationships, and the transport mechanism applied in different CO 2 selective membranes. Finally, the future direction for CO 2 selective membranes is proposed. Hybrid organic-inorganic membranes have become an expanding field of research, as the introduction of organic molecules can improve the characteristics of a matrix. Hydrotalcite-type materials, perovskite-type oxides, lithium zirconate, and lithium silicate are also suggested as candidate materials for high temperature CO 2 selective membranes.

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“…The resulting ultramicroporous layers have high selectivity for a variety of gas sepa rations. 25 " 28 The degree of branching of the precursor sols, along with the com- 31 by using processing in a class-1000 clean room, prepared amorphous silica coatings of ~30-nm thickness on top of y-alumina Supports (Figure 2b). Excellent flux, se lectivities, and reproducibility have been achieved.…”

Section: Sol-gel Membranesmentioning

confidence: 99%

Synthesis of Porous Inorganic Membranes

Tsapatsis¹,

Gavalas²

1999

MRS Bull.

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Here we will attempt a brief overview of recent synthetic efforts for micropore and lower-end mesopore membranes. We will not address the very important classes of nonporous membranes, such as dense metals and solid electrolytes with applications in H2 and O2 separations, or meso- and macroporous membranes, which find applications in food processing and water treatment. Microporous materials provide high permselectivities for molecules encountered in the chemical-processing industry but suffer from low intrinsic permeabilities. Therefore, in order to bring microporous membrane materials to commercial applications, functional composites with small effective thicknesses (in the micron or submicron range) must be developed. For example, to achieve economical membrane-reactor sizes, fluxes as high as 0.1 mol/(m2 s) are desirable. Approaches to microporous membranes include modification of mesoporous membranes by sol-gel and chemical-vapor-deposition (CVD) techniques, carbonization of polymers to form molecular-sieve carbon, and polycrystalline-film growth of zeolites and other molecular sieves.Microporous carbon is widely used for liquid or gas purification because of its strong adsorptive properties and high surface area. It is also used for air separation by pressure swing adsorption (PSA), relying on its adsorptive and molecular-sieving properties. From the standpoint of applications, microporous carbons are classified into activated carbons with pore size 0.8–2 nm, and ultramicroporous carbons or carbon molecular sieves with pores 0.3–0.6 nm. Activated carbons are used because of their strong adsorption properties, while carbon molecular sieves are useful on account of their molecular-sieving as well as adsorption properties.

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Organic “template” approach to molecular sieving silica membranes

Cited by 226 publications

References 7 publications

High performance ES40-derived silica membranes for desalination

High performance ES40-derived silica membranes for desalination

A Review of Carbon Dioxide Selective Membranes: A Topical Report

Synthesis of Porous Inorganic Membranes

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