Hatem M. Alsyouri

MICROPOROUS INORGANIC MEMBRANES

Recent development in microporous inorganic membranes represents a significant advance in materials for separation and chemical reaction applications. This paper provides an in-depth review of synthesis and properties of two groups (amorphous and crystalline) of microporous inorganic membranes. Amorphous microporous silica membranes can be prepared by the sol-gel and phase separation methods. Flat sheet, tubular and hollow fiber amorphous carbon membranes have been fabricated by various pyrolysis methods from polymer precursors. A large number of synthesis methods have been developed to prepare good quality polycrystalline zeolite membranes. Several techniques, including vapor and liquid approaches, are reviewed for pore structure modification to prepare microporous inorganic membranes from mesoporous inorganic membranes. Chemical, microstructural and permeation properties of these microporous membranes are summarized and compared among the several microporous membranes discussed in this paper. Theory for gas permeation through microporous membranes is also reviewed, with emphasis on comparison of theoretical with the experimental data. These inorganic microporous membranes offer excellent separation properties by the mechanisms of preferential adsorption, selective configurational diffusion or molecular sieving.

Catalyst impregnation and ethylene polymerization with mesoporous particle supported nickel-diimine catalyst

A nickel-diimine catalyst (1,4-bis(2,6-diisopropylphenyl) acenaphthene diimine nickel(II) dibromide, DMN) was supported on mesoporous particles having parallel hexagonal nanotube pore structure (MCM-41 and MSF) for ethylene polymerization. The effects of supporting methods and particle morphological parameters, such as pore size and length, on the catalyst impregnation were systematically investigated. Pretreating the supports with methylaluminoxane (MAO) followed by DMN impregnation gave much higher catalyst loading and higher catalytic activity than the direct impregnation of DMN. The particle structure significantly affected the catalyst impregnation and this effect was explained with a semi-quantitative molecular diffusion model. Compared to homogeneous catalysts, significant reduction in activity was observed with the supported systems in ethylene polymerization. Extraction of active sites from the supports during polymerization was observed. The mesoporous supports exerted steric effects on unleached active sites, lowering chain walking ability, and producing polymers having lower short chain branch density. Replication of the particle morphology was observed in some polymer samples.

[n]-Oligourea-Based Green Sorbents with Enhanced CO2 Sorption Capacity.

A new series of [n]-oligoureas ([n]-OUs, n=4, 7, 10, and 12) green solid sorbents was prepared following a base-catalyzed, microwave-assisted oligomerization reaction. The materials were characterized by NMR and IR spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and XRD. Decomposition temperatures at 50 % weight loss (Td50 ) were ca. 350 °C for all oligomers. Urea and urethane functional groups indicated by IR spectroscopy confirmed the formation of the sorbent. The CO2 capturing capacities were determined at 35 °C and 1.0 bar (gravimetric method). Accordingly, [10]-OU had the highest CO2 sorption capacity among the others (18.90 and 22.70 mg CO 2 gsorbent (-1) ) at two different activation temperatures (60 or 100 °C, respectively). Chemisorption was the principal mechanism for CO2 capture. Cyclic CO2 sorption/desorption measurements were carried out to test the recyclability of [10]-OU. Activating the sample at 60 °C, three stable CO2 sorption cycles were achieved after running the first cycle.

Ordered mesoporous silica fibers: effects of synthesis conditions on fiber morphology and length

Ordered mesoporous silica fibers offer potential industrial application in several areas including polymerization catalysis and separation. Understanding the effects of synthesis conditions on these fibers prepared by the interfacial self-assembly growth method is important to their production and application. The focus of this work is to understand the effect of two previously unstudied factors: silica source height (tetrabutylorthosilicate, TBOS) and the humidity, on the formation of ordered mesoporous silica fibers by the interfacial self-assembly method. Here the TBOS content, interface area, height of source, and humidity of the environment were varied to study their effect on fiber growth. The results show that the TBOS content and interface area do not have a significant impact on results of ordered mesoporous silica fibers. Increasing silica source height or environmental humidity, which lowers the water evaporation rate, gives silica fibers with lower length, less ordered inner pore structure and macroscopic morphology, and smaller pore size. Attempts to mix the growth medium eliminate the fiber morphology and yield gyroidal shapes. A mechanism that combines evaporation of water resulting in local concentration and surfactant, self-assembly, and reaction and diffusion of silica source is proposed to describe the formation of ordered mesoporous silica fibers.

Ordered mesoporous silica prepared by quiescent interfacial growth method - effects of reaction chemistry

Acidic interfacial growth can provide a number of industrially important mesoporous silica morphologies including fibers, spheres, and other rich shapes. Studying the reaction chemistry under quiescent (no mixing) conditions is important for understanding and for the production of the desired shapes. The focus of this work is to understand the effect of a number of previously untested conditions: acid type (HCl, HNO3, and H2SO4), acid content, silica precursor type (TBOS and TEOS), and surfactant type (CTAB, Tween 20, and Tween 80) on the shape and structure of products formed under quiescent two-phase interfacial configuration. Results show that the quiescent growth is typically slow due to the absence of mixing. The whole process of product formation and pore structuring becomes limited by the slow interfacial diffusion of silica source. TBOS-CTAB-HCl was the typical combination to produce fibers with high order in the interfacial region. The use of other acids (HNO3 and H2SO4), a less hydrophobic silica source (TEOS), and/or a neutral surfactant (Tweens) facilitate diffusion and homogenous supply of silica source into the bulk phase and give spheres and gyroids with low mesoporous order. The results suggest two distinct regions for silica growth (interfacial region and bulk region) in which the rate of solvent evaporation and local concentration affect the speed and dimension of growth. A combined mechanism for the interfacial bulk growth of mesoporous silica under quiescent conditions is proposed.

Counter diffusion self assembly synthesis of ordered mesoporous silica membranes

We report the synthesis of ordered mesoporous silica membranes in macroporous supports by a novel acid catalyzed counter diffusion self assembly (CDSA) method. Effect of pore size, morphology and surface chemistry of the support on the formation of oriented mesoporous silica plugs has been studied. Hydrophobically modified small pore alumina supports (0.3μm) show good quality silica membranes as sub-millimeter plugs. Preliminary observations on straight pored hydrophilic and hydrophobic track etch polycarbonate membranes supports (pore diameters 5 μm and 8 μm respectively) indicate the formation of ordered mesoporous silica plugs within the support pores, as seen by results of scanning electron microscopy and X-ray diffraction studies. Experimental results suggest that the pore size and morphology of the support play a vital role in the formation of these ordered mesoporous silica plugs, while surface chemistry seems affect the quality of the plugs formed.