Separation of gas and organic/water mixtures by MFI type zeolite membranes synthesized in a flow system

MFI type zeolite membranes were synthesized in a recirculating flow system at 95 °C where the synthesis solution was flown over the tubular α-alumina supports. The performance of the membranes for the separation of binary gas mixtures and alcohol/water liquid mixtures was investigated. A membrane synthesized by two consecutive synthesis steps had a separation selectivity of 15 and 11 for equimolar mixtures of n-C₄H₁₀/CH₄ and n-C₄H₁₀/N₂ at 200 °C, respectively. The membrane selectively permeated large n-C₄H₁₀ over small CH₄ and N₂, suggesting that the separation is essentially adsorption-based and the membrane has few nonselective intercrystalline pores. The selectivities in the pervaporation separation of 5% ethanol/95% water mixture were 43 and 23 with permeate fluxes of 0.2 and 1.9 kg/m² h at 25 and 85 °C, respectively. The separation performance of membranes showed that MFI type membranes prepared in a recirculating flow system can be used both in the separation of gas and liquid mixtures.     

Clinoptilolites of western anatolia as detergent builders

The use of clinoptilolites of Western Anatolia in detergents as phosphate substitutes was investigated. The cations present in the clinoptilolite samples were first exchanged with sodium ions. The washing characteristics of detergent mixtures containing surfactants, clinoptilolite, sodium carbonate and sodium sulphate were analysed. The stains of coffee, tea and tomato paste were tested. The washing tests were repeated for different surfactants, i.e. linear alkyl benzene sulphonate, sodium alkyl sulphate and alcohol ethoxylate and for different co-builders, i.e. sodium carbonate and EDTA. In addition, the effects of detergent dose and detergent formulation on washing were investigated. Other factors affecting the degree of soil removal such as shaking time, temperature and water hardness were also studied. The contribution of clinoptilolite to the washability was compared with zeolite A, zeolite X and sodium tripolyphosphate. Increasing the shaking time and temperature improves the degree of cleaning. LAS was the most effective surfactant for use with clinoptilolite. The washing performance of the detergent mixtures used in the present work was found to be comparable with that of commercial detergents at low washing temperatures.     

EFFECT OF SODA CONCENTRATION ON THE MORPHOLOGY OF MFI-TYPE ZEOLITE MEMBRANES

MFI-type zeolite membranes were hydrothermally synthesized as a thin layer on macroporous α-alumina discs coated with 1µm MFI-type seed crystals as seed. The effect of soda (Na₂O) concentration on the morphology of the membranes was investigated. Soda concentration, and thus the hydroxyl ion concentration, was changed between 0.25 and 6.5 mol/mol gel. At low soda concentrations the crystals forming the layer exhibited mostly (h0h)/c-axis orientation, but at high soda concentrations a membrane layer formed from randomly oriented crystals. The membranes showed high H₂/n-butane ideal selectivity of 476 and 36 at 25°C and 150°C, respectively.     

Sorption properties of synthetic ferrierite

Limiting sorption volumes of the hydrogen form of a synthetic ferrierite sample were determined for sorbates--water, methanol, propane, hexane, and o-, m-, p-xylenes--at 298 K and at a relative pressure of P/P o = 0.5 using a gravimetric sorption apparatus. Methanol, which has a kinetic diameter significantly smaller than the pore dimensions, was sorbed relatively rapidly and by the greatest amount. The sorption rates of other sorbates were very slow and for some it took several days for equilibrium to be established. The results indicated that, although their kinetic diameters are similar, the adsorption behavior of propane and hexane are quite different. Hexane is able to fill only ten-membered ring channels whereas propane is able to fill both ten- and eight-membered ring channels, at least partially. The inability of the hexane molecules to be sorbed into eight-membered ring channels is attributed to chain length effect. Xylene isomers are sorbed by the H-ferrierite but to smaller extents, consistent with the significantly larger kinetic diameters of these molecules compared to the reported pore dimensions of ferrierite. Among the xylene isomers, p-xylene, with the smallest kinetic diameter of three isomers, is sorbed to a greater extent than either o-xylene or m-xylene.     

The synthesis and sodium-silver ion exchange of sodalites

Aluminosilicate sodalites of three different types--chlorosodalite, basic sodalite, and oxalate sodalite--have been synthesized in their sodium forms using hydrothermal synthesis. The syntheses were investigated in terms of their relative rates of crystallization and final crystallinities using powder X-ray diffraction. These sodalites were subsequently loaded with silver by aqueous ion exchange. The exchange was studied primarily by monitoring the solution phase. Rate of exchange and equilibrium behavior have been established over the temperature range of 25-80°C for all three types. Extreme selectivity toward silver over sodium was observed, with little dependence on temperature. Both sodium and silver sodalites were characterized by powder diffraction, and crystallographic data for silver sodalites have been derived using Rietveld refinement. Electron micrographs of sodalites have been used for investigations of crystallite morphology and size. Silver sodalites have been observed to manifest various optical properties including photochromic, barochromic, thermochromic, and fluorescent behavior.     

SORPTION PROPERTIES OF SYNTHETIC FERRIERITE

Limiting sorption volumes of the hydrogen form of a synthetic ferrierite sample were determined for sorbates--water, methanol, propane, hexane, and o-, m-, p-xylenes--at 298 K and at a relative pressure of P/P o = 0.5 using a gravimetric sorption apparatus. Methanol, which has a kinetic diameter significantly smaller than the pore dimensions, was sorbed relatively rapidly and by the greatest amount. The sorption rates of other sorbates were very slow and for some it took several days for equilibrium to be established. The results indicated that, although their kinetic diameters are similar, the adsorption behavior of propane and hexane are quite different. Hexane is able to fill only ten-membered ring channels whereas propane is able to fill both ten- and eight-membered ring channels, at least partially. The inability of the hexane molecules to be sorbed into eight-membered ring channels is attributed to chain length effect. Xylene isomers are sorbed by the H-ferrierite but to smaller extents, consistent with the significantly larger kinetic diameters of these molecules compared to the reported pore dimensions of ferrierite. Among the xylene isomers, p-xylene, with the smallest kinetic diameter of three isomers, is sorbed to a greater extent than either o-xylene or m-xylene.