Rolf Schöllner

Crystal structure of dehydrated LiNa-A type zeolites

Abstract The crystal structures of dehydrated Li-exchanged A-type zeolites, determined by neutron and X-ray diffraction powder methods, indicate that the majority of the Li-cations are located at the six-ring centres. The framework distortion is progressive from d-K-A to d-Na-A and d-Li-A and follows the charge to radius ratio of the exchangeable cations. The shape of the framework eight-rings changes accordingly.

Magic-Angle-Spinning Nuclear Magnetic Resonance and Adsorption Studies of Dealumination and Realumination of Zeolite ZSM-5

Abstract Adsorption of nitrogen, 27Al and 1H magic angle spinning nuclear magnetic resonance show that non-framework aluminium species created by deep dealumination of zeolite H-ZSM-5 can be partially reintroduced into the framework upon treatment (2 h, 350 K) with 0.1 M aqueous solution of NaOH. However, the treatment also causes a loss of micropore volume and creates a secondary pore system. No realumination or loss of porosity are observed after dealumination performed under mild hydrothermal conditions, i.e. when the Si/Al ratio of the dealuminated material is less than ca. 25.

Adsorption of n-hexane/n-olefin mixtures by NaX zeolites from liquid solution

Abstract A study was made of the adsorption of n -hexane/ n -olefin binary mixtures of liquid solution on NaX zeolite. The shape of the excess isotherms and the influence of the olefin carbon number on it were established. A linear correlation between the logarithm of the separation factor and the olefin chain length was found. An easy model isotherm equation was used for the description of these systems.

X-ray structural investigations on hydrothermally treated (Ca4, Na4)-A zeolites

Abstract The structures of three Ca 4 Na 4 A zeolite samples were studied in the dehydrated and hydrated state by X-ray powder diffraction techniques. The structures were refined in the space group Pm3m . Normal industrially prepared, deep bed treated and deep bed treated steamed Ca 4 Na 4 A zeolites were submitted to a dehydration and a rehydration. Extra framework aluminate species were detected in the sodalite cage and were identified as AlO x (OH) 4− x −(1 + x ) complexes. They were found in the mother material and in the deep bed steamed sample. They were absent in the deep bed treated sample. A possible model for zeolite A hydrolysis is proposed.

Liquid-phase adsorption of n-alcohol/water mixtuers on zeolite NaZSM-5

Abstract A study of the adsorption of n-alcohol/water mixtures onto zeolite NaZSM-5 from solution was performed. The excess isotherms were measured at 293 K. Adsorption equilibrium constants and molar heats of immersion strongly depend on the carbon number of the alcohol. The limiting adsorption estimated from the excess isotherm was independent of the carbon number 130 mg/g. The model for the adsorption of binary liquid mixtures of nonelectrolytes, involving differences in the molecular sizes of the components and the real behavior of the mixture in bulk and surface phases, is used to describe the excess adsorption data.

Adsorption studies of n-olefin/n-paraffin mixtures on X- and Y-zeolites. II. Adsorption of tetradecene-1 /n-dodecane mixtures on modified X- and Y-zeolites

Abstract The adsorption of tetradecene-1/ n -dodecane mixtures from liquid solution on X- and Y-zeolites was studied. The obtained surface excess isotherms and the heats of immersion depend very strongly on the nature of the cations contained (Li, Na, K, Rb, Cs, and the divalent cations Ca, Sr, and Ba) and the degree of the ion exchange. The influence of the silicon/aluminum ratio on the shape of the excess isotherms and the heat of immersion was also studied. It was shown that the separation factors, obtained by evaluating the excess isotherms, and the heat of immersion can be interpreted in terms of the cation distribution and the charge to radius ratio.

Adsorption studies of n-Olefin/n-paraffin mixtures on X- and Y-zeolites. I. Comparison of liquid phase and vapor phase adsorption of hexane-1 and n-hexane on NaX-zeolite

Abstract The adsorption of hexene-1/ n -hexane mixtures of liquid solution on an NaX-zeolite ( Si Al = 1.4 ) was studied. The excess isotherms and the heats of immersion were determined on this zeolite. The difference between the molar heats of immersion determined from the temperature dependence of the surface excess is −32.4 kJ/mole the comparable value obtained by calorimetric method is −33.4 kJ/mole. A detailed thermodynamic analysis of these data showed an ideal behavior of hexene-1/ n -hexane in the bulk phase and adsorbed phase. A thermodynamic consistency test for the adsorption of liquids and their vapors was applied to our system.

Liquid-phase adsorption of binary ethanol–water mixtures on NaZSM-5 zeolites with different silicon/aluminium ratios

A systematic study was made on the adsorption of ethanol–water mixtures on NaZSM-5 zeolites, synthesized with different Si/ Al ratios. The excess isotherms were analysed by means of energetic homogeneous and energetic heterogeneous adsorbent models. For the first model, the equilibrium constants increase with increased Si/ Al ratio. Using the model of an energetic heterogeneous adsorbent, an energy difference distribution function with two maxima appears, which is due to London-type interactions and the specific interactions of the zeolites with the adsorbed molecules.

Liquid-phase adsorption of monosaccharide–water mixtures on X and Y zeolites

A systematic study has been performed on the adsorption of D-fructose–, D-glucose– and D(–)-arabinose–water mixtures on K+, Sr2+, Ca2+, Ba2+ and La3+ ion-exchanged X and Y zeolites. From the adsorption excess isotherms the separation factors K and the equilibrium diagrams xs2vs.x12 of the binary mixtures were calculated. The possible triangles of O atoms of monosaccharides, their interactions with cations, the influence of crystallographic cation positions and the Si : Al ratio of zeolites on formation of adsorption complexes were analysed.

Thermal analysis of NaMgA zeolites

Abstract Water desorption from NaMgA zeolites was investigated as a function of magnesium ion content with the help of thermal analytical methods such as combined TG-DTG-DTA, TMA and X-ray heating technique. At least five partly overlapping desorption effects of water were observed from DTA and DTG features. The amount of water corresponding to individual desorption peaks was determined by experimental methods of separation. An assignment of the desorption effects to the related adsorbed forms of water is suggested.