Hansjörg Herden

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.

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.

Heats of immersion of ZSM—5 zeolite in n-alkanes, 1-alkenes and 1-alcohols at 30°C

Abstract Integral immersional effects in ZSM—5/n-alkane, -/1-alkene, -/n-alcohol and in silicalite/n-alkane, -/n-alcohol systems have been measured calorimetrically at 303 K using an isothermal LKB-microcalorimeter 2107 modified in the part containing the BATCH-vessel. The results are discussed in terms of a chain-length dependence of integral heats of immersion.

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.

Adsorption of 1-Tetradecene/Dodecane Mixtures on Different Types of Zeolites

The influence of heterogeneity parameters on the shape of excess adsorption isotherms has been discussed. These isotherms have been calculated according to the equations corresponding to different energy distributions. Next, the isotherm equations have been applied to examine the experimental excess isotherms for 1-tetradecene/dodecane mixture adsorption on different types ofX-zeolites at 293 K, 313 K and 333 K. The zeolite samples have been prepared from NaX-zeolite by exchanging the sodium ions for ions of alkalines and calcium group. Analysis of the above adsorption data by means of different isotherm equations showed that the parameters of aDubinin-Radushkevich-type equation change correctly with temperature and the contents of alkalines in the zeolite samples.

Adsorption of hydrocarbons on activated carbons

Abstract The isotherms of several hydrocarbons (methane, ethane, propane, η-butane, isobutane, isooctane, and benzene) were measured at 273, 293, and 303 K on a number of activated carbons. By means of the Dubinin-Radushkevich (DR) method we calculated the characteristic parameters of the microporosity of the carbons used (micropore volume, characteristic energy, and the mean distance of slit-shaped micropores). The values obtained showed significant differences between the activated carbons used, depending on the materials and the activation process applied.

Liquid phase adsorption studies of octene-1 and octane on X-zeolites

Abstract A study was made of the adsorption of octene-1 and n-octane onto X-zeolites from solution. The excess isotherm was measured onto NaX at 293°K. The adsorption equilibrium constant determined by using the Gibbs adsorption equation and the concept of the surface excess was K = 58. The limiting adsorption estimated of the excess isotherm was 1.88 mmole/g, and is in good agreement with the value of 1.893 mmole/g determined by an absolute method. The heats of immersion of octene-1 and n-octane were measured by using an LKB 2102 microcalorimeter. The results show a strong influence of the nature of cations which are accommodated in the zeolites (Na, K, and Ba) and of the nature of adsorptives. Such an influence is also found for the activation energies of the self-diffusion process as studied by the NMR pulse field gradient technique. However, the selfdiffusivities for octene-1 decreased in the sequence KX > NaX > BaX.

PFG NMR study of self-diffusion of low carbon chain length paraffins in carbonaceous adsorbents

Abstract The molecular self-diffusion of different hydrocarbons in two activated carbons (ASA-H and CMS-H) was studied using pulsed-field gradient NMR. The estimated self-diffusion coefficients correspond with the half-width of the micropores of the used adsorbents and decrease with the increasing length of the hydrocarbon chain. In active carbon CMS-H the increase in activation energies with increasing molecular chain length is much more pronounced than in ASA-H.

Zur Adsorption von Olefinmolekülen in Zeolithen

The interaction between 1-olefine molecules and Na+ ions in zeolites of type NaY were studied by13C NMR spectroscopy and quantum chemical calculations. Characteristic chemical shifts of olefinic carbon atoms indicate a terminal arrangement of the cation near the olefinic part of the molecule.