Rapid Sorption Kinetics THEORETICAL TREATMENT OF RAPID SORPTION KINETICS MEASURED IN BATCH ARRANGEMENT

Universal solution of a family of sorption kinetic models which are based on superposition principle has been developed to describe sorption experiments in a closed system. The models account for the interactions of a sorbate-sorbent system with the apparatus which arise (i) from the mass balance condition in a closed system and (ii) from a finite rate of sorbate supply to the sorbent, the latter effect being of importance particularly in rapid nonstationary kinetic processes. Theoretical uptake curves for the intracrystalline sorption kinetics in zeolite crystals are exemplified using numerical solution of the corresponding Volterra integral equations which represent kinetic models of the overall transient sorption process in the apparatus. The approach appears to be promising for treatment of sorption kinetics in multi component systems. The Volterra Integral Equation (VIE) approach has recently been proposed to solve mathematical models of sorption kinetics from the gas phase measured under constant volume/variable pressure conditions 1. For fast sorption kinetics with characteristic times amounting to about one second, one arrives at the limits of the experimental method and thus, the valve used to start the experiment may distort the uptake curves considerably. In a previous publication 2 , the valve effect was analyzed thoroughly for a special type of sorption kinetics. The use of the VIE approach 1,3,4, offers a general way to compute sorption uptake curves affected by the limited rate of sorbate supply through valves and tubings of the experimental apparatus. In such a manner the limits of the experimental methods can in principle be displaced about one order of magnitude to lower intrinsic time constants of sorption kinetics whatever type of valve may be used. DESCRIPTION OF THE EXPERIMENT The principal scheme of the experimental piezometric apparatus is given i

REMOVAL OF DIQUATERNARY AMMONIUM CATIONS FROM AS-SYNTHESIZED SSZ-16 ZEOLITE

Zeolites are stable microporous aluminosilicates with numerous applications in chemical technology such as separation of species and catalytic transformations. Our study is focused on a weakly explored zeolite SSZ-16 with pore constrictions defined by 8-membered oxygen rings. Key results are the preparation of Et6-diquat-5 dication used as a structure directing agent (SDA) and finding the optimum synthesis conditions with respect to zeolite phase purity. Stability of SDA was examined in conditions similar to those of autoclave synthesis (concentration, pH, temperature). Moreover, the content and location of SDA species in zeolite phase and conditions of SDA decomposition were investigated

REMOVAL OF DIQUATERNARY AMMONIUM CATIONS FROM AS-SYNTHESIZED SSZ-16 ZEOLITE

Zeolites are stable microporous aluminosilicates with numerous applications in chemical technology such as separation of species and catalytic transformations. Our study is focused on a weakly explored zeolite SSZ-16 with pore constrictions defined by 8-membered oxygen rings. Key results are the preparation of Et6-diquat-5 dication used as a structure directing agent (SDA) and finding the optimum synthesis conditions with respect to zeolite phase purity. Stability of SDA was examined in conditions similar to those of autoclave synthesis (concentration, pH, temperature). Moreover, the content and location of SDA species in zeolite phase and conditions of SDA decomposition were investigated

• • _"'Ill Diffusion and Immobilization Mechanisms in Zeolites Studied by ZLC Chromatography*

Abstract. Zero Length Column chromatography was used to study mass transfer in zeolites involving coupled diffusion and immobilization mechanisms, A modeling based on Volterra integral equation technique was utilized to simulate sorption and desorption kinetic curves and compare results of the simulations with experimentally obtained curves, This approach was applied to analyze sorption kinetics in the model system: toluene/silicalite-l (75UC-178'~C), The system generally shows a non-Fickian behavior and can be described by diffusion coupled with immobilization

Bohemian sandstone for restoration of cultural heritage sites: 3D microstructure and mass transport properties

We characterised the microstructure of sandstone from the Msene locality (Czech Republic) by combining X-ray computed micro-tomography, back-scattered electron imaging, chemical composition analysis and textural analysis and gas permeation. Both, 2D and 3D images were commonly processed by linking an anisotropic non-linear diffusion filter and a segmentation method based on power watershed. This approach guaranteed binarised outputs that were almost the same in wide ranges of spatial-filter and power-watershed parameters, i.e., subjective choices of the parameters played the negligible role. The rock pore structure was found to be statistically homogeneous and almost isotropic with perfectly connected pore space. We also partitioned the void and solid phases into either grains or pores and throats, which enabled us to study characteristic sizes and connectivity of partitioned regions. By comparing pore and throat sizes, we demonstrated the significant convergent-divergent nature of the pore space because the throat size covered at most one half of the total surface area per pore (cavity). In addition, we calculated coordination numbers for all pores (cavities) to verify almost perfect connectivity of internal pores with those at the external surface. Effective (macroscopic) transport properties of the reconstructed pore space were simulated and the results were validated by experimentally observing steady state flow of inert gas. These findings appear to be a favorable starting point for future investigation of consolidation procedures. The well-connected pore structure with minimum occurrence of dead-end pores suggests that the consolidation agent is very likely to flood the whole pore space

Hierarchical TiO₂ Layers Prepared by Plasma Jets

Heterogeneous photocatalysis of TiO2 is one of the most efficient advanced oxidation processes for water and air purification. Here, we prepared hierarchical TiO2 layers (Spikelets) by hollow-cathode discharge sputtering and tested their photocatalytic performance in the abatement of inorganic (NO, NO2) and organic (4-chlorophenol) pollutant dispersed in air and water, respectively. The structural-textural properties of the photocatalysts were determined via variety of physico-chemical techniques (XRD, Raman spectroscopy, SEM, FE-SEM. DF-TEM, EDAX and DC measurements). The photocatalysis was carried out under conditions similar to real environment conditions. Although the abatement of NO and NO2 was comparable with that of industrial benchmark Aeroxide® TiO2 P25, the formation of harmful nitrous acid (HONO) product on the Spikelet TiO2 layers was suppressed. Similarly, in the decontamination of water by organics, the mineralization of 4-chlorophenol on Spikelet layers was interestingly the same, although their reaction rate constant was three-times lower. The possible explanation may be the more than half-magnitude order higher external quantum efficacy (EQE) compared to that of the reference TiO2 P25 layer. Therefore, such favorable kinetics and reaction selectivity, together with feasible scale-up, make the hierarchical TiO2 layers very promising photocatalyst which can be used for environmental remediation