A simple method for determining the multilayer effects in adsorption of alcohols on silica gel

The excess adsorption isotherms ofn-pentanol, pentan-2-ol and 2-methylbutan-2-ol from binary and ternary solutions in benzene andn-heptane were measured. Experimental adsorption data are discussed in terms of a multilayer model of the surface phase. The main assumption of this model is that the surface layers being near the solid surface contain the molecules of the preferentially adsorbed component only. The phase-exchange reaction of molecules between bulk phase and last surface layer has been taken into account.On the basis of this theory it has been established for the investigated systems that the surface phase contains three molecular layers. Simultaneously appropriate surface phase capacities were determined.

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Eine einfache Untersuchungsmethode für Mehrschicht-Effekte bei der Adsorption von Alkoholen an Kieselgel

Zusammenfassung Die Adsorptionsisothermen binärer und ternärer flüssiger Mischungen vonn-Pentanol, 2-Pentanol oder 2-Methyl-2-butanol in Benzol und/odern-Heptan wurden bezüglich Kieselgel gemessen. Die experimentellen Daten der Adsorption wurden mittels des Mehrschichts-Modells der Oberflächenphase diskutiert. Die Hauptvoraussetzung dieses Modells ist die Annahme, daß die Oberflächenschichten, die sich in der Nähe des Kieselgels befinden, nur Moleküle der bevorzugt adsorbierten Komponente enthalten. Es wurde auch die Phasen-Austauschreaktion von Molekülen zwischen Phaseninnerem und der letzten Oberflächenschicht in Betracht gezogen.Auf der Basis dieser Theorie wurde für die untersuchten Systeme festgestellt, daß die Oberflächenphase aus drei Molekülschichten besteht. Außerdem wurden die ermittelten Volumina der Oberflächenphase berechnet.

     

Adsorption of water vapor on modified activated carbons

Summary The adsorption isotherms of water vapor on modified activated carbons are measured in order to study the role of various surface groups in the primary adsorption of water molecules on these adsorbents. These adsorption isotherms are analysed by means of the Dubinin-Serpinsky and Jovanovic equations, which take into account the special features of water vapor adsorption on microporous activated carbons. Numerical analysis of the measured adsorption isotherms by means of the above mentioned equations showed their limited applicability for interpreting adsorption mechanism of water molecules on activated carbons.

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Adsorption von Wasserdampf auf modifizierter Aktivkohle

Zusammenfassung Die Adsorptionsisothermen von Wasserdampf auf modifizierter Aktivkohle wurden gemessen, um die Rolle verschiedener Oberflächentypen auf die Primäradsorption von Wassermolekülen auf diesen Adsorbenzien zu untersuchen. Die Adsorptionsisothermen wurden mittels der Dubinin-Serpinsky- und Jovanovic-Gleichungen analysiert, welche die speziellen Eigenheiten von Wasser auf mikroporöser Aktivkohle berücksichtigen. Die numerische Analyse der gemessenen Adsorptionsisothermen mittles der genannten Gleichungen zeigte ihre limitierte Anwendbarkeit zur Interpretation von Adsorptionsmechanismen von Wassermolekülen auf modifizierter Aktivkohle.

     

Effects of solute-solvent and solvent-solvent association in liquid adsorption chromatography with binary mobile phase

Analytical equations for the capacity ratio in liquid adsorption chromatography with a binary mobile phase, involving solute-solvent and solvent-solvent association in the mobile and surface phases, have been derived. Very simple equations have been obtained for higher values of mole fraction of the more efficient eluting solvent.     

Adsorption properties of ordered mesoporous silicas synthesized in the presence of block copolymer Pluronic F127 under microwave irradiation

Ordered mesoporous silicas (OMSs) were prepared at different temperatures by using tetraethyl orthosilicate (TEOS) as a silica source, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (Pluronic F127) as a structure directing agent and sodium chloride as an additive under acidic conditions and microwave irradiation. The small angle X-ray diffraction patterns of these samples indicate the presence of ordered mesopores, while adsorption studies show that they possess high volumes of pores, bimodal pore size distributions and large pore sizes. There is an interesting change in the hysteresis loop of nitrogen adsorption isotherms with increasing temperature of hydrothermal treatment; a delayed desorption characteristic for cage-like mesostructures is observed for the OMS samples treated at 100 and 120?°C, while the hydrothermal treatment at 140 and 160?°C leads to the samples having hysteresis loops characteristic for channel-like materials.     

Assessment of ordered and complementary pore volumes in polymer-templated mesoporous silicas and organosilicas

A method to determine the volumes of ordered mesopores and complementary small pores in polymer-templated ordered mesoporous silicas and organosilicas is proposed on the basis of the existing relation between the pore width and unit cell values obtained by the XRD structure modeling and the adsorption pore volume.     

Level Crossing Prediction with Neural Networks

A level crossing predictor or alarm system with prediction horizon k is said to be optimal if it, at time t detects that an upcrossing will occur at time t + k, with a certain high probability and simultaneously gives a minimum number of false alarms. For a Gaussian stationary process, the optimal level crossing predictor can be explicitly specified in terms of the predicted value of the process itself and of its derivative. To the authors knowledge this simple optimal solution has not been used to any substantial degree. In this paper it is shown how a neural network can be trained to approximate an optimal alarm system arbitrarily well. As in other methods of parametrization, the choice of model structure, as well as an appropriate representation of data, are crucial for a good result. Comparative studies are presented for two Gaussian ARMA-processes, for which the optimal predictor can be derived theoretically. These studies confirm that a properly trained neural network can indeed approximate an optimal alarm system quite well – with due attention paid to the problems of model structure and representation of data. The technique is also tested on a strongly non-Gaussian Duffing process with satisfactory results.     

How do commission rates influence a firm’s success? statistical analysis of a corporate strategy simulation experiment

The purpose of this paper is to analyse the relationship between commission rates and a firm’s success within a corporate strategic planning simulation experiment. Teams of students are assigned to the role of managers of a firm within a competitive market situation. They have the task to experience the complex situation in which they act as managers to increase the performance of a firm by setting specific parameters. Our most interesting parameter is the commission rate. The Marketing Game considers a reasonably complex and realistic situation for the participants. We examine to what extent subjects succeed in increasing a firm’s turnover and profit by varying the commission rates.     

Periodic mesoporous organosilicas with Im3m symmetry and large isocyanurate bridging groups

Adsorption and structural properties of periodic mesoporous organosilica with Im3m symmetry (SBA-16) and large heterocyclic bridging groups in cage-like mesopores are studied. The core of this bridging group is an isocyanurate ring integrated with three trimethoxysilyls through flexible propyl chains.     

Adsorption and Thermogravimetric Methods for Monitoring Surface and Structural Changes in Ordered Mesoporous Silicas Induced by their Chemical Modification

The current work demonstrates that the standard adsorption analysis has a limited applicability for characterization of chemically modified porous silicas. Since low-pressure nitrogen adsorption isotherms are sensitive to the surface changes caused by chemical modification of silicas, these isotherms were successfully used to evaluate their surface heterogeneity during different stages of modification. The surface analysis was accomplished by using adsorption energy distributions and high-resolution comparative plots.