Luis Alzamora

Surface methylation of aerosil and its influence on the adsorption of water

Abstract Reversible adsorption isotherms at different temperatures have been used to study the system of water adsorbed on Aerosil and on Aerosil whose surface has been partially methylated with trimethylchlorosilane. The change in the shape of the isotherm upon surface methylation from type II to type III, according to Brunauers classification, renders difficult the calculation of the capacity of the monolayer; however, in this case it can be obtained by Kaganers method. The variation in the mobility of the monolayer on surface methylation can be shown by comparing the experimental and theoretical integral entropies, while the molecules adsorbed in the multilayer region always have a high degree of freedom.

The effect of reaction parameters on catalytic activity in the polymerization of ethylene using supported and unsupported metallocene catalysts

Abstract The catalytic activities of two metallocene compounds, EtInd2ZrCl2 and Ind2ZrCl2, in the polymerization of ethylene depend heavily on certain parameters, such as Zr concentration in the reaction, type of the reactor, and stirring speed for homogeneous catalysts. One way or another, all these factors influence the catalytic activity of these systems, but catalyst concentration and stirring speed are the most important ones. In the case of heterogeneous catalysts of the same metallocenes, the most pronounced influence is related to the type of support and its porous nature. The influence of the support on activity and morphology is shown.

Study of metallocene supported on porous and nonporous silica for the polymerization of ethylene

Porous and nonporous silicas are good supports for the synthesis of coordinative heterogeneous catalysts for ethylene polymerization. The catalytic activity of nonporous Aerosil depends critically on the percentage of incorporated zirconium. The calcination of the support also affects the activity, showing the best results with nonporous silica at 1000°C, and with porous silica at 800°C.

The Hill-de Boer equation in the adsorption of water on quartz

Abstract Within the limitations imposed by the number of experimental points, it has been possible to establish that the system of water adsorbed on pure and methylated quartz has adsorption isotherms in which the quantity adsorbed increases with increasing temperature when plotted in terms of relative pressure. This behavior can be adequately described by the Hill-de Boer equation, even though the interpretation of the data by means of parameter K 1 of the equation suggests that the water shows only dispersion interactions with the silica surface. This rather anomalous behavior of the system is in agreement with the previously published values of parameter S of the Frenkel-Halsey-Hill equation.

Study of the adsorption of n-heptane and 1-heptane by aerosil

Adsorption isotherms of 1-heptene and n-heptane were determined at three near-ambient temperatures on a nonporous silica (Aerosil 200 They appear to lend support to the hypothesis that the double bond of the olefins contributes to specific interactions with hydroxyl groups. In addition, the differential enthalpies and entropies of adsorption of each hydrocarbon were determined as a function of the amount adsorbed showing restricted mobility for 1-heptene and a high surface mobility for n-heptane.

Rotational degrees of freedom in the adsorption of hydrocarbons on aerosil

A study has been made of the different contributions to the entropy of adsorption in Henrys zone of several hydrocarbons on Aerosil with different degrees of hydrophobicity. The statistical-mechanical interpretation of the experiments on the adsorption of isobutene on hydroxylated Aerosil shows that there is mobile adsorption with loss of one rotational degree of freedom.

Adsorption of hydrocarbons on Aerosil treated at different temperatures

A study of the adsorption of n-butane, buta-1,3-diene and isobutene on Aerosil treated at different temperatures has been made from 17.7 to 45 °C and over the pressure range 0–600 Torr.The isosteric enthalpy and entropies of adsorption at zero coverage together with the B.E.T. parameters C and nm of the systems have been examined; they suggest a way in which different parts of the adsorbate molecule are specifically related to the hydroxylated and non-hydroxylated regions of the Aerosil surface.

Adsorption of n-hexane, 1-hexene, and 1,5-hexadiene on aerosil

Abstract On the surface of colloidal silica 1,5-hexadiene is less strongly adsorbed than is n-hexane and 1-hexene because the delocalization of the II-bonds of the diene reduces the energy of interaction with the surface so that there is high mobility.

Adsorption thermodynamic functions and the mobility of SO2 on aerosil

Abstract A study of the adsorption and thermodynamic functions of sulfur dioxide on Aerosil has been made, leading to some conclusions about the mobility of the SO 2 molecule. The differential and integral enthalpies and entropies of adsorption, together with a statistical mechanical interpretation of the system, are discussed. Particularly, the statistical mechanical calculation of the integral entropy of adsorption allows a comparison to be made between the experimental results for the SO 2 —Aerosil system and those obtained for adsorption in two limiting cases: an immobile or localized model that can be associated with chemisorption, and a mobile film model that can be related to physisorption. The results confirm a weak gas—solid interaction with a highly mobile adsorbed phase.