Guido Peeters

Purification of gases in H-mordenite modified with silane and diborane

Silane and diborane have been found to be very suitable for the structural modification of H-zeolites, and stepwise boranation of the H-mordenite structure has been studied. The effect of the degree of modification on the pore size and the affinity of the zeolite was checked by sorption experiments with N2(77 K) and Xe and Kr (273 K). A further narrowing of the pore size was achieved by oxidation of the implanted (BH)x groups with H2O or other molecules such as CH3OH. The pore size could be ‘engineered’ in a controlled way so that it could be applied to finely tuned separations, yielding components of pure Kr from Kr + N2, Ar + Kr, O2+ Kr and N2+ O2+ Kr, pure Ar from Ar + Kr, pure N2 from N2+ Kr, pure O2 from O2+ Kr and pure CH4 from H2+ N2+ CH4 mixtures.

Encapsulation of gases in h-mordenite modified with silane and diborane

Pore closure of zeolites has been achieved by the chemical reaction of silane and/or diborane with the hydroxyl groups in the zeolite structure, followed by oxidation of the chemisorbed BH or SiH groups with H2O or other molecules such as CH3OH, resulting in a modification to the zeolite which changes its sorption properties. This has led to the successful encapsulation of noble gases in H-mordenites under ‘normal’ conditions of pressure and temperature. Thermal stability up to 473–573 K has been achieved. Krypton encapsulates have been tested for their stability against water, acids, mechanical grinding and γ-irradiation and no significant influence of such treatments on the stability has been observed.

Fourier-transform infrared photoacoustic spectroscopy of zeolites

Abstract Photoacoustic detection is shown to be very valuable for obtaining infrared-spectroscopic data for samples with characteristics that involve very difficult sampling. The modification reactions on the zeolite mordenite, a highly scattering material, are investigated by this technique and by gas-adsorption experiments. The mechanism of the reactions between borane groups inside the channels of the mordenite and amines at different reaction temperatures is described. At low temperatures, amine- and amino-boranes are formed that polymerize at elevated temperatures if steric hindrance is absent. The implantation of boron-nitrogen compounds inside the channels of the mordenite allow a continuous and controlled variation of the accessibility of the mordenite for gas molecules such as krypton and xenon at 273 K.

Modification of H-mordenite with silane and diborane. A comparative study of the reaction parameters

Silane and diborane have been found to be very suitable for the structural modification of H-mordenite. The reaction with silane or diborane reduces, in a controlled way, the effective pore size of zeolites by implantation of additional atoms or atom groups. As a result, molecular sieving effects can be controlled by pore size engineering, and gases can be encapsulated under moderate conditions of temperatures and pressures by closing the zeolitic pores by silanation or boranation techniques.The main parameter determining the efficiency of a pore closure, is the degree of modification: the amount of silane or diborane chemisorbed in the zeolite. The effect of reaction temperature, reaction pressure and reaction time on the degree of modification is studied for silanation and boranation of H-mordenite.Generally, for silanation and boranation it was observed that the modification degree increases with increasing pressure of the modifying agent. For silanation we observed that a higher reaction temperature enhances primary and secondary reactions. Increasing the pressure of silane decreases the ratio secondary/primary reactions, while the chemisorption of silane by primary reaction is favoured at higher pressure. Compared to the silanation, the boranation reaction is very fast because of the higher reactivity of diborane towards zeolitic hydroxy groups. Even at room temperature and low pressure the ultimate boranation degree could be reached. For the boranation we observed an indirect pressure effect which has an important influence on the ultimate modification and hence on the resulting porosity of the zeolite. The amount of added diborane, and hence the number of boranation steps, used to reach the ultimate boranation degree is a critical parameter in determining the pore size reduction.

Exchange of alkylammonium ions in the zeolite-L

A study has been made of the ion-exchange equilibria of NH+4, CH3NH+3, C2H5NH+3, n-C3H7NH+3, n-C4H9NH+3, (CH3)2NH+2, (CH3)3NH+, (C2H5)2NH+2 and (C2H5)3NH+ by the zeolite L. None of the alkylammonium ions could effect a complete replacement of the cations initially present in the zeolite. The maximum extent of exchange and the standard free energy of exchange were related to the molecular weight of the entering alkylammonium ions.It is suggested that there was an equilibrium distribution of the exchangeable cations over the different sites (C and D), governed by the nature and affinity of the entering alkylammonium ion and the cation initially present in the zeolite.