Organoclays: Preparation, characterisation and use as sorbents and catalysts.

WATSON, Ruth. (1997). Organoclays: Preparation, characterisation and use as sorbents and catalysts. Doctoral, Sheffield Hallam University (United Kingdom)..

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Abstract

This thesis reports the interactions of (poly)cations with a variety of clay minerals and the application of the resultant organoclays as both sorbents and catalysts. The behaviour of organoclays containing tetramethylammonium cations (TMA[+]), is compared to the behaviour of organoclays containing polycations of the formula [(Me[2]NCH[2]CHOHCH[2])[n]][n+] (Magnafloc 206), which are shown to form two distinct types of organoclay. To investigate the interactions of the (poly)cations with clay surfaces, several dry powder analysis techniques have been employed including Kjeldahl nitrogen analysis, variable temperature x-ray diffraction and thermogravimetric analysis. The studies have shown that the (poly)cations reside between the clay layers and that the nature of the clay and the resident exchange cation have a significant effect on the amount adsorbed. It is also shown that the polycations have a higher affinity than tetramethylammonium cations for all the clay minerals investigated. Sorbents exchanged with various amounts of (poly)cation are investigated for their ability to adsorb benzene and rho-nitrophenol from water. The adsorption by polycation containing sorbents is reduced compared to TMA[+] containing sorbents and the latter is comparable with that reported in the literature. The adsorption site in such sorbents is the siloxane surface in the clay interlayers, as shown by the observation that the uptake of both benzene and / rho-nitrophenol by TMA[+] exchanged SAz-1, a high charge montmorillonite, was reduced compared to TMA[+] exchanged SWy-1, a low charge montmorillonite. In SAz-1 there is closer packing of adsorbed TMA[+] cations resulting in less siloxane surface area being available. Hydration of the TMA[+] cations also increases steric constraints. High polycation loadings prevent the clay layers from expanding and thus accessibility of rho-nitrophenol to the clay surface is reduced. Partition into the organic carbon content of the polymer occurs but uptake does not increase with organic carbon content as expected. Also, TMA[+] exchanged Westone-L was expected to behave similarly to TMA[+] exchanged SWy-1 as Westone-L and SWy-1 have very similar cation exchange capacities. However, it is shown that TMA[+] exchanged Westone-L behaves more like TMA[+] exchanged SAz-1 which has a much higher cation exchange capacity. A range of organoclays containing either tetraalkylammonium cations or polycations at differing exchange levels have been subjected to acid leaching at either 25 or 90°C. The activity of these acid-activated (poly)cation-exchanged clays for the conversion of alpha-pinene to camphene and limonene was determined and compared with those from clay samples (without (poly)cations), acid-treated in the same manner. The presence of the polycation had a more marked influence on the activity of samples derived from SAz-1 than for corresponding samples derived from SWy-2, which was attributed to the increased hydrophobicity of the polycation loaded clay. Comparable yields for SWy-2 in the absence and presence of polycation suggest that SWy-2 disperses well in the nonpolar alpha-pinene. Also, octadecyltrimethylammonium and dodecyltrimethylammonium exchanged clays were generally less active than TMA[+] exchanged clays which were comparable to the most active polymer containing catalysts. It has also been shown that the octahedral iron content of the clay affects its catalytic activity. Finally, a competitive adsorption method of catalyst preparation has been developed which may replace more conventional high temperature techniques.

Item Type: Thesis (Doctoral)
Additional Information: Thesis (Ph.D.)--Sheffield Hallam University (United Kingdom), 1997.
Research Institute, Centre or Group: Sheffield Hallam Doctoral Theses
Depositing User: EPrints Services
Date Deposited: 10 Apr 2018 17:22
Last Modified: 07 Jun 2018 11:54
URI: http://shura.shu.ac.uk/id/eprint/20504

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