Carbon-sepiolite pellets

Rodriguez-Reinoso F, Molina-Sabio M, Gonztilez JC. Preparation of activated carbon-sepiolite pellets. Carbon 2001 39(5) 776-779. 

Sepiolite is a fibrous silicate, Sii2MggOjo(OH)4(H20)4, made up of microporous channels parallel to the fiber axis. The chemical composition and stmcture of sepiolite are responsible for good adsorbent behavior towards polar molecules such as water, ammonia, amines and aldehydes in both gas and liquid phases because of its hydrophilic surfaces. Activated carbon is essentially microporous and hydrophobic, making it suitable for nonpolar molecules such as hydrocarbons. As these properties are complementary, a mixture of both could be useful in specific applications such as adsorption of mixtures of molecules. The preparation of discs or pellets is straightforward because in mixtures of carbon and sepiolite, the latter acts as a binder when adding small quantities of water. 

Figure 5.48. Adsorption isotherms of N2 at 77 K for sepiolite, activated carbons, P-thermal activation - steam C-chemical activation, SP-sepiolite-activated carbon pellets (Rodrfguez-Reinoso et al, 2001).

In order to evaluate the behavior of the pellets towards the adsorption of polar molecules, the adsorption isotherms for water vapor in air were determined at 23 °C (Figure 5.49), and show the different chemical nature of sepiolite and activated carbon. Thus, granular sepiolite S exhibits a hydrophilic behavior, whereas the type V isotherm for the activated carbon is typical of a small interaction between the carbon surface and the water molecules at low relative humidity (RH). The water adsorption isotherms, on pellets SP30 and SC30, have an intermediate shape between samples S and P or C. Furthermore, the uptake at each RH is the additive of the humidity adsorption by the individual two components, taking into account the proportion of each one in the mixture. 

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