Natural clay binder based extrudates of mesoporous materials: improved materials for selective adsorption of natural and biogas components

Abstract

The effects of natural clay binder based extrusion, on the selective adsorption properties of mesoporous materials were investigated in context of natural gas and biogas purification. Two mesoporous adsorbent materials, namely porous clay heterostructures (PCH) and MCM-41 were shaped into cylindrical extrudates, using a natural montmorillite clay binder. The effect of extrusion with clay binder was evaluated in three steps; (i) effects on structural properties, which were studied with low temperature nitrogen adsorption and XRD techniques; (ii) effect on adsorption capacity, which were evaluated with high pressure adsorption isotherms (up to 1000 kPa) for three main natural gas and biogas component gases which are CO₂, C₂H₆, and CH₄; (iii) effects of extrusion on selective adsorption properties of materials were investigated, for two commercially significant binary separations (CO₂/CH₄ and C₂H₆/CH₄). Results show that, in general, extrusion caused an increase in mesoporosity of the final material; but in the case of MCM-41, an increase in microporosity has also been noticed. The order of maximum adsorption was found to be CO₂ > C₂H₆ > CH₄ with each material and the capacity of adsorption decreases to a different extent (dependent on gas) on extrusion. Variation in selectivity of these materials with pressure was studied and discussed. Both extrudates show satisfactorily high selectivity values than minimum requisite for an adsorbent to be used in separation process. However among all the four materials, the extrudate of MCM-41 was found most suitable, in terms of separation possibilities/applications.