Investigation on the pore structure of binderless zeolite 13x shapes

In the last few years novel binderless molecular sieves as high-performance materials were introduced into technical adsorption processes. Besides of the 100% active adsorption matter such material exhibits an advantageous secondary pore system. In this paper a more detailed investigation of the structure and the generation thereof is presented. To characterize the pore structure of the system SEM, EDX, Hg-porosimetry, as well as adsorption measurements (N-2 and CO2) were used. For additional investigations XRD and XRF were applied. As a result of the special manufacturing process - granulation of zeolite NaMSX powder with metakaolin/caustic under high energy input followed by an alkaline treatment - two different types of zeolite morphologies were obtained: On the outer surface of the beads typical octahedral zeolite X crystals are monitored as a result of conventional and epitaxial crystal growth. In contrast the interior of the beads exhibits polycrystalline structures consisting of zeolite X in untypical shape, which is most probably the result of zeolite formation in dense matter. Due to the confined space conventional and epitaxial growth is inhibited. Obviously the original zeolite crystals are intergrown by polycrystalline zeolite NaMSX matter originated from converted metakaolin, and by the way forming macro pores. Said structure formation is the cause for the surprisingly high mechanical stability of the binderless shaped bodies. The existence of the superior secondary pore system and the high mechanical stability of binderless type NaMSX shapes can be explained as result of different pathways of the conversion of metakaolin into zeolite matter due to the existence of areas of different densities after the granulation process. (C) 2011 Elsevier Inc. All rights reserved.