Pore analyses of highly porous diatomite and clay based materials for fluidized bed reactors

Abstract

Microstructure of diatomite-clay based granulates for fluidized bed reactors, heat treated at 800 and 1300 °C, were investigated by mercury porosimetry, nitrogen sorption using Barrett–Joyner–Halenda (BJH) model and scanning electron microscopy. Special considerations were made on characterisation of ink-bottle pores by performing a multi-cycle porosimetry. The comparison between extruded granulates and pure diatomite powders revealed that diatom structure is still intact after high shear process and that pore size distribution of the extrudates is mainly dominated by diatom structures. A mercury retention factor of 0.62 and 0.92 at 800 °C and of 0.99 and 0.98 at 1300 °C were obtained for Filter Cel and Super Cel powders, respectively. While, a retention factor of 0.28 and 0.91 has been found out for extrudates heat treated at 800 and 1300 °C. These data permits to determine the pore network heterogeneity. Coalescence of diatom frustules at 1300 °C leads to a decrease of pore volume in the meso- and macro-range when compared to at 800 °C, whereas the ink-bottle pore size did not change significantly. Apparition of large macropores occurred at 1300 °C caused by a higher shrinkage of diatoms compared to clay.