Studies in vibrofluidized beds and synthesis of silica catalysts

The effect of the solid-circulation rate and pattern as well as the air-gap size on heat-transfer coefficients between a horizontal, cylindrical heater and vibrated beds of Master Beads (spherical alumina) and glass spheres was studied. Solid piles were observed to form at specific bed locations. Solid-circulation paths were directed from the shallowest toward the deepest region of the vibrated bed. For beds in which the solid pile formed above the heating surface, local solid-circulation loops were observed above and below the heater. Air gaps developed at the top and bottom of the cylindrical heater. Heat-transfer coefficients of 140-350 W/m²K in beds of glass spheres and 180-480 W/m²K in beds of Master Beads were determined for a temperature difference of 30°C between the heater and vibrated bed. The trends in the behavior of the heat-transfer coefficient could be explained in terms of a model that accounted for the air-gap size and particle renewal in the layer closest to the heater. Increased solid-circulation rates improved the heat-transfer performance until larger air-gap sizes eventually compromised any increase in solid circulation.

The expansion of the interlayer spacing of H-Magadiite (a layered silicic acid) by the introduction of pillars containing silicon atoms was investigated. A trisiloxane and two trichloroorganosilane compounds were used as the pillaring agents. The interlayer space of H-Magadiite was successfully expanded by pillaring with trichloroorganosilanes. The minimum dimensions of the pores that access the interlayer space of the pillared compounds were determined as being 6.2 Å and 9.5 Å (dimensions at perpendicular directions). Pillaring of H-Magadiite at low pH and temperatures close to 0 °C yielded the highest surface areas, e.g., increasing the surface area from 35 to 130-200 m²/g. The pillared compounds were found to be thermally stable up to temperatures of 650°C.