Fluidized-bed Melt Granulation: The Effect of Operating Variables on Process Performance and Granule Properties

VELIZ MORAGA, SUSSY; MARTA VILLA; BERTIN, DIEGO; COTABARREN, IVANA; PIÑA, JULIANA; BUCALA, VERONICA

POWDER TECHNOLOGY

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2015 vol. 286 p. 654 - 667

0032-5910

This paper addresses fluid-bed melt granulation (FBMG) for seeds and a binder of the same chemical nature, i.e.with an identical melting point. The purpose of this work is to study the impact of seed size, bed temperature,binder flowrate, and fluidization and atomization air flowrates on process parameters, such as mass balanceclosure, fines deposited on granulator walls and granulation efficiency, and on product properties, such asparticle size distribution, percentages of particles effectively coated or agglomerated and granule crushingstrength, among others. This is done to find the operating regions capable of avoiding lump formation orout-of-specification granule production. This work is focused on operating conditions and seed diameter rangesnot addressed before. In particular, relatively large seed particles compared to the size of the droplets, highbinder/seed mass ratios, and bottom spray are used. The specific method proposed to characterize the granularproduct into three categories (fines, pure coated particles, and agglomerated/coated granules), allowed toidentify the main growth mechanisms for an extended range of operating conditions and seed sizes. Theagglomeration rate was found to increase by decreasing the fluidization and atomization air flowrates and thebed temperature, as well as by increasing the binder flowrate. The agglomerated mass fraction presented anon-monotonic behavior as a function of the seed diameter, with a minimum at a seed mean diameter ofabout 0.26 cm. Even though the operating variables were widely disturbed, the main particle growth mechanismwas pure coating for all the tested conditions. In fact, coated particles accounted for more than 68 wt.% of thegranular product. As a result, the final mass median size remained almost constant for all the studied cases. Onthe other hand, the span of the particle size distribution was extremely sensitive to the selected operatingconditions. This contribution provides some valuable guidelines to avoid agglomeration in melt granulationprocesses designed to produce coated granules.