Caracterização fisica e secagem do acido 2-hidroxibenzoico em leito fluidizado agitado mecanicamente em leito fluidizado pulsado rotativo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

This work has as primal objective the study of the viability of the use of two modified fluidized beds, the mechanically agitated fluidized bed and the rotated pulsed fluidized bed, in the drying of 2-hydroxibenzoic acid. Physical characterization analyses of the solid were conducted in order to provide useful information for the study of the drying process, since no such data was available in literature. The 2-hydroxibenzoic acid is widely used in the pharmaceutical industry due to its analgesic properties. The solid acid commercially available presents moisture content around 2,000ppm, particle size in the 53 - 355 _m range and true density of 1.443 g/cm3. The cohesive nature ofthe wet 2-hydroxibenzoic acid hampers its fluidization in the conventional system. Fluidization can be achieved by modifying the conventional system to prevent channeling of the bed and improve solid movement. In the present work two different modification strategies were tested, the addition of an internal mechanical agitator and the pulsation of the gaseous flow. The solid has pores in the mesopore range as determined by mercury porosimetry, which means its moisture is primarily superficial. The determinations of pore diameter range and thermogravimetric curves assisted in the choice of the drying gas temperature. During the drying of the solid, since the moisture is superficial, its temperature remains c1ose to the wet-bulb temperature and only begins to rise afier the water has evaporated, allowing the use of a gas temperature higher than the solid sublimation temperature of 76°C. The fluidization dynamics of the dry solid in both the conventional fluidized bed (LFC) and LFPR were analyzed determining the pressure drop versus gas flow curves. In the studied conditions, the LFPR fluidization curves were smoothed compared to the LFC as the rotation frequency increased. These results agreed with those published elsewhere (ELENKOV and DmRKOV, 2000; DmRKOV, 2001). The study of the drying in the LFAM, initiated by AMBROSIO (1999), showed that, during the drying process, the agitation can be interrupted when the moisture content of the solid is about 0.7% d.b., afier which point the conventional fluidization system suffices. The drying curves showed the existence of two distinct periods, a falling rate period and a constant rate one, in the drying process, which ended with the solid reaching a moisture content of about 2,OOOppm. The drying curves for the LFPR exhibited similar behavior. Therefore, both the LF AM and the LFPR equipment were found to be efficient in the drying of the 2-hydroxibenzoic acid. Particle sized distributions and SEM microphotographs were used to compare the solid dried in this work with the commercially available solid. The LF AM and LFPR break the crystals to a lesser extent than the currently industrially employed drying equipment, the pneumatic flash dryer, producing solids with larger dimensions and therefore better fluidity. The determined values of the Carr s lndex and the Hausner ratio verified the better fluidity of the dry solids from this work

ASSUNTO(S)

particulas fluidização secagem

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