Study of a microwave assisted vacuum drying process applied to the granulated pharmaceutical drug hydrochlorthiazide

• Published in: The Journal of microwave power and electromagnetic energy Vol. 40; no. 4; p. 241
• Main Authors: Berteli, Michele N, Marsaioli, Antonio Júnior, Rodier, Elisabeth
• Format: Journal Article
• Language: English
• Published: United States 01-01-2007
• Subjects: Absorption; Adsorption; Calorimetry; Chemistry, Pharmaceutical - methods; Equipment Design; Hydrochlorothiazide - chemistry; Kinetics; Microwaves; Pressure; Solvents; Technology, Pharmaceutical - methods; Temperature; Time Factors; Vacuum
• ISSN: 0832-7823
• DOI: 10.1080/08327823.2005.11688542

Drying processes have evolved considerably over the years, aiming at the best conditions to shorten the processing time, but maintaining the highest final product quality. The application of vacuums to the microwave drying process might be interesting, especially for thermally sensitive products because the reduced boiling point of the solvent allows a lower temperature processing. The objective of the present work is to study and evaluate the process of drying a granulated product that is the basis of the drug hydrochlorthiazide, with an initial moisture content of 21% in dry basis. This study monitored the drying kinetics, product temperature and power absorbed by the sample using a bench scale vacuum microwave dryer. The equipment consisted of a cylindrical pressure vessel crossed by a wave guide, setting up a system whereby the vacuum pressure, the sample weight and the incident, reflected and residual microwave powers could be measured and evaluated, throughout the entire process. The experimental runs were established with an approximate incident microwave power at 20 W for absolute pressure levels of 50 and 75 mbar, working with samples of about 1.4 g. It was observed that the vacuum microwave process kinetics at both pressure levels showed little difference. The processes were carried out almost entirely in a regime of water evaporation, the product's temperature remaining below the solvent boiling temperature. The drying times were similar for both processes, whereas the absorbed power was slightly higher at the pressure of 75 mbar.