Solid/liquid extraction of caffeine from guaraná with methylene chloride/Extracción solido-liquido de cafeina de guarana con cloruro de metileno

Methylene chloride decaffeination processes for ground and whole guaraná seed cores were evaluated. Ground seeds were contacted with solvent in shaking flasks in a controlled temperature water bath. The experimental design included three solid/liquid ratios [1:4, 1:6, 1:8 (w/w)] and two temperatures (25 and 30°C). Caffeine was also extracted from 100 g batches of whole seed cores in a solid/liquid packed bed extractor with a solid/liquid ratio of 1:50 (w/w); this was used with three solvent flow rates (436, 522, and 667 ml/min) at two temperatures (21 and 30°C). For optimal extraction of caffeine from the ground seeds a solid/liquid ratio of 1:6 was adequate at 30°C (- 90% extraction after 23 h) but not at 25°C. However, with a solid/liquid ratio of 1:8 the temperature effect was not significant ( p < 0.05), both temperatures yielded a 93% extraction after 23 h. Caffeine was extracted from unground seed cores at a lower rate because of decreased contact surface area and a greater radial mass transfer distance. At 21°C, there was no significant difference (p > 0.05) between extraction rates with solvent flows of 522 and 667 ml/min. This indicated that caffeine diffusivity was limiting mass transfer and boundary layer effects had become negligible. Caffeine extraction at 30°C continued to increase with solvent flow because of a higher diffusivity. Diffusivity values calculated from the mass transfer model were 0.29 x 10 -6 cm 2 /s at 21°C and 0.95 x 10 -6 cm 2 /s at 30°C. For industrial applications, design of a solid/liquid packed bed extractor with high solvent flow and temperature capability would probably be economically justified.