Mass transfer coefficients of eurycoma longifolia batch extraction process

Eurycoma longifolia, or Tongkat Ali as it is locally known is a traditional Malay herb available as a spray dried water extract for the nutritional supplement market. The yield of the extract is dependent on the quality of the raw materials and the operating conditions of the batch solid-liquid extraction process. The yield can be increased by optimising the operating parameters of the batch solid liquid extraction process such as solvent, solvent to raw material ratio, particle size, temperature, duration, and agitation rate. To optimise the operating parameters a mathematical model of the extraction process needs to be developed. The partition coefficient, K, the initial solid concentration, C'o, solid diffusivity, Ds and overall diffusion coefficient, k' were evaluated. The operating parameters studied were the effects of extraction temperature and particle size. The range of parameters studied were 60°C to 100°C for temperature and 0. 5 mm to 4mm for particle size. The extractions were carried out for 2 hours with a solvent-to-raw material ratio of 25:1 w/w determined from preliminary experiments. The solute partition coefficient, K, was 0.818 and the initial solid concentration, C’o, was 0.0150 g/ml. Solid diffusivity, Ds, was the rate limiting factor in the extraction process and was found to increase from 5.0 x 10(-12) to 1.3 x 10(-10) m2s-1 with increasing particle size but did not have a clear relationship with temperature. The comparison of the overall diffusion coefficient, k’, values calculated through the dynamic mass balance equation as well as solid diffusion rate limiting step assumption equation revealed similar values confirming that solid diffusion is rate limiting.