Effect of process variables on volumetric mass transfer coefficient in wet purification of crude biodiesel

Abstract

ABSTRACTIn this study, the effect of process variables on the volumetric mass transfer coefficient (Kca) of residual solutes in biodiesel during wet purification was investigated. A purification process was carried out using distilled water batch-wise at varying washing times, temperatures and biodiesel-to-water (BW) ratios. The amounts of solutes in biodiesel and water phases were determined at each washing stage using standard methods. The linear driving force kinetic model equation was used to estimate the Kca. The concentration of solutes in the crude biodiesel were 12.02 mg/dm3, 0.0168%, 0.00159% and 0.02749% for catalyst, methanol, soap and glycerol, respectively. Using a BW ratio of 1:2, a time of 30 min and a temperature of 40°C in a single-stage washing process, optimum solute removal was achieved. A minimum of 250 cm3 of water sufficiently washed 100 cm3 of the biodiesel in a five-stage washing process at 40°C to achieve a solute concentration of 0.13 mg/dm3, 0.002 × 10(-4)%, 0.13 × 10(-4)% and 0.057 × 10(-4)% for catalyst, methanol, soap and glycerol, respectively. There was increase in Kca as the BW ratio was decreased from 2:1 to 1:4. The Kca also increased as the temperature was increased from 30 to 50°C.