The objective of this study was to develop a mathematical model of the mass transfer in a modified
brewery tank for producing fuel ethanol. To reduce fossil fuel consumption, 50 flat-plate solar collectors
were used as the heat source for the two stages of a distillation process for increasing the ethanol
concentration. A 350-L distillation tank with 10%v/v (Stage 1) and a 70-L distillation tank with 40%v/v
(Stage 2) were employed in the experiment used to develop the mathematical model of the mass
transfer. A difference of approximately 10% was observed between the model predictions and the
experimental results of the distillation product of Stage 1, whereas the predicted concentration was
approximately 30% higher than that of the experiment, although this was reduced to approximately 5%
by homogeneous mixing of the solution. Regarding the distillation process of Stage 2, there was
approximately 10% difference between the predicted and experimental products, and approximately 3%
difference between the predicted and experimental concentrations. The differences are attributed to
errors in the heat transfer rate prediction of the model, which varies directly with the solar radiation
values.