Rate-based modelling and simulation of pilot scale distillation column

Abstract

Abstract Batch distillation is perhaps the oldest operation used for separation of liquid mixtures. It is commonly used to produce fine chemicals and specialised products as alcoholic beverages, essential oils, perfume, pharmaceutical and petroleum products. Rigorous modelling of batch distillation can be developed by assuming phase equilibrium, or by rate-based approaches. The last approach represents in a more realistic way the phenomena occurring in the column, since it considers the heat and mass transfer rates for vapor and liquid phases. Due to the nature of their operation, batch distillation columns are modelled by a set of differential and algebraic equations (DAE). The present work concerns the simulation of a batch distillation column using the rate-based model, using a simplified approach for the calculation of the mass transfer rates. The pilot scale column modelled in this work has four trays, a total condenser and a pot. This column was used for separating a mixture of 75% mol methanol and 25% mol ethanol. As a first approach, mass transfer rates are obtained through rate-based simulations in Aspen Plus V8.8 for a pseudo-batch distillation column, using the Ideal thermodynamic model. The set of equations representing the rate-based batch column was solved using a specialized software (Polymath 6.0), taking the mass transfer rates as constant and equal to those obtained in the Aspen Plus simulation. The operating time of the batch column was 80 minutes, the thermal duty was kept as 500 W for the whole operation time, and the final composition in the pot was 72% mol methanol. The proposed strategy allows obtaining the composition and temperature profiles for the column, although it is still necessary to develop a proper mass transfer model to be included in the set of equations.