Screening of pervaporation membranes with the aid of conceptual models: An application to bioethanol production

Abstract

In this paper, we assess the performance of a given hydrophobic membrane from the conceptual design of a hybrid process formed by the hydrophobic membrane itself and the separation train located downstream. To this end, a single pervaporation experiment with a model ethanol?water mixture is needed to estimate the minimum area requirement of the hydrophobic membrane. Short-cut methods, on the other hand, can be used to estimate the minimum number of stages and reflux ratio of the distillation column. Estimation of the minimum area requirement for a hydrophilic membrane, which is considered to overcome the azeotropic composition, requires the integration of a spatially one-dimensional isothermal mass transfer model of the unit until the desired biofuel purity is achieved in the corresponding retentate stream.The idea behind the approach is that the performance of a given membrane must be measured taking into account the overall hybrid process given that the hydrophobic membrane itself performs only a part of the desired separation.The hybrid process is then assessed on the basis of a cost estimate using the minimum membrane areas of the two membrane units together with minimum number of stages and minimum reflux ratio of the distillation column among other structural and operating variables.The outcome allows for the screening of pervaporation membranes, and yields valuable insights into the nature of the process as well as the constraints that a hybrid process may face. Membranes can be assessed based on their overall process performance by this method; only the subset of membranes presenting the best economic figures can be considered for a further analysis.