Performance evaluation of membrane distillation configurations: Process conditions and membrane selection at lab scale

In membrane distillation, a variety of methods is used to impose a vapor pressure difference over the membrane, which is the driving force in membrane distillation. While a huge amount of papers can be found on modelling, membrane synthesis or application testing of a specific configuration, only a few papers compare the performance of two or more configurations. In this contribution, the flux and energy efficiency of a lab scale direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD) with a 2 mm gap, permeate gap membrane distillation (PGMD) with a 2 mm and 0 mm gap thickness and vacuum membrane distillation (VMD) were compared using the same driving force. To cover different applications, a number of process conditions were tested using a design of experiments. A high and low level for temperature difference (15 and 35°C), flow velocity (0.13 and 0.26 m/s) and salinity (0 and 150 g/l) were selected. Three different membranes were tested, including a supported PTFE membrane and two unsupported membranes from PE and PP. The highest flux was observed for VMD, followed by DCMD, PGMD and AGMD (Figure 1). It was also observed that the different configurations are not equally sensitive to the applied process conditions. Moreover, it was found that the optimal DCMD membrane differs from the best performing membrane of other configurations.status: publishe