2014 Membrane Symposium and Poster Day location:Aachen date:08 September 2014
Membrane distillation (MD) is an emerging separation technology, used for separation of non-volatile components from an aqueous stream. The most known application is desalination . The main advantages of MD are: the possibility to use waste heat, the high recovery rates and the easy scalable modules. In contrast to its great potential, the process has not yet been widely accepted in industry. The main problems are the lack of good performing membranes, adequate module configurations and uncertain energetic and economic costs . One way to improve the performance of the membranes is the synthesis of dual layer hydrophilic/hydrophobic membranes . In this contribution, commercially available hydrophilic membranes are coated with different hydrophobic materials, including cheap commercial coatings. Overall treatment of a hydrophilic membrane with a hydrophobic coating results in a single layer hydrophobic membrane structure, while the treatment of only one side of membrane results in a dual layer hydrophilic/hydrophobic membrane structure. The coated membranes have the same membrane morphology as the commercial hydrophilic membrane enabling a comparison between one layer and dual layer membranes. Additionally, the performance of these membranes in direct contact membrane distillation (DCMD) is compared with the performance of commonly used PTFE-membranes. All membranes have a water contact angle above 110° and a liquid entry pressure above 2 bar, indicating excellent wetting resistance. DCMD-experiments are carried out in counter-current, with a flow velocity of 0.13 m/s and feed and permeate temperature of 60°C and 45°C respectively. These experiments reveal an increase of the flux and energy efficiency of the dual layer membranes compared to the single layer membranes for all combinations of coating materials and supports. For the best performing combination, the flux increases from 12 kg/m2.hr for a single layer membrane to 22 kg/m2.hr for a dual layer membrane, while energy efficiency increases from 34% to 63%. Moreover, the flux of the best performing dual layer membrane is 20% higher compared to the standard PTFE membrane. The energy efficiency of the best dual layer membrane is comparable to the PTFE membrane.