Kolorimetrische bepaling van gerstpolyfenolen Enzyminhibitie en bijdrage tot de troebelgenese in een proanthoc yanidinevrij bier

SIGLEKULeuven Campusbibliotheek Exacte Wetenschappen / UCL - Université Catholique de LouvainBEBelgiu

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

Application of hydrophobic coatings on commercially available hydrophilic membranes for direct contact membrane distillation

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 [2]. 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.status: publishe

Benchmark study on algae harvesting with backwashable submerged flat panel membranes

The feasibility of algae harvesting with submerged flat panel membranes was investigated as pre-concentration step prior to centrifugation. Polishing of the supernatant coming from the centrifuge was evaluated as well. The effect of membrane polymer (polyvinyl chloride [PVC], polyethersulfone polyvinyl-pyrollidone [PES-PVP], poly vinylidene fluoride [PVDF] ), pore size (microfiltration [MF], ultrafiltration [UF]), algae cell concentrations and species were investigated at labscale. In addition, backwashing as fouling control was compared to standard relaxation. PVDF was the superior polymer, and UF showed better fouling resistance. Backwashing outperformed relaxation in fouling control. The backwashable membranes allowed up to 300 % higher fluxes compared to commercial flat panelbenchmark (PVC) membranes. Estimations on energy consumption for membrane filtration followed by centrifugation revealed relatively low values of 0.169 kWh/kg of dry weight of algae compared to 0.5 kWh/kg for algae harvesting via classical centrifuge alone.status: publishe

Application of a hydrophobic plasma coating on commercially available hydrophilic membranes for direct contact membrane distillation

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 costs. In this contribution, a commercial hydrophilic membrane is coated with a hydrophobic top layer using atmospheric plasma technology. The performance of these membranes in DCMD has been compared with the performance of commonly used and commercially available PTFE-membranes. The coatings and therefore the membrane properties have been optimized as a function of the nature of the chemical precursors and the different process parameters such as activation step, dissipated power, plasma carrier gas or gas flows. Additionally, changing the plasma treatment time for the most promising coating has enabled to link the coating thickness to the membrane performance in direct contact membrane distillation (DCMD).status: publishe

Wetting Resistance of Commercial Membrane Distillation Membranes in Waste Streams Containing Surfactants and Oil

Water management is becoming increasingly challenging and several technologies, including membrane distillation (MD) are emerging. This technology is less affected by salinity compared to reverse osmosis and is able to treat brines up to saturation. The focus of MD research recently shifted from seawater desalination to industrial applications out of the scope of reverse osmosis. In many of these applications, surfactants or oil traces are present in the feed stream, lowering the surface tension and increasing the risk for membrane wetting. In this study, the technological boundaries of MD in the presence of surfactants are investigated using surface tension, contact angle and liquid entry pressure measurements together with lab-scale MD experiments to predict the wetting resistance of different membranes. Synthetic NaCl solutions mixed with sodium dodecyl sulfate (SDS) were used as feed solution. The limiting surfactant concentration was found to be dependent on the surface chemistry of the membrane, and increased with increasing hydrophobicity and oleophobicity. Additionally, a hexadecane/SDS emulsion was prepared with a composition simulating produced water, a waste stream in the oil and gas sector. When hexadecane is present in the emulsion, oleophobic membranes are able to resist wetting, whereas polytetrafluoretheen (PTFE) is gradually wetted by the feed liquid

Hydrophilic/hydrophobic composite membranes for membrane distillation

Membrane distillation is an emerging separation technology, used for desalination. The mass and heat transfer through the membrane depends on membrane structure and process conditions. In this contribution, hydrophilic membranes are coated with different hydrophobic materials. Immersion of the membrane in the hydrophobic solution results in a single layer hydrophobic membrane structure, while coating the solution only on one side of membrane results in dual layer hydrophilic-hydrophobic structures. All membranes have the same pore size, porosity and tortuosity and therefore, a good comparison can be made between one layer and dual layer membranes. Direct contact membrane distillation experiments reveal the improved performance of the dual layer membranes compared to the single layer membranes.status: publishe