A coffee machine, a water softener or an artificial kidney machine: they all use the same technology: membranes, or filters with tiny holes capable of separating even the smallest molecules. They can be used to purify water or air, generate and store green energy, but also produce nutrients or pharmaceutical compounds. The bioengineers of KU Leuven are conducting research on the newest generation of membranes.
“We don’t realise it, but membranes are a big part of our daily life. A teabag or a coffee capsule is a membrane, as is the oil filter in your car, or the Gore-Tex coat that lets through vapour - your sweat - but is waterproof. In planes, membranes provide oxygen-rich air for the passengers and nitrogen-rich air to prevent explosion of the kerosin tank. And during kidney dialysis, the blood flows along a membrane that filters out harmful substances”, explains Professor Ivo Vankelecom of the KU Leuven cMACS research group (Centre for Membrane Separations, Adsorption, Catalysis And Spectroscopy for Sustainable Solutions).
Membranes are filters that separate substances from each other: they let through one substance and block another, just like your typical coffee filter. But the membranes the researchers are working with are of a different nature: “They’re high-tech nanomembranes. We start from a polymer – a synthetic material – in which we create minuscule nanopores – a billionth of a metre or even smaller – that are often invisible, even under the best electron microscope. Certain particles pass through such a membrane faster than others, effectively separating them from each other.”
The research group already developed a similar membrane for biogas. “You can extract biogas when organic waste, such as vegetable, fruit and garden waste, starts to ferment. The bio-methane in this gas can be used to generate electricity, run your car or heat your house. But methane is never found in its pure form. The biogas, for instance, contains a good amount of CO2 – the greenhouse gas carbon dioxide. To separate the bio-methane from CO2, membranes are used in most cases. Our research group has recently developed a membrane that requires less pumps and less electricity to realise this separation. We’re now looking at how we can apply this technique on a large scale, allowing it to be used in the industry as well.”
There are various other uses for membranes as well: “We're working on membranes that turn sea water into drinking water using less energy and chemicals, or membranes that battle climate change by separating CO2 from nitrogen. Even batteries contain membranes. We’re currently part of a big European project centred around making batteries that don’t contain metals, but work with paper waste. The pharmaceutical and medical sectors also provide many opportunities. Membranes can be found in quick diagnostic tests, such as the Predictor pregnancy test, for instance.”
No chemical waste, less energy
In recent years, the researchers have already developed and patented several membranes for this array of applications. “We’re now testing them further so that they can be used in both the lab and the industry, and possibly produced on a large scale. In general, the advantage of membrane technology is that it’s very environmentally friendly: there are no waste streams, and less energy is used than in more conventional separation methods, sometimes even 100 times less.”
Many companies that are interested in membranes come to Professor Ivo Vankelecom's research group. This has to do with a new pilot-line for membrane production that was recently installed at KU Leuven. “It's called the Smartcoater 300 and it's actually designed to make coatings for the paint and textile industry. But we’re using it to make membranes. It’s unique for a university to have such a pilot installation, as it costs around one million euros. Luckily, we were able to call upon an industrial sponsor. This equipment is a crucial step between the lab and the manufacturing hall. Many companies want to come here to use this equipment, and then test the membranes for their separating properties. Our testing equipment allows us to simultaneously test over 100 membranes in our lab”, says Vankelecom.
The equipment is 8 metres long and 2 metres high and can industrially produce membranes per running metre. “The end product sort of resembles a roll of wallpaper. We apply a polymer coating on a support layer, after which this layer is physically and/or chemically treated to actually realise the separation at the nanoscale. We sometimes also mix in nanomaterials to further improve the separating properties. You can actually best compare it to a car wash: the layer goes through an oven, a water bath, an air blower to dry, sometimes a sunbed with UV radiation, etc., and is then rolled up. Depending on the treatment, you get a membrane with very specific properties, for instance one that is suitable for brewing a new drink.”
The installation already produces such a support layer. “However, a layer that was stable in extreme conditions and that could be used to deposit quasi any type of selective layer didn't exist yet. We have now developed this type of polyvalent support layer, partly in collaboration with another industrial partner, and will start commercialising it. We're already supplying it to labs at universities abroad. The product is a first step: we will now use this support layer to finalise the membranes for the many other applications.”