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Better understanding of continuous chemistry performance

17 Dec 2014

Efficient use of raw materials, better product quality and energy savings: these are important benefits of smart process technology. In recent months TNO has been comparing two continuous reactors in collaboration with the University of Toulouse. Thanks to the knowledge gained, companies wishing to switch from batch chemistry to continuous chemistry can calculate the pros and cons in a trial.

The Helix Reactor

‘We’re developing process technology that provides better material and energy efficiency than the existing processes’, says Dr Mark Roelands of TNO. ‘Many chemical plants still use batch processes. They can be fine, but you don’t have much control over reaction conditions, especially in multi-phase reactions. That’s much easier in a continuous process. If you’re dealing with a single phase – 100% liquid – we can put continuous chemistry into practice fairly easily. But as soon as you have more phases – with bubbles, droplets or particles – it gets more complicated: then you need equipment to simulate the movement of the stirrer, for example generating additional vortices by means of smart obstacles. We decided to look into that in the Flow Connect project. We had two technologies in mind: the Oscillating Baffled Reactor (OBR) and the Helix Reactor.’

Visit from Toulouse

‘The OBR is a commercially available tube with baffles’, Roelands explains. ‘You superimpose an oscillation on the flow using a pulsating pump that makes ten steps forwards and nine steps backwards, as it were. In other words, a lot of movement but just a small amount of transport. You can also increase the temperature, as the reactor is enclosed in a heating mantle. Looking for an organization that has knowledge of this we found Alex Mazubert, a PhD student at the University of Toulouse, where they’re doing research into the re-use of used frying fat. As Alex “only” had access there to a glass reactor that he could heat to 80ºC at a pressure of 2 bar, he was happy to come to the Netherlands for a few months and use our steel reactor, which can handle up to 160ºC and pressures of at least 10 bar.’

Chugging reactor

As well as the effects at higher temperatures, Mazubert is interested in the selectivity of the reaction. Roelands goes on: ‘Alex assembled the system, and after a few hiccups he soon had it working – it looked great. Under pressure a reactor of this kind chugs at a frequency of 1 hertz. It’s a bit like continuous deep frying: two cold liquids are mixed and given a good shaking while being heated very rapidly. After about 20 minutes’ residence time, with a cooler at the end of the tubes, the pressure is released and we collect the product. While experimenting, Alex varied some parameters and carried out measurements. He got conversion rates of over 50%. That’s presumably the maximum we can achieve with this equilibrium reaction. To increase the conversion rate the reaction water needs to be removed in situ. Our own team then continued the work by building in the Helix Reactor.’

The great thing about TNO

TNO’s Helix Reactor, based on a spiral tube, is particularly suited to temperature-sensitive and shear-sensitive reactions, especially multi-phase reactions. ‘Just as with the OBR we used it to collect data. The result is a benchmark for off-the-shelf technology and our own technology, which enables us to compare the performance of technologies for companies in a trial and offer them some process optimization. I think it’s fantastic that we have a continuous process that achieves conversion. The young PhD student provided the input and our team of technicians and scientists helped him. For me that’s the great thing about TNO: all of us getting something to work – that performs and has market potential – in only a short time.’

Interested in a trial?

Please contact Mark Roelands

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