Screen test

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Inorganic nanomaterials are used in a wide range of applications, from fuel cell and battery components through to sunscreen, speciality chemicals and dielectric and magnetic materials.

All these applications need the powdered chemicals to exhibit consistent quality and nanoparticle properties. The challenge for suppliers is maintaining these standards while increasing production volumes.

Leeds University and University College London (UCL) are collaborating to scale up continuous hydrothermal flow synthesis (CHFS), a laboratory method for producing nanomaterials, to industrial capacity.

Principal investigator Prof Xue Wang, from the Institute for Particle Science and Engineering at Leeds, said: 'Our purpose is to develop a methodology that can guarantee the product can be made on the large scale at the same quality as in the laboratory.'

While Leeds will measure and model the process, UCL will concentrate more on the physical side, making the materials and building and adjusting the reactor.

Dr Jawwad Darr, soon to take on a readership in chemistry at UCL, originally developed the CHFS system at Queen Mary, London. Its advantages over other methods include that it is a green technology, using supercritical water instead of organic solvents. It also uses inexpensive metal nitrate salts as precursors and it produces high-quality nanomaterials in fewer steps than conventional methods.

'The quality of the nanomaterials it makes is very good,' said Wang. 'The particles vary by only a few nanometres, which has attracted a lot of interest from industry.'

Although consistent, high quality can be achieved in the laboratory, industrial production will require 10 to 100 times the capacity.

'When it comes to scaling up, the challenge is not just to make a reactor that is bigger,' said Wang. 'A lot of things change on a larger scale, for example hydrodynamics, which can affect the mixing of the materials, the feed transfer and the reaction mechanism, making it difficult to achieve the same quality.'

Darr added: 'The good thing is we'll be able to modify the mixing arrangement and try out different approaches. It'll be flexible enough that on a lab scale we can create a totally different mixing arrangement in a matter of minutes.'

The Leeds researchers will use techniques such as process analytical technology, data mining, chemometrics and multi-scale modelling to study the controlled manufacture of chemicals. They will develop technologies to measure how variables, such as the size of the particles, change in real time as factors such as temperature and catalytic activity are varied. These will be incorporated into their model.

The team will use on and offline techniques to try to develop relationships on how the operating conditions and feeder properties will affect product quality. Online techniques involve putting sensors into the process and measuring variables such as temperature and pressure in real time.

'Particle size distribution is probably the most important variable for product quality,' said Wang. 'At the moment, there is no reliable technique to measure them in real-time. So we are investigating methodologies like dynamic light scattering.'

This will lead to online management techniques to support product quality during industrial-scale production.

The project will run for three years and be carried out with a number of industrial partners involved in the manufacture of nanomaterials, including Malvern Instruments, Johnson Matthey and Advanced Material Resources.

One of the first nanomaterials the researchers will investigate is titanium dioxide, which is used in photocatalysts and sunscreen. A pilot plant will be built at UCL, then it will be scaled up and controlled manufacturing instruments will be introduced to apply the methodology. When this is achieved, the team hopes to work on a spectrum of materials that are of interest to the industrial partners.

'We're hoping that by providing them with enough quantities of material they would decide to commission a full-scale plant in the future,' said Darr. 'We need to be able to show that when we scale it up to this extent you can still get very good-quality powders that you can incorporate into your products.'

The next step will be to apply what has been learnt to build a generic approach to the scaling up processes. 'The role is to understand the operation envelope of the reactor and this means trying to understand how what you change in the process affects the product that you get out,' said Darr.

'That's a challenge, as you're trying to build up a predictive capability. If you know what the parameters are, you should be able to calculate what the product's going to be like.'