Foiled again

Materials World magazine
,
1 Sep 2017

Chemists at Queens University Belfast have developed a method to turn used aluminium foil into single-crystalline alumina catalysts for biofuel production. Simon Frost reports. 

‘I have always been inspired by chemistry and I believe that catalysis especially can make the world a better place,’ Queen’s University Belfast (QUB), UK researcher Dr Ahmed Osman Ahmed told Materials World. His new study, published in Nature Scientific Reports, offers a novel process for synthesing highly active mesoporous alumina catalysts from aluminium foil waste – a material that is more often incinerated or landfilled than recycled, as contaminants such as grease and oils can damage recycling equipment.

‘One day I decided to make something good for the environment,’ Ahmed said. ‘I took a walk at QUB’s David Kier building laboratories to find out what is the largest waste material that I could recycle and reuse in something useful.’ He found that around 20,000t of aluminium waste is sent to landfill in the UK alone every year – ‘enough to stretch 770,000km to the moon and back,’ he said. In 2012, roughly a century after the first aluminium foil rolling plant began operation in Switzerland in 1910, the global annual production capacity for aluminium foil was estimated at 4.6Mt.

Alumina is most commonly extracted via electrolysis from bauxite, a mineral that occurs predominantly in tropical and sub-tropical areas. It is largely mined in West Africa, Australia, China, India, the West Indies and South America. Bauxite mining can create significant tailings of red mud – a highly alkaline combination of iron oxides, titanium dioxide, silicon oxide and undissolved alumina – as well as emitting perfluorocarbons and CO2 during production. 

Ahmed and his colleagues at QUB’s School of Chemistry and Chemical Engineering created a method for turning aluminium foil waste into mesoporous alumina catalysts, which are widely used in the production of biofuels such as dimethyl ether from methanol alcohol, a reaction that requires the acidity of a solid acid catalyst. Ahmed claims that his team’s foil-derived catalysts offer better surface and bulk characteristics than commercial alumina, in terms of surface structure (morphology, surface area and pore volume) and surface acidity.

A simple process

To produce them, he dissolved foil waste in different acidic solutions, then kept the solution in a desiccator – a moisture-supressing sealed container – until different single crystallites formed. ‘After the recrystallisation, we decided to prepare the γ-Al2O3 via ammonia precipitation, so that the preparation procedures did not create emissions or waste,’ Ahmed explained. 

The team tested the alumina as a catalyst support for palladium in the methane combustion reaction, with palladium as the active species. ‘The significance of this catalyst system is that it can be used in the after-treatment of natural gas vehicles,’ Ahmed said. ‘There are more than 16 million such vehicles in use, but burning methane as a fuel is difficult due to its high stability. With a global warming potential 20 times that of CO2, any release of unburned methane is problematic. Presently, there are no catalytic converter technologies to treat unburned methane in an engine exhaust.’

Ahmed also claims that no research had previously been performed on the potential preparation of an ultra-pure single-crystalline alumina catalyst from aluminium foil waste, nor its applications in bio-fuel production. The potential environmental benefits of the process are fourfold – diminishing the reliance on virgin aluminium from bauxite mining, reducing the end-of-life waste stream of aluminium foil, providing possible methods for producing biofuel from agricultural waste and treating unburned methane. 

‘The applications of alumina as a support or catalyst are phenomenal,’ Ahmed said. ‘Furthermore, it can be used for cooking and heating as a replacement for propane (LPG), or in transportation as a fuel in cars or even in power generation to produce electricity.’  

To prepare 1kg of alumina catalyst, 265g of foil waste is needed, along with around nine litres each of hydrochloric acid and ammonia solution, amounting to a total cost of £120 per kilogram of the alumina catalyst. ‘The average cost of the commercial alumina catalyst is about £305 per kilogram, so our novel idea can make a highly active catalyst at less than half the cost of currently available commercial catalysts,’ Ahmed explained. ‘The market we could open up in the application of alumina catalysts derived from foil feedstock is phenomenal.’ 

Recyclers’ reservations

Rick Hindley, Executive Director at The Aluminium Packaging Recycling Organisation (Alupro), UK, was impressed by Ahmed’s study, but sceptical of its practical application. ‘It is clearly an interesting chemical process, but it strikes me that it might not be a realistic way to re-use foil – I struggle to see how enough used foil could be collected in the first place to make it a viable process,’ he told Materials World. ‘At Alupro, we would always prioritise the product-to-product processes.’

Over the past few months – between the study being submitted and published – Ahmed and his colleagues have been exploring the application of the modified alumina catalyst in the catalytic converters of natural gas vehicles. ‘Currently, we are seeking funds to improve the catalytic process and then commercialise the products. I have finished my PhD study and am seeking a postdoctoral position to further investigate the synthesis process, before contacting companies with interests in biofuel production and catalytic converters for natural gas vehicles.’ He estimates that another year of research will bring his technology to commercial readiness.  

Ahmed’s key aim is to find ways of producing biofuel from agricultural waste or natural gas less expensively and more accessibly than currently available. ‘I want it to be widely available to a global community and not limited to those who can afford it,’ he said. ‘Using this novel crystallisation method to produce different types of alumina with different structures, each catalyst’s structure and the whole catalyst design can be controlled from the beginning and throughout the process.’

To read the study, A Facile Green Synthetic Route for the Preparation of Highly Active γ-Al2O3 from Aluminum Foil Waste, visit go.nature.com/2vpf950