Microbubbles method benefits biofuel production

Microbubbles of around 50–500 microns in diameter are highly valued for gas and energy transfer due to their considerable surface area per unit volume.

They are not a new invention but Sheffield University spin-out Perlemax has patented a novel fluidic oscillator to create them more efficiently.

Perlemax founder and engineering professor Will Zimmerman said: ‘Basically we push gas just enough to displace the water needed to create the interface and the bubble. The concept is you use a packet of gas about the same size as the pore and the result is that you get a bubble about the same size — the smallest we’ve gone down to is an average of 28 microns.

‘It’s hard to imagine you could come up with a more energy-efficient way of making bubbles of those sizes.’

Alternate methods revolve around compressing gases into liquids then transferring the saturated liquid into a pressurised liquid to nucleate microbubbles, which is very expensive.

Zimmerman believes the Perlemax fluidic oscillator can save 90–95 per cent on running costs and a considerable amount on capital, since the unit costs only around £100 to make.

He said the newly formed company is investigating around 50 separate applications but the closest to market are for biofuel and biogas manufacture. Biofuel reactors need gas exchange for input of nutrients, namely CO₂ and removal of byproducts, chiefly oxygen. While CO₂ can be pumped in at a rate that exceeds the metabolic demands of the algae, oxygen removal has proved more difficult.

’If you use smaller bubbles you also extract the oxygen produced by the algae, which stunts its growth and eventually kills it. Our field trials have shown supra-exponential growth,’ Zimmerman said.

Biogases, meanwhile, are readily available from landfill sites and wastewater treatment plants but are typically 60 per cent methane and 40 per cent CO₂, giving a poor burn.

Currently water scrubbing is used to remove some CO₂, but that requires a lot of electricity and microbubbles can potentially provide a much more efficient alternative.

In addition, Zimmerman recently published data on a potential medical application for the precise delivery of drugs.

’You immobilise a drug on the surface of small microbubbles. These bubbles move throughout the body by ultrasonic focusing — sort of like using tweezers — by picking up the bubbles with an ultrasonic field and then releasing them at the point where you want the drug to be delivered by collapsing the bubble.’

Most recently, Perlemax has been in consultation with an aquafarm in Ireland. Zimmerman said: ’Fish farms have a tremendous requirement for oxygen, if you don’t oxygenate them very well, the fish just linger, they don’t thrive.’

Perlemax’s technology has the potential for retrofit onto existing plant, or as an OEM component in new plant. A number of pilot-scale trials with commercial partners are underway.

In accordance with its agreement with Sheffield University, holding company Fusion will start with a 60 per cent shareholding in Perlemax; however, given the investment profile of the company, it is anticipated that the longer-term shareholding will be between 30 to 40 per cent.