Celtic Renewables’ process. Click to enlarge.

Celtic Renewables Ltd uses an enhanced ABE (acetone-butanol-ethanol) fermentation process with the two main by-products of the whisky production—“pot ale” (the copper-containing liquid from the stills) and “draff” (the used barley grains)—to produce bio-butanol, acetone and ethanol, as well as high-grade animal feed.

The foundational research at the BfRC concentrated specifically on organic residues or by-products which have little or no value, but have sufficient quantity of unused sugars, which can be fermented to produce biofuel. The Celtic Renewables microbes can convert both the complex sugars, such as xylose and arabinose, and simple glucose into biofuels.

Celtic Renewables mixes the draff and pot ale, then ferments them to produce a broth. During fermentation a number of gases— particularly hydrogen— is produced. The broth is then distilled to produce butanol, acetone and ethanol, and the remainder is separated into solid material, which can be dried to produce a high-grade animal feed; and an effluent.

The whisky industry annually produces 1,600 million liters of pot ale and 500,000 tonnes of draff which could be converted into biofuel. While Celtic Renewables’ original proof-of-concept research, conducted at Edinburgh Napier, was at a small lab-scale of three liters of pot ale, the envisioned industrial scale second phase testing will systematically scale up to 10,000 liters.

Tullibardine has the capacity to provide 6,500 tonnes of draff and two million liters (528,000 gallons US) of pot ale— by-products which are currently spread on agricultural fields, turned into animal feed or discharged into the sea under license, at a cost of about £250,000 (US$404,000) per year.

The pilot demonstration project, a first for Scotland, is being funded with the help of a £155,000 grant from Zero Waste Scotland. The project has the support of ministers who believe it can contribute to the Scottish Government’s target of reducing carbon emissions by 42% by 2020 as well as contributing to the EU mandated biofuel target of 10% by 2020.

Because distilleries currently produce around three times more pot ale than draff, Celtic Renewables is also considering other sustainable sources of sugar-rich raw materials, such as the by-products from breweries or paper waste, to help it convert the excess into biofuel, according to Mark Simmers, CEO of Celtic Renewables.