Process Overview

The critical commercial aspect of Celtic Renewables Ltd's patented process is that it utilises a biological by-product stream as the raw material -cutting the usual dominant cost of substrate supply and adding both environmental and economic sustainability to Scotland's pivotal whisky industry.

The innovative process was researched over two years at the Biofuel Research Centre, which was established at Edinburgh Napier University in 2007 by Professor Martin Tangney, who is a world-authority in biobutanol production. Professor Tangney has being researching the ABE fermentation process for many years, but it is only now that due to the environmental pressures around carbon emissions, the economic pressures of high oil prices, and the desire of countries for security of energy supply, that there is huge interest in the potential production of biofuels. 

At present most biofuel, especially bioethanol, is made from fermenting food crops which are grown specifically for the purpose. The economic viability and environmental advantages of this are questionable. Consequently the research at the Biofuel Research Centre concentrated specifically on organic residues which have little or no value, but have sufficient quantity of unused sugars, which can be fermented to produce biofuel.

Celtic Renewables Ltd's technology uses bacteria which can convert the sugars xylose, arabinose and glucose into biofuels. The initial primary source of the by-products is from the Scotch Whisky Industry.

The process is anaerobic (done in the absence of oxygen), similar to how yeast ferments sugars to produce ethanol for wine, beer, or fuel. The process produces Acetone, Butanol and Ethanol. The solvents are typically produced in a ratio of 3-6-1. 3 parts acetone, 6 parts butanol and 1 part ethanol. 

The process uses a strain of bacteria from the Clostridia Class (Clostridium Family). ABE-producing clostridia possess two distinct characteristic phases in the metabolic pathways. Typically, during acidogenesis, acetic acid and butyric acid are produced with the formation of ATP. During solventogenesis, organic acids are re-assimilated and Acetone, Butanol and Ethanol are produced.

Draff by-product from Tullibardine Distillery
Draff by-product from Tullibardine Distillery
Gram stained Clostridium
Gram stained Clostridium

 The Process

This diagram shows the process by which the two by-products: draff and pot ale are mixed, treated and fermented to produce a broth.

During fermentation, the bacteria convert the sugars in the broth to butanol, acetone and ethanol. Gases, mainly carbon dioxide and hydrogen are also produced.

The broth is then separated into solid and liquid components, the liquid is distilled to extract solvents, leaving an effluent. The solids are dried to produce a high-grade animal feed.

It is anticipated that the effluent will be further treated to produce other gases and water, this will provide additional value or energy for the enterprise.

The outputs from the fermentation of draff and pot ale are butanol, acetone, ethanol, animal feed and gases (hydrogen and carbon dioxide)