A recent PCT patent application discloses a green method of producing n-butanol, ethanol and acetone (Jenkinson et al., WO2019073254, Green Biologics Limited, GB).
The process involves culturing microbes called Clostridium saccharoperbutylacetonicum on gamma-cyclodextrin (GCD) containing medium. This bacterial species has peculiar ability of using GCD as carbon source. GCD containing culture medium can only support specific bacteria, therefore outcompeting of potential rivals (e.g those producing lactic acid) can be supressed.
Usually it is difficult to maintain sterile conditions during fermentation. Lactic acid bacteria, the most common contaminants, however, do not grow on GCD (Fig.1). In a mixed culture no lactic acid can be detected.
Fig. 1 Clostridium saccharoperbutylacetonicum cells are able to grow on gamma-cyclodextrin as carbon source, while Lactobacillus delbrueckii are not
It was surprisingly found that Clostridium saccharoperbutylacetonicum may not use alpha-cyclodextrin as carbon source and (probably due to limited solubility), while beta-cyclodextrin does not enable effective culturing either.
Using the Clostridium saccharoperbutylacetonicum culture, fermentation process leading to valuable solvents utilizing cheap lignocellulosic feedstocks such as agricultural residues (e.g. from corn & sugar production), woody residues, energy crops and municipal waste as well as sucrose from feedstocks such as molasses, sugar beet or sugar cane can be established.
The global n-butanol market, largely feeding into the paints, coatings, adhesives and inks sectors, is valued at greater than $6 billion (~3.7 million tons) and growing. Presently, bio-n-butanol production is only a small fraction of this, but the fermentation route has the potential to replace petro-derived butanol, acetone and hydrogen with cheaper, more sustainable and environmentally-friendly chemicals.
Jenkinson, E., Harding, A.J., Davies, E.T., Atmadjaja, A.N. PCT/GB2018/052937 (2018), WO/2019/073254 (2019) https://patentscope.wipo.int/search/en/detail.jsf?docId=WO2019073254&tab=PCTBIBLIO&maxRec=1000