Abstract
Over the last decade, microbes have been engineered for the manufacture of a variety of biofuels. Saturated linear-chain alcohols have great potential as transport biofuels. Their hydrocarbon backbones, as well as oxygenated content, confer combustive properties that make it suitable for use in internal combustion engines. Herein, we compared the microbial production and combustion characteristics of ethanol, 1-butanol, and 1-octanol. In terms of productivity and efficiency, current microbial platforms favor the production of ethanol. From a combustion standpoint, the most suitable fuel for spark-ignition engines would be ethanol, while for compression-ignition engines it would be 1-octanol. However, any general conclusions drawn at this stage regarding the most superior biofuel would be premature, as there are still many areas that need to be addressed, such as large-scale purification and pipeline compatibility. So far, the difficulties in developing and optimizing microbial platforms for fuel production, particularly for newer fuel candidates, stem from our poor understanding of the myriad biological factors underpinning them. A great deal of attention therefore needs to be given to the fundamental mechanisms that govern biological processes. Additionally, research needs to be undertaken across a wide range of disciplines to overcome issues of sustainability and commercial viability.
Highlights
Over the last decade, microbes have been engineered for the manufacture of a variety of biofuels
In another study, based on the process of reverse β-oxidation reported by Inui et al (1984) in which carbon chain elongation proceeds via acyl-CoA intermediates, Dellomonaco et al (2011) obtained ~100 mg 1-octanol L−1. By applying this principle of fatty-acid chain elongation instead with fatty acyl ACP intermediates, Akhtar et al (2015) reported a titer of ~62 mg L−1, which was developed without any attempt at chromosomal engineering hinting at the possibility that extensive genetic modifications could lead to higher titers
Of the three fuels considered in this article, we would conclude that for spark iginition (SI) engines, ethanol is the most suitable choice, while for CI engines it would be 1-octanol
Summary
Microbes have been engineered for the manufacture of a variety of biofuels Both ethanol and 1-butanol have notable histories that stretch back to more than a century and only in modern times have their production, via microbial approaches, been revived (Green, 2011; Buchholz and Collins, 2013). These alcohols have great potential as transport biofuels. Their linear hydrocarbon backbones, as well as oxygenated content, confer combustive properties that are suitable for use in internal combustion engines. We summarize research findings relating to the microbial synthesis of ethanol, 1-butanol, and 1octanol; and describe their combustion characteristics in internal combustion engines, with particular emphasis given to 1-octanol
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