A patented process to pretreat corn-crop waste before conversion into ethanol means extra nutrients do not have to be added, cutting the cost of making biofuels from cellulose.
The AFEX (ammonia fibre expansion) pretreatment process, developed by Bruce Dale, university distinguished professor of chemical engineering and materials science at Michigan State University, uses ammonia to make the breakdown of cellulose and hemicellulose in plants 75 per cent more efficient than when conventional enzymes alone are used.
Cellulose in plants must be broken down into fermentable sugars before they can be turned into biofuel.
Dale said: ‘It is possible to use AFEX to pretreat corn stover (cobs, stalks and leaves) and then hydrolyse and ferment it to commercially relevant levels of ethanol without adding nutrients to the stover.
‘It’s always been assumed that agricultural residues such as corn stover did not have enough nutrients to support fermentation. We have shown this isn’t so.’
Doctoral student, Ming Lau, added: ‘The research also shows that the chemical compounds created when the stover goes through the AFEX process can improve the overall fermentation process.
‘This is at odds with the general perception that these compounds are detrimental and should be removed.’
Currently, pretreating cellulose with acid is a common way to break the material down into fermentable sugars.
But after acid pretreatment, the resulting material must be washed and detoxified. That removes nutrients, leading to the mistaken idea that crop waste lacks the necessary nutrients, Dale said.
Cellulosic material pretreated with the AFEX process does not have to be washed or detoxified, allowing ethanol to be created from cellulose without added nutrients or other steps.
Dale said: ‘Washing, detoxifying and adding nutrients back into the pretreated cellulose are three separate steps.
‘Each step is expensive and adds to the cost of the biofuel. Breaking down cellulose into fermentable sugars cost-effectively has been a major issue slowing cellulosic ethanol production.
‘Using AFEX as the pretreatment process can dramatically reduce the cost of making biofuels from cellulose.’
The next step could be a pilot plant, Dale said, perhaps at MBI International. MBI, a subsidiary of the MSU Foundation, partners with universities and companies to commercialise technology.
Dale said: ‘There are several companies – including Mascoma, which plans to open one of the nation’s first cellulosic ethanol plants in Michigan – that may be interested in using this technology.
‘We are working to make the AFEX technology fit these companies’ needs.’