Nov 5, 2009
Molasses sweetens the biofuel mix
How do you squeeze the maximum out of a sugarcane plant? New calculations reveal that using the molasses (a by-product from the sugar-making process) in biofuel production helps to produce a super low-carbon fuel.
Currently, much of the ethanol biofuel imported to California is made from a feedstock of fresh, mill-pressed sugarcane juice, usually produced in a Brazilian factory. In many other countries, including Indonesia, India, the Caribbean and Brazil, the sugarcane is processed differently to produce raw table sugar and ethanol. Molasses, the by-product from the sugar-making process, is channelled back and used to make ethanol biofuel.
Anand Gopal and Daniel Kammen, from the University of California, Berkeley, US, have developed an add-on to GREET (Greenhouse Gases, Regulated Emissions and Energy Use in Transportation), the widely adopted lifecycle-analysis tool for transport fuel, to assess whether California should consider molasses-based biofuel in their carbon standards.
Previous calculations have shown that if the average Brazilian factory uses only fresh cane juice to make ethanol, which is then exported to California, the resulting fuel has a lifecycle greenhouse-gas rating of 26.6 grams of carbon dioxide per mega-joule of energy.
Gopal and Kammen gathered data from sugarcane factories in Brazil, Indonesia and India. Using these data they calculated the carbon footprint of fuel made in factories that first process the sugarcane juice into sugar and then use the by-product, molasses, to make ethanol. They found that when all other factors are kept the same, ethanol produced from pure molasses has a lifecycle greenhouse-gas rating of 15.1 grams of carbon dioxide per mega-joule of energy – significantly less than the pure sugarcane-juice-based fuel. Their findings are published in Environmental Research Letters.
There are a number of advantages associated with this production pathway. “The main benefit is that transportation fuel is manufactured from a low-value product (even a waste product in some areas), which reduces pressure on food prices and land conversion,” Gopal told environmentalresearchweb.
Currently, California consumes around 3.5 billion litres of ethanol every year. Gopal and Kammen estimate that 2 billion of these litres (approximately 60%) could be sourced from molasses ethanol. This would make molasses responsible for around 2% of California’s total fuel consumption each year.
However, molasses is not a panacea for all problems associated with biofuel. If molasses became widely used then the price would likely increase relative to raw sugar and molasses ethanol would start to become too expensive and lose its advantage. In addition, diverting molasses into ethanol production could push up the prices of animal feeds, because molasses is commonly used as a feed supplement.
What’s more, creating high demand for molasses-based ethanol could encourage factories to use intermediate molasses (a high-value product that can be further upgraded into raw sugar) to make ethanol.
“Differentiating between cane juice and molasses ethanol may lead to a reduction in world sugar production over the baseline, which would be a particularly harmful effect,” said Gopal. “We recommend regulatory audits to verify that producers are using final molasses, rather than intermediate.”
But in moderation, and with good regulations in place, molasses could be a truly sweet fuel.
About the author
Kate Ravilious is a contributing editor to environmentalresearchweb.