Chemical engineers at Worcester Polytechnic Institute (WPI) in the US state of Massachusetts will use a grant worth just under $2 million (€1.8 million) from the US Department of Energy (DOE) to broaden attempts to convert waste into biofuels.
WPI associate professor of engineering Michael Timko has been developing methods to significantly improve the yield of biofuel that can be produced from food waste. The three-year grant from the DOE, in addition to $275,000 (€249,239) from the Massachusetts Clean Energy Center, will help to expand earlier research to mix food waste with municipal green waste, including yard trimming, leaves and sticks.
By combining the two waste sources, Timko aims to create even more energy-dense oil that can be upgraded into a liquid biofuel. Others working on the project include Andrew Teixeira, assistant professor of chemical engineering, and Geoffrey Tompsett, assistant research professor of chemical engineering.
“We have shown that we have methods to convert food waste into energy products,” said Timko. “Increasing scale is a big goal. If you can handle more waste – different kinds of waste – you can have a larger-scale process. There’s no one silver bullet to creating green energy, but this is a piece of that puzzle. Every time you can add a piece of that puzzle, it matters.”
The US generated over 262 million tonnes of municipal solid waste in 2015, of which approximately 34% comprised food and green waste. This waste is typically disposed of in landfills, however space is reaching existing limits and the landfills often leach water pollutants, toxins and greenhouse gases such as methane.
According to Timko, there is significant energy potential in this kind of waste, as it has a relatively high energy content of around 20 megajoules per kilogram.
A goal of the project is to develop a new catalytic method for converting the municipal solid waste components into an energy-dense oil, rather than using anaerobic digestion, as this process is unable to easily handle yard waste, especially if it contains whole biomass, such as wood.
The researchers are therefore investigating the use of hydrothermal liquefaction, a process that uses moderate heat and high pressure to convert wet biomass into crude-like oil. This process is faster than anaerobic digestion and also can be used with wet waste, which saves costs associated with drying the waste.
This process converts carbon contained in the feed into products that separate into oil, gas, char and water phases. The team is working to improve the hydrothermal process to get the highest-quality fuel possible, to divert the carbon lost to the water into the production of oil, and to minimise the amount of energy put into the process, while maximising the energy produced.
In order to do so, they are adding various catalysts, such as red mud, which is an inexpensive, stable, and reliable waste product created during the production of aluminium. Another approach is promoting carbon-carbon coupling reactions that save carbon from being lost in the water, so it can be used to create more oil while also decreasing the cost of treating waste water.
“A big challenge in the field is the amount of carbon you lose to the water phase of biofuel production,” added Timko. “If you look at all the challenges to make this competitive with fossil fuels, cost is the biggest one.”
The chemical engineers also are investigating the best temperature to use and the best mixture of food waste to yard waste to create different oils of different qualities. A working pilot is anticipated by the end of the three-year grant, according to Timko.
Collaborators on the DOE grant include researchers at Massachusetts Institute of Technology, University of California in Riverside, Woods Hole Oceanographic Institution and Mainstream Engineering.
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