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Oak-based biofuel offers 80% greenhouse gas reduction over petroleum

Second-generation biofuels made from managed trees and perennial grasses may provide a sustainable fuel resource, according to newly published research.

A team from the universities of Oklahoma and Pittsburgh investigated the full life cycle of second generation biofuel produced from short-rotation oak, in order to check if it really offered greenhouse gas emission reductions relative to petroleum based fuels. Their results have now been published in the journal Energy and Environmental Science.

“Corn ethanol environmental impacts weren't really studied until after its commercialisation," explained Vikas Khanna, assistant professor of civil and environmental engineering at the University of Pittsburgh and corresponding author of the study. "The great thing about this project is it addresses full life cycle sustainability questions of new fuel sources before they come up later down the road."

The UN called for a five year moratorium on food-based (first-generation) biofuels out of concerns they would consume farmland used to grow food, leading to global food shortages. Khanna and colleagues focused on wood from oak trees, as it can be harvested year round and reduces the need for large-scale infrastructure.

"Second-generation biofuels differ from first generation biofuels because they don't come directly from food crops like corn and soy," said Dr. Khanna. "They include woody crops, perennial grasses, agricultural and forest residues, and industrial wastes."

Two key results were found in the team’s study. Firstly, that multistage second-generation biofuel systems have an Energy Return on Investment (EROI) ratio ranging from 1.32:1 to 3.76:1.  (Corn ethanol has an EROI of 1.3:1). Secondly, and perhaps most crucially, the study found that the oak based biofuel showed an 80% reduction in greenhouse gas emissions when compared to petroleum diesel. In addition, there was a 40% reduction in hydrogen consumption relative to a single-stage pyrolysis system.

"Pyrolysis is the process of heating biomass to high temperatures in the absence of oxygen to create biofuel," said Dr. Khanna. "If it's done quickly, in one stage, a lot of carbon will be lost. Our research showed that a multistage, lower temperature system of pyrolysis can increase the carbon chain length, create more liquid fuel and improve the energy output of the entire process."





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