A team from the University of Pittsburgh and the University of Oklahoma investigated the full life cycle impact of one promising ‘second-generation biofuel’ produced from short-rotation oak. The study found that second-generation biofuels made from managed trees and perennial grasses may provide a sustainable fuel resource.

This is a schematic showing the stages modeled in the biomass-to-fuel life cycle assessment. The image first appeared in the Royal Society of Chemistry journal Energy & Environmental Science, Issue 5, 2017.
Image Credit: Vikas Khanna. Click image for the largest view.

Over the years numerous studies have raised critical concerns about the promise of corn ethanol’s ability to mitigate climate change and reduce dependence on fossil fuels. Some of the studies have suggested that after a full life cycle assessment – meaning an analysis of environmental impact throughout all stages of a product’s life – biofuels like corn ethanol may not offer any greenhouse gas emissions reductions relative to petroleum fuels. The assertion remains a dubious allegation after nearly thirty years of experience.

Meanwhile, this team’s study results have been published in the Royal Society of Chemistry journal Energy & Environmental Science.

The study titled, “Multistage Torrefaction and In Situ Catalytic Upgrading to Hydrocarbon Biofuels: Analysis of Life Cycle Energy Use and Greenhouse Gas Emissions” took a novel approach to the production of second-generation biofuel while also comprehensively accounting for all of the steps involved in the full supply chain.

Vikas Khanna, assistant professor of civil and environmental engineering at the University of Pittsburgh and corresponding author of the study said, “Corn ethanol environmental impacts weren’t really studied until after its commercialization. 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.”

In 2007, the United Nations called for a five-year moratorium on food-based (or first-generation) biofuels because of concerns that they would consume farmland and lead to worldwide food shortage. It was an idea that went essentially nowhere.

Dr. Khanna and his team’s study used wood from oak trees, as they can be harvested year-round and reduce the need for large-scale storage infrastructure.

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

A significant metric for determining the efficacy of fuel is the Energy Return on Investment (EROI) ratio. The EROI of petroleum crude production remains high at about 11:1, meaning an investment of one unit of energy will yield 11 units of energy. However, the EROI has been steadily decreasing since 1986 and will continue to worsen as fossil fuels become more scarce and difficult to access.

When researchers study potentially promising energy sources, they look for a ratio greater than 1:1. Corn derived ethanol, for example, has a EROI of 1.3:1. The study found the median EROI for multistage second-generation biofuel systems ranges from 1.32:1 to 3.76:1. This is another construct rife with opportunities to mislead. The assertion that America’s record 15 billion+ bushel corn crop last year, producing nearly a million barrels a day of ethanol for about 40% of the crop and the other 60% going to feed and chemical products would suggests the American corn crop alone is a huge part of industrial petroleum use. EROI is a good idea that gets turned into nonsensical assertions.

The Energy Independence and Security Act of 2007 states that cellulosic biofuels, like the ones used in the study, must outperform the greenhouse gas emissions of fossil fuels by reducing relative emissions by 60 percent to receive economic incentives from the government. The study surpassed minimum requirements and showed an 80 percent reduction in greenhouse gas emissions relative to baseline petroleum diesel. Additionally, there was a 40 percent reduction in hydrogen consumption relative to a single-stage pyrolysis system.

Now it gets interesting.

Dr. Khanna said, “Pyrolysis is the process of heating biomass to high temperatures in the absence of oxygen to and create biofuel. 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.”

This is easily one of the leading bewildering press releases your humble writer has seen. The gem is the innovations in pyrolysis, of which very little is said. These innovations are likely the most important part of the team’s work and yet, is a minor part of the press release.

On the other hand, corn and sugar cane ethanol are both raging successes with decades of experience and improvements, billions invested worldwide and a nemesis to OPEC and oil companies. For this team though, there is not a huge crop with large amounts going to waste and producers in deep financial trouble to drive a new use and market.

The team instead, is faced with a new crop, with little existing market, if any, hardly any motivated producers and would be yet another nemesis. Moreover, for those familiar with working woods, handling a saw or axe with popular or aspen is one thing, tearing up oak for processing is a whole other matter.

We can hope the team has a broader view than seen in the press release. There are likely raw materials in abundant supply, looking for new markets with a motivated producer base that will irritate the petroleum industry in a big way. That’s when their low temp pyrolysis could get going. Perhaps the team will pyrolysis cook some other things and they’ll start getting somewhere.


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