Purdue University chemical engineers are proposing the creation of mobile processing plants that would rove the Midwest to produce the fuel with a newly developed method to process agricultural waste and other biomass into biofuels.

Rakesh Agrawal, the Winthrop E. Stone Distinguished Professor of Chemical Engineering said,  “What’s important is that you can process all kinds of available biomass  — wood chips, switch grass, corn stover, rice husks, wheat straw …,”

The proposed harvest to production method bypasses a problematic economic barrier for using biofuels: Transporting biomass is expensive because of its bulk volume, whereas liquid fuel from biomass is concentrated and thus far more economical to transport.

Agrawal and his team are making the point, “”Material like corn stover and wood chips has low energy density. It makes more sense to process biomass into liquid fuel with a mobile platform and then take this fuel to a central refinery for further processing before using it in internal combustion engines.”  If they can come up with a low investment processor, they team could have a kind of home run.

The new method is called fast-hydropyrolysis-hydrodeoxygenation, which works by adding hydrogen into the biomass-processing reactor. The hydrogen for the mobile plants would be sourced from natural gas or the biomass itself. However, Agrawal envisions the future use of solar power to produce the hydrogen by splitting water, making the new technology entirely renewable.

The method, which has the shortened moniker of H2Bioil — pronounced H Two Bio Oil — has been studied extensively through modeling, and experiments are under way at Purdue to validate the concept.

Mobile Biomass to Fuel Block Diagram. Click image for more info.

Fast pyrolysis isn’t new, but kicking in an added hydrogen source is and taking the fast pyrolysis on to de oxidizing the product is as well.  It’s a combination of processes that looks innovative.

Singh, who is now a researcher working at Bayer CropScience, said, “Another major thrust of this research is to provide guidelines on the potential liquid-fuel yield from various self-contained processes and augmented processes, where part of the energy comes from non-biomass sources such as solar energy and fossil fuel such as natural gas.”

Results outlining the process, showing how a portion of the biomass is used as a source of hydrogen to convert the remaining biomass to liquid fuel is detailed in a research paper appearing online in June issue of the journal Environmental Science & Technology. The paper was written by former chemical engineering doctoral student Navneet R. Singh, Agrawal, chemical engineering professor Fabio H. Ribeiro and W. Nicholas Delgass, the Maxine Spencer Nichols Professor of Chemical Engineering.  The abstract says in part:

We have estimated sun-to-fuel yields for the cases when dedicated fuel crops are grown and harvested to produce liquid fuel. The stand-alone biomass to liquid fuel processes, that use biomass as the main source of energy, are estimated to produce one-and-one-half to three times less sun-to-fuel yield than the augmented processes. In an augmented process, solar energy from a fraction of the available land area is used to produce other forms of energy such as H2, heat etc., which are then used to increase biomass carbon recovery in the conversion process. However, even at the highest biomass growth rate of 6.25 kg/m2· per year considered in this study, the much improved augmented processes are estimated to have sun-to-fuel yield of about 2%. We also propose a novel stand-alone H2Bioil-B process, where a portion of the biomass is gasified to provide H2 for the fast-hydropyrolysis/hydrodeoxygenation of the remaining biomass. This process is estimated to be able to produce 125−146 ethanol gallon equivalents (ege)/ton of biomass of high energy density oil but needs experimental development. The augmented version of fast-hydropyrolysis/hydrodeoxygenation, where H2 is generated from a nonbiomass energy source, is estimated to provide liquid fuel yields as high as 215 ege/ton of biomass. These estimated yields provide reasonable targets for the development of efficient biomass conversion processes to provide liquid fuel for a sustainable transport sector.

The Purdue group is also developing reactors and catalysts to experimentally demonstrate the concept. In another paper addressing various biofuels processes, including fast-hydropyrolysis-hydrodeoxygenation, that appeared in June’s Annual Review of Chemical and Biomolecular Engineering.  The full paper is available at this link.

The new method would produce about twice as much biofuel as current technologies when hydrogen is derived from natural gas and 1.5 times the liquid fuel when hydrogen is derived from a portion of the biomass itself.

Biomass along with hydrogen will be fed into a high-pressure reactor and subjected to extremely fast heating, rising to as hot as 500 degrees C, or more than 900 degrees Fahrenheit in less than a second. The hydrogen containing gas is to be produced by “reforming” natural gas, with the hot exhaust directly fed into the biomass reactor.

Agrawal explains, “The biomass will break down into smaller molecules in the presence of hot hydrogen and suitable catalysts. The reaction products will then be subsequently condensed into liquid oil for eventual use as fuel. The uncondensed light gases such as methane, carbon monoxide, hydrogen and carbon dioxide, are separated and recycled back to the biomass reactor and the reformer.”

Purdue has been pioneering the concept of combining biomass and carbon-free hydrogen to increase the liquid fuel yield.  An older design called “hybrid hydrogen-carbon process,” or H2CAR also use additional hydrogen to boost the liquid-fuel yield. However, H2Bioil is more economical and mobile than H2CAR, Singh said.

Singh continues, “H2Bioil requires less hydrogen, making it more economical.  It is also less capital intensive than conventional processes and can be built on a smaller scale, which is one of the prerequisites for the conversion of the low-energy density biomass to liquid fuel. So H2Bioil offers a solution for the interim time period, when crude oil prices might be higher but natural gas and biomass to supply hydrogen to the H2Bioil process might be economically competitive.”

Regular folks have only a slight impression of what say, the planetary daily oil use of 85 million barrels would look like. The equivalent in biomass to be made into fuel would be an awe-inspiring mound, indeed.

Punching up the total fuel produced is likely the main benefit until political and economic types catch on to the transport issue.  By any measure the Purdue effort is getting somewhere worth going and its something that could go worldwide in local areas as modern farming practices reach further into the under developed world.

This is worthy research from Purdue.  The original article was written by Emil Venere.


12 Comments so far

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    I had a lot trouble following the diagram. The explanation helped a little but it was unclear to me what was going in the total picture. A lot of the chemistry seems unexplained for instance. Also, some sort of indicator of efficiency would help as well.

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    Concentrating the feedstock into liquid form would reduce transport costs and improve efficiency. What we need to keep in mind is the efficiency of the mobile process platform.

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