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Cracking Open the Coconut Without Spoiling the Prize

Posted on September 22nd, 2016 by in New Materials & Applications

Coconut image

A hammer is a good tool for cracking a coconut. When used properly it unveils the “milk” and “meat” of the coconut without unwelcomed pieces of the woody shell and its fiber.  The hammer must hit the shell just hard enough but not too hard.  But what if it was impossible to adjust the impact of the hammer’s head and it always hit the coconut shell too hard?  At the minimum we would need an extra step to take the shell out of the smashed coconut.

The scientists at the JEBI faced a similar fate to coconut cracking in their endeavor to convert biomass to biofuel. To be clear, we are not talking about cultivated corn that has a dubious net energy benefit.  The JEBI focus is on the conversion of biomass that grows around the world in massive quantities.  World production of biomass is estimated at 146 billion metric tons a year, mostly from the growth of wild vegetation. The proverbial “hammer” the JEBI scientists used to unlock the biomass was effective but it also smashed some useful things.

The Joint BioEnergy Institute (JBEI) is a U.S. Department of Energy (DOE) Bioenergy Research Center dedicated to developing advanced biofuels—liquid fuels derived from the solar energy stored in plant biomass that can replace gasoline, diesel and jet fuels. Figure 1 shows a comparison of biomass cycle with the use of oil.  The former recycles the existing atmospheric carbon dioxide as opposed to the latter that introduces new carbon, sequestered underground, into the atmosphere.  The participating organizations in the JEBI include several national laboratories and universities.

CO2

Figure 1 A comparison of biomass and underground oil consumption (source: www.ecogreenbuildings.co.uk)

Biomass is made up of complex polysaccharides unlike the simple starch-based sugars in corn and other grains. Those polysaccharides comprise the plant cell walls of non-food lignocellulosic biomass.  They are locked within a tough material called lignin that is very hard to break down (Source: www.jbei.org). Indeed, this lignin enclosure (Figure 2) has been a major impediment in the economically viable conversion of biomass to other materials.

Sina coconut 2

Figure 2 Structure of Primary Cell Wall of Plant Cells

(Source: http://ibimapublishing.com/articles/IJREB/2014/506376/)

Researchers in JBEI’s Deconstruction Division are developing new ways to release these polysaccharides and reduce them to fermentable sugars that can be synthesized into biofuels and chemicals. This process is called deconstruction. The traditional deconstruction process has two steps: (1) pretreatment, typically a thermochemical process that perturbs the structure and chemistry of the plant cell walls, followed by (2) enzymatic depolymerization of the polysaccharides and lignin generated after pretreatment into monomers suitable for bioconversion into biofuels and chemicals. It is necessary to reduce the biomass processing cost to enhance its commercialization chances.  Because the second step is indispensible the focus has been on the pretreatment step.

JEBI scientists have been developing ionic liquids, molten salts that are liquid at room temperature, as a means (a hammer!) of pretreating lingo-cellulosic biomass and producing intermediates such as sugars and lignin-derived compounds. Unfortunately, a major setback emerged in that ionic liquids proved toxic to the microorganisms used in the second step (fermentation) for biofuel production.  That would require the mixture to be purified in a separate step, after the biomass after pretreatment, to remove the ionic liquids.

JEBI scientists have been searching for a solution. They just (Sep 2016) announced a major discovery: addition of carbon dioxide during the pretreatment step can neutralize the toxicity of the ionic liquids by adjusting the alkaline pH. Consequently, ionic liquids would not poison the fermentation microorganisms.  The use of CO2 as a reversible method to adjust pH is expected to eliminate the need for a purification step altogether.  The result is a whopping cost reduction of 50% compared to traditional biomass-pretreatment techniques.  This finding is both exciting and disruptive. Some hammer the JEBI scientists have found!

Cracking open a coconut won’t ever be the same, will it?

Watch this space in the future for more information about biomass chemicals and biofuels.


 

All opinions shared in this post are the author’s own.

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