Researchers from North Carolina State University have developed a new way to free the carbohydrates from plant lignin. By exposing the plant matter to gaseous ozone, with very little moisture, the NC team is able to produce a carbohydrate-rich solid with no solid or liquid waste.

This may well be the breakthrough. It’s still early, but the lignin and cellulose problem remains a significant barrier for biofuels with a great deal of effort in finding solutions.

Currently, to make ethanol, butanol or other biofuels, producers have used sugarcane, corn, sugar beets or other plant matter that is high in starches or simple sugars. But, those crops are also significant staple foods putting biofuels in competition with animals and people for those crops.

The problem is other forms of biomass – such as switchgrass, inedible corn stalks and cobs, miscanthus, poplar trees and many others – can also be used to make biofuels. But this crop arena poses its own problem: the energy potential is locked away inside the plant’s lignin – the woody, protective material that provides each plant’s structural support. Breaking down that lignin to reach the plant’s component carbohydrates is an essential first step toward making biofuels.

Dr. Ratna Sharma-Shivappa of North Carolina State University. Click image for more info.

Dr. Ratna Sharma-Shivappa, associate professor of biological and agricultural engineering at NC State and co-author of the research says in the NC State University press release, “This technique makes the process more efficient and less expensive. The technique could open the door to making lignin-rich plant matter a commercially viable feedstock for biofuels, curtailing biofuel’s reliance on staple food crops.”

The current technology treats this so-called “woody” plant matter with harsh chemicals that break it down into a carbohydrate-rich substance and a liquid waste stream. The remaining carbohydrates are then exposed to enzymes that turn the carbohydrates into sugars that can be fermented to make ethanol or butanol.  But, this technique often results in a significant portion of the plant’s carbohydrates being siphoned off with the liquid waste stream. Researchers must either incorporate additional processes to retrieve those carbohydrates, or lose them altogether.  Think complex, expensive and wasteful – solutions here are huge opportunities.

Sharma says of the ozone technique, ““This is more efficient because it degrades the lignin very effectively and there is little or no loss of the plant’s carbohydrates. The solid can then go directly to the enzymes to produce the sugars necessary for biofuel production.”

At this stage Sharma-Shivappa notes that the process itself is more expensive than using a bath of harsh chemicals to free the carbohydrates, but is ultimately more cost-effective because it makes more efficient use of the plant matter.  Yet experienced process engineers are just becoming aware of the research.  Commercial scale can have an impressive effect on operating costs.

The North Carolina team has recently received a grant from the Center for Bioenergy Research and Development to fine-tune the process for use with switchgrass and miscanthus grass. “Our eventual goal is to use this technique for any type of feedstock, to produce any biofuel or biochemical that can use these sugars,” Sharma-Shivappa says.

Congratulations!  Using a recyclable gas in the process could well be a huge process improvement and putting much more feedstock into product would improve the economics.

Here’s the official plug – The research, “Effect of Ozonolysis on Bioconversion of Miscanthus to Bioethanol,” was co-authored by Sharma-Shivappa, NC State Ph.D. student Anushadevi Panneerselvam, Dr. Praveen Kolar, an assistant professor of biological and agricultural engineering at NC State, Dr. Thomas Ranney, a professor of horticultural science at NC State, and Dr. Steve Peretti, an associate professor of chemical and biomolecular engineering at NC State. The research is partially funded by the Biofuels Center of North Carolina and was presented June 23 at the 2010 Annual International Meeting of the American Society for Agricultural and Biological Engineers in Pittsburgh, PA.

There isn’t a published paper listed – yet, but the North Carolina press release does include an abstract, “Miscanthus is an energy cane capable of producing high quality lignocellulosic biomass for bioethanol production. However, the conversion of this biomass into fuel ethanol has not been investigated in depth and depends to a great extent on the pretreatment technique.  Ozonolysis is a novel pretreatment method that can enhance biomass digestibility with minimal generation of chemical waste streams and degradation of the carbohydrate components. It employs ozone, a powerful oxidant, which forms highly reactive free hydroxyl ions upon decomposition thus degrading lignin in the absence of inhibitory degradation products such as furfural and HMF. This study investigates the effect of ozonolysis as a pretreatment method under room temperature and pressure.  Ozone concentrations up to 60 ppm at flow rates up to 0.5 l/min are being used to pretreat several varieties of miscanthus for varying times to enhance enzymatic hydrolysis. The efficiency of pretreatment will be determined by measuring the reducing sugars generated after hydrolysis. It is expected that the results of this study will help in the development of a pretreatment process that provides higher specificity towards lignin removal compared than other delignifying agents/pretreatments.”

The main question would be what the technique leaves as a waste material.  Is that a resource or a problem?  Time will tell.

One might hope that the ozone gas treatment would have a major impact.  There’s a lot of lignin and cellulose around left for natural fungus and mold degradation.  Picking that resource up and using it, and raising crops to build the volume are worthwhile.  The technology would put humanity in much closer harmony with the planet’s natural carbon cycle.


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