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Zia Abdullah, Laboratory Program Manager, National Renewable Energy Laboratory

Author: Zia Abdullah, Laboratory Program Manager, National Renewable Energy Laboratory

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Achieves high sugar yields with low enzyme loadings

Deconstructing Biomass with a Common Pulp and Paper Industry Method

Ozone treatment (aka "ozonolysis") of lignocellulose pulp is a widely practiced method for bleaching in the commercial-scale pulp and paper industry (greater than 1,000 tons/day). National Renewable Energy Laboratory (NREL) researchers Xiaowen Chen and Melvin Tucker experimented with the ozonolysis method to see how well it could breakdown the lignin in corn stover. Results showed several cost-saving benefits:

  1. Decreased enzyme usage and chemical/power requirements during biomass deconstruction through NREL-developed deacetylation and mechanical refining (DMR). DMR is a biochemical conversion process to help overcome lignocellulosic biomass' natural resistance to being broken down (aka "recalcitrance").
  2. Increased enzymatic hydrolysis sugar yields, which means increased drop-in fuel production.
2 researchers looking at a ozone concentration in the pretreatment reactor
Researchers at NREL carefully monitor the ozone concentration in the pretreatment reactor. Photo credit: Alexa Schwartz.

NREL's Method

To test the hypothesis, NREL researchers used an ambient temperature ozonolysis reactor to ozone-treat deacetylated corn stover prior to mechanical refining. NREL then performed mechanical refining and high-solids enzymatic hydrolysis to produce fermentable sugars.

With this new, ozonolysis-assisted approach, NREL achieved monomeric glucose and xylose yields greater than 90% at a total enzyme loading of 12 milligrams/gram (mg/g) (Figure 1). Even with a reduced enzyme loading of 10 mg/g, monomeric glucose and xylose yields are 88% and 90%. Without the ozonolysis-assisted approach, the monomeric glucose and xylose yields were 10% lower. Increased yields of sugar can reduce the cost of biofuel or bioproduct production.

a graph with Ozonolysus yield over time.
Figure 1. NREL scientists discovered that a total enzyme loading of 12 mg/g in an ozonolysis reactor achieves glucose and xylose yields greater than 90% particularly after 30 minutes of ozonlysis time. Illustation by NREL.

The Impact of Ozonolysis for Biomass Deconstruction

Ozonolysis represents a potential near-term solution to achieving targeted enzymatic hydrolysis sugar yields using existing commercial enzyme preparations by adding a processing step to improve the hydrolysis of highly recalcitrant feedstocks. Preliminary techno-economic analyses by NREL indicate that the performance advantages for the use of ozonolysis outweigh its costs and result in lower prices for sugar and downstream upgrading.