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Clean Fractionation

National Renewable Energy Laboratory

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Technology Marketing SummaryBiorefinery production costs are driven by efficient pretreatment processes. To help lower production costs, researchers at the National Renewable Energy Laboratory (NREL) have developed an efficient and economically favorable biomass pretreatment process for upgrading feedstocks for biorefining and other end uses. Using a single-phase mixture digestion process followed by a phase separation, Clean Fractionation segregates cellulose, hemicellulose, and lignin into three high-purity streams for conversion into value-added products, including ethanol biofuel. DescriptionPulping processes have previously been used for separating cellulose from lignin and other components of lignocellulosic materials; however, most present technical or economic challenges. For example, processes using either inorganic chemicals or organic solvents face difficulties in the low-cost recovery or destruction of those chemicals. The solution provided by NREL’s Clean Fractionation Technology utilizes a single-phase mixture of alcohol, water and a water-immiscible organic solvent (e.g, a ketone) to digest biomass at elevated temperatures. Following digestion, water or solvent levels are adjusted to cause a phase separation wherein each phase contains a highly-purified portion of the segregated biomass. Cellulose is amassed in a solid pulp cake; hemicellulose and dissolved sugars are present in an aqueous phase; and lignin remains present in the organic solvent. The lignin is subsequently isolated (and the organic solvent recovered) through simple evaporation.
The improved extraction efficiencies provided by this solvent fractionation technique lead to reduced conversion times and increased yields, allowing biomass to be processed more economically. Recovery rates for each of the three resulting product streams approach 95 percent, with additional removal of noncellulosic materials possible through post-treatment bleaching. NREL has tested the method on numerous woody and herbaceous biomass feedstocks (including several mixed feedstocks), indicating high potential for a variety of biomass feedstocks to be used to produce a wide range of chemical products.
  • Provides high recovery and purity levels for segregated biomass components
  • Enables cost effective recovery of organic solvents used in pretreatment process
  • Lowers ethanol production costs by significantly reducing fermentation times and increasing yields
  • Enables hemicellulose and lignin to be used for production of other value-added chemicals (i.e., Xylitol from hemicellulose)
Applications and Industries
  • Ethanol
  • Pulp and paper
  • Chemical
  • Food processing
  • Packaging
  • Fuels
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Patent 5,730,837
Method of separating lignocellulosic material into lignin, cellulose and dissolved sugars
A method for separating lignocellulosic material into (a) lignin, (b) cellulose, and (c) hemicellulose and dissolved sugars. Wood or herbaceous biomass is digested at elevated temperature in a single-phase mixture of alcohol, water and a water-immiscible organic solvent (e.g., a ketone). After digestion, the amount of water or organic solvent is adjusted so that there is phase separation. The lignin is present in the organic solvent, the cellulose is present in a solid pulp phase, and the aqueous phase includes hemicellulose and any dissolved sugars.
National Renewable Energy Laboratory 03/24/1998
Technology Status
Development StageAvailabilityPublishedLast Updated

Contact NREL About This Technology

To: Eric Payne<>