Sugars from Trees to Power the Next Generation

By Patrick Young

A doctoral student in the Department of Forest Products at Mississippi State University (MSU) is on a mission to produce sugars from trees —not for high-energy drinks consumed by many college students, but for production of ethanol and hydrocarbons.  Using a new pyrolysis process that she co-developed with researchers in the department, Qi Li, a native of China, is discovering the best method to produce high yields of sugars from bio-oil. 
The MSU auger pyrolysis reactor achieves 65% yield of bio-oil, equating to 130 gallons per dry ton. Qi applies a pretreatment to the biomass—pine wood particles—that obtain an increase in what are termed anhydrosugars, principally levoglucosan.
Her method increases anhydrosugars yield by more than 18% above previous research results.  This success provides a means to sugars production from lignocellulosic feedstocks, such as trees, grasses and others.
 The current sugars path requires breakdown by hydrolysis with a weak acid followed by enzymatic processes.  These processes require expensive cellulases for sugars production that the pyrolysis process does not require.
Qi’s process divides raw bio-oil into separate aqueous and lignin fractions by the addition of water. Sugars are fractionated into the aqueous portion, which is 70 percent of the weight and which contains the anhydrosugars. 
“The anhydrosugars can be reformed to produce liquid hydrocarbons.  Alternatively, the anhydrosugars can be hydrolyzed to simple sugars such as glucose and provide a feedstock for ethanol production,” said Phil Steele, Bio-oil Research Group Thrust Leader with the Sustainable Energy Research Center (SERC) and professor in the Forest and Wildlife Research Center.
Qi has only applied her process to pyrolysis oils produced from bio-oil pyrolyzed from pine wood particles. Future work will utilize feedstocks with higher cellulose content such as switchgrass, sorghum, sudan grass and energy cane. Sugar yields are expected to increase for these feedstocks.
“The process is being refined,” Steele said.  “The sugar types produced must be purified to be suitable for either hydrocarbons or ethanol production.”
A byproduct of this process is that the lignin contained in the raw bio-oil is captured in the lignin fraction. Other researchers in the department have successfully converted these liquid lignin fractions to mixed hydrocarbons containing gasoline, jet fuel and diesel fractions.
“The total carbon energy capture for the combined process is considerably more than either method applied alone to raw bio-oil,” Steele said.  “This new process will utilize all of the biomass with less loss of valuable carbon energy.” 

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