The Integrated Forest Product Biorefinery (2)

A modern pulp mill employs about 70% of the technologies needed by a biorefinery and provides a means of “fast tracking” the development of innovative biorefinery technologies.

Although the conversion of wood cellulose into a sugar-rich process stream has been extensively studied, it is frequently overlooked that economic factors favor the manufacturing of paper over biofuels/biochemicals, making the practical success of this approach doubtful. In sharp contrast, wood glucomannans are rapidly extracted and degraded in the Kraft pulping process to isosaccharinic acids and not utilized as a significant part of pulp fibers. Degraded glucomannans end up as energy during black liquor gasification. Because of the relatively low heating value of hemicellulose, it contribute only 15-20% of heating value to black liquor. Therefore, hemicellulose is worth more as ethanol/chemicals than as energy.

Energy values of different fuels in an IFBR
Fuel Heating Value(GJ/MT)
Oil 43.5
Biomass (20% H2O) 15
Black liquor (80% ds) 12.6
Lignin 26.9

Carbohydrates 13.6

Hemicellulose (mainly xylose in hardwood, grass and agricultural crop residuals and glucomannan in softwood) comprise ~ 5 – 26% of biomass and are an under utilized biochemical resource that could be readily converted to bioethanol/biochemicals. The removal of these hemicellulose prior to kraft pulping should improve the overall kraft pulping process by reducing cooking times and improving chemical impregnation. These process benefits will facilitate practical implementation of this biorefinery concept.

Prior to Pulping Approach:

• Uses hot water extraction vessels to extract hemicelluloses
• Acetic acid is separated, and sugars are fermented to fuel grade ethanol with known processes as shown below
• Removing the “sugars”improves throughput potential of existing operations such as pulping and chemical recovery
• Ethanol is at the low end of potential products
• Development of further value includes biorefining systems to produce high-value chemicals as well as biodiesel and ethanol

Post-Pulping Approach:
• Extraction of cellulose- and lignin-derived chemicals from black liquor
• Recovery of tall oil soap and extractives from black liquor
• Gasification of black liquor residuals, wood waste, and other biomass to produce syngas
• Conversion of syngas to methanol, DME, ethanol, Fischer-Tropsch fuels, etc.