(44b) Conceptual Net Energy Output for Biofuel Production from Lignocellulosic Biomass Through Biorefining: A Review

J.Y. Zhu^1,2

¹ USDA Forest Service, Forest Products Laboratory, Madison, WI, USA

² Dept. Biological Systems Engineering, University of Wisconsin-Madison, WI, USA

Abstract

The concept of producing lignocellulosic biofuel, bioproducts, and chemicals through a biorefinery using lignocelluloses has been around for 70 years or more.  The recent interest in this old concept arises from the promises of mitigating climate change by substituting some biomass energy for petroleum or other fossil-fuel energy; achieving national energy independence and sustainable economic development; and advances in biotechnology in the past 2-3 decades.  Geopolitical and national security reasons have greatly contributed to the need for seeking alternative energy, especially using domestic renewable and sustainable sources. 

However, there is a lack of comprehensive information in the retrievable literature on pilot scale process and energy data using promising process technologies and commercially scalable and available capital equipment for lignocellulosic biomass biorefining, despite several pilot scale and demonstration plants are under construction.  Unfortunately, bioenergy production is not sustainable without net energy production.  Recognizing the heated debate on energy production from lignocellulosic biomass in the scientific community and most arguments were not based on actual laboratory data for biorefinery operation, this presentation is intended to provide an objective view on energy production from lignocellulosic biomass.  The process data from approximately a dozen studies that represent state-of-the-art in cellulosic biofuel production concepts, along with literature energy input data for agriculture operations, were analyzed to provide estimates of net energy production.  Several scenarios were created for proper allocation energy input to biomass and major agriculture co-product, such as corn or lumber.  

For biorefinery operations, increasing solids loading in pretreatment to at least 25% is critical to reducing energy input in a biorefinery.  Post thermo-chemical pretreatment size reduction approach should be adopted for energy efficient woody biomass processing.  When appropriate pretreatment technologies are used, woody biomass can be processed as efficiently as herbaceous biomass and agricultural residues.  Net energy output for cellulosic ethanol was estimated to range approximately from -500 to 2000 MJ/ton biomass (HHV base); indicating that the energy input/output ratio is approximately 1:1 for cellulosic ethanol.  However, net energy can reach approximately 4000-7000 MJ/ton of biomass when energy from lignin is included.