EGEE 439
Alternative Fuels from Biomass Sources

4.3h Summary

4.3h Summary

Of the methods we’ve discussed, there are pretreatment options that lead the others (some under commercialization). The current leading pretreatment options include dilute acid, AFEX, liquid hot water, lime, and aqueous ammonia, with dilute acid and water, AFEX, and lime under commercialization. The figure below shows switchgrass before pretreatment and after several pretreatment options, i.e., AFEX, dilute acid, liquid hot water, lime, and soaking in aqueous ammonia (SAA).

Resulting Switchgrass Solids after Different Pretreatment Technologies
The Resulting Switchgrass Solids after Different Pretreatment Technologies.
Click Here for a text description of the switchgrass solids.

Control: mix of yellows and brown sticks

AFEX: dull brown sticks

Dil. Acid: red-brown clumps

LHW: dark brown red sticks

Lime: yellow-brown clumps and sticks

SAA: light brown sticks

Credit: Donohoe et al., 2011. Bioresour. Technol.

To summarize the methods of pretreatment, the table below shows some of these pretreatment methods and the major and minor effects on lignocellulosic biomass. All methods (AFEX, dilute acid, lime, liquid hot water, soaking aqueous ammonia, and treatment with SO2) have an effect on increasing surface area, removing hemicellulose, and altering lignin structure. Only AFEX, lime, and SAA pretreatment remove lignin, and AFEX and SAA decrystallize cellulose.

table showing Effects of Pretreatment of Biomass Recalcitrance
Effects of Pretreatment of Biomass Recalcitrance.
Click Here for a text alternative to the image.

Effects of Pretreatments of Biomass Recalcitrance
Pretreatment Increases Accessible Surface Area Decrystallizes Cellulose Removes Hemicellulose Removes Lignin Alters Lignin Structure
AFEX Major Effect Major Effect Minor Effect Major Effect Major Effect
Dilute Acid Major Effect Major Effect Major Effect
Lime Major Effect Not Determined Minor Effect Major Effect Major Effect
Liquid H2O Major Effect Not Determined Major Effect Minor Effect
SAA Major Effect Major Effect Minor Effect Major Effect Major Effect
SO2 Major Effect Major Effect Minor Effect
Credit: Mosier et al., 2005. Bioresour. Technol., 96: 673-686

This table shows the conditions for ideal pretreatment of lignocellulosic biomass for dilute acid, steam explosion, AFEX, and liquid hot water.

Comparison of Pretreatment Processesa
Pretreatment Process Dilute Acid Steam Explosion AFEX Liquid Hot Water
Reactive Fiber Yes Yes Yes Yes
Particle Size Reduction Required Yes No Nob No
Hydrolyzate Inhibitory Yes Yes No Slightly
Pentose Recovery Moderate Low High High
Low-Cost Materials of Construction No Yes Yes Yes
Production of Process Residues Yes No No No
Potential for Process Simplicity Moderate High Moderate High
Effectiveness at Low Moisture Contents Moderate High Very High

Not Known

a Modified from (86); AFEX ratings from Bruce Dale (personal communication).

b For grasses, data for wood not available.

Credit: Lynd, 1996. Annual Rev. Energy Environ., 21: 403-465