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5.3h: Summary

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    48881
  • 5.3h 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. Figure 5.28 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
    Figure 5.28: The Resulting Switchgrass Solids after Different Pretreatment Technologies.

    Click Here for a Text Alternative of Figure 5.28

    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, Table 5.3 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
    Table 5.3: Effects of Pretreatment of Biomass Recalcitrance.

    Click Here for a Text Alternative of Figure 5.28

    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

    Table 5.4 shows the conditions for ideal pretreatment of lignocellulosic biomass for dilute acid, steam explosion, AFEX and liquid hot water.

    Table 5.4: 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

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