5.3h: Summary

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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).

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 Processes^a

Pretreatment Process	Dilute Acid	Steam Explosion	AFEX	Liquid Hot Water
Reactive Fiber	Yes	Yes	Yes	Yes
Particle Size Reduction Required	Yes	No	No^b	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

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