Chemical preconversion: application of low-severity pretreatment chemistries for commoditization of lignocellulosic feedstock

Figures & data

Figure 1.  The regionally distributed feedstock preprocessing concept.

Reproduced with permission from [13].

Table 1.  Summary of low-solids pretreatment classes and their expected chemical/structural effects at reduced severity for use as a chemical preconversion.

Pretreatment class	Reduced-severity effect as chemical preconversion treatment
Acidic	Partially depolymerize hemicellulose and some lignin depending on temperature and pH
Alkaline	Partially solubilize lignin and some hemicellulose depending on temperature and pH
Lignocellulose solvents: ▪ Organosolvents ▪ Ionic liquids ▪ Supercritical solvent	▪ Partially solubilize lignin and some hemicellulose ▪ Completely solubilize polysaccharides and lignin ▪ Solvent dependent; potentially any of the above

Table 2.  Summary of high-solids pretreatment classes and their expected chemical/structural effects at reduced severity for use as a chemical preconversion.

Pretreatment class	Reduced-severity effect as chemical preconversion treatment
Ammonia based
Ammonia	Partially depolymerize hemicellulose and lignin
AFEX™	Partially depolymerize hemicellulose and lignin; redistribute lignin to surface of particles
Oxidative
Ozone	Partially depolymerize lignin and hemicellulose; oxidize lignin
Chlorine dioxide	Moderate polysaccharide depolymerization, lignin oxidation
Acidic
Nitrogen dioxide	Partially depolymerize hemicellulose
Sulfur dioxide	Partially depolymerize hemicellulose and some lignin
High-energy irradiation
All types	Treatment dependent; also free radical crosslinking with ionizing radiation
Biological
Whole cell	Partially depolymerize polysaccharides and lignin; dependent on organism and whether sterile or unsterile
In vitro enzymatic	Partially depolymerize hemicellulose and lignin; dependent on enzyme activity(ies) applied

AFEX: Ammonia Fiber Expansion.

Table 3.  Applicability of full-severity pretreatment technologies and reduced-severity chemical preconversion treatment chemistries to various types of feedstocks.

Pretreatment/chemistry	Applicable feedstock type
	Full-severity pretreatment	Reduced-severity chemical preconversion
Low-solids treatments
Acidic: ▪ Liquid hot water ▪ Dilute aqueous acid ▪ SPORL	HB HW, SW, HB, MSW HW, SW, HB, MSW	HB HB HB
Dilute aqueous alkaline: ▪ Sodium hydroxide ▪ Calcium hydroxide ▪ Ammonia	HW, SW, HB, MSW HW, SW, HB, MSW HW, SW, HB, MSW	HB HB HB
Lignocellulose solvents: ▪ Organosolvents ▪ Ionic liquids ▪ Supercritical solvent	HW, SW, HB, MSW HW, SW, HB, MSW HW, SW, HB, MSW	HW, SW, HB, MSW HW, SW, HB, MSW HW, SW, HB, MSW
High-solids treatments
Ammonia based: ▪ Ammonia ▪ AFEX™	HB HB	HB HB
Oxidative: ▪ Ozone ▪ Chlorine dioxide	HW, SW, HB HW, SW, HB	HW, SW, HB HB
Acidic: ▪ Nitrogen dioxide ▪ Sulfur dioxide	HW, SW, HB, MSW HW, SW, HB, MSW	HW, SW, HB, MSW HB
High-energy irradiation	HW, SW, HB, MSW	HW, SW, HB, MSW
Biological: ▪ Whole cell ▪ Enzymatic	HW, SW, HB, MSW HW, SW, HB	HW, SW, HB, MSW HB

AFEX: Ammonia Fiber Expansion; HB: Herbaceous biomass (e.g., grasses, straw and stover); HW: Hardwoods; MSW: Municipal solid waste; SPORL: Sulfite pretreatment to overcome recalcitrance of lignocellulose; SW: Softwoods.

Hess JR, Kenney KL, Ovard LP, Searcy EM, Wright CT. Commodity-Scale Production of an Infrastructure-Compatible Bulk Solid from Herbaceous Lignocellulosic Biomass. Idaho National Laboratory, Idaho Falls, ID, USA (2009).

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