Lignocellulose HydrolysisLignocellulosic biomass, primarily comprised of cellulose, hemicellulose, and lignin, is an abundant and renewable resource that holds great promise as a source of biofuels and renewable biobased chemicals and biomaterials. Lignocellulosic biomass can be processed in a number of ways, one is through the hydrolysis of the structural polysaccharides (cellulose and hemicellulose) into their constituent sugars, a reaction commonly facilitated by acid or enzymes, followed by the fermentation of these sugars by yeast or other microorganisms.
Acid HydrolysisHydrolysis of lignocellulose can be catalysed with acids. These can be used in either dilute or concentrated forms, with each approach having its own advantages and disadvantages.
Dilute-Acid ProcessDilute-acid hydrolysis involves the use of acids, in relatively low concentrations, to catalyse the hydrolysis of lignocellulosic biomass. The approach is often used as a pretreatment to hydrolyse hemicellulose, leaving the cellulose and much of the lignin in the solid which can then be subjected to further hydrolysis. This subsequent hydrolysis can be using enzymes or it can again use dilute-acid, but under more severe process conditions. Click here to read more about the use of dilute-acid in biomass pretreatment. The rest of this page focuses on the use of dilute acids for the more extensive hydrolysis of biomass, including cellulose.
Sugar Degradation ProductsIt can be possible for the production of the monosaccharide to not be the end-point of the dilute-acid process. Some sugars may be further degraded to a variety of different products. For example, furfural can result from the acid-catalysed degradation of pentose (5-carbon) sugars (such as xylose) hydrolysed from hemicellulose. Hydroxymethylfurfural and, with further degradation, levulinic acid and acetic acid, can result from the acid-catalysed degradation of hexose (6-carbon) sugars, such as cellulose-derived glucose.
Effect of Process ConditionsThe efficiency and output of dilute acid hydrolysis are heavily influenced by several key process variables, detailed below:
Hemicellulose vs. CelluloseGiven that the hydrolysis of hemicellulose requires much less severe process conditions than the hydrolysis of cellulose, and also given that the sugars liberated from hemicellulose are highly susceptible to further conversion to an array of different sugar degradation products, dilute-acid hydrolysis technologies focused on the use of dilute-acid to hydrolyse both polysaccharides tend to involve two stages.
Processing Beyond SugarsIt can be difficult to stop dilute-acid hydrolysis at the production of monomeric sugars. Additionally, sometimes the resulting hydrolysate can be challenging for subsequent fermentation due to the presence of fermentation inhibitors arising from the degradation of these sugars.
1. Understanding Your Requirements
2. Detailed Feedstock Analysis
3. Hemicellulose Hydrolysis
4. Cellulose Hydrolysis
5. Downstream Processing
6. Product Recovery
7. Valorisation of Remaining Biomass
8. Validation at Higher TRLs
9. Technoeconomic Analysis (TEA)
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