Lignin energy content

Discussion. The overall effect of lignin hydroxy content on the interaction with HPC is illustrated in Figure 4. As the hydroxy content is reduced, the interaction energy increases until a maximum is reached at a DS of ca. 

The CASH process was developed by cooperation between Canada, the USA and Sweden. In this method, hydrolysis occurs in two steps with dilute sulfuric acid at a temperature around 200 °C (pressure 8-25 bar) and the fermentation of sugars by yeast to ethanol. It has been shown that by using SO2 and dilute sulfuric acid in two steps, this increases the sugar and ethanol yield, since the amount of inhibitors such as furfural is decreased. The process was developed for raw materials such as sawdust and other residues from trees. The ethanol yield is about 30% of the energy in the raw material and there are also by-products, with up to 40% of the energy content in solid form (lignin), which can be used as biofuel. 

Extractives and lignin have a higher energy content than cellulose and hemicellu-loses due to the difference in oxygen content of these fractions. An example of an estimated energy distribution by fraction in two wood species is given in Figure 2.3.3. 

Lignin is a high-energy content biopolymer rich in phenolic components. It provides structural integrity to plants. The combination of hemicellulose and lignin provide a protective sheath around the cellulose and this sheath must be modified or removed before efficient hydrolysis of cellulose can occur. 

For example, in a (thermochemical) biorefinery, biomass is converted into energy carriers such as transportation fuels (e.g., ethanol), heat, and power and/or chemicals. In terms of energy content, the amount of biomass for (transportation) fuels and CHP (e.g., by combustion) is much higher than the amount used for the production of chemicals. However, in terms of added value, chemicals can provide a significant contribution to the overall cost effeaiveness of the refinery. When the main product of a biorefinery is (hemi) cellulose bioethanol, the lignin ends up in a residue that mostly is used as a fuel to generate heat. The economics of the biorefinery will benefit much from the valorization of this lignin-rich residue to value-added aromatic chemicals. 

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