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Biomass

Biomass is a source of diverse chemicals and materials and renewable energy. There are various ways to categorise biomass: by origin (location and organism), by chemical composition, and whether it is designated as a primary crop, waste or by-product. The useful chemical components of corn are shown in the following diagram. Note that a portion of the biomass is edible (the corn kernel) but the remainder (corn stover) is inedible.

The main constituents of biomass are now examined in turn to look more closely at the types of molecules that can be made from them in a biorefinery.

Carbohydrates

Common edible carbohydrates like starch and sucrose are extensively utilised for platform molecule synthesis and can be directly employed in various processes, including fermentation and thermal treatments. The polysaccharides cellulose and hemicellulose are typically hydrolysed prior to further conversion, but diverse products are obtainable (Takkellapati et al., 2018). It is important to use the cellulose and hemicellulose from the inedible portion of plants because it comprises the majority of its mass.

As an illustration of the bio-based chemicals that can be obtained from carbohydrate, levulinic acid has significant promise in pharmaceuticals (Zhang et al., 2022). The production of levulinic acid passes through the intermediate 5-hydroxymethylfurfural (HMF). Levulinic acid has been successfully utilised in the synthesis of a variety of drugs with significant pharmacological activities, including anticancer, antiparasitic, antibacterial, antiviral, anti-inflammatory, and psychoactive drugs. A derivative of levulinic acid, 5-aminolevulinic acid, is already used in photodynamic therapy to target tumor cells (Mahmoudi et al., 2019). Levulinic acid can be further modified into gamma-valerolactone (GVL) which is a solvent and fragrance molecule.

Lignin

Lignin constitutes a significant portion of lignocellulosic material and holds potential as a primary source of bio-based aromatics. However, its complex and robust structure has limited its usefulness, and so lignin wastes are mostly confined to burning for energy recovery, gasification, or the synthesis of lignosulfonates for applications as dispersants, concrete admixtures, binders and adhesives (Jong et al., 2020). Pyrolysis generates a complex bio-oil mixture, while gasification followed by Fischer–Tropsch processing is more suitable for producing chemical intermediates. Hydrothermal treatments tailored for gasification or liquefaction, and hydrogenolysis under milder conditions show potential for producing platform molecules from lignin.  

Recent developments in the oxidation and breakdown of lignin to generate compounds such as benzoic acid derivatives have produced crucial intermediates for the production of active pharmaceutical ingredients (APIs) (Dong et al., 2023). Aniracetam (a cognitive enhancer) can be synthesised from lignin-derived p-hydroxybenzoic acid. Comparing traditional synthesis methods for APIs like trimebutine, diethylstilbestrol, dopamine, and acetaminophen (paracetamol) with lignin-based approaches, the latter can potentially reduce the number of reaction steps as well as the reliance on petroleum-based resources.

Proteins

The protein component of biomass is crucial for human and animal nutrition, and has greater economic value than the edible carbohydrate fractions. In addition to their nutritional importance, there is a growing interest in utilising proteins for the production of platform molecules and peptide-based pharmaceuticals. While many peptides are synthesised using chemical means, some are obtained from biomass-utilising microorganisms (for example, insulin) (Baeshen et al., 2014). Hydrolysis of peptide bonds provides a route to platform molecules, yielding a diverse set of amino acids (Farmer and Mascal, 2014). While the separation of amino acids is challenging, their varied functionalities presents extensive options to the chemical industry. Glutamic acid (Lammens et al., 2011) and proline (List et al., 2000) have broad roles in chemical synthesis for instance.

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