number of possibilities for the synthesis of petrol‐like or new molecules. However, apart from established processes such as those of sorbitol and glycerol, all other biomolecules generally suffer from high production costs that might be caused by
1 high price of feedstocks (depending on the required sugar purity).
2 low resource efficiency (e.g. synthesis of by‐products that lower conversions and intensify purification/separation processes).
3 high investment and operational cost required for the reactor volumes or design, or need to maintain sterile conditions during production.
4 inefficient catalysts, which could be (a) biological (enzyme and bacteria), which require metabolic engineering for higher efficiency and durability; (b) homogeneous, which tend to be corrosive, toxic, or difficult to reuse and recycle; or (c) heterogeneous, which have lower conversions even if they can be recovered and reused, but are prone to irreversible adsorption of organic molecules, leading to coke and thus reactor fouling.
Particularly, when compared to petrol‐like compounds, the disadvantages of chemicals from biomass processing become increasingly apparent in terms of overall costs. Even when only considering feedstock transportation, the advantage goes to petroleum, as it is a fluid that can be pumped (or natural gas through pipelines). Biomass tends to occupy larger volumes, given its physical nature, and is much more difficult to transport as a result. Nevertheless, the most notable difference that gives petrol‐like compounds the slight edge is the absence of oxygen functionalities (aliphatics/aromatics/olefins), which reduces their reactivity but yields larger production volumes by the addition of heteroatoms. In fact, although fossil compounds are modified via oxidation, bio‐derived compounds often require oxygen removal. In this sense, larger initial volumes are required for biomass to reach the same final product volume, making it economically inefficient. Moreover, the reactivity of oxygen groups in biomass gives inefficient processes, especially if targeting petrol‐like compounds. In this regard, a better route is to build off these different functionalities and explore new platform chemicals that are specific for biomass products. Most of the advances have been achieved largely because of catalytic pathways that allow for lower energy requirements and higher resource efficiency.
Table 1.1 Key examples of the possible bio‐based products, state‐of‐the‐art processes, and challenges [44–47].
| Bio‐product platform (example) | Process | Industrial application | Technological challenge |
|---|---|---|---|
| 1,4‐Diacid (succinic acid) | Anaerobic fermentation | Pharmaceutical, food, polymers, solvents | Separation/purification of products |
| Furanics (HMF) | Acid‐catalyzed dehydration of C‐5 and C‐6 sugars/oxidation | Food/cosmetics, polymers, construction, textiles, fuels | Low resource efficiency |
| 3‐Hydroxypropionic acid (acrylic acid) | Aerobic fermentation | Polymers, textiles | Low resource efficiency |
| Under metabolic engineering research | |||
| Amino acid (aspartic and glutamic acids) | Microbial process | Biodegradable polymers, pharmaceuticals | Need of sterile conditions |
| Complex separation | |||
| Under metabolic engineering research | |||
| Gluconic acid (methylglucoside) | Aerobic fermentation/catalytic oxidation | Food, pharmaceuticals | Low resource efficiency/catalyst deactivation |
| Itaconic acid (itaconic anhydride) | Aerobic fermentation | Specialty polymers (including biodegradable) | Low resource efficiency |
| Under metabolic engineering research | |||
| Glycerol (dihydroxyacetone) | By‐product of biodiesel/soap manufacture | Cosmetics, food, pharmaceuticals, lubricants, polymers, Li batteries | Low market price |
| Expensive purification | |||
| Catalyst separation/deactivation in upgrade | |||
| Levulinates (γ‐valerolactone) | Acid‐catalyzed dehydration of C‐6 sugars | Fragrances, food, fuels, solvents, pharmaceuticals, polymers | Low resource efficiency |
| Sorbitol (isosorbide) | Hydrogenation of C‐6 sugars | Food, pharmaceuticals | Established technology |
| Low market price | |||
| Lactones (3‐hydroxybutyrolactone) | Oxidative degradation of C‐5 and C‐6 sugars | Pharmaceuticals, chiral building block, polymers | Inefficient oxidation |
| Low resource efficiency unless starch is used | |||
| Inhibitory effect of biomass | |||
| Lactic acid (oxalic acid) | Anaerobic fermentation | Cosmetics, pharmaceutical, biodegradable polymers | High feedstock cost (high‐purity lignocellulosic sugars or food derived) |
| Separation/purification of products | |||
| Biohydrocarbons (isoprene) | Aerobic fermentation | Polymers | Investment cost (reactors) |
| High feedstock cost (high‐purity lignocellulosic sugars or food derived) | |||
| ABE (acetone, butanol, ethanol) | ABE fermentation | Fuels, solvents | High feedstock cost |
| Low resource efficiency | |||
| Lignin | Catalytic decomposition | Polymers, food, pharmaceuticals, fuels | Low resource efficiency |
Sources: Werpy et al. [44], Bozell et al. [45], Gallezot [46], Isikgor et al.