In the push towards reducing our reliance on fossil fuels, biomass has become a key feedstock for the production of renewable products, fuels, and energy. In particular, new efforts focus on the transformation of sugar and starch crops, cellulose, and municipal waste into chemical products typically derived from fossil fuels.
What biomass and bio-derived products are, and what they are not
Biomass commonly refers to any organic matter, particularly that which can be used to generate chemical products or energy. Traditional examples are wood, crops, marine plants, animal waste, and municipal waste. Some of these examples, such as sugar and starch crops, are dedicated feedstocks, planted specifically to be refined into chemical products or energy, whereas others, such as municipal waste, aim to maximise usage efficiency of already existing materials.
One key benefit of using biomass feedstocks is that they are either largely renewable or they aim to maximise usage efficiency of waste stream from other industries, such as logging and paper. Further, especially when considering plant-derived biomass, carbon dioxide is absorbed from the atmosphere during crop growth, making the usage of such biomass feedstocks close to carbon neutral.
However, despite being renewable, the distinct chemical products derived from biomass are structurally identical to those produced from traditional fossil fuel sources, and their usage and disposal must still be considered. For example, a polyethylene carrier bag produced from sugar cane is no different (and no more biodegradable) than one produced from crude oil. Further, although fuel sources such as wood are typically regarded as being carbon neutral, burning biomass such as municipal waste for energy still releases carbon dioxide into the atmosphere.
Another key consideration for production of biomass is that many purpose-grown feedstocks, such as sugar and starch crops, require large amounts of land and resources to grow effectively. This can lead to tensions, especially when consideration is given to increased fresh water usage and the conversion of arable land to biomass production as opposed to food production. As a result, particular interest is being given to the usage of non-competing biomass such as cellulose, non-edible biomass, and waste streams for bio-processing.
Common examples of biofuels and bio-derived products
Bio-derived products and fuels are becoming increasingly common in our everyday life. One major development in the biofuel sector that took effect in September 2021 in Great Britain and November 2022 in Northern Ireland was the transition of standard grade petrol to E10, meaning that it contains up to 10% renewable (bio-)ethanol. As well as being an efficient fuel additive, bio-ethanol is a key platform molecule in bio-refinery processes, as it provides a highly functionalisable two carbon building block. Bio-ethanol is readily produced from the fermentation of sugars and starches, and can be further transformed into other platform molecules, such as ethylene and acetaldehyde, or higher value products such as butanol, butadiene, and pyridine. The technology to produce bio-ethanol, namely fermentation of carbohydrates, is essentially unchanged from centuries ago when beer was first brewed. Whilst it has been shown that low volume fermentation broths can be catalytically converted to high-value products (including even beer and wine, see Catal. Sci. Technol., 2017, 7, 5128-5134), azeotropic distillation allows high-purity anhydrous ethanol to be produced, which is typically more suitable for further transformation on an industrial scale.
Another example of a bio-derived product found commonly in everyday life is polylactic acid (PLA). PLA is readily produced via either direct condensation of lactic acid or ring-opening polymerisation of lactide (a cyclic dimer of lactic acid), both of which are sourced primarily from fermentation of sugars and starches. PLA exhibits properties similar to common plastics, such as polyethylene, polypropylene and polystyrene, but has the advantage of being biodegradable owing to the ester bond within the polymer backbone. As a result of these beneficial features, PLA is slowly replacing traditional plastics in typical applications such as food packaging, disposable tableware, and fabrics. PLA also finds use in medical implants, such as pins and screws, which slowly degrade into lactic acid in the body over the course of 6 to 12 months in order to gently transfer their load to the body.
Outlook and future development of bio-refineries
In terms of future outlook, the Global Bio-refinery Market Report for 2022 to 2027 published by Research and Markets, indicates that further growth can be expected in the area of bio-derived products and fuels. The report presents an expected growth in the global bio-refinery market from around USD 141.8 billion to USD 210.3 billion over the five-year period to 2027, representing a compound annual growth of 8.2%. As such, it is clear that there is sustained interest in continued development of bio-derived fuels and products.
At present, many industrial scale chemical processes are optimised for hydrocarbon feedstocks and are typically unsuitable for bio-processing, owing to the increased levels of water and oxygen in bio-derived products. We can therefore continue to expect substantial research effort to be dedicated to the discovery and optimisation of catalysts and chemical processes able to refine biomass into useful products and fuels. Particularly, we can expect further developments in the production of key platform molecules which may be introduced as replacement feedstocks into existing chemical infrastructure.
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