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Biorefineries

A biorefinery is a facility that combines various biomass conversion processes to produce fuel and valuable chemicals. Much like an oil refinery, a biorefinery must optimise the use of its feedstock to maximise the value obtained while minimising waste. 

According to the Joint European Biorefinery Vision for 2030, a significant proportion of the overall European demand for chemicals, energy and materials could be met using biomass as a feedstock by 2030. Exploiting waste biomass in particular is advantageous because it circumvents the competition for agricultural land, and utilises materials that might otherwise be discarded in landfill. 

A biorefinery may often focus on a single product but contemporary research focuses on maximising the value of as many of the constituents within the biomass as possible.  For example, after first removing low-volume extracts (essential oils, triglycerides, waxes, pigments, aroma molecules, etc.), the next step would ideally be to target easily accessed components (sugars and starches) by fermentation, before further processing the more recalcitrant carbohydrate (e.g. cellulose) and recovering the protein (potentially for feed). Then if possible, the remaining lignin should be utilised, usually as fuel but potentially upgraded into chemicals. 

Platform molecules

The materials present in biomass can be used directly as products, or modified slightly before use, examples being cotton, hemp, flax, wood (e.g. as furniture) and paper. However, in the production of chemicals, far fewer useful compounds exist naturally in biomass. Those chemicals that are found in nature can be extracted from suitable biomass. These include certain flavour and fragrance molecules, oils, and some bioactive compounds suitable as medicines. However, most chemicals are obtained by a synthetic transformation of readily accessible precursors. In petrochemistry, crude oil and natural gas yield syngas, alkenes and aromatic compounds which are converted into plastics, pharmaceuticals, and everything in-between. In a biorefinery, biomass is converted into platform molecules.

The suite of potential platform molecules has enormous chemical diversity, allowing access to complex molecules and potential pharmaceuticals. Economically viable production methods appears to be the biggest barrier to further commercialisation of these compounds. An update to the US Department of Energy report that first proposed the twelve aforementioned platform molecules in 2004 was later revisited (Jong et al., 2020). Aspartic acid, glucaric acid, glutamic acid, itaconic acid, and 3-hydroxybutyrolactone were de-proioritised due to unfavourable market conditions, and in their place the established bioethanol and lactic acid were included alongside renewable sources of hydrocarbons. Where needed, pyrolysis can be used to reduce biomass to the same base chemicals produced by oil refineries (syngas, ethylene, propylene, butylenes, benzene, toluene, and xylenes).