Biorefining is a transformation process of biomass resources that aims to optimise the use of all components of the plant into a wide range of products: food, drugs, molecules of interest, chemicals, materials, and bioenergy. In this, biorefining can be likened to petroleum refining: crude oil is refined into a multitude of fractions (chemicals, fuels, lubricants, etc.).
Biorefineries are generally classified according to the type of biomass they use:
> First Generation Biorefineries use raw material that can be used as food: beet or cane sugar, cereals, vegetable oils, etc.
> Second Generation Biorefineries consist mainly of cellulose, hemicelluloses and lignin materials that cannot be eaten: agricultural byproducts, byproducts from the wood industry, miscanthus, short-rotation coppice, waste, etc.
How does it operate?
The processes present in biorefinery will depend on the incoming biomass. They follow the following logic:
- The various constituents of the biomass are separated by physical means: grinding, extraction (e.g. separation of flour and bran by grinding the grain of wheat, then extraction of the gluten from the flour to obtain the starch).
- This step is essential in second-generation biorefineries, to convert the fibrous part of biomass (lignocellulose) into simple sugars.
- This is actually the central stage of biorefining processes. Two alternative routes could be used to transform biomass:
- Biochemical conversion which includes enzymatic hydrolysis and fermentation. Example: hydrolysis of starch to glucose, which is fermented to obtain bioethanol.
- Thermo-chemical conversion by gasification or pyrolysis. Syngas from gasification of biomass can be converted into longer chain molecules by a Fischer-Tropsh process or by fermentation.
- Downstream treatments. The aim of this step is to purify the products of interest at the end of the transformation by separation processes (filtration, centrifugation, extraction, distillation, etc.). One obtains then, among others, platform molecules. Example: The ethanol resulting from the fermentation is present in low concentrations (5%) and undergoes several distillation stages to obtain a purity of 99%.
Biotechnologies are very important in biorefinery where they can intervene in the “pretreatment” and “transformation” stages. Microorganisms are used directly to produce molecules of interest, or to transform, digest and degrade materials into relevant components and/or derivatives.