There are three biomass feedstocks: carbohydrate (starch, cellulose and hemicellulose) and lignin from lignocellulosic biomass, triglycerides (soybean, palm, rapeseed, sunflower oil) and mixed organic residues. Ligno — cellulosic feedstocks can be obtained through the production of dedicated crops such as miscanthus or short rotation woody crops such as willow or poplar. Agricultural residues such as rice or wheat straw and paper pulp from the paper industry are other examples of sources of lign — ocellulosic material. Figure 1.5 shows the two main types of biomass feedstocks.

Biorefineries can be subdivided via over simplification into biorefineries of phase I, II and III according to the feedstock and process used, as well as product targeted (chemicals or energy) (Cherubini et al, 2009; Kamm and Kamm, 2004). A table listing examples of different technological processes to be used in a biorefinery are listed in Table 1.3.

Phase I biorefineries focus on the conversion of one feedstock, using one process and targeting one product. A biodiesel production plant would be a good example of a phase I biorefinery: rapeseed or sunflower is used for oil extraction, which is subsequently transesterified to produce fatty acid methyl esters or biodiesel using methanol and a catalyst (Shahid and Jamal, 2011).

Phase II biorefineries differ from phase I biorefineries by the number of outputs they can produce. A typical example of a phase II biorefinery is the production of starch, ethanol and lactic acid together with high fructose syrup, corn syrup, corn oil and corn meal from corn wet mil operations (EPA, 2011).

1.5 The two main types of biomass feedstocks available (adapted from Cherubini et al., 2009).

Phase III biorefineries allow for a wider range of technologies, to be combined (e. g., supercritical CO2 extraction followed by biological transformation), in comparison to phase I and II biorefineries. They also allow for a higher number of valorized outputs since several constituents of the feedstock used can be treated separately. Biorefineries falling into that category can also be called ‘product-driven biorefineries’. They generate two or more bio-based products and the residue is used to produce energy (either fuel, power and/or heat). Examples of phase III biorefineries include whole crop biorefineries which make use of several agricultural by-products originating from the same crop. Phase III biorefineries are typically the

ones targeting the production of chemicals and fuels. Sub-categories also exist according to the type of technology used (thermo-chemical or biochemical biorefineries).

Another classification has now been adopted by the IEA Bioenergy Task in 2010 to take into account the complexity of the biorefinery concept and its future developments around new technologies. It is based around the four cornerstones of the biorefinery concept: feedstock used (i. e., dedicated crop, process or agricultural residue, algae), platform products obtained (i. e., C5 sugars, pyrolysis oil or syngas), final products obtained (energy or chemicals) and process used (Cherubini et al, 2009). This classification has the advantage of accounting for the need to apply a given technology to different feedstocks and will therefore include biorefineries developed in the future. Biorefineries should not be designed in a generic way but should be adapted to the best technology and the best feedstock available in the geographical location chosen.