The first step is “the fractionation” that aims to extract the 3 major components of the biomass:
This step is critical because it governs the feasibility and efficiency of all subsequent operations and, largely determines how fractions can be valorized.
Lignocellulosic biomass is a particularly difficult feedstock to fractionate, because it is a composite material that is both chemically and structurally complex, being held together by both covalent and non-covalent bonds.
The exact composition of the biomass, in terms of the proportions of the three major components, varies according to botanical origin. Moreover, the chemical structure of the components is also subject to variation from one species to another. In particular, the hemicellulose component is mainly composed of xylans in grasses and deciduous wood, but in resinous species it is composed of glucomannans. Moreover, xylan is a generic term that covers an extremely large spectrum of chemical and structural diversity.
Lignified tissues generally play a structural role, conferring mechanical and chemical resistance to plants. Therefore, the overall resistance of lignocellulosic biomass to fractionation is high, especially towards biological agents such as microorganisms and enzymes. On the other hand, the use of harsher catalysts such as acids combined to physical effects, such as elevated temperatures, can lead to poorly controlled fractionation and overshooting beyond the desired endpoint. The result is the decomposition of certain biomass components, especially the pentose sugars that are the building blocks of xylans.
At present no cost-effective full scale industrial technology for biorefining is available. To circumvent many of the problems that are associated with current fractionation technologies, BIOCORE will use an innovative organosolv technology to extract the fractions. Organosolv technology for biomass fractionation is highly promising, and pilot operations are underway.
In Europe, the CIMV company, a BIOCORE partner, has developed an acetic / formic acid based process (US Patent 7,402,224). The CIMV process cogenerates partially depolymerised hemicelluloses and sulphur-free, low molecular weight lignins. In preliminary studies, cellulose extracted by the CIMV process appeared to be highly amenable to cellulase liquefaction/saccharification, with >90% of glucose being recovered in monomeric form.
What will be achieved in BIOCORE?