Characterization of residual liquors from lignocellulosic biomass fractionation and its exploitation for biomass production: closing the loop and contributing to the circular economy

Reusing and establishing new purposes for the effluents generated during a given technological process is one of the biggest challenges that industries face to achieve the environmentally friendly status. Lignocellulosic biomass is one of the least used bioresources in the world, consisting chiefly of lignin, cellulose, and hemicelluloses, and could be obtained from several sources, among which are the residues from agricultural and industrial lignocellulosic crops. The cellulose extracted from these residues can be depolymerized giving rise to nanocellulose (NC), a multipurpose nanometer-scale bio-based material. Abundance, biodegradability, renewability, and low-cost, coupled with excellent mechanical properties appoint NC as one of the most promising nanometric biomaterials. Behind the polysaccharides present in the fiber, lignin is a heterogeneous natural aromatic biomacromolecule, and one of the most abundant biopolymers in nature. With proper and selective depolymerization, lignin has the potential to be converted into a broad spectrum of oxygen-containing aromatics. To extract cellulose from lignocellulosic biomass, it is essential to apply a combination of pre treatments and bleaching steps to the fibers. These procedures will help to surpass the recalcitrance presented by the lignocellulosic biomass and thus to isolate the cellulose from the remaining components. The employment of an alkaline chemical pre-treatment to remove lignin and hemicellulose constituents and other extractable materials from the biomass, generates a very dark liquor by-product (black liquor). The sequential bleaching step produces a yellowish liquor by-product. Despite the fact that black liquor is frequently used for heat and power generation, the separation and upgrading of the lignin present in the liquors can significantly enrich the process economics. Consequently, extracting lignin from these by-products can be considered a key issue in the successful development of biorefineries. Therefore, in these study, different biomasses were tested (hemp, castor bean and giant reed) for the lignocellulosic fractionation. The fiber content of these crops and their different composition, affects the composition of the residual liquors. The resultant liquors, before and after lignin precipitation and removal, were then characterized. Tests are being made to evaluate the effects of the application of the different liquors on the germination and production of crambe seeds (with high potential to be used by the oleochemical industry). Preliminary tests indicate that its application to produce biomass is valid and that the loop (Biomass production → biomass fractionation → byproducts recovery → biomass production), can be closed, this way contributing to the circular economy and to a resource efficient economy.