Processes and apparatus for producing nanocellulose, and compositions and products produced therefrom
Processes disclosed are capable of converting biomass into high-crystallinity nanocellulose with surprisingly low mechanical energy input. In some variations, the process includes fractionating biomass with an acid (such as sulfur dioxide), a solvent (such as ethanol), and water, to generate cellulose-rich solids and a liquid containing hemicellulose and lignin; and mechanically treating the cellulose-rich solids to form nanofibrils and/or nanocrystals. The crystallinity of the nanocellulose material may be 80% or higher, translating into good reinforcing properties for composites. The nanocellulose material may include nanofibrillated cellulose, nanocrystalline cellulose, or both. In some embodiments, the nanocellulose material is hydrophobic via deposition of some lignin onto the cellulose surface. Optionally, sugars derived from amorphous cellulose and hemicellulose may be separately fermented, such as to monomers for various polymers. These polymers may be combined with the nanocellulose to form completely renewable composites.
1. A process for producing a nanocellulose material, said process comprising:
(a) providing a lignocellulosic biomass feedstock;
(b) fractionating said feedstock in the presence of an acid, a solvent for lignin, and water, to generate cellulose-rich solids and a liquid containing hemicellulose and lignin;
(c) following step (b), mechanically treating said cellulose-rich solids to form cellulose fibrils and/or cellulose crystals, thereby generating a nanocellulose material having a crystallinity of at least 60%; and
(d) recovering said nanocellulose material,
wherein said nanocellulose material consists essentially of nanofibrillated cellulose, nanocrystalline cellulose, or a mixture of nanofibrillated cellulose and nanocrystalline cellulose.
2. The process of claim 1 , wherein said acid is selected from the group consisting of sulfur dioxide, sulfurous acid, sulfur trioxide, sulfuric acid, lignosulfonic acid, and combinations thereof.
3. The process of claim 1 , wherein step (c) does not employ any enzymes or acids.
4. The process of claim 1 , said process further comprising bleaching said cellulose-rich solids prior to step (c) and/or as part of step (c).
5. The process of claim 1 , said process further comprising bleaching said nanocellulose material during step (c) and/or following step (c).
6. The process of claim 1 , wherein said crystallinity of said nanocellulose material is at least 75%.
7. The process of claim 6 , wherein said crystallinity of said nanocellulose material is at least 85%.
8. The process of claim 1 , wherein said nanocellulose material consists essentially of nanofibrillated cellulose.
9. The process of claim 1 , wherein said nanocellulose material consists essentially of nanocrystalline cellulose.
10. The process of claim 1 , wherein said nanocellulose material consists essentially of nanofibrillated cellulose and nanocrystalline cellulose.
11. The process of claim 1 , said process further comprising hydrolyzing amorphous cellulose into glucose in step (b) and/or step (c), recovering said glucose, and optionally fermenting said glucose to a fermentation product.
12. The process of claim 1 , said process further comprising recovering, fermenting, or further treating hemicellulosic sugars derived from said hemicellulose.
13. The process of claim 12 , said process further comprising fermenting said hemicellulosic sugars to produce a monomer or precursor thereof; polymerizing said monomer to produce a polymer; and combining said polymer and said nanocellulose material to form a polymer-nanocellulose composite.
14. The process of claim 1 , wherein said nanocellulose material is at least partially hydrophobic via deposition of at least some of said lignin onto a surface of said cellulose-rich solids during step (b).
15. The process of claim 1 , wherein said nanocellulose material is at least partially hydrophobic via deposition of at least some of said lignin onto a surface of said nanocellulose material during step (c) or step (d).