Processes and apparatus for producing nanocellulose, and compositions and products produced therefrom
View Patent ↗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 total mechanical energy may be less than 500 kilowatt-hours per ton. 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 hydrophobic nanocellulose material produced by a 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, wherein a portion of said lignin deposits onto a surface of said cellulose-rich solids, thereby rendering said cellulose-rich solids at least partially hydrophobic;
(c) mechanically treating said cellulose-rich solids to form cellulose fibrils and/or cellulose crystals, thereby generating a hydrophobic nanocellulose material having a crystallinity of at least 60%; and
(d) recovering said hydrophobic nanocellulose material,
wherein said hydrophobic nanocellulose material contains nanocellulose particles having a concentration of surface lignin that is greater than a concentration of internal lignin within said nanocellulose particles, and wherein said surface lignin includes precipitated lignin.
2. The hydrophobic nanocellulose material 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 hydrophobic nanocellulose material of claim 1 , wherein during step (c), said cellulose-rich solids are treated with a total mechanical energy of less than about 1000 kilowatt-hours per ton of said cellulose-rich solids.
4. The hydrophobic nanocellulose material of claim 3 , wherein said total mechanical energy is less than about 500 kilowatt-hours per ton of said cellulose-rich solids.
5. The hydrophobic nanocellulose material of claim 1 , wherein said crystallinity of said nanocellulose material is at least 70%.
6. The hydrophobic nanocellulose material of claim 5 , wherein said crystallinity of said nanocellulose material is at least 80%.
7. The hydrophobic nanocellulose material of claim 1 , wherein said nanocellulose material comprises nanofibrillated cellulose, nanocrystalline cellulose, or both nanofibrillated and nanocrystalline cellulose.
8. The hydrophobic nanocellulose material of claim 7 , wherein said nanocellulose material comprises both nanofibrillated and nanocrystalline cellulose.
9. The hydrophobic nanocellulose material of claim 1 , wherein said nanocellulose material is characterized by an average degree of polymerization from about 100 to about 1500.
10. The hydrophobic nanocellulose material of claim 9 , wherein said nanocellulose material is characterized by an average degree of polymerization from about 300 to about 700.
11. The hydrophobic nanocellulose material of claim 10 , wherein said nanocellulose material is characterized by an average degree of polymerization from about 150 to about 250.