Systems and methods for dewatering and drying nanocellulose
View Patent ↗The present invention allows the production of nanocellulose in dry form, enabling incorporation into a wide variety of end-use applications. Some variations provide a nanocellulose-slurry dewatering system comprising: a nanocellulose slurry feed sub-system; a pre-concentration unit (e.g., a centrifuge) to remove at least a portion of the water from the nanocellulose slurry; an inlet for a dispersion/drying agent; a twin-screw extruder in flow communication with the nanocellulose slurry feed sub-system, wherein the twin-screw extruder intimately mixes the nanocellulose slurry and the dispersion/drying agent, wherein the twin-screw extruder shears the nanocellulose slurry, and wherein the twin-screw extruder is configured with one or more extruder vents to remove water from the nanocellulose slurry; and an extruder outlet for recovering a nanocellulose-dispersion concentrate. A milling device may be employed to generate a fine powder of the nanocellulose-dispersion concentrate. Methods of making and using the dewatered or dried nanocellulose are also described.
1. A method to dewater a nanocellulose slurry, said method comprising the following steps in sequence:
(a) providing a nanocellulose slurry comprising nanocellulose and water;
(b) providing a dispersion/drying agent that is selected for compatibility with said nanocellulose;
(c) in a twin-screw system, intimately mixing said nanocellulose slurry and said dispersion/drying agent;
(d) in said twin-screw system, removing at least a portion of said water from said nanocellulose slurry via one or more system vents, to generate a nanocellulose-dispersion concentrate;
(e) optionally milling said nanocellulose-dispersion concentrate to generate a powder; and
(f) recovering said nanocellulose-dispersion concentrate in solid form or liquid form,
wherein said nanocellulose slurry is pre-concentrated in a nanocellulose slurry pre-concentration step to remove at least a portion of said water from said nanocellulose slurry, prior to step (c),
wherein said dispersion/drying agent is added to said nanocellulose slurry prior to step (c),
wherein said nanocellulose is present at a concentration of about 10 wt % to about 90 wt % in said nanocellulose-dispersion concentrate, and
wherein said dispersion/drying agent is present at a concentration of about 5 wt % to about 65 wt % in said nanocellulose-dispersion concentrate.
2. The method of claim 1 , wherein said nanocellulose slurry pre-concentration step is centrifugation.
3. The method of claim 1 , wherein said nanocellulose slurry pre-concentration step is filtration.
4. The method of claim 1 , wherein said dispersion/drying agent is selected from the group consisting of waxes, polyolefins, olefin-maleic anhydride copolymers, olefin-acrylic acid copolymers, polyols, fatty acids, fatty alcohols, polyol-glyceride esters, polydimethylsiloxanes, polydimethylsiloxane-alkyl esters, polyacrylamides, starches, cellulose derivatives, particulates, and combinations or reaction products thereof.
5. The method of claim 1 , wherein said twin-screw system is operated with an average temperature from about 120° C. to about 300° C.
6. The method of claim 1 , wherein said twin-screw system is operated with a maximum system temperature that is less than the thermal-decomposition onset temperature of said nanocellulose.
7. The method of claim 1 , wherein said twin-screw system is operated with a maximum system temperature that is less than the thermal-decomposition onset temperature of said dispersion/drying agent.
8. The method of claim 1 , wherein said twin-screw system is a twin-screw extruder containing a plurality of extruder zones, and wherein zone temperatures for each of said extruder zones are independently controlled.
9. The method of claim 8 , wherein said zone temperatures increase along the length of said twin-screw extruder.
10. The method of claim 1 , wherein at least one of said system vents is operated under vacuum.
11. The method of claim 10 , wherein step (d) utilizes multiple system vents, and wherein each of said system vents is operated under vacuum.
12. The method of claim 1 , wherein said nanocellulose includes cellulose nanocrystals, cellulose nanofibrils, microfibrillated cellulose, or a combination thereof.
13. The method of claim 1 , wherein said nanocellulose includes lignin-containing nanocellulose.
14. The method of claim 1 , wherein said nanocellulose includes lignin-coated nanocellulose.
15. The method of claim 1 , wherein said method is continuous or semi-continuous.
16. The method of claim 1 , wherein said method is a batch process.