Hydroxide catalysts for lignin depolymerization
View Patent ↗Solid base catalysts and their use for the base-catalyzed depolymerization (BCD) of lignin to compounds such as aromatics are presented herein. Exemplary catalysts include layered double hydroxides (LDHs) as recyclable, heterogeneous catalysts for BCD of lignin.
1. A method for treating lignin, the method comprising contacting the lignin with a layered double hydroxide (LDH) catalyst comprising a nitrate anion, wherein the contacting depolymerizes the lignin resulting in a mixture comprising an aromatic compound.
2. The method of claim 1 , wherein the aromatic compound comprises at least one of p-coumaryl alcohol, coniferyl alcohol, or sinapyl alcohol.
3. The method of claim 1 , wherein the contacting is carried out in a solvent.
4. The method of claim 3 , wherein the solvent comprises at least one of water, an alkane, an alcohol, or a ketone.
5. The method of claim 4 , wherein the solvent comprises at least one of water, methanol, ethanol, propanol, isopropanol, acetone, methyl isobutyl ketone, heptane, tert-butanol, 2-ethyl-1-hexanol, or 3-methyl-3-pentanol.
6. The method of claim 1 , wherein the LDH comprises hydrotalcite.
7. The method of claim 6 , wherein the LDH has a metal counter ion comprising at least one of nickel, chromium, manganese, cobalt, copper, zinc, or gallium.
8. The method of claim 7 , wherein the nitrate anion and the metal counter ion are associated with the LDH as at least one metal salt.
9. The method of claim 7 , wherein the metal counter ion is present in the LDH at a concentration between about 5 wt % and about 15 wt %.
10. The method of claim 6 , wherein the LDH has a concentration of basic sites between about 0.1 mmol hydroxide anions per gram of the LDH on a wet basis and about 2.0 mmol hydroxide anions per gram of the LDH on a wet basis.
11. The method of claim 6 , wherein the LDH further comprises Ni(OH) 2 .
12. The method of claim 1 , further comprising, prior to the contacting, separating the lignin from a biomass feedstock comprising the lignin, a cellulose, and a hemicellulose.
13. The method of claim 12 , wherein the separating is by a Kraft process.
14. The method of claim 1 , wherein the contacting is performed at a temperature between about 150° C. and about 300° C.
15. The method of claim 1 , wherein the contacting is maintained for a period of time between about 1 minute and about 8 hours.
16. The method of claim 1 , further comprising separating the aromatic compound from the mixture.
17. The method of claim 16 , wherein the separating is performed by at least one of a chromatographic method, electrophoresis, solvent extraction, filtration, centrifugation, isoelectric focusing, or HPLC.
18. The method of claim 17 , wherein the chromatographic method comprises at least one of affinity chromatography, ion exchange chromatography, hydrophobic interaction chromatography, gel filtration chromatography, reverse phase chromatography, chromatofocusing, or differential solubilization.