Metal catalyzed oxidation of lignin and related compounds
View Patent ↗Disclosed are methods for the benzylic oxidation of the lignin and related compounds. The methods include contacting lignin with a mixture containing manganese and iron, in the presence of oxygen to produce a carboxylic acid from lignin or a related compound. In some embodiments, the mixture includes cobalt.
1. A method for oxidizing lignin, comprising:
contacting lignin with manganese(II), iron(III), and a cobalt compound in the presence of molecular oxygen; and
heating the composition at a reaction temperature for a reaction time sufficient for oxidation of the lignin, thereby oxidizing lignin.
2. The method of claim 1 , wherein oxidizing lignin provides a carboxylic acid.
3. The method of claim 1 , wherein the manganese(II) comprises a compound comprising an Mn 2+ ion.
4. The method of claim 3 , wherein the compound comprising an Mn 2+ ion is Mn(NO 3 ) 2 or a hydrate thereof.
5. The method of claim 1 , wherein the iron(III) comprises a compound comprising a Fe 3+ ion.
6. The method of claim 5 , wherein the compound comprising an Fe 3+ ion is Fe(NO 3 ) 3 or a hydrate thereof.
7. The method of claim 1 , wherein the cobalt compound comprises a Co 2+ ion.
8. The method of claim 7 , wherein the compound comprising a Co 2+ ion is Co(NO 3 ) 2 or a hydrate thereof.
9. The method of claim 1 , wherein there are about 0.01 mmols to about 1 mmol of manganese to about 10 mmols of lignin monomer.
10. The method of claim 1 , wherein there are about 0.01 mmols to about 1 mmols of iron to about 10 mmols of lignin.
11. The method of claim 1 , wherein there are about 0.01 mmols to about 1 mmol of cobalt to about 10 mmols of lignin monomer.
12. The method of claim 1 , wherein the molecular oxygen is present in a partial pressure from about 15 psi (1 atmosphere) to about 100 psi at 25° C.
13. The method of claim 1 , wherein the reaction temperature is in the range of about 80° C. to about 140° C.
14. The method of claim 1 , wherein the reaction time is from about 4 hours to about 30 hours.
15. The method of claim 1 , wherein the end groups of the lignin are selected from the group consisting of aryl ketones, aryl alkyls, aryl alcohols, acetophenones, and benzylic alcohols.
16. The method of claim 1 , further comprising recovering an oxidation product of the lignin.
17. The method of claim 16 , wherein recovering the oxidation product of the lignin comprises recovering a carboxylic acid of the lignin.
18. The method of claim 16 , wherein recovering the oxidation product of the lignin comprises one or more of:
removing at least a portion of the acetic acid;
treating the oxidizing composition with a neutralizing agent;
separating the aqueous fraction from the organic fraction; and
acidifying the aqueous fraction to precipitate the product.