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1. (WO2017171652) PROCESS FOR THE DEPOLYMERIZATION OF LIGNIN UNDER NEUTRAL OXIDATIVE CONDITIONS
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Claims

1. A process for depolymerizing lignin to monomers and/or oligomers characterized in that the lignin is reacted with an oxidation agent at a pH between about 5.0 and about 8.0 in the presence of a polar aprotic solvent at elevated temperatures.

2. The process of any of the preceding claims, wherein the polar aprotic solvent has a dielectric constant of at least 20.

3. The process of any of the preceding claims, wherein the polar aprotic solvent is a polar aprotic solvent or a mixture of polar aprotic solvents selected from the group consisting of dichlorome thane, tetrahydrofuran, ethyl acetate, acetone, N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, γ-valerolactone, γ-butyrolactone ethylene carbonate, butylene carbonate and propylene carbonate.

4. The process of any of the preceding claims, wherein the reaction occurs in a solvent that comprises at least 90% by volume of aprotic solvent.

5. The process of any of the preceding claims, wherein the reaction occurs in the absence of a metal catalyst.

6. The process of any of the preceding claims 1 to 4, wherein the reaction occurs in the presence of a metal catalyst, optionally wherein the metal is selected from a transition metal.

7. The process of claim 6, wherein the transition metal is selected from the group V to group IX elements.

8. The process of claim 6 or 7, wherein the metal catalyst is a metal oxide or a metal complex selected from the group consisting of rhenium trioxide, vanadium pentoxide, molybdenum di- or trioxide, rhenium (IV) oxide, rhenium (VII) oxide, ammonium perrhenate, potassium perrhenate, tetrabutylammonium perrhenate and methyl rhenium trioxide.

9. The process of claim 1 wherein the oxidation agent is oxygen.

10. The process of claim 9, wherein the oxygen is present in at least 2% by volume when being used in an ambient gas.

11. The process of claim 10, wherein the oxygen is used in the form of air or as diluted oxygen in a matrix gas.

12. The process of claim 10, wherein the oxygen is substantially undiluted oxygen gas.

13. The process of claim 1, wherein the depolymerization is performed under pressure of at least 3 bar.

14. The process of claim 1, wherein the temperature is at least 80 °C.

15. The process of claim 1, wherein the reaction is performed in a reaction time of about 1 h to 12 h.

16. The process of claim 1, wherein the lignin or its precursor is selected from any kind of cellulosic biomass.

17. The process of claim 1, wherein the process comprises the steps of a) reacting lignin or lignin containing biomass with an oxidation agent under pH neutral conditions in a polar aprotic solvent at elevated temperatures,

b) separating the reaction mixture to obtain a first product mixture comprising the monomers and/or oligomers and the solvent and a second product mixture comprising the remaining lignin and by-products.

18. The process of claim 17, wherein the first separating step is performed by filtration.

19. The process of claim 17, further comprising a purification step to remove the solvent of the first product mixture from the monomers and/or oligomers by co-distilling the monomer together with a high boiling solvent.