Progress in oxidation of industrial lignin from 2015 to 2021.

Raw material	Lignin type	Oxidant	Reaction temperature (°C)	Solution	Catalyst	Productivity (wt%)	Main products after degradation	Ref.
Cork	AL	H2O2	80–120	1-Ethyl-3-methylimidazole acetate solution	Nb2O5	0.26–0.99	G, SYA, V, acetovanillone, homovanillic acid	91
					CoCl2	0.41–0.90
—	Dealkylated lignin	O2	160	NaOH	LaFe0.2·Cu0.8O3	10.0	SD	92
—	KL	O2	120	Phenol	ReOx/γ-Al2O3	7.3	V	93
Black liquor	AL/KL	TEMPO/Cu(OAc)2	110	Ionic liquid (ammonium 2-hydroxyethyl formate)/formic acid and sodium formate		75	Ethyl acetate soluble product	94
—	Supercritical hydrolysis of lignin	TEMPO, HNO3/HCl, O2	150	Methanol	Polyoxometalates	19.4	Aromatic monomer	95
Bagasse, poplar, bamboo or Miscanthus powder	OL	O2	160	Water, n-octane, n-propanol	CuSO4	6.09 ± 0.38	PA	96
						2.37 ± 0.25	CA
						0.56 ± 0.08	SA
Poplar	—	O2	190	Buffer and NaOH	CuSO4	7.8	V	97a and 97b
						23.4	SD
Pine	KL	Nitrobenzene	180	NaOH	—	10.9	V	98
Cryptomeria japonica	Soda anthraquinone lignin	Nitrobenzene	180	NaOH	—	8–11.2	V
Cryptomeria japonica	Extraction of lignin with neutral solvent	Bu4NOH aqueous solution	120	NaBr, NaCl, NaOH, Na2SO4	Bu4NCl	21.0	V	99
						1.7	HM
Straw	AL	Battery anode stainless steel	25	NaOH	Current density: 50 mA cm−2	6 (Vanillin)	V, acetosyringone, phthalic acid	100
Black liquor	KL	Battery anode nickel base material	80	NaOH	Current density: 1.9 mA cm−2	0.34 mg ml−1 (Vanillin)	V, HM, acetovanillone	101
—	KL	Battery anode nickel base material	80	Strong alkaline electrolyte, desorption of ethyl acetate and acetic acid	Current density: 38 mA cm−2	1.3	V	102
—	KL	—	—	Acetonitrile and deionized water	TiO2 : lignin = 1 : 0.5	1.68	V	103
—	AL	H2O2	27	H2O	UV-vis radiation	—	About 64% reduction in COD values	104