Table 2.

Structures and isolations of DES lignin, and corresponding pyrolytic behaviors

Raw material	DES synthesis	Isolation	Lignin	Lignin properties	Pyrolysis temperature	Pyrolytic property		Refs.
						Yield	Major compositions in oils
Populus deltoides	DESs: ChCl coupled with urea and imidazole with molar ratio of 1:2 and 3:7, followed by heating at 60 °C until a homogeneous liquid formed	Lignin regenerated and purified from pretreated Populus by DESs (115/150 °C, 15 h) via ethanol/water (1:9, v:v)	Lyophilized lignin labeled as ChU-115 (26.4%), ChI-115 (27.0%), ChI-150 (12.1%)	ChU-115/ChI-115/ChI-150: G/S-type lignin with Mw = 2562–1544 g/mol, Ðe ≤ 1.60, ASL = 7.23/8.18/3.5%, AIL = 19.2/18.9/8.5%, total carbohydrates = 5.26/3.76/1.65%, aliphatic OH = 3.61/3.65/3.60 mmol/g, total phenolic OH = 1.18/0.94/1.28 mmol/g, COOH = 1.18/0.94/1.28 mmol/g, β-O-4 = 50.3/48.3/46.9%, β–β = 10.9/13.7/6.4%, β-5 = 5.5/2.5/2.8%, S/G = 1.38/1.42/2.27	RT-650 °Ca	600 °Cb—char (ChI-115 > ChI-150 > ChU-115)	650 °Ca: ChI-115, ChI-150, ChU-115 (phenol)	[240]
Oil palm empty fruit bunch (EFB)	DESs: choline chloride/lactic acid (CC-LA) with molar ratio of 1:1 and 1:15, and choline chloride/formic acid (CC-FA) with molar ratio of 1:2, heated at 80 °C until homogeneous phase	Lignin isolated and purified from pretreated EFB using DESs (120 °C, 8 h) via ethanol/water (1:2, v:v)	DES-extracted lignin (DEEL) by LA/CC-LA (1:1)/CC-LA (1:15)/CC-FA	LA/CC-LA (1:1)/CC-LA (1:15)/CC-FA-Lignin: G/S/H-type lignin with lignin content = 75.15/78.89/80.64.85.84%, glucan = 1.42/1.94/0.00/1.39%, xylan = 5.94/0.62/1.02/0.00%, C = 52.87/52.50/53.89/47.86%, H = 5.78/5.39/5.17/5.44%, N = 0.00/1.36/0.77/2.48%, O = 41.98/40.00/38.80/42.83%, S = 0.49/0.75/1.37/1.40%, G (unit) = 13.97/29.79/49.91/35.65%, S (unit) = 83.85/64.78/50.09/62.01%, H (unit) = 2.18/5.43/0/2.34%, methoxy = 14.16/10.32/29.04/25.95%	RT-650 °Ca	900 °Cb—char (CC-FA > CC-LA 1:15 > CC-LA 1:1 > LA)	650 °Ca: LA, CC-LA (1:1), CC-LA (1:15), CC-FA (phenol)	[241]
Commercial softwood lignin (SL)	DESs: ChCl/EG (CE), ZnCl2/EG (ZE), ChCl/Aa (CA) with the same molar ratio of 1:2 at 60 °C	Lignin treated by DESs at 120 °C for 2 h and collected by acid precipitation	CEL, ZEL, CAL	CAL/CEL/ZEL: G/H-type lignin with C = 63.05/63.11/62.95%, H = 5.85/6.15/6.02%, N = 0.13/0.13/0.13%, O = 30.04/29.48/29.93%, S = 0.49/0.75/1.37/1.40, HHV = 25.76/26.22/25.94 MJ/kg, H/Ceff = 0.38/0.45/0.42, Mw = 2650/2574/2529 g/mol, Mn = 1233/1238/1204 g/mol, Ðe = 2.15/2.08/2.10, β-O-4 = 2.9/1.7/0.3, β–β = 2.3/2.2/2.4, β-5 = 4.0/3.9/4.1, G-type OH = 2.23/2.16/2.05 mmol/g, C-type OH = 0.29/0.26/0.40 mmol/g, H-type OH = 0.06/0.11/0.05 mmol/g, condensed G-type OH = 2.15/2.12/2.14 mmol/g, aliphatic OH = 0.85/1.07/1.10 mmol/g, COOH = 0.65/0.54/0.46 mmol/g, methoxy = 4.02/3.76/3.45 mmol/g	RT-550 °Ca	900 °Ca-gas/oil/char: CEL, ZEL, CAL (15/35/50%)	550 °Ca: CEL (phenol, p-cresol, guaiacol, creosol), ZEL (creosol, catechol, guaiacol), CAL (guaiacol, creosol, catechol, toluene)	[229]
Eucalyptus tenuifolia	DESs: choline chloride/formic acid (FDES) and choline chloride/lactic acid (ADES) with the same molar ratio of 1:10, heated at 60–80 °C until homogeneous phase	Raw material extracted by toluene/ethanol (2:1, v:v) for 6–8 h, followed by DESs treatment at 110 °C for 2, 4, 6 h, and lignin isolated and purified by acetone/water (7:3, v:v)	A2, A4, A6, F2, F4, F6	A2/A4/A6/F2/F4/F6: G/S-type lignin with glucan = 5.69/3.34/12.17/0/1.12/0.23%, xylan = 9.25/8.86/13.29/8.11/4.96/4.98%, galactan = 1.34/1.33/1.86/3.64/1.64/1.50%, C = 58.85/58.24/58.79/60.24/59.86/60.84%, H = 5.72/5.75/5.60/5.70/5.94/5.75%, N = 0.28/0.35/0.21/0.95/1.66/1.02%, O = 34.28/35.33/35.18/29.86/29.50/30.59%, methoxy = 23.15/22.86/21.57/23.25/23.50/22.50%	RT-800 °Cc	800 °Cb—char: F4 > A4	200–600 °Cc: products rich in aromatic structures, of which the functional groups are temperature-induced to form light gases, H2O, CO2 CO, and CH4	[236]

^aPy-GC/MS

^bTG-DTG

^cTG-FTIR