Table 2 Structures and isolations of DES lignin, and corresponding pyrolytic behaviors

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 M_w = 2562–1544 g/mol, Ð^e ≤ 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 °C^a

600 °C^b—char (ChI-115 > ChI-150 > ChU-115)

650 °C^a: 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 °C^a

900 °C^b—char (CC-FA > CC-LA 1:15 > CC-LA 1:1 > LA)

650 °C^a: 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/C_eff = 0.38/0.45/0.42, M_w = 2650/2574/2529 g/mol, M_n = 1233/1238/1204 g/mol, Ð^e = 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 °C^a

900 °C^a-gas/oil/char: CEL, ZEL, CAL (15/35/50%)

550 °C^a: 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 °C^c

800 °C^b—char: F4 > A4

200–600 °C^c: products rich in aromatic structures, of which the functional groups are temperature-induced to form light gases, H₂O, CO₂ CO, and CH₄

[236]