Table 4 Structures and isolations/treatments of ionic liquid lignin, and corresponding pyrolytic behaviors

Empty fruit bunches (EFB), palm mesocarp fiber (PMF) and palm kernel shells (PKS)

Pyridinium formate [PyFor]

Biomass pretreated by [PyFor], and lignin regenerated via dissolving in acetone/water followed by acetone evaporation

EFB lignin, PMF lignin, PKS lignin

EFB lignin, PMF lignin, PKS lignin: with C = 42.02/42.95/45.59%, H = 6.48/5.70/6.21%, N = 5.74/6.56/7.02%, O = 44.59/44.63/40.90%, S = 0.18/0.16/0.28%, acid insoluble lignin = 17.82/32.23/45.54%, HHV = 27.05/27.40/28.20 MJ/kg

50–550 °C^a

800 °C (10 °C/min)^b—char (exp.): EFB lignin (3.87%), PMF lignin (5.79%), PKS lignin (9.25%)

550 °C^a: EFB lignin (cyclotetradecane, naphthalene, 4-t-butylcyclohexanone), PMF lignin (naphthalene, 4-t-butylcyclohexanone, phenol), PKS lignin (phenol, 2-methoxy-phenol, 2,4-dimethylphenol)

[271, 274]

Sugarcane straw (SCS)

1-Ethyl-3-methylimidazolium acetate [Emin][OAc]

SCS pretreated by [Emin][OAc] at 90 °C for 5 h, and lignin recovered via dissolving in acetone/water followed by acetone evaporation

Recovered lignin

N/A

50–700 °C^c

700 °C—char^d: 44%

350 °C^c: phenols, methanol, formaldehyde

[125]

Industrial lignin

1-Butyl-3-methylimidazolium chloride (BMIC)

Lignin pretreated in a microwave apparatus using BMIC at 50, 100, 150 °C for 30 min and precipitated using water

BMIC-lignin₅₀, BMIC-lignin₁₀₀, BMIC-lignin₁₅₀

N/A

RT-300, 400, 500, 600, 700, 800°C^e

300–400 °C^e-liquid (exp.): BMIC-lignin₅₀ (~ 0.150 g/g_lignin), BMIC-lignin₁₀₀ (~ 0.125 g/g_lignin), BMIC-lignin₁₅₀ (~ 0.125 g/g_lignin)

300–500 °C^f: BMIC-lignin₅₀, BMIC-lignin₁₀₀, BMIC-lignin₁₅₀ (phenolics, arenes, alkanes)

[280]

Industrial lignin

1-Sulfonic acid butyl-3-methylimidazolium trifluoromethanesulfonate [B(SO₃H)min]-OTf

Lignin pretreated in a microwave apparatus using [B(SO₃H)min]-OTf at 50, 100, 150, 200 °C for 1 h under N₂, and regenerated by washing with water

Lignin-50, lignin-100, lignin-150, lignin-200

Industrial lignin: ash = 3.77%, volatiles = 56.73%, C = 66.22%, H = 6.30%, O = 25.58%, N = 1.09%, S = 0.81%

RT-300, 400, 500, 600, 800°C^e

300–400 °C^e—tar (exp.): Lignin-50 (0.1889 g/g_lignin) lignin-100 (0.1231 g/g_lignin) lignin-150 (0.1338 g/g_lignin) lignin-200 (0.0751 g/g_lignin)

300–500 °C^f: Lignin-50, lignin-100, lignin-150, lignin-200 (phenol, guaiacol, 2-ethylphenol, 4-methoxyguaiacol)

[279]

Industrial lignin

1-Butyl-3-methylimidazolium dihydrogen phosphate [Bmin]H₂PO₄

Lignin pretreated in a microwave reactor using [Bmin]H₂PO₄ at 50, 100, 150 °C for 30 min, and washed out by water

Lignin-50, lignin-100, lignin-150

Industrial lignin: moisture = 2.6%, ash = 2.5%, volatiles = 62.4%, C = 63.9%, H = 5.6%, O = 28.6%, N = 1.1%, S = 0.8%

RT-300, 400, 500, 800 °C^e

300–400 °C^e-liquid (exp.): Lignin-50 (~ 0.15 g/g_lignin) lignin-100 (~ 0.12 g/g_lignin) lignin-150 (~ 0.12 g/g_lignin)

300–500 °C^f: lignin-50, lignin-100, lignin-150 (phenolics, arenes, alkanes)

[270]