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Table 2 Humification of biomass and non-lignin materials by alternative methods

From: Latest development in the fabrication and use of lignin-derived humic acid

Raw material

Chemical processes

Conditions

Yield

Refs.

Corn stalk

Two-stage Hydrothermal

180 ℃, 4 h, pH 1

180 ℃, 4 h, pH 13

HA-28.7%

[83]

Wheat straw

Hydrothermal

220 ℃, 4 h

HA-30.2%

[88]

Broccoli stem

Hydrothermal

204–220 ℃, 10 min

HS-198 g/kg

HA-50.7 g/kg

FA-28 g/kg

[89]

Sugarcane exocarp

Hydrothermal

200 ℃, 1 h

HA-14.85%

[86]

Cabbage leaf

Alkali- Hydrothermal

KOH (25%), NH4OH (20%), 195 ℃, 4 h

Not available

[87]

Glucose, saw dust, tulip tree leaves

Alkali-Hydrothermal

KOH

HA-1.8%

[84]

Food wastes (rice, meat, cabbage, potatoes)

Hydrothermal

215 ℃, 1 h

HA-43.5

[91]

Fermented Furfural

Alkali dissolution and acidification

KOH (8%)

70 ℃, 2.5 h

HA-49%

[85]

Carbohydrates monomer

Hydrothermal

([BMIM]Cl) (10 g)

CrCl3 (0.74 g)

110 ℃, 4 h

HA-56.6%

[92]