Table 5 Various integrated pretreatment methods and their outcome

Microwave + acid + alkali pretreatment

Rice straw

42.54% cellulose, 24.51% hemicelluloses, 9.16% lignin

60.07% cellulose, 14.90% hemicellulose, 4.52% lignin

1% NaOH 1% H₂SO₄ 2450 MHz frequency, 850 W and 150 ℃ for 3 min

[15]

Two-stage liquid Hot water with alkali oxygen pretreatment

Wheat straw

46.65% cellulose, 20.26% hemicellulose, 29.05% lignin

63.98% cellulose, 18.28% hemicellulose, 16.37% lignin

18% (w/w) Na₂CO₃ oxygen pressure 689 kPa, 12 h, 60 ℃, LHW^a 216 ℃ for 10 min

[97]

Extrusion + ultrasound

Rice hull

35.56% cellulose, 13.68% hemicellulose, 19.21% lignin

77.5% conversion rate of cellulose and hemicellulose

60 mesh, temperature 143 ℃; speed of screw at 350 rpm

[24]

Ball milling + alkali pretreatment

Sugarcane bagasse

37.3% cellulose, 16.6% xylan and 24.9% lignin

62.5% cellulose, 18.8% hemicellulose and 18.4% lignin

100 ℃ for 50 min

4% NaOH

[33]

Hot water treatment + wet disk milling (mechanical process)

Rice straw

31.2% glucose, 12.9% xylose, 2.6% arabinose

94% glucose, 84%xylose, 69% arabinose

135 ℃ for 60 min 9000 rpm for 10 min

[34]

Alkaline twin-screw extrusion pretreatment

Miscanthus sacchariflorus biomass

40.3% cellulose, 24.1% hemicellulose, 24.1% lignin

58.9% cellulose,

34.1% hemicellulose, 12.6% lignin

100 ℃, 0.6 M NaOH screw speed of 80 rpm for 8 min

[36]

Microwave-assisted dilute Acid

Wheat and rye stillage

16.80% cellulose, 29.62% hemicellulose, 15.57% lignin

29.67% cellulose, 28.16% hemicellulose, 9.72% lignin

0.2 M H₂SO₄ applied power at around 300 W, 15 min, 372 kPa

[38]

Ultrasonic + alkaline pretreatment

Rice straw

52.38% cellulose, 14.98% hemicellulose,

23.69 lignin

71.27% cellulose, 7.95% hemicellulose, 19.61% lignin

30 min ultrasonication

0.5% (w/v) NaOH

[40]

Sonification assisted with dilute Acid pretreatment

Rice straw

36.5% glucan, 20.8% xylan, 16.9% lignin

Total sugar yield 31.78 g/ 100 g of biomass

Sonification at 80 ℃ for 50 min, 10% (v/v) H₂SO₄

[42]

Alkali pretreatment and hydroxymethyl reagent

Sugarcane bagasse

46.88% glucan, 22.73% xylan, 22.52% lignin

61.46% glucan, 24.10% xylan, 12.38% lignin

1 M NaOH, 1.5 M formaldehyde, 80 ℃ for 2 h

[51]

Alkali salt soaking pretreatment

Sugarcane bagasse

38.11% glucan, 22.61% xylan, 16.67% lignin

36.2% glucan, 21.48% xylan, 6.45% lignin

Alkali salt- 0.5% K₂CO₃ and 0.068% K₂SO₃ at 120 ℃ for 40 min

[55]

Alkali pretreatment assisted with high pressure

Cotton stalk

39.85% cellulose, 24% hemicellulose, 23.92% lignin

64.07% cellulose

3% NaOH, 130 kPa pressure for 40 min

[56]

Phosphoric acid and hydrogen peroxide (PHP) pretreatment

Wheat straw

33.3% cellulose, 19.8% hemicellulose, 21.7% lignin

87.12% cellulose recovered, 30.1% lignin removal

74.92 g H₃PO₄ (85% w/w), 5.08 g H₂O₂ (30% w/w), 180 rpm, 40.2 ℃ for 2.9 h

[60]

Microwave-assisted with CaCl₂/CrO₃/NiCl₂ + H₃PO₄

Rice straw

24.9% cellulose, 30.9% hemicellulose

CaCl₂ + H₃PO₄- 12.4% cellulose, 14.77% hemicellulose, CrO₃ + H₃PO₄-30.5% cellulose, 21.7% hemicellulose, NiCl₂ + H₃PO₄ 39.2% cellulose, 27.4% hemicellulose

0.25 M CaCl₂/NiCl₂/CrO₃ and 3% (v/v) H₃PO₄, 700 W magnetron, 155 ℃ temperature for 20 min

[65]

Microwave-assisted ionic liquid Pretreatment

Rice straw

34.32% cellulose, 17.87% hemicellulose, 20% lignin

35.58% cellulose,

17.09% hemicellulose,

15.86% lignin

20 gm [BMIM]Cl^b

130 ℃ for 45 min

400 W power

[67]

PEG-assisted ionic liquid pretreatment

Sugarcane bagasse

42.3% glycan, 22.7% xylan, 22.7% lignin

65.3% glycan, 27.8% xylan, 3.3% lignin

[BMIM]Cl + 5% polyethylene glycol

154.6 °C, 60 min

[74]

Deep eutectic solvent assisted with ultrasonic wave

Sugarcane bagasse

38.6% cellulose, 20% hemicellulose, 24.68% lignin

42.7% cellulose, 27.86% hemicellulose, 5.4% lignin

1 mol of ChCl^c, 10 mol glycerol, ultrasonic wave of frequency 20 kHz for 20 min

[82]

Liquid Hot Water + sodium carbonate-oxygen pretreatment

Reed

38.7% glucan, 21.8% xylan, and 24.4% lignin

80.4% glucan, 16.3% lignin

Oxygen pressure 0.8 MPa, 16% N₂CO₃,

160 ℃ for 60 min

[93]

High-pressure CO₂ hydrothermal pretreatment

Peanut shell

35.7% cellulose, 20.6% hemicellulose, 34.1% lignin

38.8–45.3% cellulose, 12.4% hemicellulose, 40.8% lignin

190 ℃ for 1 h at 60 bar CO₂

[109]

CO₂ + ammonia explosion pretreatment

Rice straw

31.8% cellulose, 17.5% hemicellulose, 18.2% lignin

41.5–57.6% cellulose, 17.2–23.7% hemicellulose, 7.3–15.5% lignin

Ammonia concentration at 14.3%, 2.2 MPa CO₂,

165.1 °C for 69.8 min

[104]

Acid-impregnated steam explosion pretreatment

Corn cob

41.5% cellulose, 35.8% hemicellulose, 16.2% lignin

64.4% cellulose, 5.2% hemicellulose, 26.5% lignin

2% H₂SO₄ 100 ℃, 120 min

[88]

Steam explosion + green liquor solution (Na₂S and Na₂CO₃

Bamboo

38.29% cellulose, 28.50% hemicellulose, 28.41% lignin

62.44% cellulose, 13.38% hemicellulose, 20.08% lignin

Steam explosion at 213.3 ℃ for 5 min, green liquor 31% (w/w), 166.41 ℃ for 28.01 min

[89]

Steam explosion assisted with potassium hydroxide (SEKOH)

Rice straw

37.4% cellulose, 24.46% hemicellulose, 28.8% lignin

65.6% cellulose, 4.58% hemicellulose, 8.5% lignin

Steam explosion with the applied temperature at 170 °C for 10 min with 2% (w/v) KOH and autoclave at 121 °C for 30 min

[92]

Liq. Hot water + sodium hydroxide/oxygen pretreatment

Reed

39.54% glucan, 22.23% xylan, and 21.03% lignin

34% glucan, 5.46% xylan, and 11.3% lignin

Oxygen pressure 0.6 MPa, 8% (w/w) NaOH, 160 ℃ for 60 min

[96]

Biphasic 2-methyl tetrahydrofuran (MeTHF) + oxalic acid + water pretreatment

Bamboo

46.88% cellulose, 26.73% hemicellulose

72.17% cellulose, 0.44% hemicellulose

1 mol/L oxalic acid as catalyst + 2-MeTHF^d frequency 2500 MHz

180 ℃ for 20 min

[99]

AFEX^e + hydrogen peroxide presoaking

Energy crops (bamboo, giant reed, and Miscanthus

66.2% glucose, 26.2% xylose,

76% glucose, 12.7% xylose

30% H₂O₂, 2.0 ammonia loading, 130 ℃ for 10 min

[101]

Milling, along with microbial treatment followed by acidic pretreatment

Sesame plant residue

22.80% cellulose, 37.76% hemicellulose, 7.35% lignin

41.23% cellulose, 19.34% hemicellulose, 3.66% lignin

400 µm biomass size, Phanerochaete chrysosporium, 1% H₂SO₄

[121]

Steam explosion + Choline chloride (ChCl)

Corn Stover

46% cellulose, 19.26% hemicellulose, 20.31% lignin and 2.51% ash

74.59% glucan, 7.51% xylan, 6.22% lignin

1 MPa, 184 °C for 15 min

Biomass and ChCl ratio 1:2.2 (w/w)

[139]