Hydrolytic depolymerization of hydrolysis lignin: Effects of catalysts and solvents

• Depolymerized hydrolysis lignin (DHL) was produced from HL for rigid PU foams.
• DHL with Mw ∼ 1000 g/mole was obtained in water–ethanol mixture.
• Alkaline hydrolysis of HL at 10 wt.% NaOH loading produce DHL with Mw ∼ 850 g/mole.
• Acidic hydrolysis of HL in water led to high yield of solid residues ∼39 wt.%.
• Acidic catalyst in water–ethanol mixture improved DHL yield up to 75 wt.%.

Hydrolytic depolymerization of hydrolysis lignin (HL) in water and water–ethanol co-solvent was investigated at 250 °C for 1 h with 20% (w/v) HL substrate concentration with or without catalyst (H2SO4 or NaOH). The obtained depolymerized HLs (DHLs) were characterized with GPC-UV, FTIR, GC–MS, 1H NMR and elemental analyzer. In view of the utilization of depolymerized HL (DHL) for the preparation of rigid polyurethane foams/resins un-catalyzed depolymerization of HL employing water–ethanol mixture appeared to be a viable route with high yield of DHL ∼70.5 wt.% (SR yield of ∼9.8 wt.%) and with Mw as low as ∼1000 g/mole with suitable aliphatic (227.1 mg KOH/g) and phenolic (215 mg KOH/g) hydroxyl numbers. The overall % carbon recovery under the selected best route was ∼87%. Acid catalyzed depolymerization of HL in water and water–ethanol mixture lead to slightly increased Mw. Alkaline hydrolysis helped in reducing Mw in water and opposite trend was observed in water–ethanol mixture.