Analysis of Lignins Solubilized in Two-Stage Organosolv and Alkaline Peroxide Treatments from Haloxylon ammodendron and Elaeagnus angustifolia

Abstract

The chemistry of acidic organosolv and alkaline peroxide delignification of dewaxed Haloxylon ammodendron and Elaeagnus angustifolia was studied by analysis of lignin fractions solubilized during pretreatment with ethanol-H 2 O (60/40,v/v) under acid catalyst (0.2 N HCl) at 70°C for 4 h and post-treatment with 2% H 2 O 2 at pH 11.5 for 16 h at 45°C, respectively. It was found that alkaline peroxide post-treatment gave higher solubility and degradation of lignin (8.0% from Haloxylon ammodendron and 7.8% from Elaeagnus angustifolia ) than that of acidic organosolv pretreatment (5.5% from Haloxylon ammodendron and Elaeagnus angustifolia , respectively). The two-stage treatments together solubilized or degraded over 80% of the original lignins from Haloxylon ammodendron or Elaeagnus angustifolia . For lignins isolated from acidic organosolv pre-treatment, it was shown that the treatment gave lignin fractions that are chemically different from those released during the alkaline peroxide post-treatment by having enriched guaiacyl units, and slightly higher molecular weight and thermal stability. The depolymerization of lignins from the acidic organosolv pretreatment was lower as compared to lignins from alkaline peroxide post-treatment. Particularly, lignin preparations solubilized during the alkaline peroxide post-treatment contained carboxyl groups, indicating substantial oxidation of the lignins during post-treatment.