Combining the effects of pulping severity and alkali concentration to optimize the lignocellulose-based AlkaPolP biorefinery concept

Fractionation of lignin from rice straw using an acidified biphasic solvent system

To obtain lignin from lignocellulosic biomass, phenoxyethanol (EPH) was employed to construct a biphasic solvent system. The concentration of EPH in this biphasic solvent system was first studied to determine a pretreatment condition for fractionation of lignin. Then, the fractionation of lignin from rice straw was performed under the conditions of temperature 130 °C, cooking time 60 min and sulfuric acid concentration 0.1 M, in 70 % aqueous EPH solvent system. The results showed that 50.97 %, 49.52 % or 82.02 % of the removed lignin with the purity of 89.04 %, 91.30 % or 84.76 % was regenerated from EPH liquor using dimethyl carbonate (DMC), dimethoxymethane (DMM) or diethyl ether (DE) as precipitant, respectively. Additionally, the weight-average molecular weight (Mw) and dispersity index (Đ) of the regenerated lignin decreased to 4247-4809 g/mol and 1.26-1.60 compared with that of the original lignin (5654 g/mol and 4.78). Finally, the compositional and structural characteristics of lignin, e.g., molecular weight and molecular structure, were also investigated by DSC, HSQC and elemental analysis.

Pretreatment of Leucaena leucocephala wood by acidified glycerol: optimization, severity index and correlation analysis

In this study, Leucaena leucocephala wood was pretreated with aqueous glycerol having H₂SO₄ as the catalyst. Response surface methodology (RSM) and artificial neural network (ANN) were used to optimize the process parameters, catalyst concentration (1-3%), duration (120-300 min) and temperature (100-150 °C). ANN gave more accurate predictions for total reducing sugar yield than RSM. ANN also had lower values for error functions. Severity index (SI) was calculated based on the temperature, duration and catalyst concentration. Increase in SI from 0.21 * 10³ to 2.06 * 10³ increased total reducing sugar (TRS) production from 39.97 g/kg to 321.8 g/kg. Further increase in SI reduced the TRS and this change positively correlates with the loss of cellulose content. Correlation analysis showed that severity index can also be used to describe pretreatment process.

Increasing the lignin yield of the Alkaline Polyol Pulping process by treating black liquor with laccases of Myceliophthora thermophila

The Alkaline Polyol Pulping process separates cellulose from lignocellulosic biomass by dissolving lignin to a great extent. Due to the pulping conditions the dissolved lignin depolymerises and only 75% can be precipitated. To increase this amount, a 24 h reaction of laccases of Myceliophthora thermophila with lignin dissolved in black liquor of the AlkaPolP process was investigated. The influence of pH, temperature, enzyme concentration and partial oxygen pressure was examined in a batch stirred tank reactor using a Box-Behnken factorial design. Due to the enzymatic reaction the lignin polymerises which results in an enhanced lignin precipitation. The addition of a mediator improves the polymerisation but decreases the amount of precipitable lignin. The influence of the parameters on precipitation yield and molecular mass can sufficiently be described with a second-order model and optimum conditions can be assessed. FT-IR spectra of the obtained lignins revealed that its typical phenolic structure is preserved.