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

Engel, Norman, Hundt, Martin, Schapals, Tino
Bioresource technology 2016 v.203 pp. 96-102
Fourier transform infrared spectroscopy, Myceliophthora thermophila, biomass, cellulose, enzymatic reactions, laccase, lignin, lignocellulose, models, molecular weight, oxygen, pH, polymerization, polyols, pulping, temperature, waste liquors
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 24h 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.