Abstract
Previous studies showed that aromatic compounds such as lignin, phenols, and furans were main inhibitors of cellulase hydrolysis in recycled alkali black liquor (RBL), which should be removed to improve alkali utilization. In this study, three polymeric resins, XAD-4, XAD-16N, and XAD-7HP, were evaluated for their abilities to remove lignin from alkali black liquor recycled at the third time. Adsorption conditions of adsorbent dose and equilibrium time, isotherms, and kinetics were investigated. Of three tested adsorbents, XAD-16N was the most efficient, which can remove 89.84% of lignin after adsorption at an adsorbent-to-solution ratio of 1:4 for 2.5 h. Pseudo-second-order model was efficient to represent XAD-16N and XAD-7HP adsorption kinetics. Adsorption behavior of XAD-4 on RBL was fitted better to Langmuir model, while XAD-16N and XAD-7HP adsorption were more consistent with Freundlich model. The cellulase hydrolysis rate of corn straw treated with RBL after XAD-16N adsorption combined with ozone was 86.89%, which was only 0.89% lower than that of sodium hydroxide combined with ozone treatment. Structure characterization proved that the damage of XAD-16N adsorbed RBL to corn straw was similar to that of sodium hydroxide. It indicated that adsorption was effective in inhibitor removal from RBL to improve alkali utilization.
Highlights
Alkali black liquor produced by corn straw treatment contains alkali, inorganic matters, and organic chemicals, such as polysaccharides, lignin, and cross-linked macromolecules composed of aromatic groups, which has significant impacts on the environment as the toxic and hazardous waste [1,2]
Previous laboratory studies have found that the lignin removal and cellulase hydrolysis efficiency of the corn straw treated by recycled alkali black liquor (RBL) gradually decreased with the increasing cycle times, and the optimal circulation time was the third time [5]
The results showed that XAD-16N adsorption with the highest of delignification rate, followed by XAD-4 and XAD-7HP
Summary
Alkali black liquor produced by corn straw treatment contains alkali, inorganic matters, and organic chemicals, such as polysaccharides, lignin, and cross-linked macromolecules composed of aromatic groups, which has significant impacts on the environment as the toxic and hazardous waste [1,2]. Goshadrou found that RBL treatment of Cogongrass for ten times could save 45% of the alkali consumption and 59% of the water usage, and the final enzymatic hydrolysis yields of biomass were in the range of 66.40–88.70%, which showed a downward trend by further recycling [1]. Previous laboratory studies have found that the lignin removal and cellulase hydrolysis efficiency of the corn straw treated by RBL gradually decreased with the increasing cycle times, and the optimal circulation time was the third time [5]. The components of RBL were studied in the previous study, and it was found that aromatic compounds, such as lignin, phenols, benzene ring heterocycles and furans were
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