Effects of Lignin Contents and Delignification Methods on Enzymatic Saccharification of Loblolly Pine

Lignin detaching from the oxidative delignified softwood during enzymatic hydrolysis and its effect on carbohydrate saccharification

Most studies about the influence of lignin on enzymatic digestibility of lignocellulose have focused on the content and properties, but less on the detaching behavior of lignin. The samples were prepared from Pinus massoniana wood chips by kraft cooking followed by delignification using oxygen/alkali (KP-O) and chlorine dioxide (KP-D), respectively. Two oxidative delignified samples with a similar lignin content were subject to enzymatic hydrolysis at both pH of 5.0 and 5.5 to investigate the effects of lignin detached rate (LDR) on substrate enzymatic digestibility (SED). The LDRs and the SEDs from both samples increased with the enzymatic hydrolysis time, and the situations of KP-D were much higher than those of KP-O under the same enzymatic hydrolysis time. The results of enzymatic hydrolysis at an elevated pH of 5.5 and the changes in concentration of free cellulase of the two samples indicated that the lignin detaching increased the free cellulase concentration, and thus promoted the enzymatic digestibility. Moreover, lignin distribution analysis by X-ray photoelectric spectroscopy and confocal laser scanning microscopy indicated surface lignin being preferentially detached. This work provided a reference for rationally designing pretreatment strategies, which can improve the efficiency of enzyme hydrolysis of lignocellulosic biomass.

Recyclable deep eutectic solvent coupling sodium hydroxide post-treatment for boosting woody/herbaceous biomass conversion at mild condition

A novel recyclable deep eutectic solvent (DES) consisting of p-toluene sulfonic acid (p-TsOH) and choline chloride (ChCl) was developed for efficient woody poplar sawdust (PL) and herbaceous miscanthus (MC) conversion at mild condition. The extraction of leftover lignin on the surface of DES pretreated residues using NaOH solution at room temperature greatly improved the enzymatic hydrolysis efficiency. Near complete cellulose conversion of PL and MC residues were obtained with a degree of delignification and xylan removal over 90% at 100 °C within 40 min. The strong correlations between xylan (R² = 0.95) and lignin (R² = 0.82) removal with cellulose conversion were observed in MC as well as positive correlations (R² > 0.77) in PL. The results demonstrated that the DES system coupling NaOH post-treatment was a promising method to achieve an economically feasible biomass conversion process, which was effective for both woody PL residues and herbaceous MC.