Pretreatment optimization from rapeseed straw and lignin characterization

The objective of this work are (1) to optimize the operating conditions of chemical pretreatments (organosolv, soda), (2) to present a comprehensive and comparative assessment for delignification of rapeseed straw to make the cellulose more accessible to hydrolysis and (3) to characterize for the first time the rapeseed straw lignin. Evaluation criteria for optimization of the pretreatment conditions were based on high lignin yield in the hydrolysate and high sugars recovery from the solid residues obtained after filtration of whole pretreated materials for further valorization into eco-sourced polymers. Several experiments have been conducted according to a central rotatable design in which reaction temperature, holding time and NaOH concentration were varied and different aspects have been observed. The optimized results showed a sugar recovery yield of 59% and lignin removal of 31% at soda conditions 4.4 h, 89 °C and 0.4 M NaOH compared to 63% sugars recovery and 43% lignin removal with Organosolv pretreatment at conditions of 78 min, 162 °C and 1.6% H2SO4. Cellulolytic enzyme lignin, soda and organosolv lignins extracted from rapeseed straw were subjected to structural analysis by FTIR,13C NMR and HSQC. The rapeseed lignin is mainly composed of S and G basic units with S/G = 1.64. The lignin produced with the organosolv process appears to be primarily unaltered and potentially suitable for future applications.