Production of second-generation bioethanol from lignocellulosic biomass requires pretreatment to open the plant cell wall structure and improve enzyme access. Many different thermochemical pretreatments have been extensively developed and employed but, the exact nature of plant cell wall recalcitrance and the most efficient and economical approach to alter plant cell wall structure via pretreatment still remains elusive. In order to understand the role that non-cellulosic plant cell wall polymers have on the overall efficiency of pretreatment, the structural evolution of the amorphous plant cell wall polymers was investigated during dilute acid pretreatment by employing in-situ small-angle neutron scattering (in-situ SANS). In this study, we observed real-time structural changes not possible by any other technique. To deconvolute the structural contributions of the lignin and hemicellulose, raw switchgrass (NATV) and isolated fractions of holocellulose (HOLO) and cellulose (CELL) from NATV were studied. Our results show aggregate particles first appear around 80 °C for NATV and HOLO samples. These particles at a low severity are presumably composed of hemicellulose oligomers. The formation of much larger aggregate particles presumably composed of lignin were only observed in the NATV sample. For HOLO sample, an increase in the aggregate particle size presumably composed of pseudo-lignin was observed at relatively much higher severity. These particles become progressively more compact and denser with increasing pretreatment temperature/time. Consistent with our interpretation of structural evolutions in NATV and HOLO samples, no such aggregate particles were observed in CELL samples for the entire duration of the pretreatment. These results suggest that not only lignin, but also hemicellulose can form aggregate particles within the plant cell wall during pretreatment and potentially have an influence on the pretreatment efficiency.

Switchgrass lignin and hemicellulose structural reorganization observed in situ during dilute acid pretreatment

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.