(386c) Evolving Topochemistry of Acer Saccharum Chips during Pretreatment Determined By Confocal Raman Microscopy

The utilization of dedicated biomass crops as a renewable resource of platform chemicals requires a thorough understanding of the physical and chemical processes inherent to the industry. Due to the complex network of physically and chemically recalcitrant polymers which comprise woody biomass, a pretreatment to deconstruct the material is a necessary preliminary step required for its use. Among the large variety of treatments that have been investigated, liquid hot water (LHW) pretreatment has been demonstrated to have some of the greatest potential. The technology balances low capital and operating costs with an acceptable increase in hydrolysis yield. It is well established that the primary effect of LHW pretreatment is the removal of hemicelluloses via a combination of autohydrolysis and dissolution (creating a sugar-rich side stream).As hemicelluloses are a large component of the inter-dependent network of polymers that is the cell wall, this creates more pore space and increases cellulose susceptibility to hydrolysis (enzymatic or otherwise). Also, while it is known that bulk lignin concentrations are largely unchanged, it is hypothesized that they undergo a process of plasticization and re-deposition. These facts have been corroborated by many gravimetric experiments, as well as visualization by electron and atomic force microscopy. However, in light of the as-yet unrealized potential of dedicated biomass crops, it is clear that a more fundamental knowledge describing these phenomena is required.

To this end the authors have made use of an analytical instrument finding increasing utility in the field, the confocal raman microscope (CRM). Acer sacchrum wood chips were subject to hot water pretreatment at 160^o C for varying times. Samples from this treatment were transversely microtomed into 10μm thick sections for analysis by CRM. This was coupled with gravimetric analyses as well as other spectroscopic techniques. Quantitative and qualitative analysis at the sub-cellular level for whole wood chips at real industrial reaction conditions is shown for the first time. A preferential de-lignification from the secondary wall to the compound middle lamella was observed. As pretreatment severity increased, it was seen that samples lost the clear delineation between morphological layers of the cell wall, becoming internally heterogeneous as compared to untreated samples. It is deduced this is due to limited mass transport capabilities within the wood chip, as previous works have shown that in non-mass transport limited scenarios the cell wall maintains its distinct, homogeneous layers. The quantitative data gained herein presents the possibility to increase our understanding of and model the physio-chemical processes occurring within the cell wall as a result of LHW and similar hydrolytic pretreatments.