(691a) Evaluation of Structure, Topochemistry and Transport Reaction Processes in Plant Biomass during Pretreatment

Porous bio-based materials such as wood and paper have a complex internal porous structure that has a significant influence on the efficiency of further conversion processes, the properties of the materials synthesized and their end-use applications. Plant biomass is a renewable and sustainable raw material for a wide variety of bio-based products which include pulp and paper, bio-plastics, biofuels, wood plastic composites etc. The process of conversion of plant biomass to other useful products is heavily dependent on our understanding of the topochemical structure of plant cell walls and its influence on the reaction and transport properties. This is achieved through a combination of 2D and 3D characterization techniques such as Raman Spectroscopy, X-ray tomography (XRCT) and Transmission Electron Microscopy-Computed Tomography (TEM-CT).

The first step in the conversion process is the pretreatment step, which achieves the disruption of the recalcitrant structure of lignocellulose and increases the efficiency of the subsequent hydrolysis. One or more of the cell wall components are dissolved during this process which affects the structure, properties and topochemistry significantly. Hence is extremely important to evaluate these characteristics in order to develop effective pretreatment strategies. The topochemical changes in the plant cell walls during pretreatment are mapped using Raman spectroscopy. Based on this information, a transport reaction model based on a hybrid random walk and reaction is proposed to provide further insight into the pretreatment process. A fixed number of particles of the reagent used for the pretreatment process, which is representative of its concentration, diffuse through the lumen and pore spaces of the cell wall and follow a random walk path until they encounter the cell wall interface. At the interface, based on the probability of reaction and the ratio of diffusivities between the pore spaces and cell wall, they either react with one or more cell wall components or diffuse further. This stochastic dynamic approach keeps track of the spatial concentration of both the cell wall components and the reagent used for pretreatment in real time. This model can also be extended to 3D images obtained from TEM-CT. Additionally, changes in structural properties such as porosity, specific surface area and geometric tortuosity can be evaluated from TEM-CT images. Thus, using a combination of characterization techniques, it is possible to correlate the changes in 3D nanoscale architecture and topochemistry of the plant cell walls with the transport and reaction, thereby giving a fundamental insight into the pretreatment process. Ultimately, this would enable determination of effective conversion strategies not just for plant biomass, but for other similar porous materials as well.