(435f) Online Monitoring of Lignin Liquid Phase Conversion Processes By in-Situ ATR-IR Spectroscopy

Lignocellulosic biomass is becoming an increasingly important alternative resource for biofuels production. Lignocellulosic biorefinery operations must produce chemicals as well as energy vectors in order to be competitive, making use of allthe major components of lignocellulose including lignin. Indeed, this aromatic polymer holds great potential for the sustainable production of renewable aromatics and phenolics. [1] Typical lignin valorization efforts entail the study of depolymerization and defunctionalization steps and almost inevitably involve complex reaction mixtures. In order to develop more efficient catalytic lignin valorization processes, more insight is clearly needed in the chemistry of lignin linkage cleavage and defunctionalization.

Our group has, for instance, reported on the solubilization and catalytic conversion of a wide variety of lignins in aqueous or ethanolic solvents. [2] A two-step route involving lignin depolymerization by liquid phase reforming step followed by hydrodeoxygenation of the resulting lignin-oil to yield, amongst others, lignin-derived BTX. [3] Improvements in the efficiency of this two-step conversion process requires further insight into the changes in molecular weight upon dissolution and depolymerization as well as insight in the changes in the chemical structure of lignin upon conversion. The application of in situ spectroscopic techniques for online monitoring of the liquid phase lignin conversion processes can prove very useful in this respect. Here, we report on our efforts to further develop the use of in situ spectroscopic techniques such as ATR-IR for on line monitoring of catalytic lignin conversion processes. Liquid phase reforming reactions are run in the presence of a heterogeneous Pt catalyst in ethanol/water at 225°C and 58 bar in a semi-batch autoclave equipped with an ATR-IR crystal. Changes in the fingerprint region provided insight into the rate, nature and extent of lignin depolymerization. The approach taken is expected to be of interest to the various liquid phase lignin depolymerization strategies that are currently being developed.

[1] Zakzeski, J., Jongerius,  A. L.,  Bruijnincx, P. C. A. and Weckhuysen, B. M., Chem. Rev. 110 (2010) 3552.

[2]  Zakzeski, J., Jongerius,  A. L.,  Bruijnincx, P. C. A. and Weckhuysen, B. M., ChemSusChem, 5 (2012) 1602.

[3] Jongerius, A. L., Bruijnincx, P. C. A. and Weckhuysen, B. M., Green Chem., 15 (2013) 3049.