(726e) Depolymerization of Commercial Lignin Via Bifunctional Zeolite Catalysis

Conversion of lignocellulosic biomass into fuels and chemicals is the centerpiece of biorefinery development.  Lignin makes up 15-30% of lignocellulosic biomass, and currently is an underutilized material stream. Lignin has the potential to be a valuable feedstock for chemical production due to its predominantly aromatic structure.  The goal of this project is selective depolymerization of a commercially available softwood lignin feedstock into simple monomeric phenolics and alkylbenzenes.  By developing an efficient process for converting lignin into chemicals, the goal of producing fuel and other products from lignocellulosic biomass in biorefineries becomes more attainable.

Depolymerization of lignin was accomplished through a catalytic thermochemical process, in an aqueous environment, and at a moderate temperature (~ 250°C).  The catalyst, HZSM-5, is a heterogeneous, hydrogenolysis and hydrogenation bifunctional catalyst; H₂gas was the hydrogen source for these experiments. The lignin model compound used, 2-phenoxy-1-phenylethanol (PPE), contains a β-O-4 linkage which is abundant in lignin.

Additional experiments with HZSM-5 and PPE were performed in aqueous solution, at 250ºC and 5 MPa of H₂ gas for up to 4 hours in order to observe the progress of the reaction over time.  Reaction mechanisms and kinetic parameters were developed and quantified. Additional preliminary experiments were performed using HZSM-5 and a commercial softwood lignin to obtain insight into how well the reaction system is able to convert full lignin prior to development of the catalyst system.

The overall goal is to achieve and understand the desired linkage cleavage mechanisms using the model compounds.  The knowledge will then be used to develop a catalytic system which can depolymerize the commercially available lignin into desired aromatic products.  The developed catalytic thermochemical conversion process will serve as a step towards developing a more complete biorefinery that makes use of all parts of biomass (for maximum efficiency) allowing it to not only be economically viable, but allows the global community to move towards greater sustainability.