(144c) The Impact of Acid Site Concentration and Pore Diameter on the Cracking of Lignin Derived Monomers in Zeolites

Authors: 
Stellato, M., Georgia Institute of Technology
Sievers, C., Georgia Institute of Technology
Bommarius, A. S., Georgia Institute of Technology
In the forest bioproducts industry, tens of millions of metric tons of pulp are produced every year. An important byproduct of the pulping process is lignin, the irregular aromatic biopolymer that acts as a natural glue to hold plants together. Currently, most of the industry burns this complex biopolymer for energy rather than attempt to salvage the valuable aromatic carbon inside. One of the major hurdles to commercializing lignin based organics is that during depolymerization, lignin breaks down into a complex mixture of products. To make lignin valorization an economically feasible process, we must find a way to convert this complex stream into easily separable products.

Using lessons learned from petroleum refining, we show how a mixture of lignin monomers can be converted to an easily separable stream of light hydrocarbons and oxygenated aromatic rings by removing alkyl site chain through cracking reactions. Specifically, this talk focuses on the cracking of propylene from a phenol ring over various types of zeolites. We explore how different aspects of the catalyst, such as the concentration of Brønsted and Lewis acid sites, micropore diameter, and hierarchical structure impact conversion, selectivity, and deactivation, as well as the required regeneration procedure for restoring the original activity. We suggest that strongly bound phenolate species form on the Lewis acid sites, which hinder diffusion of reactants and products into and out of the particles. By selectively removing these sites, we show a change in reactivity and selectivity of the cracking products. Using operando IR spectroscopy, we study how these compounds interact with our catalyst surface and how the various surface species evolve over time, helping us design better and more reliable zeolites.