Pyrolysis and Electrocatalysis of Extractive Ammonia-Processed Lignin to Increase the Value of Sugar-Platform Based Bioenergy Systems

Lignin is the second most abundant biomass component after cellulose and accounts for 15-30% of the lignocellulosic biomass by weight (40% by energy). In the nascent alcohol-based biofuels industry, only cellulose and part of the hemicellulose are used for liquids production, while the remaining lignin is burned to provide heat, using it as a low value fuel. Upgrading and sale of higher value products would improve the economics of liquid fuel bioenergy systems. 

            The extractive ammonia process (EAP) is being considered for deployment in decentralized biomass processing depots, small-scale centers that pretreat and densify biomass to produce bioenergy feedstock and animal feed. In lieu of combustion, we propose to convert ammonia extracted lignin to hydrocarbon fuels and chemicals using a combination of pyrolysis and electrocatalytic reduction. These flexible, simple technologies can be safely deployed at local biomass processing depots to diversify their product slates and improve the value proposition of future biorefineries.  The utility of this approach can also be realized at larger, centralized biorefineries that make lignin co-products.

This research established a pyrolysis protocol for depolymerizing lignin with heat treatment and investigated the electrocatalysis of authentic model compounds, model compound mixtures, bio-oil derived from EAP lignins and bio-oil from raw biomass.  Two fractions of lignin were obtained from the EAP pre-treatment step. The composition of these two fractions was determined using proximate and ultimate analysis and characterized using thioacidolysis, pyrolysis-GC/MS, thermogravimetric analysis and bomb calorimetry.  The results of these analyses suggest that EAP lignin bio-oil can be successfully stabilized using electrocatalysis at small-scale depots are larger biorefineries.