(403c) Impact of Alkaline Deacetylation and Pelleting of Corn Stover at the Depot

Authors: 
Aston, J. E., Idaho National Laboratory
Thompson, D. N., Idaho National Laboratory
Currently, approximately 258 million tons of the Billion Tons (DOE goal) is considered accessible in the existing feedstock supply systems. Additionally, much of this biomass is highly variable in properties important to handling, densification and conversion. An important role of the distributed processing concept is to deliver feedstock to biorefineries with low variability and consistent conversion performance. Achieving this goal would decrease risk to the biorefinery and reduce operating expenses. This work examines the impact of deacetylation at the depot on both the feedstock supply chain and the conversion facility.

Single-pass corn stover was ground to 1 inch using a Wiley Mill and stored at room temperature and humidity. The corn stover was split and deacetylated in a stirred-batch reactor. The recovered solid residuals were collected and compared against raw corn stover using analyses that measured total ash, ash composition and proximate/ultimate. In addition, the chemistry of the deacetylation medium was determined along with the ash and CHNO composition of solids precipitated from the deacetylation medium. In this manner, data was collected to support a full mass balance of the process. The energy to grind and pellet the raw material and alkaline deacetylated material was measured. The alkaline deacetylation resulted in a 13.8% decrease in required grinding energy, and a 23.1% decrease in required pelleting energy. It also resulted in increased carbohydrate content and reduced ash for the biorefinery feedstock. In addition, it was observed that the deacetylated material could be ground at much higher moisture contents. This would allow corn stover to be pelleted, and then dried using a more efficient process. Finally, raw and deacetylated material was subjected to different pretreatment severities with and without disc refining. Key findings were that deacetylation and pelleting were found to: 1) negate the need for disc refining; 2) increase sugar yields by over two-fold with when no pretreatment was applied; 3) require significantly lower severity of pretreatment to achieve the same, or greater, sugar yield; and 4) increase maximum sugar yield to near 100%.