Production of Biocrude from Biomass using Supercritical Water

Auburn University, Auburn AL

Investigators

Abstract

CBET-0828269 R. Gupta Biomass, the fourth largest energy source worldwide, can fill in gaps in fuel supply created by the depletion of petroleum. A key step in the utilization of biomass is its liquefaction to biocrude. Once in liquid form, biocrude can utilize well established pipeline transportation, refining and chemical processes that have been perfected/optimized by the petrochemical industry. For example, biocrude can be hydrogenated to produce gasoline or reformed to produce hydrogen. The use of sub- and supercritical water (above 374 PoPC and 220 bar) for liquefaction is advantageous as it can utilize biomass without drying. Due to its special characteristics (e.g., non-polar nature, high diffusivity, and low viscosity), supercritical water can solubilize organic compounds including biomass. The high reaction rates allow for the design of a compact reactor, needing typical reaction times of less than a minute. Rapid depolymerization of cellulose, lignin, and hemicelluloses results in the formation of the respective monomers and oligomers. This process, also termed as hydrothermal liquefaction, is the subject of this project. During this process, the oxygen content of the organic material is reduced from 40 wt% to between 10-15 wt%, with oxygen leaving as COB2B and HB2BO. The resulting cyclic molecules (e.g., glucose, furans, and oligosaccharides) from hemicelluloses and cellulose, and aromatic cyclic molecules (e.g, phenols) from lignin can be hydrogenated to produce fuel similar to gasoline which is an approximate mixture of cyclohexane, toluene, and iso-octane. Also the biocrude can be reformed in supercritical water itself to produce high pressure HB2B and high pressure COB2B (ready for sequestration). Intellectual merit of the project is in the fundamental study of the various steps involved including depolymerization, hydrolysis, oxidation, dehydration, and decarboxylation so that rational reactor/process design can be done. A novel reactor configuration is to be used that makes use of the differences in the de-polymerization kinetics of hemicelluloses, cellulose, and lignin components of the biomass. The reaction temperature and time can be reduced by the use of inexpensive alkali catalysts (e.g., KB2BCOB3B, NaB2BCOB3B, KOH). This project will utilize the concept of supercritical antisolvent (note: alkali salts are insoluble in supercritical water due to low dielectric) to in-situ produce catalyst nanoparticles whose newly generated high surface is expected to be highly catalytic. Biomass of interest for this study includes hemicelluloses, cellulose, lignin, switch grass, corn stover, and southern pine. Impact of various process parameters on the overall energy efficiency will be studied. Broader impact of the project is in the utilization of biomass to address critical fuel supply needs. In this project itself, the biocrude will be hydrogenated to produce gasoline, and reformed to produce hydrogen. If successful, the results can open up a novel solution to the liquid fuels for conventional transportation use and hydrogen for future fuel cell cars. Biomass derived liquid or gaseous fuels have potential to provide a cost-effective and sustainable supply of energy, while meeting the greenhouse gas reduction targets. The training of the graduate and undergraduate students (including minority students) will help transfer technology to the US industry enhancing its competitiveness. In addition, interaction with K-12 teachers will help bring the concepts of sustainable fuel to their classrooms. The successful completion of this project could have an impact on the profitability of farming, forest product, and pulp industries in the United States.