The July 2012 issue (Volume 5, Number 7) of the important journal Energy & Environmental Science will feature a cover story by Paul Dauenhauer of the Chemical Engineering Department. The title of the cover article is “Pyrolytic conversion of cellulose to fuels: levoglucosan deoxygenation via elimination and cyclization within molten biomass.” As Dauenhauer explains the research described in his article, “In short, we discovered that wood, when heated, has a previously unknown second chemistry. We reveal what these 'secondary reactions' are and how they work.” The findings can be used to create molecular-level models and thereby perfect pyrolysis technologies capable of competing with fossil fuel refining. The authors are Matthew S. Mettler, Alex D. Paulsen, Dionisios G. Vlachos, and Dauenhauer.
“Specifically, we identify cyclization and elimination as secondary pyrolysis reactions with intermolecular hydrogen exchange playing a role in the latter process,” as the authors explain. “Although secondary pyrolysis chemistry has long been speculated to exist, this work is the first experimental evidence for such pathways, and these findings can be used to construct molecular-level models which are required for optimization of pyrolysis technologies.”
The broader context of the research is that pyrolytic biofuels are an attractive alternative to petroleum-derived fuels. By simply heating solid biomass up to reaction temperature (400–600 C), the feedstock is depolymerized and deoxygenated to form small-molecule products (i.e., bio-oil) that are liquid at room temperature. The bio-oil product can be readily transported to centralized biorefineries for catalytic upgrading to fuels or chemicals. This work uses powder and thin-film co-pyrolysis experiments to show that primary volatiles break down within molten biomass to form secondary products with higher energy content.
Energy & Environmental Science is a journal linking all aspects of the chemical, physical, and biotechnological sciences relating to energy conversion and storage, alternative fuel technologies, and environmental science. The journal publishes important, very high-quality, agenda-setting research that is of significant general interest to the community-spanning readership.
Here’s Dauenhauer’s abstract:
Fast pyrolysis of biomass thermally cracks solid biopolymers to generate a transportable liquid (bio-oil) which can be upgraded and integrated with the existing petroleum infrastructure. Understanding how the components of biomass, such as cellulose, break down to form bio-oil constituents is critical to developing successful biofuels technologies. In this work, we use a novel co-pyrolysis technique and isotopically labeled starting materials to show that levoglucosan, the most abundant product of cellulose pyrolysis (60% of total), is deoxygenated within molten biomass to form products with higher energy content (pyrans and light oxygenates). The yield of these products can be increased by a factor of six under certain reaction conditions, e.g., using long condensed-phase residence times encountered in powder pyrolysis. Finally, co-pyrolysis experiments with deuterated glucose reveal that hydrogen exchange is a critical component of levoglucosan deoxygenation. (June 2012)