4. Chemical Conversion of Cellulosic Biomass

4. Chemical Conversion of Cellulosic Biomass: Paving the Way for Tomorrow’s Biofuels

Scott Auerbach (Chemistry) and Wei Fan (Chemical Engineering)

Biofuels provide a promising, renewable route to liquid transportation fuels such as gasoline, diesel and jet fuel. Even though utilization of biofuel does produce carbon dioxide, the subsequent growth of biofuel crops such as corn or switch grass sequesters and reduces that carbon dioxide for future fuel production. As such, biofuels offer an ideally carbon neutral renewable energy technology. In addition, replacement of petroleum based commodity chemicals with biomass is crucial for sustainable economy. Expanding the biofuel industry from corn ethanol (10% of today’s gasoline by volume) requires new chemical and engineering technologies to process cellulosic biomass, a readily available and cheap feedstock. Collaborative research in chemical theory in the Auerbach group [1,2], and in chemical engineering practice in the Fan group [3], is paving the way for developing highly efficient catalytic chemical conversion processes to produce chemicals and fuels.

In a biorefinery, biomass can be depolymerized into C5 and C6 sugars by hydrolysis-based approaches. However, to make gasoline-, diesel-, and jet-fuel-range alkanes that are between C8 to C15, C–C bond forming reactions must occur. Aldol condensation is one key C–C bond forming reaction that can be catalyzed by Brønsted and Lewis acid and base catalysts. Zeolite catalysts with tunable pore structures and acidities have shown promise in liquid-phase aldol condensation between biomass-derived furfural and acetone (see Fig. 1). However, catalyst deactivation from reactive oxygenated species and low selectivities to desired products require fundamental understanding of the catalytic reaction pathways within zeolite catalysts, using both computational and experimental methods, which will dramatically push forward the frontiers of biofuel production. In this collaborative project, students will model and measure reaction kinetics of aldol condensation over Brønsted (e.g., Al-MFI) and Lewis acid zeolite catalysts (e.g., Sn-MFI).

Fig 1. Zeolite nanopore with adsorbed aromatic species.

  • Catalyst synthesis and Kinetic study: An REU student in the Fan group will synthesize Brønsted and Lewis zeolites with controllable properties to obtain experimental parameters describing reaction kinetics of aldol condensation within in these zeolites.
  • Atomic level simulation: An REU student in the Auerbach group will learn the application of quantum chemistry methods to model the structures, host-guest interactions, and reaction pathways that govern zeolite-based aldol chemistry.
  • Collaborative Effort: The two REU students and their research mentors will meet regularly to combine their understandings to provide complete chemical and engineering insights into rational design zeolite catalysts for aldol condensation of biomass derived molecules and the production of diesel and jet fuel range alkanes.

CITED REFERENCES:

  1. J. Jae, G.A. Tompsett, A.J. Foster, K.D. Hammond, S.M. Auerbach, R.F. Lobo and G.W. Huber, “Investigation into the shape selectivity of zeolite catalysts for biomass conversion” J Catal, 2011, 279, 257-268.
  2. V. Agarwal, P.J. Dauenhauer, G.W. Huber and S.M. Auerbach, “Ab initio dynamics of cellulose pyrolysis: nascent decomposition pathways at 327 and 600 °C” J Am Chem Soc, 2012, 134, 14958-14972.
  3. A.R. Teixeira, X.D. Qi, C.C. Chang, W. Fan, W.C. Conner and P.J. Dauenhauer, “On Asymmetric Surface Barriers in MFI Zeolites Revealed by Frequency Response” J Phys Chem C, 2014, 118, 22166-22180.
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