(356f) Etherification of Biomass Derived Molecules for Effective Diesel Fuel Production

Etherification of Biomass Derived
Molecules for Effective Diesel Fuel Production

Eric Sacia and Alex T. Bell*

Energy
Biosciences Institute and Department of Chemical Engineering, University of California, Berkeley, CA 94720

Email: alexbell@uclink.berkeley.edu

The Environmental
Protection Agency has estimated that anthropogenic CO₂ emissions due
to the transportation sector in the United States account for nearly 1/3 of net
CO₂ emissions (1.7 billion metric tons in the year 2009)¹. Since the combustion of fossil
fuels is considered to be a major contributor to the growth of atmospheric CO₂
levels, there is currently significant interest in finding ways to reduce the
net carbon footprint from transportation fuels. One approach is to convert
biomass to both gasoline and diesel range fuels. Toward this aim, the EU has
set a target that 10% of transportation fuels should be biomass sourced by 2020
in addition to the DOE's estimate that 20% of U.S. fuels will be sourced from
biomass by 2030.

To produce high quality
diesel fuels, compounds with high cetane numbers must be formed that can
replace the C11-C22 hydrocarbons derived from petroleum. While biodiesel can be
produced by transesterification of palm, rapeseed, or soybean oil, the supply
of these oils is limited. Further, there are challenges in scalability and in the
development of effective heterogeneous catalysts for transesterifaction². An alternative method is to form
diesel components from sugars generated through the hydrolysis of the
cellulosic components of lignocellulosic biomass. The reaction pathways in this
work have been  focused on producing furanic ethers since it has been shown
that such products have high cetane numbers and can be blended into
petroleum-derived diesel up to 17 wt% ³.

 Our work has focused on two
paths of utilizing the hydroxymethyl furfural (HMF) that is generated from
dehydration of glucose. First, we have carried out the direct etherification of
HMF with each primary alcohol from methanol through 1-butanol with emphasis on
ethanol and 1-butanol since these alcohols can already be readily formed from
biomass. The second pathway involves etherification of the hydrogenation
products of HMF as the aldehyde is reduced to an alcohol, forming
bis-hydroxymethyl furan (BHMF), then to a methyl group, forming methylfurfuryl
alcohol (MFA) ⁴. This effort has examined both
liquid and solid acids as catalysts and the effects of solvent on the rates of
etherification. By examining the effect of acid choice, it was determined that
specific solid acids could be used to increase selectivity beyond the
homogeneous result through catalyst shape selectivity and environment. Under
optimum conditions ether yields in excess of 98% have been achieved.

 The kinetics of
etherification have been investigated and found to be first order in the
furfuryl alcohol and the acid catalyst but zero order in ethanol. Further, the
rate of etherification is highly sensitive to the ring substituents. As the
substituent on the 2 position of HMF is altered from an aldehyde to a hydroxymethyl
group (BHMF), and finally to a methyl group (MFA), the substituent becomes more
electron donating. Increasing electron donation to the ring decreases the
activation energy of the etherification and increases the rate significantly. Decreasing
solvent polarity has also been observed to increase reaction rate by less
stabilizing charged reaction intermediates. Rate parameters for each step of
etherification have been measured and the variations in these parameters can be
interpreted in terms of the structure and composition of the reactants and the
solvent. The results of this work will contribute to a better understanding of
the means for converting biomass-derived sugars into products suitable for
blending into diesel.

1.            Inventory of U.S. Greenhouse Gas Emissions and Sinks:.
Agency, U. S. E. P., Ed. Washington DC, 2011.

2.            Huber, G. W.; Iborra, S.; Corma, A., Synthesis of
transportation fuels from biomass: Chemistry, catalysts, and engineering. Chem
Rev 2006, 106 (9), 4044-4098.

3.            Imhof, P.; Dias, A. S.; de Jong, E.; Gruter, G.-J., OA02
- Furanics:  Versatile Molecules for Biofuels and Bulk Chemicals Applications. NAM
Abstract 2009.

4.            Chidambaram, M.; Bell, A. T., A two-step approach for the
catalytic conversion of glucose to 2,5-dimethylfuran in ionic liquids. Green
Chemistry 2010, 12 (7), 1253-1262.