| Reaction pathways for conversion of GVL to butenes and CO2, and the integrated conversion of
GVL to both a liquid stream of alkenes for use in transportation fuels and a gaseous stream rich in CO2 that is appropriate for further processing options. Credit: Bond et al., Science. Click to enlarge. |
Researchers at the University of Wisconsin, led by Dr. James Dumesic, have developed a process to convert aqueous solutions of γ-valerolactone (GVL), an intermediate produced from biomass-derived carbohydrates, to liquid alkenes in the molecular weight range appropriate for drop-in replacement transportation fuels by using an integrated catalytic system that does not require an external source of hydrogen or precious metal catalysts.
Not requiring hydrogen or precious metal catalysts could contribute to a lower cost for a commercial-scale version of the process than some other renewable hydrocarbon fuel technologies. The system also captures carbon dioxide under high pressure for future beneficial use, such as sequestration; conversion to methanol upon reaction with a renewable
source of hydrogen; or copolymerization with epoxides to yield polycarbonate.
The integrated system consists of two flow reactors, two phase separators, and a simple pumping system for delivery of the GVL solution, thereby minimizing secondary processing steps and equipment (e.g., purification of feeds, compression and
pumping of gases). A report on their work appeared in the 26 February issue of the journal Science.
The catalytic system described in this report provides an efficient and inexpensive processing strategy for GVL. The cost of producing either butene or jet fuel with the approaches described here would be governed by the market value of GVL, and further research should be carried out toward optimizing production of GVL from renewable biomass resources, thereby minimizing the cost of the GVL feed to our process, and toward utilization of the high-pressure CO2 coproduct stream formed in our process. Additionally, the yield of high molecular weight alkenes from GVL would benefit from the development of
water-tolerant oligomerization catalysts.
—Bond et al.
GVL has previously been identified as a potential feedstock in the production of both energy and fine chemicals. GVL is produced by hydrogenation of levulinic acid, which can be produced, potentially at low cost, from agricultural waste by commercial-scale process. By using formic acid that is formed in equimolar amounts with levulinic acid through the decomposition of cellulose and C6 sugars, researchers have minimized the demand for an external source of hydrogen in GVL production.
GVL retains 97% of the energy content of glucose and performs comparably to ethanol when used as a blending agent (10% v/v) in conventional
gasoline. However, limitations of GVL include high water solubility; blending
limits for use in conventional combustion engines; and lower energy density compared to petroleum-derived fuels. These limitations, the authors note, would be completely eliminated by converting GVL to liquid alkenes (or alkanes) with molecular weights targeted for direct use as gasoline, jet, and/or diesel fuels.
The sequence they developed entails the catalytic decarboxylation
of GVL to butene and CO2, combined with the oligomerization of butene at elevated pressures.
It really is very simple. We can pull off these two catalytic stages, as well as the requisite separation steps, in series, with basic equipment. With very minimal processing, we can produce a pure stream of jet-fuel-range alkenes and a fairly pure stream of carbon dioxide.
—Jesse Bond
The first step converts GVL to produce a mixture of unsaturated pentenoic acids, which then undergo decarboxylation to produce butene isomers and a stoichiometric quantity of CO2. Both of these reactions are carries out over a solid acid catalysts, SiO2/Al2O3, in the presence of water in a fixed bed reactor. These reactions can be carried out at pressures ranging from ambient to 36 bar.
After a separation step, the butene/CO2 gas stream is upgraded in a second reactor to higher molecular weight alkenes through acid-catalyzed
oligomerization. This oligomerization process is favored at elevated pressures and can be tuned to yield alkenes with a targeted range of molecular weights and varied degrees of branching in the product stream. In a second separation step, the alkenes are condensed to form a liquid product stream, while CO2 remains as a
high-pressure gas.
Dumesic and his researchers are also working at developing more efficient methods for making GVL from biomass sources such as wood, corn stover, switchgrass and others.
Resources
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Jesse Q. Bond, David Martin Alonso, Dong Wang, Ryan M. West, James A. Dumesic (2010) Integrated Catalytic Conversion of γ-Valerolactone to Liquid Alkenes for Transportation Fuels. Science Vol. 327. no. 5969, pp. 1110 – 1114 doi: 10.1126/science.1184362