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A potassium tert-butoxide and hydrosilane system for ultra-deep desulfurization of fuels

Nature Energy volume 2, Article number: 17008 (2017) Cite this article

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Abstract

Hydrodesulfurization (HDS) is the process by which sulfur-containing impurities are removed from petroleum streams, typically using a heterogeneous, sulfided transition metal catalyst under high H2 pressures and temperatures. Although generally effective, a major obstacle that remains is the desulfurization of highly refractory sulfur-containing heterocycles, such as 4,6-dimethyldibenzothiophene (4,6-Me2DBT), which are naturally occurring in fossil fuels. Homogeneous HDS strategies using well-defined molecular catalysts have been designed to target these recalcitrant S-heterocycles; however, the formation of stable transition metal sulfide complexes following C–S bond activation has largely prevented catalytic turnover. Here we show that a robust potassium (K) alkoxide (O)/hydrosilane (Si)-based (‘KOSi’) system efficiently desulfurizes refractory sulfur heterocycles. Subjecting sulfur-rich diesel (that is, [S] ∼ 10,000 ppm) to KOSi conditions results in a fuel with [S] ∼ 2 ppm, surpassing ambitious future governmental regulatory goals set for fuel sulfur content in all countries.

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Figure 1: Strategies for the hydrodesulfurization of petroleum streams and model compounds.
Figure 2: Reductive cleavage of C–X bonds by the KOSi system.
Figure 3: Free energy profile for KOSi processes.
Figure 4: Proposed mechanism for hydrodesulfurization (HDS) of dibenzothiophenes and hydrogenative cleavage of diarylethers by KOSi.

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Acknowledgements

Support of this work by BP under the XC2 program is gratefully acknowledged. A.A.T. is additionally grateful to the Resnick Sustainability Institute at Caltech, Dow Chemical, and Bristol–Myers Squibb for predoctoral fellowships, and to NSERC for a PGS D fellowship. K.N.H. is grateful to the US National Science Foundation (CHE-1205646 and CHE-1361104) for financial support and to the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the US National Science Foundation (OCI-1053575). Y.L. thanks the ‘National Thousand Young Talents Program’ and ‘Jiangsu Specially-Appointed Professor Plan’ in China for financial support. E.P.A.C. thanks K. Lammertsma (Division of Organic Chemistry, Vrije Universiteit Amsterdam, The Netherlands) for access to, and SURFsara (www.surfsara.nl) for their support in using the Lisa Computer Cluster. G. Huff, G. Sunley, D. Braden, P. Metelski, M. Pinderski, E. Doskocil, A. Lucy, C. Buda, A. Dinse, R. Taylor, J. Bercaw, J. Labinger, M. Howard, M. Desmond, J. Elks, D. Leitch and F. Bell are gratefully thanked for technical contributions and/or invaluable discussion.

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Authors and Affiliations

  1. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA

    Anton A. Toutov, Alexey Fedorov, Kerry N. Betz & Robert H. Grubbs

  2. BP Products North America, 150 West Warrenville Road, Naperville, Illinois 60563, USA

    Mike Salata, Renan Cariou & John W. Shabaker

  3. Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich, Switzerland

    Alexey Fedorov & Erik P. A. Couzijn

  4. Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA

    Yun-Fang Yang & Kendall N. Houk

  5. State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China

    Yong Liang

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  1. Anton A. Toutov
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Contributions

A.A.T., A.F. and R.H.G. had the idea and designed experiments with M.S., J.W.S., R.C. and K.N.B. A.A.T., M.S., A.F. and K.N.B. performed experiments and analysed data. Y.-F.Y., Y.L., E.P.A.C. and K.N.H. designed, performed, analysed, and interpreted density functional theory calculations. A.A.T., A.F., M.S., K.N.B. and E.P.A.C. wrote the manuscript with contributions from all authors. All authors contributed to discussions.

Corresponding authors

Correspondence to John W. Shabaker, Kendall N. Houk or Robert H. Grubbs.

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Competing interests

A company commercializing the technology reported in this paper is being founded and one of the authors (A.A.T.) will be a co-founder. The other authors declare no competing interests.

Supplementary information

Supplementary Information

Supplementary Notes 1–7, Supplementary Figures 1–7, Supplementary Table 1. (PDF 1014 kb)

Supplementary Data 1

Cartesian coordinates of calculated structures. (XLSX 60 kb)

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Toutov, A., Salata, M., Fedorov, A. et al. A potassium tert-butoxide and hydrosilane system for ultra-deep desulfurization of fuels. Nat Energy 2, 17008 (2017). https://doi.org/10.1038/nenergy.2017.8

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