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Open Access Publications from the University of California

Scholarly Works (9 results)

  • Article
  • Peer Reviewed
UC Berkeley Previously Published Works (2016)
This review presents developments in the chemical processing of fermentation-derived compounds, focusing on ethanol, lactic acid, 2,3-butanediol and the acetone-butanol-ethanol mixture. We examine pathways from these products to biologically-derived drop-in fuels, polymers, as well as commodity chemicals, highlighting the role of homogeneous and heterogeneous catalysts in the development of green processes for the production of fuels and high-value-added compounds from biomass.
    Cover page: Combining microbial production with chemical upgrading
    • Thesis
    • Peer Reviewed
    UC Berkeley Electronic Theses and Dissertations (2015)

    The condensation of mixtures of acetone, butanol and ethanol (ABE), derived from

    fermentation processes has recently been reported as a viable pathway to diesel fuel

    precursor molecules. This process is catalyzed by bifunctional catalysts that include a metal functionality to dehydrogenate the alcohols and a basic functionality to catalyze the aldol condensation between the aldehydes and the acetone. However, the currently used catalysts are poorly understood, in terms of the driving forces of their selectivity, reactivity and stability.

    Based on screening reactions, we show that monometallic Pd and Cu catalysts supported on mixed metal oxides derived from hydrotalcites are the most active catalysts for this reaction. Kinetic analysis of these catalysts reveals that the dehydrogenation over the metal catalysts proceeds via a rate‐determining C‐H bond scission. On the other hand, the aldol condensation over the mixed oxide support takes place via an equilibrated enolate formation and its subsequent abstraction from the surface by an aldehyde. However, the decarbonylation of aldehydes over Pd and the formation of esters over Cu via the Tishchenko reaction limits the usability of monometallic catalysts.

    Supporting Pd and Cu on hydrotalcite‐derived supports results in the elimination of the

    Tishchenko side reaction and a reduction of the decarbonylation rates. Complete elimination of decarbonylation was not possible with these supports, due to the incorporation of Cu (II) ions in the Mg‐Al oxide structure. For this reason, TiO2 was used as a support; this resulted in complete alloying of Cu and Pd and, in turn, in significant selectivity improvements, combined with enhanced stability in the liquid phase.

    The liquid phase stability is due to the absence of any transformation from the anatase to the rutile phase. Kinetic analysis of the C‐C bond formation reactions over TiO2 reveals anatase to be the active phase for these reactions over TiO2. In contrast to the C‐C bond formation reactions over the mixed Mg‐Al oxide, the aldol condensation reaction over TiO2 proceeds via a rate‐determining alpha‐hydrogen abstraction and enolate formation over an acid‐base pair on the TiO2 surface. Similar analysis for a ZrO2 catalyst shows that the enolate formation is also rate‐determining over ZrO2.

    Apart from the ABE mixture, fuel precursors can also be derived by condensation of furfural and alcohols. These reactions proceed over transition‐metal‐free basic oxides via a rate-determining hydride transfer from a butoxide to an adsorbed furfural molecule, as shown by kinetic experiments in the gas and the liquid phase, as well as kinetic isotope effect experiments.

      Cover page: Monometallic and Bimetallic Catalyst Systems for the Upgrading of Biomass Products to Diesel Fuel Precursors
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2018)
      A critical challenge for the bioenergy research community has been producing drop-in hydrocarbon fuels and chemicals at yields sufficient to compete with their petroleum-derived counterparts. Biological production of highly reduced compounds poses fundamental challenges. Conversely, glucose, xylose, and sucrose can be fermented to ethanol at near-theoretical yields. Just as olefin crackers are often considered a gateway for petrochemical complexes that produce an array of downstream products, catalytic ethanol upgrading can potentially enable an entire biorefining complex able to produce renewable, low-carbon fuels and chemicals. By doping the Ta2O5/SiO2 catalyst with different transition metals, we show that Ostromyslensky catalysts can be utilized for direct conversion of ethanol to varying ratios of 1,3-butadiene (1,3-BD), dietheylether (DEE), and ethylene. These results are integrated into the first comprehensive analysis of ethanol conversion to 1,3-BD, DEE, and ethylene that incorporates empirical data with chemical process modeling and life-cycle greenhouse gas (GHG) assessment. We find that the suite of products can replace conventional rubber, plastics, and diesel, achieving as much as a 150% reduction in GHG-intensity relative to fossil pathways (net carbon sequestration). Selecting the route with the greatest ethylene and DEE output can maximize total potential emission reductions.
        Cover page: Hybrid Biological–Chemical Approach Offers Flexibility and Reduces the Carbon Footprint of Biobased Plastics, Rubbers, and Fuels
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2015)
        © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The Back Cover shows a depiction of the carbon cycle for a tunable set of chemistry that can be used to synthesize exceptional jet fuel via n-alkyl methyl ketones. In this work, methyl ketones, which can be derived from biomass in either chemical or hybrid biological-chemical pathways, are selectively transformed to cyclic trimers by aldol condensation and Michael addition. By altering the ratio of starting methyl ketones, an alkane blend can be generated after hydrodeoxygenation that not only satisfies the low freezing point necessary for jet fuel, but also the broad volatility distribution typical of petroleum-derived fuels. The carbon generated by combustion of these fuels then produces further biomass, completing the carbon cycle. More details can be found in the Full Paper by Sacia etal. (DOI: 10.1002/cssc.201500002).
          Cover page: Back Cover: Highly Selective Condensation of Biomass‐Derived Methyl Ketones as a Source of Aviation Fuel (ChemSusChem 10/2015)
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2015)
          Aviation fuel (i.e., jet fuel) requires a mixture of C9 -C16 hydrocarbons having both a high energy density and a low freezing point. While jet fuel is currently produced from petroleum, increasing concern with the release of CO2 into the atmosphere from the combustion of petroleum-based fuels has led to policy changes mandating the inclusion of biomass-based fuels into the fuel pool. Here we report a novel way to produce a mixture of branched cyclohexane derivatives in very high yield (>94 %) that match or exceed many required properties of jet fuel. As starting materials, we use a mixture of n-alkyl methyl ketones and their derivatives obtained from biomass. These synthons are condensed into trimers via base-catalyzed aldol condensation and Michael addition. Hydrodeoxygenation of these products yields mixtures of C12 -C21 branched, cyclic alkanes. Using models for predicting the carbon number distribution obtained from a mixture of n-alkyl methyl ketones and for predicting the boiling point distribution of the final mixture of cyclic alkanes, we show that it is possible to define the mixture of synthons that will closely reproduce the distillation curve of traditional jet fuel.
            Cover page: Highly Selective Condensation of Biomass‐Derived Methyl Ketones as a Source of Aviation Fuel
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2018)
            The efficacy of tandem dehydrogenation-condensation catalysts for the upgrade of bio-derived intermediates is largely determined by their relative (de-)hydrogenation and decarbonylation activity. Here, the effects of support and particle size of heterogeneous PdCu alloy catalysts on (de-)hydrogenation and decarbonlylation reactions were investigated using kinetic measurements, X-ray absorption spectroscopy and density functional theory (DFT). The chemical mismatch of Cu2+ with Ti4+ and Ca2+ prevents the substitution of Cu into the lattice of TiO2 or hydroxyapatite supports, and facilitates its alloying with Pd, resulting in improved selectivity for hydrogenation-dehydrogenation reactions compared to decarbonylation reactions. Based on kinetic measurements of butyraldehyde reactions over Pd and PdCu/SiO2 model catalysts, decarbonylation activity is attributed to the presence of Pd surface ensembles, while (de-)hydrogenation reactions are catalyzed by PdCu sites on the surface. This is consistent with selectivity and CO coverage trends with increasing conversion, and DFT-based microkinetic modeling. Selectivity control can also be achieved using the PdCu nanocluster size. Smaller nanoparticles favor the C-CO bond scission step of the decarbonylation reaction, due to the stronger binding of CO and alkyl species to sites of lower coordination. CO-induced segregation of reactive Pd atoms to under-coordinated step/edge sites also amplifies the geometric effect on the catalytic behavior.
              Cover page: Selectivity tuning over monometallic and bimetallic dehydrogenation catalysts: effects of support and particle size
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2017)
              Herein, we present work on the catalyst development and the kinetics of acetone-butanol-ethanol (ABE) condensation. After examining multiple combinations of metal and basic catalysts reported in the literature, Cu supported on calcined hydrotalcites (HT) was found to be the optimal catalyst for the ABE condensation. This catalyst gave a six-fold increase in reaction rates over previously reported catalysts. Kinetic analysis of the reaction over CuHT and HT revealed that the rate-determining step is the C−H bond activation of alkoxides that are formed from alcohols on the Cu surface. This step is followed by the addition of the resulting aldehydes to an acetone enolate formed by deprotonation of the acetone over basic sites on the HT surface. The presence of alcohols reduces aldol condensation rates, as a result of the coverage of catalytic sites by alkoxides.
                Cover page: ABE Condensation over Monometallic Catalysts: Catalyst Characterization and Kinetics
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2015)
                Life-cycle analysis (LCA) allows the scientific community to identify the sources of greenhouse gas (GHG) emissions of novel routes to produce renewable fuels. Herein, we integrate LCA into our investigations of a new route to produce drop-in diesel/jet fuel by combining furfural, obtained from the catalytic dehydration of lignocellulosic pentose sugars, with alcohols that can be derived from a variety of bio- or petroleum-based feedstocks. As a key innovation, we developed recyclable transition-metal-free hydrotalcite catalysts to promote the dehydrogenative cross-coupling reaction of furfural and alcohols to give high molecular weight adducts via a transfer hydrogenation-aldol condensation pathway. Subsequent hydrodeoxygenation of adducts over Pt/NbOPO4 yields alkanes. Implemented in a Brazilian sugarcane biorefinery such a process could result in a 53-79% reduction in life-cycle GHG emissions relative to conventional petroleum fuels and provide a sustainable source of low carbon diesel/jet fuel.
                  Cover page: Upgrading Lignocellulosic Products to Drop‐In Biofuels via Dehydrogenative Cross‐Coupling and Hydrodeoxygenation Sequence
                  • Article
                  • Peer Reviewed
                  UC Berkeley Previously Published Works (2016)
                  Condensation reactions such as Guerbet and aldol are important since they allow for C-C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts. A combination of XRD, EXAFS, TEM, and CO chemisorption and TPD revealed the formation of CuPd bimetallic nanoparticles with a Cu-enriched surface. Finally, density functional theory studies suggest that the surface segregation of Cu atoms in the bimetallic alloy catalyst produces Cu sites with increased reactivity, while the Pd sites responsible for unselective decarbonylation pathways are selectively poisoned by CO.
                    Cover page: Synergistic Effects in Bimetallic Palladium–Copper Catalysts Improve Selectivity in Oxygenate Coupling Reactions
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