Upgrading Lignocellulosic Products to Drop-In Biofuels via Dehydrogenative Cross-Coupling and Hydrodeoxygenation Sequence

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

Novel pathways for fuels and lubricants from biomass optimized using life-cycle greenhouse gas assessment

Decarbonizing the transportation sector is critical to achieving global climate change mitigation. Although biofuels will play an important role in conventional gasoline and diesel applications, bioderived solutions are particularly important in jet fuels and lubricants, for which no other viable renewable alternatives exist. Producing compounds for jet fuel and lubricant base oil applications often requires upgrading fermentation products, such as alcohols and ketones, to reach the appropriate molecular-weight range. Ketones possess both electrophilic and nucleophilic functionality, which allows them to be used as building blocks similar to alkenes and aromatics in a petroleum refining complex. Here, we develop a method for selectively upgrading biomass-derived alkyl methyl ketones with >95% yields into trimer condensates, which can then be hydrodeoxygenated in near-quantitative yields to give a new class of cycloalkane compounds. The basic chemistry developed here can be tailored for aviation fuels as well as lubricants by changing the production strategy. We also demonstrate that a sugarcane biorefinery could use natural synergies between various routes to produce a mixture of lubricant base oils and jet fuels that achieve net life-cycle greenhouse gas savings of up to 80%. biofuels | lubricants | life cycle assessment | methyl ketones | greenhouse gases C ountries around the world are enacting legislation to curb greenhouse gas (GHG) emissions. Strategies for decarbonizing road transportation include an array of options from improving engine efficiency and blending bioethanol/biodiesel with gasoline/diesel to using plug-in electric vehicles (1-3). Aviation fuels pose a unique problem because stringent specifications require oxygen-free compounds, limiting the options available (4). Biofuel solutions such as farnesane have been proposed; however, these offer only modest GHG reduction benefits (SI Appendix) and the wide boiling range requirement for jet fuels sets a limit on the amount of single-component renewable fuels that may be blended. At the other end of the spectrum are automotive lubricant base oils where a narrow range of compounds is highly desirable. Poly-α-olefins (PAOs) containing 30 carbon atoms obtained from oligomerization of fossil-derived 1-decene are considered as the benchmark of superior performance for crankcase oils and have a high demand (5). Importantly, the GHG footprint associated with PAO base oils can be higher on a per-mass basis than petroleum-derived fuels if even a fraction of the lubricant is repurposed as fuel at its end of life (6). The goal of our work was to develop a strategy for the flexible production of jet fuels and lubricant base oils in a Brazilian sugarcane refinery designed to achieve a meaningful reduction in life-cycle GHG emissions. Our approach involves conversion of sugars in sugarcane-derived sucrose and hemicellulose to ketones using a combination of chemical and biocatalytic processes. For example, 2-butanone, can be obtained by the dehydration of fermentation-derived 2,3-butanediol (7, 8) or via chemical/biochemical (9, 10) decarboxylation of levulinic acid (11). The fermentation of various biomass-derived sugars using Clostridia strains produces a mixture of acetone, butanol, and ethanol (ABE), which can be used to synthesize a mixture of monoalkylated/dialkylated ketones (12), specifically 2-pentanone and 2-heptanone. Additional synthons may be produced from bioalcohol-derived olefins (13) or biomass-derived furanic platform molecules, such as 2,5-dimethylfuran and 2-methylfuran, via hydrogenolysis to produce 2-hexanone and 2-pentanone, respectively, with as high as 98% selectivity Results and Discussion We begin by identifying heterogeneous catalysts and appropriate reaction conditions for the self-condensation of ketones (1) to produce dimer/trimer condensates 2-4 in high overall yield Significance The development of renewable liquid fuels and bioproducts is critical to reducing global reliance on petroleum and mitigating climate change, particularly for applications where few lowcarbon alternatives exist. We combine chemical catalysis with life-cycle greenhouse gas (GHG) modeling to create a new platform for producing biobased aviation fuel and automotive lubricant base oils. The recyclable catalysts we developed are capable of converting sugar and biomass-derived alkyl methyl ketones into cyclic enones via condensation reactions. These products can subsequently be hydrodeoxygenated to create a new class of aviation fuel and lubricant candidates with superior cold flow properties, density, and viscosity that substantially reduce GHG emissions relative to conventional petroleum

A new strategy towards the total synthesis of phenanthridone alkaloids: synthesis of (+)-2,7-dideoxypancratistatin as a model study

A new strategy towards the synthesis of phenanthridone alkaloids has been reported through the synthesis of (+)-2,7-dideoxypancratistatin from D-(-)-quinic acid employing PET initiated carbocyclization of an electron rich aromatics by silylenol ether as a key step

Selective hydrogenation of furan-containing condensation products as a source of biomass-derived diesel additives.

In this study, we demonstrate that while the energy density and lubricity of the C15 and C16 products of furan condensation of biomass-derived aldehydes with 2-methylfuran are consistent with requirements for diesel, these products do not meet specifications for cetane number and pour point due to their aromatic furan rings. However, a novel class of products that fully meet or exceed most specifications for diesel can be produced by converting the furan rings in these compounds to cyclic ether moieties. Full hydrodeoxygenation of furan condensation products to alkanes would require 55-60% higher hydrogen demand, starting from biomass, compared to the products of furan ring saturation, providing an additional incentive to support the saturated products. We also report here on a tunable class of catalysts that contain Pd nanoparticles supported on ionic liquid-modified SiO2 that can achieve complete saturation of the furan rings in yields of 95% without opening these rings

Highly selective condensation of biomass-derived methyl ketones as a source of aviation fuel.

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