A team at UC Davis has optimized the levulinic ester self-condensation reaction and the efficient conversion of its products—which are highly branched cyclopentadienes—into a mixture of substituted cyclopentanes with high octane ratings and excellent density and flow properties.

In a paper in the RSC journal Green Chemistry, they reported that the optimized process delivered C₈–C₁₀ plus C₁₂ and C₁₃ products in high yield with very good fuel properties which, being only four efficient steps removed from raw biomass, may provide a competitive basis for cellulosic gasoline production.

The production of bio-based fuels by the condensation of biogenic aldehydes or ketones with carbohydrate-derived platform molecules, often furfurals, followed by hydrodeoxygenation generally leads to C₉₊ products. The application of this approach has given rise to dozens of papers describing routes to diesel-type fuels, which consist mainly of linear alkanes in the C₁₀–C₂₀ range.

The paraffinic fraction of motor gasoline, on the other hand, is comprised of hydrocarbons up to about C₁₂, a key characteristic of which is the extent of branching in the carbon chains. In general, the more highly branched the molecule, the higher the performance of the fuel, as measured by the antiknock index, expressed in terms of research octane number or “RON”.

… To date, few reports of cellulosic biomass-derived alkanes sufficiently branched to serve as biogasoline or even mid-performance gasoline blendstocks have surfaced. Those that do emerge generally involve the cracking, pyrolysis, or gasification of biomass or its derivatives in combination with catalytic upgrading or reforming methods commonly employed in the petroleum industry, i.e. essentially using biomass as a feed for refinery practices.

—Li et al.

In earlier work, the researchers had shown that it is possible to produce branched C₇-C₁₀ hydrocarbons in processes using levulinic acid derived from cellulosic biomass. The new work describes the optimization of one of the levulinic-acid-based pathways to yield C₈–C₁₃ branched hydrocarbons characteristic of motor gasoline.

Resources

• Zheng Li, Andrew L. Otsukia and Mark Mascal (2018) “Production of cellulosic gasoline via levulinic ester self-condensation” Green Chemistry doi: 10.1039/C8GC01432A