A fundamental understanding of synergistic (better than linear) blending for RON will allow design of better bioblendstocks and optimization of refinery BOBs. Researchers used flow reactor studies to reveal key features of the chemistry underlying this synergism. Synergistic blending for RON was exhibited by all the most promising boosted SI blendstocks and is emerging as an important feature of MM blendstocks. The top chart shows the additional RON above that predicted by a linear molar blending model (RON Synergy) for three blendstocks blended into a gasoline surrogate. These blendstocks exhibit RON Synergy at three levels, the lowest for ethanol (and other alcohols), intermediate for prenol (and other olefins) and highest for 2,5-dimethylfuran (DMF). Researchers examined the chemistry underlying this phenomenon by blending these components with n-heptane or 2-ethylhexyl nitrate (2EHN) and observing the effect on autoignition at 600 K. N-heptane is representative of the most reactive components in petroleum refinery-derived gasoline while 2EHN is well known to decompose yielding hydroxyl radicals. DMF begins to shut down heptane’s autoignition at only 1 mol%, and completely shuts it down by 5 mol% as shown in the lower chart. Observed reaction intermediates and kinetic simulations indicate that this is because hydroxyl and hydroperoxyl radicals generated by n-heptane (or 2EHN) can react with DMF in chain terminating reactions that have zero activation energy. Prenol and ethanol also shut down n-heptane’s autoignition but require higher blend levels. Observed intermediates and simulations also show the formation of chain terminating species from these blendstocks. These species are likely less effective than DMF because they have higher activation energy for these reactions. Ongoing research is seeking to more quantitatively relate bioblendstocks-radical reactions to RON.

Revealing the fundamental chemistry that underlies synergistic blending

Macromolecular Chemistry: The Second Century

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