Researchers from the Naval Air Warfare Center Weapons Division (NAWCWD) have developed an efficient three-step process for the conversion of cellulosic feedstocks to both a valuable chemical precursor and high-performance jet fuel blendstock. Their paper appears in the journal ChemSusChem.
In it, the team describes the synthesis of sustainable methylcyclopentadiene and dimethyldicyclopentadiene (DMDCPD) via a three-step process consisting of aldol condensation; catalytic chemoselective hydrogenation; and dehydration.
Synthesis of methylcyclopentadiene (4), dimethyldicyclopentadiene (5), and RJ-4 from biomass sugars. Woodroffe & Harvey (2020)
Although ground vehicles, including cars and light trucks, can be easily powered by renewable electricity or hydrogen, the immense power requirements of commercial and military jet aircraft are currently dependent on hydrocarbon fuels. Petroleum-derived jet fuels are composed of n-paraffins, isoparaffins, cycloalkanes, and aromatic compounds. These complex mixtures contain up to 25% aromatic compounds which have low gravimetric heats of combustion and can increase particulate emissions. To address these issues, a significant amount of research has been focused on the production of a diverse portfolio of full-performance bio-based jet fuels with reduced aromatic content.
… Due to growing interest in the development of high-performance bio-based jet fuels that can outperform conventional jet fuels, while reducing net CO2 emissions, a number of new technologies for the conversion of biomass feedstocks to sustainable cycloalkane fuels have been explored. These studies have even extended to high-density, bicyclic compounds with applications as missile fuels. For example, our group demonstrated the conversion of the acyclic terpenoid linalool to dimethyltetrahydrodicyclopentadiene (RJ-4) in 2011. RJ-4 has a gravimetric and volumetric NHOC of 42.21 MJ/kg and 39.04 MJ/L (up to 17.7% higher than Jet-A), respectively, with a density of 0.925 g/mL. Zero-aromatic, high-performance jet fuel surrogates prepared from RJ-4 and various SPKs have recently been studied with RJ-4 concentrations as high as 50%. … More recently, researchers have shown that RJ-4 can be efficiently converted to 1,3-dimethyladamantane, a thermally stable jet fuel of interest for high speed applications.
… Leveraging the potential of [2,5- hexanedione] as a readily available bio-based substrate, this work describes the synthesis of sustainable methylcyclopentadiene [MCPD] and dimethyldicyclopentadiene [DMDCPD] via a three-step process consisting of aldol condensation, catalytic chemoselective hydrogenation, and dehydration. Through this approach, we demonstrate the ability to generate both a valuable chemical precursor and high-performance jet fuel blendstock from ubiquitous biomass feedstocks.—Woodroffe & Harvey (2020)
Base-catalyzed aldol condensation of 2,5- hexanedione resulted in the formation of 3-methyl-2-cyclopenten-1-one (MCO), which was then converted to 3- methyl-2-cyclopenten-1-ol (MCP) by chemoselective reduction with a ternary Ru catalyst system RuCl2(PPh3)3/NH2(CH2)2NH2/KOH].
The hydrogenation proceeded with 96% chemoselectivity. MCP was then dehydrated over AlPO4/MgSO4 at 70 °C under reduced pressure to yield methylcyclopentadiene. MCPD can subsequently be converted to tetrahydrodimethyldicyclopentadiene (RJ-4) high-density fuel.
Woodroffe, J. and Harvey, B..G. (2020), “Synthesis of Bio‐Based Methylcyclopentadiene from 2,5‐Hexanedione: A Sustainable Route to High Energy Density Jet Fuels.” ChemSusChem. Accepted Author Manuscript. doi: 10.1002/cssc.202002209