Researchers in China produce highest octane gasoline fuel reported from biomass

11 November 2014

Researchers in China have generated gasoline fuel with a research octane number of 95.4 from biomass-derived γ-valerolactone (GVL)—the highest octane number reported for biomass-derived gasoline fuel—using an ionic liquid catalyst. A paper on their work is published in the RSC journal Green Chemistry.

In the study, they converted biomass-derived γ-valerolactone into gasoline by the decarboxylation of valerolactone to produce butenes and the subsequent alkylation of the produced butenes with butane using [CF₃CH₂OH₂][CF₃CH₂OBF₃] as an efficient catalyst. The obtained gasoline was rich in trimethylpentane (isooctane), with the RON of 95.4.

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Production of high octane number gasoline from GVL. Xin et al. Click to enlarge.

Much effort has recently gone into pathways to produce hydrocarbons with extended carbon chains by the hydrogenation of carbohydrate derivatives. These efforts include the aqueous phase reforming (APR) process, by which sugars are converted to alkanes by hydrogenation with noble metals as catalysts. Subsequently, other approaches explored the use of intermediates such as 5-hydroxymethyl furfural and furfural derived from C₆ and _C5 sugars. However, the authors noted, the production costs of these intermediates are high due to high energy consumption in separation and their relatively low availability.

Recently, Professor James Dumesic at the University of Wisconsin-Madison and his colleagues developed an approach for the production of alkenes by polymerization of butenes obtained from decarboxylation of γ-valerolactone using a solid acid catalyst. However, the products are alkanes/alkenes without a branch or with a single branch—i.e., they can only be used as substitutes for diesel fuel or additives of jet fuels.

The research on the production of bio-based alkanes for the purpose of production of gasoline, the largest consumed transportation fuel, is very rare. The main obstacles may be concluded as follows: (1) it is difficult to control the carbon numbers of alkanes from 6 to 12, especially to control the C₈ content of the highest fraction; (2) it is difficult to control the antiknock index to satisfy the requirement of gasoline motors.

The carbon number of alkanes is crucial for the density, fluidity, viscosity, ignition, distillation and vapor pressure parameters of gasoline, while the antiknock index indicates the resistance to auto-ignition. As one of the most important fuel properties of gasoline, the antiknock index is indicated by the Research Octane Number (RON) or Motor Octane Number (MON). Linear alkanes always have very low RON and MON. For example, the RON of n-heptane is 0, while that of isooctane (2,2,4-trimethylpentane) is 100. Gasoline with a higher octane number is less prone to auto-ignition and can withstand a greater rise in temperature during the compression stroke of an internal combustion engine without auto-igniting, thus allowing more power to be discharged by a higher compression ratio.

In order to meet the requirement of antiknock properties, additives including MTBE, ETBE, isooctane and toluene tetraethyllead or oxygenated compounds are usually added into gasoline. However, these additives have many confirmed or non-confirmed drawbacks. The best choice is to produce gasoline with more C₈ alkanes and more branches.

To achieve this, the researchers from the Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex System, Institute of Process Engineering, Chinese Academy of Sciences, developed a process for the production of highly branched alkanes rich in trimethylpentane (TMP) as a high-octane gasoline.

The first step of the process is the decarboxylation of GVL—which can be produced by hydrogenation of biomass-derived levulinic acid or directly from fructose—to give butenes including 1-butene, trans-2-butene and cis-2-butene with SiO₂/Al₂O₃ as the catalyst. A portion of the butenes are hydrogenated and isomerized to produce isobutane. (Isobutane also can be produced via bioethanol in a high yield.) The remaining butenes then react with isobutane to produce isooctane as the gasoline fuel.

The use of the acidic ionic liquid provides a high yield of highly branched alkanes and thus ensures a high octane number for the products.

The products are a mixture of alkanes rich in TMPs, which have a RON of 100 and serve as the most suitable component for high octane gasoline. The highest octane number of the product is 95.4, indicating that high quality gasoline can be produced from biomass-derived oxygenated compounds without hydrodeoxygenation and without any additives.

The researchers are developing plans to scale up this method and are also continuing to develop more efficient and feasible routes to produce high quality fuels.

As reported in the RSC’s Chemistry World, Liang-Nian He from Nankai University in China, describes the work as a significant breakthrough that will “stimulate further interest in more cost-efficient processes to produce biomass-based gasoline on a larger scale.”

Resources

• Jiayu Xin, Dongxia Yan, Olubunmi Ayodele, Zhan Zhang, Xingmei Lua and Suojiang Zhang (2015) “Conversion of biomass derived valerolactone into high octane number gasoline with an ionic liquid” Green Chem. doi: 10.1039/C4GC01792G