Researchers have developed a new Metal Organic Framework (MOF) that might provide a better and cheaper method for separating the different hexane molecules of gasoline. The National Institute of Standards and Technology (NIST) measurements help to explain how the MOF works.
The new MOF was created in the laboratory of Jeffrey Long, professor of chemistry at the University of California, Berkeley. The MOS is a kind of screen that sifts the molecules by their shape. The NIST work shows the microscopic holes to be triangular in shape.
Metal Oxide Channels for Purifying Gasoline by Octane.
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The interior walls of the MOF are laid out like the wires in a screen forming triangular channels that selectively trap only the lower-octane components based on their shape. The channel shape still allows the higher-octane molecules to pass through. It’s thought the MOF could prove a far less expensive process than the industry’s current method.
High-octane gasoline seen for sale as ultra or premium blends at fuelling stations, are more expensive than regular unleaded gasoline due to the difficulty of separating out the right type of molecules from petroleum. Gasoline includes several slightly different versions of the same molecule that have identical molecular formulae but varying shapes that are called isomers. Creating premium fuel requires a refinery to heat raw gasoline stock at precise temperatures to separate the isomers into purer products with the desired octane. The problem is four of the isomers, two of which are high octane and the other two far lower, have only slightly different vapor temperature points, making the overall process both challenging and costly.
The new MOF, however, could allow refineries to sidestep this problem by essentially trapping out the lower octane isomers while letting the higher-octane isomers pass through. The lower octane isomers are more linear and can nestle closer to the MOF’s walls, so when a mixture of isomers passes through the MOF, the less desired isomers stick to its surface, somewhat like the way a wet piece of paper sticks to a wall.
Matthew Hudson a postdoctoral fellow and his colleagues at the NIST Center for Neutron Research (NCNR) used neutron powder diffraction, a technique for determining molecular structure, to explore why the MOF has the right shape to selectively separate the isomers. Their research was essential to validate the team’s model of how the MOF adsorbs the low-octane isomers.
Hudson explains, “It’s easier to separate the isomers with higher octane ratings this way rather than with the standard method, making it more efficient. And based on the lower temperatures needed, it’s also far less energy-intensive, meaning it should be less expensive.”
Hudson added that while industrial scientists will need to work out how to apply the discovery in refineries, the new MOF appears to be robust enough in harsh conditions to be used repeatedly a great many times, potentially reducing the necessary investment by a petroleum company.
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The octane rating of gasoline is directly related to an engine’s thermal efficiency. Generally lower thermal efficiency comes from lower compression ratios or the air fuel mixture isn’t compressed and dense enough to extract the full measure of energy from the fuel component. The problem is both a fuel chemistry matter and an engineering issue.
It may be somewhat rude to say so directly, but the regulators, engine designers and fuel purveyors haven’t been terribly considerate on explaining that low compression on to low octane and low thermal efficiency lead to energy waste in a big way. Pressed on the matter the three will only point fingers at one another.
It seems odd that the importance of efficiency has been so studiously overlooked. Even in the ethanol added to gasoline fight the substantial benefits to consumers, opportunities for designers and savings to the whole national gasoline economy from better octane numbers isn’t talked about or explained.
Still, we’re getting closer. If the refinery industry can adapt the technology and close the regular to premium gasoline price gap more consumers might see their way to purchasing higher efficiency engines.
By. Brian Westenhaus