In the Digest’s Sometimes We Wonder department, we see a glut in US ethanol markets and ethanol production, but we see no effort to dehydrate ethanol to make fuel ethylene. As the final installment in our look this week at Carbon Re-Use, we’ll look at this alternative for ethanol producers.
Since ethylene is primarily used in the US as a chemical commodity (think Polythene Pam), but in a world of $1.45 ethanol, sometimes we wonder if a technology was available to readily convert ethanol to ethylene during times of oversupply, we might see better markets for ethanol and an interesting option for drivers.
Chemists long ago unlocked the process to make ethylene from ethanol with a sulfuric acid catalyst, and fresh water being the only byproduct. You get a theoretical 4.2 pounds of ethylene from a gallon of fuel ethanol.
As you’ll see in this research paper from 2008, it works well as a fuel, and there’s one outstanding factoid worth noting above all the others. Ethylene gets 30% more mileage than gasoline, and gasoline gets much more than ethanol. You can expect 70 percent better mileage when driving on ethylene when compared to ethanol. And it’s a hydrocarbon, so fewer concerns about blend volumes. Yes, you lose a lot of volume (33%) from ethanol to ethylene because the oxygen drops out, but you gain a lot more than you lose.
It may seem counterintuitive that you drop weight but gain fuel mileage — it might sound impossible at first. But think of it this way, as a metaphor rather than strict science. A dry piece of wood will burn more effectively than a green log that’s been left out in the rain. Combustion relates not only to weights but to structure.
Well, recent data is not yet robust because this 2014 study did not have a catalytic converter on during the ethylene burn — so, emissions as well as mileage would have to be carefully computed under test conditions. But there appears to be slight increases in NOx and big drops in CO2 emission, compared to gasoline, as much as 25%. Put that together with a nice renewable feedstock carbon gain, and there’s an interesting low-carbon fuel profile.
Based on a 70 percent gain in mileage, on the surface of it, fuel ethylene should be worth something in the $2.40 range before taking into account its carbon profile, and it would take roughly $2.16 in ethanol to make it. So, there’s not much spread, but there’s some, to work with.
A 25% drop in CO2 emissions compared to baseline gasoline is nothing to be sneezed at. With credits trading at $195 per ton of carbon in California, that’s roughly 0.7 tons of carbon saved per ton of fuel ethylene used based on the report data we have, and that has a value of $137 per ton, added to the differential in energy value.
Something for today?
It’s something to look at today, for sure — why overlook any commodity that could give potential relief to farmers, ethanol producers, boost investment in value-adding technology, reduce emissions, extend fuel economy, and possibly offer some savings at the pump for beleaguered consumers? Handling issues, blending, pathways, testing, verifying, process development, scale-up, and on and on go the challenges. And that’s NOx issue, and did this report really nail down the numbers correctly. And are there engine performance issues that manufacturers will blanch at, as ever they do.
Some people look at fuels that we use today, and ask why; others might dream of fuels that never were, and ask why not?
Why not? Maybe there are energy answers hidden away in a roll of Glad Wrap.