- Bacterial Biobutanol
- Assembling Gasoline Molecules from Renewable Methane
- Assembling Gasoline from CO2 and H2
- What About Ethanol?
Electrification as the dominant propulsion system for the automobile may be inevitable, but the good news is that through the miracle of modern science, we suck-squish-bang-blow fans will may very well be able to enjoy our quaint old noise-makers guilt-free using carbon-neutral drop-in replacement fuels. The CO2 produced by burning these fuels will not be additive to the atmosphere because the fuel itself will either have been made from biological feedstocks that consumed as much or more CO2 while growing, or by using feedstocks that would have naturally released the same CO2 had fuel not been produced from it, or even from CO2 pulled directly out of the atmosphere.
The energy used in the fuel’s production will also be green. Such fuels will almost certainly cost way more than today’s dinosaur juice, and it may be harder to find than gasoline is now, but it’ll be stocked wherever combustion-car-nuts gather to let their ponies run free. Below is a recap of and update on several e-fuels and green gasoline concepts we’ve previously covered in our monthly Technologue column.
Bacterial Biobutanol
In April 2011 we explained how biobutanol is a stretch-limo version of ethanol, its chemical formula cut in half with two more carbons inserted. This makes it act a whole lot more like gasoline, boasting nearly the same energy density and octane rating as petro gasoline. It was originally produced much like ethanol, from corn or other bio feedstocks, just with different catalysts, and making carbon-neutral biobutanol was near impossible with the feedstocks in use in 2011. Then in July 2013 we reported on research coming out of the University of Georgia and North Carolina State University that was developing bioengineered bacteria capable of converting a stream of CO2 and hydrogen gas directly into biobutanol. A carbon-neutral biobutanol production process has yet to be perfected, and biobutanol’s very low vapor pressure makes it unsuitable for cold-start conditions in concentrations above 50 percent with gasoline. These aren’t insurmountable technological hurdles, but they put this drop-in biofuel behind the next several in the race to a fuel pump near you.
Assembling Gasoline Molecules from Renewable Methane
Natural gas is comprised primarily of methane (CH4), which can be upgraded to more complex hydrocarbons through a series of catalytic reactions that first produce methanol, then add hydrogen and carbon molecules to the chain via various chemical processes. These give off CO2, but by locating the production facility near oil fields, Houston-based Nacero can both source its methane from flare gas (thus burning the fuel in a vehicle produces no net new CO2 that wasn’t destined to be burned already) and the CO2 that is produced in the conversion process can be returned to the oil well, where it both pressurizes the well to aid in production and gets permanently sequestered there.
Using methane sourced from municipal waste dumps qualifies the resulting gasoline as renewable. “Constructing” gasoline by assembling smaller molecules naturally avoids all the sulfur and other contaminants present in crude oil, and after the gasoline is produced, there’s no filthy “bunker oil” left over as there is when refining petro crude oil, which ends up being burned by industrial or ship engines, resulting in the worst air pollution. Nacero’s first plant is currently under construction. How far into the inEVitable future Nacero’s Blue and Green Gasolines remains viable, as crude oil fields and their methane flares get abandoned, remains to be seen.
Assembling Gasoline from CO2 and H2
The concept of driving a mile in someone else’s carbon footprint by assembling gasoline from carbon molecules scrubbed directly from the atmosphere was first covered in Technologue columns in July 2008, March 2012, and October 2018. First it was sodium-hydroxide scrubbers and exotic catalysts. Then it was ionic amine fluids and a formic-acid fuel cell. Then it was an elaborate combo of cooling-tower, paper-mill, and gold-ore-separating technologies. The technological and cost hurdles presented by these schemes ultimately proved insurmountable, but there are two new direct carbon capture techniques that seem to be marching toward volume production:
Prometheus Fuels: In October, 2020 we covered California-based Prometheus Fuels, which developed a means of scrubbing CO2 from the air by capturing it in water and then turning this aqueous CO2 directly into ethanol using a fancy and ultra-efficient system of electrolysis that employs graphene sheets featuring nano-spikes doped with copper nanoparticles. The ethanol is then separated from the water via carbon nanotubes, eliminating an energy-intense distilling step. Finally, the ethanol is upconverted to gasoline via zeolite catalysts in a process that creates its own heat. The whole system’s input energy can easily be supplied by clean electricity from the California grid, and volume production is expected soon.
Haru Oni: Way down on the windy southern tip of South America, just north of Punta Arenas, Chile, the Haru Oni hydrogen-to-e-fuels plant has just broken ground with a goal of producing enough green hydrogen and scrubbing sufficient CO2 from the atmosphere to produce almost 200,000 gallons of green methanol by the end of 2022. A portion of this will subsequently be converted into roughly 34,000 gallons of green gasoline—all of which will be shipped to Porsche for use in motorsports. Atmospheric CO2 will be extracted using an amine-based sorbent coating on a porous ceramic honeycomb matrix, and the hydrogen required for this process will be produced via proton-exchange membrane using green power provided by the strong williwaw winds that blow constantly around the southern tip of South America. Porsche pegs the initial price at 10 Euro/liter ($44.73/gallon!) but expects efficiencies of scale and technology to reduce that to $7.57/gallon by 2026. In a mostly electric mobility world, combustion enthusiasts will happily pay $8/gallon.
What About Ethanol?
MotorTrend’s Ron Grable authored a Technologue in February 1985 titled “Alternative Engine Fuels: What’ll We Do When the Tank Runs Dry?” that focused on biofuels—primarily ethanol. Corn ethanol can’t generally clear the carbon-neutral hurdle, in part because of all the (typically fossil) energy involved in cultivating and transporting the corn, and because unless the corn is planted somewhere that never grew crops before, the CO2 it consumes while growing isn’t considered “net-new” carbon absorption. That absorption was already taking place in support of food or livestock production.
Cellulosic ethanol generally scores better on both accounts. Using corn stover (the discarded stalks, etc.) creates fuel out of carbon that would otherwise have been released as CO2 when the stalks decayed. The picture improves even further by using renewable feedstocks like garbage, or crops like miscanthus grass, which needs little or no cultivation and can grow on former brown-field sites, but to date the processes required to produce the less energy-dense ethanol fuel still cost way too much to warrant further development in the face of cheap oil. In the end, today’s gasoline engines can’t start and run everywhere in North America on neat ethanol, and in a post petro-gasoline world, producing expensive carbon-neutral cellulosic ethanol to blend with the pricier green gasolines above seems absolutely pointless. Of course, if Oak Ridge National Lab’s direct aqueous CO2-to-ethanol nanotube catalyst pans out, as we covered in January 2017 maybe scientists will find a transportation use for it…
Keyword: E-Fuels and Green Gasoline: Beyond Today’s Dinosaur Juice