Prometheus Fuels -- petrol from water, air and electricity

Source: Prometheus Fuels

I talked about this nearly three years ago. Today, I checked back to see how this fascinating startup was going. Of course, it's all taken much longer than they were forecasting then. All the same, there seems to have been clear progress. I've taken the text below from a piece written by the founder and CEO of Prometheus Fuels.

Written by Rob McGinnis, Founder and CEO, Prometheus Fuels


As you know, Prometheus converts renewable electricity from solar and wind power into zero net carbon gasoline, diesel, and jet e-fuels (short for “electro-fuels”) that compete with fossil fuels on price. What some readers may not know is that the process we use to do this is new, is only recently possible, and is unlike anything that anyone else is doing to make synthetic fuels today. It is because of this new process that we are the only company making e-fuels that can compete with fossil fuels without new laws or subsidies — our fuels can compete simply by being better and costing less than the fossil fuels they will replace. This is a truly exciting breakthrough in our ability to solve some of the world’s most intractable problems, like climate change, energy security, and the need for increased energy-driven prosperity. But as often happens with breakthroughs of this magnitude, our process has provoked some dramatic responses - It sounds too good to be true! — and raised a lot of questions: How is it possible that your e-fuels are so much cheaper than everyone else’s? And if you can make these fuels, then where are they? Why aren’t they for sale yet? I’m here to answer these questions.

What’s everybody else doing?

If we ignore biofuels and waste-to-fuels and just focus on fuels made partially or fully from electricity from renewable sources, then everyone else who’s making e-fuels is using high temperature, high pressure synthesis. It’s been possible for almost a hundred years to make synthetic fuels from H2 and CO2 by using the Fischer Tropsch process, (invented in 1925), or similar processes that use high temperature and pressure with a catalyst to combine carbon and hydrogen into fuels. Currently, there are many companies using Fischer Tropsch or related processes that call their products e-fuels, which technically can be true if they only use electricity for CO2 capture and desorption, hydrogen generation, CO2 to CO conversion, synthesis reactions, and downstream cracking and distillation. In practice, it’s common to use fossil methane for the heat needed in these processes and to try to justify the additional CO2 this emits by promising to capture it also. Regardless of how closely they keep to the electricity-only ideal, however, none of these approaches can compete with fossil fuels on price.

What’s new about our process and why do our e-fuels cost so much less that they can compete with fossil fuels?

- Electricity is really cheap now

The first reason our fuels have such a low cost is not specific to us — it’s the recent abundance of really cheap renewable power. E-fuels are stored renewable energy. The day has long been anticipated when the cost of renewable electricity would become low enough to enable e-fuels, and that day has come. Specifically, it arrived in 2018, when the cost of utility scale solar power dropped to $0.02/kWh for the first time in a purchase by the city of Los Angeles. This marks a drop of over 90% in just ten years. The most recent record for the lowest utility scale solar bid was achieved last year at $0.01/kWh. The dramatic drop in costs is due to massive investment in solar panel manufacturing and in learning-by-doing cost reductions from making lots of solar panels. Low cost electrons mean low cost e-fuels.

- We don’t need pure CO2

The second reason our fuels are low cost, and one that is specific to us, is that we don’t need pure CO2. In order to make hydrocarbon e-fuels at scale one needs to capture CO2 from the air by direct air capture (DAC). For everyone else making e-fuels, this is a large cost. This is because their processes all require pure, pressurized CO2 gas. One obtains CO2 from the air by adsorbing the CO2 into or onto something, typically an amine liquid or amine functionalized bead, or in a hydroxide solution in water, or something more exotic, like an ionic liquid. This part isn’t so hard, and doesn’t require much energy, just a fan to blow air. In some cases, passive wind is used, but in either case, it’s not the main energy consumer.

The main energy cost is in getting the CO2 to release from the absorbent — to desorb. And that’s when things get really expensive, because this requires a lot of energy, almost always in the form of heat from burning fossil methane or a portion of the fuel produced. This is why most DAC CO2 processes cost $500-$600/ton of CO2 with a far distant and hopeful target of $100/ton at scale. But even at $100/ton CO2, any fuel one goes on to make is already too expensive to compete with fossil fuel.

At Prometheus, we don’t make or need pure CO2 gas, so we don’t need to desorb it. Therefore, we avoid the vast majority of this cost. Instead, we capture CO2 in water and then use it in water to make fuel. ARPA-E refers to this as “reactive CO2 capture” and identifies it as a significantly lower-cost DAC approach. Because our DAC tech is fundamentally different, our cost to capture CO2 is only $36/ton, the lowest in the world, and the only one low enough to enable fuel that competes on price with fossil. (More on this below.)

- We use electrocatalysts, not catalysts that need high pressure and temperature

The third reason our fuels are low cost, and another reason that is specific to us, is that we use electrocatalysts to do what only pressure and temperature could do before. The first widely read paper on this showed that CO2 in water could be turned into ethanol at a faradic efficiency of 63%. This means that 63% of the electrons that went into products in the process went into ethanol. We licensed a second-generation of this catalyst that has even better performance, making much larger and more complex carbon-based fuels with electricity alone.

Using electrocatalysts instead of the high pressure and temperature catalysts everyone else uses gives us a big reduction in cost because we can do the same job at room temperature and pressure while using much less expensive materials. It’s also great for our system performance because we can turn our process on and off quickly, matching intermittent solar and wind power. High pressure and temperature systems can’t operate like that.

- We’re the only ones who don’t need distillation

The fourth reason our fuels are low cost is that we’re the only company in the world that can replace distillation with nanotechnology to separate fuels from the water in which they’re made. In my previous startup, Mattershift, I commercialized a carbon nanotube (CNT) membrane, and published on it in 2018. Numerous academic publications have shown that membranes like this could separate alcohols from water, but until Mattershift produced them, no commercial CNT membranes were available. Previously, the only way to separate alcohols from water was to use distillation, another highly inefficient and expensive heat-based separation process. The CNT membranes solve this problem, using over 90% less energy than distillation and dramatically lowering the cost of extracting our fuel. This is a big deal because it reduces what is a major cost for other e-fuel makers to a minor cost for us.

Ok, that sounds good, but how does all this compete with fossil oil and gas?

The math on the cost of our e-fuel is pretty simple. The only inputs are air (CO2 and water) and electricity, and the only outputs are oxygen and fuel. The cost of the inputs plus the cost of the equipment and its maintenance make up nearly all of the [operating] cost. There are some other operating costs, like the vacuum pump and coolers on the CNT membranes or the power for pumps and controls, but these are less than 1% of total operating costs. I won’t include taxes or delivery fees since these vary a lot from place to place.

The main cost is electricity. The energy density of liquid e-fuels is very high, the main reason that they have long been desired as a solution for decarbonizing long-haul shipping and aviation. For gasoline, the energy density is approx. 33 kWh/gallon. In a TEA study we did last year with a third-party engineering firm, the estimate for the overall efficiency of our process (chemical energy in the fuel / electrical energy used to make it) is approx. 43%. This is a really great efficiency, because it includes everything involved from start to finish, including DAC of CO2, synthesis of the fuel, and separating the fuel so it’s ready to use. At this efficiency, our gasoline will need approx. 77 kWh of electricity per gallon. If the cost of power is $0.02/kWh, then the electricity cost of our e-gasoline is $1.54/gallon.

The next cost is CO2. The third-party TEA put our DAC cost at $36/ton of CO2 at $0.02/kWh, making it the lowest cost DAC in the world, and this cost drops further with lower costs of electricity. A gallon of gasoline contains approx. 8.9 kg of CO2 per gallon, so at a cost of $36/ton, this results in a CO2 cost for us of $0.32/gallon.

The most important cost after electricity is equipment cost, typically called capital cost. Adding up the electricity and CO2 costs, we get $1.86/gallon. If we want to stay below $3.00/gallon (for example), then we need to keep the capital and maintenance costs less than $1.14/gallon. Our cost models tell us that we can have capital and maintenance costs that are significantly lower than that, due to the advantages listed above, including not needing CO2 desorption or fuel distillation equipment, using low cost materials due to low temperatures and pressures, and deploying mass manufacturing methods like those used to make cars.

[Read more here ---the rest of the article is interesting, too.] 

The critical part of this process is the carbon nanotube membrane.  Without that, dissolving CO2 into water to produce hydrocarbons by electrolysis would be pointless, because you'd need distillation, which needs lots of energy and is expensive.  With the membrane, you just simply "sieve" the water, and the alcohols---from which petrol, diesel and jetfuel can be made---are left behind.

Petrol is currently trading at bulk at ±$2.50 per gallon, or $0.60 per litre.  So for this process to be profitable, it would need to have a capital and maintenance cost below $0.50 per gallon.   Except, that, if this works, then it will qualify for carbon credits.  For example, at a carbon price of $50/ tonne of CO2 emissions, a carbon credit would be worth roughly ±$0.45 per gallon.   For each $10 rise in the carbon price, petrol prices will rise by roughly 10 cents a gallon. 

More to the point, long-distance air and sea transport is still not possible with batteries, though it may well be in 10 years from now.  Also, fossil fuels will provide long-term storage for the grid---diesel generators using green diesel will be able to back up the grid.  We wouldn't have to worry about "dunkelflaute"---when it's cold and still and dark, so electricity demand is high but renewables supply is low.  

Let's hope that this process does work and that it soon scales up.  In my opinion, it looks as if we're still a couple of years away from commercialisation.  But by then, the pressure to de-carbonise will only have grown, as El Niño drives global temps towards the 1.5 degrees above pre-industrial times.