Viewpoint: The Path to Cost-effective CO2 Utilisation

CO2-based alternatives to high-volume fossil-fuel commodities often fall foul of the so-called green premium. However, Todd Brix says that by focusing on products that can be made from molecules with high molecular weight-to-electron ratios we can have a cheaper, greener future

IN THE quest for a comprehensive solution to carbon management, regenerating CO2 to make useful products that displace incumbent fossil fuel-based pathways is a more impactful process than CO2 sequestration. Though this method closely resembles natural mechanisms for CO2 removal, with the most familiar example being photosynthesis, the central challenge lies in determining what products should be synthesised from CO2 to achieve the most significant impact, most expeditiously, at the lowest cost.

While it’s technically feasible to produce a range of products from CO2, only those that are less expensive to make than fossil-based alternatives have a real chance to impact purchasing decisions. The key question remains economic feasibility: at scale, can CO2-derived carbon-based products compete cost-wise with carbon sourced from fossil fuels and refined using traditional petrochemical processes? 

For almost all fuel, chemical, and material products today, the petrochemical approach is more economical. And not by a little bit. Thanks to highly optimised, mature, and large-scale fossil fuel-based processes, high-value commodities such as aviation fuel, ammonia, and methanol can be three to seven times cheaper than their less mature, lower-scale CO2-based counterparts. Who among us is willing to pay three to seven times more for something that is molecularly identical? The short answer is very few.

These “green premiums” would be lower if the cost of fossil fuels (particularly natural gas) was higher. Yet fossil fuels (in inflation-adjusted terms) are getting less expensive as supplies become more accessible due to new technologies like fracking and horizontal drilling.

An electro-molecule solution

The green premium often arises because sustainable options, such as renewable energy, green hydrogen, or electric vehicles, currently require more investment to produce, even though they offer long-term environmental and societal benefits that fossil fuels do not.

Instead of targeting large commodity markets with the highest green premiums, like ammonia, sustainable aviation fuel, or methanol – which require significant subsidies to be competitive at any scale – our focus should shift to molecules that can be produced more affordably today or in the near future. These molecules, produced at small or moderate scales using technologies that take advantage of the falling cost of clean electricity, have a better chance of succeeding in the market and displacing less competitive fossil-fuel-based processes.

Electro-molecule (e-molecule) precursors made from CO2, water, and electricity, if cheaper and cleaner than their fossil-based counterparts, would see rapid adoption, scaling, and cumulative learning effects, further driving down costs. As costs fall, downstream industries would develop new processes and products, accelerating both decarbonisation and cost reduction across the chemicals, fuels, and materials markets.

Key considerations

So, what molecules can actually or conceivably be made from CO2 and electricity? The answer resides in the exacting match of cost of production and industry price of the fossil alternative.  

Scientifically, there are three considerations for a molecule that can be made more economically than the fossil pathway:

1. Stoichiometry: The bigger the molecule you can make from CO2 using the fewest electrons (ie least amount of energy input required) the more product-mass bang you get for your energy-investment buck. This can most easily be expressed as the ratio of the molecular weight of a product divided by the number of electrons needed per molecule to make it. This is the M:E ratio
2. Thermodynamics: The more carbon-carbon bonds you make from CO2, the more carbon-oxygen double bonds you have to break and that costs more energy in large stepwise increases. For example, you get more energy out of burning a mole of C6-C7 hydrocarbon chains found frequently in gasoline, than you do from one mole of methane, which weighs much less and lacks carbon-carbon bonds
3. Kinetics: The more demanding kinetics of making larger molecules is harder to explain. Simply put, the more carbon-carbon bonds that are formed, the higher the energy input required to overcome a higher activation energy. This is the empirical observation that the activation energy for a reaction is proportional to the change in free energy of the reaction

The solution in practice

Researchers have already explored the economic viability of producing molecules from CO2, basing their analysis on these same factors. Among the chemicals that can be derived from CO2, only hydrogen formate (aka formic acid) and carbon monoxide (CO) have a likely production cost much lower than their fossil-fuel-based equivalents with reasonable electricity cost assumptions (US$30/MWh).

The Electric Power Research Institute (EPRI) has published papers over the past decade concluding that formic acid was the​ most economic molecule that could be produced from CO2. While largely overlooked since its publication, this conclusion underscores the importance of considering economic and chemistry factors when evaluating CO2 utilisation.

We are not aware of anyone producing formic acid commercially from CO2…yet. At OCOchem we are currently producing 11,340 kg/y in a single CO2 electrolyser cell and will be expanding production in early 2025 to 56,700 kg/y in a small multi-cell pilot plant.

Both formic acid and CO (carbon monoxide) are C1 (one-carbon molecules). Formic acid is a hydrogen-rich liquid which can be transported and easily donates its hydrogen to enable a variety of ionic, condensation, and esterification reactions to make a wide variety of derivative molecules. Carbon monoxide, while more difficult to transport as a gas, is also one of the primary constituents of syngas, useful in synthesising a wide variety of molecules. Interestingly, formic acid can be dehydrated to make carbon monoxide and water, and carbon monoxide can be hydrated to make formic acid, showing the cousin-like relationship between these two molecules.  

As you can see in the Figure 1, formic acid (23) and carbon monoxide (14) have the highest molecular M:E ratio of any CO2-derived product and therefore enable the largest mass of product to be made with the least energy input at the lowest equipment cost. These two e-molecules provide the best opportunity today to displace their fossil-based alternatives and provide carbon-rich but sustainable and low carbon emission derivative products and should be the focus of entrepreneurial and industrial effort.

In summary, many products can technically be made from CO2, but only a couple of molecules with high molecular mass to electron ratios, specifically formic acid and carbon monoxide, can be made electrochemically at a cost competitive to fossil fuel-based pathways as clean electricity costs decline. 

To move beyond the conventional wisdom of targeting large markets with massive subsidies, we should instead focus on products that can be made less expensively at scale, ensuring long-term success, lower costs for customers and impact in reducing CO2 emissions.