Next-Best Thing to a Cow-Gas Catalyst?

French biofuels startup promises to unlock the renewable methane in smaller-operation livestock farming.

Update: Since the story below first published in the Fall 2024 issue of MotorTrend, Sublime Energie has indeed made good on its promise to open a facility in 2026. On April 14, the company inaugurated its demonstrator plant “Charlie” in Plélo, Côtes-d’Armor, Brittany, France. Sublime says it’s the world’s first facility capable of liquefying biogas directly on a farm via anaerobic digestion. Importantly, it is able to produce a renewable fuel without relying on gas grid infrastructure.

By densifying and enabling the transport of biogas produced on-site—using a model inspired by the traditional milk collection system—the startup is deploying a decentralized industrial model. In this system, biomethane is converted into bioLNG for heavy-duty mobility, while bioCO₂, a co-product of biogas, replaces fossil CO₂ across a range of agricultural and industrial applications. With this demonstrator, Sublime Energie is scaling up to unlock the full value of a fragmented agricultural resource, turning it into renewable energy and biogenic CO₂.

Most environmentally concerned or interested folks in our corner of the mobility space are laser-focused on CO2. Our combustion vehicles figured out long ago how to eliminate virtually all the other harmful stuff, and our electric ones relocate or eliminate the problem entirely. But our neighbors just outside of town in the farming world face a more daunting global-warming challenge: The methane emitted by their livestock is a greenhouse gas 80 times more potent than CO2. Sorry, science has yet to devise a cow-fart/burp catalytic converter. But it has recently devised a way to harness methane from excreta to make a legit biofuel.

The nugget of this technology is nothing new. Large corporate farms long ago began collecting farm effluents (urine and manure), letting anaerobic bacteria have their way with it, and then capturing the combustible gasses they release as biogas (a mixture of methane, CO2, and other trace compounds). Early on this was used to generate heat and electricity via “cogeneration,” but that’s expensive and highly inefficient (most of the energy ends up as unused heat).

Alternatively, the methane can be separated from the biogas, purified and liquified or compressed to run vehicles or equipment, or it can be injected into the natural-gas distribution infrastructure. But the high cost of this purification, liquification, and/or pressurization gear has up to now excluded smaller farming operations (the American Biogas Council [MF1] counts just 520 anaerobic digesters on farms, noting that 8,600 more dairy, poultry, and swine farms are, ahem, “ripe” for such a development). Smaller farms generally just spread their manure on their fields as fertilizer, where it releases all its methane (and the hydrogen-sulfide gas you smell) into the atmosphere.

Sublime Energie to the Rescue

French tech startup Sublime Energie was formed in 2019 to commercialize technology developed at the research institute Mines Paris PSL. Their magic bullet is a proprietary “carrier agent,” or solvent, that helps liquify the biogas produced by the anaerobic digester system.

Here’s how it works: The products of this digestion process undergo pretreatment to remove impurities including water, volatile organic compounds, that stinky hydrogen-sulfide, and more. Then it gets pressurized and dried, before entering the liquefaction and solubilization process with the carrier agent. Much of the Sublime Energie magic lies in the fact that its solvent helps liquify both the methane and the CO2 produced by this digestion process before the CO2 forms solid ice crystals that would otherwise clog the equipment.

This liquid brew of solvent, methane, and CO2 then gets shipped—inexpensively by tanker trucks—to a centralized hub and combined with similar tankerfuls from perhaps ten other small farming operations, bringing it up to large-farm scale for profitability. Here another proprietary operation separates the bio-sourced liquified natural gas (LNG) and bioCO2 as liquids (in a roughly equivalent 50/50 mix). The carrier agent is also recovered and shipped back to the farms in the same tankers, for reuse.

Marketable BioLNG and BioCO2

This LNG can remain in agriculture, powering tractors (New Holland was first to market with such a solution), but it can also fuel heavy transport. There are several semi-tractor manufacturers offering LNG engines (usually heavy diesel engines converted to spark ignition). Shorter-range marine ships can even be powered by LNG, with bunkering currently available at the ports of Amsterdam, Rotterdam, Antwerp, and Mannheim (talk about a transport mode in desperate need of decarbonization). Initial climate life-cycle analyses suggest using bioLNG produced in this way results in 80 percent less greenhouse-gas emissions than conventional petro LNG.

BioCO2 can be used today to replace fossil-derived CO2 for use in agriculture (e.g., to boost growth in greenhouses), drink carbonization, etc. Soon it could be a compelling source of carbon for use in the production of new sustainable biofuels—biomethanol, e-gasoline, or perhaps most likely, sustainable aviation fuel (another mobility sector that’s struggling mightily to decarbonize).

But Wait, There’s More

Back down on our little family farm, there are additional benefits. After the bacteria is done with the excreta, it becomes an even more attractive fertilizer. In contrast to simply spreading raw manure, the digestate process transforms the nitrogen in the manure into ammonium. This more effective fertilizer reduces the need for energy-intense commercial fossil-based fertilizers. Sublime Energie’s operations also create non-relocatable jobs in farming communities—an estimate of 15 per site. This strengthens the rural communities even as it combats the dreaded greenhouse effect.

Bio natural gas is a bigger deal in France, where 592 current-technology digesters produced 10.5 TWh of CNG last year, injecting it into the natural-gas infrastructure. That’s expected to rise to between 50 and 85 TWh by 2035. Production of bioLNG by Sublime Energie’s methods could add 5.5 TWh by 2030 and 26 TWh by 2050. Sublime Energie set up a demo facility in 2020 to prove out the technology, and a second one will open next year in Plélo, Brittany (see note at top), increasing output by 40 percent, to near commercial scale. The first commercial facility, planned for 2026, will pool from ten methanizers. If the concept goes global, perhaps one day you’ll be able to smugly fly first class over farmlands or cruise the oceans blue, knowing that the animal sacrificed for your Beef Bourguignon, crown roast of pork, or chicken cordon bleu may have contributed to producing the fuel that’s powering your journey.