CO2 valorisation: methods & competitive landscape
This article is part of our CO2 valorisation series. Read the main CO2 valorisation article here. Keen to know the basics of chemistry for climate tech investors? Go for our chemistry 101 article. Want to deep dive into market opportunity? Get all the details here.
🔥 Thermochemical conversion
Thermochemical CO2 conversion utilises heat as an energy source. Typically, a catalyst is added to the mix, lowering the CO2 conversion energy barrier as well as speeding up the conversion reaction. Essential parameters around thermal catalysis are conversion rate, product selectivity, product yield, and catalyst stability. The products that can be made from CO2 via thermal catalysis are touched upon below:
CO2 to methane (natural gas)
Creating synthetic natural gas is not a novel process. The first commercial plant opened almost 40 years ago in North Dakota. The Great Plains Synfuels Plant is still operational and produces more than 170 million standard cubic feet (±1500 MW) of synthetic natural gas per day. Since the opening of this plant, other commercial facilities have been opened and a variety of carbon sources, such as wood chips, can also be used as input.
In the light of renewable energy, CO2 to methane conversion has been used to mitigate excess electricity generated by wind, solar, hydro, etc. The excess electricity is first used to make hydrogen via water electrolysis. Instead of using hydrogen directly for transportation or energy storage, it can undergo a transformation into methane together with CO2 and more renewable energy. The advantage of methane over hydrogen is that methane can be injected into the existing gas network. Additionally, methane can be used for electricity generation to compensate for the intermittency of renewable energy sources when desired. A downside of converting power into methane is that, like any energy conversion process, energy is lost.
✅ Pros:
- Carbon-neutral natural gas.
- Relatively simple one-step process.
- No infrastructure changes are required: the produced methane can be fed directly into the existing natural gas grid.
❌ Cons:
- Energy losses: process efficiencies of up to 80% can be achieved.
- 4 equivalents of green hydrogen are required to convert CO2 into methane.
- Commercial viability depends largely on the availability of cheap renewable energy.
CO2 to long-chain hydrocarbons (e-fuels)
Apart from making methane, CO2 can be converted to long-chain hydrocarbons, also referred to as synthetic fuel or e-fuel. This concept was discovered in the 1920s by Franz Fischer and Hans Tropsch. During these times, their home country Germany did not have oil readily available and therefore a fuel shortage arose. In a quest to solve this societal problem, they first gasified coal to create a mixture of carbon monoxide (CO) and hydrogen (H2) gas, also known as synthesis gas. When the synthesis gas was led over a cobalt- or iron-based catalyst, they discovered that a mixture of long-chain hydrocarbons was formed. This mixture could be distilled with the same methods as oil was distilled to create fuels, such as gasoline, diesel, and kerosene.
Since the discovery of the so-called Fischer-Tropsch (FT) synthesis, the popularity of this process has been fluctuating during the past century with the oil price being one of the main drivers. Every time that oil became expensive, the FT process gained popularity. Now in the light of renewable energy, the FT process has recently gained popularity again, as it could be a pathway to utilising carbon.
✅ Pros:
- Carbon-neutral fuel, as no new fossil resources are utilised.
- A drop-in solution that is possible today. The FT process yields an e-crude that has a similar composition to regular crude oil. No adaptation has to be made in terms of the refinery steps required to process the e-crude into a particular fuel category (e.g. diesel, kerosene, gasoline).
- Less green hydrogen is required compared to methane synthesis.
❌ Cons:
- Relatively large energy input is required.
- Energy losses: typical process efficiencies range from 60 to 80%.
- Although circular, burning synthetic hydrocarbons still leads to CO2 emissions. The approach may therefore be a good interim solution for the next decades, but in the long term, hydrogen fuel cells or battery electric vehicles may take over.
CO2 to methanol
Another well-established process is methanol production from CO2, CO, and H2 mixtures. Methanol is an important chemical building block and is used as a precursor for many commodity chemicals, such as formaldehyde, acetic acid, and long-chain hydrocarbons. This chemical reaction was first carried out commercially in 1966 by Imperial Chemical Industries using a copper-zinc oxide-alumina catalyst. Currently, over 90 methanol plants have a combined production capacity of 110 million tonnes and generate $55B in economic activity every year. Methanol is an important chemical building block and is used as a precursor for many commodity chemicals, such as formaldehyde, acetic acid, and long-chain hydrocarbons.
In the light of renewable energy, methanol is a promising energy carrier: it is a liquid at room temperature and therefore easier to store than hydrogen or natural gas. Methanol is occasionally used as fuel directly in internal combustion engines (ICEs). Although its energy density is lower than gasoline, a methanol-based economy would only require small adaptations to engines and the general infrastructure. The advantage of methanol over gasoline is that the former is easier to synthesise selectively (up to 100% selectivity towards methanol can be achieved) from CO, CO2, and H2 mixtures, while the FT reaction always leads to a broad product spectrum and thus requires post-processing steps similar to oil processing in refineries. The shipping industry can greatly minimise their emissions of sulphur and nitrogen oxides (SOx and NOx) by using methanol instead of hydrocarbons. Besides, methanol can be used efficiently in marine diesel engines after minor modifications.
✅ Pros:
- Methanol can be a drop-in fuel for combustion engines (particularly shipping) with only minor modifications needed.
- Methanol can be synthesised selectively and efficiently from CO, CO2, and H2 mixtures (up to 100% selectivity towards methanol can be achieved) and (in contrast to e-crude) does not require post-processing steps.
- Methanol is a liquid at room temperature and easier to transport than methane, which is a gas at room temperature.
- Less green hydrogen is required for methanol synthesis compared to methane production.
❌ Cons:
- Methanol has a lower energy density compared to gasoline.
- Burning methanol still emits CO2.
CO2 to ethanol
Ethanol and other long-chain alcohols are widely used in commercial fuel blends for internal combustion engines to increase combustion efficiency and the octane number of gasoline. Long-chain alcohols are typically produced through fermentation of e.g. corn or sugar cane and increasing production puts strain on agricultural resources and land use. If an efficient catalytic process is developed, long-chain alcohols could be produced from CO, CO2, and H2 mixtures instead. The production could either be from CO2 directly or using a two-step (via CO). Other commercial uses of ethanol include cosmetics and alcoholic beverages.
Although ethanol is quite similar to methanol in terms of chemical structure, the major difference is that ethanol has two carbon atoms and methanol has only one. This means, similarly to the difference between methane and long-chain hydrocarbons, that ethanol is dependent on a carbon-carbon coupling step, while methanol is not. As the carbon-carbon coupling step is difficult to control, a process aiming for ethanol as a reaction product will typically create a broader spectrum of products and typically includes methanol, propanol, butanol, and potentially other hydrocarbons as well.
✅ Pros:
- Ethanol is a liquid at room temperature and thus is easier to transport compared to gases.
- Ethanol has a higher energy density than methanol.
- Ethanol has a wide variety of applications. Synthesising it catalytically from CO, CO2, and H2 mixtures would additionally mitigate the strain that fermentation-based processes are currently putting on land use and agricultural resources.
❌ Cons:
- It remains difficult to selectively synthesise ethanol from CO, CO2, and H2 mixtures.
- Burning ethanol still emits CO2.
CO2 to polymers
CO2 can be incorporated in polymers, more commonly known as plastic, using a variety of technologies. A polymer is a molecular structure consisting of a chain with many (poly) repeating units (n). Polymers are typically used as everyday plastic products. A plastic bottle, for example, consists of a polyethylene (PE) cap and a polyethylene terephthalate (PET) body.
CO2 can either be converted to a polymer via synthesis gas or it can be directly incorporated into a polymer chain using a homogeneous catalyst. Homogeneous refers to the fact that the catalyst and the reactants/products reside in the same (liquid) phase. The advantages of this approach are that the energy-intensive carbon-oxygen bond-breaking step is omitted and that infrastructure for industrial polymerisation already exists. Challenges include reaching cost parity, as plastic is a commodity produced at low cost and separation/reuse of the homogeneous catalyst.
CO2 to formic acid
One way to avoid the energy-intensive carbon-oxygen bond cleavage step is to produce formic acid from CO2. The total process would require 4 kWh/kg of formic acid electricity, which includes H2 production via water electrolysis. This multi-step process is not yet widely commercialised due to challenges around formic acid extraction from the reaction mixture as well as the relatively high price of ruthenium-based catalysts (51% of the OPEX are catalyst costs). This route is thus unlikely to become economically viable in the near future (net present value (NPV)<0).
CO2 to other specialty chemicals
CO2 can additionally be converted into a variety of specialty chemicals or used in industrial processes to replace other chemicals. Every process to create specialty chemicals has its own pros and cons. The most common con is generally high energy input requirements.
Plasma-assisted CO2 conversion
There is increasing interest in plasma technology for CO2 conversion because it can operate at mild conditions. Plasma is created by applying electricity to a gas. The gas becomes ionised and then consists of electrons, ions, radicals, atoms, and molecules beyond their neutral state. This is a very reactive environment and in the case of CO2 conversion, it could activate the CO2 molecules at low temperatures. Although this approach could be used to create a wide variety of reaction products, challenges include the relatively low energy efficiency of max. 50% thus far.
⚡ Electrochemical conversion
As became clear from the previous sections, breaking the carbon-oxygen bonds of a CO2 molecule requires energy. Instead of using heat as an energy source, electricity can be used. This form of catalysis is referred to as electrocatalysis or electrochemical CO2 conversion. An electrochemical reactor (see Figure 1) typically consists of two electrodes submerged in the electrolyte (water with ions): a negatively charged cathode (where CO2 is converted) and a positively charged anode (where water is oxidised). Besides, a membrane normally separates the two compartments of the reactor cell and only lets certain ions through, for example, protons (i.e. positively charged hydrogen atoms, also noted as H+).
Important parameters to understand in the electrocatalysis space are Faradaic Efficiency and current density. The Faradaic Efficiency is a measure for selectivity of electron transfer from the electrode to the desired reaction product and is typically reported in %. The (partial) current density gives insights into the catalyst activity (towards a certain reaction product). The current density is typically reported in mA/cm2, where the “mA” refers to the current passed through the electrode and “cm2” refers to the electrode’s surface area. Besides, reactor design can greatly increase the overall product yield. Especially reactor designs aiming to tackle the limited CO2 solubility in water are promising for commercial purposes.
A variety of reaction products can be formed this way, such as CO, formic acid, methane, methanol, and ethylene. Although its popularity has certainly grown over the past years, electrocatalysis is generally less developed in terms of technology readiness level (TRL) compared to thermal catalysis. Below we will elaborate on some potential reaction products that can be formed via the electrocatalytic pathway:
CO2 to CO
Turning CO2 into CO is the most mature pathway for electrochemical CO2 conversion at this point. Partial current densities for CO production have surpassed 1 A/cm2, which is similar to commercial water electrolysis producing hydrogen. CO2 reduction happens at the negatively charged cathode, while complementary water oxidation happens at the positively charged anode. The electrolyte is typically water-containing ions to enhance electron transport. A commonly used compound to provide ions is, for example, potassium hydroxide (KOH).
The main challenges that have to be overcome for successful commercialisation are low energy efficiencies and reactor instabilities. Besides, low CO2 conversion rates and low product selectivities may lead to additional downstream separation costs. The CO2 conversion rates could generally be improved by enhancing the CO2 solubility or CO2 availability to the electrodes. Although water is the most commonly used electrolyte, CO2 solubility is limited. Considering non-aqueous electrolytes could be a solution. Alternatively, by choosing the right reactor design, the contact between the electrodes and CO2 can be optimised.
✅ Pros:
- High Faradaic Efficiency (50–80%) can be achieved.
- High CO selectivity (95–98%).
❌ Cons:
- Precious metals are typically required for the anode (Pt, Ir) to obtain high energy efficiencies.
- Low conversion rates are leading to low yields.
- CO2 solubility in water is limited, which limits the overall conversion of CO2.
- Significant energy input required (2.9 kWh/kg CO2 converted at 2.3 V and 95% CO selectivity).
CO2 to formic acid
Similar to thermochemical conversion, the energy-intensive carbon-oxygen bond cleavage step can be omitted by producing formic acid (CHOOH) from CO2. Ideally, formic acid is produced at the cathode and oxygen at the anode. However, an unwanted side reaction is a reduction of water into H2 and OH- at the cathode, which reduces the Faradaic Efficiency to formic acid.
A challenge that has to be overcome for commercialisation purposes is the limited solubility of CO2 in water, leading to low conversion rates and low current densities. For industrial applications, a current density of 200 mA/cm2 should be demonstrated. Two ways are currently being investigated to increase the current density. The first is to use a gas diffusion electrode (GDE) reactor design, which maximises the contact between gaseous CO2, the liquid electrolyte, and the solid electrode. The second is to use supercritical CO2 as a solvent, which would lead to higher CO2 concentrations at the cathode. The downside of the second approach is that using CO2 as a solvent is not as developed as using water as a solvent. In terms of commercialisation, there are a handful of projects, startups, and larger companies working on this. In 2013, for example, Mantra Venture Group constructed a 100 kg CO2/day (35 t formic acid/year) plant in Canada. More recently, several initiatives have popped up in the EU to commercialise electrochemical formic acid production.
✅ Pros:
- Omitting the carbon-oxygen bond cleavage step.
- Potentially lower energy requirements compared to the thermochemical route (1.75 kWh/kg formic acid (assuming 100% Faradaic Efficiency) vs. 4 kWh/kg formic acid)
- No additional hydrogen is required; hydrogen is sourced directly from the water.
- Oxygen and hydrogen are the only by-products.
- Likely to become an economically viable process (NPV>0), especially with larger plant capacities (±350 kt formic acid per year).
- Electricity price is the main cost driver (64% of OPEX).
❌ Cons:
- Formic acid is a specialty product and the market size may be limited.
- Energy-intensive process and energy efficiency optimisation is still required.
- The low solubility of CO2 in water limits the formic acid yield.
- High-cost electrocatalysts are typically required.
CO2 to C1
Methane and methanol (C1 products; see Figure 2 in the Chemistry 101 article) can be produced electrolytically from CO2. Although technically feasible on copper-based catalysts, the thermochemical route is far more established at this point. It is therefore unlikely that electrochemical methane and methanol production will be able to compete with thermochemical routes on an industrial scale in the near future.
CO2 to C2
Direct conversion of CO2 to ethylene (side note (see Figure 2 in the Chemistry 101 article): ethylene (C2H4) is ethane (C2H6) with a double bond between the 2 carbon atoms and has 2 less hydrogen atoms) or ethanol (C2 products; see Figure 2 in the Chemistry 101 article) has been reported in the academic literature. Creating C2 instead of C1 products would be beneficial, as longer (hydro)carbon chains store more energy. Besides, C2 products have broader market applications. Ethylene is a common chemical building block for example to create plastics, while ethanol is widely used as fuel. However, commercialisation is still in its infancy due to low efficiencies. Copper-based catalysts have most commonly been postulated as promising candidates to facilitate C2 production.
The challenges to overcome for commercialisation purposes are a combination of fundamental science and engineering. From a scientific perspective, new catalyst designs should be invented to achieve higher Faradaic Efficiencies and better product selectivities. Research in the field is ongoing. For example, ethylene could be produced on a laboratory scale at a current density of 1.3 A/cm2 by increasing CO2 diffusion to the catalyst surface through the combination of ionomer and catalyst particles. From an engineering perspective, general issues like low CO2 solubility in water and reactor instability apply here as well.
✅ Pros:
- C2 products have a higher market value than C1 products.
❌ Cons:
- Fundamental research challenges will have to be overcome to achieve commercialisation.
- Low product yields.
- Low product selectivity.
CO2 to carbon nanomaterials
Carbon nanomaterials have numerous applications; they are, for example, used in the battery industry and the fuel cell industry in the form of graphite (see Figure 2). Carbon nanotubes (CNTs), another structure of carbon nanomaterials (Figure 2), are for example used for energy storage applications, in the automotive industry, and for water purification. These materials are typically produced from fossil fuels or mined (in the case of natural graphite). Its mining and processing occur mostly in China. Around 2015, rapports started appearing in the academic literature regarding molten salt CO2 capture and electro-transformation (MSCC-ET) to produce various carbon nanomaterials from CO2 instead. The approach is very interesting, as it can be CO2-negative and has a lower energy input compared to the current fossil-based processes. The energy input is roughly 10–11 kWh/kg CO2 converted for MSCC-ET vs. 11–17 kWh/kg graphite for synthetic graphite production from fossil-based resources. For CNTs, however, the energy input is between 30,000 and 300,000 kWh/kg and could thus be reduced drastically through MSCC-ET. The carbon footprint would be reduced significantly as well: -3.7 kg CO2e per kg carbon material for MSCC-ET vs. 2.1–14 kg CO2e per kg of graphite and 0.5–29 kg CO2e per kg of CNTs from fossils.
The electrolytic process is carried out at relatively high temperatures (450–800°C) and the best results so far have been obtained in a molten lithium carbonate (Li2CO3) salt (see Figure 3). The molten salt functions as an electrolyte, similar to water with ions in other electrolysis processes. The carbon originating from CO2 eventually deposits on the Ni- or Fe-based cathode, while oxygen complementarity evolves on the anode, which can for example be tin oxide (SnO2). The exact type of carbon nanomaterial (see Figure 2) that is formed during the process depends on the reaction conditions (e.g. temperature and current density), the electrolyte composition, and the catalyst.
The main challenges around MSCC-ET are currently engineering challenges, such as efficiently removing the carbon nanomaterials from the electrodes after deposition. The commercialisation of this process thus seems promising and is currently being pursued by a handful of startups and/or larger companies, which are listed below.
✅ Pros:
- Potentially carbon-negative carbon nanomaterials production.
- Earth-abundant metals (Fe and Ni) can be used as electrodes.
- Flue gas or potentially ambient air could be used as an input gas stream directly.
- High-value end product.
- Large market potential due to growing carbon nanomaterial demand coming from the battery and fuel cell industry.
❌ Cons:
- Handling high temperature (450–800°C) molten (lithium-based) salts.
- The carbon nanomaterials have to be scraped off of the electrode.
- Impurities in the carbon nanomaterials have to be removed during the cleaning step.
💡 Photochemical conversion
Photochemical CO2 conversion utilises (solar) light as an energy input source. The concept is similar to photosynthesis in green plants, where CO2 and water are converted into sugars and oxygen under the influence of light. Photocatalysis, discovered in the 1970s, is a light-induced chemical reaction catalysed by a semiconducting material. At the moment, photocatalysis has only a limited number of commercial applications, which are not necessarily related to CO2 conversion. For example, air and water purification with titanium oxide-based catalysts as well as hydrogen production. Below, we will discuss some CO2-related opportunities, which are currently mostly ongoing research at universities.
Thus far, the most commonly investigated reaction products from photocatalytic CO2 conversion are CO, formic acid, methane, methanol, and ethanol. For commercialisation purposes, however, cell-level efficiencies and product selectivities should improve. The most promising pathways towards commercialisation would likely be to leverage photocatalytic material properties with other modes of energy input for CO2 conversions, such as photothermal catalysis (combining heat and light), photoelectrochemical catalysis (combining electricity and light), or biophotocatalysis (combining microorganisms and light).
☣️ Biological conversion
Biological CO2 conversion utilises microorganisms to convert CO2. Although scientists and engineers have mainly focused on the three methods discussed above, photosynthetic microorganisms have been converting CO2 and water into organic matter (e.g. sugars or other biomass) for more than two billion years. On a global scale, such microorganisms convert more than 100 Gt CO2 into biomass per year. Optimising their capabilities, for example through genetic or metabolic engineering, could become a disruptive technology for CO2 valorisation.
Microorganisms for CO2 valorisation can generally be divided into two types. The first one is photosynthetic, which are microalgae and cyanobacteria that both derive energy from light. Microalgae are considered to have the highest CO2 fixation rate of 1.8 tonne of CO2 per tonne microalgae. The second one is non-photosynthetic, which are lithoautotrophic microorganisms that derive energy from reduced compounds of mineral origin.
Important for efficient CO2 conversion is selecting the appropriate microorganism strain with the right cell density, growth characteristics, CO2 fixation rates, and high product yields. Besides, the choice of the bioreactor (continuously stirred tank, fixed bed, photobioreactor, electrobioreactor) is an important parameter. Combining microbes with electricity could be a particularly interesting approach to boost the product yield from biological CO2 conversion. Promising reaction products from biological CO2 conversion are elaborated on in the sections below.
Below we will briefly elaborate on a few potential pathways for biological CO2 conversion:
CO2 to methane
A promising biological CO2 valorisation pathway is to use methanogens, the microorganisms that produce methane as a byproduct in anaerobic (without oxygen) conditions. Such microorganisms are common in wetlands and the digestive tracts of animals. They use CO2 as an electron acceptor and H2 as an electron donor.
CO2 to e-fuels
Although photosynthetic microorganisms have the natural capability to convert sunlight and CO2 into fuels already, they typically have a low sunlight conversion efficiency of 3–6%. To overcome this issue, artificial devices such as photovoltaic cells can be used to convert solar energy into electricity with 10–40% efficiency. Electron transfer to the microorganisms can occur directly from an electrode, for example, an electron-accepting microbial film on the cathode, or indirectly via an electron mediator, such as formic acid.
To support the microorganisms, nutrients are required. The largest fraction of such nutrients are ammonium (NH4+), which is essential for amino acids (building blocks of proteins) and nucleotides (building blocks of RNA and DNA) synthesis. To avoid ammonia (NH3) usage, which has a significant carbon footprint when produced through the classical Haber-Bosch process, biomass waste could be used as a nitrogen source too (Figure 4). Cyanobacteria can use N2 from the air directly, but are mostly not relevant for biological e-fuel production.
Most efforts so far focused on algae growth in large open ponds that use atmospheric CO2 as an input source directly. A downside of this approach is that it has large land requirements. Besides, CO2 concentration in the air is relatively low, which makes the process very slow.
Microorganisms in bioreactors could make the CO2 conversion process more efficient through optimised operating conditions, higher CO2 concentrations, and optimised light conditions. However, multiple challenges to be overcome for widespread commercialisation. For example, photobioreactors with microalgae or cyanobacteria have high capital investment and operating costs, which drives the eventual price of the produced e-fuels up. Other major challenges are the efficiency of light transfer, oxygen poisoning, and insufficient heat removal in such reactors. Using lithoautotrophic microorganisms (deriving energy from reduced compounds of mineral origin) is still in a lab-scale or proof-of-concept stage. In theory, the lithoautotrophic microorganisms could be fixated in a bioreactor and CO2 and H2 could be bubbled through the column to produce e-fuels. However, the right cultivation conditions and how to optimise the yield at larger scales are still unknown.
✅ Pros:
- Flue gas and other CO2-rich waste gas streams could be used.
- High product selectivity could potentially be achieved if the right strains are selected.
- Hydrogen production could be omitted.
❌ Cons:
- Low efficiencies and product yields.
- High OPEX and CAPEX costs.
CO2 to fatty acids
Combining a cathode with microorganisms can be used to create short-chain fatty acids (C1-C6) directly from CO2. This concept, which is also applied in biological e-fuel production, is called microbial electrosynthesis. The cathode is then used as an electron source for the microorganisms. Acetate (C2) could, for example, be produced by microbial electrosynthesis from CO2 with 58% efficiency by combining an iron-manganese cathode with microorganisms.
Microalgae can also produce C16-C18 fatty acids from CO2. Their lipid content is typically 20–50% of the dry cell weight. The other weight is generally biomass and/or carbohydrates. Challenges to address in this approach include selecting an algae strain with high lipid content, culture conditions, and nutrient concentration.
Two-stage fermentation could yield longer-chain fatty acids (C16-C18). In the first step, CO2 and H2 are converted to a short-chain fatty acid, such as acetic acid (C2) produced by an anaerobic acetogen. In the second step, the first reaction product can be converted into a long-chain fatty acid by another microorganism, such as yeast. Using this method, a lipid content of 36% has been reported on a lab scale.
✅ Pros:
- The process can be carried out at mild conditions (low temperatures and ambient pressure).
❌ Cons:
- Relatively low time yields and productivity.
- Separation of fatty acids from the reaction mixture requires additional steps and chemicals (e.g. methanol/chloroform).
CO2 to amino acids and proteins
Apart from fatty acids, amino acids could also be extracted from microalgae. Typically, the fatty acids are extracted first and from the remaining defatted microbial biomass, amino acids can be extracted. Amino acids are the building blocks of proteins and thus several value-added products can be imagined.
Alternatively, amino acids and proteins could be created from CO2, a nitrogen source, and water directly with the right microorganisms and bioreactors. The resulting reaction products could be used, for example, as fish feed or meat alternatives.
Hydrogen-oxidising bacteria is a special group of bacteria that can use hydrogen as an electron donor and oxygen as an electron acceptor to fixate CO2. They are potentially interesting for protein production, as they have a higher growth rate, lower resource needs, and a higher protein content (70–80%) compared to others. In terms of nitrogen sources, the hydrogen-oxidising bacteria are versatile and could even take nitrogen-containing waste streams, such as agricultural waste (containing NH4+).
A two-stage microbial electrosynthesis approach yielded 55% amino acids by mass. In this approach, CO2 and H2 were first converted into methane and water during electrochemical methanogenesis. In the second step, methane was oxidised aerobically by methane-oxidising bacteria. For edible protein production, methane-oxidising bacteria are the only bacteria that have been approved so far by the European Union.
✅ Pros:
- Mild operating conditions (low temperatures and ambient pressure).
- The approach could reduce land usage for protein production.
❌ Cons:
- A nitrogen source is required.
- Low productivity and low amino acid yield.
- Edible proteins produced by microorganisms may be subject to regulations.
Competitive landscape
We’ve identified companies working on the specific CO2 valorisation methods mentioned above and classified them based on the (estimated) stage/scale that they are currently operating at. Selected startups are graphically visualised below:
