INERATEC ($23M for converting recycled carbon dioxide and green hydrogen into e-fuels for aviation and marine)

INERATEC, an German cleantech startup founded in 2016, uses recycled carbon dioxide and green hydrogen to produce e-fuels and e-chemicals. The company has developed compact microstructured reactors, which enable efficient, safe, and dynamic operation of exothermic and endothermic chemical reactions. The company offers Power-to-X and Gas-to-Liquid modular chemical plants that produce sustainable fuels and products.

Challenges: carbon-neutral fuels

E-fuels, also known as synthetic fuels or electrofuels, are produced through the synthesis of recycled carbon dioxide (CO₂) and green hydrogen (H₂). CO₂ can be obtained from the air through the use of Direct Air Capture (DAC) systems that are powered by renewable electricity. Green hydrogen can be produced via water electrolysis powered by renewable electricity.

When these fuels–e-kerosene, e-methane, or e-methanol–are used in an engine, they release CO₂ into the atmosphere. However, those emissions are equal to the amount recycled from the atmosphere that is used in the synthesis of fuels, making it CO₂-neutral overall.

However, the production of e-fuels is energy-intensive and currently expensive. Despite these challenges, e-fuels are perceived as a promising solution for reducing greenhouse gas emissions, particularly in sectors that are difficult to electrify, such as long-distance freight, marine, and air transport.

INERATEC Technology

INERATEC has developed systems that produce methane (CH₄), syngas, and liquid fuels from recycled CO₂ and green hydrogen. INERATEC’s core technology is its compact microstructured reactors that enable dynamic, safe, and efficient operation of methanation or reverse water gas shift reactions. The design of microstructured reactors are detailed in the patents. Here, we describe how INERATEC’s systems produce methane and liquid fuels.

INERATEC methanation

The diagram below depicts how INERATEC converts CO₂ to methane.

INERATEC converts carbon dioxide and water to methane (ref. US11229894B2).

A solid oxide electrolysis cell (SOEC) is powered by renewable energy. Preheated H₂O vapor and CO₂ reactants are fed to the SOEC. The electrolysis operates at a high temperature between 730 and 850 ºC. This process produces hydrogen (H₂), oxygen (O₂), and carbon monoxide (CO), with a conversion efficiency of 60% for CO₂ and 70% for H₂O.

The oxygen stream is cooled via a heat exchanger which preheats reactants of CO₂ and water vapor. The cooled oxygen is removed.

The hot oxygen-free products of H₂ and CO and unconsumed CO₂ and water vapor from the SOEC are guided to the first and second heat exchangers. The first heat exchanger preheats the CO₂ and water vapor which will be fed to the SOEC. The second heat exchanger preheats the liquid water that will be used as coolants in the methanation reactors (reactor A and reactor B).

After passing two heat exchangers, the cooled stream consisting of H₂, CO and unconsumed CO₂ and water is guided to a gas-liquid separation device. The removed liquid water is introduced to the aforementioned second heat exchanger and used as coolant for the methanation reactors and then as reactant for the SOEC.

The water-free gas stream is guided to a further heat exchanger. Before the stream is fed to the methanation reactors, it is preheated by the hot, moist methane product.

In the methanation reactor A, the reactions of H₂ CO, and CO₂ yield methane and water:

CO + 3H₂ ⇆ CH₄ + H₂O

CO₂ + 4H₂ ⇆ CH₄ + 2H₂O

The output of the reactor A comprises CH₄, H₂O, and unconverted CO₂ and H₂. It is sent to reactor B, which further converts CO₂ and H₂ to methane and water vapor.

The hot, moist methane product is guided to the heat exchanger described above to heat the reactants of the methanation reactors. This heat exchange is followed by a gas-liquid separation. The gaseous, dry methane is led off from the system and used for energy generation. The remaining water is recycled and used as coolant for the methanation and then reactant for the SOEC.

INERATEC power to liquid

INERATEC has developed a system that converts CO₂ and H₂ to liquid fuels. The process uses a reactor to convert CO₂ and H₂ into syngas, which mainly consists of carbon monoxide (CO) and hydrogen. Subsequently, the syngas is subjected to the Fischer-Tropsch synthesis (FTS) to yield long-chain hydrocarbons.

The syngas reactor is modular. It consists of a bundle of microreactor tubes that are resistant to both pressure and temperature. By simply increasing the number of microreactor tubes, the reactor can be easily scaled up. Each microreactor tube uses CO₂ and H₂ to produce syngas via endothermic reverse water gas shift (RWGS) reaction:

CO₂ + H₂ ⇆ CO + H₂O ∆H = 41 kJ/mol

The microreactor tube is a one-stage reactor, which means that the reactants of CO₂ and H₂ are passed only once through a catalyst bed. In contrast, the multi-stage reactor requires reactants to pass over a catalyst bed several times to achieve the highest possible yield. Accordingly, INERATEC’s one-stage reactor reduces the cost and enhances overall process efficiency.

INERATEC syngas reactor is depicted in the diagram below.

INERATEC converts carbon dioxide and hydrogen to syngas (ref. DE102017120814A1).

During operation, individual microreactor tubes are heated with renewable electrical energy. The use of capillary heaters is particularly suitable for rapid heating-up and preventing soot formation.

Independent reactant fluids of CO₂ and H₂ are fed to the reactor. Their respective flow paths lead them to the reaction zone, where they combine to produce syngas. Before entering the reactor zone, they pass through a first and second heat exchange zone in the opposite direction of the hot syngas product discharge path. The hydrogen reactant fluid further passes through a third heating before entering the reactor zone.

Within the reaction zone, a catalyst bed containing nickel catalyst facilitates the RWGS reaction between CO₂ and H₂ at 800 to 900 º. The produced syngas discharges in the opposite direction of the feeding reactant fluids. This countercurrent flow path maximizes temperature and minimizes space requirements by the high reaction rate at high temperature. Maximizing the temperature allows for a high reaction conversion since the RWGS is an endothermic reaction.

The produced syngas is used to produce long-chain hydrocarbons via Fischer-Tropsch synthesis (FTS) according to the following process.

INERATEC Fischer-Tropsch synthesis process (ref. DE102021110735A1).

The syngas is fed to a first fixed-bed synthesis reactor with catalysts containing cobalt. At 200 ºC, H₂ and CO are catalytically converted to short- and long-chain hydrocarbons. The product stream leaving the first fixed bed synthesis reactor is fed to a first separation device, in which long-chain (>C₂₄) hydrocarbons are separated. The remaining short-chain (C₁-C₂₄) hydrocarbons, CO, CO₂, and H₂, are fed to a second fixed-bed synthesis reactor and catalytically converted to long-chain hydrocarbons.

The CO conversion is between 50 to 60 mol%, and the H₂ conversion is 99 mol%.

INERATEC Patent

US10150093B2 Microstructure reactor for carrying out exothermic heterogenously-catalysed reactions with efficient evaporative cooling
US11229894B2 Micro-reactor and method implementation for methanation
DE102017120814A1 Conversion reactor and process management
DE102021208923A1 Plate element for reaction modules or systems and corresponding processes
DE102021110735A1 Process for the production of hydrocarbons

INERATEC Applications

Solid oxide electrolysis cell

INERATEC uses solid oxide electrolysis cells (SOECs) in its methanation reactor system to convert CO₂ and water to CO and hydrogen which are further used to produce methane in methanation reactors.

Green hydrogen

INERATEC uses green hydrogen and CO₂ to synthesize syngas in a syngas reactor. The syngas is then used to produce liquid fuels.

Carbon capture

INERATEC uses recycled CO₂ from the air by using Direct Air Capture technologies and converts CO₂ to methane or liquid fuels.

E-fuels

INERATEC’s technologies can convert CO₂ and hydrogen to carbon-neutral fuels or e-fuels. E-fuels are promising to reduce carbon emissions in sectors that are difficult to electrify, such as long-distance freight, marine, and air transport.

INERATEC Products

INERATEC e-fuels

In 2022, INERATEC started the construction of a pioneer plant for the production of sustainable synthetic fuels. This plant, located at the Industriepark Höchst site, is expected to be commissioned in 2023. When regular operations start, it will produce up to 2,500 tons of sustainable products per year. The synthetic fuel blend produced will be upgraded to e-kerosene for aviation, e-diesel for marine and automotive fuels.