Synhelion ($45M for producing jet fuel)

Synhelion produces solar fuels to decarbonize transportation. They use concentrated solar energy to turn CO2 and water into syngas, which can be converted into solar kerosene, diesel, gasoline, or hydrogen. Their mission is to replace fossil fuels with economically viable synthetic fuels using high-temperature solar heat.

Challenges: jet fuel

Due to its high specific gravimetric energy density, kerosene is widely used as a jet fuel for long-haul aviation. Kerosene jet fuel combustion produces carbon dioxide (CO₂) emission. A round-trip flight from Frankfurt to New York, for example, burns about 156,500 kg of jet fuel. This results in about 570 tonnes of CO₂ or an average of 870 kg CO₂ per passenger. Global aviation is responsible for approximately 5% of the current anthropogenic emissions causing climate change, and this percentage is expected to rise.

Kerosene is produced by fractional distillation of crude oil in an oil refinery. Alternatively, kerosene can be synthesized from syngas—a specific mixture of hydrogen (H₂) and carbon monoxide (CO)—using the well-established Fischer-Tropsch synthesis process. However, the technological challenge is to generate renewable syngas from water (H₂O) and CO₂ using solar energy.

Synhelion Technology

Synhelion develops a solar receiver-reactor that uses concentrated solar energy in a solar tower configuration and reticulated porous ceria redox material to convert CO₂ and water into syngas with a desirable molar ratio of H₂ and CO. The syngas is then used to synthesize kerosene via the established Fischer-Tropsch synthesis process.

The image below shows a solar tower power fuel plant that uses Synhelion’s solar receiver-reactor on the tower to produce solar jet fuel at the IMDEA Energy solar concentrating plant in Madrid (ES).

The SUN-to-LIQUID project produced solar jet fuel at the IMDEA Energy solar concentrating plant in Madrid (Source: Synhelion).

As schematically depicted in the figure below, the solar tower power fuel plant integrates three subsystems:

the solar tower concentrating facility,
the solar receiver-reactor, and
the gas-to-liquid unit.

Schematic of the solar tower fuel plant with Synhelion's solar receiver-reactor. — Schematic of the solar tower fuel plant with Synhelion’s solar receiver-reactor.

The solar tower concentrating facility is equipped with a solar tower and heliostat field. It deflects concentrated sunlight of 2,500 suns to 4,000 suns (1 sun = 1 kW/m²) onto a solar receiver-reactor. The solar receiver-reactor is mounted on top of the solar tower and aimed at the power-weighted center of the heliostat field. It converts CO₂ and H₂O into syngas with a desirable molar ratio of H₂ to CO for Fischer-Tropsch synthesis. The products together with unreacted CO₂ and H₂O are delivered to a gas-to-liquid unit on the ground adjacent to the solar tower. The gas-to-liquid unit uses over 90% of syngas to produce kerosene. Unreacted CO₂ and H₂O are injected back to the solar receiver-reactor.

The most critical subsystem in the solar tower power fuel plant is the Synhelion’s innovative solar receiver-reactor. The diagram below schematically depicts the structure of the solar receiver-reactor.

Schematic of Synhelion's solar receiver-reactor (ref. US20210229988A1). — Schematic of Synhelion’s solar receiver-reactor (ref. US20210229988A1).

The solar receiver-reactor consists of a quartz (melting point: 1,650 ºC) glass window, a ceria (CeO₂) absorber, and an absorption area between the quartz window and the ceria absorber. Around the quartz window, inlet nozzles introduce CO₂ and H₂O gas flow into the absorption area. CO₂ and H₂O are heated in this area and converted into CO and H₂ on the hot surface of the ceria. Behind the porous ceria absorber, a central outlet nozzle extracts both product and unreacted gasses.

This innovative design of the solar receiver-reactor improves the energy conversion efficiency. Ceria (melting point: 2,400 ºC) exhibits a high degree of absorption in a slightly reduced state, allowing it to be readily heated by concentrated solar radiation. The high temperature ceria emits corresponding black-body radiation (essentially infra-red radiation) into the absorption area via its surface. The wall of the absorption area reflects black-body radiation. CO₂ and H₂O in the absorption area absorb infra-red radiation effectively and are heated to a high temperature for thermochemical reactions.

If black-body radiation from the ceria surface is not absorbed and emitted through the quartz window, the efficiency of the solar receiver-reactor will be reduced. Thus, the Synhelion’s solar receiver-reactor is ideally suitable for a reactor of greenhouse gasses (infrared absorbing gasses) such as methane (CH₄) and CO₂.

Ceria is the key material of the solar receiver-reactor. Due to its rapid redox kinetics and long-term stability, ceria is currently regarded as the most advanced redox material. The following reduction and oxidation represent the two-step thermochemical redox cycle necessary to produce syngas.

Reduction :

CeO₂ → CeO_2-δ + δ/2 O₂

Oxidation :

CeO_2-δ + δH₂O → CeO₂ + δH₂

CeO_2-δ + δCO₂ → CeO₂ + δCO

where δ denotes the nonstoichiometry—a measure of the oxygen exchange capacity and therefore of the syngas yield per cycle. A typical value of δ is 0.04. Thus, the high temperature and removal of oxygen gas (O₂) during the reduction cycle can improve syngas yield.

For typical operating conditions, during the reduction step under vacuum conditions, the ceria temperature increases rapidly to the reduction end temperature of 1,500 ºC. O₂ is released. At the end of the reduction step, the solar input is interrupted (solar input is cut off), and O₂ release rate rapidly decreases to zero, while the ceria naturally cools down to the nominal oxidation start temperature of 900 ºC.

The oxidation of ceria is initiated by simultaneously injecting CO₂ and H₂O, which are full selectivity converted to CO and H₂, respectively. There are no by-products produced. CO and H₂ production rates peak shortly thereafter and decrease monotonically until the ceria is fully oxidized after the oxidation end temperature reaches 654 ºC. The molar ratio of H₂ to CO in syngas is around 2, which is suitable for Fischer-Tropsch synthesis.

The solar-to-syngas energy conversion efficiency of the solar receiver-reactor is defined as the ratio of the calorific value of the syngas produced over the cycle to the sum of solar radiative energy input and additional parasitic energy inputs associated with inert gas consumption and vacuum pumping. The energy conversion efficiency depends primarily on the amount of syngas produced during the oxidation step, compared with the amount of solar energy required to release O₂ during the reduction step. The solar-to-syngas conversion efficiency of the solar receiver-reactor is about 4% at an average solar input of 42 kW. The energy efficiency of the entire solar fuel plant should also consider the optical efficiency of the solar concentrating tower facility and the energy efficiency of the gas-to-liquid unit.

Around 91% of the produced syngas is subsequently processed on-site by the gas-to-liquid unit, yielding a liquid phase containing 16% kerosene and 40% diesel, and a wax phase containing 7% kerosene and 40% diesel.

Synhelion Patent

CH713961A2 Method of transferring the heat and heat exchanger contained in a gas therefor
CH714967A2 Solar receiver reactor
US20210229988A1 Solar receiver-reactor
EP3790842A1 Solar receiver-reactor
CN112512961A 太阳能接收反应器
WO2019213787A1 Solar receiver-reactor
AU2019266372A1 Solar receiver-reactor
CL2020002860A1 Reactor that operates with solar reception
CH715241A2 Process for the production of syngas with the help of solar radiation and a solar reactor receiver
CH715527A2 Procedure for operating a receiver and receiver for executing the procedure.
WO2018205043A9 Method for operating a receiver and receiver for carrying out the method
AU2019374744A1 Method for operating a receiver and receiver for carrying out the method
CN113227670A 用于运行接收器的方法和用于实施该方法的接收器
WO2020093179A1 Method for operating a receiver and receiver for carrying out the method
EP3877706A1 Method for operating a receiver and receiver for carrying out the method
CL2021001196A1 Method of operation of a receiver and receiver to carry out the method
CH716993A2 Receiver
CN115038914A 接收器
WO2021127791A1 Receiver
AU2020412969A1 Receiver
EP4081743A1 Receiver
CH715206A2 Method for isolating a process unit and process unit with an isolating area.
WO2020019087A1 Method for insulating a process unit and process unit having an insulating region
EP3830495A1 Method for insulating a process unit and process unit having an insulating region
AU2019312089A1 Method for insulating a process unit and process unit having an insulating region
CN112888904A 用于过程单元的隔离的方法和带有起隔离作用的区域的过程单元
US20210310599A1 Method for insulating a process unit and process unit having an insulating region
CL2021000211A1 Method of isolating a process unit and a process unit that has an insulating region
ZA202100559B Method for insulating a process unit and process unit having an insulating region
CH714589A1 Method of transferring the heat and heat exchanger contained in a gas therefor
MA51115A PROCESS FOR TRANSFERRING THE HEAT CONTAINED IN A GAS AND CORRESPONDING HEAT EXCHANGER
US20200217561A1 Method for transferring the heat contained in a gas, and heat exchanger for this purpose
CN111033165A 用于传递气体中所含热量的方法以及用于该目的热交换器
AU2018297399A1 Method for transferring the heat contained in a gas, and heat exchanger for this purpose
EP3649420A1 Method for transferring the heat contained in a gas, and heat exchanger for this purpose
WO2019006565A1 Method for transferring the heat contained in a gas, and heat exchanger for this purpose
CL2019003904A1 Method of transferring the heat contained in a gas, and a heat exchanger for this purpose
CN114829294A 制备合成气的方法
AU2020398350A1 Process for the production of syngas
WO2021110667A1 Process for the production of syngas
EP4069635A1 Process for the production of syngas
CN114174218A 用于裂解烃气体的方法和装置
EP3953301A1 Process and apparatus for cracking hydrocarbon gases
US20220315421A1 Process and apparatus for cracking hydrocarbon gases
WO2020206561A1 Process and apparatus for cracking hydrocarbon gases
CL2021002593A1 Process and apparatus for cracking hydrocarbon gases
CH716996A2 Solar power plant with solid heat storage and process for loading a solid heat storage
WO2021134134A1 Solar power plant having a solid-matter heat collector and method for loading a solid-matter heat collector

Synhelion Products

The first industrial-scale solar fuel plant, DAWN, is located in Jülich, Germany. The construction began in September 2022.

The DAWN plant consists of a 20-meter-high solar tower and a 1,500 m² mirror surface of the heliostat field. The solar tower houses Synhelion’s solar receiver-reactor and thermal energy storage that enables cost-efficient operation.

The DAWN facility will produce several thousand liters of fuel annually. If the same plant were built in a particularly sunny location and operated around the clock, it could produce about 150,000 liters of fuel annually. The produced fuels (solar kerosene and gasoline) will be used to demonstrate various possible use cases. SWISS will be the first airline to use Synhelion’s solar kerosene.

Synhelion Funding

Synhelion has raised a total of $45.8M in funding over 4 rounds, including a Grant round, a Corporate round, a Series B round, and a Series C round. Their latest funding was raised on Dec 15, 2022 from a Series C round.