Emerging technologies for sustainable hydrocarbons

Author credit – Stephen B. Harrison, sbh4 consulting

Eliminating carbon from hydrocarbons is not an option. Circular use of carbon is therefore a key pillar of sustainability. And, circular carbon dictates circular use of carbon dioxide (CO2).
CO2 circularity can be on an annual timescale, such as the growth of annual crops and their combustion. Or it can be on an evolutionary timescale such as the generation of fossil fuels, their use and sequestration of the CO2 emissions during their use.

Sustainable metals, petrochemicals and fuels

When natural gas is reformed to make syngas, the CO2 emissions can be sequestered in sub-surface geological formations. That is an example of CO2 circularity over the longest imaginable timeframe. When biomethane from grass is converted to syngas, the CO2 capture, utilisation and release cycle is reduced to less than 12 months.
Syngas is a mixture of predominantly carbon monoxide (CO) and hydrogen and may also contain some carbon dioxide (CO2). It is one of the most common chemical intermediates. Coal is converted to coke for use in iron and steel making. During that process, syngas is released. It can be used as a fuel and reducing agent in the blast furnace.
Today, syngas is the building block at the front of the value chains related to ammonia, methanol and a host of petrochemicals. In the future, low-carbon syngas can be used to make sustainable liquid hydrocarbon fuels. Over time, these can progressively substitute fossil fuels to support net-zero ambitions.
A range of technologies is emerging to produce low-carbon syngas from biogas, biogenic CO2 and green hydrogen. These are the starting points in the production of sustainable fuels and petrochemicals.

Reverse Water Gas Shift for green syngas

Partial Oxidation (POx) of green hydrogen and captured, recycled CO2 produces a renewable, circular syngas. During this process, hydrogen combines with oxygen and CO2 to produce water and CO. This is the ‘reverse water gas shift’ reaction, or RWGS.
Shell has patented (WO 2020/114899 A1) a non-catalytic POx-based RWGS system that operates in the temperature range of 1,000 to 1,500 °C enables RWGS without catalyst. The equipment would resemble classical natural gas-fed POx reactors currently used by industrial gases majors, such as Linde’s POx reactor at La Porte and Singapore. And, as with the classical POx units, an air separation unit (ASU) or pipeline could be used to supply the oxygen.
Johnson Matthey (JM) has patented (US 2023/0264955 A1) a nickel-based catalyst for their catalytic  POx process (CPOx). This technology which would resemble an autothermal reformer. It proposes to use the oxygen co-product from the hydrogen electrolyser to feed the RWGS POx reactor. This process integration would reduce, or eliminate, the need for ASU oxygen supply.
VTT, a Finnish research institute, patented (WO 2019/175476 A1), a CPOx process for the RWGS reaction using a Rhodium-based catalyst. This process operates at 800 to 950 °C and 20 bar, lower than the range proposed by Shell in their non catalytic RWGS POx reactor. It is generally the goal that a catalyst will enable a process to operate at a reduced temperature.

Electrically heated reforming

The heat for the POx and CPOx RWGS systems is derived from thermal oxidation of green hydrogen with oxygen.
When a thermal process is electrically heated, the feedstocks can be fully utilised to ensure better product yields. Is one of the concepts at the heart of the electrically heated reforming.
In Germany, the SYPOX electrically heated reformer (e-SMR) has been demonstrated with a biogas feed. This is an annually circular feedstock because it is derived from grass and maize. Electrical heating of the SMR ensures that the maximum amount of biogas is converted to green syngas since none of the biogas is burned to generate heat for the endothermic reforming reactions.
The SYPOX e-SMR operates with a Nickel-based catalyst, at around 10 bar and 900 °C. These conditions are similar to conventional flame-fired SMR. However, the heat is applied in a honeycomb matrix close to the catalyst which achieves extreme process intensification.
An e-SMR reactor is two orders of magnitude smaller than a conventional SMR. This brings down the footprint and capital cost. The compact unit can also be retrofitted onto existing conventional SMRs to expand their syngas production capacity or incrementally decarbonise their operation.
Despite the high temperature operation in the reactor, a refractory lining ensures that the outer surface of the SYPOX e-SMR is at around 80 °C. Using a cold-steel design means that the system can be built from low-cost grades of steel and we minimise the issues associated with thermal expansion which can cause operational difficulties on fired SMRs.
Biomethane contains around 50% CO2 and 50% biomethane. When steam is added to the biogas feed, Bi-reforming is achieved. In comparison to dry methane reforming, b-reforming avoids coke formation on the catalyst. In comparison to reforming of pure methane, the CO2 in the bi-reforming feed gas increases the syngas yield.
Hydrogen, methanol or Fischer Tropsch Synthesis (FTS) for liquid fuels can be made from the syngas which is produced from biogas bi-reforming.

Plasma decomposition of CO2

Chemical reactions, such as reforming, rearrange molecules in the feedstock to syngas. Plasma activates these molecules by splitting them and letting them recombine in more favourable products with its intense heating. Essentially, it is an electrified process for molecule conversion. The Belgian startup D-CRBN exploits a non-thermal plasma reactor for CO2 circularity.
When CO2 is fed to the D-CRBN plasma system under the right conditions, it is split into carbon monoxide and oxygen atoms. When an methane is introduced along with CO2, dry methane reforming is performed. Oxygen is converted to CO and hydrogen is produced.
For hydrogen production, methanol synthesis or generation of liquid hydrocarbon FTS fuels, the ideal ratio of hydrogen to CO in the syngas is 2:1. When steam is added to the biogas passing that through the plasma, new reaction pathways are introduced. Methane reforms not only with the CO2, but also with the water. This is known as bi-reforming of methane (BRM). In this case, the atoms recombine to produce syngas at the ideal 2:1 ratio in a bi-reforming process.