Decarbonisation Chemistry

The decarbonisation of hydrocarbons is performed through their gasification, or reforming, into other chemical compounds. This can be performed through a variety of chemical reactions at different temperatures and pressures. In order to separate the Hydrogen [H] atoms from the Carbon [C] within a Hydrocarbon [C_nH_(2n+2)] based compound, the chemical bond must be broken between the carbon and hydrogen, which requires energy. This is most commonly done through Steam Cracking or Steam Reforming.

Methane, CH₄ (commonly known as Natural Gas)

Our patented Zero Carbon to Surface concept uses nature’s own energy in oil and gas reservoirs to reduce the process energy input required to initiate a series of high temperature wellbore reformation reactions. Our wellbore technology is designed to produce hydrogen from oil and gas, while crucially separating out the reformation produced (internal) carbon dioxide (CO₂) for immediate, at-source capture in subsurface geological formations.

A further enhancement exists with the optional injection from surface of additional, externally sourced, carbon dioxide to further enhance the process efficiency by producing a higher H₂/CO ratio. An additional revenue stream is therefore obtained in the form of more carbon credits, by also capturing this external carbon dioxide.

Once the methane reforming reactions commence, the produced (internal) carbon dioxide (CO₂) released at point-source together with the market sourced (external) carbon dioxide (CO₂) are immediately captured downhole and injected directly into a selected geological reservoir. This simultaneous carbon capture within the wellbore prevents the carbon’s release to the atmosphere and so enables truly clean hydrogen production to surface.

The Gasification (or Reforming) of Hydrocarbons

Steam Methane Reforming (SMR) is responsible for the majority of worldwide hydrogen (H₂) production (>90%), and is currently made via surface-based, industrial, high-cost, high-energy, processes which emit CO₂ in a net-positive emission cycle.

SMR is likely to remain the dominant technology for large-scale hydrogen production in the near term because of its favourable economics and the large number of industrial SMR units in operation today. Overall, less than 0.7% of current hydrogen production is from renewables or from fossil fuel plants equipped with technology for Carbon Capture and Storage (CCS).

[Ref. : https://iea.blob.core.windows.net/assets/9e3a3493-b9a6-4b7d-b499- 7ca48e357561/The_Future_of_Hydrogen.pdf ]

Reactions at Supercritical Conditions

A Supercritical Fluid (SCF) is any substance at a temperature and pressure above its critical point , where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid .

Pressure-Temperature Phase Diagram : Water

[Ref. Jonathan Kamler : https://en.wikipedia.org/wiki/Supercritical_water_oxidation ]

Pressure-Temperature Phase Diagram : Carbon Dioxide

[Ref. Ben Finney Mark Jacobs : https://en.wikipedia.org/wiki/Supercritical_carbon_dioxide]

Pressure-Temperature Phase Diagram : Hydrogen

[Ref. The Engineering Toolbox: https://www.engineeringtoolbox.com/hydrogen-d_1419.html ]

Depending on the vertical depth within oil & gas or geothermal wellbores, the above supercritical conditions are provided wholly, or in part, by the fluid column and natural reservoir temperatures and pressures when in fluid communication with the surrounding geology.

For the case of water, the remaining incremental temperature increase, required for water supercritical conditions and the gasification reactions to occur, is supplied through energy and air delivered from surface. This natural wellbore environment saves significant process energy costs.

In addition, the surrounding geology and wellbore construction create a thermos flask effect, providing natural insulation for the wellbore to slow heat dissipation and the pressure vessel. This again reduces energy input requirements.

A variation of the steam cracking of hydrocarbons, performed at these supercritical conditions for water, is used in the gasification of biomass. It is referred to as Supercritical Water Oxidation (SCWO) or Reforming in Supercritical Water (RSW).

When used at surface these processes are typically net-positive, CO₂ addition cycles. The subsequent CCS of the CO₂ emissions from these processes is an additional high-cost, high-energy and time-consuming process which is only implemented in a small number of cases.

There are numerous chemical energy benefits from reactions conducted when the water and carbon dioxide phases are in their supercritical states.

• Unlike two-phase flow, the single-phase nature of supercritical fluids eliminates the necessity of heat input for a phase change (reducing thermal fatigue and corrosion).
• Lower viscosities – no surface tension as there is no liquid/gas phase boundary, higher diffusivities (reduces thermodynamic barriers and increases kinetics, providing very short reaction times).
  These elevated temperatures will also improve relative permeabilities, reducing the reservoir pressure drawdowns at production wells and similarly the pressure build-up at injection wells.
• Increased hydrogen yields – supercritical water, acts as a solvent, a supplier of bond-breaking thermal energy, a heat transfer agent and as a source of hydrogen atoms.
• Supercritical water can be used to decompose biomass for hydrogen production.
• Supercritical water behaves much less like a polar solvent, and as a result oxygen and organics become soluble in the water, however this also causes salts (polar) to precipitate and so a continuous flow process is required.
  Note: Water corrodes and scales piping and turbine blades, especially if it is saturated with minerals.
• Supercritical water oxidation (SCWO) is used in industrial applications such as petroleum refining, lowering auto-ignition temperatures.
• Supercritical CO₂ has a much lower tendency to dissolve minerals and other substances than water (which greatly reduces scaling and corrosion of system components).
• Supercritical CO₂ at high pressures has antimicrobial properties (of benefit to Geothermal energy).
• Supercritical CO₂ can be applied to various power generation applications to increase efficiency and power output in closed-loop power generation, its’ superior thermal stability allows direct heat exchange from high temperature sources (permitting higher working fluid temperatures and higher cycle efficiency for the benefit of Geothermal energy).
• Supercritical CO₂ is used to enhance oil recovery in mature oil fields.

[Ref. : https://en.wikipedia.org/wiki/Supercritical_fluid ]

Alternative Competing Reactions

There are potentially competing, gasification reforming reaction routes to obtaining hydrogen, however, each have their own specific energy requirements. Comparable processes, namely, POX (Partial Oxidation) and ATR (Auto-Thermal Reforming), both follow similar chemistry and energy intensive pathways. However, their Methane (CH₄) source is still directly from the oil & gas industry’s hydrocarbon reservoirs.

Full methane combustion (oxidation) is highly exothermic.

However, by providing limited, controlled volumes of air (Oxygen) POX reactions can be triggered at-source, within the deep-set wellbore tool to produce hydrogen.

Importantly, in addition to the hydrogen created from these chemical reactions, a valuable biproduct of carbon monoxide (CO) is also generated. This carbon monoxide (CO) is then further utilised to create more hydrogen from water through the Water Gas Shift reaction.

Auto-Thermal Reforming (ATR) combines steam reforming (SMR) and partial fuel oxidation (POX) into a single process with a net reaction enthalpy of zero, where the exothermic oxidation provides the heat for the endothermic reforming process.

Combining the ATR and WGS processes sequentially, results in a production ratio for CH₄: H₂ of 1: 3.0-3.5 mols (which is equivalent to approximately 1: 0.38-0.44kg), and similarly, an approximate CH₄: CO₂ ratio of 1: ~4 kg, and a H₂: CO₂ ratio of 1: ~10 kg.

A mixture of O₂ and CO₂ can also be used within the process without negatively affecting the hydrogen yield significantly.

This combines the heat source with the heat sink. The reaction heat is produced within the reaction vessel, in contrast to an SMR plant which requires an external furnace. The advantage of ATR is this oxidation reaction heat source. As it does not require external heat, it is less expensive than the endothermic SMR process which requires heat to proceed. ATR is popular for smaller scale hydrogen generation , as it gives higher H₂ production than POX and faster start-up and response times than steam reforming.

Independent control of the steam-to-carbon and air-to-fuel ratios means that effective heat management can be achieved. When the reactants are combined at the natural, near-supercritical conditions, deep within a wellbore, the requirement for the oxidation reaction heat provided by ATR is reduced, and therefore also the air requirement.

External CO₂ injection (via CCS) to Enhance Hydrogen Generation

Both the Boudouard reaction and Dry Methane Reforming (sometimes referred to as Methane CO₂ reforming) require more energy than SMR, however any externally supplied CO₂ injected from surface will assist with biasing the reaction’s equilibrium to the right (Le Chatelier’s Principle), generating more hydrogen and carbon monoxide (CO) for the WGS reaction.