Hydrogen production: Electrolysis, Gasification …

Today, hydrogen production is dominated by processes emitting lot of carbon (steam reforming and gasification of hydrocarbons), but electrolysis and carbon capture hold out hope for carbon-free hydrogen to replace oil.

Hydrogen carries a lot of hope: it can be produced from water and only releases water when used. Jeremy Rifkin even claimed that it could use it to replace oil and thus develop a real hydrogen economy from small production units powered by solar energy.

However, we are still far from it: hydrogen production is currently the source of 6% of greenhouse gas emissions. 96% of hydrogen is produced through fossil fuel processing … without carbon capture. Its production is a complex subject and, today, it emits a lot of CO2.

This gas is also a core part of our economies : it is mostly needed for fertilizer and refinery, but also for electronics. It might also be used to replace oil in transport and decarbonize steel production. In short: there is a growing demand, we need a sustainable (green) supply.

We are going to what are the methods of production of hydrogen before delving into the current reality of its production. We will see :

  • The methods of production of hydrogen using fossil fuels
  • Water electrolysis
  • Process not used today, either because their are not mature or because they have been put aside.

At the end of the article I will give you links to other articles on the subject.

The production of fossil hydrogen

The main hydrogen production processes are:

  • Steam reforming of light hydrocarbons (mostly methane)
  • Gasification of heavy hydrocarbons (mostly coal)
  • Partial oxidation (POX) (still working on this one)

These technologies emit lot of greenhouse gases, because they core principe is to liberate the hydrogen from carbon and oxygen of hydrocarbons (“crack”). They might become “green” if they implemented carbon capture devices (Carbone Capture, Use and Storage, CCUS). However, the technology does not appear to be mature.

Current data on hydrogen production

All the figures are unanimous: hydrogen is mainly produced from fossil fuels through processes emitting loads of carbon dioxide. According to the IAE’s report, “Future of Hydrogen” 76% of production is produced from natural gas and 23% of production comes from coal. Only 4% comes from electrolysis. Second challenge: most (88%?) of this production is said to be “captive” or “non-commercial”, i.e. it is integrated into internal production processes (or almost, like two neighboring factories connected by a pipeline) and that it is a co-product of several productions (mainly coking and the refinery). Thus, decarbonating hydrogen production is going to be very complicated.

Currently, the main H2 suppliers on the market are Linde-Praxair, Air Liquide and Air Products. If the price of electrolysis is currently high (>5€/kg) compared to the price of steam reforming (1-1.5€/kg), it is possible that the two will come together because of two reasons :

  • the economies of scale and research (fall in the price of electrolysis) and
  • the development of carbon taxation (rise in the price of steam reforming).

The steam reforming of hydrocarbons (usually methane)

Steam reforming makes it possible to produce hydrogen from hydrocarbons. Mostly methane is used. This is called SMR (Steam Methan Reforming).

There are two reactions, first that of steam reforming itself (H2O + CH4 → CO + 3 H2), which produces a mixture of carbon monoxide and dihydrogen called synthesis gas or “Syngas“, then Gas Water Shift (= Catalytic conversion) (CO + H2O → CO2 + H2). This whole process involves heating the gas to an extremely high temperature (700-1100°C) and releases 10 times more CO2 than it produces hydrogen (by weight).

When it comes to price, estimates vary. According to Fossil Fuel Hydrogen, Technical, Economic and Environmental Potential, the price of hydrogen production by steam methane reforming, without a carbon capture device, would be between $0.55 and $2.04 /kg of H2 with a median of $1.3 . With carbon capture, the price allegedly is $2. The CEA (2012) estimates its price at €1.5/kg of H2. These are somewhat murky points (e.g. I hear quite a bit that carbon capture would not be operational), which I will have to dig deeper into.

For further details, you can read our article on Hydrogen production by steam methane reforming (SMR).

Hydrogen production by gasification

Gasification makes it possible to produce hydrogen from coal (mainly), heavy hydrocarbons and biomass. It is a combination of several reactions taking place at temperatures that can rise very high (500-1400°C) and high pressures (>33 bars). (Garcia 2015) It seems to me that a reforming and catalytic conversion phase is also added. (to check)

The price of hydrogen production by gasification of coal is between 0.83 and 1.7$ per kg of H2. Carbon capture would raise the price by 10% (Fossil Fuel Hydrogen, Technical, Economic and Environmental Potential).

For further details, see our article on hydrogen production by coal gasification.

Partial oxidation (POX)

[Work in progress]

The problem of carbon capture and storage (CCUS)

The problem of carbon capture and storage (CCUS)

Fossil hydrogen produces, in principle, a lot of CO2. Nevertheless, some believe that the CCUS would resolve this difficulty and make it viable, at least in the short or medium term. This hydrogen is called “blue”.

This is the thesis defended by William J. Nuttall and Adetokunboh T. Bakenne in “Fossil Fuel Hydrogen, Technical, Economic and Environmental Potential”.

Capturing 90% of steam reforming emissions would only represent a cost of $80/tCO2 captured for market production and $90-115/tCO2 for integrated production (ammonia, urea, methanol). (IEA 2019)

However, I hear a lot that this technology is not yet ready. In addition, in August 2021, the president of the association defending the interests of the hydrogen sector in the United Kingdom, UK Hydrogen & Fuel Cell Association, would have left his post at the announcement of the British government’s strategy on the subject of hydrogen. blue would be “at best an onerous distraction, and at worst a lock-in for the continued use of fossil fuels that guarantees us that we will fail to meet our decarbonization goals”.



Water electrolysis: “green” hydrogen

Turning water into fuel, awesome isn’t it? This is what the electrolysis of water allows. The principle is to send an electric current between two electrodes: an anode and a cathode. At the first, electricity releases oxygen (4 OH– → O2 + 2H2O + 4 e–) and, at the second, releases hydrogen (2 H2O + 2 e– → H2 + 2 OH–). That’s what is called “green hydrogen”.

Price estimates vary. According to Fossil Fuel Hydrogen, Technical, Economic and Environmental Potential, the price of producing hydrogen by electrolysis using wind energy would be between $2.85 and 7.3 per kg of H2, with a median of $4.8. The CEA (2012) estimates its price at between €5 and €30/kg of H2 depending on the size of the farm. It could nevertheless decrease to €3/kg of H2 with large-scale installations, with electricity at €40/MWh. Caroline Rozain (2013) uses the figure of €3 kg-1 H2 for an electricity price of €40 MWh-1.

One of the uses of this technology might be to absorb the production peak from renewable energy (wind and solar). However, there is a problem : the electrolyzer would supply hydrogen at full capacity only sometimes. The production capacity used would be too low to make it financially viable. Coupling it mostly with nuclear ou hydrolic power seems more promising.

For further details, you can read our article on water electrolysis.

Other hydrogen production methods

There are other methods, which nevertheless seemed minor to me. However, I find it interesting to mention them:

Ammonia cracking

This is an important reaction because ammonia is envisioned for use in long-range transport of hydrogen.

The reaction is as follows: 2NH3 => N2+3H2. It occurs “generally at high temperatures (>900°C) in a process called “cracking”. It is endothermic and requires 46.22kJ per mole (of hydrogen?) produced. (Zhong Zhang 2014, p.18)
Methane cracking

The reaction is: CH4 = C + 2H2. The reaction is endothermic (74.8 kJ/mol). Its great advantage is that it does not emit carbon monoxide, but solid carbon). It can be done at 500°C with certain catalysts and 1000°C without. (Zhong Zhang 2014, p.22)

Pyrogasification or thermolysis of biomass

It is the grail of the hydrogen production: the pyrogasification or thermolysis of biomass. The idea is to progressively heat biomass so that it releases the hydrogen (and various components) present, so that only a carbonaceous residue remains (solid in principle, the biochar, or liquid). Thus, not only do you use a material that has absorbed CO2 (we are in the logic of carbon neutrality of biogas), but also part of this carbon remains fixed after the operation. The process can already be carbon-negative, depending on the quantity of the residue. Thus, Hynoca, one of the most advanced processes announces to capture the equivalent of 12 kg of CO2 per kg of hydrogen produced. We imagine that, once the CCUS is perfected, we will be able to do even better.

The second strong point is that this process could be used for biomass that is not currently used, such as certain sawmill residues or agricultural waste (which would make it possible, for example, to use the numerous agricultural waste products in the Ivory Coast, particularly those from cocoa production).

To go further, you can read our article on pyrogasification or thermolysis of biomass.

Experimental ways of producing H2

Biohydrogen

Some organisms naturally produce hydrogen during phytosynthesis. Hydrogen is obtained directly from solar energy. This is particularly the case for certain green algae and cyanobacteria.

Thermochemical dissociation of water vapor

This involves heating the water so much that it dissociates into a molecule of hydrogen and one of oxygen. To succeed at atmospheric pressure, it would require a heat of 3500°C. To reduce this need, other atoms are used. For example, iodine and sulfur are used:

                                      I2 + SO2 + 2 H2O → 2 HI + H2SO4

Hydrogen and iodine are then dissociated. The heat required by this process is much less, but still extreme: between 900 and 1000°C.

This heat could be co-produced by nuclear or solar energy.

Note that it has been abandoned by the CEA and the United States:

“The high temperature water decomposition processes “by thermochemical cycles” were studied in the 2000s at the CEA. This technique consists of implementing a series of chemical reactions in a closed cycle (i.e. with full recycling of intermediate reagents), in order to break down water to produce hydrogen and oxygen.

In principle, this approach is very suitable for mass production: from a practically inexhaustible raw material (water), the hydrogen flow rates are proportional to the flow of reactants and energy inputs, and not to the phenomena of diffusion at the interfaces, and this without supply of electricity.

In 2009, the CEA stopped its “laboratory” studies on different cycles, the processes having no proven economic interest in the short/medium term. The United States has also chosen to stop R&D in this sector; other countries like Japan are continuing their programs.”CEA (2012)



The photoelectrolysis of water

It would be possible to transform water directly into hydrogen by the action of the sun. That would be photoelectrolysis. This technology involves the use of semiconductors.

It is still at the experimental stage, but a team of researchers have found a method for this process to produce hydrogen at 5€/kg.

Fatal hydrogen or co-produced hydrogen

Fatal hydrogen is the result of a process that does not have its production as its object. It is a “co-product”. Among its producers, there is the chlorine industry, the production of coke (a coal…) and the refining of petroleum products. This is the context of hydrogen production and not a specific mode of production. For example, the production of chlorine produces “fatal hydrogen” by electrolysis. Similarly, the production of coke produces fatal hydrogen by gasification. They are both co-products.

Conclusion

Thus, there are two main modes of hydrogen production:

  • From steam reforming or gasification of fossil fuels, which produces a lot of greenhouse gases (until CCUS is viable);
  • From water, by electrolysis, which consumes a lot of electricity. Many advances are underway to improve the profitability of these facilities.

At first glance, electrolysis seems an obvious choice. Nevertheless, it should be kept in mind that electricity is currently very carbon-intensive in Europe: approximately 300g of CO2/kWh (compared to <100 in France). Any additional demand for electricity will mobilize coal or gas-fired power stations, which respectively produce an average of 950g and 350g of CO2/kWh. The energy required “is typically of the order of 50 electrical kWh per kilogram of hydrogen produced” (Durville et al. 2015) If the electricity comes from a coal-fired power plant, this would represent 47.5 kg CO2, which would be roughly 5 times more than for steam reforming…

Several projects propose coupling hydrogen production with green energy, such as a dam or photovoltaics. Nevertheless, these projects also suffer from this criticism: why not, above all, decarbonize (European) electricity?

[Rq: this article is being deepened, I will have to read a lot of scientific studies before proposing its final form]





Bibliographie :

  • Durville J-L., Gazeau J-C., Nataf J-M. (2015), Filière hydrogène-énergie, rapport N° 2015/07/CGE/SG rendu au ministère de l’écologie et de l’économie en septembre 2015, 161p.
  • William J.Nuttall et Adetokunboh T.Bakenne (2020), Fossil Fuel Hydrogen, Technical, Economic and Environmental Potential, éd. Springer, 143 pages
  • Zhong Zhang J., Li J., Li Y., Zhao Y. (2014), “Hydrogen Generation, Storage, and Utilization”, éd. Wiley, 2014