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“Turquoise hydrogen” a viable solution without CO2 ?

Laurent Fulcheri
Laurent Fulcheri
Research director at PERSEE, MINES-ParisTech
Key takeaways
  • Black, brown and grey hydrogen are made from fossil fuels, and blue hydrogen is a similar process combined with CO2 capture and storage to reduce emissions.
  • Green hydrogen is produced via electrolysis of water, but it requires large amounts of electricity from the grid or renewable energy.
  • Turquoise hydrogen uses both electricity and methane, but with 4–7.5 times less electricity than electrolysis depending on the technology used – making it a hopeful technology for the future.
  • Moreover, if the methane comes from biogas it has captured CO2from the air, meaning it actually has a negative carbon footprint.

Though the use of hydro­gen ener­gy is clean, its pro­duc­tion is high­ly pol­lut­ing, par­tic­u­lar­ly when it comes to COemis­sions. Green­er solu­tions, such as elec­trol­y­sis, do exist but they are still too expen­sive. Nev­er­the­less, new, effi­cient low-emis­sion tech­nolo­gies are emerg­ing, such as methane pyrol­y­sis. Here is a quick run­down of the colours of hydro­gen: grey, blue, green or turquoise?

Is hydro­gen the ide­al ener­gy solution?

Hydro­gen is inher­ent­ly a ‘clean’ ener­gy: when you burn it or you use it in a fuel cell, it only pro­duces water and ener­gy. How­ev­er, it is almost non-exis­tent in gaseous form on Earth so it must there­fore be pro­duced some­how. Unfor­tu­nate­ly, hydro­gen pro­duc­tion requires a lot of ener­gy, which makes it far less clean. As such, today about 95% of hydro­gen is made from fos­sil fuels. Pro­duc­ing 1 ton of hydro­gen results in 10 tons of CO2 emis­sions. It is one of the ener­gies with the worst car­bon foot­print and so the chal­lenge is to find a way of pro­duc­ing hydro­gen with­out emit­ting CO2.

Today, this is pos­si­ble thanks to water elec­trol­y­sis, which rep­re­sents 5% of glob­al hydro­gen pro­duc­tion. It is called “green” hydro­gen. The process involves split­ting water into oxy­gen and hydro­gen, but it uses huge amounts of elec­tric­i­ty. Ener­gy con­sump­tion is there­fore inevitable: the chem­i­cal reac­tion requires at least 40kWh to pro­duce each kilo­gram of hydro­gen, if elec­trol­y­sers oper­ate at max­i­mum effi­cien­cy. But today, their per­for­mance is only about 60% of max­i­mum, mean­ing that pro­duc­ing 1kg of hydro­gen con­sumes as much as 60 kWh. 

“Green” hydro­gen can be fur­ther clas­si­fied as “pink” or “yel­low” if the elec­tric­i­ty used is pro­duced by renew­able ener­gy, nuclear ener­gy (both of which have low CO2 emis­sions) or a com­bi­na­tion of these.

It is easy to under­stand why methane reform­ing (using fos­sil fuels) is the pre­dom­i­nant method com­pared to elec­trol­y­sis. At cur­rent elec­tric­i­ty prices, 1kg of green hydro­gen costs 4–6 €. In con­trast, hydro­gen pro­duced through reform­ing costs less than 1€. Giv­en the cur­rent mar­ket, a mas­sive deploy­ment of green hydro­gen is hard­ly possible. 

Table pre­sent­ing the sources and tech­niques used as well as the amount of CO2 emit­ted dur­ing the pro­duc­tion of each type of hydrogen.

What are the options to make hydro­gen pro­duc­tion “green­er”?

One of the options is to com­bine COreform­ing with the cap­ture and stor­age of CO2 (see our dossier on CO2 cap­ture and stor­age). The sce­nar­ios show that it would dou­ble or triple the cost of hydro­gen, that is a price of 2–3 €/kg. This is called “blue” hydro­gen. “Grey” hydro­gen is pro­duced by methane reform­ing, and “black” hydro­gen is made from coal.

But there is a dif­fer­ent way. Indus­tri­al and polit­i­cal cir­cles recent­ly dis­cov­ered this process, but it is not new: I have been work­ing on it since 1995 and have based my whole car­ri­er on this sub­ject. Referred to as “turquoise” hydro­gen, it uses both elec­tric­i­ty and methane. It involves decom­po­si­tion of methane by pyrol­y­sis at very high tem­per­a­tures (1 000 to 2 000 °C). Hence, it still requires elec­tric­i­ty, but 4–7.5 times less than elec­trol­y­sis depend­ing on the tech­nol­o­gy used. This process pro­duces car­bon and hydro­gen, but not CO2. One kilo of methane is used to pro­duce 250g of hydro­gen and 750g of car­bon, a prod­uct with high added val­ue. More impor­tant­ly, this reac­tion requires 7 times less elec­tric­i­ty than water elec­trol­y­sis for each quan­ti­ty of pro­duced hydro­gen (but it pro­duces two times less hydro­gen than water reform­ing per methane molecule).

How far along is indus­tri­al pro­duc­tion for turquoise hydrogen? 

This pyrol­y­sis process is cur­rent­ly under indus­tri­al devel­op­ment in the USA, with our Amer­i­can indus­tri­al part­ner Mono­lith Mate­ri­als. They devel­oped a con­clu­sive pilot between 2012 and 2017 in Cal­i­for­nia and have start­ed indus­tri­al­i­sa­tion. The first unit has been built and 11 oth­er units are soon to fol­low. Tech­no­log­i­cal prob­lems relat­ed to change of scale have been solved, and first mar­ket­ing is expect­ed in the com­ing months. This unit will con­sume 20,000 tons of nat­ur­al gas and will pro­duce 15,000 tons of black car­bon as well as 5,000 tons of hydrogen.

At first, the eco­nom­ic mod­el will con­sist of adding val­ue to the car­bon pro­duced, which is wide­ly used in tyre man­u­fac­tur­ing and sold at approx­i­mate­ly 1€/kg. A tyre con­tains about 30% of black car­bon, which increas­es resis­tance to wear, UV radi­a­tion or heat. In the sec­ond phase, hydro­gen will become promi­nent from an eco­nom­ic per­spec­tive. Today, the tech­nol­o­gy is opti­mised for black car­bon pro­duc­tion (the tem­per­a­ture is set accord­ing to the desired grade for black car­bon). In the future, it will be opti­mised for hydro­gen pro­duc­tion, and new appli­ca­tions for black car­bon will need to be devel­oped. For instance, it could be used in con­struc­tion mate­ri­als, road infra­struc­tures, or even in agri­cul­tur­al soils. It is cheap­er and safer than stor­ing CO2!

Bet­ter yet: if the methane comes from bio­gas (obtained by the decom­po­si­tion of organ­ic mate­ri­als, in bio­gas plants or land­fill sites, for exam­ple), it has cap­tured CO2 from the air. In this case pyrol­y­sis actu­al­ly has a neg­a­tive car­bon foot­print since it reduces the quan­ti­ty of CO2 in the atmosphere.

Are there oth­er tech­nolo­gies for turquoise hydro­gen pro­duc­tion technologies? 

Yes, but only at the lab­o­ra­to­ry or demon­stra­tor stage. There are “liq­uid met­al bath” meth­ods in which methane is inject­ed and decom­posed in columns con­tain­ing molten met­al. Pilots were built in Cal­i­for­nia and in Aus­tralia. For its part, the Ger­man indus­tri­al­ist BASF stud­ies the decom­po­si­tion of methane using cat­a­lysts. These are seri­ous com­peti­tors, but they must still over­come sev­er­al tech­no­log­i­cal challenges.

Interview by Cécile Michaut


Laurent Fulcheri

Laurent Fulcheri

Research director at PERSEE, MINES-ParisTech

After a thesis at the CNRS, he joined the Centre d'Energétique (now known as PERSEE) in 1989 and created the Plasma group. Laurent Fulcheri is a specialist in thermal plasma hydrocarbon conversion processes. He has been working in particular for more than 25 years on the pyrolysis of methane for the production of decarbonated hydrogen and solid carbon.

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