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Turquoise hydrogen takes a step towards the next level

Laurent Fulcheri
Laurent Fulcheri
Research director at PERSEE, MINES-ParisTech
Key takeaways
  • “Turquoise” hydrogen is formed from methane that is fed into a reactor, which heats it to a high temperature (~2,000°C) in the absence of oxygen.
  • In this process, the methane breaks down into hydrogen (H2) and solid carbon black (C), while avoiding the production of CO2 in return.
  • “Grey” hydrogen – which accounts for 95% of hydrogen produced today – emits 9.89 kg CO2e/kg. This is almost 10 times more than “turquoise” hydrogen!
  • Today, the production of “turquoise” hydrogen is close to the emission level of “green” hydrogen (0.03 to 0.37 kg CO2e/kg), but it is 3 times less energy-intensive, a figure that could theoretically rise to 7 with improved processes.
  • If the reactor is fuelled entirely with biogas from household waste, the carbon intensity drops to -5.22 kg CO2e/kg! In a scenario where fossil gas and biogas are mixed, only 10% biogas is sufficient for zero carbon intensity.

Green, grey, blue, pink… There are more and more colours for hydro­gen, each describ­ing the way it is pro­duced. And, a lit­tle-known for­ma­tion process is mak­ing its way into the list, par­tic­u­lar­ly in the Unit­ed States: “turquoise” hydro­gen. Like reform­ing (the so-called SMR process, which pro­duces “grey” hydro­gen), “turquoise” hydro­gen is formed from methane. But here the methane is fed into a reac­tor which heats it to high tem­per­a­tures (1,000 to 2,000°C) in the absence of oxy­gen – this is known as pyrol­y­sis. The gas (CH4) is then bro­ken down into hydro­gen (H2) and sol­id car­bon black (C). The process has the advan­tage of not cre­at­ing any CO2 mol­e­cules – a potent green­house gas – but does con­sume elec­tric­i­ty. It is cur­rent­ly 3 times less ener­gy inten­sive than water elec­trol­y­sis (“green” hydro­gen), and this fig­ure could the­o­ret­i­cal­ly rise to 7 times with process improve­ments1.

Is turquoise hydro­gen there­fore the ide­al solu­tion for the ener­gy tran­si­tion? To answer that ques­tion, an inter­na­tion­al research team is cal­cu­lat­ing its Life Cycle Assess­ment (LCA) for the first time. This indi­ca­tor is tra­di­tion­al­ly used to assess the cli­mate foot­print from pro­duc­tion to end of life. The analy­sis is based on a com­mer­cial pro­duc­tion unit, Mono­lith Mate­ri­als’ Olive Creek plant, which con­verts elec­tric­i­ty from wind pow­er plants into arc plas­ma to heat gas. Lau­rent Fulcheri is one of the authors of this study pub­lished in July 2022 in the Inter­na­tion­al Jour­nal of Hydro­gen Ener­gy2.

What does the life cycle assessment (LCA) tell us about the climate footprint of turquoise hydrogen?

We imag­ined that this pro­duc­tion method had an extreme­ly inter­est­ing car­bon foot­print, but here we quan­ti­fy it for the first time: the pro­duc­tion of one kilo of turquoise hydro­gen emits 0.91 kg of CO2 equiv­a­lent (kg CO2e/kg). “Grey” hydro­gen, which accounts for as much as 96% of hydro­gen pro­duced today, emits 9.89 kg CO2e/kg. This is almost 10 times less than “turquoise” hydro­gen3 ! The main advan­tage of our study is that it is based on data from the first full-scale indus­tri­al unit: it is there­fore rep­re­sen­ta­tive of the real car­bon footprint.

The cal­cu­la­tion method used con­sid­ers all emis­sions: those from the process, from the elec­tric­i­ty used, but also from hydro­car­bons. Most of the emis­sions do not come from the process itself, but from leaks through­out the gas sup­ply chain (extrac­tion, dis­tri­b­u­tion, etc.). Today, the pro­duc­tion of “turquoise” hydro­gen is close to the emis­sion lev­el of “green” hydro­gen (0.03 to 0.37 kg CO2e/kg), but it has the advan­tage of using much less electricity.

The Monolith plant, which is used here to calculate the LCA, uses methane. Is it possible to use it from waste or sewage plants?

The Unit­ed States has large reserves of shale gas, and this will be the most favourable route for deploy­ing turquoise hydro­gen. In Europe the sce­nario is dif­fer­ent, espe­cial­ly since the war in Ukraine: bio­gas will prob­a­bly be the pre­ferred raw material.

This is a mode of pro­duc­tion that we have mod­elled: “turquoise” hydro­gen then becomes more ben­e­fi­cial than “green” hydro­gen. If the reac­tor is fuelled entire­ly with bio­gas from house­hold waste, the car­bon inten­si­ty drops to ‑5.22 kg CO2e/kg! This is because agri­cul­tur­al plant pro­duc­tion helps to store car­bon through pho­to­syn­the­sis, which makes the whole process a CO2 “store”. As bio­gas is only avail­able in lim­it­ed quan­ti­ties, one can also imag­ine a sce­nario where fos­sil gas and bio­gas are mixed. For 10% bio­gas, the car­bon inten­si­ty of turquoise hydro­gen is zero.

What explains the low climate impact of turquoise hydrogen?

The reac­tion itself does not pro­duce CO2, unlike oth­er process­es such as SMR (grey hydro­gen). More­over, from one kilo of methane, 250 g of hydro­gen are pro­duced, but also 750 g of sol­id car­bon black. The lat­ter can be used in many indus­tries: we have allo­cat­ed the total CO2 emis­sions to the hydro­gen and car­bon black pro­duced, which there­fore helps to reduce the car­bon foot­print of hydrogen. 

And what about carbon black emissions? 

This is the oth­er major advan­tage of this process. 15 mil­lion tonnes of car­bon black are pro­duced each year world­wide. The process­es used emit an aver­age of 2.6 kg CO2e/kg: pyrol­y­sis of fos­sil gas reduces emis­sions to 0.9 kg CO2e/kg.

It is impor­tant to under­stand that replac­ing the cur­rent “grey” hydro­gen pro­duc­tion units with pyrol­y­sis process­es requires colos­sal invest­ments. For exam­ple, Monolith’s first com­plete plant will con­sist of 12 iden­ti­cal units, with an invest­ment of around €1 bil­lion. Car­bon black, a high val­ue-added tech­ni­cal prod­uct, is there­fore a very impor­tant ele­ment in the ini­tial eco­nom­ic equation.

So, the economic viability of turquoise hydrogen is based on carbon black?

Car­bon black is main­ly used in tyres, but also in dyes, paints, bat­ter­ies, and cells. This by-prod­uct makes the process eco­nom­i­cal­ly inter­est­ing, but also strate­gic: there is cur­rent­ly a short­age of car­bon black in Europe, as most of the pro­duc­tion comes from Rus­sia and Ukraine.

Isn’t there a risk that we will end up producing more carbon black than we need?

If all of our cur­rent hydro­gen pro­duc­tion were replaced by turquoise hydro­gen, the mar­ket would be sat­u­rat­ed very quick­ly, and we would end up with “moun­tains” of sol­id car­bon. Indus­tri­al­ists are already study­ing 2nd or 3rd gen­er­a­tion pyrol­y­sis. Car­bon black could be used for mas­sive new appli­ca­tions, such as in con­struc­tion mate­ri­als or soil improve­ment. The last solu­tion would be to bury it. Rather than stor­ing CO2, stor­ing car­bon black could help reduce GHGs. But this stage would only be reached if the process is devel­oped on a phe­nom­e­nal scale.

What role does turquoise hydrogen have to play in the energy transition?

In the medi­um to long-term, turquoise hydro­gen could play a major role in cur­rent hydro­gen appli­ca­tions by replac­ing SMR process­es. The cur­rent pro­duc­tion of hydro­gen (used in the steel indus­try, agri­cul­ture or refin­ing) amounts to 60 mil­lion tonnes each year. This rep­re­sents almost 2% of total CO2 emis­sions world­wide, as 96% of it is pro­duced by methane reform­ing. We should there­fore start by reduc­ing these emis­sions before devel­op­ing new applications!

Turquoise hydro­gen has a major role to play in decar­bon­is­ing the hydro­gen indus­try. Despite the cur­rent craze for water elec­trol­y­sis, this process is extreme­ly ener­gy-inten­sive and is not prof­itable today: turquoise hydro­gen has reached tech­no­log­i­cal matu­ri­ty and an eco­nom­ic mod­el that is already sustainable.

Anaïs Marechal
1Han J, Mintz M, Wang M. Waste-to-wheel analy­sis of anaer­o­bic-diges­tion-based renew­able nat­ur­al gas path­ways with the GREET mod­el (No. ANL/ESD/11–6). Argonne, IL (Unit­ed States): Argonne Nation­al Lab (ANL); 2011.
2Diab, J., et al. (2022), Why turquoise hydro­gen will be a game chang­er for the ener­gy tran­si­tion, Inter­na­tion­al jour­nal of hydro­gen ener­gy, vol­ume 47, issue 61, pages 25831–25848.
3World Ener­gy Coun­cil (2019), Inno­va­tion Insights Brief, New hydro­gen econ­o­my – Hope or hype?

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