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Hydrogen from other sources

A very small quantity of the hydrogen produced today comes from biogenic sources and other industrial processes[i].

Just as hydrogen can be extracted from a fossil fuel, it can be extracted from a from biomass or a biomass based-fuel [ii],[iii]

Hydrogen can also be produced as a by-product in processes that aim to primarily produce another molecule.

Image by Thomas Peham

How it's made

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If available, sustainable biomass such as algae[iv] or organic waste can be processed through gasification or pyrolysis to 'extract' hydrogen.


If the biomass has already been processed into biogas, the hydrogen can be produced by biogas reforming, which is similar to natural gas reforming. In this process, the resulting CO2 can be captured and geologically stored, thereby improving the climate performance of the hydrogen produced. Just as natural gas, the biogas can be heated in the absence of oxygen to split it into hydrogen and carbon black which can then be permanently stored. 


The biomass can also be directly converted into gas with heat and in the absence of oxygen, resulting in a synthesis gas (i.e. a gaseous fuel mixture including H2, CO, CO2) that can be further refined to hydrogen[v].

In some industrial production processes, H2 is produced as a by-product. One such process is the production of chlorine and caustic soda. An electric current is passed through salt water, which dissociates and recombines through exchange of electrons into chlorine, caustic soda and hydrogen. 0.03t of hydrogen is produced per ton of chlorine during this process[vi].


However, most of the hydrogen by-products created in industrial processes are usually used on-site already[vii], so their further use in other applications is very limited.  

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Climate impact

The climate impact of hydrogen will depend on the indirect impact of inputs going into its production, the type of electricity used and amount of the CO2 stored. 

While this report only covers a few examples, hydrogen can be produced in many ways - which is why every case has a distinct climate footprint of its own. Overall, it is important to keep in mind that the climate impact of any given hydrogen molecule is dependent on three major factors:


Hydrogen is only as clean as the ingredients it’s produced from: Indirect emissions of the feedstock for H2 production, such as biomass land use change and upstream methane emissions, need to be taken into account.


Only low-carbon electricity makes low-carbon hydrogen: If the H2 is produced from a water-based brine or water and electricity is used to extract the hydrogen, the origin (GHG intensity in gCO2/kWh) of the electricity must be taken into account.


Unabated production of fossil hydrogen is no longer acceptable: If the H2 is produced from a carbon-based molecule, the CO2 or carbon produced in the process must be isolated and permanently stored to achieve emission reductions -  particularly if the carbon content comes from a fossil source such as natural gas.

It’s important to note that the more steps there are in hydrogen production, the less efficient the process will be. These differences in process efficiency also influence the final climate impact of the hydrogen. Finally, the chosen application of the hydrogen is the last factor determining its effectiveness as a climate change mitigation tool. Targeted large-scale applications (e.g. in industry) of very low-carbon hydrogen (e.g. from electrolysis with only renewable electricity) will always achieve the highest emission reductions, but might not be available on a large scale in the near future. This is why other low-carbon alternatives for hydrogen production are relevant in the decades to come.




Climate score 

for hydrogen from sustainable EU biomass


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Climate change mitigation 

Even when biomass is produced with low indirect emissions (e.i. from land use change), it's production cannot reach a large scale in Europe[viii]. If the biogenic CO2 or carbon resulting from the production process is permanently stored, then the climate change mitigation potential could be higher. 

Efficient use of resources 

The production of biomass incurs large resource requirements in terms of water and land, both directly and indirectly. 

Deployment readiness 

Projects using thermochemical or biological conversion of biomass to produce hydrogen are already being rolled out and the conversion processes are well researched. However, while the production of hydrogen from biomass might be advantageous on a small scale, there will be a limited availability of sustainable biomass for its large scale production. 

Climate score 

for hydrogen by-products from chlor-alkali production

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Climate change mitigation 

Most chlor-alkali production processes are still carbon intensive , making the hydrogen by-product carbon intensive as well. The climate change mitigation potential could improve if only low-carbon electricity was used for the process and the hydrogen was re-used or combusted for heat on-site. The scale of the production remains a challenge, since the aim is to make the main product and not hydrogen itself. 

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Efficient use of resources 

Using hydrogen from the chlor-alkali production process increases the efficient use of resources. The most efficient scenario would include the reuse the hydrogen on-site or its combustion in a boiler to generate heat for the production process itself. 

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Deployment readiness 

The chlor-alkali production process is already well developed and is an established industrial activity. However, since the resulting hydrogen is only a by-product, there is no prospect for the process to deliver large amounts of hydrogen in the future.

Know of relevant research or projects to add to our library?


[i] Baykara, S.Z. 2018. Hydrogen: A brief overview on its sources, production and environmental impact. International Journal of Hydrogen Energy: 1-10. Available at:

[ii] Acar, C. and I.Dincer. 2014. Comparative assessment of hydrogen production methods from renewable and non-renewable sources. International Journal of Hydrogen Energy 39 (1): 1-12. Available at:

[iii] Milne et al. 2002. Hydrogen from Biomass State of the Art and Research Challenges. Available at:

[iv] Lakaniemi et al. 2011. Biogenic hydrogen and methane production from Chlorella vulgaris and Dunaliella tertiolectabiomass. Biotechnology for Biofuels 4 (34). Available at:

[v] Bakhtyari, A. et al. 2017. Encyclopedia of Sustainability Science and Technology: Hydrogen Production Through Pyrolysis. Available at:

[vi] Hydrogen Europe. 2020. Hydrogen production. Available at :

[vii] Khasawneh et al. 2019. Utilization of hydrogen as clean energy resource in chlor-alkali process. Energy Exploration and Exploitation 37 (3). Available at:

[vii] T&E and Birdlife. How much sustainable biomass does Europe have in 2030?. Available at:

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