Sustainability is high up on the political agenda. Our previous blogs on liquid hydrogen already briefly described how hydrogen is gaining importance as a sustainable energy carrier and fuel for various industries.
In this blog, we take a more in-depth approach to the different ways of producing hydrogen. We review gray, blue, and green hydrogen and explain what steam methane reforming entails, probe the problems with this method, and how we are gradually moving towards a world full of sustainable hydrogen.
Hydrogen in three colors
Hydrogen can be produced in a variety of ways. Some methods are significantly more sustainable than others, and this is why the processes are often represented by colors. The three most common hydrogen production methods are labeled gray, blue, and green.
Gray hydrogen (steam methane reforming)
Currently, about 95% of all hydrogen in Europe is produced by steam methane reforming (natural gas reforming). This method uses steam at a high temperature (700-1000 °C) to produce hydrogen from a methane source, such as natural gas or coal. The two elements combined with a catalyst give rise to a reaction at a pressure of 3-25 bar (1 bar = 14.5 psi). This reaction generates CO (carbon monoxide), CO2 (carbon dioxide), and hydrogen.
Next, in a second step, called the “water-gas shift reaction,” the hydrogen content is further enriched. During this step, a reaction is induced between steam and CO, again with the help of a catalyst. This results in a small amount of heat and CO and a large amount of hydrogen.
The chemical formulas of this process are as follows:
Steam methane reforming
CH4 + H2O → CO + 3H2
CO + H2O → CO2 + H2
Steam methane reforming is great for energy efficiency, but unfortunately, quite damaging to the environment.
For every kilogram of hydrogen produced with this method, as much as 7 kilograms of CO2 is released.
A slightly more sustainable alternative is blue hydrogen. Blue hydrogen is basically the same as gray hydrogen (produced by steam methane reforming), but the vast majority of the CO2 is captured and stored underground (carbon capture and storage) or reused (carbon capture and usage).
In the process of carbon capture and storage (CCS), the released CO2 is transported through pipelines to empty gas fields, and for example, injected into underground sandstone layers. The CO2 can also be captured and reused in, for example, the production of biofuels, plastics, or concrete. This process is known as carbon capture and usage (CCU).
Blue hydrogen is a lot more sustainable than gray hydrogen, but capturing CO2 requires additional infrastructure and energy. As a result, the cost of blue hydrogen is higher than that of gray hydrogen.
The most sustainable, but unfortunately, also the most challenging alternative is green hydrogen. Green hydrogen is produced through electrolysis. This chemical reaction is achieved by using an electric current to separate compound substances into single substances. To produce green hydrogen, water is split into oxygen and hydrogen.
Electrolysis and green hydrogen are currently fully in the spotlight. When using only green energy (such as wind or solar energy), the process is CO2-neutral.
However, the production of green hydrogen is costly. Electrolysis requires relatively large amounts of green electricity, and the efficiency of the overall green hydrogen production process – including electrolysis – is still under development. All these challenges affect scalability; as a result, green hydrogen production is yet very limited worldwide. In the near future, this is expected to change.
From steam methane reforming to green hydrogen
How do we eventually reach that green hydrogen economy? How will the development from steam methane reforming, which is currently the method of choice, towards sustainable green hydrogen proceed from the year 2021 onward?
As SINTEF recently described in a blog, “The future is green, but the path there is multicolored.” Before green hydrogen prevails over gray hydrogen, we expect to be at least several decades in the future. The exact timeline remains guesswork, but there are predictions of the production methods we will witness between now and 2050.
Predictions by SINTEF
The table below is based on the Hydrogen for Europe pre-study results and slightly modified by SINTEF. The different colors represent a prediction of the production methods of hydrogen in the coming decades.
The black line
First, the black dotted line points to the expected growth in hydrogen production overall. There is no doubt about it: the demand for hydrogen will increase significantly between now and 2050.
The gray line
The gray line (H2 from natural gas) indicates hydrogen produced by steam methane reforming. While most hydrogen in 2021 is still produced this way, the gray line will likely go down sharply from this year onward. Gray hydrogen is still by far the quickest and cheapest production option in 2021, but with blue and green hydrogen on the rise, less and less gray hydrogen will be needed in the near future.
The blue line
The blue line indicates blue hydrogen. Blue hydrogen is, in essence, gray hydrogen, with the CO2 captured during production. Because the production processes are otherwise similar, blue hydrogen is a logical first step toward sustainability. After all, the infrastructures for steam methane reforming already exist. The only addition needed for the production of blue hydrogen is the system for carbon capture and storage (CCS) or carbon capture and usage (CCU).
The Green Line
While blue hydrogen serves as an intermediate technology, green hydrogen (produced with renewable resources and electrolysis) is the ultimate objective within most strategies. However, green hydrogen and its processes are still in the early stages; hence the green line is unlikely to overtake the blue line anytime soon.
Fortunately, the developments pertaining to the production of green hydrogen are in full swing. A good number of countries have invested in pilot projects related to the production, storage, transport, and of course, the application of green hydrogen (see our recent blog, “What is hydrogen used for?”).
However, achieving the desired green hydrogen economy will require even more investment, more research, and a reduction in costs. This takes time, which is clearly reflected by the green line.
The yellow line
Finally, the graph shows a yellow line. This method uses biomass (and CCS) for the production of hydrogen. In principle, the use of biomass is sustainable as long as this biomass is a residual waste. However, since generating hydrogen with biomass is a less efficient process and less biomass is available, hydrogen production using renewable energy will have a larger share of the total amount of hydrogen produced.
A future without CO2 emissions
What do these developments imply for total CO2 emissions in Europe in the coming decades? This, of course, remains to be seen, but the predictions are optimistic. According to SINTEF, the use of clean hydrogen could result in a reduction of more than 800 Mt CO2 per year by 2050. This comprises 19% of the current greenhouse gas emissions.
This significant reduction in CO2 emissions will require the expected growth in green hydrogen production. A tenfold increase of the current market size is even necessary, while production must be entirely sustainable.