Most hydrogen today is produced by exposing natural gas to high temperature, pressure and steam, which produces carbon dioxide as a by-product. In the so-called "gray" hydrogen, all this carbon dioxide is released into the atmosphere. In blue hydrogen, carbon dioxide is captured in factories and sold or stored, usually deep underground.
Blue hydrogen is seen by some as an intermediate fuel, a way to create a hydrogen economy in anticipation of lower prices for green hydrogen. At the same time, blue hydrogen is expected to be less polluting than gray hydrogen, natural gas, or other carbon-intensive fuel sources.
However, blue hydrogen may not be low carbon at all, according to a new peer-reviewed study highlighted in a report by Ars Technica: In fact, the study says the climate could be better if we burn coal instead.
There are two ways to make blue hydrogen, and both are based on steam reformation - the process of using high temperature, pressure and steam that breaks down methane and water to produce hydrogen and carbon dioxide. In both cases, carbon dioxide from steam reformation is captured and stored or used.
The difference between the two approaches is whether carbon dioxide is captured from the generators that power the steam reformation and carbon capture processes. Putting it all together, capturing carbon from all parts of the process - steam reformation, energy supply, and carbon capture - eliminates only 3 percent of greenhouse gas emissions, compared to carbon capture from steam reformation alone.
Emissions of blue hydrogen with the lowest carbon content were only 12% lower than gray hydrogen. The Achilles' heel of blue hydrogen is the methane used to produce it. Methane is the dominant component of natural gas, and although it burns cleaner than oil or coal, it is a potent greenhouse gas in itself.
In 20 years, one ton of this gas heats the atmosphere 86 times more than one ton of carbon dioxide. This means that leaks in the supply chain could negate many of the climatic benefits of methane.
In a new study, Robert Howarth and Mark Jacobson, the article's authors and two prominent climatologists, suggest a leakage rate of 3.5 percent of consumption.
They came to this number by analyzing 21 studies that examined the emissions of gas fields, pipelines and storage facilities using satellites or aircraft. To see how the 3.5 percent figure affected the results, Howarth and Jacobson also ran their models suggesting 1.54%, 2.54% and 4.3% leakage.
These ratios are based on EPA estimates at the bottom and at the top on stable carbon isotope analyzes that have identified emissions from shale gas production.
No matter what leak rate they used, producing blue hydrogen generated more greenhouse gas equivalents than simply burning natural gas.
And at a leakage rate of 3.5 percent, blue hydrogen turned out to be worse for the climate than burning coal.
"The combined emissions of carbon dioxide and methane are greater for hydrogen gray and hydrogen blue (whether the exhaust flue gas is treated to capture carbon or not) than any of the fossil fuels," Howarth and Jacobson write.
"Methane emissions are the main contributors to this, and methane emissions from both gray and blue hydrogen are greater than any fossil fuel."