Brown hydrogen is hydrogen gas produced by gasifying lignite, a soft, low-grade type of coal sometimes called brown coal. It is the most carbon-intensive way to make hydrogen, releasing roughly 19 kg of CO2 equivalent for every kilogram of hydrogen produced. The term is part of a color-coded system the energy industry uses to distinguish hydrogen by its production method and carbon footprint.
How the Color System Works
Hydrogen itself is a colorless gas regardless of how it’s made, but the industry labels it by source. Grey hydrogen comes from natural gas. Green hydrogen comes from water electrolysis powered by renewables. Blue hydrogen is grey or brown hydrogen paired with carbon capture. Brown and black hydrogen both come from coal gasification, with the color indicating the type of coal: lignite (brown) or bituminous coal (black). Of all these categories, brown and black hydrogen carry the heaviest emissions burden.
As of 2021, about 27% of global hydrogen production came from coal, 47% from natural gas, 22% from oil as a byproduct, and only around 4% from electrolysis. Coal-based hydrogen remains significant largely because of its role in countries with abundant coal reserves and established gasification infrastructure, particularly China.
How Brown Hydrogen Is Made
The process starts with coal gasification. Lignite is fed into a gasifier, a high-temperature reactor where it reacts with a controlled mixture of oxygen and steam. Instead of burning the coal outright, the gasifier partially oxidizes it, breaking it down into a gas mixture called syngas. Syngas is mostly hydrogen and carbon monoxide, along with smaller amounts of CO2, methane, and various impurities.
The carbon monoxide in the syngas then goes through a reaction with steam (called a water-gas shift reaction) that converts it into additional hydrogen and CO2. After that, the hydrogen is separated out and the CO2 is vented to the atmosphere, unless the facility includes carbon capture equipment (which most do not). The most commercially established approach uses entrained flow gasifiers, where finely ground coal particles react at very high temperatures. Research on Australian brown coal, for instance, has found this method competitive under current market conditions, though alternative gasifier designs could become viable at larger scale.
Carbon Emissions and Pollutants
The core environmental problem with brown hydrogen is straightforward: producing one kilogram of it generates about 19 kg of CO2 equivalent emissions. For context, grey hydrogen from natural gas produces roughly 9 to 12 kg of CO2 per kilogram. Brown hydrogen is essentially twice as dirty, which makes sense given that lignite has a lower energy density than natural gas, so you need to process more material to get the same amount of hydrogen.
CO2 is the headline concern, but it’s not the only one. Coal gasification also produces trace amounts of mercury, arsenic, selenium, cadmium, and acidic gases like hydrogen chloride. Dioxins, furans, and volatile organic compounds can form as well. Modern gasification plants use activated carbon filters and other sorbents to capture many of these pollutants, and U.S. regulations have required existing power plants to cut mercury emissions by 90%. Still, even with controls in place, coal gasification generates a waste stream of spent sorbent material and ash that requires careful disposal.
Where Brown Hydrogen Gets Used
Most hydrogen produced from coal doesn’t get labeled and sold as “brown hydrogen” on a retail market. It feeds directly into industrial processes at or near the production site. The biggest use globally is ammonia production, which underpins the fertilizer industry. Ammonia manufacturing consumes enormous volumes of hydrogen as a chemical feedstock, and in coal-rich regions, gasification is often the cheapest local source.
Beyond fertilizer, hydrogen from coal supports chemicals manufacturing (including products like melamine and acrylonitrile), explosives production, metals refining, and petroleum refining. About 20% of the ammonia market alone goes to industrial applications like wastewater treatment, electronics manufacturing, and refrigeration. In all of these cases, the hydrogen is valued as a chemical input, not as a fuel.
Why It Still Exists
Brown hydrogen persists for one reason: cost and availability in coal-dependent economies. Countries sitting on large lignite deposits can produce hydrogen from coal more cheaply than importing natural gas or building out renewable electricity for green hydrogen. China, which produces and consumes more hydrogen than any other country, relies heavily on coal gasification because coal is its most abundant domestic energy resource.
The economics shift, however, when you factor in carbon costs. If governments price carbon emissions through taxes or trading schemes, the 19 kg of CO2 per kilogram of hydrogen becomes a significant financial liability. Some research has explored pairing coal gasification with carbon capture and storage to reduce emissions, which would reclassify the output as blue hydrogen. But adding carbon capture increases both capital costs and operational complexity, and the technology has not yet been deployed at scale for coal-to-hydrogen plants in most regions.
As green hydrogen costs continue to fall with cheaper renewable electricity and more efficient electrolyzers, brown hydrogen is widely expected to lose its cost advantage in the coming decades. For now, though, it remains a substantial share of global hydrogen supply, particularly in Asia.