“Hydrogen is the most abundant element in the universe.”
As an entrepreneur, this brilliant bit of marketing makes me smile. It’s a true statement – about 90% of atoms in the universe are hydrogen, according to scientists who know that kind of thing. And it makes people think that it's as easy as turning over the nearest rock and, “Oh! Look at the hydrogen! Quick, put it in your tank and let’s be off with this amazing fuel!”
As an engineer, the statement makes me groan – loudly, if you believe Mr. Motlow and Mr. Kemper. Because the hydrogen in the universe is either inaccessible (nobody has figured out how to mine the sun yet), or is already tied up in compounds such as water (H2O, 67% hydrogen atoms) and methane (80%), and makes up part of everything from tigers (60%) to Levi’s jeans (50%). When it comes to using hydrogen as a fuel, that’s a problem. We can’t just put water or jeans in our gas tanks and expect the car to go. We need to pull the hydrogen out of where its hiding, separate it, and use it by itself. That’s not easy, but fortunately people have figured out a few ways to do this.
99% of all hydrogen made today comes from fossil fuels, specifically natural gas (76%) and coal (23%). Fossil fuels are essentially different combinations of carbon and hydrogen, so it is just a matter of separating the hydrogen from the carbon.
To produce hydrogen from methane (CH4), which is what natural gas is mostly made of, and water (H2O), you mix them together and heat them up to around 900 °F in a special tank called a reformer. At this temperature, and with the help of a special material called a catalyst, both the methane and water break apart, then recombine to make hydrogen (H2) and carbon monoxide (CO). Although a decent fuel by itself, carbon monoxide is quite poisonous, so this and some more water is passed through another reactor called a shift reactor which makes more hydrogen and turns the carbon monoxide into carbon dioxide (CO2). If all this is making your head spin, just think of it as some weird chemical square dance where everyone ends up with a different partner in the end.
Although as we saw this is a two-step process, most people just talk about the overall result and call that “Steam Methane Reforming” or “SMR” for short. The heat required for the SMR process comes from burning some extra natural gas, which releases air pollutants and CO2 (a greenhouse gas and a primary cause of climate change).
The mixture of CO2 and H2 coming out of the SMR is passed through separation equipment to get a pure stream of H2 and a stream of CO2. Today at most H2 production plants, this CO2 is also released into the air, although some newer plants are capturing the CO2.
Coal is converted to hydrogen in a similar way, but since it is a solid and a more complex molecule than methane, a simple reformer won’t work. Instead, coal is ground into fine particles and blown through a furnace with oxygen and water. What comes out is H2 and CO. And you know what happens next: this is fed into a shift reactor to make hydrogen and carbon dioxide. Except this time, because coal has much more carbon in it than methane does, you get about two times more carbon dioxide per ton of hydrogen produced than you do from methane, and you get more pollution and CO2 from the coal burned to provide heat for the process.
It’s understandable if all this talk of methane, coal, fossil fuels, and greenhouse gases is making you a little sick to your stomach. “Wait,” you say, “I thought hydrogen is a clean fuel. What is this, some big scam?” There are two points to remember here. The first is that is how hydrogen is made today, and the second is there is another way to make it that I think you’ll like better.