Turquoise Hydrogen

Part of a Plan that Adds Up?

Figure 1. Monolith's Methane Pyrolysis Plant, 4700 tons/year of hydrogen.

There has been a tremendous amount of blather about green hydrogen and synfuels. The Gordian Knot News has no desire to add to this nonsense, but perhaps a few hopefully corrective paragraphs are in order. First and foremost, there is no point of even thinking about green hydrogen as a substitute for fossil fuels, unless you have truly cheap, 24/7, very low CO2 electricity. By truly cheap, I mean no more than 3 cent/kWh, preferably 2 cent or less.

Green hydrogen by water electrolysis could conceivably be used as a backup source of electricity in all renewable grid. But when we applied that strategy to Germany, which is blessed with pretty good wind, and ample salt domes for hydrogen storage, the cost of the electricity was 21 cents/kWh at the plant gate, despite a series of clearly optimistic assumptions about both the cost and availability of wind and solar, and the economics of electrolysis. I suppose Germany could go that route for its grid, if she were willing to completely deindustrialize and accept a much lower standard of living. But such expensive electricity is a non-starter just about anywhere else, and cannot be used to power an industrial facility.

The only way out is cheap nuclear. If and only if we had 3 cents or less nuclear, then not only will nuclear gradually replace fossil in generating electricity, we can start thinking about non-grid energy markets.

Figure 2. USA 2015 energy consumption

Currently, in the United States, about 40% of primary energy consumption is already in the form of electricity. If we had a lot of truly cheap, on-demand power, electricity would push into a substantial portion of the non-grid residential and commercial demand (mainly heating) in the form of heat pumps. I live close to the Bonneville Dam, and enjoy some of the cheapest power in the country. My old house, built in the 1960's, is fully electric as is most of my neighbors. If we had truly cheap, on-demand power, we could reasonably expect as much as 75% of this market to end up electric. That's about 8% of total primary energy.

A little over half of transportation is cars and light trucks, Figure 3. If we had truly cheap on demand electricity, we can expect a sizable portion of that market to switch over to EV's. However, EV's production is CO2 intensive, so the net reduction in CO2 emissions will be something like half the switchover. Plug-in hybrids are cheaper than pure EV's, less CO2 intensive to make, and, if we had truly cheap electricity, would run mostly on grid power for most owners for most trips. If we had reliable electricity at less than 3 cents/kWh, it would not be unreasonable to expect that well over half the light transportation vehicle-miles would end up running on grid power, say 60%, or about 12% of total primary energy.

Figure 3. USA energy consumption in transportation

This leaves the non-grid industrial market. If we had 24/7 electricity at less than 3 cents/kWh, we might be able to make green hydrogen close to economic. Hydrogen is difficult and expensive to distribute and dangerous to handle. Only large point sources of demand can economically be equipped to handle hydrogen directly. However, that's a sizable market, pretty much the bottom half of Figure 4, or at least 10% of overall primary energy.

Figure 4. USA industrial energy consumption by industry.

How would we go about producing that hydrogen? The usual suggestion is water electrolysis. Water electrolysis, splitting H2O into hydrogen and oxygen, means going up against some very daunting thermodynamics. The theoretical energy required to split water is 40.6 MJ/kg H2. A realistic target is 45 MJ/kg H2. That's a lot of energy, about 1.4 times the LHV of H2.

Fortunately, there's another way. If truly cheap nuclear pushes gas out of a most of electricity generation, natural gas will be very cheap. The theoretical energy required to split methane into hydrogen and carbon via methane pyrolysis is 5.4 MJ/kg H2. A realistic target is 7 MJ/kg H2 which is more than 6 times less than the water splitting energy.¹ The byproduct is solid carbon. For most methane pyrolysis methods, the carbon is in a powdery form called carbon black.²

Carbon black has a range of industrial uses, mainly in tires and inks. But methane pyrolysis creates 3 kg of carbon for every kg of hydrogen. At scale the amount of carbon will swamp the carbon black market. This is good for consumers of carbon black, and most of us have automobile tires.

Most of the carbon will have to go to soil replenishment and nourishment. Ukraine's black soil or chernozem is the reason she has been the break basket of Europe for centuries. High carbon content holds moisture and other nutrients. Needs less ploughing. Promotes microbial activity, and reduces the need for other fertilizers. Chernozem is so valuable that when the Ukrainian government outlawed trading in it, a black market developed in black soil, with the price ranging from $80 to $180/ton.\cite{krasnozhon-2011} The carbon content of most chernozem is 5 to 10%.

Unlike CO2, carbon black can be safely buried at zero (actually negative) cost. The carbon stays in the soil for millenia. Pre-Columbian indians in the Amazon basin understood this. The soil in this region is quite infertile. So starting before the time of Christ, they took char from clearing the forest by burning, and mixed it into the ground, creating large fertile plots of terra preta. They are still there.

Commercially, methane pyrolysis is not as well developed as water electrolysis. BASF has been working on pyrolysis since 2010, and began operation of a multi-story prototype in 2020. They claim they will be in large scale production by 2030. Monolith is further along. They have been operating a 14,000 t/y carbon black plant in Nebraska since 2020, Figure 1. They are expanding to 180,000 t/y carbon, which they claim will be online in 2026. That plant will produce 60,000 t/y hydrogen, about 0.6% of the US market and roughly 0.06% of the global market. Methane pyrolysis has a ways to go; but, if we have truly cheap 24/7 electricity, I'm confident that pyrolysis will be cheaper than electrolysis at producing nearly CO2-free hydrogen, resulting in a larger penetration of the industrial market. Pushing fossil out of 60% of this market represents 13% of all primary demand.

Putting it all together, the combination of 3 cent/kWh or less 24/7 electricity and methane pyrolysis could supply 40 + 8 + 12 + 13 = 73 percent of primary energy consumption, before we need liquid synfuels. Zero CO2 emissions is neither possible nor desirable. The goal is maximizing human welfare. At some point the marginal cost of reducing CO2 any further will be larger than the marginal benefit. We can haggle over where that point is, but we can be sure it is well before we get to zero.

But I'm putting the cart before the horse. It's pointless to debate pyrolysis versus electrolysis, unless we have 24/7 3 cent/kWh, very low CO2 electricity. We don't have that and we won't have it, unless we completely change the way we regulate nuclear power.

1. Hydrogen has more colors than a pride flag. Some idiot has dubbed this turquoise hydrogen. Now I'm aiding and abetting this nonsense.

2. Some methods use nickel based catalysts. This has two advantages:

1) It lowers the heat at which the separation takes place to around 500C. This temperature can be produced thermally in high temperature nuclear reactors, avoiding the better than factor of 2 loss in going from heat to electricity to very high temp electric heat.

2) The carbon grows as high strength whiskers, possibly even nanotubes, which are far more valuable than carbon black. This could be a low CO2 route to low cost carbon fiber composites.

However, these efforts are still at the lab scale. We cannot count on them.