Occasionally in the land of energy pretense we hear all about the putative "hydrogen economy" wherein it is represented that vehicles that burn the gas hydrogen - like say the Hummer driven by the steroid crazed Gropenator of California - are "clean" "ZEV's" or zero emission vehicles.
The same media that wants to present Arnold Schwarzenegger as a neo-environmentalist often (but not always - at least recently) skims over the fact that hydrogen is not a source of energy at all; hydrogen is merely a chemical agent for the storage of energy. The real question of whether or not hydrogen is actually a clean fuel has nothing to do with the relatively trivial fact that water is the only combustion product when the hydrogen itself is burned. The real question, the real risk, depends whence the hydrogen comes.
Many people, seek to claim that hydrogen is available easily and readily from renewable sources. The design of making this (dubious) statement is to further enhance hydrogen's "clean," image. Usually this is a case of lying, either to the public or to one's self, because, although hydrogen has long been an industrially available element, almost all of it is obtained by the use of fossil fuels as a primary energy source.
In fact all three of the major fossil fuels, coal, oil and gas have been and continue to be used industrially to obtain hydrogen. Originally the bulk of the world's hydrogen was obtained from coal. More recently natural gas has wider use, although some residual coal production is employed around the world. In fact all so called "syn fuels" programs - known technically as Fischer-Tropsch chemistry - coal to petroleum, garbage to petroleum, biomass to petroleum, rely on hydrogen as a chemical intermediate. In these processes, some fuel is burned to heat the carbon source, the fossil fuel or other organic material, in the presence of water, to give a mixture of carbon monoxide, carbon dioxide, and hydrogen. Sometimes the hydrogen is captured in these processes for use for things like powering the Gropenator's Hummer, but more frequently, in the overwhelming majority of cases, the hydrogen is used for chemical reactions. One possible chemical reaction, depending on the type of catalysts and conditions used, is to make either crude oil, gasoline, diesel fuel, jet fuel or some other petroleum related product.
Going back to the days of Jimmy Carter, there has been a great hoopla about some of the latter options - the "anything into oil," option, which is technically feasible and has, indeed been industrially applied, most famously by the World War II Nazi's, but also by the Apartheid era South Africans.
Of course, making hydrogen from coal or garbage and even from natural gas is a net energy loser for thermodynamic reasons. It turns out that one of the most fundamental laws of science - the second law of thermodynamics - requires that you use more energy in making the hydrogen and ultimately the "syn fuel" than you would have used if you had just burned the coal or natural gas in the first place. So why on earth would anyone invest a lot of time and effort in this wasteful process?
The answer to this last question resides not in the intrinsic energy itself, but in the convenience with which these fuels can be used. It is (relatively) easy to use, store, and transport liquid fuel. One can pass it through fine fuel lines to deliver it to automotive or diesel cylinders at precise rates. Moreover, being liquid, it has a high energy density. A lot of energy, enough to drive hundreds of kilometers at high speeds, can be stored in a relatively small space - without too much risk - is something like a gas tank.
So the difference between coal and petroleum is largely an issue of physical form, and nothing else.
Of course, these days, unlike in the 1970's when all of this stuff was on the table for reasons having to do with supply more than climate change, there is little talk about syn fuels and far more talk about hydrogen.
So how does hydrogen stack up as a fuel in comparison to say, petroleum? Not very well actually. Although hydrogen has a very high mass density (a little bit of weight has a lot of energy), it has a terrible - disastrous actually - volume density. The gas simply cannot be liquefied without appeal to extreme and energy intensive conditions. In fact, with the exception of helium, hydrogen has the lowest critical temperature known. The critical temperature is the maximum temperature at which a gas can be liquefied using any amount of pressure. To be liquefied, hydrogen needs to be cooled to temperatures that are under thirty degrees from absolute zero. Moreover, considerable pressure needs to be applied.
That's all well enough, but another aspect of hydrogen makes it far more problematic. The gas has a very low viscosity. It leaks easily, quickly, and is difficult to seal off. Further the gas diffuses rapidly through the environment, having the fastest molecular speed of any known substance, so it is easy to make an explosive mixture quickly. The result of a rear ended hydrogen containing bus in the Lincoln Tunnel could, quite easily, result in a tragedy of rather monumental proportions, particularly in the case where there were lots of hydrogen containing vehicles there.
So what is the appeal of hydrogen? Well again, there is the issue of water being its combustion product, no direct air pollution when it is burned, just water, and the fact that, as people tell you anyway, that it can be made not only from fossil fuels but - via electrolysis - everybody's favorite renewable fuels like wind and solar. It can also be made by nuclear means - but while that fact is far more realistic and, in fact, cleaner than renewable energy, it's certainly no where near the same in the important sphere of public imagination. Thus hydrogen, when evoked from either largely clueless end of the spectrum, from George Bush to Greenpeace, is used to make believe that all of our energy, and environmental problems, as well as the related political problems, like the chimerical "energy independence," can be solved.
I am here to tell you that both Greenpeace and George W. Bush are full of shit. Hydrogen is not a convenient fuel; it is not safe; and again - it's production is still dependent on fossil fuels. For the foreseeable future in fact - if one's focus is on global climate change as mine is - hydrogen is a special disaster. Making it from coal, or natural gas (if it is available) is an incredible risk to the atmosphere. What environmentalists must fight is coal based Fisher Tropsch or coal based hydrogen. These fuels are environmentally unacceptable under all terms.
Suppose though that hydrogen were available by totally renewable (or nuclear means)? Suppose the important environmental risks of its manufacture could be minimized. It is true that there are places where hydrogen is made by relatively clean means. In Norway, for instance, hydrogen is made via electrolysis using hydroelectricity. (Recently Norway has begun building fossil fuel plants to make electricity, so some of the patina is off.) If we could make all of our hydrogen from solar based power - wind, solar, and hydroelectric - and cost is no option, would hydrogen then be a good idea?
Actually there is a better option. It is a fuel known as dimethyl ether, or DME, and in countries where wishful thinking does not rule the day, it is being seriously developed. DME is the simplest ether, that is it is two molecules of methane (which comprises most natural gas) linked together by an oxygen atom. Normally DME is a gas. It is, for instance, the propellant that has replaced CFC's in hair spray cans. But like CFC's it has an important difference with natural gas: It has a high critical temperature. In fact even above the normal boiling temperature of water it is possible, via the use of pressure, to keep DME as a liquid. This makes it easy to ship and store, much easier than natural gas, which has a very low critical temperature, lower than the temperature of dry ice.
DME has yet another advantage that makes it far superior to natural gas.
The second most important gas in the global climate change game, after carbon dioxide, is methane, natural gas. Methane gets into the atmosphere by some natural processes, but humans are responsible for a fair share of it, primarily from flaring oil wells, from gas line leaks, from process chemistry, and from agriculture. Although it is flammable, methane proves to be a rather persistent bugger. The lifetime of a methane molecule in the atmosphere is thought to be on the order of decades. Moreover, methane traps heat far more efficiently than carbon dioxide does. Much smaller concentrations of methane are required to heat the atmosphere than would be required for carbon dioxide.
In contrast, DME, which is totally non-toxic, has a very short atmospheric half-life. It persists for a matter of days. Thus the environmental risk of DME is extraordinarily low when compare to methane. It can never accumulate in concentrations that will effect the heat flow of solar radiation.
DME is valuable for still yet another reason. It is ideally suitable for use with the existing infrastructure. It turns out that DME can be used as a fuel for diesel engines. In fact, diesels fueled on DME are extremely clean. The use of DME fuel eliminates completely one of the most serious pollutants associated with the use of diesels, the particulates. This is because DME lacks a carbon-carbon bond. While there are a few complications, in particular relating to the use of seals and some issues in lubricity, DME has been used to make clean running diesel vehicles - mostly in Japan and China, but also in Philadelphia.
Further, DME can easily be used in any infrastructure that now relies on natural gas or liquefied petroleum gas. Unlike the case of hydrogen, DME does not require a completely new infrastructure at all.
Finally DME has one other interesting property: It is a useful refrigerant and could, in theory, be used to replace the still problematic HFC's that replaced the even more problematic ozone depleting CFC's.
So what's the downside? Why isn't everyone rushing into the DME game? Why do we not talk DME instead of hydrogen?
Well, you may not hear much about it in this increasingly technically illiterate country, but I assure you, the huge advantages of DME - as well as a few important risks - are the subject of huge amounts of international attention and commercial interest. The DME revolution may be under the radar, but it is nonetheless already under way.
I will talk more about DME in future diary entries.