Reactions

Lightening up on hydrogen

Thanks for the interesting articles on hydrogen in the Aug. 22 issue. As I read the Point-Counterpoint with Steven G. Chalk and Joseph J. Romm (page 30), I was struck by a comment from Romm. He says that we are decades from the time when investments in hydrogen make sense and continues by saying, “While we wait, we must push fuel efficiency and advanced hybrid vehicles.”

While we wait? Does he believe that by waiting 10 or 20 years, the technology will suddenly work without investment in it today? I would prefer to see the U.S. investing in hydrogen fuel-cell technology while concurrently pushing fuel efficiency and hybrids. As consumers, we can do a lot to improve fuel efficiency and advance hybrids. If more consumers purchase fuel-efficient vehicles (and there are many to choose from), then car companies will make more of them, plain and simple. I wonder how many people would rather see the government regulate industry than give up the convenience of their gas-guzzling SUVs or pickup trucks. I hope that anyone fighting for environmental causes would first look at his or her own personal habits before pointing fingers at the government.

In the meantime, I'm glad to see the government investing in technology that will provide security, help the environment, and lead to more efficient and reliable sources of energy not only for transportation, but also for stationary and portable power.

Adrienne E. O'Connor
Chaska, Minn.

There has been much hype published about prospective energy sources, some of which contradicts accepted laws of thermodynamics. Some proponents of the “hydrogen economy” have suggested that there is no problem, since water is a source of hydrogen. They often neglect, however, that the energy is released when the hydrogen combines with the oxygen from air to form the covalent O-H bonds in water. To get the hydrogen from water, one must resupply this energy. If it comes from conventional processes such as electrolysis, the energy required is more than that obtained from the hydrogen, either in fuel cells or by burning.

A recent publication reports that hydrogen could be obtained from water through the reaction of an organosilane using a rhenium-derived catalyst. One must ask where the energy to do this must come from. It must be from the organosilane. While no energy balance is provided, thermodynamics assures us that there must be energy input from some other source in order to make the organosilanes.

There has also been the suggestion of biological sources of hydrogen. In these cases, the energy ultimately comes from the sunlight involved in the photochemical processes required to bring about the biological reactions. While the total amount of the sun's energy reaching Earth greatly exceeds energy use, the fraction of it so employed is small. The economics of having a biological collector of sufficient area to collect a sufficient fraction of this energy is a problem.

An example of this comes from the consideration of corn-produced ethanol as a substitute or additive for gasoline. With gasoline prices currently soaring, this can be competitive, provided the ethanol production is subsidized. But it has been estimated that to provide enough energy by this route, an unrealistic fraction of U.S. land would have to be devoted to growing corn. Thus, to provide an economically viable energy source by this means, a more efficient means for solar energy collection than corn growing is needed.

Richard S. Stein
Amherst, Mass.

Am I alone in wondering if hydrogen, whether from on-purpose or by-product sources, would make a better substitute for natural gas in heating applications than for liquid hydrocarbon fuels in transport applications? Not only do the obstacles to the supply of hydrogen for heating applications appear to be smaller, but the costs of converting home and plant burner-boiler configurations to hydrogen usage are also likely to be lower than those for vehicle fleets. Natural gas could then be conserved for intrinsically higher value end uses (such as methanol production), assuming, of course,thatnatural gas pricing regimes can be aligned to consistently reflect the long-term value of this resource to different end users.

Jonathan Targett
Cleveland

I read with great interest the debate between Romm and Chalk. While both authors make lucid arguments, both of them miss the one opportunity available to make an immediate and lasting impact on tailpipe emissions in the U.S. If federal, state, and local governments, as well as businesses, would provide incentives and encouragement for mass-transit use, emission levels from automobile use could be cut significantly. Even in large metropolitan centers, bus and subway lines remain underused and serve only limited areas. The situation in smaller cities and towns is even worse. I challenge each author to calculate the impact to tailpipe emissions (not to mention the reduction in stress from less gridlock) if even 30% of the private vehicles currently used to commute to and from work were replaced with mass transit. Fewer vehicles driving fewer miles equals less emissions.

Mark Carpenter
New London, Mo.

I thought it was interesting that the scope of the discussion by both Romm and Chalk was limited to the transportation sector and particularly to personally owned automobiles. To that extent, both totally missed the bus by being blind to the concept of mass transit, where more efficientand environmentally friendly electric-driven (rail) and hybrid fossil-fueled on-road vehicle technologiesare now readily available.

Bruce Appelbaum
Yorktown Heights, N.Y.

I was amazed that C&EN devoted only one paragraph in “Filling Up With Hydrogen” to the use of ammonia as a source of hydrogen and that the story mentioned only one academic investigator (C&EN, Aug. 22, page 42). Other workers have developed the concept much further.

I believe that hydrogen from liquid ammonia has the greatest potential for replacing gasoline as an automotive fuel in the near term. The Department of Energy's target of 5–10 kg of hydrogen, mentioned elsewhere in the article, can be achieved with liquid ammonia in a 20-gal tank, which is a reasonable size for most vehicles. The vapor pressure of liquid ammonia is similar to that of propane; both the transportability and residential use of propane in pressurized tanks are well-known and accepted. Furthermore, an extensive distribution system for ammonia as an agricultural fertilizer is already in place. And the only by-product is nonhazardous nitrogen; there is no solid or liquid waste.

Generation of hydrogen from ammonia requires a catalyst and elevated temperature. Consequently, some auxiliary power source, probably batteries, would be needed for start-up. But this requirement would apply to any mode of hydrogen storage other than compressed H₂ gas.

Some may object over the toxicity of ammonia. Of course it is toxic; what isn't? I am not familiar with the history of ammonia poisonings, but I suspect that most cases have occurred with ammonia used as a commercial refrigerant, where the victims were in confined spaces. That will certainly not be the case in filling stations or on the open road.

Richard V. Cartwright
Essex Junction, Vt.