Is Urea the Best Storage Medium for Hydrogen?

With all the issue of storing hydrogen and the need for other transportation fuel options, urea is getting a few strong looks. Urea was the first natural compound synthesized. Urea is an organic compound with two HNH chains connected to a single CO molecule. That gives urea a reasonable hydrogen density in a stable and common compound.

There are a variety of uses for Urea, one of the more important is as a fertilizer. With methane or syngas as a feed stock, Urea is produced using nitrogen in the air. Since syngas can be produced through a variety of fuels including, bio-mass, coal, natural gas, petroleum and even alcohols, feed stocks are not difficult to come by. In a pinch, urea can even be produced with electrolized hydrogen and air. There is also of course natural urine from mammals.

Urea can be separated in solution into ammonia which can be used in internal combustion engines with an energy density of about half of diesel fuel. In an alkaline fuel cell, urea is more easily split into the hydrogen gas needed for our hydrogen economy.

Because of the non-hydrogen components, in the alkaline fuel cell potassium carbonate is a by produce which has uses of it own. If urea is used as a primary fuel storage medium, there would likely be an over abundance of potassium carbonate which would have to be dealt with.

With a two stage electrolysis process, converting the urea to hydrogen and potassium carbonate and then the hydrogen to energy and water, the overall efficiency would be reduced and complexity of the system would be increased. That will require more research, but there is some promise.

Another down side is urea and nitric acid can be used to make some pretty impressive explosives. Just about any energy source can be used to make a big bang, but in our terror filled world, someone will probably make and issue of the obvious.

The biggest advantage is that urea could be used in most gasoline, gas turbine and diesel engines while hydrogen fuel cell or direct ammonia fuels cell costs are brought down to more competitive levels.

Another advantage is in the production process. As a common component in fertilizer, urea, potassium carbonate and charcoal combined make an excellent soil conditioner and CO2 sequestration method. Since potassium carbonate is alkaline, it would be most useful in sandy soils that are typically acidic. An important consideration when agricultural soils tend to degrade with time. With additional hydrogen provided by high temperature electrolysis or even less efficient direct electrolysis from water, the total product chain could be profitable and beneficial.

Urea in crystalline form is not a requirement for the ammonia processes, it does though provide simple storage for easy transportation. Where pipeline infrastructure is available, ammonia would likely be a lower cost alternative. In either case, Urea and/or ammonia have serious potential as a transportation energy staple.

Did the EPA Give us Coal for Christmas?

Just before Christmas of the past year, the EPA announced with a certain amount of political pomp and circumstance, that the new Mercury and Air Toxin Standards MATS for fossil fuel users. The standard is based on the top 12 percent of coal power plants which will put about 10 percent of older coal plants out of business and require the remaining plants to retrofit to meet the standard or switch to another fuel likely natural gas. 25megaWatts is the minimum size plant that the standards apply. A possibly unintended consequence, it that the standards may very well have an equal or strong impact on cleaning up the renewable energy sector, biomass in particular.

Coal got its toxins from the biomass that became coal of millions of years. Depending on the growing conditions, renewable biomass can contain a significant, at least with respect to MATS, amount of toxins. The range of Mercury content varies and I have not seen a complete study of biomass Mercury content, but 0.026 micrograms per gram, the average for dried peach leaves, is a fair estimate for biomass grown in the marsh or swampy location typical of timber products. Timber products tend to promote swampy conditions, which is an important factor in maintaining water shed efficiency.

Of course, the Mercury content in coal is not listed in micrograms per gram, that would be too simple, coal is listed in grams per ton, short ton in the United States. There are 907184.7 grams per short ton and average quality coal contains about 0.1 grams per short ton. That converts to 0.11 micrograms of Mercury to gram of coal versus 0.026 for dried peach leaves. So the Mercury in peach leaves is much less than the Mercury is coal right?

Well, so is the energy content. Coal has 28 Mj/kg while peach leaves, which I would estimate to be about the same as switch grass or wood products, has about 5Mj/kg wet. It takes energy to dry stuff and if you use enough you can convert that switch grass or wood to charcoal or biopellets for a wood stove. If you adjust the Mercury content of the peach leaves to allow for the energy difference, Peaches leaves would produce 0.146 micrograms of Mercury per equivalent coal gram of energy. That by the way does not include the differing amount of energy required to dry to biomass for use as a fuel.

This would tend to reinforce my suggestion of Coal/Biomass co-generation as a responsible use of existing resources and the reduction of the massive mountains of waste buried all across our great nation.

I am sure though, that there must be a warm and fuzzy reason to regulate this crazy idea into oblivion.