Tuesday, September 6, 2011

Running cars on zinc

The federal government has been pushing hydrogen research, and after looking over several research papers I'm astounded at how complicated approaches seem to take all the attention. It is as if people are more interested in playing with science than with solving practical problems.

One concept that caught my eye was an Israeli solar project, which proposed a zinc/zinc oxide/water/hydrogen cycle. Even there, extreme heat is used in the process of reducing water to hydrogen. Six hundred degrees may me manageable, but it isn't really necessary.

But is the zinc process practical? Well, a gallon of gas is equivalent to about 1kg of hydrogen. Hydrogen weighs about 1.01g per mole, so it would take about 990 moles of H to get the power of a gallon of gas. You need one mole of zinc to release two moles of hydrogen from a mole of water, or 495 moles.

Since zinc weighs in at 65g per mole, you'd need 32178g of zinc to liberate enough hydrogen to equal a gallon of gasoline. So now we are talking about 70 lb of zinc in a powdered or slurry form. That's not counting the weight of the water you'd have to consume. The weight of 495 moles of water is about 8910g or 20 lb.

It would take 10 gallons to provide for a typical commuter vehicle. Carrying around a 900 lb tank of zinc and water doesn't seem at all a good trade off to a 10 gallon gas tank. Gasoline itself weighs in at about 90 pounds.

We could do the same sorts of computations to find that aluminum or magnesium would cut the weight by somewhere around 2/3rds, or around 300 pounds, which is certainly more competitive, although either metal would require more energy to reclaim.

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