Would it be efficient to store energy like that:
CaO + 2 H2O <==> Ca(OH)2 + H2
==> heat the Ca(OH)2 when heat is available ==> CaO is formed
==> get the hydrogen out of it when needed, by adding water
Since the reaction requires some Temperatrure, the efficiency may be low; but on the other hand CaO from CaCO3 is cheap ...
The Idea is to store thermal energy from solar radiation, concentrated by mirrors, and then to optionally use the H2 in fuel cells or elsewhere.
Since the direct photovoltaic approach only yields 10 % and is expensive, why not have something with maybe even more than 10 %, that is cheap ??
Maybe another reaction is better, one that runs on lower temperatures ...
Main thing: It's low tech, and the _big_ companies, who always take more than they give, may stay outside ...ScienceSquirrel - 8-7-2008 at 04:53
Calcium oxide does not react with water to produce hydrogen.
The reaction is;
CaO +H2O = Ca(OH)2
While the reactions is quite exothermic a lot of heat is required to drive it the other way.
Practical methods of storing heat usually involve something like 'melting' hydrated sodium sulphate on a large scale.
The salt dissolves in it's own water of crystallisation on heating, heat is liberated when it returns to the solid state.
Sodium acetate trihydrate and hydrated sodium thiosulphate can be used on a small scale.blogfast25 - 8-7-2008 at 04:53
CaO (lime, quicklime, unslaked lime, calcium oxide) does not react with water in that way. Like all base-forming oxides, with water it produces the
hydroxide only:
CaO + H<sub>2</sub>O ==> Ca(OH)<sub>2</sub>
Only metallic calcium would generate hydrogen too:
Ca (s) + 2 H<sub>2</sub>O (l) ==> Ca(OH)<sub>2</sub> (s, aq) + H<sub>2</sub> (g)chief - 8-7-2008 at 05:10
From the equation, as well as from my textbook-memories, it should form H2 !
The H2 comes from the one-too-much-H-atom in H2O compared to the OH-group; check your equations, and you will see they are wrong ..., while mine ist
stoechiometrically correct !ScienceSquirrel - 8-7-2008 at 05:19
Your equation balances but the chemistry is wrong.
Our equations balance nad the chemistry is correct
This is a common reaction carried out on an industrial scale, the quenching of quicklime to form slaked lime, and no hydrogen is evolved!DJF90 - 8-7-2008 at 05:20
No you are wrong, plain and simple. Your oxygens are not balanced.ScienceSquirrel - 8-7-2008 at 05:21
Wrong Squirrel!
Have a look at your equation Chief, you have three oxygen atoms on the left and only two on the right hand side. chief - 8-7-2008 at 05:31
I was wrong with equation, sorry. But ,my idea is great: Find a simple reaction that runs on cheap stuff, and that takes heat on input, giving H2 on
output.
Have you any ideas ?ScienceSquirrel - 8-7-2008 at 07:13
Quote:
Originally posted by chief
I was wrong with equation, sorry. But ,my idea is great: Find a simple reaction that runs on cheap stuff, and that takes heat on input, giving H2 on
output.
Have you any ideas ?
There have been plenty of things put forward as a means of storing hydrogen.
A cheap, high capacity one would be a boon to all sorts of industries.
If I could think of one that has not already been tried I would be keeping it very much to myself until I could flog it off to a major company.
There are plenty of good ideas out there, the only problem is making them work.
Consider nitrogen fixation. The industrial process uses high temperatures and pressures and burns loads of energy.
Some plants carry out the process using bacteria in little nodules on their roots.
The search for an industrial catalyst that would mimic this is one of the holy grails of organometallic chemistry but despite decades of work and
oodles of money we are not even close.
Needless to say the chemist that achieved it would get a Nobel prize, medals galore, near Einstein status etc
So there are plenty of incentives!
