hydrogen seperation from water

jack001

hello folks,

i was wondering if any other possible process of separating hydrogen from water without or less risk, any alternative method of electrolysis.

i have googled this thing and stuck to process of introducing a catalyst 'titania(titanium oxide)' in the presence of sunlight, directly converts water into the molecules of hydrogen and oxygen.
But now what? I mean how to separate this two different gases?
i suppose semi-permeable membrane can help in separation.

guide me if i am wrong.

jedishrfu

wont the hydrogen float above the oxygen?

Drakkith

I don't think you want to be mixing hydrogen and oxygen. They tend to explode when combined. Hence the need to separate them before they get out of the water.

jack001

^^ yes of course, they explode, so i need to separate them.

Q_Goest

Take a look at PSA's.

jedishrfu

so if hydrogen floats above oxygen then you could separate them by knowing where the dividing line is amd by placing valves at two distinct vertical levels to remove some gas at a time while the reaction is taking place.

Q_Goest

Gasses do not separate just because one of them is 'lighter' than the other. They will mix just like two different sized ping pong balls bouncing around in a box.

jedishrfu

Agreed, unless you cool the mix and separate via liquefaction.

jack001

but wont it explode as soon as it is converted into gas?

jack001

can you please elaborate this technology.

MrSid

The Wiki article describes PSA pretty well- it somewhat fits into the first method below for semipermeable membrane separation, but needs a driving force to release the adsorped molecules from the pores (usually atomic dimensioned channels in Xeolites).


-semi-permeable membranes rely on pores that can be used to exclude by one of several mechanisms. The most obvious one is to select by size and that H2 molecules are smaller than O2 molecules, so pores on the order of a few Angstroms can reject O2- a pressure differential exists between the two sides to drive the process.

Other methods can place an electrical or Donnan potential barrier at the pore's mouth that helps reject one type of molecule over another (mostly seen in R.O. membranes where charged dissociated salts are rejected while largely neutral H2O passes through).

Some vander Waal's forces can also create a selectivity for one type of molecule over the other, and the attractive forces used to help coax the right molecule through a pore. In this sense, the metals that are known to adsorb H2 can act as an appropriate barrier for other molecules- the downside is that these metals also recombine O2 and H2 to water catalytically, so efficiency suffers.

Thus the interest in CNT and graphenes as H2 separators; O2 stability is still a problem.