German boffins turn ALCOHOL into hydrogen at low temp

Re: 24 litres per second?

It's been along time since I had physics inflicted on me, but wouldn't the pressure the gas was under affect the volume? i.e. 24L at low pressure could contain less hydrogen than 24L at high pressure?

Re: 24 litres per second?

Remembering 30 years ago to school chemistry, the avogadro constant for gases is 22.4 dm^^3 at STP, 24 liters is a fraction over this, so ~2.1g of Hydrogen every second - seems reasonable.

Re: 24 litres per second?

Could be right. A 2 liter engine, spinning at 3000 rpm, tries to suck in ..mumble... (4 stroke engine probably) mumble.... 3000L of air per minute. Divide by 60 gives 50L per second, assume 50/50 air/hydrogen mix. Yeah, that kinda works.

Re: 24 litres per second?

24 litres of hydrogen at STP is about 2 grammes. If a BMW uses only 4 grammes of hydrogen per 100km, that sounds like thermodynamics just started taking magic mushrooms.

2 grammes a second = about 7kg per hour. That sounds a bit high; at 70mph my car uses a little under 4kg of petrol an hour.

So yes I think the number is wrong, but the number quoted for the BMW is not even wrong.

as the cheapest hydrogen is produced from methane.

You missed the memo where somehow hydrogen was going to be produced by electrolysing water using too cheap to meter wind and nuclear energy. The whole thing has been thought up by people who have never tried electrolysing water on industrial scales or handling hydrogen. I'm reasonably blase about industrial risk; I've worked with radioactive isotopes, cyanides, oxidising agents and other nasties, but hydrogen scares me stiff. Just containing it has challenges known to nothing else. An industrial chemist I once worked with doesn't agree; he thinks mercury is slightly nastier. But it was his company that had to pay for the cleanup, and that affected his viewpoint.

The proponents of hydrogen as a mobile fuel sound like they should be an unholy coalition of chemical plant makers, rare metal suppliers, scientifically illiterate greens, and IC engine designers who don't care what the problems are, they just like the idea of an engine that doesn't carbonise its valves and cylinder heads.

Re: produces co2

Yes, indeed you need the same amount of CO2 to make it from Hydrogen (perhaps extracted from sea water by fusion power?).

The Catalyst life is a problem though. But can the catalyst be regenerated or is it gradually evaporated into the Hydrogen and then into the fuel cell water?

Re: The attraction is Methanol is *easy* to handle.

Key problem is preventing ignorant people from stealing and drinking it...

Re: The attraction is Methanol is *easy* to handle.

The trouble is that it has carbon in it, which manipulates the carbon cycle. Since most methods of making methanol on the necessary industrial scale aren't carbon-negative and since most processes that convert methanol to energy release CO2 as a byproduct, making it carbon-positive, you hit a bugbear in that using methanol is essentially carbon-positive and bad for the environment. At least pure hydrogen is carbon neutral when you use it (no carbon in it).

Re: *potentially* very good indeed.

Starve the world by growing crops for fuel instead of food, ban the use of any genetically modified food strains, and then ban the use of pesticides and fertilizers most of which are derived from oil.

That'll sort the world out.

Re: So..

Once you have a fuel cell with enough kilowattage, you'll find electric motors are damned potent things. More potent than internal combustion (even a big V8) for less weight, and torque all the way from 0RPM up to max. Problem is a 50kw+ PEM fuel cell is rather pricey right now.

Re: 24l/s?

286kW at 100% efficiency perhaps: An automotive IC engine is at best 30% efficient (yes, I know engines can get slightly better but only under constant load)

Having said that, at motorway cruise the average car is expending somewhere between 2-5kW, so 24l/sec sounds like a slipped decimal point somewhere along the line.

24litres at STP, plus allowing sufficient air (O2 content ~20%) to allow it to burn, translates to a 2 litre engine spinning at ~80-100revs/second - 4-6000rpm. Allowing for 25% efficiency that's about 65kW and you really only need that for a few seconds at at time.

Re: Hindenburg + Hydrogen = ?

Whether it is a fire or an explosion is just a matter of where you put the dividing line on the flame velocity scale. A lot of people think that the petrol/air mix in a car explodes, but vehicle engineers are well aware of the difference between explosion (detonation) and the desirable controlled burn.

If the volume of hydrogen is big enough that it cannot mix with the air instantly, hydrogen will burn. I used to demonstrate this by blowing big hydrogen bubbles, which burn impressively but quietly, and very much smaller hydrogen/air bubbles, which leave ringing eardrums.

A hydrogen filled airship burns.

"All I know is I can turn beer into water, sodium, and potassium at room temp at a rate of 16oz per 1/2 hour."

That rate seems a bit slow, slacker.