Originally Posted by codprawn
Hydrogen can be produced by many methods - often as a byproduct but the 2 most promising are the new method of converting waste products such as sewage using microbes
as far as I am aware there are no microbes capable of producing hydrogen at the rate that would be necessary to replace petrol. There are certainly some anaerobic microbes which contain enzymes that break down e.g. glucose to acetate plus 4 H2 - but then you get left with shitloads of acetate waste for not a lot of gas. You could use other bacteria to break down the acetate but then you get CO2 as well.
Microbes are also bloody temperamental (they are my dayjob) so one day they are fermenting away and the next they stop. On top of that you need to keep the process sterile (or you will get competing organisms in there which mean you don't get H2 (or not as much) or get eg. H2S in their too.) - thats not hugely practical if you are processing waste. (most approaches to sterilisation are either hugely eco-unfriendly or energy internsive). Now microbes will produce gas at atmospheric pressure - it takes a reasonable amount of energy to presurise and/or liquify that gas so it is suitable for storage and transportation. And this all assumes you have pure H2 in the product (which I don't think is possible today) - if you have to purify / separate the product then you are looking at more energy required.
Personally I think it is viable on a local scale - but its not how BP or anyone else would do it for vehicle fuel.
and even more important - using surplus nightime electricity that just goes to waste to electrolyse seawater instead of powering millions of streetlights and floodlit buildings.
that electricity is still largely produced by - burning gas or coal - so its not carbon neutral. Biodiesel and bioethanol are already with us - and are effectivel much more carbon neutral, and existing engines would run them with little or no modifications, the delivery mechanisms already exist etc. Call my cynical - but the reason they have not been more widely adopted/produced is that the countries which currently control the oil are not exactly the ideal countries for growing high yield crops.
PS sorry for hi-jacking the thread.