Future Energy Sources 3.1.3 Hydrogen from Oil

Hydrogen in the form of H₂ is highly reactive and will explosively combust in air at concentrations as low as 4% V/V. As a result H₂ is only found on Earth in its elemental form as traces in the atmosphere at concentrations of around 500 parts per billion. If we were to replace all fossil fuels with H₂ the annual production of H₂ would need to be around 3.5 Tg (3.5 billion tonnes) per year which is slightly over twice the amount of H₂ in the atmosphere. Not only does the H₂ economy need vast quantities of H₂ but the production method needs to be efficient and pollution free. It's no good using H₂ as a fuel to reduce greenhouse gases if the production of the H₂ produces more than the fossil fuels do in the first place.

There are currently no process that converts liquid fossil fuels into H₂ on a large scale commercial basis, however, H₂ is generated from natural gas using a process called steam reforming. The process involves combining natural gas and steam at temperatures between 700-1,100° C forming H₂ and carbon monoxide CO. The CO is then combined with water at around 130° C producing more H₂ and carbon dioxide CO₂. The equations for each of the reactions is:

CH₄ + H₂O → 3H₂ + CO -191.7 kJmol^-1

CO + H₂O → H₂ + CO₂ + 40.4 kJmol^-1

The whole process is about 80% efficient but it still produces CO₂ and the more carbon in the hydrocarbon the more CO₂ you end up with at the end of the process.

Most of the H₂ currently produced is used to either improve the characteristics of existing fossil fuels or create ammonia NH₃ which is then used to create things like fertilizer and explosives. If H₂ produced this way were to be used as part of the hydrogen economy there are several problems that first need to be overcome.

1. If the CO₂ is released into the atmosphere as it currently is, we end up being worse off that if we used the fossil fuel directly. For the H₂ to have any benefit the CO₂ needs to be collected and stored infinitely using something like carbon sequestration.
2. Using fossil fuels to generate H₂ for the hydrogen economy would actually increase our dependence on fossil fuels not reduce it and only make things worse than they currently are.
3. The current scale of H₂ production is less than 1.5% of the sort of production that would be needed to supply H₂ to a pure hydrogen fueled economy.

For the hydrogen economy to work there needs to be an economically viable and pollution free source of H2 and the use of liquid fossil fuels as that source raises several questions:

1. If using oil to create H₂ is only going to increase our consumption and dependence on it, is it worth investing in the technology at all?
2. Since the concept is dependant on the development of a viable carbon sequestration system is it worth working on before carbon sequestration is proven practical?
3. Can we expand the process by a factor of around 70 fold to cover our current fossil fuel consumption?

So, what do you think about extracting H₂ from oil?