Is this a potential solution to the production of hydrogen-fueled cars? Danish Researchers Reveal New Hydrogen Storage Technology. What are the possible pollution side-effects?
- In the process described in the article, ammonia (NH3) is produced as an intermediate step. The biggest challenge of this technology is creating a safe fuel tank that can hold ammonia, which can be harmful or fatal to people and animals in the vehicle, because:
- NH3 is immediately toxic at 500 ppm,
- NH3 reacts with water, producing ammonium hydroxide (NH4OH), producing a lot of heat (‘exothermic reaction’) which could (say) blow up the car,
- NH3 is very cold when it is vaporized.
So these seem like ‘safety’ rather than ‘pollution’ issues–that is, it only affects the immediate occupants of the car, and for only a short period of time. Details of the solid used are not given, nor is the catalyst given; there may be pollution dangers from these. NH3 should not be released into the air.
Another possible problem is the production of a lot of CO2 when making the ammonia, but this can probably be dealt with, since the CO2 production is centralized.
Based on what I read, I do not believe ammonia is released into the air. The article (really just a restatement of a press release) states:
Within the tablet, hydrogen is stored as long as desired, and when hydrogen is needed, ammonia is released through a catalyst that decomposes it back to free hydrogen. When the tablet is empty, you merely give it a “shot” of ammonia and it is ready for use again.
I read this as something like: from ammonia-based solid (their ‘storage technology’), NH3 is released through a catylist, which produces H3, which is used for the fuel. The solid can be filled up again with ammonia.
This letter to Physics Today (Thoughts on Starting the Hydrogen Economy) suggests some of the pollution and safety challenges:
- capturing CO2 as ammonia is produced (but this can be done efficiently because producing ammonia is well understood and happens at large industrial centers)
- “However, NH3 is toxic, chills its surroundings rapidly on vaporizing, and releases heat on contact with water. Engineering a safe fuel tank for an ammonia-fueled vehicle would be a key priority.”
Here are the toxicity levels of ammonia, According to this article at Emedicine:
Permissible levels of exposure to toxic gases are defined by time-weighted average (TWA), short-term exposure limit (STEL), and concentration at which toxic gasses are immediately dangerous to life or health (IDLH). The TWA is defined as the concentration for an 8-hour workday of a 40-hour workweek that nearly all workers can be exposed to without adverse effects. Similarly, the STEL is the concentration to which an exposure of longer than 15 minutes is potentially dangerous and may produce immediate or chronic compromise to health. Anhydrous ammonia has a TWA of 25 ppm, an STEL of 35 ppm, and an IDLH of 500 ppm.
So, if the atmosphere in (say) the car reached 550 parts per million, you’d be in immediate danger.