Solar ammonia process may spur fertilizer revolution

Low-energy ways to make ammonia - a vital constituent of
fertiliser - could enable developing countries to
manufacture their own fertiliser instead of importing it.
One such technology published last month (8 August) in
Science produces the chemical directly from air, steam and
sunlight, and could offer an alternative to the conventional
Haber-Bosch method. This relies on high temperatures and
pressures, and so requires vast amounts of energy: globally
it consumes more than 1 per cent of total energy generated
each year.
The new method, developed by Stuart Licht of George
Washington University in the United States and his
colleagues, makes ammonia by bubbling steam into a
cheap molten salt mixed with nanoscale iron particles, and
passing an electric current through.
Core to the team's concept is 'Solar Thermal
Electrochemical Production' (STEP), a process where
sunlight is harvested and used to help power chemical
reactions, reducing the need for energy input from other
sources. Licht's team has also developed methods for
making cement and treating water using STEP.
Although their published ammonia production method uses
mains electricity, solar energy can in principle provide both
the electrical current and heat required.
"STEP ammonia does not need connection to the electrical
grid and hence is suitable for poor and rural areas which
have less developed infrastructure," Licht says. He adds
that any STEP process could be used on a small scale.
Paul Makepeace, a fertiliser specialist at the International
Fertilizer Development Center in Nairobi, Kenya, says such
an approach "is certainly of interest" in Sub-Saharan Africa.
Currently Nigeria is the only country in the region that
makes ammonia, and it does this using the Haber-Bosch
process.
"This method's use and development will depend on its
competitive advantage and the ability to deliver
manufacturing capacity to African countries where fertiliser
is a significant foreign exchange-spend," says Makepeace.
But he adds that the STEP process "seems like it has a long
way to go" to reach commercialisation. Licht concedes that
his group is "not geared towards technology spin-out", and
says he hopes industry or government will fill that role.
Indeed, another electrolytic approach to making ammonia
from air and water is due to be commercialised this year,
says Makepeace. NHThree, a company based in Richland,
United States, is building an ammonia synthesis plant for
Bolivia's Royal Silver Company.
NHThree heats steam to form hydrogen ions and applies an
electrical current to drive them across a membrane to react
with nitrogen from the air to form ammonia. The company's
method does not directly exploit solar energy, but still uses
30 per cent less energy than the Haber-Bosch method,
according to its website.
NHThree's founder Jason Ganley says the method "will be
best suited to sites with plentiful cheap, or off-cycle,
renewable power".
This is because to compete with current technologies it will
need very low energy prices, but "there may be
opportunities present in Africa such as Ethiopia's Grand
Renaissance Dam , that make this technology viable," says
Makepeace.
"The important thing is to keep our eyes open to this
technology," he adds.