Gases - Fundamentals of Industrial Chemistry: Pharmaceuticals, Polymers, and Business - page 28

The reaction uses a catalyst, typically an iron catalyst. Magnetite (Fe 3 O 4 )
is used with other oxides such as alumina, calcium oxide, potassium oxide,
magnesium oxide and silica. The magnetite is reduced in the process to the
active iron catalyst [23]. Alumina acts as a structural stabilizer and gives
improved surface area in the catalyst. Particle size must be balanced. Smaller
particles are more effective catalysts but very small particles can cause
pressure drops through the reactor. Certain substances may interfere with the
catalyst. These are called poisons. In general, a catalyst that is resistant to
poisons is desirable, but there must still be efforts to exclude poisons from the
reactor feed.
Although Haber invented his process more than 100 years ago, it is
still very much an important process. For example, in late 2012 several
companies announced plans for capacity expansion or new facilities [24].
Illinois-based CF Industries announced it will spend $3.8 billion through
2016 on new ammonia and ammonia derivative capacity at its plants in
Louisiana and Iowa. Orascom Construction Industries announced plans for a
$1.4 billion nitrogen fertilizer plant in Iowa and CHS Inc. announced plans
for a $1 billion plant in North Dakota.
One major derivative of ammonia is nitric acid. Nitric acid is used for
fertilizer applications such as to make ammonium nitrate or potassium
nitrate. It also has widespread use in organic chemistry especially in the
nitration of aromatic rings. Nitric acid is made by the Ostwald process.
Ammonia is oxidized first to nitrogen oxide and then to nitrogen dioxide,
followed by absorption in water resulting in nitric acid. Nitric acid forms
an azeotrope with water at 68% nitric acid. Because of this, it cannot be
purified further by simple distillation. More concentrated grades of nitric
acid can be prepared by use of a dehydrating agent such as sulfuric acid
and distillation. Fuming nitric acid is prepared by passing nitrogen dioxide
through concentrated nitric acid. Depending on the concentration of nitrogen
dioxide, the solution takes on a yellow to reddish-brown color.
The oxidation of ammonia proceeds through a series of steps. In the first
step, ammonia is oxidized with a platinum catalyst. The catalyst is usually
used in the form of a gauze made from a platinum - rhodium alloy. Compared
with platinum, an alloy of platinum with 5 to 10% rhodium improves the
mechanical strength of the gauze, improves the yield, and reduces the activity
loss of the catalyst [25]. Typically a knitted gauze with three-dimensional
geometry and high porosity is used. As ammonia is oxidized, platinum is
slowly lost from the gauze. After ammonia, catalyst consumption is the
second largest raw material cost. Ammonia is oxidized commercially at pres-
sures ranging from one to ten atmospheres and temperatures ranging from