Nitric acid is a chemical intermediate primarily used in the synthesis of
ammonium nitrate, which is used in the manufacture of fertilizers. The acid
also is important in the production of other nitrates and in the separation of
metals from ores. Nitric acid may be produced by oxidizing ammonia to nitric
oxide over a platinum-rhodium catalyst, then oxidizing the nitric oxide to
nitrogen dioxide in a separate unit where it is absorbed in water to form an
aqueous solution of nitric acid.The reaction sequence is as
follows:$$\begin{aligned}
4 \mathrm{NH}_{3}+5 \mathrm{O}_{2} & \rightarrow 4 \mathrm{NO}+6
\mathrm{H}_{2} \mathrm{O} \\\4 \mathrm{NO}+2 \mathrm{O}_{2} & \rightarrow 4
\mathrm{NO}_{2} \\\4 \mathrm{NO}_{2}+2 \mathrm{H}_{2}
\mathrm{O}(\mathrm{l})+\mathrm{O}_{2} & \rightarrow 4
\mathrm{HNO}_{3}(\mathrm{aq})
\end{aligned}$$.Ammonia vapor produced by vaporizing pure liquid ammonia at
820 kPa absolute is mixed with air, and the combined stream enters the ammonia
oxidation unit. Air at \(30^{\circ} \mathrm{C}, 1\) atm absolute, and \(50 \%\)
relative humidity is compressed and fed to the process. A fraction of the air
is sent to the cooling and hydration units, while the remainder is passed
through a heat exchanger and mixed with the ammonia. The total oxygen fed to
the process is the amount stoichiometrically required to convert all of the
ammonia to HNO \(_{3},\) while the fraction sent to the ammonia oxidizer
corresponds to the stoichiometric amount required to convert ammonia to NO.The
ammonia reacts completely in the oxidizer, with \(97 \%\) forming NO and the
rest forming \(\mathrm{N}_{2}\). Only a negligible amount of \(\mathrm{NO}_{2}\)
is formed in the oxidizer. However, the gas leaving the oxidizer is subjected
to a series of cooling and hydration steps in which the NO is completely
oxidized to \(\mathrm{NO}_{2}\) which in turn combines with water (some of which
is present in the gas from the oxidizer and the rest is added) to form a 55
wt\% aqueous solution of nitric acid. The product gas from the process may be
taken to contain only \(\mathrm{N}_{2}\) and \(\mathrm{O}_{2}\).
(a) Taking a basis of \(100 \mathrm{kmol}\) of ammonia fed to the process,
calculate (i) the volumes \(\left(\mathrm{m}^{3}\right)\) of the ammonia vapor
and air fed to the process using the compressibility-factor equation of state;
(ii) the amount (kmol) and composition (in mole fractions) of the gas leaving
the oxidation unit; (iii) the required volume of liquid water
\(\left(\mathrm{m}^{3}\right)\) that must be fed to the cooling and hydration
units; and (iv) the fraction of the air fed to the ammonia oxidizer.
(b) Scale the results from Part (a) to a new basis of 100 metric tons per hour
of 55\% nitric acid solution.(c) Nitrogen oxides (collectively referred to as
\(\mathrm{NO}_{x}\) ) are a category of pollutants that are formed in many ways,
including processes like that described in this problem. List the annual
emission rates of the three largest sources of \(\mathrm{NO}_{x}\) emissions in
your home region. What are the effects of exposure to excessive concentrations
of \(\mathrm{NO}_{x} ?\) (d) A platinum-rhodium catalyst is used in ammonia
oxidation. Fxplain the function of the catalyst, describe its structure, and
explain the relationship of the structure to the function.
Explanations 
Textbooks 
Flashcards 
91影视 AI 
Notes 
Study Plans 
Study Sets 
Find a degree 
Magazine 
