Question $2($Total: $34$ marks$)$

Nitric acid $(HN{O}_3)$ is used extensively for the production of inorganic and organic nitrates,

various kinds of metal treatments and photoengraving. $HN{O}_3$ is produced by oxidizing ammonia

to nitric oxide $($NO$)$ in a catalytic converter $($Equation $1),$ followed by further NO oxidation and

hydration in a second reactor $($Equation $2).$

Equation $1$:

$4N{H}_3(g)+5O_2(g)4NO(g)+6H_{2}O(g)$

Equation $2$:

$4NO(g)+3O_2(g)+2H_{2}O(l)4HN{O}_3(aq)$

An undesired reaction $($Equation $3)$ that lowers $HN{O}_3$ yield is the oxidation of ammonia to

nitrogen and water vapor in the converter.

Equation $3$:

$4N{H}_3(g)+3O_2(g)2N_2(g)+6H_{2}O(g)$

Saturated ammonia vapor, produced by vaporizing pure liquid ammonia at $820$kPa absolute$,$ is

mixed with a stoichiometric quantity of air $($i$.$e$.$ consisting the quantity of oxygen theoretically

required to convert all of the ammonia to $HN{O}_3),$ and the combined stream enters the converter.

The air enters at $30C$ and $1$atm with a relative humidity of $50\%.$

In the converter, the ammonia reacts completely, with $97\%$ forming NO and the balance forming

$N_2.$ The product gas exiting the converter is subjected to further oxidation and hydration in the

second reactor, in which all NO is completely oxidized and combined with all the water $($some of

which is present in the product gas leaving the converter, the rest of which is added as liquid

water$)$ to form a $55wt\%$ aqueous nitric acid solution. The product gas from the process may be

taken to contain only $N_2$ and $O_2.$ A simplified flowchart of the process is shown below:

a$)$ Write the equation for the overall reaction of $N{H}_3$ by oxidation and hydration to form

$HN{O}_3.$

$(2$ marks$)$

b$)$ Taking a basis of $100mo\frac{l}{h}$ of ammonia fed to the process, calculate

$($i$)$ The volumetric flowrate $(\frac{m^3}{h})$ of the ammonia vapor and of the air fed to the

process, using the compressibility factor equation of state for ammonia, $z=0\mathrm{.}92$;

$(12$ marks$)$

$($ii$)$ The molar composition of the gas leaving the converter;

$(12$ marks$)$

$($iii$)$ The required liquid water feed rate $(\frac{m^3}{h})$ to the second reactor, taking density of

water $=1\frac{g}{c}{m}^3.$