Dear Francisco,

The process has three steps

1.       Oxidation of anhydrous ammonia with air to nitric oxide .

2.        Oxidation of nitric oxide to form nitrogen dioxide .

3.        Absorption in water to give a solution of nitric acid and nitric oxide.

Single and Dual Pressure Plants

The efficiency of the first step is favoured by low pressure whereas those of the second/third steps are favoured by high pressure. These considerations give rise to two types of nitric acid plants known as single pressure plants and dual pressure plants

In the single pressure plant, the oxidation and absorption steps take place at essentially the same pressure. In dual pressure plants absorption takes place at a higher pressure than the oxidation stage.

Single pressure plants operate at either medium (1.7 and 6.5bar) or high (between 6.5 and 13bar) pressure. Dual pressure plants operate at medium pressure for the oxidation stage and high pressure for the absorption.

The yield of nitric oxide depends on pressure and temperature as indicated in the table attached.

NO yield as a function of temperature and pressure.

Air is filtered and compressed to produce high purity air that is mixed with ammonia. The air/ammonia mix is then oxidised over catalytic platinum/rhodium alloy gauzes. Nitric oxide with a 93 to 98 percent yield and water are formed in this process

higher catalyst temperatures increasing the reaction selectivity towards NO production. Lower catalyst temperatures tend to be more selective toward less useful products – nitrogen (N2) and nitrous oxide (N2O).

Please find attached herewith links & articles,

regards,

Prem Baboo

Thesis Mian Project

Article Role of nitrous acid decomposition in absorber and bleacher ...

Dear Prem:

I'm familiar with the "classic" nitric acid production process that you describe.

Although here we are not producing nitric acid that way (we recover some nitric acid by absorption of NOx gases produced during thermal decomposition of residual nitrated explosives in the spent acid, and of the gas from the vents of the nitric acid tanks).

We have the problem of dissolved gases in the spent acid recycled to the nitric acid distillation tower (with uses sulphuric acid also), contrary to the acid bought from a external supplier which is crystal clear.

I started researching the nitric acid production process because after the absorption stage (be it low, medium or high pressure) a "bleaching" operation is mentioned, my problem is that the bleaching operation is not described in detail, or a design procedure referenced, which could allow me to estimate the equipment requirements to bleach the acid that we have here.

The paper that your attached, by Ingale, is the same that I mentioned, to my understanding, it doesn't treat dissolved gases explicitly.

I will review the thesis that you provided to see if I can find some clue :D.

Thanks for your answer.

Hi, i´m working on a project about adipic acid production and I have a problem similar to yours. In the reactor, where adipic acid is formed, nitrogen oxides are also formed and some of them, mainly the NO2 are dissolved in the liquid product. After the reaction step, the liquid product is treated  in a bleacher to convert the NO dissolved into NO2 gas. My problem is that I don’t know the solubility of this gases on the liquid stream. I read your question and I wonder if you can help me, giving me some papers or books. Thank you.

HI Pablo, I didn't arrive at a satisfactory solution to my specific issue. And switched job after a while, so I can offer too much  help.