Patent GB-418916-A (GB)
Title: A process for the production of concentrated nitric acid
IPC: C01B21/26
Filed: 1933-05-26
Abstract: <PICT:0418916/III/1> In the continuous production of concentrated nitric acid by interacting water or dilute nitric acid with nitrogen oxides and oxygen at elevated pressure by passing the liquid components down a column-type apparatus in intimate contact with the gaseous reaction components through a temperature gradient produced by supplying heat to the lower part of the column and condensing the vapours formed in the upper part of the column, the heat supply to the lower part of the column is so regulated, whilst introducing the oxygen into the lower part of the column, that the temperature at this point only reaches the boiling point at the prevailing pressure of the nitrogen tetroxide-containing nitric acid, and does not in any part of the column reach the boiling point of nitric acid free from nitrogen oxides and water, a liquid nitric acid having a substantial content of nitrogen tetroxide, amounting for example to 5--20 per cent, being obtained at the lower end of the column.  The acid after removal from the column may be bleached in known manner, say in a separate column directly connected to the reaction column.  The reaction may be conducted in a fractionating column a provided with perforated plates b, a dephlegmator c provided with a cooling jacket d cooling the upper end of the column.  Water or dilute nitric acid are fed through a pipe g by means of a cog-wheel pump h, nitrogen oxides being introduced at k.  Oxygen is introduced through a pipe n and perforated plate o into the nitric acid collecting in the sump l which is heated by means of a steam jacket.  The continuous discharge of the nitric acid is regulated by a floating element q.  An electric safety device r stops the gas and liquid inflow if disturbance of the floating element takes place.  The outflow of acid is regulated by a valve t.  Waste gases are blown off through a device e while a safety valve f is provided.  Raschig rings &c. may be employed instead of perforated plates.  According to a modification, the discharge of the acid, and also if desired of the waste gases, can be effected through a liquid seal when working at relatively low pressures.  The oxygen may be introduced into the lower portion of the column above the level of the liquid and the nitrogen oxides may be introduced into the lower part of the column.  The sump may be replaced by a sufficient number of column bases or may be subdivided into smaller sumps.  The introduction of the liquids may be effected by plunger pumps or rotating slide valve pumps instead of cog wheel pumps. Parts of the apparatus exposed to the acid may be constructed of ferro-silicon, tantalum, quartz, aluminium &c. or may be lined with such material.  Examples describe the production of 70--80, 84--85 and 97 per cent nitric acid, the respective excess pressures in atmospheres employed being 0,8--1,2, 3,2 and 50 and the respective temperatures being at the top of the column 20--25 DEG  C., 25 DEG C., and 50--70 DEG  C. and at the bottom of the column 30--35 DEG C., 40 DEG  C., and 100 DEG  C.  Specifications 131,336 and 321,728, [both in Class 1 (ii)], are referred to.