GB401121A - Improvements in and relating to process and apparatus for the production of nitrates - Google Patents

Abstract

A process for the production of a nitrate by treatment of a nitrite with a gas containing nitrogen tetroxide is characterized by treating the nitrite in solution with a plurality of portions p of the gas, said portions being separately introduced into the solution in successive stages, so that in each stage the nitrite solution is contacted with a different portion of the fresh gas. As liquors from which the nitrite is obtained, milk of lime or liquors containing basic alkali compounds such as sodium or potassium hydroxide or carbonate are specified. The process applied to the production of sodium nitrate is as follows. Nitrogen oxide gases are cooled say to 30 DEG C. in chamber 1 by contact with dilute nitric acid circulating therethrough. The chamber may be of chrome iron and contains packing material 63. Oxidation to the extent of say 80 per cent or more occurs in this chamber. The gases are divided into a plurality of portions, each passing through one of the coke-packed towers 6a-f wherein they react with the nitrite solution. The merged exit gases pass to absorption towers 8, 9. Sodium carbonate solution from 12 is circulated through tower 9, finally passing to tower 8. The liquor is pumped via cooler 68 through this tower and then passes to the towers 6f-a. About 15--20 per cent of the nitrogen in this liquor may be present as nitrate, although in some cases the nitrate-nitrite ratio may be unity. Oxidation air is supplied at 15. The towers 8, 9 may be of iron <PICT:0401121/III/1> and contain packing material 14, preferably ceramic rings. The temperature of the liquid in the towers is below about 40 DEG C. The liquor passes through the towers 6f-a, being circulated through each and maintained below about 40 DEG C. That discharged from the last tower contains nitric acid and nitrogen oxides, the latter being removed by air in tower 53. The liquor is then neutralized in tank 58 with sodium carbonate solution, and concentrated in a multiple effect evaporator 61, the solid being removed by filtration at 64. Mother liquor from the filter is returned to the evaporator. To prevent accumulation of sodium carbonate and nitrite in the solution, a portion of the returning liquor is passed to the liquor passing through towers 6f-a. Alternatively, part of the liquor from the last effect of the evaporator is so returned. The number of absorption towers is not necessarily that shown. The solution and gases may pass in countercurrent through tower 9. The tower 1 may in some instances be omitted, or be replaced by separate cooling and oxidation plants.