| 摘要 |
The invention provides integrated continuous processes for concentrating "weak" nitric acid and concurrently reconcentrating the spent dehydrating agent used to break the nitric acid azeotrope to obtain "strong" nitric acid, the processes involving direct coupling of the nitric acid concentration with the reconcentration of the spent dehydrating agent so that less energy input is required than in equivalent prior art processes. The major proportion of the feed "weak" nitric acid is vaporized before being fed countercurrently into a column to contact a large volume of the dehydrating agent, this vaporization being one of the two major sources of energy input, the second being through the reboiler at the bottom of the column. Energy input is balanced by energy rejection through condensation of strong nitric acid vapor and water vapor. The nitric acid vapor injected into the lower part of the column is subsequently contacted in succession with a mixture of nitric acid and a portion of the dehydrating agent to further increase the strength of the nitric acid vapor, then with a third portion of the dehydrating agent and finally a small reflux of concentrated "strong" nitric acid to remove further water and residual dehydrating agent from the concentrated "strong" nitric acid vapor in the upper part of the column. The spent dehydrating agent is reconcentrated by flashing under vacuum or alternatively through evaporative cooling with air without further substantial energy input, and is recycled back to the nitric acid concentration column without being cooled, avoiding consequent rejection of energy. The preferred dehydrating agents are aqueous solutions of sulfuric acid and of magnesium nitrate.
|
