Spent acid purification process

摘要

Contaminants in spent nitric-sulfuric nitration acid can be removed by mixing the spent acid with urea and heating to 75 DEG -150 DEG C. Off-gas from the spent acid/urea reaction is passed through a Group IB, VB, VIB or VIII metal containing catalyst to decompose nitrous oxides and the so-treated off-gas is contacted with spent acid, denitrated spent acid, or fresh sulfuric acid, and optionally air (i.e. oxygen), to absorb oxides of nitrogen. The spent acid scrubbing fluid is then subjected to the same process for removing contaminants.