Purification of nitro T acid raffinate by nanofiltration membrane technology

Production of nitro T acid which is an intermediate of H acid produces a large amount of waste acid. In this paper, the complex extraction coupled with nanofiltration membrane using trialkylamine (N235) as extracting agent was adopted to purify this waste acid in order to remove the residual extractant and soluble sulfonated naphthalene. The suitable extraction condition for nanofiltration processing was N235 volume fraction of 33%, water over oil ratio of 2:1 without addition of n-octanol. After secondary extraction, the removal rate of CODCr was 79%. When the secondary raffinates were concentrated to one sixth of the volume by nanofiltration, the average fluxes of the membranes were 9.9—20.9 L·m −2 ·h −1 . Sulfuric acid with 27% concentration (mass fraction) was recovered. The total removal rates of CODCr and chroma were 94%—97% and 99%, respectively. This coupling method could greatly reduce the pollutant emissions in production of nitro T acid.