Elimination of Redwater Formation from TNT Manufacture

The US Department of Defense requires an environmentally benign synthesis route for the manufacture of military grade trinitrotoluene (TNT) which eliminates the production of redwater arising from the sulfiting process for removing unsymmetrical trinitrotoluene isomers. QinetiQ has found that by using a novel nitrating system, N2O5 in dichloromethane, the proportion of meta-substituted nitrotoluenes can be reduced to 1.3-1.5%, instead of the 4-5% levels in current processes. Additional improvements have been made to the following di- and tri-nitration steps by using alternatives to traditional mixed (sulfuric-nitric) acid systems, namely 100% nitric acid and N2O5-sulfuric acid respectively, resulting in reduced emissions of pollutants (NOx off-gas and tetranitromethane). As a result, TNT with a set point within 0.3 deg C of the Mil Spec (80.2 deg C) can be made by the QinetiQ process, without the need for sulfite washing; one recrystallization raises this figure to 80.6 deg C. A study of the process economics has shown that the cost (at 4.5 million lb per annum scale) is not disproportionately greater than current processes. The original document contains color images.