(105a) Lurking in Small Amounts - Concentration of an Unstable Nitrate Due to a Subtle Process Change

An industrial accident occured in the spring of 2000 that fortunately did not result in fatalities but ended production of a di nitro analine herbicide..

The harsh conditions of reactions involving organics, sulfuric and nitric acids produced a very small amount (100ppm) of tetra nitro methane which is shock sensitive with the energy of nitroglycerin. (not known before the accident). For 20 yrs, no problems were experienced and the low level of TNM passed thru the process. But two process changes were made. The first a recycle stream that boosted overall content, The second was the most serious; the TMN exited the reactor with other process vapors to the vent where it was scrubbed with a water spray. This spray also decomposed the TMN. In an attempt to reduce water load, a vent chiller was installed which stabilized the TMN and permitted it to accumulate as a separate phase in a wastewater sump. It was estimated that at least a hundred gallons of TMN solution had accumulated by the time a sump steam out was carried out at a plant turnaround. The material exploded destroying much of the plant. This was obviously a MOC error with unintended consequences but it is unclear that anyone was aware of the presence of this reactive light.

Key learnings were;

• Ensure you have a complete material and
  energy balance of your process
• Be cautious of adding or modifying
  recycling loops that may build up impurities
  and cause chemical transformation
• Be highly suspicious of lights formation in nitration operations.....look for them at low levels analytically.

But be aware that there is a potential for similar issues with;

• Ethers + O2 = peroxides
• Cl2 + ammonia or amines = NCl3
• Nitro moiety on a wide range of molecules
• Peroxide & Azo initiators in polymer processes