This project contributes to the reduction/minimization of acid mixtures (and hence waste streams), avoidance of the use of solvents that may be contaminated and need to be considered as a waste stream, and minimization of post processing (e.g. purification) of the product (reducing energy consumption).
The objective of this research was to avoid the use of any solvent and the liquid nitration acids by switching to the gas phase nitration agent using NO2. Nitrogen dioxide can be activated by irradiation with light of specific wavelengths and will subsequently attack the moiety of the compound in question to convert it into its nitro analogue. In a light reactor, this reaction is executed and can be augmented by the addition of a solid catalyst. To test the reactor system to the extreme, a solid – gas reaction was executed in the reactor by converting 1,2,4-triazole-5-one (TO) to 3-nitro-1,2,4-triazole-5-one (NTO). This was achieved by using nitrogen dioxide as the fluidizing agent, activating the nitration reaction by supplying light to the reactor. Where appropriate, a catalyst was added to enhance the yield of NTO and to reduce the reaction time. The effect of the enhancement of the nitration reaction with microwaves was also studied.
The nitration of benzene with nitrogen dioxide under the influence of light was successfully shown and yields of up to close to 100% nitrobenzene were demonstrated. For this, the most ideal ratios of substrate, nitrogen dioxide, and oxygen were established. However, the time needed for reaching such yields was too high (up to two hours). It was then shown that the application of catalysts can significantly reduce the reaction time needed to achieve the same yields in a matter of minutes. This means that a sound business case for a continuous process seems to be achievable.
The nitration of a solid material, 1,2,4-triazole-5-one (TO), with nitrogen dioxide in a fluidized bed has been successfully demonstrated, albeit the yields found for nitro-1,2,4-triazole-5-one (NTO) were low. This was predominantly due to the morphology of NTO, which can be best described as pancake-like. Due to unfavorable particle shape, the fluidization of TO was troublesome, resulting in low yields of NTO.
It was found that the application of microwave radiation on the nitration reaction (both the gas phase nitration of benzene to nitrobenzene as well as the nitration of TO to NTO) did not have a discernable influence.
The reactor did not use liquid acid mixes for nitration purposes or solvents for facilitating the reaction, thereby minimizing the waste streams significantly. The reactor could be highly flexible to nitrate almost any compound regardless of the state of the substance (gas, liquid, solid) and be modular in nature, enabling adjustment of the output at any given moment in time.