(164d) Kilogram-Scale Production of Energetic Materials in a Remote-Controlled Microreactor Plant

Today, microstructured reactors having internal fluidic structures in the sub-millimeter
domain are well known to provide far better heat exchange characteristics and mass transport performance than attainable in macroscopic batch or continuous reactors.  In the last decade, a large number of studies have impressively demonstrated that the accumulation of strong reaction heats and hot spots, which result in unwanted side, subsequent and decomposition reactions, can be successfully suppressed in microstructured reactors. Hence, the hazardous potential associated with reactions that are strongly exothermic or potentially explosive can be significantly reduced.  Greater safety is also attained with handling thermolabile substances due to the small hold-up of microfluidic reactors.

Here we report on our recent developments of using microstructured reactors for the safe synthesis and subsequent purification of different liquid nitrate esters classified as energetic materials. The hazardous potential of these reactions is due to the huge reaction exothermicity (reaction of alcohols with nitrating agents) and a considerable thermolability of the reaction products and intermediates.  A continuous production plant has been developed which is operated in a completely remote-controlled way. At the heart of this technical plant are microreactors made of glass, which have been specially developed for high-throughput applications for both synthesis and downstream processing (washing and extraction). Due to its modular design, the plant allows the production of different nitrate esters at different process conditions. For example, microreactors and pumps can be quickly exchanged for a new production campaign depending on the viscosities of the starting materials and product. The appropriate microreactors are integrated into the production plant to match the throughput, mixing intensity, hold-up, and pressure drop that are required.  The entire plant has a wide range of safety features, is under permanent video surveillance and every technical aspect is controlled.

The microreactor plant has been particularly developed for the production of the following nitrate ester oils: ethylene glycol dinitrate (EGDN), butanetriol trinitrate (BTTN), methyl nitrate (MN), and trinitroglycerin (NGL). The oils are synthesized in the microreactor by continuously mixing the corresponding alcohol with a nitrating agent such as HNO3/H2SO4 under precisely controlled stoichiometric and thermal conditions. Afterwards, the energetic raw products (raw oil) are automatically transferred to the downstream process where they are purified and stabilized in further tailor-made microstructured reactors by continuous washing and extraction steps.

The produced nitrate esters fulfill all necessary specifications with respect to (pharma-grade) purity as well as thermal, impact and friction stability.