Study of the Phase Behavior of Mono-Nitrated Poly-Substituted Aromatic Nitrocompounds
Abstract
Mixed-acid nitration is a well-established process that has been conducted industrially for over 70 years. It involves highly exothermic reactions that must be managed to avoid thermal runaway events, a risk complicated by monomolecular decomposition reactions undertaken by the reaction products at elevated temperatures. Process disturbances that have the potential to cause thermal shocks or unexpected heating in the process are therefore a severe threat to the process and must be investigated. Recent work in literature shows that nitrobenzene is capable of forming microemulsions and undergoing transitions between different types of emulsified systems detailed by PA Winsor. This work was therefore undertaken to observe representative mixtures of sulfuric acid, water, and select simple aromatics to determine if microemulsions were forming in the system in composition and temperature ranges typical of industrial processes and to determine what, if any, impact the substitution of small functional groups onto the aromatic ring had on the microemulsion formation. Literature was reviewed to search for appropriate models that could be used to predict the formation of microemulsions in these and similar systems.
Microemulsions were determined to be forming in the mixed-acid nitration system and that additional functional groups on the aromatic ring could affect the microemulsion formation within the system, usually adversely. However, the formation of three phases including a middle phase microemulsion – a key point of interest to this work with regard to operability of the process – did not occur in compositional ranges commonly seen and expected in industry. Additionally, the type-III and type-IV microemulsions which where the central focus of this work all collapsed at temperatures of around 30°C, well below the 60-100°C expected of continuous industrial nitration processes.
It was determined that existing models in literature for prediction microemulsions are ill suited to describe the behavior of this system. However, experimental results showing that this behavior poses no threat to the process show that developing a new model for systems such as this one is of little practical value.
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Citation
Pittman, William C (2015). Study of the Phase Behavior of Mono-Nitrated Poly-Substituted Aromatic Nitrocompounds. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /155445.