Abstract
The salting out of acetonitrile from water in the presence of ammonium bicarbonate was studied at atmospheric pressure from 4 to 35 °C. The coexisting phases were analyzed independently with H1 nuclear magnetic resonance, ion chromatography, calorimetry, and titrations. The binodal region was described with semiempirical functions and with the UNIQUAC thermodynamic model. The critical composition at ambient temperature is given by 0.02 g/g of salt and 0.58 g/g of acetonitrile: at lower salt concentrations; this mixture is widely employed in liquid chromatography, thanks to the buffering properties of the bicarbonate. The separation of acetonitrile and water for extraction purposes, instead, is often obtained with other ammonium salts. These ternary equilibrium data can then be useful to develop extraction and analysis procedures at buffered, mildly alkaline pH. In addition, this mixture can be encountered during the acetonitrile synthesis proposed from bioethanol and bioethylene, so these multiphase equilibria govern the separation and purification of acetonitrile in specific reactors that allow the recovery of ammonium bicarbonate as a valuable byproduct. Furthermore, the solubility of this salt in alcohols and its decomposition were investigated to target its stability in multiphase reactors, extractors, and driers.
Highlights
Acetonitrile is a solvent of major importance for research experiments and for the pharmaceutical industry,[1−4] but its separation from water cannot be achieved with one distillation unit, given the formation of an azeotrope, so usually a pressure swing[5,6] or an extractive distillation[3,6−8] technique is used
This passage is necessary when acetonitrile is produced, because water is a byproduct of the consolidate Sohio process,[9] as well as of the oxidative routes sought by many researchers.[10−15] All the more important, it is fundamental for the recovery and reuse of acetonitrile from effluents.[3,16−19]
Phase-splitting substances that can affect the pH are of interest where proteins or other pH-sensitive molecules are involved.[46,58−60] For this reason, adding ammonium bicarbonate to acetonitrile−water eluents is foreseen in several HPLC and extraction procedures, even when a phase separation is not foreseen, because other salts could adjust the ionic strength without granting a buffering effect.[61−64] Selected reactions can be carried out in the homogeneous phase, achieving phase separation when needed through salting out
Summary
Acetonitrile is a solvent of major importance for research experiments and for the pharmaceutical industry,[1−4] but its separation from water cannot be achieved with one distillation unit, given the formation of an azeotrope, so usually a pressure swing[5,6] or an extractive distillation[3,6−8] technique is used. The general procedure is consolidated, newer particular systems are continuously devised and tested.[56,57] In this context, phase-splitting substances that can affect the pH are of interest where proteins or other pH-sensitive molecules are involved.[46,58−60] For this reason, adding ammonium bicarbonate to acetonitrile−water eluents is foreseen in several HPLC and extraction procedures, even when a phase separation is not foreseen, because other salts could adjust the ionic strength without granting a buffering effect.[61−64] Selected reactions can be carried out in the homogeneous phase, achieving phase separation when needed through salting out In this way, the reactor is dealt as a solid− liquid−liquid multiphase one, needing the computing of phase equilibria to model its output. The solubility of ammonium bicarbonate in different solvents was reviewed and its sublimation heat was estimated
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