International Journal of Chemical Reactor Engineering
Ed. by de Lasa, Hugo / Xu, Charles Chunbao
12 Issues per year
IMPACT FACTOR 2016: 0.623
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Acceleration of Chemical Reactions Using a Supercritical Water Microreaction System
Water is an environmentally friendly chemical species that can be employed either as catalyst or as reactant. The use of water has attracted much interest for many acid-catalyzed organic syntheses. These reactions have been studied under hot water conditions with maximum formation of ions. Under these circumstances, long reaction times are required to obtain suitable yields however with poor selectivities given the influence of side reactions. The microreaction system of the present study can heat up a substrate solution very quickly from ambient conditions to the supercritical water state (scH2O) and can then quench rapidly the same solution to sufficiently low temperatures. This allows epsilon-caprolactam production with close to 100% selectivity and 80% yield in a acid free reaction system in less than 1-second reaction time. To justify these results, first principle molecular dynamics calculations and in situ IR measurements are employed as they can be applied to the structural and electronic properties of water in the near critical point region. Close to the critical point at low fluid densities, small clusters, mainly dimers and trimers, are the dominant features with no H-bonds expected. The significant reduction of H-bond strength in H2O, peculiar to near the critical point, leads to the activation of protons or H3O+. Hence, in the scH2O microreaction system, the acidic properties of H2O at the supercritical state are considered as the likely pathway promoter which prevents the hydrolysis and the pyrolysis of cyclohexanone-oxime as well as the pyrolysis of epsilon-caprolactam. It is also observed that dilute acids at supercritical conditions further enhance the epsilon-caprolactam process with close to 100% yield and 100% selectivity.
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