An alternative to current production routes to cyclohexanol, the esterification of cyclohexene with formic
acid and subsequent splitting of the ester can overcome many of the drawbacks associated with conventional
processes. The process that is being considered could be carried out in a reactive distillation column. To
develop such a process, reliable data on liquid−liquid and vapor−liquid phase-splitting behavior and on
reaction kinetics is of high importance. The current publication focuses on the reaction kinetic aspects of
such a process. Reaction kinetic data for the three equilibrium reactions are being presented
The six-component system cyclohexene + water + cyclohexanol + cyclohexane + formic acid + formic acid cyclohexyl ester is currently being studied with the aim of carrying out the reaction of cyclohexene and water to cyclohexanol in a reactive distillation (RD) column. Because the direct reaction path of cyclohexene hydration is strongly limited by slow reaction rates with the known catalysts, an intermediate ester-formation step with formic acid was included in the studies. The challenge that this six-component system poses for a reactive separator such as an RD column lies in the liquid-liquid phase splitting behavior. This adds a third effect besides reaction and distillation. Cyclohexane is included in these studies to represent any inert C 6 components present under industrial conditions. To be able to design an RD column, measurements were conducted of the liquid-liquid and vapor-liquid equilibria, and appropriate NRTL parameters matching both vapor-liquid and liquid-liquid phase splitting behavior were identified.
In the conventional process for cyclohexanol production, large amounts of energy are consumed and a considerable quantity of side products is formed. In addition, the process is inherently unsafe. The alternative process of cyclohexene direct hydration requires large amounts of catalyst to overcome kinetic limitations. This publication shows the feasibility of a new route from cyclohexene to cyclohexanol by means of reactive distillation using formic acid as a reactive entrainer. This allows overcoming kinetic limitations with moderate amounts of catalyst and makes large-scale cyclohexanol production by reactive distillation an interesting alternative. The suggested coupled reactive distillation process allows producing cyclohexanol in an inherently safe and energetically advantageous way without incurring significant amounts of side products.
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