The electrolytic production of para-anisidine
In this thesis the electrochemical reduction of nitrobenzene in a methanol / sulphuric acid electrolyte is studied. Major products are shown to be para-anisidine, ortho-anisidine, para-aminophenol and aniline. A simple reaction model is derived, based on the well accepted mechanism for nitrobenzene reduction. Kinetic constants are determined from experimental results using a laboratory scale glass cell. Predictions as to potential - current behaviour and product formation as a function of mass transport and current density are made. It is shown that the rate of mass transport and the current density are crucial parameters in determining the chemical yields of the products formed. High rates of mass transfer and low current densities favour para-anisidine formation, whilst aniline is preferred under poor mass transfer conditions and high current densities. Results from a bench scale parallel plate cell fit the model predictions for the conditions used. The use of packed and fluidised bed electrodes is also investigated for the production of para-anisidine. Using copper particles, serious dissolution is shown to occur which leads to an increased yield of aniline. The copper dissolution is shown to have an electro-catalytic effect for the reduction of nitrobenzene to aniline. Results using Monel as an electrode material showed an improvement over copper, but preferential dissolution of nickel occurred. On the basis of the work in this thesis, copper or Monel packed and fluidised bed electrodes are not suitable for the production of para-anisidine.