Spatially and chemically resolved measurement of intra- and inter-particle molecular diffusion in a fixed-bed reactor Original Research Article

This work demonstrates for the first time the ability to spatially and chemically resolve inter- and intra-particle apparent diffusion coefficients in a packed bed during reaction using Nuclear Magnetic Resonance. The measurements were performed using a diffusion preconditioned one-dimensional chemical shift imaging pulse sequence; all the data are recorded within a single measurement. The reaction studied was the continuous liquid phase esterification of acetic acid and ethanol to form ethyl acetate and water over an ion-exchange resin at ambient temperature and pressure. Inter- and intra-particle apparent diffusivities of the hydrocarbons were resolved at four different spatial positions along the length of the catalyst bed. Absolute composition measurements were obtained of the liquid in the inter-particle space of the bed. Relative concentration measurements of the chemical species in the intra-particle space are also reported. The development of these measurement methods advances our ability to characterise mass transfer limitations in situ within a working fixed-bed reactor.