Concentration‐dependent diffusivity of benzoic acid in water and its influence on the liquid–solid mass transfer

The diffusion coefficient of benzoic acid in water at 25°C has been measured as a function of concentration using the Taylor dispersion technique. The diffusion coefficient was found to decrease from 1.25 × 10 −9 m 2 /s to 1.07 × 10 −9 m 2 /s when the concentration increased from 0.27 mol/m 3 to 5.44 mol/m 3 . Two different models describing the concentration dependence of the diffusion coefficient have been developed. They are fitted to the measured data and experimental data from literature at infinite dilution ( D = 1.57 × 10 −9 m 2 /s) and at higher concentrations up to 20 mol/m 1 ( D = 0.75 × 10 −9 m 2 /s). The significance of the concentration dependence is evaluated by measurement and by computer simulations of liquid–solid mass transfer in a tube. The simulations show that 0.80 × 10 −9 m 2 /s is the constant diffusivity that gives the best approximation in dissolution studies.