Nuclear magnetic resonance measurement of ammonia diffusion in dense solid-liquid slurries
Executive Summary The diffusion of ammonium ions in aqueous solutions was measured by nuclear magnetic resonance (NMR) using the pulsed field gradient (PFG) method. The ammonium ions were obtained from aqueous solutions of ammonium chloride, ammonium sulfate, ammonium bicarbonate, and ammonium hydroxide. The translational diffusion of the ammonium ions was determined by measuring the diffusion of nitrogen nuclei (14N and 15N) in solution. Our results showed that the ammonium diffusion
... diffusion coefficient can be measured in aqueous solutions with concentrations as low as 20 x 10-3 M. Typical values measured for the diffusion coefficient of the ammonium ion are 2 x 10-5 cm2h (&lo%), similar to the values found for pure water. Due to the effect of the solution pH upon the NMR relaxation parameters for 14N, measurements are constrained to pH values below 8.5. However, 15N labeled ammonia is less sensitive to the solution pH, extending the measurement range to pH of 9.5. Diffusion measurements were conducted with solutions of varying viscosity and porosity. The results show that the solution viscosity has a measurable impact on the diffusion coefficient. The diffusion coefficient is almost inversely proportional to the relative viscosity of the solution, irrespective of how the viscosity is increased. Further, a randomly-packed porous bed of 200 mm PMMA resulted in a reduction of -30% in the diffusion coefficient as a result of hindered diffusion.