This is the number of sites where exchange actually takes place during one cycle.the number of exchangeable monovalent ionsīoth volume and dry weight capacity values must be reported. In the USA, particle size is often expressed in mesh. For all applications requiring separation of different resins in the same column, such as stratified or mixed bed units, selection of the right particle size is of critical importance. Coarse beads on the other hand are frequently more sensitive to osmotic stress and have slower kinetics, thus giving a lower operating capacity. The choice of particle size is a compromise: fine resins deliver a higher capacity, but cause high head loss, and excess fines may produce nozzle clogging. See the bell curve and the Gaussian-logarithmic plot for a resin with uniformity coefficient 1.10. with a uniformity coefficient equal to 1.00. They would be identical for resins totally uniform, i.e. The characteristic values for this example are:įor resins with uniform particle size, the median diameter, harmonic mean size and effective size are close to each other. The points are not exactly aligned due to imprecision in the sieving, and due to the fact that the actual distribution is not exactly Gaussian. This example displays the results corresponding to the bell curve above. In the past, this paper was used to calculate mean diameter, effective size and uniformity coefficient based on the laboratory results. Using a Gaussian-logarithmic paper, a normal distribution (cumulated percentage through the sieves) will appear as a straight line, as shown on the picture here. Both values are almost identical for resins with uniform particle size. For practical purposes, the value of HMS is close to the median diameter, but a little smaller. HMS is useful for theoretical considerations regarding hydraulic properties and kinetics of a resin. The harmonic mean size abbreviated as HMS is a mathematical expression calculated from the distribution function. Amberjet resins have a UC of 1.05 to 1.20, Ambersep and SB grades 1.15 to 1.30, RF grades 1.20 to 1.50, standard grades 1.3 to 1.7. If all beads had the same size, it would be equal to 1.0. This coefficient measures the "width" of the distribution, and is reflected in the width of the Gaussian bell curve. The uniformity coefficient is defined as: UC = d 60 / d 10.The effective size is the value of the sieve opening through which exactly 10 % of the resin sample passes.In the language of statistics, it is called median diameter. that retains exactly 50 % of the resin sample. The mean diameter is the value of the (theoretical) sieve opening through which exactly 50 % of the resin volume passes, i.e.A Gaussian bell curve has been superimposed on the graph. In theory, and very roughly in practice as well, the particle size distribution of conventional "kettle polymerised" resins is normal, or Gaussian. The values "between sieves" have been plotted on a graph with a logarithmic scale for the sieve openings. The number of active groups in a resin sample is obviously constant, so that when the resin swells, the density of these active groups decreases, and the volume capacity is a measure of this active groups density.Įxample: analysis of a batch of new resinĮxample of traditional analysis measuring the volume of resin retained on each sieve: The difference is just due to resin swelling: it swells by up to 30 % between the Cl - and the OH - form. For example, Amberjet 4400 has a total capacity of about 1.5 eq/L in the Cl - form and 1.2 eq/L in the OH - form. This applies in particular to the following properties:Īnd to a lesser extent to the particle size. In expressing the results of most resin properties, the ionic form should always be mentioned, as the values are different according to the ions in the resin beads. The structure (matrix and functional groups) of ion exchange resins is described in other pages, as well as details of total and operating ion exchange capacity. Ion exchange resin properties Introduction
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