This laboratory is designed to illustrate the principles and physics of ion exchange chromatography and to allow for the observations of relationships between theory and experiment. There are two experimental units, batch and column adsorbers. The batch adsorbers are stirred flasks with which one determines the sorption isotherms and diffusion in the ion exchange resin. The second apparatus is a column packed with ion exchange resin through which flows the sorbate. Data taken from this device may be used to determine intra- and extra-particle mass transfer.

The laboratory consists of two experimental parts, linked by a section of theoretical, computer modeling. The modeling is used to predict the results from the second (column) experiments, given data from the first (batch).

The parameters that can be varied are:

• resin size
   
• ion concentration
   
• temperature
   
• bed volume
   
• flow rate

• sorption isotherms
   
• break-through curves
   
• bed efficiency
   
• effective ion diffusivities
   
• dispersion
   

Adsoprtions are performed in batch mode or within a packed column under flow. Ion concentration in solution is measured using UV/Vis spectrophotometry. Cupric sulfate is good choice for these experiments as the cupric ion absorbs strongly at 660 nm, and the sulfate counter-ion is nonabsorbing. Cupric sulfate is commonly used and aqueous solutions have been well characterized in the literature (densities found in CRC Handbook). A personal computer, A/D board and LabView software automates data capture and analysis for both column and batch experiments. For the cationic resin we use the Dowex 50W-X8 resin in the acid form at sizes of 20-50 and 200-400 mesh.

Batch experiments are used to determine equilibrium sorption isotherms and effective ion diffusion in the particles. The equipment must be calibrated and care must be taken with respect to the range and precision of the measuring devices.

Experiments with an adsorption column can determine the effect of mass transfer and dispersion on the performance of a column. Here variables include particle size, flow rate, bed depth and temperature.

What is the effect of temperature on equilibrium sorption of copper sulfate from water solution ? Determine the sorption isotherms for ion exchange resins of two different sizes at at least three different temperatures. What are the batch sorption kinetics ? Can the intraparticle diffusion be measured ?

What is the effect of flow rate on the breakthrough of copper sulfate in a packed column adsorber ?

How does particle size affect the performance of an ion exchange column? How severe is axial dispersion on breakthrough ?

Can you obtain good correspondence between the adsorption model and the experimental measurements ?

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