Ion Exchange Resins for Chromatographic Separation

Chromatographic separation using ion exchange resins is a rather interesting application because the resin is not performing ion exchange. The resin is serving as the media, stationary phase, or adsorbent in a liquid chromatographic separation process system. Other sources are available to learn about chromatographic separation processes; however, note that much is written about chromatographic separation as a measurement technique and very little is written on chromatographic separation as a manufacturing process. And much of what is written on chromatographic separation as a process operation is misguided and written from an analytical measurement perspective.

Chromatographic separation is a manufacturing process which uses ion exchange resins as a selective medium to separate one dissolved chemical from another. Used primarily in the sugar industry and with compounds related to the sugar industry, chromatographic separation happens at the chromatographic “packing” or “stationary phase”. Some example compounds purified by chromatography are sucrose, glucose, fructose, oligosaccharides, raffinose, maltose, xylose, sugar alcohols, betaine, xylitol, sorbitol, and mannitol. In addition, this process has been used in purifying amino acids and various organic acids as well as to separate salt from glycerol.

The chromatographic separation can occur through various interaction mechanisms, including ligand-exchange chromatography (LEC), size exclusion chromatography (SEC), ion exclusion chromatography (IEC), and reverse phase adsorption chromatography (ADS). Irrespective of the particular mechanism, the engineering basics of the process are the same.

Chromatographic Separation of Fructose and Glucose Using DOWEX MONOSPHERE 99Ca Chromatographic Separation Resin (82KB PDF)

Most industrial chromatography today uses Simulated Moving Bed (SMB) technology. [An older term for SMB is Pseudo-Moving Bed Chromatography.] By utilizing SMB, solvent use and separation media are minimized, leading to a greatly reduced cost of operation when compared to traditional batch chromatography.

Example Applications

DOWEX MONOSPHERE 99 separation resins have established themselves as the standard in the industry for efficient, economical chromatographic separations including separations designed for fructose enrichment, dextrose purification, and molasses desugarization (also known as ion exclusion). There are several particle sizes, the selection of which depends on the pressure drop constraints of the particular separator. The most commonly used nominal sizes (volume median diameter) are 310, 320 and 350 microns.

These products are extremely consistent lot-to-lot and are produced to the tightest specifications in the industry. The particle size distributions are extremely narrow. The lack of large beads minimizes the smearing of component profiles. The lack of small beads minimizes the operating pressure drop.

For chromatographic industrial processes, the important factors are the consistency of the particle size, the Water Retention Capacity (WRC) of the resin and the uniformity of the particle size of the beads in the resin used as the chromatographic separation packing. Dow's resins have the tightest specifications in the industry, ensuring that the resins provide the most economical tradeoff between separation ability (purity), production capacity (as high as possible, i.e., minimizing pressure drop), and solvent consumption. Since the majority of the operating cost of a large-scale chromatographic separation is due to the energy required to evaporate and recycle the solvent (usually water), a low specific water consumption in process operation is key to minimizing operating costs.

Dow not only provides resins capable of low water use, but also has experts in this field who can optimize operating parameters to reduce energy costs. We also offer operations training seminars which teach operating personnel how to reduce energy costs. Plant troubleshooting and optimization services are also available through Dow.