Dow Water & Process Solutions

Picking the Right DOWEX Resin

Many ion exchange separations are known and widely practiced in the chemical processing industry. When a specific contaminant cannot be identified, a mixed bed ion exchange resin is best because it is capable of removing both cations and anions. Other components, such as boron, requiring special chelating resins, are described in the Periodic Table Product Selection Guide.

High purity gases can be produced using the DOWEX MONOSPHERE UPW family of resins and DOWEX OPTIPORE polymeric adsorbents. Ion exchange resins are typically supplied water wet and must be dried for good contact with gases.

Cationic components such as ammonia can be removed with DOWEX MONOSPHERE 650C UPW (H). Anionic contaminants such as acid gases can be removed with DOWEX MONOSPHERE 550A UPW (OH) or DOWEX M-43 acid adsorber. Since gases are often used in a compressed form, they are often contaminated with compressor lubricants. DOWEX OPTIPORE polymeric adsorbents have been shown to work well to remove these lubricants from compressed gas streams.(1)

Testing and Evaluation
Testing media for a chemical separation is usually carried out with equilibrium isotherms (23KB PDF). The high level of removal required for ultra pure applications, however, rely on the multiple equilibrium established in chromatographic separations so column testing is necessary. Please see the section of this site that described Laboratory Column Studies (170KB PDF).

Metal contaminents can be present as particles that must be removed by filtration. Sometimes metal/salt particles are so small (colloids) that they can't be removed by standard filtration. In this case the macro pores of an ion exchange resin can trap and remove colloidal particles of salts and metals. Products to consider are DOWEX MARATHON™ MSA resin and DOWEX MARATHON MSC resin.

Since DOWEX MONOSPHERE UPW resins are supplied water wet, they must be dried for organic media applications so that organic solvents can fully interact with the ion exchange sites. For more information see Recovery of Metals from Organic Media. To learn more about the basics of ion exchange resins see DOWEX Ion Exchange resins: Powerful Chemical Processing Tools (175KB PDF).

The Art of Making Ultra Pure Chemicals.
Making UP chemicals is as much an art as it is a science. The cost of making these high purity materials must be justified in the higher end user prices. Since such low levels of contaminants are desired, many use clean room type of production facilities with special air handling systems to control particulate contaminants. Special equipment such as low leachable columns, tubing and packaging systems are required. Attention must be paid to details like the materials of construction of the internals of valves and pump heads as sources of contamination. Glass equipment may require special cleaning or passivation such as soaking with nitric acid to extract residual metals.

Ion exchange resins require special considerations when making ultra pure chemicals. Chromatographic separations are critical to ultra pure operations. To optimize the separations, the height to diameter ratio of the equipment should be as high as possible. Counter current regeneration of the resin with the highest quality of regenerant is necessary. The amount of acid or base used can often be 2-10 times the amount recommended for industrial applications.

Due to the extensive amount of effort required in equipment, preparation and operations, doesn't it make sense to use the highest purity and quality media for your separation?

References
(1) "Removal of oil from compressed gas with macroporous polymeric adsorbents" Bowman, R.H. and Goltz, H.R. US Patent 5,700,310, MG Generon, December 23, 1997.