By Matthew Wirth
In the water industry, the UPS acronym stands for uniform particle size ion exchange resin and it describes a type of resin bead sizing. What it is, why it matters, where it applies and how it works are all important to expanding one’s ion exchange knowledge. For this article, the concentration is on ion exchange softening. The stated goal of this knowledge sharing is to present existing resin technology and describe how its use may further industry efforts toward increased efficiency and improved functionality.
What is UPS resin?
Uniform particle size resin beads are similar in size – they are uniform by design. When looking at UPS resin beads under a magnifying glass, they stack evenly in the resin column (see Image A). Conventional resin products are not uniform; their size varies in a Gaussian distribution and a typical particle size distribution stacks randomly (see Image B). By design, smaller beads in the conventional product fill in the void space between the larger beads. A common particle size for UPS resin is 20 to 40 mesh (0.8 to .4 mm) to 30 to 50 mesh (0.6 to 0.3 mm) bead diameter with a uniformity coefficient (UC) of 1.2.[1] Conventional resin,
Image A: (Courtesy of ResinTech, Inc.) 
Image B: (Courtesy of ResignTech, Inc.)
using typical Gaussian particle size distribution, is 16 to 50 mesh (0.3 to 1.2 mm) with a uniformity coefficient of 1.6.2 Size distribution can vary by manufacturer. Note: A 16 mesh (0.3 mm) bead is approximately twice the size of a 30 mesh (0.6 mm) bead.
There are two ways of making a UPS product. One is to screen a Gaussian resin and keep the beads of similar size. It is hard to get UC below 1.2 this way and it is more expensive due to extra processing time and wasted polymer that does not make the cut. The second manufacturing process is making the beads by a two-step jetting process. This method can create a UC below 1.1 and has a potentially lower manufacturing cost due to less waste.[2] This does not mean that conventional Gaussian resin is bad. It plays a huge role in the industry. What is Gaussian particle size distribution? Gaussian distribution confirms that the resin sizing is normal and fits within a bell curve – the different size beads are distributed in a manner that fits the application (see Image C).
Before continuing, for those new to resin science, resin beads are not solid plastic spheres. They are a molecular sieve with a matrix of pathways – they are porous. The exchange sites (functional groups) reside throughout the bead. For the new learner, think of a spaghetti ball to help conceptualize a resin bead (see Image D). Over 99 percent of the ion exchange happens on the surface area inside the bead.[3] Seasoned pros know the beads are polystyrene strands held together with divinylbenzene crosslinking (see Image D1).
Image D: Spaghetti Ball
Image D1: Bead matrix
Smaller uniform beads demonstrate faster kinetics (chemical reaction rates) than conventionally sized product. Improved kinetics typically result in improved brining efficiency, higher operating capacity, reduced salt usage (reduced chloride discharge) and a reduction of water used for regeneration. By removing the larger beads from a resin bed, the diffusion path (distance ions travels through the bead) is reduced; water travels faster through smaller beads and this is advantageous for ion exchange, including ferrous iron and manganous manganese. This will be discussed later. Without getting too far into the science, getting hard water into and out of the resin beads improves the predictability of outcome (capacity and flowrate), while allowing the system to regenerate evenly and effectively.
Using varied sizes of bead allows the resin bed to fill in with the smaller beads occupying the voids between the larger beads (see Image B). Images C and E show examples of conventional Gaussian size distribution for resin.[4] Note: Ninety-five percent of the Gaussian resin batch would fall between 23 and 45 mesh (0.80 – 0.40 mm). It works well for conventional softening and ion exchange applications. It is a cost-effective practice that utilizes the largest portion of beads produced in manufacturing. It goes without saying, UPS products cost more to produce.
Why use a UPS product?
The water industry landscape is changing. Government entities are asking for reduced chloride discharge. Industrial users are looking for ways to reduce water use. Consumers expect greater efficiency. As stewards of best water practices, it is prudent to consider available design options to comply with current economic and environmental needs. Moving water and ions evenly through resin, both in service and during regeneration, provides consistency of outcome. When chemical reactions happen at the same time, one can better predict how much brine is truly needed and how much water is needed to rinse the brine from the system.
When beads vary from 0.3- to 1.2-mm diameter, the larger beads require more time to react than the smaller beads. Simply put, the larger beads are four times the size of the smaller beads and these larger beads dictate the process. Consistently leads to efficiency. In addition, UPS product uniformity allow the use of smaller beads without experiencing increased pressure drop. The even voids space between the beads allows water flow without undue pressure loss. Note: The even void space does result in less surface area in the bed – using a finer mesh UPS can even out the surface area loss.
Ion exchange is an excellent option for controlling metals such as iron and manganese when they are in solution. When iron is ferrous and manganese is manganous, they are divalent and will exchange with sodium in a salt regenerated water softener. When these metals oxidize, they do not exchange, and can plug and coat the beads – destroying their functionality. Using smaller beads and other short-path technology, helps the resin bed strip these nuisance metals from water while the short path through the resin helps prevent suspended metal solids from becoming lodged inside the bead. Larger beads have a longer diffusion path and metals can oxidize and/or lodge in the bead and plug off future access to the interior of the bead. Remember, 99 percent of a bead’s capacity is inside the outer shell. If the bead is plugged, it doesn’t function properly. Resin beds with smaller beads, or short-path technology, do a better job of managing metals in solution over conventional resin.
What a scientist might say and what it means:
Scientifically engineered resin utilizes nanotechnology to help propagate ions into and out of the beads at the fastest possible rate, thus reducing hardness leakage in the exhaustion cycle and minimizing salt use in the regeneration cycle. The enhanced diffusivity, optimized kinetics and better surface to volume ratio make resins with shorter paths superior to Gaussian resin by reducing leakage and optimizing water and regenerant use.[2] What this means is that utilizing smaller beads with shorter paths allow ions to spread (diffuse) across and through the resins (inside and outside) surface area (surface-to-volume ratio), improving the rate of ion exchange (optimized kinetics.)
Again, for most softening applications, using Gaussian resin is a standard practice and totally acceptable. The introduction of UPS and short path technology puts another tool in your toolbox. The industry is asked to start policing itself to increase efficiency to reduce water waste and chloride discharge. UPS is an existing technology with years of historical data that lends itself to building systems for regions requiring water conservation and reduced waste solids. Please consider both existing technologies and new advancements for creating best practices – it will save our industry and more…
References
- Uniformity coefficient is the numerical value obtained by dividing the sieve opening (in millimeters) which retains 40 percent of the sample by that which retains 90 percent.
- Meyers, P. (2022, January 6) Personal Correspondence – E-Mail
- DeSilva, F. (1999, March 17). Essentials of Ion Exchange. Paper, Presented at the 25th Annual WQA Convention, p. 2
- Dardel, F. (2017). Ion Exchange Resin Properties. Retrieved from http://www.dardel.info/IX/resin_properties.html
About the author 
Matthew Wirth is a Water Professional with 42 years of experience, working at multiple levels in the water industry. The scope of his experience includes heavy industrial and commercial systems to public and private well applications – both customer direct and nationwide distribution. In addition to front line field support (including design, application and service troubleshooting), Wirth is an approved trainer for several industry organizations, state CEU programs and an author for trade periodicals. He holds a Water Conditioning Master license in the State of Minnesota, a BA Degree in organizational management and communication from Concordia University (St. Paul, MN) and received his engineering training at the South Dakota School of Mines and Technology in Rapid City, SD. Wirth is the General Manager of the Pargreen Sales Engineering-Water Division in Chicago, IL. He can be reached at (630) 433-7760.