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Mixing Resins in Your Float:
Can You? Should You? And What to Look Out For
By Dick Chmielewski

Summary: A little of this and a little of that may work in spicing a pot of stew, but when it comes to ion exchange float, you'd better know all the considerations in choosing new resin to add. More often than not, it's a like-to-like equation. Here, such issues are discussed in detail for the dealer, who may also do commercial/light industrial work.

Substitutions of resin in softeners or demineralizers can be made if proper attention to physical and chemical characteristics of the resin are kept in mind. What should you consider when facing the choice of mixing different manufacturers' products when you need to top-off tanks or add to your float of resin? Not all resins are identical, even from the same supplier and with the same brand name.

Important characteristics include particle size, capacity, moisture content, physical strength, resin color and taste and odor factors. In addition, floats that contain anion resins require attention to the type of anion resin to be used. This article outlines the steps you should take when faced with this choice. In all cases, the first step is to make sure you know what's in your float and all of its qualifying characteristics. Make sure your resin supplier knows what's in the float as well.

Softener floats
In many cases, softening resins can be interchanged without undue difficulty. Attributes such as capacity and moisture of the new resins should be closely matched if the resin being topped off has given satisfactory performance. Also, a float containing fine mesh resin should generally not be mixed with one of coarse mesh resin. A resin that has increased water retention due to swelling from chlorine attack may best be topped off with similar used resin from other resins from the same float when practical. Although macroporous resins can be mixed with gel resins in some circumstances, there is some danger that the stronger resin will crush and or grind down the weaker resin. Therefore, most substitutions should be of the same type gel-to-gel or macroporous-to-macroporous resins as those already in the float.

Finally, while there's no technical reason, some customers perceive an advantage to dark color or to light color resin, so it's usually desirable to specify resin color such that there's no surprise (see Table 1).

Mixed Resin Glossary

acrylic—Resin base made of polyacrylate rather than the more common polystyrene.

coarse mesh—The larger end of bead size spectrum. Normal bead size is 16-50 mesh (0.3-1.2 mm). Coarse grade is typically 16-30 mesh (0.6-1.2 mm). Results in lower pressure drop for equivalent bed depth.

color throw—The tendency for a new resin to impart "throw" color to the water being treated. It's common to have some initial color throw with new resin for the first several bed volumes.

crosslinking—Most resin beads are made with a polystyrene crosslinked (chemical bonds
formed between polymer chains) using divinylbenzene (DVB) as the crossslinking agent.

DVB—Divinylbenzene the common crosslinking agent for making resin beads.

fine mesh—The smaller end of the bead size spectrum. Normally 30-50 mesh (0.3-0.6

float—The inventory of resin in PEDI (portable exchange deionization) operation. If it's not designated to a specific customer or account, it's part of the operator's "float".

gel or gelular—Chemical definition of a gel is a colloid consisting of macromolecules with
adsorbed water, although the macromolecules themselves are not water soluble. Gels are clear and appear to be uniform under low power magnification.

macroporous—Resin polymer structure contains discrete pores or holes. These pores increase the total surface area but reduce the capacity. Under low power magnification, one can see the porous nature of a macroporous resin. Macroporous resins are opaque.

moisture content—Resin beads contain a certain percentage water. This is known as the moisture content. Oxidation (or chlorination) of resin beads will increase moisture content, decreasing bead hardness and strength. In extreme cases, beads become "mushy" or "gummy".

styrenic—Resin base made of polystyrene crosslinked with DVB.

SBA—Strong Base Anion resins have the ability to split a neutral salt, for example, exchanging OH- for Cl-.

Type I/Type II—Refers to functional group used in SBA resins. Type I uses trimethylamine. Type II uses dimethylethanolamine.

WBA—Weak Base Anion resins do not have the ability to split a neutral salt.

Separate bed deionizer
In separate bed deionization (DI), or demineralization, floats, the above comments referring to softener resins generally apply to those of the cation exchange resins.

Weak base anion resins
In a separate bed DI, the choice of anion resin is far more complicated than the choice of cation resin. There are many more choices. Some separate bed floats include weakly basic anion (WBA) resins. These are almost exclusively macroporous, styrenic weak bases. Here, the issue of resin color isn't important except for personal taste and appearance, but the issue of moisture content and capacity is even more important. The very high capacity weak based resins with low moisture, such as are used in the sugar industry are undesirable as make up of demineralizing resins because they are slow kinetically and don't exchange ions rapidly enough to perform well.

These resins also have a small and sometimes significant fraction of strong base capacity depending on their intended application. With some WBA resins, the strong base capacity is significant, resulting in high pH and fishy odors coming from the weak based resin. This would not be a good choice for potable water, unless specific conditioning of the resin is practiced. On the other hand, some weakly basic floats depend on the strongly basic functionality to help remove alkalinity and carbon dioxide. Here, the weak base acrylic and weak base polyamine have advantages over their styrenic counterparts, but they're gel types with different kinetic rates and should be considered only for total replacement. The polyamine weak base resins are known to have poor physical stability and are not the best choice in a float where the resins are regenerated frequently.

Overall, the styrenic macroporous weak base resins have been the industrial choice due to the best combination of capacity, durability and cost.

(See Table 2.)

Strong base anion resins
Strong base anion (SBA) resins include Type I, Type II and acrylic resins. Type I resins are more thermally and chemically stable than Type II resins. The ion exchange functionality in strong base resins gradually converts from strongly basic to weakly basic. The rate at which this happens slows dramatically after the first year but not until a substantial amount of this conversion has already happened. Since Type II resins lose salt-splitting capacity faster than Type I resins, they're not the best choice for floats where silica leakage is important to the end user. The resulting combination of efficiently regenerated weak base and silica- and CO2-removing strong base make these resins excellent performers on certain waters especially those high in chlorides where silica removal is also desired. Some operators use topping off as way to maintain higher levels of strong base capacity of these mixed anion beds.

The Type I resins are popular because they provide better water quality, particularly from a silica leakage standpoint. And, because they're more chemically stable, they tend to last longer than the Type IIs. However, Type I resins are more prone to organic fouling, than Type II resins and aren't the best choice in waters with a tendency of organic fouling-that is for waters with high total organic carbon (TOC) and/or color. Acrylic resins are sometimes used in waters that have high levels of organics, since their functional group makes them a Type I anion resin that's made on a different polymer backbone. They enjoy the same improved ability to remove silica.

Acrylic anion resins are thermally and chemically less stable than styrenic anion resins and instead of conversion from strongly to weakly basic, they simply lose capacity. Except for color removal applications, they're rarely used in portable exchange because of the stability issues and economics.

In separate bed applications, particle size and color are seldom important issues. However, operators who identify resin strictly by color can be confused if a new batch of resin of a different color is ordered. Keep in mind that batch-to-batch variations occur in all resins, so some color variation will always occur.

Mixed bed demineralizer
In mixed bed floats, color and particle size become extremely important issues. Both cation and anion components need to be evaluated and initial color and final color need to be considered. Resin color is quite important in mixed beds because color difference between the cation and anion resin is the primary means of verifying proper separation during regeneration. In most cases, where Type I anion resin is used, the cation resin should usually be dark brown or black. However, when Type II anion resins are used-since these resins turn very dark red during service-it may be better to have a light color cation resin.

Particle size in a mixed bed is far more important than in a separate bed, because the separation of the two resins depends in part on particle size difference. However, all resins deteriorate physically over time and an older mixed bed may not have a significant particle size difference between the cation and anion resin.

From a chemical standpoint, it's generally unwise to mix the Type I and Type II resins together. Thus, a mixed bed float using a Type II anion would generally not be well served by topping off with the Type I. This is because of stability and performance differences between the two types resins.

Before making any decision as to resin addition or full replacement, the float resin should be evaluated to determine its present condition. This is generally done by taking several samples at random and having them analyzed by a qualified laboratory. The result of this analysis is a prediction of the floats capabilities and overall opinion as to resin condition. This information is used to determine whether it's time to replace part or all of the resin or to simply add more resin to make up for losses. The use of the float and end-user requirements must be taken into account when deciding what type of resin needs to be in the float. The industrial customers have far different needs than pharmaceutical or semiconductor customers. Working mixed beds have far less stringent purity requirements than polishing mixed beds but may have faster kinetics, which suggests the same resin may not do as well in both applications.

All of these factors need to be reviewed before the decision is made as to whether to top off or fully replace a resin. It is usually a decision based on performance and economics. Table 3 provides guidelines on replacing resin. The brand of resin to use for replacement or a determination if a particular resin from one manufacturer is compatible with an existing float resin can be made using these facts instead of basing the decision on fear or ignorance. In the final analysis, it's a combination of planning, the technical ability and support of the resin supplier in helping the user to make a good choice.

About the author
Dick Chmielewski is West Coast technical representative for ResinTech Inc., of Cherry Hill, N.J., and has been in the water treatment industry for 20 years. He has a bachelor's degree in chemical engineering from the New Jersey Institute of Technology and a master's degree in the same study from University of California-Berkeley. Chmielewski can be reached at (760) 918-0803, (760) 918-0831 (fax) or email:

Table 1. Features to Consider with Softening (Cation) Resin

Crosslinking Level (7, 8 or 10% DVB)

  • Total exchange capacity: Higher crosslinking = higher capacity
  • Moisture content: Higher crosslinking = lower moisture
 Bead Size
  • Standard distribution
  • Coarse mesh
  • Fine Mesh
16 - 50 mesh (0.3 - 1.2 mm)
16 - 30 mesh (0.6 - 1.2 mm)
30 - 50 mesh (0.3 - 0.6 mm)

Gel vs. Macroporous

  • Gels are clear
  • Macroporous are opaque
Bead Color (and variations)
  • Amber
  • Gold
  • Brown
  • Black

 Table 2. Anion Resin Choices

 Strong Base

  • Styrenic Type I and Type II (gels)
  • Styrenic Type I and Type II (porous gels)
  • Acrylic Type I (gels)

 Weak Base

  • Styrenic macroporous
  • Acrylics
  • Epoxy polyamine

Table 3. Guidelines for Replacing Resin
Strong Acid Cation Resin
  • Total capacity falls below 85% of new capacity
  • Moisture content increases more than 10% above specification
  • Performance
For 8% crosslinked with spec of 1.95 meq/ml, consider replacing when total capacity falls below 1.7 meq/ml
—For resin with 45% moisture, consider replacing when moisture increases beyond 50%
—When quality can no longer be obtained
Strong Base Anion Resin
  • Capacity

  • Performance

  • Moisture content
For Type 1, when salt splitting capacity falls to 75% of specification
—For Type II, when salt splitting capacity falls to 50% of specification

—When silica leakage is excessive
(higher than your customer requires)
—When resin no longer rinses to quality and cleaning isn't effective

—Increases more than 10% above spec
Weak Base Anion Resins
  • Capacity
  • Performance
  • Moisture content
—When capacity falls to 75% of spec
—When resin no longer rinses to quality
—Increases more than 10% above spec
All Types of Resins
  • When irreversible fouling occurs
  • Bead integrity

—When more than 20-25% beads broke


Security Basics
By Pete Simpson

Summary: The online attacks directed at and earlier this year—as well as the Y2K bug threat and imbedded viruses from last year—have businesses large and small concerned with breaches of their information systems and data security. But it's often the things you do to protect against the small things that will offer you the most peace of mind.

Information technology, or IT, is a broad concept.

Breach of IT security can result in unauthorized access of resources, intrusion of viruses, theft of data and loss of competitive advantage.

Media exposure leads the public to believe that most security violations are the results of hackers or "outsiders." However, many unauthorized acts-including malicious acts-are carried out by disgruntled employees or "insiders." This illustrates the importance of securing computer-based resources from both "outsiders" and "insiders."

Who is affected?
Technology has become so prevalent that it affects almost every aspect of daily life. Computers are at the core of most businesses, ranging from accounting to credit checking. Computers are responsible for maintaining bank accounts, medical records, Department of Motor Vehicles reports and personal and business credit history. Clearly, everyone who has a credit card or uses an automated teller machine must be concerned with the accuracy and privacy of their personal information and, therefore, must be concerned with IT security.

Why is there concern?
Home users and businesses are finding online shopping, or e-commerce, appealing because of the convenience, simplicity and robustness (not to mention the often lack of sales taxes required). This widespread availability and acceptance of computers has dramatically increased the number of people with the ability to compromise data.

As prices continue to drop and people become more comfortable with technology, the reliance on computer-based resources will continue to increase. As this dependence develops, security exposures may lead to disastrous results with possible financial and legal ramifications. At a minimum, a security breach will result in lost time and decreased productivity while a "clean up" effort occurs. More than likely, however, the results will be much worse. Financial loss as well as non-monetary effects will occur. For example, if a water conditioning dealership's customer information was stolen, it would lose credibility, no longer be able to attract clients and have their valuable information sold to the highest bidder.

Security objectives
Make information unavailable to those who are unauthorized to access it. Strict controls are a must to ensure that only those persons who need access to certain information have that access. The "need-to-know" works well as the key. The concept of allowing access to information or resources only to those who need it is called access control.

Passwords are the most common form of access control and the most common form of security breach is the compromising of these passwords. Requiring strong passwords is the first step in preventing unauthorized individuals from accessing sensitive information. Protecting these passwords is one of the most fundamental principles of computer security.

Imagine your business as a typical suburban house. A password can be likened to a front door key. No one can enter the house without the key, but it can easily be lost, misplaced or stolen. Implementing a strong password policy is inexpensive, doesn't require technical skills and should be taken extremely seriously. Businesses should create and implement computer security policy that educates employees on good password selection, use duration and confidentiality.

Poorly chosen user passwords constitute the most common threat to computerized data.

There are several recent, dangerous security vulnerabilities that have been highlighted in national news-but nothing matches the threat and ubiquity of poorly chosen passwords. In fact, you could probably combine all the current buffer overflows, input-validation attacks and data-driven attacks and still not match the menace of easily guessed passwords.

Figure 1. Password policy
In general, the following guidelines should be a part of any password policy:
1. Each Windows 95/98/NT password must be seven or 14 characters long. Having any other length jeopardizes the strength of the password.
2. Passwords should never contain proper nouns or dictionary words.
3. Passwords should never be popular words, phrases, movies, names and so on.
4. Each password must differ from the user's login name and any reverse or circular shift of that login name.
5. Each password must contain at least one numeric character.
6. The new password must differ from the old one by at least three characters.

There are certain policies that can be instituted (see Figure 1) to make things more difficult for those that would try to compromise your internal security. There's no easy way to enforce these guidelines, but their importance has to be impressed on employees at all levels. For instance, company policy should dictate that users change their passwords immediately to something more difficult to guess.

Feel nervous about imposing strict password policies and guidelines? The alternative is easily hack-able systems. And for those managers and owners who can't understand why data processing staffs have to make such demands, imagine your salary, stock options and personal and corporate emails in the hands of the wrong person. Then reconsider this "inconvenience." Are your systems vulnerable?

Access control
Limit resources available to an employee once they have been authenticated into the computer network or computer. For example, the entire human resources department might need access to employee information such as addresses and birthdays, but only certain individuals within the department need access to compensation information. Access control can be paralleled in our model house as well. The maid has the front door key so she can come in and clean, but that key does not unlock the door to your home office or the safe in the bedroom that contains your important documents.

Integrity ensures that information cannot be modified in unexpected ways. Loss of integrity could result from human error, intentional tampering or even catastrophic events. The consequences of using inaccurate information can be disastrous. Efforts must be made to ensure the accuracy and soundness of data at all times.

When the validity of information is critical, it's often helpful to design controls and checks to ensure accuracy such as batch balancing and control logs.

As individuals and businesses increase information sharing and communication via the Internet, vulnerability to attack or intrusion rises. Authorization, access controls, confidentiality requirements and education are some examples of the technological components available in multi-layered IT security policy. In the world of technological evolution, everyone is a target of electronic crime and needs to be concerned about security.

About the author
Pete Simpson is general manager of UNCO Data Systems of Minneapolis, Minn. His master's degree in business administration and information sciences is from Pepperdine University, and he's with UNCO since 1994. UNCO has been in business since 1969 and specializes in information technology for the water conditioning and bottled water industries.

If you have questions concerning this column, or if there's a topic you would like addressed, please let us know. Contact "ComputerWare: or "Dr. IT" at WC&P Magazine, 2800 E. Fort Lowell Road, Tucson, AZ 85716; (520) 323-6144, (520) 323-7412 (fax) or email: