1. Understanding Bleach Degradation
Presentation introduction slide
Bernard Bubnis
NovaCem Laboratories, Inc.
Oxford, OH USA
Sponsored by: Powell Fabrication

2. NovaChem Laboratories, Inc.
Testing bleach since 1989
1990’s - AWWA Bleach Decomposition Study
Collaboration with Powell Fabrication & Manufacturing
Decomposition Model Studies
Chemistry Validation
Measurement Protocols for
Inorganic disinfection by-products
Transition metal ions
NovaChem Laboratories, Inc introduction slide

3. Bleach Degradation Parameters That Influence Decomposition
Concentration
Temperature
Ionic Strength
Transition Metal Ions
Bleach Degradation
Bleach loss or degradation (decomposition) is largely dependent on 4 parameters (concentration, temperature, ionic strength, and transition metal ions). Each of the parameters if not managed properly will lead to bleach loss, shorter bleach storage times or increased oxygen formation in the stored bleach. This presentation will address each of these areas in order to show that with proper consideration, higher bleach concentration in stored bleach can be attained.

4. that controls decomposition disinfection by-products ?
What is the chemistry
that controls decomposition
and the formation of
disinfection by-products ?
Question – What is the chemistry that controls decomposition and the formation of disinfection by-products?

5. Bleach Decomposition 2nd Order Rate = k2 [OCl-]2
Primary Pathway OCl- + OCl- → ClO Cl-
OCl- + ClO2- → ClO Cl-
Stoichiometry 3OCl- → ClO Cl-
Secondary Pathway OCl- + OCl- → O Cl-
“uncatalyzed” and “catalyzed”
Bleach Decomposition – Chemistry
The chemistry of bleach decomposition is well understood.
Bleach decomposition is a second order process with respect to hypochlorite ion concentration. The means that for each mole of bleach, the rate of bleach loss is equal to the square of the hypochlorite ion concentration. In simple terms … if the moles of hypochlorite ion equal 2, then, the rate is equal to 4… 2 squared …. If the moles of hypochlorite ion equal 4, then, the rate is equal to16 … 4 squared. Higher bleach concentration decomposes faster than bleach at lower concentrations.
The mechanism of the decomposition requires 2 hypochlorite ions to react to form a short-term intermediate …chlorite ion, ClO2- …which in turn rapidly reacts with hypochlorite ion to form chlorate ion, ClO3- and chloride ion, Cl-. Chlorite ion does not build up in bleach solutions. It is rapidly consumed, so no need to monitor chlorite ion concentration in bleach solutions.
Thus, the Stoichiometry of the decomposition is every 3 moles of hypochlorite ion lost to decomposition will result in the formation of 1 mole of chlorate ion and 2 moles of chloride ion.
There is a secondary minor bleach decomposition pathway that leads to oxygen formation and chloride ion. The “uncatalyzed reaction” is minor, <10% of the decomposition. However in the presence of certain transition metal ion, a “catalyzed reaction” occurs that accelerates the formation of oxygen.

6. OCl- Lost …ClO3- Formed Plot of hypo lost vs. chlorate ion formed
The data in this slide developed during the AWWA bleach project in the early 1990’s clearly shows the hypochlorite ion – chlorate ion formation relationship and confirms the stoichiometry of the decomposition mechanism.

7. Decomposition Comparison (90°F) Concentration Effect
Plot of hypo concentration loss during storage at 90°F
As noted, concentration is a very important parameter to consider when trying to minimize bleach loss during storage. As predicted by the rate law, the plot of bleach (at 2 concentrations) over time at 90°F clearly shows a much faster and greater bleach loss for the bleach with the larger initial bleach concentration. The 13% bleach after 60 days has a half-life of 48.5 days with a bleach concentration that is 43% of the initial stored bleach. In contrast, the 10% bleach after 45 days has a calculated half-life of 94.7 days and 60% of the original concentration is retained.
This slide shows the power of using decomposition software to model decomposition. The use of this tool enables both bleach manufactures and consumers to better understand how to maximize bleach storage over a wide-range of concentrations and temperatures. Additional examples of modeling will show other aspects that will be helpful for the management of bleach products.

8. 2nd Order Plot vs. Temperature
Plot of 1/OCl- vs. time at varying temperature
As mentioned, temperature is also very important in managing bleach decomposition. The slope of the second order plots shows that the rate of decomposition increases with increasing temperature.

9. Decomposition Comparison (13%) Temperature Effect
Plot of Temperature Effect
In this slide, the decomposition of 13% bleach is modeled over 60 days at 68°F and 90°F. The modeled data show a much greater bleach loss for the bleach stored a 90°F. A quick look at the modeled data shows that the bleach stored at 68°F is almost 2x as strong in bleach compared to the bleach stored at 90°F. Thus, storage at higher temperatures will lead to more bleach loss.
A quick review of the chemistry up to this point shows how bleach decomposes with respect to concentration and temperature. The next slide will show how ionic-strength affects bleach decomposition.
As you know, when bleach is produced using chlorine and caustic, 1 mole of chloride ion is produced for every mole of hypochlorite ion produced….thus, bleach has a high chloride ion (salt) concentration. In addition, bleach loss by the primary decomposition pathway produces 2 moles of chloride ion for every 3 moles of hypochlorite ion. Further, the minor oxygen formation pathway produces2 moles of chloride ion for every 2 moles of hypochlorite ion …. the chemistry predicts that stored bleach has a lot of chloride ion originating from bleach production and bleach decomposition. It has a high ionic strength. So, how does this contribute to bleach loss?

10. Rate Constant as a Function of Ionic Strength
Decomposition Rate Constant as a function of ionic strength
To assess how the ionic strength affects decomposition, the plot of experimentally determined rate constants at various ionic strength and temperatures is presented.
If one looks at any one temperature, it is quickly observed that the rate constant increases as the ionic strength increases.
In addition, it is also quickly observed that the rate constant increases with an increase in temperature.
Thus, the data show that with an increase in ionic strength, one can expect to observe faster bleach decomposition and more bleach loss.
The next slide shows the difference in bleach decomposition for typical 13% bleach and bleach that has a lower chloride ion concentration and thus a lower ionic strength.

11. Decomposition Comparison (90°F) HSLS vs. Typical 13%
HSLS vs. Typical Bleach Decomposition
The typical 13% bleach after 60 days has a bleach concentration that is 43% of the initial stored bleach. In contrast, the HSLS – High Strength Low Salt - 13% bleach after 60 days has 59% of the original concentration. What we can conclude from the data is that ionic strength matters and that it can be managed.

12. HSLS Bleach “High Strength Low Salt”
30 Wt% NaOCl
385 GPL Available Chlorine
≈1 Wt% NaOH
8.5 Wt% NaCl
13 Wt% NaOCl (traditional)
10.4 Wt% NaCl
HSLS vs. Typical Info
Note the initial chloride ion concentration … 30% HSLS bleach has a much lower initial chloride ion concentration compared to typical 13% bleach. 8.5% vs. 10.4%

13. HSLS Bleach “High Strength Low Salt”
13% Wt NaOCl (traditional)
10.4% Wt NaCl
13% Wt HSLS % Wt NaCl
6% Wt HSLS % Wt NaCl
Diluted HSLS
When diluted, HSLS has an even lower salt (NaCl) concentration
13% % vs 10.4%
6% -- even less 1.7%

14. It is not obvious that ionic strength might affect oxygen formation … but it does (30% less) Less oxygen ….more bleach
Ionic strength and oxygen formation
Oxygen is the final parameter that can be managed. This slide shows oxygen formation of typical 13% bleach and 13% HSLS bleach at 90F. The modeled data show that 30% less oxygen is formed … less oxygen formed means more bleach strength retained in addition oxygen formation can lead to other long-term storage issues.

15. Decomposition Comparison (90°F) Transition Metal Ions
Bleach loss due to 0.5 mg/L Nickel
The formation of oxygen is best illustrated by modeling the bleach loss in the presence of 0.5 ppm nickel. The graphs show that additional bleach loss can be expected when the catalyzed oxygen forming pathway is operating. Typical 13% can be expected to retain 43% of the original bleach concentration after 60 days. Under the same conditions, when typical 13% bleach contains 0.5 ppm nickel only 24% of the original concentration is expected.

16. OCl- Lost … Catalyzed Reaction
Hypo lost vs metal ion
In a way previously shown for bleach loss vs temperature, a 2nd order plot for various metals shows that Nickel ion has a profound catalytic effect on bleach loss and oxygen formation. Copper also can be problematic … mostly in combination with nickel. It should be noted that the concentration of iron does not initiate the catalytic formation of oxygen until the concentration approaches 40 ppm. Thus, iron is not so much a problem for oxygen as it is for solution clarity and color due to the rust tint that it imparts on the manufactured bleach.

17. Oxygen Comparison (90°F) 0.5 mg/L Ni vs. Typical 13%
Oxygen formation with 0.5 ppm nickel
As mentioned very early in this presentation, both decomposition pathways operate and lead to bleach loss. This slide shows this in a different way…
It is quickly observed that the amount of oxygen typically produced in the low-transition metal ion bleach is much lower than that produced in bleach that contains 0.5 ppm nickel. Up to 11x more oxygen can be expected after 60 days storage.

18. Decomposition as a Function of pH
It is very important to maintain the pH of bleach solutions. As the pH of the bleach solution approaches pH 11, the decomposition will begin to accelerate as shown by the plot of the rate constant vs. pH. In practice, we have seen at NovaChem that most of the bleach pH measurements are between pH 12.5 – One should remember that pH below 11 initiates a more rapid decomposition pathway. At a pH above pH 13.5, it appears that decomposition is accelerated due to an ionic strength effect.

19. Chlorate Formation as a Function of pH
As mentioned throughout this presentation, when bleach decomposes it primarily forms chlorate ion. This also holds for the accelerated pathway operating below pH 11.

20. What Happens in UV-light ?
This slide summarizes what one might see when bleach is subjected to UV-light.
The hypochlorite ion concentration goes down … bleach is lost
Chlorate ion concentration goes up … chlorate ion is formed
Oxygen level goes up … oxygen is formed
Steady-state level of chlorite ion … intermediate in the concentration

21. Unwanted By-Products What are they ? How do they get into the bleach?
Bromate BrO3-
Chlorate ClO3-
Perchlorate ClO4-
How do they get into the bleach?
Raw materials and decomposition
Unwanted By-Products
Outside of the typical bleach production analyses, the end-users of manufactured bleach are asking the producers to provide documentation on 3 unwanted by-products in the bleach….chlorate ion, bromate ion and perchlorate ion.
It is not unusual for end-use customers to require documentation on their concentration in the delivered bleach. So, how do these unwanted by-products get into the bleach?
We have discussed how chlorate ion is the primary product of bleach decomposition. It can also be found in lower grades of caustic … thus, some care and consideration needs to be given to the caustic source.

22. Bromate Ion, BrO3- Bromide ion in salt used to make Cl2
Forms Br2
Reacts with caustic to form BrO3-
Impurity in caustic
Bromate Ion
Bromate ion originates from the presence of bromide ion in the salt used to make chlorine. Just as chloride will form chlorine, the presence of bromide ion will form bromine. Bromine once formed will undergo a series of reactions that lead to the formation of bromate ion. Similar to chlorine, it can also be found in caustic.

23. Perchlorate Ion, ClO4- Reaction OCl- + ClO3- → ClO4- + Cl- Rate Law
Source: Water Research Foundation, 2009, An Assessment of the Factors that Influence the Formation of Perchlorate and Other Contaminants
Reaction
OCl- + ClO3- → ClO Cl-
Strongly dependent on Temperature and Ionic Strength
Rate Law
d[ClO4-]/dt = kClO4- [OCl-] [ClO3-]
Rate Constant
log (kClO4- ) = (I) + log (2.084 x 1016 x T x e -1.01x10^5/RT x e -10^6/R)
Perchlorate Ion
Perchlorate ion has become a bleach issue due to health concerns. Numerous studies have been undertaken to assess the health issues and more recently a study was undertaken by the Water Research Foundation to understand how it is formed in bleach.
Perchlorate ion is produced in bleach when chlorate ion reacts with hypochlorite ion. It’s formation is strongly dependent on
Chlorate ion
Temperature
Ionic strength
Thus, from a chemistry point of view, if chlorate ion formation is managed, perchlorate ion can be minimized.
The 2009 research project developed the rate law. With application of the Eyring Equation, the rate constant for perchlorate ion formation can be calculated at any storage temperature.
Because we have kinetic information and we know how the relationships for temperature and ionic strength , it is now possible to model perchlorate ion formation.

24. Perchlorate Ion, ClO4- Perchlorate Ion Curves in Stored Bleach
The modeled formation of perchlorate ion is shown for typical 13% bleach and 13% HSLS bleach at 90F. Again, we know that if we manage chlorate ion, we manage perchlorate ion. The information in this slide illustrates that HSLS bleach has a lower perchlorate ion concentration compared to typical 13% bleach. The difference is the ionic strength of the solutions … >10% NaCl in typical 13% bleach and <4% NaCl in HSLS bleach diluted to 13%.

25. Basis of a Chemical Model
Chlorate and Oxygen Formation
(3kCl + 2kox)t = 1/[OCl-]t – 1/[OCl-]0
Perchlorate Ion Formation
d[ClO4-]/dt = kClO4- [OCl-] [ClO3-]
log (kClO4- ) = (I) + log (2.084 x 1016 x T x e -1.01x10^5/RT x e -10^6/R)
Basis of a Chemical Model
As a direct result of the studies on bleach decomposition, the kinetic information can be applied to develop a predictive model.

26. Decomposition Software Modeling
What can you model ?
Bleach Loss
Chlorate Ion Formation
Oxygen Formation
Perchlorate Ion Formation
What factors can you manipulate?
Concentration
Temperature
Caustic strength
Ionic strength
Metal ion concentration
Time parameters
Decomposition Software Modeling
The chemistry detail allows for the modeling of …bleach loss …chlorate ion formation … oxygen formation … and perchlorate ion formation post production.
Modeling software allows both producers and end-users to evaluate various storage scenarios by adjusting various parameters that are important for understanding bleach loss and by-product formation : concentration … temperature … caustic strength … transition metal ion concentration … ionic strength … time parameters.

27. Powell Software Powell Software
This is a screen shot of the information page for the software program developed by Powell Fabrication. There are a number of input windows that allows for customized modeling. One should note that the Powell Software is structured for the engineering side of bleach production and storage. I say this because the species and units coincide with the information that might be typically expected and requested within the industry. For example g/L NaCl as opposed to g/L Cl-. This small change is very helpful and a time saver because is removes the need to convert concentrations to reportable and normally expected chemical species.

28. Powell Software Powell Software
The software package also permits various comparisons to be presented. This chart shows the simultaneous comparison of bleach loss and chlorate ion build-up for 2 bleach sources.

29. Powell Software Powell Software
This chart shows the simultaneous comparison of bleach loss and oxygen build-up for 2 bleach sources.

30. Powell Software Powell Software
This chart shows the simultaneous comparison of bleach loss and perchlorate ion build-up for 2 bleach sources.

31. Bleach Testing Essential Analyses: (Tier 1)
Wt% NaOCl g/L Available Cl2 Specific gravity
Wt% NaOH Wt% Na2CO3 mg/L chlorate
Optional Analyses I: (Tier 2)
mg/L bromate mg/L perchlorate mg/L Fe, Cu, Ni
Optional Analysis II: (Tier 3)
Filter test Dissolved Solids Suspended Solids
Bleach Testing
There are many tests that can be performed on bleach to evaluate quality. Our observation at NovaChem have led to a tier system to help producers and end-users decide on which analyses should be performed regularly and which analyses might need to fun less frequently.
Tier 1 analyses are fundamental tests to assess bleach strength and quality.
Tier 2 analyses are tests that provide information on by-products and oxygen formation.
Tier 3 analyses are additional tests that might be required to meet bleach specification or end-user quality standards.
It is a common request for bleach samples arriving at NovaChem to undergo any or all of the above tests.

32. ClO3- Normalized Result Calculation
INPUTS
Maximum Use Level (MUL), mg/L 80
Trade % Bleach
Vol of Hypo Rec'd, mL
Vol of Peroxide, mL
Vol of Hypo Sample, mL 125
Peroxide Dilution Correction
Hypo Density, g/mL
Chlorate analysis value, mg/L 128
Normalization Factor (NF)
NF = (MUL) (Peroxide Dil Correction) (1/Hypo Density) ( 1/10^3) (1/10^3) NF = E-05
Normalized Result (NR)
NR = Test Result * NF * 10^3 ug/L
NR = ug/L <200 ug/L is acceptable
Chlorate Ion Normalized Result
An example of why a test might be requested is the chlorate ion normalized result calculation. This calculated number may be required of the producer to certify that delivered bleach meets a standard. Based on the inputs of known and measured data, a calculation is performed to produce a normalized result (NR). The calculated NR must be <200 ug/L to meet the standard.
Based on the equation shown and used to calculate the NR, the measured chlorate ion concentration should be less than 2,000 to meet the 200 ug/L standard.

33. Filter Test Operations Tool Particulate matter causes problems
In-field testing determined the parameters
At 20 inches of Hg, 1 liter of bleach should filter through 0.8 micron filter paper in < 3 minutes
Filter Test
The filter test is a widely used test to assess the level of particulate matter in delivered bleach. As everyone is aware, over-time it is not unusual for solid matter to fall out of solution. When this happens, operational issues can develop. This test was initially developed at East Bay Municipal Authority (San Francisco) where it was observed that bleach that was more easily filtered resulted easier handling and application. This process was standardized and formalized through a study funded by Powell Fabrication with NovaChem Laboratories.

34. Suggested Bleach QA Manage the Decomposition Temperature
Concentration
Temperature
Transition Metal Ions
Ionic Strength
Manage the Storage and Delivery
Model the Bleach and Verify
Make Measurements
Tier I analysis (minimum)
Suggested Bleach QA
The industry has made great progress in the production of liquid bleach. Many new and innovative products are available and producers keep finding ways to improve upon the quality of the delivered product.
Paramount to delivering a premium product is the management of bleach delivery and storage. It is my personal opinion that a very high quality product can be produced and delivered to a growing end-user customer base by adhering to a QA plan that includes
Managing the Decomposition
Managing how bleach is delivered and stored
Modeling and Verification
Make Measurements
This concludes this presentation. I want to thank you for your attention and I would like to acknowledge and thank Powell Fabrication for their support.