ION EXCHANGE RESIN TESTING HOW DO I UNDERSTAND WHAT HAS BEEN REPORTED?

Transcription

1 ION EXCHANGE RESIN TESTING HOW DO I UNDERSTAND WHAT HAS BEEN REPORTED? PRESENTED AT: THE 35th ANNUAL ELECTRIC UTILITY CHEMISTRY WORKSHOP AT THE UNIVERSITY OF ILLINOIS JUNE 2 4, 2015 HAWTHORN SUITES BY WYNDHAM CHAMPAIGN, ILLINOIS Presented by: Donald Sales Manager Canada Purolite Corporation Paris, ON Canada Don.Downey@purolite.com

2 Resin capacity, moisture content, bead size, metals fouling, etc. What does it all mean? At last count, there were over twenty five separate ion exchange resin tests (analyses) that were available to end users. Standard testing procedures identify the resin properties but more specific procedures can be used to identify problems with equipment operation. Then, there is the cost to consider; simple cation resin testing (moisture content, total capacity and bead integrity) is in the $200/sample range. However, add to this Chatillon, HIAC particle size, metals and % regeneration test procedures and the lab work can increase to over $1000/sample. In this paper, the author will explain the must do test procedures and why they are important and the key to understanding optional testing and how the results can help with on site equipment trouble shooting. In this paper, we will explore: Introduction to polymer chemistry. Test procedures that will help understand some of the properties of resin beads. The most important test results. Test procedure results that will assist to trouble shoot the equipment. Some of the new technology labs have today. Sampling how to obtain a core sample of the bed. 2

3 Introduction to polymer chemistry Ion exchange resins (IEX) are synthetic resins having a chemical structure based on a cross linked threedimensional polymer molecule into which functional groups such as sulfonic acid and quaternary ammonium are introduced. Most of the polymer bases used for IEX are copolymers of styrene and divinylbenzene (DVB), generally consisting of spherical particles of µm. The cross linked copolymer is synthesized by mixing styrene (which has one vinyl group) with DVB (which has two vinyl groups) and carrying out a suspension polymerization in water. The ion exchange resin is then manufactured by introducing functional groups into this copolymer matrix by means of chemical reactions. The ion exchange groups introduced are chemically bonded to the polymer, and as they cannot move freely, they are known as fixed ions. Mobile ions of opposite sign to the ion exchange groups (H + ions in the case of R SO 3 H) are known as counter ions. If the quantity of the bi functional monomer DVB is increased in the polymerization, a tight porous structure with considerable chain branching is obtained, whereas if, on the other hand, the quantity of DVB is decreased, a loose porous structure without much branching is obtained. As DVB determines the tightness of the porosity, it is known as a cross linking agent. The proportion of DVB in % is referred to as the cross linkage. Since IEX contain pores, the pores are filled with liquid (for the purpose of this paper we will assume water). Ions diffuse throughout these pores and give rise to ion exchanges. The more cross linked the resin is, the more ion diffusion will be difficult. Conversely a low degree of cross linkage will facilitate a greater diffusion of ions. If the cross linkage is too low, however, moisture content becomes excessive, so the resin will be softer and difficult to use, and its strength also decreases. Resins are, therefore, generally used with a cross linkage of about 8%. Ion exchange reactions are carried out with a diffusion of counter ions in the resin particles. The pore structure of the polymer matrix has a considerable effect on these reactions, and cross linkage is, therefore, an important factor when it comes to analyzing the properties of the resin. The styrene DVB copolymer does not absorb water until the functional groups are added. Water absorption is due to hydration of the fixed and counter ions as resins absorbs water, the chains of the polymer matrix elongate and swell until a balance is reached between the water absorbing capacity of the resin and the elastic forces of the polymer. This keeps the resin in its swollen state with stable moisture content. The higher the cross linkage, the less polymer matrix can elongate resulting in a resin with a lower moisture content. Low cross linkage results in a bead with a high moisture content as the swelling increases. As the resin swells during the functionalization phase, micro pores are created in the beads. The ion exchange resin manufactured by simple polymerization of styrene with DVB is transparent and has a gel structure; hence it is known as a gel type ion exchange resin. Using special polymerization techniques, however, IEX resins of higher porosity can be manufactured, creating a macroporous resin. 3

4 Weak acid cation beads Macro strong base anion beads Dyed strong acid cation resin 4

5 Tests that will help understand some of the properties of resin beads. The periodic lab testing of resin samples taken from demineralizer equipment is generally done for two reasons: 1) Maintenance to anticipate any problem. 2) Troubleshooting to help explain any deficiency in the operating units. Often resin testing is delayed for too long (over one year) or until some malfunction occurs. In many cases, the resin may be too far gone in fouling or deterioration and the lab testing may confirm that the resin needs replacement. Then again, lab testing shows the resin to be "normal" in the routine testing but the operating performance is still poor. This is due to the fact that kinetically the resins are "not normal" and may be organically fouled or clogged with extraneous matter those routine lab procedures or excessive regenerations do not remove. Between 1991 and 1999, ASTM developed eight procedures intended to provide data from sample testing to help with trouble shooting in the demineralizer industry. The procedures are as follow: D JUN 1991 Standard Test Method for Operating Performance of Particulate Cation Exchange Materials D (R1998) 15 JUN 1991 Standard Test Method for Operating Performance of Anion Exchange Materials for Strong Acid Removal D JUN 1991 Standard Test Method for Anion Cation Balance of Mixed Bed Ion Exchange Resins D (R1998) 15 DEC 1991 Standard Guides for Detection of Fouling and Degradation of Particulate Ion Exchange Materials D (R1999) 15 APR 1994 Standard Test Method for Physical and Chemical Properties of Particulate Ion Exchange Resins D (R1999) 15 NOV 1994 Standard Test Method for Water Extractable Residue from Particulate Ion Exchange Resins D JUL 1996 Standard Test Method for Precoat Capacity of Powdered Ion Exchange Resins D JUL 1998 Standard Practices for Evaluating the Kinetic Behavior of Ion Exchange Resins D JUN 1999 Standard Test Methods for Physical and Chemical Properties of Powdered Ion Exchange Resins 5

6 What is interesting about the successive development of the test on the preceding page is that they deal with the ion exchange operating performance as a priority and physical, chemical and kinetics properties as secondary. Ion exchange manufacturers reverse this order. This leads us into what resin manufacturers consider the priority for testing resins. I have divided the tests into three categories: standard, operating and optional. Standard tests are ones conducted on every batch of resin manufactured and include the resins and moisture holding capacity, total capacity, and bead integrity. Standard tests MOISTURE HOLDING CAPACITY (MHC): Weighing the moist resin and then drying the sample to constant weight in an oven at 105 o C determines the resin moisture content. An increase in MHC indicates a loss in DVB (cross linkage) from oxidation, and a decrease of MHC shows fouling. At 10% over the upper limit, or 10% below the lower limit, resin should be replaced. TOTAL CAPACITY (TC): A known volume, (weight) of resin is placed in a column and an excess of chemical solution is passed through the resin to be certain it is in known ionic form. The known ions are then eluted from the resin using an excess of a (different) regenerant. The concentration of known ion eluted (or exchanged) is determined quantitatively. The capacity is generally reported as milliequivalent capacity per milliliter (meq/ml) of resin, based on a reference ion form. TC is used to judge a used resin s rate of deterioration and to determine when resin replacement is advisable. The difference in total capacities does not always translate in operating capacity differences. At 30% less capacity than specification, the resin should be replaced. BEAD INTEGRITY (BI): the procedure is to examine the resin under a microscope at 20 to 100X magnification. This is a subjective evaluation of the number of cracked or broken beads reported as a percentage of the total number of beads being viewed through the microscope. Whole beads show no flaws or cracks. Cracked beads allow for faster kinetics to the internal exchange sites of the bead, which will result in lower ion leakage and/or higher throughput capacity. Broken beads are the small fragments that can fill the void spaces between the whole beads, resulting in increased pressure drop across the bed. A photo from the microscope usually accompanies this test. 15% broken beads is the maximum acceptable level 6

7 With these three tests completed, one can usually conclude whether or not the IEX system has a resin problem. If the MHC and TC are within the acceptable limits, then there is no resin oxidation or fouling that is interfering with the resin ability to work. If the BI is good, then there is no pressure stress or osmotic shock causing the bead to fail to exchange. Since resin manufacturers have been asked to help solve IEX problems, we have developed some unique test to check the resin s operating conditions. Operating tests tests that will help you trouble shoot equipment % STRONG BASE (or salt splitting) capacity: Reports % Strong Base exchange sites on strong base anion resins. Most significant loss of % strong base is traceable to organic fouling and leads to poor demineralizer performance. EXTRACTIBLE ORGANICS (mg C/kg resin): Reports the level of extractable organic matter stripped from 10 grams of dewatered AS RECEIVED resin. High levels of organic will lead to long rinsing times. Levels reported: < 5 is acceptable for resin with less than 3 years operation. < 10 are acceptable for resin with less than 5 years operation. > 10 should be replaced regardless of age PERCENT (%) REGENERATION: Reports level of last regeneration done by the sender on a regenerated sample. This test is similar to the total capacity tests except that the elution is performed without first converting the resin to the reference ionic form. A good range for sample from the field is 65 80% METALS CONTENT (PPM): Also referred to as Ash Analysis, this reports quantities of extractable metals (Fe, Cu, Zn, Mn, etc.) stripped from 10 grams of dewatered AS RECEIVED resin. The results are reported in ppm and can help determine resin foulants or regeneration efficiencies. < 400 ppm (total of all metals) is considered low. > 400 to 3500 ppm is considered moderate. > 3500 ppm is considered heavy. HIAC PARTICLE SIZE: Reports % distribution of various beads by size. HIAC is the name of the instrument used. CATION/ANION RATIO: For mixed bed resin samples, reports ratio of anion to cation or stratified beds reporting the ratio of weak to strong in the mixed sample. 7

8 Optional Tests HARDNESS FOULING: Reports the hardness fouling on any resin sample. SILICA FOULING: Usually done on weak base anion resin from demin train where caustic from a SBA is recovered and used for the WBA. OIL FOULING: A blue dye test usually did on a cation resins because of it oleophilic characteristics. % SWELLING: For weak acid cation resins only, full sodium conversion, reports % bead swelling to show possible de cross linking. RINSE REQUIREMENTS: For anion resins only, samples are fully exhausted using 1N H2SO4 then regenerated using 1N NaOH. The sample is then slow rinsed for 3 BV, and then fast rinsed with DI water and the conductivity is checked every BV. OSMOTIC SHOCK: Subjects resin to successive acid and base regenerations continuously for 100 to 300 cycles, reports bead integrity at the end of the cycle. CHATILLON: Reports crush strength of representative sample of beads. POROSITY: Reports resin bead porosity. Some of the new technology labs have today One of the published papers I found provided a very good description of some of the old method of doing ion exchange analysis. George Critz in his IWC paper describes doing metals analysis by titration, particle sizing with sieves/screens, and bead integrity by counting beads under a microscope. Today we have moved from the wet lab of the 1950 s, to the ultra modern facilities which are computer based: 8

9 Particle size analysis of beads has moved from screen/sieve analysis to liquid particle classification: TOC analysis has graduated from PPM levels using UV Vis to low PPB levels with Online TOC monitoring: Metal analysis has gone from titration methods, to liquid chromatography: 9

10 And probably one of the most beneficial improvements is the quality of photos we are getting going from regular telescopes pictures to highly defined images: A selection of the highly define images follow: 300 µm gel resin bead 400 µm macro resin bead 10

11 600 µm resin bead scale fouling 500 µm resin bead bacteria fouling 1 Sampling how to obtain a core sample of the bed. Proper sampling of the resin in an ion exchange unit for analysis is of paramount importance since the results of analysis should lead to positive recommendations for cleaning or replacing the resin. Follow these instructions very carefully to ensure that the sample taken is representative of the whole bed: 1. Operate the unit to its normal exhaustion endpoint; backwash as usual; then regenerate and rinse as normal practice. 2. Isolate the unit; then open the drain valve after opening the manhole (A hot process or condensate polishing unit must be cooled before draining to prevent dehydration of the resin). Inspect the appearance of the top inlet distributor and regenerant distributor, e.g., are they level? Are the openings clogged with resin fines? Do they show any other signs of damage or abnormal condition? 3. Drain the unit to a level slightly above (1 2 ) the bed surface. Observe (and record) the appearance of the bed surface, e.g., clean, dirty, level, hilly, cracks, sloped to side, pulled away from shell, or other abnormal conditions. Using a digital camera take photographs. If bed surface is not level, location of high and low spots should be recorded. The cause should be 11

12 established if possible. (Possible causes: inlet distributor broken or damaged, regenerant distributor broken or damaged, underdrain system problems). 4. Measure and record the elevation of the top of the bed from a standard bench mark e.g., from the inlet distributor or backwash outlet (this determines the actual backwash freeboard). Calculate the actual resin bed depth if possible. 5. Obtain a representative core sample (preferred) or a composite sample taken at three different elevations. Using a 1" diameter PVC pipe with a thread end and cap at the top Push the sampler directly down into the bed. This operation must be very carefully done gently to avoid disturbing the supporting bed or damaging the underdrain system or any mid collector (especially if made of plastic). Attached the cap to the top and withdraw slowly with a twisting motion to retain the full depth of the core. Empty the sample into a 5 gallon plastic bucket, and repeat sampling in a uniform pattern across the surface of the bed if possible, until sufficient sample is collected. (A minimum of 0.5 L is required for a single bed and a minimum of 1.0 L for layered or mixed beds). For vessels 48 Ø and smaller sample form the middle of the vessel will provide a suitable sample. For vessel larger than 48 Ø it is recommend that the area of the top of the bed be divided into 3 quadrants and each quadrant sampled and then all the collected samples mixed into one compensent. Soak resin in container with water from an operating unit. 1/2" of water above resin sample is sufficient. Identify the sample completely i.e. Resin type: Resin Manufacturer: Resin Designation: Type of Ion Exchange Unit: Regenerant Chemical Used: Is sample regenerated or exhausted: Resin age: In cold weather, prevent the sample from freezing. Send the sample to the Ion Exchange Laboratory. If specific operating problems have been encountered, any description or comments are most helpful. 12

13 Concluding notes: When an ion exchange unit is not performing to specification, suspecting resin degradation should be the last resort, ninety nine percent (99%) for WTP problems are not resin. Avoid taking a resin sample scraped quickly from the top of the bed because the condition of the top resin is totally irrelevant of the condition of the bed in general. Such an analysis would not be a beneficial. More than often the resin is dirty due to improper backwash. Air scour if possible and backwash at a flow rate higher than usual but avoiding resin carryover, fines and broken beads are excepted to show up in the backwash water. Review regeneration procedure, carefully checking if proper amount, proper strength and flow rates of regenerant are used. Proper valve operation should also be checked in automatic systems. The best time to take a sample of resin is after normal regeneration. This is especially important if the levels of any contaminants are required. References 1. IWC George Crits: The Significance and Limitations of Laboratory Resin Analysis in Evaluation IEX Operating Performance 2. With permission of John Soper, Process Research Manager, Archer Daniels Midland Co. Decatur, Illinois

14 IEX RESIN TESTING How Do I Understand What Has Been Reported PRESENTED AT: The 35 th ANNUAL ELECTRIC UTILITY CHEMISTRY WORKSHOP UNIVERSITY OF ILLINOIS JUNE 2 TO HAWTHORN SUITES BY WYNDHAM CHAMPAIGN ILLINOIS Presented by: Donald Downey Canadian Sales Manager, Purolite Corporation Paris, ON Canada Don.downey@purolite.com

15 IEX Resin Testing In this paper we will explore: Introduction to polymer chemistry. Test procedures that will help understand some of the properties of resin beads. The most important test results. Test procedure results that will assist to trouble shoot the equipment. Some of the new technology labs have today. Sampling how to obtain a core sample of the bed. Page 2

16 IEX Resin Testing Polymer Chemistry IEX synthetic chemical X linked three dimensional polymer. Most are copolymers of styrene and DVB, µm. High DVB tight porous bead. Low DVB loose porous bead. DVB is cross linking agent. % DVB referred to as the cross linkage. IEX is made up of functional groups or fixed ions and exchange or mobile ions Page 3

17 IEX Resin Testing Polymer Chemistry IEX pores filled with liquid (we will assume water): Ions diffuse throughout pores giving rise to ion exchanges. Higher X linked difficult diffusion, lower X linkage greater diffusion. (Kinetics) Very low X linkage softer bead difficult to use. Resins generally 8% X linkage. Page 4

18 IEX Resin Testing Polymer Chemistry Polymer chains X linked very strong. Insoluble and resistance to melting. Page 5

19 IEX Resin Testing Polymer Chemistry Weak acid cation resin Macro strong base anion resin Dyed strong acid cation resin Page 6

20 IEX Resin Testing TEST The periodic lab testing of resin generally done for two reasons: 1. Maintenance to anticipate any problem. 2. Troubleshooting to help explain any deficiency in the operating units. Many times, after equipment malfunction resin highly fouled or deterioration, lab testing confirms replacement. Page 7

21 IEX Resin Testing ASTM TEST 1991 and 1999, ASTM procedures D JUN 1991: Standard Test Method for Operating Performance of Particulate Cation Exchange Materials D (R1998) 15 JUN 1991: Standard Test Method for Operating Performance of Anion Exchange Materials for Strong Acid Removal D JUN 1991: Standard Test Method for Anion Cation Balance of Mixed Bed Ion Exchange Resins D (R1998) 15 DEC 1991: Standard Guides for Detection of Fouling and Degradation of Particulate Ion Exchange Materials D (R1999) 15 APR 1994: Standard Test Method for Physical and Chemical Properties of Particulate Ion Exchange Resins D (R1999) 15 NOV 1994: Standard Test Method for Water Extractable Residue from Particulate Ion Exchange Resins D JUL 1996: Standard Test Method for Precoat Capacity of Powdered Ion Exchange Resins D JUL 1998: Standard Practices for Evaluating the Kinetic Behavior of Ion Exchange Resins D JUN 1999: Standard Test Methods for Physical and Chemical Properties of Powdered Ion Exchange Resins Page 8

22 IEX Resin Testing ASTM TEST Interesting point successive development ASTM test 1 st 4 in 1991 IEX operating performance Next 2 in 1994 physical, chemical and kinetics properties as secondary. IEX manufacturers reverse this order. The following divides testing into 3 categories: Standard, Operating and Optional. Page 9

23 IEX Resin Testing Standard Test MOISTURE HOLDING CAPACITY (MHC): Drying the sample at 105 o C determines MHC. Increased MHC loss in DVB oxidation Decrease MHC shows fouling. At 10% over the upper limit, or 10% below the lower limit, resin should be replaced. Page 10

24 IEX Resin Testing Standard Test TOTAL CAPACITY (TC): Resin treated excess chemical to known ionic form. Known ions eluted different regenerant. Concentration eluted determined quantitatively. TC reported meq/ml r based reference ion form. At 30% less capacity than specification, the resin should be replaced. Page 11

25 IEX Resin Testing Standard Test BEAD INTEGRITY (BI): Examine IEX at 20 to 100X magnification. Subjective evaluation cracked broken beads. Reported % all beads viewed. Whole beads no flaws or cracks. Cracked beads (> kinetics) lower leakage & higher OC Broken beads fragments fill voids > ΔP. Photo accompanies reports. 15% broken beads is the maximum acceptable level Page 12

26 IEX Resin Testing Standard Test Page 13

27 IEX Resin Testing Standard Test With these three tests completed, one can usually conclude whether or not the IEX system has a resin problem. If the MHC and TC are within the acceptable limits, then there is no resin oxidation or fouling that is interfering with the resin ability to work. If the BI is good, then there is no pressure stress or osmotic shock causing the bead to fail to exchange. Page 14

28 IEX Resin Testing Operating Test Since resin manufacturers have been asked to help solve IEX problems, we have developed some unique test to check the resin s operating conditions. We call them Operating Test which are designed to help trouble shoot system equipment. Page 15

29 IEX Resin Testing Operating Test % STRONG BASE (or salt splitting) capacity: Reports % Strong Base sites SBA resins. Significant loss % SB organic fouling. EXTRACTIBLE ORGANICS (mg C/kg resin): Reports TOC on AS RECEIVED resin. High levels TOC long rinsing times. Levels reported: < 5 acceptable < 3 years operation. < 10 acceptable < 5 years operation. > 10 replace. Page 16

30 IEX Resin Testing Operating Test PERCENT (%) REGENERATION: Reports last regeneration from site. Similar TC elution performed as received. Good range is 65 80% METALS CONTENT (PPM): Reports extractable metals (Fe, Cu, Zn, Mn, etc.) Results reported ppm Determine resin foulants or regeneration efficiencies. < 400 ppm (total of all metals) low. > 400 to 3500 ppm moderate. > 3500 ppm heavy. Page 17

31 IEX Resin Testing Operating Test HIAC PARTICLE SIZE: Reports % distribution of various beads by size. HIAC is the name of the instrument used. CATION/ANION RATIO: Mixed bed samples, reports ratio of anion to cation. Stratified beds reporting the ratio of weak to strong. Page 18

32 IEX Resin Testing Operating Test The paper also refers to other optional troubling shooting test: HARDNESS FOULING: Reports the hardness fouling on any resin sample. SILICA FOULING: Usually done on weak base anion resin from demin train where caustic from a SBA is recovered and used for the WBA. OIL FOULING: A blue dye test usually did on a cation resins because of it oleophilic characteristics. % SWELLING: For weak acid cation resins only, full sodium conversion, reports % bead swelling to show possible de cross linking. Page 19

33 IEX Resin Testing Operating Test RINSE REQUIREMENTS: For anion resins only, samples are fully exhausted using 1N H2SO4 then regenerated using 1N NaOH. The sample is then slow rinsed for 3 BV, and then fast rinsed with DI water and the conductivity is checked every BV. OSMOTIC SHOCK: Subjects resin to successive acid and base regenerations continuously for 100 to 300 cycles, reports bead integrity at the end of the cycle. CHATILLON: Reports crush strength of representative sample of beads. POROSITY: Reports resin bead porosity. Page 20

34 IEX Resin Testing New Lab Technology In a George Critz he describes doing metals analysis by titration, particle sizing with sieves/screens, and bead integrity by counting beads under a microscope. The following is a brief on the new lab Page 21

35 IEX Resin Testing New Lab Technology Particle size analysis of beads has moved from screen/sieve analysis to liquid particle classification: Page 22

36 IEX Resin Testing New Lab Technology TOC analysis has graduated from PPM levels using UV Vis to low PPB levels with Online TOC monitoring: Page 23

37 IEX Resin Testing New Lab Technology Metal analysis has gone from titration methods, to liquid chromatography: Page 24

38 IEX Resin Testing New Lab Technology And probably one of the most beneficial improvements is the quality of photos we are getting going from regular telescopes pictures to highly defined images: Page 25

39 IEX Resin Testing New Lab Technology 600 µm resin bead scale fouling 500 µm resin bead bacteria fouling Page 26

40 IEX Resin Testing How to sample Proper sampling is of paramount importance results lead recommendations for cleaning or replacement. Regenerate and rinse as normal before. Isolate the unit and drain. Inspect for damage. Take photos. Measure record top of the bed from a standard bench mark. Calculate the actual resin bed depth if possible. Obtain a representative core sample taken different locations. 1" Ø pipe with a thread end and cap at the top Page 27

41 IEX Resin Testing How to sample 48 Ø and smaller sample middle vessel Larger than 48 Ø divide 3 quadrants mix into one sample Soak resin in container with water from an operating unit. 1/2" of water above resin sample is sufficient. Identify the sample completely Note any operating problems Page 28

42 IEX Resin Testing Concluding Notes When IEX performing suspecting resin last resort 99% WTP problems are not resin. Avoid sampling top of the bed totally irrelevant of the bed analysis not beneficial. Often IEX dirty poor backwash. Air scour or backwash higher flow rate fines excepted Purolite 2012

43 IEX Resin Testing Concluding Notes Review regen procedure check amount, strength and flow rates of regenerant Best time to sample after normal regeneration. Purolite 2012