Sources of to Cindi Water

7/29/2019 Sources of to Cindi Water

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\\Ressrv5\g\MASTERS\Presentations\Peter\Iwc98\Sources of TOC in DI Water, IWC, 1998, PSM.doc 1

Sources of TOC in Deionized Water

PETER S. MEYERS, ResinTech, Inc.

IWC-98-37Keywords:

Summary: Sources of TOC in water can be from man-made or natural organic matter (NOM) present inthe raw feed-water, or can be caused by leachables from ion exchange resins. In the case of NOMs, theionized portion can be readily removed by anion ion exchange resins. Manmade organics are removed byion exchange only if they are ionized. In ultra-pure water systems, the organic removal resin should beseparate from the deionized resin to avoid the consequence of organic fouling. The best candidates fororganic traps are acrylic strong based anion resins and styrenic resins with high gel phase porosity.

In ultra-pure water systems, leachables coming from the resins themselves are important. New resins usedin ultra-pure water applications require vigorous cleaning to remove leachables. The key to any system

design that requires low TOC is to understand the nature of the organics that are present in the feedwaterand then to select appropriate equipment technologies for their removal

INTRODUCTION

The purpose of this paper is to explore what theterm organics means when used in contextwith water treatment and to describe therelationship between the presence of organicsand ion exchange.

Thirty years ago, ultra-pure water wasdetermined by conductivity or (resistivity) alone,both in the microelectronics industry and in thepower industry. Only the pharmaceuticalindustry was interested in the organic content of the treated water.

If any attention was paid to the organic contentof water in other industries, it was usually due tothe concern of organic fouling of the anion resincomponent in the deionization system.Methods of determining organic content at thattime were rather crude and indirect. Thepharmaceutical industry used a nitrogen ornitrogenous matter test while other industriesused chlorine demand, oxygen demand, and/orpermanganate demand.

Evolution of TOC LimitsPharmaceutical Grade Water

USPStandard

WaterFor

Injection(pre 1998)

WasterFor

Injection(1998)

TOC limit

ppb

None 500

Evolution of TOC LimitsSemiconductor Grade Water

SEMIGuidelines 1989 1992

ppb TOCAttainable 20


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Today, the organic content of water is importantto many industries. The preferred method of describing organic content has become the TotalOrganic Carbon (TOC) measurement. Thismeasurement has replaced mo st of the earlier,less direct methods of measuring organic

content. TOC is a (relatively) simple test that(more) directly measures the organic content of water. However, as of 1998, the availablemethods to measure TOC do not recover 100%of all organic matter that might be present.

TOC measurements will always be somewhatlimited because they only describe concentrationand dont tell us anything about the chemicalstructure of the organics. Future requirementsfor ultra-pure water will almost undoubtedlynecessitate even more accurate methods of determining both the structure, as well as theconcentration of organic matter that may bepresent.

The concern about organic content varies widelyfrom industry to industry. For example, thepharmaceutical industry has adopted a newstandard of 500 ppb of TOC for Water forInjection. The boiler industry has a maximumstandard of 25-50 ppb TOC for high-pressureboilers to prevent corrosion caused by organicchlorides and sulfates. The microelectronicsindustry has a minimum standard of no morethan 10 ppb of TOC.

Most state-of-the-art ultra-pure water systemsexpect 1 or 2 ppb; some hope to produce under1 ppb of TOC. Since low TOC in one industrymay be 500 times what low TOC in anotherindustry means and the reasons for removingTOC are not always the same, the differencesmust be defined in any discussion about thesubject.

The term TOC or Total Organic Carbon, refersto a direct or indirect method of measuring theconcentration of carbon present in a watersupply, and excluding the inorganic forms of

alkalinity (CO 2 , HCO 3 CO 3).

In relatively high TDS water supplies, TOC isgenerally measured by U.V. persulfate oxidationand I.R. detection of carbon dioxide. Inorganiccarbon is removed by acidification and gasstripping. The remaining organic carbon thenreacts with an oxidant (in the presence of acatalyst). The organic carbon is converted tocarbon dioxide, which is removed by a carrier

gas. The concentration of carbon dioxide createdfrom the organics is then determined by infrareddetection.

In order to perform this analysis, the initialinorganic carbon content (large, compared to the

organic content) must first be removed. This isgenerally done by purging the sample withoxygen. Solvents and other purgable organicsare lost during this sample preparation step. Inaddition, some forms of organics are difficult orimpossible to oxidize. The oxidation method of determining organic carbon does not alwaysresult in 100% recovery of the total organiccarbon present.

Another method of measuring TOC involves aless direct approach and is limited to lowconductivity water. Organic carbon is oxidizedin the presence of UV light and an electricaland/or metallic catalyst. The increase inconductivity due to formation of carbon dioxideis used to calculate the concentration of carbondioxide produced in the analyzer.

This method has its own unique advantages anddisadvantages. The conductivity method islimited to relatively low T.D.S. waters and is atits best in ultra-pure water. Since many organiccompounds contain ions other than carbon,hydrogen and oxygen, (such as, chlorine,nitrogen, phosphorous and sulfur), the

conductivity measurement can be distorted bythe presence of inorganic acids created duringthe oxidation step. Various methods are used tominimize this distortion. Another problem withTOC analyzers that use conductivity inference isthat many ultra-pure waters today have lowoxygen contents. Since the oxidation reactionrequires oxygen to convert the organic carbon tocarbon dioxide, the analysis of low levels of

Early TOC Analyzer SchematicUV Persulfate Oxidation

IRDetector

Integrationof CO2 co nc..

Reaction Chamber

UV Light

TOC

PersulfateReagent

SampleInjection

(Sparged?)

Carrier Gas(Oxygen)

Pump


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TOC in deoxygenated water by this type of device is questionable.

Part 1 - Raw Water Organics

The goal of this paper is to put organics intoperspective with respect to their relationshipbetween ion exchange resin and processrequirements. Naturally, the place to start is theraw water, with a brief discussion about whatorganics are.

The text book definition of organics includes allcompounds that contain carbon, except certainsimple compounds designated as inorganiccarbon. The distinction is made somewhatarbitrarily and there are exceptions to everydefinition. For instance, some amines (nitrogencompounds) contain no carbon at all and yet areconsidered organic. Inorganic carbon dioxide

in some cases is clearly derived fromdecomposition of larger organics and belongs inthe organic grouping. TOC is truly an exampleof this. Rather than defining organic compoundsby the classical methods, from our standpoint, itis easier to define them as natural organic matter(NOM) or man-made; and further to classifythem as ionized or non-ionized.

Most naturally occurring organic matter falls intothe broad category of large carboxylic acids;primarily tannic acid and humic acid. Man-madeorganics cover a much broader grouping. Many

man-made organics are purified by ion exchange.Two of the largest applications are that of sugarrefining and the production of MTBE for use ingasoline. However, in the world of ionexchange, we are generally concerned with eitherthe removal of organics and/or the consequenceof organic fouling of the ion exchange resins.

With respect to removal, it is important toremember that ion exchange materials only

remove ionized forms of organics. Non-ionizedorganics (including many, if not most of theman-made organics) are generally not removedto any significant extent by ion exchangeprocesses. This is one reason (among many),that most ultra-pure water systems include

membrane processes, as well as ion exchange.

MOMs Manmade Organic Matter

In any discussion about the affect of man-madeorganics on ion exchange resins, it is necessaryto have some knowledge about the basicchemical functional groups. The TOCconcentration by itself, is of very little value.For instance, amines are cationic and areremoved by cation exchange, organic acids arepartially ionized anions and are partiallyremoved by anion resin, while sugars are non-ionized and are not removed by ion exchange.

Ionized man-made organics are generally wellremoved by ion exchange resins; sometimes, toowell removed. Certain classes of man-madeorganics, such as alkylsulfonates and benzenesulfonates, are so strongly exchanged by anionresins that they poison the resin and irreversiblyfoul it. Other groups of man-made organicsundergo chemical reactions in the presence of ion exchange resins. Ion exchange resins areused in a number of organic synthesis reactionsand as catalysts. Certain classes of organics,

such as sugars, glycols and alcohols have little orno effect on resins, but resins are used to purifythem during their production.

Man-made organics that are not ionized present amore difficult challenge in the design of ultra-pure water systems that require low TOC.Simple low molecular weight organics (havingfewer than 6 carbon atoms) such as alcohols,aldehydes and solvents do not damage ionexchange resin. Indeed, ion exchange resin canbe used in the purification of these chemicals.However, low molecular weight non-ionized

organics are not removed by ion exchange resin.Unfortunately, low molecular weight organicsare not readily removed by granular activatedcarbon or by membrane processes. At present,there is no truly satisfactory method of removingthese types of organics, although there are somerecently developed absorbent materials that showpromise for removal of simpler organiccontaminants. Higher molecular weight non-ionized organics (having more than 6 carbon

Early Conductivity InferenceTOC Analyzer

ConductivityIntegration

Cell 2Cell 1Sample

InletSampleDrain

UV Light

Reaction Chamber(Titanium catalyst)

TOC


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atoms), are usually absorbable by granularcarbon and are well rejected by reverse osmosismembranes.

Part 2 Removal of NOMs

Fortunately, most water supplies do not containhigh concentrations of man-made organics. The

main concern with respect to ultra-pure water isthe removal of naturally occurring organics.Naturally occurring organics are generallycomposed of tannins and humic material fromdecaying vegetation. Their molecular weightvaries tremendously on a geographical basis,and their structure is not well defined. However,they share a common trait in that the majority areat least partially ionized and contain carboxylicacid functional groups. NOMs are, therefore,categorized by having a high fraction of carboxylic acid functionality. This means thatthey are anionic in nature and are exchangeableby anion resins.

There have been many papers presentedconcerning the natural organics. In this paper wewill limit our discussion to a review of the keyfeatures with respect to removal of NOMs byanion exchange.

1. The natural organic materials haveaffinities for ion exchange resins similarto sulfate ion.

2a. NOMs have various molecular weightsfrom as low as 100 to as high as 80,000.The higher molecular weight NOMs areusually not fully soluble in water.

2b. For the most part, organics withmolecular weights greater than 10,000are removed in potable water systemsby means of coagulation and filtration.

2c. The behavior of the remaining organicswith respect to ion exchange resin isgoverned by kinetics rather thanequilibrium.

3. The presence of (large) organic ions onanion exchange resin interferes with theexchange of (smaller) inorganic ions byblocking surface exchange sites. Thiscreates the kinetic impairment typicallyassociated with organic fouling.

4. Carboxylic acids function as cation

exchangers picking up sodium duringthe regeneration cycle. Thisphenomenon increases the sodiumleakage out of the anion resin and isassociated with the characteristic longrinse of organically fouled anion resins.

ANIONRESIN

MATRIX

AMINEGROUP

IMMOBILE BOND

MOBILE BOND

ORGANIC ACIDMOLECULE

COO

C O

O

Cl

OR

CARBOXYLICGROUP

HOROR FeNa

SIMPLIFIED ORGANIC MODEL

Comparison of Various ResinsTannic Acid Inlet (approx.. 20 ppm of TOC)

0

5

10

15

20

5 605 1205 1805 3305 3905

Bed Volumes

P P M

o f T O C L e a

k a g e

SBG1 40.7%

SBG1P 52.5%SBG1VP 59.6%SBMP1 54.4%SIR-22P 80.8%SBACR 59.0%

Comparison of Various ResinsHumic Acid Inle t (approx.. 4 ppm of TOC)

0

0.5

11.5

22.5

3

3.5

15 30 45 60 75 90 105 120 135 150 165 180

Bed Volumes

P P M

o f T O C L e a k a g e

SBG1PSBG1SIR-22PSBACR1


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5. Natural organics are dominantlyanionic in nature. A small portion isnon-ionic. A small portion is alsocationic.

6. Whatever polymer matrix is chosen for

the polymer structure, it will alwayswork best when the gel phase porosityis high. Increasing gel phase porosityalways increases the mobility of theorganic ions and improves kinetics.

7. The acrylic polymer matrix is provento have superior transport propertiesover the styrenic matrix and is alwaysa better choice from a kineticstandpoint. However, this does notalways translate into the best choice of resin for an organic trap as otherfactors also play a ro le.

8. Increased surface area of a resinincreases the number ion exchangesites available to transport ions fromthe surface of the resin to sites deeperwithin the polymer. Fine mesh resinswill generally work better than coarsemesh resins. A macroporous resin willgenerally work better than a gel resinof the same gel phase porosity.However, most macroporous anionresins have lower gel phase porosity,macroporous resins often do not

perform well in organic traps.

9. The balance between the elution of organics during regeneration and theloading of organics during the servicecycle determines whether a resin willor will not ultimately fail. Failure iscaused by one of two factors:

a. The resin no longer worksbecause it has loaded an excessiveamount of organic during theservice cycle, and there is not

sufficient time for the organic toexchange out of the resin duringthe regeneration cycle. Thiscondition causes the surfaceexchange sites to be overcrowded, reducing the availablesites for exchange and creatingthe condition known as kineticimpairment.

b. The presence of excessive amountsof organics on a resin bead can leadto bio fouling organic acids andions are generally good growthmedia for bio-organisms. Theacrylic polymer supports bio-

growths better than syrenicpolymer and is, therefore, moreprone to this type of fouling.

10. Whatever the design of the organic trap,the key to success is controlling theregeneration process to ensure that theorganics are properly removed duringregeneration. Periodic extendedcleaning procedures can also be used topurge accumulated organics from theresin.

11. Organics are never completely removedfrom a resin in the period of timeassociated with typical regenerationprocesses. In systems that are designedto accommodate the presence of organics, some allowance must alwaysbe made for fouling.

12. Organic acids are more soluble atalkaline pH than at neutral pH. Thismeans that during the service cycle, theremoval will always be better when thepH is high. It also means that theremoval of organics during regeneration

is enhanced by increasing the pH of theregenerant solution.

13. Proper pre-treatment of the feedwater toan ion exchange system can prevent thehigh molecular weight fractions of NOMs from reaching the resin. Sincethese fractions are the most difficult toremove from the resin, their removalcan dramatically enhance theperformance of the resin downstream.Techniques for removing these organicsinclude absorption by granular carbon,

coagulation and filtration, and variousmembrane processes.

14. Choices for organic trap resins.

a) Acrylic

The acrylic resins are superior fromthe standpoint of the transport of organic ions into and out of the


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polymer. They are ideally suitedfor large municipal installations.High moisture content and discreetporosity (macroporosity), are alsohelpful. These resins are ideal inplants where careful attention is

placed on the proper loading andregeneration factors. Acrylic resinsare not always the best choice forsmaller systems where little or noattention is placed on theregeneration requirements andwhere alkaline brine cannot be usedto elute the organics.

b) Very High-Moisture Gel Styrenic

These resins have good transportcharacteristics, compared to regularporosity gel resins. Their capacityis about half that of acrylic resins,but they do not have the tendencyto foul out. They are virtuallyequal to acrylic resins with respectto tannic acid removal, but aresignificantly worse with the highermolecular weight humic acid basedorganics.

c) Macroporous Syrenic Resins

These resins have significantlyincreased surface area, which may

make them good candidates fororganic trap resin providing theyhave high gel phase porosity. Thehigh degree of surface area makesup for the relatively poor gel phasetransport properties. Macroporousresins may have superior physicalstrength over gel resins and may bemore tolerant to harsh treatment byregeneration and other cleaningprocesses. Macroporous resinsalways function better when theyhave high gel-phase porosity, as

well as discreet porosity.

15. The presence of sulfate in a feed waterdirectly competes against the organicions for exchange sites, thus the loadingcharacteristics of any resin in an organictrap application depends on the sulfatecontent of the feed-water. As thesulfate concentration increases, theavailable capacity for organic removal

decreases. This phenomenon helpsprevent resin from fouling, but limits itsability to remove organics effectively.

Section 3 - High-Purity, Low TOC Requirements

So far, in this paper, we have discussed theremoval of organic ions by ion exchange resin,now we come to a different aspect of the subject.Since ion exchange resins are made from organicmaterials, there is opportunity for the resinsthemselves to leach organics into ultra -purewater. New resins can release part per millionlevels of organics. Even after cycling, theleaching of organics from ion exchange resinscan create intolerably high levels of TOC inultra-pure deionized water.

In the case of ultra-pure water, particularly tha tused for microelectronics manufacturing andwafer cleaning; the requirements for TOC are sostringent that the leaching of organics from ionexchange resins is a major cause of TOC in thefinal product water.

In the processing of ultra-pure water, thepretreatment stages; including membraneprocesses, often produce a feed-water to the finalpolishing demineralizers in the single digit ppbrange of TOC. The UV TOC destruct lightsfurther reduce the concentration of TOC suchthat the main concern with respect to the res ins isthat of leaching very low levels of TOC into the

product water.

In cation resin the dominant leachables aresulfonated aromatic compounds. Theirmolecular weight depends on the cross-linkageand conditions of polymerization. The molecularweight and chemical structure of cationleachables is subject to some disagreementamong polymer chemis ts. However, there is aclear relationship between the age of a cationresin and the concentration of organic sulfonateleaching off the resin. There are also differencesamong resins depending on the conditions of

polymerization and with respect to the extent of post-treatment prior to use. Generally, theirmoleculor weights are multiples of the benzenesulfate monomer.

Hydrogen form cation resins, if not very recentlymanufactured, usually bleed these organicsulfonates. These leachables increase the TOClevel that the resin is otherwise capable of


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maintaining. They also affect anion resinperformance and can cause fouling.

Leachables from anion resins are significantlydifferent than the leachables from cation resins.Anion leachables are predominately caused by

amine instability. The dominant leachable fromType I resins is trimethylamine, which can beremoved by cation exchange resin. However,there are secondary oxidation routes that createnon-ionized leachables such as methanol thatwill escape from the deionization system andappear as TOC in the effluent. Organicleachables from anion resins are usually lowmolecular weight materials and unlike cationresins do not usually have an aromaticcomponent.

Removal of Leachable TOC from New Resins

It is impossible in the manufacturing process of ion exchange resins, to completely avoidleachable TOC. No matter how careful thepolymerization and subsequent functionalizationsteps, there is always some residual monomerand other contaminants left in the resin. Resinsgradually deteriorate as they age and may alsocontain deep inside the beads, slow to diffuseTOC left over from the manufacturing. Theresult is a gradual increase of TOC if the resinsare left in storage. It is practically impossiblefor an end-user to purchase and use a resinwithin hours or days of its manufacture. This

means that new resins will always contain someleachable TOC.

In todays semiconductor and high pressureboiler applications, the minimization of TOCleachables is extremely important. It isincreasingly necessary that both the cation andanion resins be vigorously treated shortly beforeuse to reduce the concentration of organic

leachables. Cycling new ion exchange resinsmany times prior to use is one method of purgingorganics, but can contribute unacceptable levelsof sodium and other inorganic ions to the resins.Some resin suppliers now offer special grades of virgin resins in with extremely low levels of leachable organics, in some cases, the very firstcycle produces virtually no organic leachableswhile still maintaining virgin purity levels forinorganic ions.

Key Points with Respect to Leachables:

1. Type II resins (and for that matter anynon Type I resins), when oxidized,produce a relatively high fraction of non-ionized leachables. Their low TOCapplications are for the time being,not practical.

2. Acrylic resins are less stable thanstyrenic resins. They also have lowerselectivities for inorganic ions. Acrylicresins for the time being, are notpractical in polishing beds used forultra-pure water applications.

3. The dominant leachables from cationexchange resins are sulfonated aromaticcompounds that can kinetically foul theanion exchange resins.

4. Hydrogen form cation resins are slightlyunstable and can develop high levels of sulfonated aromatic leachables duringstorage. For this reason, hydroge form

Illustration of Cation & AnionContribution to Leachables

TOC Rinse down of Seperate Beds

0

102030

4050

1 6 11 16 21 26 31 36 41 46

Bed Volumes of Rinse

p p

b o

f T O C

Mixed BedCation/AnionAnion/Cation

Aging study of LTOC Mixed Beds

Solid line MBD-15 LTOC made in Sept 96Dashed line MBD-15 LTOC retested in May 97

1

10

100

1000

0 5 10 15 2 0 25 3 0 35 40Bed Volumes of Rinse

p p

b o

f T O C

MBD-ULTRASeries of Mixed Beds

MBD-10 ULTRALot 5528

0.1

1

10

100

0 10 20 30 40 50Bed Volumes of Rinse

P P B o

f T O C

15

16

17

18

19

20

M e g o

h m s

R e s

i s t i v

i t y


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cation resins should be used relativelysoon after manufacture or must berinsed or cleaned prior to use.

5. Increasing cross-linkage increasesoxidative stability (and reduces gel

phase diffusion rates) thus decreasingthe buildup of TOC leachables overtime. This is true both in cation and inanion resins.

6. Whatever cleaning process is used toremove leachables, it must be done insuch a way as to not damage thephysical characteristics or chemicalpurity of the resin.

.

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Sources of to Cindi Water