Institute of Paper Science and Technology A tanta, Georgia

IPST Technical Paper Series Number 825

Rapid and Direct Pulp Kappa Number Determination Using Spectrophotometry

X.S. Chai and J.Y. Zhu

November 1999

Subm itted to Journal of Pulp and Paper Science

Copyright@ 1999 by the Institute of Paper Science and Technology

For Members Only INSTITUTE OF PAPER SCIENCE AND TECHNOLOGY PURPOSE AND MISSIONS

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The Institute of Paper Science and Technology assures equal opportunity to all qualified persons without regard to race, color, religion, sex, national origin, age, disability, marital status, or Vietnam era veterans status in the admission to, participation in, treatment of, or employment in the programs and activities which the Institute operates. To be published in J Pulp & Paper Sci., 25( 1l), 1999 (in press) Also Presentedat the 1Uh ISWPC Main Symposium, June 7-10, 1999,Yokohama, Japan Rapid and Direct Pulp Kappa Number Determination Using Spectrophotometry

X.S. Chai andJ.Y. Zhu’

Institute of Paper Scienceand Technology 500 ltih Street, N. W. Atlanta, GA 30318 (404) 894 -5310,(404) 894-5752(Fa

ABSTRACT

A spectrophotometricmethod has been developed for rapid pulp kappanumber measurements understrongly acidic reactionconditions. Pulp kappanurnber is derived from the ratio of the absorptionspectral intensities at a specificwavelength measured at the beginningand end of the reactionof the pulp with permanganate.Therefore, no calibration is necessary.Strong acidification is usedto preventMnO, precipitationand interference with the permanganateabsorption spectrum. A methodis proposedto determinethe end of the pulp oxidationreactions with permanganateusing the reactionkinetics andrate derived from the time-dependentspectrophotometric measurements of the reactingsolution. It was found that the pulp oxidationwas completedin lessthan 3 minutes. Themeasured kappa numbersof three pulp samplesof two wood species,with andwithout bleaching,agreed well with thoseobtained by the current TAPPI standardmethod using thiosulfate titration.

Thepresent method is simple,rapid, andaccurate.

Key Words: Kappanumber; pulp; spectrophotometry;UWVis absorption;

lignin oxidation;permanganate.

l Author to whom correspondenceshould be addressed

1 Accepted for Publication by J. Pulp & Paper Sci., 25( 1l), 1999 (in press)

BACKGROUND

Thekappa number of pulp is one of the importantparameters in pulp manufacturing becauseit relatesto the bleachability,or degreeof delignification,of the pulp. The kappa numberis definedas the volume of 0.02 mole/L (0.1 normality) potassiumpermanganate solutionconsumed by one gram of moisture-freepulp in an acidic mediumthrough the following reactions,depending on the acidity of the medium:

MI@‘; + 8H+ +5e E”=+lslV >ib2+ + 4H,o (1 a>

MnO~ + 4H’ + 3e E”=+1*6gv) it&O, + 2H,O (lb)

The current, commonlyused method for kappanumber measurements, such as TAPPI Test Method T236 cm-85 [l], was first proposedin 1934by Wiles [2] and later developedin the 1950’sbased on researchby Watson[3], Valeur and Torngren[4], and Tasmanand Berzins [S]. The methodcalculates the volume of 0.02 mole/L (0.1 N) potassiumperrnanganate consumed by one gram of moisture-freepulp by the difference betweenthe initial andthe final excessvolumes of potassiumpermanganate after a lo- minute reactionat 25OCunder weakly acidic conditions. The final excessvolume of potassiumpermanganate after the lo-minute oxidationreaction is determinedby titrimetry using a standardthiosulfate solution after addingan excessof potassiumiodide to the slurry to react with the excesspertnanganate to form iodine.

The key assumptionsof this methodare: (1) the perrnanganateconsumed was mainly due to reactionwith lignin, and the rapid oxidationwas completedin 10 minutes; (2) the effects of reactiontemperature, time, andthe variationin excesspermanganate volume are not significantand canbe correctedby a non-constantcorrection factor as tabulatedin the TAPPI method [l]; and (3) the thiosulphatetitration methodis accurate.The disadvantages of this method are: (1) thiosulfatetitration of iodine is tediousbecause a blank experiment (without pulp, andusing exactly the sameprocedures) is neededto reducethe experimental error in the titration due to the high volatility of iodine; (2) the thiosulfatetitration requires that the reactionbe kept underweakly acidic conditions,which causeslarge variations in kappameasurements as reportedby Valeurand Torngren[4]; (3) the lOominuteoxidation Accepted for Publication by J. Pulp & Paper Sci., 25( 1 1), 1999 (in press) reaction time is arbitrary and can causeerrors in determiningkappa numbers for various pulps, becausepermanganate can be both oxidizedand decomposed by other organic materialsin pulp as explainedby Tasmanand Berzins[5]; the actualoxidation time is much shorterthan 10 minutes,as found by Li andGellerstedt [6] and in the presentstudy; (4) the methodrequires that the volume of consumedpermanganate after the lo-minute reaction shouldbe around50% of the initial volume to obtain goodmeasurements; this is impossible becausethe final excesspermanganate volume can only be known after the kappanumber has beendetermined; (5) the non-constantcorrection factor is purely empirical,derived through experimentalcalibration, and cancause errors; and (6) compoundsother than lignin in a pulp, suchas a significantamount of hexenuronicacid in bleachedpulps, canbe oxidizedby permanganatein the first lo-minute reaction. As a result,the existing kappa test methodshave many shortcomingsand the kappanumber itself is not scientificallywell defined;however, the kappanumber of a pulp obtainedby thesemethods has significant practical importance. A commerciallyavailable instrument, based on thesemethods, has beendeveloped (KAPPAMAT, Kebo Lab, Sweden).

Spectroscopicmethods can provide direct and instantaneousmeasurement of chemicalconcentrations in reactions. Spectroscopicmethods using W andFTIR absorptionto determinepulp kappanumber have been reported [7,8]. In thesemethods, the linear relationshipbetween the lignin contentof the pulp and the light absorptionwas used to determinepulp kappanumber. Unfortunately,the perrnanganateconsumption by different types of lignin is different. Therefore,calibration is requiredfor a specificpulp sampleusing the traditional methodof kappanumber determination [l].

By the time the presentstudy was completed,Li and Gellerstedt[6] had reportedthe resultsof a study on the kineticsand mechanism of pulp-permanganatereaction under conditionssuggested in standardkappa testing methods. They directly measuredthe permanganateconcentration in lignin-permanganatereaction solutions using W/Vis spectrophotometry. Accordingto Li and Gellerstedt[6] and Stewart [9], both reactions(la) and (lb) can takeplace under conditions suggested in commonkappa number test methods, suchas TAPPI Test Method - T236 cm-85 [ 1] and SCAN-Cl Test Method [lo], wherethe dominantreaction is an overallconversion of permanganateto MnO, accordingto reaction Accepted for Publication by J. Pulp & Paper Sci., 25( 1l), 1999 (in press)

(lb). Becausethe numberof electronsrequired b for thesetwo reactionsto takeplace is different (as shownin reactions(1 a) and (lb)), andbecause the amountof permanganate consumedin the reactionsvaries with the initial amountof permanganateavailable in the pulp slurry, Li andGellerstedt [6] concludedthat the useof iodometrictitration and the definition of a 30.70% permanganateconsumption range prescribed in the commonlyused kappanumber test methodsleads to erroneousresults. Furthermore,they found the precipitatedMnO, strongly interferedwith the measuredabsorption spectrum of the reaction solution,and causedsignificant measurement difficulties in determiningthe excess permanganatein the final reactionsolution. Nevertheless, they concludedthat direct spectrophotometrycan be usedto calculatethe kappanumber of pulp samples.

We would like to point out that the conclusiondrawn by Li and Gellerstedt[6], i.e., “iodometric titration andthe definition of a 30.70% perrnanganateconsumption range used in the commonly usedkappa number testing methods is erroneous,”is not correct. The precipitatedMnO, formed in reaction(lb) underthe conditionsused in thesekappa number test methodsis convertedto Mn*+with the additionof potassiumiodide (ICI) accordingto lowing reaction,

Mno, + 4H’ + 2e E”=+1s224V) Mn2+ -t 2H,O (1 C ) which requires2 electrons. Thetotal numberof electronsrequired for reactions(lb) and (lc) is 5, equalto that requiredfor reaction(la). Whetherthe pioneerswho developedthe current kappatest methodsthought of this or not, thesekappa number test methods,such as [ 1, lo], arevalid. However, it is not possibe to use spectrophotometryto determinepulp kappanurnber under the reactionconditions (weak acidification) used in thesemethods, as in the work by Li and Gellerstedt[6]. The amountof precipitatedMnO, in the pulp- permanganatereaction solutions cannot be determined,and the errorscaused by spectral interferencefrom the precipitatedMnO, cannotbe ignoredor eliminated.

In this study, we developeda spectrophotometricmethod for the rapid determination of pulp kappanumber through direct measurementof the permanganateconcentration in pulp-permanganatereaction solutions. Unlike the studyby Li and Gellerstedt[6 weak acidificationas in standardkappa testing methods[ 1, 10 , we proposedthe use of strong acidificationto preventthe precipitationof MnO,. As a result, spectralinterference

4 Accepted for Publication by J. Pulp & Paper Sci., 25( 1l), 1999 (in press) from the precipitatedMnO, was eliminatedand reaction(la) then becomesthe dominant oxidationreaction. Furthermore,we accuratelydetermined a representativepulp oxidation reactiontime and the final excesspermanganate in the reactionsolution from the measured permanganateabsorption spectral intensities. We then directly determinedpulp kappa numbersof severalpulp samplesusing the permanganateabsorption data without calibration and corrections. Becauseof strongacidification, we were ableto eliminatethe effect of the amountof excesspermanganate or the massof the pulp sampleon the measuredkappa number. The focus of the presentresearch was to developa methodthat can obtainkappa numbersconsistent with existingmethods because of the practicalimportance of the kappa number. Therefore,this study did not addressthe effect of oxidationreactions of compoundsother than lignin, suchas hexenuronicacid, on measuredkappa number.

THEORY AND METHODOLOGY

Mathematicallythe pulp kappanumber is definedas -

K=plw (2) whereK is kappanumber,p is the amountof 0.02 mole/L (0.1 N) permanganatesolution actually consumedby the test samplein mL, and vvis the massof the moisture-freepulp samplein grams.

In a permanganate-pulpreaction experiment, the initial volume of 0.02 mole/L permanganateadded is a mL, and the amountof pulp usedis M/grams. At the endof the oxidation reaction,the excessvolume of 0.02 mole/L permanganateis b mL. Therefore,the consumedvolume,p, of 0.02 mole/L permanganatecan be written as

b p=a-&a I-- ( a 1

The concentrationof permanganatein the reactionsolution at the beginningand the end of the oxidation can be written as

=- 0.1-a C 0 (4) VT and Accepted for Publication by J. Pulp & Paper Sci., 25(1l), 1999 (in press)

0.1.b c e =- (5) 9 VT respectively,where VT is the total volume of the reactionsolution, which includesthe addition of sulfuric acid.

Accordingto Beer’s Law, the absorptionis proportionalto the concentrationof the test sample;thus, we canhave A, =& l z*c, (6) and

A, =E +C, (7) 9 respectively. Where 4 and A, arethe permanganateabsorbances (or spectralintensity) in the solutionat the beginningand end of the oxidationreaction, E and I arethe molar absorptivityof the solutionand the optical path-lengthof the cell, respectively.

From Eqns.(4) to (7),

-=-b Ae (8) a A0

SubstitutingEqn. (8) into (3), the volume of permanganateconsumed can be written as

(9)

We can determinethe kappanumber using the following expression:

a A K =- 1 e- e (10) W ( A0 1

Eqn. (10) indicatesthat kappanumber can be calculatedfrom the ratio of the permanganateabsorption spectral intensities at a given wavelengthat the beginningand end of the perrnanganate-pulpreaction and that absoluteabsorption measurements are not required. Therefore,quantitative calibration is not necessary,and the measurementswill be much more reliable, accurate,and simplified than the existingquantitative titration method. Accepted for Publication by J. Pulp & Paper Sci., 25( 11), 1999(in press)

EXPERIMENTAL

Apparatus

All experimentswere conductedusing a flow loop. The flow loop consistsof a peristalticpump @P-l, Rainin), tubing and connectors,a 25-mL beaker,a homemadenet filter (200 mesh)to separatethe fibers from the reactionsolution, and a UWVis optical flow cell. Figure 1 showsa schematicdiagram of the experimentalsetup. Thepermanganate- pulp reactionwas carriedout in the beaker. Thereaction solution containing permanganate and sulfuric acidwas recirculatedby a peristalticpump with a flow rate of 2 mllmin and flowed through the UVMs optical flow cell with a l-mm optical path length. Thepulp fibers were separatedfrom the circulatingsolution by the stainlesssteel net filter to permit spectrophotometicmeasurements. All absorptionmeasurements were continuously performedover the whole UVMs rangeby a spectrophotometer(W-8453, Hewlett- Packard)equipped with an HP ChemStationfor real-time datacollection and analysis. The reactionsolution was well mixed by magneticstirring during the experiment.

Chemicals and Reagents

Standardized0.02 k 0.0001mole/L (0.1 k 0.0005N) potassiumpermanganate solutionwas usedto react with pulp samplesunder acidic conditionsby addingstandard sulfuric acid of concentration2.0 mole/L.

Measurement Procedures

Distilled water was usedas a blank solutionfor UV/Vis measurements.Pipettes of 5 mL (& O.OlmL) of potassiumpermanganate solution and 20 mL of standardsulfuric acid solutionwere placedin a 25-mL beakerunder strong magnetic stirring to makethe 1.6 mole/L concentratedsolution of sulfuric acid. The solutionwas circulatedthrough the optical flow cell by the peristalticpump. Therequired amount of moisture-freepulp (from 0.05 to 0.15 gram) was accuratelyweighed out and addedto the beakerafter the spectrophotometerhad startedto recordreal-time data. The time-dependentabsorption spectraof the filtered solutionwere recordedby the ChemStationfor 5 minuteswith a time interval of 1 second. Accepted for Publication by J. Pulp & Paper Sci., 25( 1 l), 1999 (in press)

RESULTS AND DISCUSSIONS

Time-Dependent Absorption Spectra of the Reaction Solution

The real-time absorptionspectra collected during pulp oxidationby the permanganatesolution allow us to obtain time-dependentconcentrations of the chemicals under-reaction.Figure 2 showstypical UV/Vis absorptionspectra of a reactionsolution after separationof pulp fibers usingthe net filter. Eachspectrum is a superpositionof absorptionby various chemicalsin the reactionsolution. Becauselignin and other organic moleculesproduced in the reactiondo not absorbin the region of interest,the spectral intensity at 546 nm is due purely to the absorptionof potassiumpermanganate. It is importantto point out that the typical relativestandard deviation of spectrophotometric measurementsis only about 0.1%,which gives a negligiblerelative error in the ratio of the absorption spectralintensities in Eqn. (10) of 0.1%.

Determination of the End of the Oxidation Reactions and Pulp Kappa Number

One problem associatedwith the existingmethod [l] for kappanumber determinationis that the pulp oxidationreaction time is arbitrarily taken as 10 minutes, irrespectiveof the reactionconditions, such as acidity, the species,the amountof pulp, and the excessvolume of permanganateused in the reaction. With the time-dependent concentrationsof the reactionchemicals determined from spectrophotometic measurements,we shouldbe ableto accuratelydetermine an effective endpoint of any given pulp oxidationreaction with permanganate.According to Beer’sLaw, or Eqns.(6) and (7), the permanganateconcentration in the reactionsolution is linearly proportionalto the absorptionspectral intensity A; therefore,we call the plot of time-dependentspectral intensityA a kinetic curve. We can describethe permanganatereaction kinetics using the time-dependentpermanganate absorption at 546 nm. We found that all the kinetic curves from reactionswith different amountsof pulp andpulp speciesfall on a singlecurve after propernormalization as shownin Fig. 3, indicatingthat the normalizedreaction rate (or permanganateconsumption per gram of pulp) doesnot changewith the absoluteamount of excesspermanganate or pulp and the pulp speciesused. From Fig. 3, we then can calculate the time derivativeof the normalizedpermanganate absorption or concentration,or the reaction rate. Figure 4 plots the normalizedreaction rates that areaveraged over the 7

8 Acceptedfor Publicationby J. Pulp& PaperSci., 25( 1 l), 1999(in press) experimentsshown in Fig. 3. Accordingto Tasmanand Berzins [5], there aregenerally two main (groupsof) reactionsoccurring simultaneously in a pulp-permanganatesolution, i.e., rapid oxidation of lignin (recentstudies [6, 1l] indicatethat other compounds,such as hexenuronicacid, can alsobe oxidized)by permanganateand slow decompositionof permanganateby other organicmaterials. Our data shownin Fig. 3 validatethis assumption.The activationenergies of thesetwo groupsof reactionsare different. Lignin and hexenuronicacid can be easilyoxidized by pertnanganate;the decompositionreactions betweenpermanganate and someother organicmaterials will dominateonly after the oxidationreactions are over. We can thereforefit the normalizedkinetic data to a two-rate model. We found that the following equationfits the datain Fig. 3 very well,

y = 1.0 - m[l- exp(-Et)] - Bt , (19 where m = 0.615,E = 0.029,B = 0.0015,y is the non-dimensionalpermanganate absorption at 546 nm, andt is the reactiontime in seconds.In this two-rate model, we usedan exponentialfunction to representpermanganate consumption by the group of rapid oxidationreactions of lignin, hexenuronicacid, etc., early in the reaction,and a linear decay function for the slow decompositionby other organicmaterials. Eqn. (11) clearly indicates that the exponentialdecay function is importantonly during an initial short time period, while the linear decayfunction will dominatelater in the reactionat a longervalue oft. The time derivativeof Eqn. (11) is then usedto obtainthe fitted normalizedreaction rate equationas follows:

du - -- -ma E exp(-Et) - B (12) dt

The purposeof the aboveanalysis is to determinean effective reactiontime te when oxidation reactions(lignin oxidationin particular)end, so that the permanganateabsorption

A, at time te can be determinedfrom Fig. 3 and usedto calculatethe samplepulp kappa numberby Eqn. (10). If the reactionenergies of the two permanganatereactions differ significantly, a clearbreak point in the curvesof the permanganateconsumption and of the reactionrate can be seen.Unfortunately, this is not the casein this reactionsystem, as shown in Figs. 3 and 4 wherethe solid lines areEqns. (11) and(12), respectively. Because Accepted for Publication by J. Pulp & Paper Sci., 25( 1l), 1999 (in press) of the asymptoticnature of the oxidationreaction rate curve,we definethe endpoint of the oxidationreactions as the point at which the rapid oxidationreaction rate (the exponential decayfunction part of Eqn. (12)) is reducedto only 4% of its maximum rate (at t = 0), or

wt l E = 0.0178,according to Eqn. (12)). Mathematically,we can define te as

dY --m*E- -&-B=[ -m l E exp(-Et,)] - B (13) dt t=t,

By solvingEqn. (13) for te, we have

ln(qllO0) ln(q/lOO) =- =- (14) c? E 0.029

In this study we arbitrarily take 4 = 1 as a good approximationfrom an engineering point of view. For a given temperatureof 25OCand strongacidification, as usedin this study, the oxidationreaction end point te is a constantand is equalto 159 secondsfor all experimentsconducted with different amountsof pulp, pulp species,and final excess permanganatevolume. This time of 159 s (or 2.65 minutes)is only about one quarterof the 10 minutesrequired in the current TAPPI test method[ 11. It is alsomuch shorterthan the 5 minutes suggestedby the recentmodified method [ 121proposed by the CanadianPulp and PaperAssociation.

To demonstratethe effect of the above-proposedmethod of determiningthe oxidationreaction end point, te, on measuredkappa number, we calculatedthe kappa numbersof three different pulp samplesfrom the measuredspectral intensity data using different 4 or oxidationreaction end point, te. We found that the relativedifferences in measuredkappa numbers of thesethree pulp samples(based on 4 = 1) were lessthan 10% when varied from 0.32 to 3.3 (more than an order of magnitudevariation), correspondingto an effective oxidationreaction end point, te, of 198 to 118 seconds(about 70% variation) as shown in Fig. 5. This calculationdemonstrates the accuracy,versatility, andvalidity of the proposedmethod to determinethe end of the oxidationreactions for kappanumber calculationsusing the presentspectrophotometric method.

10 Accepted for Publication by J. Pulp & Paper Sci., 25( 1l), 1999 (in press)

Comparison of the Present Method with the Traditional. Titration Method

Although the existingkappa measurement method based on titration [l] hasmany problems,and the measurementresults for the samepulp sampleare a strongfunction of the operator,the existing methodhas been widely acceptedby the pulp andpaper industry as well as by academicresearchers throughout the world. From a practicalpoint of view, the pulp and paperindustry will benefit from any new kappadetermination method that can give results consistentwith the existingmethod. To demonstratethe agreementof kappa measurementsusing the proposedspectrophotometric method with the existingmethod, we measuredthree pulp samplesderived from two wood species(pine andbirch), with and without bleaching,with significantvariation in kappanumbers (from 4 to 26). We found that the measuredkappa numbers of thesethree samplesagreed with thoseobtained using the traditional TAPPI Test Method - T236 cm-85. Themaximum relativedifference in kappanumbers between the two methodswas lessthan 5% at low kappanumbers as shown in TableI.

Effect of Pulp SampleSize on Measured Kappa Number

One of the problemsof the existingkappa number measurement method [l] is that the measured kappanumber for a givenpulp varieswith the amountof pulp sampleor the excessvolume of permanganatesolution used. However, with strongacidification, this effect on kappanumber is diminished,as shownby Valeur and Tomgren [4]. The mechanismof the effect of acidificationon measuredkappa number has not been understoodand is not the subjectof the presentstudy. We eliminatedthe variation in measuredkappa number by using strongacidification (the initial sulfuric acidconcentration in the reactionsolution was 1.6 moles/L), andthe effective pulp oxidationreaction end point was determinedusing the method describedabove. We usedbirch pulp of samplesize from 50 mg to 150mg to test the effect on the measuredkappa number of the amountof pulp sampleor the excesspermanganate used. We found that the measuredkappa number of the pulp sampleusing the presentmethod andapparatus based on Eqn. (1) doesnot changewith the amountof pulp sampleused. The resultsare listed in TableII. Themean kappa number was 25.8 with a relativestandard deviation of only 2.3%. Comparedwith the measured kappanumber of 25.4 usingthe traditionalmethod [ 11,the differenceis only 1.6%. We also Accepted for Publication by 3. Pulp & Paper Sci., 25( 1 I), 1999 (in press) found that the measuredvolume of permanganateconsumed is linearly proportionalto the amountof pulp sampleused in the experimentsbecause the samepulp samplewas used. Furthermore,we were ableto reducethe oxidationreaction end point to only 2.65 minutes.

CONCLUSIONS

Absorption spectrophotometryhas been used to analyzethe permanganate concentrationin pulp-permanganatereaction solutions. By using strongacidification, the precipitationof MnO, was preventedand the reactionwas forcedto follow reaction(la); as a result, spectralinterference from precipitatedMnO, was eliminated. We found that the normalizedtime-dependent permanganate absorption spectral intensity (or kinetic curve) in the reactionsolution is not dependenton eitherthe pulp speciesor the samplesize. We also found that an empiricaltwo-rate model(an exponentialand a linear decayfunction) fits the normalizedkinetic datavery well. Thepulp kappanumber was derivedfrom the ratio of permanganateabsorption spectral intensities at a specificwavelength measured at the beginningand the endof the pulp oxidationreactions. Therefore,it was possibleto determinethe pulp kappanumber from spectralanalysis without calibration. Unlike the traditional titration kappanumber measurement method in which the pulp oxidation time is arbitrarily taken as 10 minutes,a methodwas developedto determinethe end of the pulp oxidation reactionusing reactionkinetics and the two-rate modelderived from the spectral measurements.We found that an oxidationreaction duration of lessthan 3 minutesis sufficient to obtainreliable kappa number measurements. The method also eliminates the effect of pulp samplesize or final excessvolume of permanganateon the measuredkappa number.Using the presentspectrophotometric method, the measuredkappa numbers of three pulp samplesfrom two wood specieswith and without bleachingagreed well with thoseobtained by the current TAPPI test methodusing thiosulfatetitration. The present method is simple,rapid, versatile,and accurate.

ACKNOWLEDGEMENT

This work was partially supportedby the U.S. Departmentof Energyby Grant No. DE-FC07-96ID13418.

12 Accepted for Publication by J. Pulp & Paper Sci., 25( 1 l), 1999 (in press)

REFERENCES

1. TAPPI Test Method, T236 cm-85, TAPPI Press,1996.

2 . Wiles, R.H., (1934),Paper TradeJ., 98(11):34(1934).

3 . Watson, A.J., “The influenceof the methodof samplepreparation on the permmgmate consumingcapacity of chemicalpulp,” APPITA, 12, 137 (1959).

4 . Valeur, C. andTorngren, I., “A proposedmethod for determiningthe permanganate numberof pulp,” SvenskPapperstidning, 60(22):829 (1957).

5 . Tasman,J.E., and Berzins,V., “The PermanganateConsumption of Pulp Materials,” TappiJ., 40(9):691(1957).

6 . Li, J. and Gellerstedt,G., “Kinetics andMechanism of KappaNumber Determination,” Nordic Pulp and Paper ReserchJ, 13(2): 147 (1998)

7 . Plonka,A.M., Surewicz,W., and Wandelt,P., “Determinationof Total Lignin Content in FibrousMaterials,” Zellstoff Papier, 23(1 I):327 (1974). -

8 . Michell, A.J., “Kappa Number Determinationin Kraft Pulpingby FTIR Spectroscopic Measurementson SpentLiquors,” TappiJ, 74(4):235(1990).

9 . Stewart,R., in “Oxidation in OrganicChemistry,” Wiberg Ed., AcademicPress, New York, 1965.

10. SCAN-Cl :77, “Kappa Number,” ScandinavianPulp, Paper and Board Testing Committee, 1977.

11. Gellerstedt,G. and Li, J., “An HPLC Method for the QuantitativeDetermination of HexenuronicAcid Groupsin ChemicalPulps,” 21I* AmericanChemical Society Meeting, New Orlean,March, 1996. 12. CPPA TechnicalSection, “Rapid Determinationof KappaNumber,” CPPAUseful Method G.8U (1992).

13 Accepted for Publication by J. Pulp& PaperSci., 25( 1 l), 1999 (in press)

List of Figures

Fig. 1 A schematicdiagram of the experimentalapparatus

Fig. 2 Typical time-dependentUWVis absorptionspectra of the reactionsolution

Fig. 3-Normalizedtime-dependent KMnO, absorptionspectral intensity at 546 nm

Fig. 4 Time derivativeof the normalizedKMnO, absorptionspectral intensity at 546 nm

Fig. 5 Effect of parameterq on measurementuncertainty

List of Tables

TableI Comparisonof measuredkappa number with that obtainedusing the traditional TAPPI Test Method - T236 cm-85

TableIX Effect of pulp samplesize on measuredpulp kappanumber

14 Accepted for Publication by J. Pulp & Paper Sci., 25( 1 l), 1999 (in press)

Fig. 1 Computer

Flow Cell Spectrometer

Phot\ometric Array Detector

Stirring Meter

2.0 1.8

16n 14m 1.2 108 0.8 0.6 0.4 0.2 0.0 200 300 400 500 600 700 Wavelength (nm) Accented for Publication by 3. Pulp & Paper Sci., 25( 1 I), 1999 (in press)

-y = 1-0.615[1-exp(-O.O29t)]-0.001~

d q Unbleached Birch, 0.0516 g 08-. Q Unbleached Birch, 0.0620 g A Unbleached Birch, 0.0822 g v Unbleached Birch, 0.1183 g 0.6 - . o Unbleached Birch, 0.1423 g + Unbleached Pine, 0.0505 g 0.4 - x BIeached Birch, 0.0502 g

0.2 -

oo-.

0 50 100 150 200 250 300 Reaction Time, t (s)

Fig. 4

Averaged Experimental Data -O.O178exp(-0.029t) - 0.0015

0 50 100 150 200 250 300 Reaction Time, t (s)

16 Accepted for Publication by J. Pulp & PaperSci., 25( 1 l), 1999 (in press)

Fig. 5

Reaction Time (s) 238 159 79 30, 1 198I I 118I I I K = 4.5 I . I q I 1I 1 20 - II I) K = 14.9 1 I I I - II I = 25.8 1 0 I A K \ -...... l...,..,...--...l...-l* I ---II------~------I e, IO- I . f 1 l-40 I I 1I I I 4 I DJE 0 1 0 3? . I3 I 0 I 0 > ...... -r------‘-“-”l + e.-“.....-...... e-s..“..l-.... -IO-- I l A I i I 2 . 31 I 3I i1 &aJ -2o- 31 d3t t . 1I 3d q 1I i I 30 “I . I I,,.,. . I I 1 , I 1I I 0.1 1 10

17 Accepted for Publication by J. Pulp & PaperSci., 25( 1l), 1999 (in press)

TableI. Comparisonof measuredkappa number with thoseobtained using the traditional TAPPI Test Method - T236 cm-85

No . - Pulp Pulp Mass MeasuredKappa Number (cl Present Tappi Relative Method Method [I] Difference (%) 1 I birch, bleached 0.0501 4.5 43 45. 2 pine, unbleached 0.0505 14.9 1;3 -2 .6 3 birch, unbleached 0.0516 25.8 25’4. 16.

TableII. Measuredkappa number using different arnountsof pulp sample

No . Pulp Mass(g) A, A, KMnO, Measured Consumed(mL) KappaNo. 1 1 0.0516 10.922 1 0.682 1 1.302 125.2 - 2 1 0.0620 10.921- 1 0.619 I 1.636 126.4 - 3 1 0.0832 1 0.922 1 0.519 I 2.217 126.3 - 4 1 0.1183 1 0.920 10.356 13.071 I 25.9 5 I 0.1403 1 0.919 I 0.272 I 3.515 125.1 Mean I I I I 1 25.8 - RSD I I I I 1 2.3 %