20688 Correlation of Scale Inhibitor Structure of Barium Sul

7/24/2019 20688 Correlation of Scale Inhibitor Structure of Barium Sul

1/7

.

SPE 20688

SPE

ecfL%4JofF%doun Gv

Correlation of Scale Inhibitor Structure With Adsorption

Thermodynamics and Performance in Inhibition of Barium Sulfate

in Low-pH environments

P.J. Breen, Bat., r Performance Chemicals Inc.; B.N. Diel, Chemical Waste Management Inc.;

and H.H, Downs. Baker Performance Chemicals Inc.

SPE Member

n

Copyr ,ghl 1990. SocIe Iy of Powoleum Engmoors, Inc

Th,s paper was pr6pared tor presontatfion l the 65th Annue. Techn c 4 Conference and Exhlbmon ot lhc Somety ofPetrolaum Engmeer$ held m New Oljean% IA, September 23-26, 1990

Th ts paper was selec ted for p resenlahon by an SPE Prqram CommlMee fol lowlng rev iew of mtormahon con ta ined m en abs lr ac t subm,t ted by the au tho r(s) Coraents ot the pape r

as presented. have not bean rewawed by the Society of PeIro leum EnQmeer$ and are .W qecl to Corrochon by the aid her(s) The nlaterwl. M PreSented. 100s not necessari ly ret iec

any posmon otthe SocIe y of PeCroleum Engmaers, I IS ofhcers. or mambers Papers presented at SPE meetmgs are subject 10pubhcat ion rewew by Eddon,l CommWsas otme Society

of PoUoleum Engineers Permission tocopy laresfmc[o Oan abstra- t ofWI more than 300 words I lluswahona may not ba cop,ed The absl.ac l should Cc.1am conaplcuous acknowled

ment o f whe re and by whOi_I It hO pape r ISp resented . Wrle Pubhcauons Manage r, SPE , P .O Box 833836, R, *hardson , TX 75083 .3636 U S A Telex , .30989 SPi3AL

ABSTRACT

eXPERIMENTAL

In order to de 2(OP i nproved bari un sul fate

All i nhibi tors were

i nhi bi tors f or aci di c (pH 4) envi romnents, adsorpti on to check f or puri ty and

thermodynamccs heavebeen masured for severat

Bari un sul fate (pwder)

hrxnol ogous seri es of i nhi bi tors uherei n the mol ecul ar

Scienti fi c Products ad

structures have been vari ed systemat i ca( [Y.

Correlati ons betueen thermodynamc, structural ew

A.

Static Bott le Test

performance data H I t be di scussed.

prepared and characteri zed

ccarpl eteness of reacti on,

was purchased fromFisher

was used as recei veal ,

I NTRCWCTI ON

The di ff i cul t i es associated u,th the inhibi t i on oi

bsr iun su( fate ; c~ e in acidi c (PH 4)

environments Zfre

ue Li

docunwnted - . Thi s has been comnonl y attri twted

to the decreasing amount of ionized inhibi tw as the pH

is [o~er~s. Overcmng thi s prob[em is essent ial to

preventing scale format ion in certain North Sea oi I

f i elds, uhi ch tend to have acidi c format ion br iws wth

high (ea. 1000 ppn) tevel s of bariun.

We have measured scal e i nhi bi tor performance as a

functi on of systemati c changes i n structure, ari d

adsorpti on thcwnoclynamcs (on bori urt sul fate) in art

eff ort to devel op a more fl rdmnenta~understandi ng of

the mechani sms of scal e i nhi bi ti on. Our sttxi i es have

l nhi bi tc, performance uas eval uated i n a stati c

bott(e test. Syntheti c formati on and seti uater bri

used i n the test uere prepared based on uater ana(y

fromNorth Sea formati on bri ne and seawater. The

composit i ons of these brines are l i sted in Tab(e 1.

The formati on bri ne contai ned 730 mg/ L bari um on,

uhi Le the seawater contained 2650 wL sul fate

i on.

The test procedure involved pi aci ng the i nhi bi t

the formation brine, fol towd by PM adjustment uith

to the desired va(ue (usual l y 4.0). San@es were

equi ti bratad i n a water bath (85C) al ong ui th samp

of pH-adj ustM sea water bri ne. Upon teqw?aturc

equi I i brati on, the sea uater was addad to the forma

water/i nhi bi tor sampl es i n a 15:8S ML rati o.

Thi s

corresfwwds to a SOL

2- :Ba2+ rati o of apfwoxi matety

lad tc the deve

bari um su(f ate

ph 4 than any o

tested.

opnent of several new proprietary

The bott les were at~owd to stand in the bath at 85

nhi bi t ors whi ch are more ef fecti ve at overni ght ( approx. 17 hrs. ) . A~fwot $ uere taken a

the c-merci al product s uhi ch \ e have di l utad 75% i n dei oni zed uat er and i rm adi atel y

analyzed for resfdual bariun using Wait absorptio

spectroscopy. Fi (trat ion of the Sanp(ea through a

w f i(ter was observed to have no ef feet on measure

i eval s of bar un ion.

References and f i gurea et end of paper.

A va~ue of O% inhibi t i on uas taken to be the

711


2/7

CORI (ELATIONOF SCALE l NHI BI TOR STRUCTURE UI TH ADSORP71W THERMl ~YNAMCS

2

AND PERFORMANCE IN .NHI BI TI ON OF BARI UN SULFATE IN I .WPM ENVI i WNHENTS

concentrateior (mg/L ot bsrlun in a % ankj sanpl e whi; h

contained no inhi j i tor . 100% inhibi t i on was taken to

be 621 mg/ 1 bari un.

Percent i nhibit i on for any given

i nhi bi tor sanpl e was ther cal cul ated accordi ng to

equati on 1.

(sar.$nl e- bl ank)

% Inhibi t i on =

. x 100

1

(621

- bl ank)

Seeded gronth bott(e tests Mere conducted as

descri bed above except ttrat 0.5 g of pwti ered bari un

sul fa*e Has t .kkd to the format ion brine prior to PH

adjustment.

B.

i nhi bi tor Adsorpti ti , Test

~~sorptionhermodyn mi s of state inhibi tors on

bsrim sul fate Mere determned according to the

fol( ow ny procedure. 20 mL of a 500 pgsnsol ution of

act ive inhibi tor in deionized uat : r were p~aced in a

test tube contei ni nS a precise~y uei gh~ amount (5-2Q)

of baritxnsulf ate. A BET surface anatysis reveal ed the

bariun sul fate to possess a surface area of 2.994 x 104

cm2/ g. The tube uas capped and vi gorousl y stskenat

regul ar i ntervals over the course of a day and a(l o~ed

to set overni ght.

Inhi bi tors uere at(oued to absorb at

roan temperature and at 85C in a water bath. The

tubes uere then centr i fuged for 1-2 mnutes. The clear

supernatant uas removed ar- dti r~e:xl for phosti onate

concentrati on, usi ng a Zr (I V)-arsenazo ti trati on

devetoped for thi s purpose.

Fol l oui ng the methods of Naono6, Mads uas

cal cul ated from

Gads

= -RTi n[(Ci f ) V/ gCfATl

(2)

Uhere ci=51313ppr?, Cf=f i na( phOSphOf%te concentrati on,

g=grams of bari un su(fate i n the tube, A=bari un sul fate

surface area pw gram T=mono(ayer thi ckness and V=voi -

una of solut ion. AHadS was cal culated from

T1T2 (n

cT2ci -cT2cTl

AH CR

ads

T1-T2

cTl ci - cT2cTl

uhcre CT, orti CT2 are the ffna( phosphonate

concentrati ons at temperatures T, and T2.

AS ads uas calculated frMaGads at i~ads using,

as ads = AH

adS-AGadS)/T .

(4)

Since ue have no info mst ion about t , the

monoi ayer thi ckness i n equati on 2, we have used for the

purpose of our ca~culat ions a value of 1X10-7 cm This

i s the va(ue gi ven by Naono6 for sodi um tri ~ yphosphate.

The nccuracy of this val ue shoul d have mnimal i mpact on

c~ usi ons ar~;i n~ from corrperisons of

AGadS

sim[ar types of inhibi tors. since t i s not ex

to vary si gni fi cantl y.

RESULTS ANO DI SCUSSION

Figure 1 is a p[ot of percent inhibi t i on

versus l og mo, ecul ar uei ght of a horm~gous se

phosphonete i nhi bi tors, for non-seeded condi ti

25 w of i nhi bi t or i n t he st at i c bot tl e t est.

i s al so i i st ed i n Tabl e 2. As can be seen i r ,

the performance goes thrcugh a maxi mun ui th re

mol ecul ar wei ght.

This effect most l i kely ref

d.angi ng edsorpti on characteri sti cs as nw e.~

i s vari ed.

Fi gure 2 i s a pl ot of l og mol ecul ar wei gh

same seri es of i nhi bi tors versus the me3sured

The data in Figure 2 i l lustrate that as molecu

i ncreases, &a4s beccmes i ncreasingl y negati ve

suggesting that adsorpti on i ncreases ui th i nc

mecular ueigh t l t o a poi nt . Such a resul

consiste).t w th l dti -sesvnental attachment; a

nei ght i ncr~ases, adsorpti on i ncreases and the

reversibi l i ty of the adsorption decreases, due

i ncreasing nurber of poi nts of attachment.

Co

t hi s t rend i s a decrease i n di f f usi on rat e wt

i ncreasi ng motecul ar uei ght, resul ti ng i n feue

col l i sions between i nhi bi tor and bari un sul fat

The result is that at hi gh mo(ecutar weight,

effi ci ency drops off, as demonstrated i n Figur

If the pri mary mechani sm OT scal e i nhi bi t

i nvo~ved the bl ockage of act:ve growth si tes

crystal surface, then i t brouldbe reasonabl e

correl at ion betueen~ads and percent inhibit i

correl ati on appears to be absent between Fi gu

ho~ever, since the mexi rnun i n these two fi gure

for di fferen: mecular uei ghts. An exce~~ent

occurs, however, betueen Fi gure 2 and Fi gure

a plot of percent inhibi t i on obtained for the

of i nhi bi tors under seeded grouth condi ti ons.

unseeded experi ment, bari um sul fete parti c(es

exceed a cr i t i cal si ze (~ t i cal nucteus) bef

thermodynamcal l y stabl e due to the unfavorab

chemcet potenti ai associ ated ui th surfac~ si

so(vated i ons.

A very sma(( crystat embryo h

rat io of sur face awns to tw~k atoms, so that

stage there i s an energy barri er to homogeneou

nucleat ion. I f stabie growh sites exist , ho

as on the ual l s of t he cont ai ner , or on t he s

relat ively Large crystat seeds, then there is

reducfxl energy barri er to crystal l i zati on.

U

I eterogcneous l

corn?iti ons. b(ockage o j rot i

expected to be the prl l i cpvmechani sm of i nhi b

tne good corrc[at i on betueer, _&ad~ i n Fi gure

Fercent inhibit i on in Fi gure 3 support thi s c

An addi ti onal mechani sm of i nhi bi ti on, o


3/7

SPE20. 88

PATRi CK J . BREEN, BRUCE N. DI EL AND HARTLEY I f. OWNS

pro~sed by Naonod ,

can be used to expiain the

di ff erence i n the performance maximum for Fi gues 1 and

.

c. As i l l ust rat ed i n Tabl e 3, AHads i s gm ti ve

(endothermc adsorption) for a( 1 of .he i nhibitors

tested. Tni s mws that inhibi tor adsorpt ion ui l l

cnuse the chemcal potent ia( of sur fs@ & tes to be

even nme unf avora~(e, thereby rai sing the energy

barrier for further grouth needed to reach cri t icat

nucl eus si ze. Thus, endothermc adsorpti on i ncreases

the probsbi Ii ty that the embryo ui I I redi ssolve.

Si nce the msxirman in Figure 1 OC(WS at a lower

motecular ueigl , t than in Figure 2, i r a%ars that thi s

type of homogeneous contri buti on t, ) the mechani sm of

sca e inhibi t i on t s more i J ni f i cant for lower

mol ecul w wei gh: i nhi bi tor:.

The isoelectr ic point of bef iun sul fate uas

reported by Wl l i ams, et al . 8

to corre~pord to a pl l of

3.8, msaning th,at at PH 4.0 there i s a sl i ght excess of

cvera.( negati ve charge on the surface.

Thus, the

erdothermcity of the adsorption derives from

el ectrostati c repul s~-

xtueen the negati vel y charged

bsri un sul fate :, urfaceand the negati vel y chargd

functiona( groups of the i nhi bi tor motecute.

I n order for adsorpti on to be si %maneous

(energet i ca( \y favorabl e), the posi t ive& ads must be

over c~ by a Large posi t i ve &ads. The di ssoci at i on of

uater mol ecul es whi ch are hydrogen-bonded to the

inhi bi tor motecule, as the inhibitor adsorbs to the

bsr iun sul fate surface, can impart such a vaiue to

As.

I t i s i nt erest i ng t o not e t hat scal e

i r %ors ui t hASads < 16 caL;mol K (Tabt e 3) gi ve

poor performance in the stat ic btt (e test (Table 2).

The Loi iervalues for&ads presmab~y arise from the

smal l er hydrati on s~ere such i nhi bi tors possess

pri or to adsorpti on. The data sugges that

successful state i nhi bi tors shou~d possess structures

ui th mnimal hyti ophobi c content.

This conclusion

Has

al so reached by van der Leeden ard van Rosma[en i n a

publ i shed $tui y eval uati ng w ycarboxyl ate scal e

i nhi bi tors .

The percent inhibi t i on as a funct i cn of PH is

presented for severel di fferent inhi bitors i n Fi gure 4.

Most i nhi bi tors tested showed i n+roved i nhi bi ti on w th

i ncreasi ng pH. The i ncreased ioni zation, due to higher

pH, along w th an increased negative charge on the

bsri un sutfate embryss, shoutd resul t i n adsorpti on that

is more endothermc and therefore more (i kely to

destabi l i ze bsriun sul fate embryos, whi ch are smsl{er

than crit i cat nucl eus size. In spite of the increasingly

posit i veAHads - + ads coutd sti [( increase due to an

increasingl y posi t ive Asads arisin9 from the iar9er

hydrati on smere 9enerated by the added charge on the

i nhi bi tor.

Thi s i s exact(y what was observed uhen

ads ads

ad &ads were determned for i nhi bi tor

A at PH 8.0 (Tabte 2).

The adsorpti on curves i n Fi gure

5 for i nhi bi t or s A and

D

appear to be representati ve for

rwxt non-pel~ric scale inhibi tors.

H gher mo(ecul ai wei ght. ~ ymeric scale i nhibito

( t , G, and H in Figure 5) however , ah~ di f ferent

adsorpt ion behavior. Figure 5 i 1lustrates that at pH

5.5, the amount of aosorbed i nhi bi tor decreases ui th

imeasi~ natecu~ar we; ght whil e at < 4.0, adsorpt

aeema to i rwrease w th i ncreasi ng nmecul ar wei ght.

These trends al ao seem to corre.ate ui th data presente

in Fi gure 4, where (OWmol ecular uei ght i nhibitors (B

C; out~rform higher molecul ar weight inhi bi tors (E, I

and J ) at pH ~ 5. 5.

Li terature precedent exists which can ~ d in

expl ai ni ng t hese resui t s. Ui l l i sms et i~

. - .

observed

decrease i n the adsorpti on of sodi un carboxycel l ui ose

bsr iun sul fate as the pH uas rai sd, and at t ributed th

effect to increased charge den~ ty on the polymer at

higher pH which Leads to J bui l chp of charge near the

bari trnsul fate surface duc to msdsorbed pol yner

segments.

Thi s shi etdi ,~y charge hi l dtq then reps(s

other, si ml arty charged F~ yners away frcm the surfec

Thus, as pH i s rai sed, charge density of the po(ynwr

i ncreases and adsorpti on decreases.

Inhibi tors E, 1 md J represent a hcmogous ser i

wherei n the total nurber of phosF ~nate groups per

mol ecute i s steadi (y decreased, correspondi ng to a

decrease i n charge density. Fi gure 4 i l~ustrates that

as the nwber of phosphonate groups i s decreased

(E > I > J ) , the area of msximun per formance shi f t s t

hi gher PH. Thus i t a~ars t hat t here i s an opt ims(

charge densi ty for such i nhibi tors whi ch al( ows for t

greatest amount of adsorpti on, and whi ch an be

controt(sd by PH or degree of substi tuti on.

Our dots supports the hypothesis that two mechani

of sca(e inhibi t i on are operat ive: one lvoLving

endothermc adsorpti on resul ti ng i n di r,ol uti on of bs

sul fate embryos, and another i nvo(ving essenti al l y

i rreversi bl e

Wiymer

adsorpti on at the acti ve grouth

si tes Of bariun sulf ate nuclei

, r esul t i ng i n t hei r

biockage.

The fi rst mechani sm i s expected to be nwre

important for (OWmecular weight inhi bi tors si nce s

nw ecul es uoul d have di ffi cul ty b(ocki ng gro~th sites

si nce adsorpti on i s expected to be hi ghl y reversi bl e.

Endothermc adsorpti on i s not as essenti a( for pol ymer

i nhibitors si nce they can i rreversib~y adsorb to the

crysta( growth sites. The thermodynamc date in Table

supf .wrt such a statement:

Wyner i c i nhi bi t or s such

inhibi tors F, G and H tend to have Vatues Of ~Hads n

1200 cal / mol , uhereas sma[l motecul e i nhi bi tors such

A, L and N often have Va(ues for ~ad~ c~oser to 200

cal/ mol.

SUMMARY

Low nmecu(ar wei ght i nhi bi tors perform best i n

regions of relat ively high pH (z7) where they are

i onized to a greater extent. Polyneric i nhi bi tors,

especial l y pol ymeric phosphonates, are l l uety to show

performance maxims as a function of pH, due to

713


4/7

CORRELATION OF SCALE I NHI BI TOR STRUCTURE WTH ADSORPTION THERNCOYNAHICS

4

AND PERWRWNCE IN I NHI CI TION Of BARIUM SULFA , . . N LOU PH ENVIRONMENTS

el ectrostatic shiel di ng effects at the scale surface,

uhich are deperdent on tbe extent of ionizaticm

Eff estive l ow mol ecu(ar wei ght i nhi bi tors operate

by destebi l i zi r,gbari m su(fa:e txrbrycs through hi ghl y

endothermc adsorpti on, dri ven by fabu, abl e ent, -opy

condi ti ons ass~ci ated w th the rei ease upon aciso-pti on

of a Large nunber of waters of hydration.

i ydrophobic

secti ons are therefore undesi rab[e for good i nhi bi t i m

Increasing molecul ar weight :to a point) leads to better,

ard l ess reversibl e, sdswpti on:

a mechani sm i nvol vi ng

blockage of act ive grouth si tes is therefore inpl ied fcr

such i nhi bi tors.

For thi s reason, ~[ymeric inhibitors

are most l i kely to yie d good inhibi t i on in si tuat ions

uhere a signif icant nurber of nucl eating sites a[ready

exi st.

REFERENCES

1. G. R. Chesnut , G. D. Chappe Ll , D. H. Emnons, The

Devel opment of Scal e I nhi bi tors and I nhi bi tor

Eval uati on Techni ques for Carbon D oxi de EOR

Fl oods, Paper SPE 1A260, presented at the SPE

I, i ternat ional S~siun on O lf i eld Chemstry,

San Antoni o, Texas, 1987.

2.

E. R. McA, tney, A. E. A(exander, J . Col i oid Sci . ,

Vol . 13, p. 383, 1958.

3.

4.

5.

6.

7.

8.

9.

J . E. Ramsey, L. M Cenegy, A LalWriorY

Evacuati on of Bari un Sul fate Scal e Inhi bi tors

Lou pH for Use in Carbn D oxide [OR Floods, i

Paper S~E 14407, presented at the SPE Smual

Conference, Las Vegas, Nevada, 1W5.

D. u. Gr i f fi t hs, S. O. Rober ts, S. - T. Lt 1,

S

a

l) lnhibi t ion of Caicim S ~fate D hydrate CrYsta

Grouth by Phosphoric Aci ds - I nfl uence of

I nhi bi tor Structure and Sol uti on pH, Paper SPE

7862 presented at the SPE I nternati onal Symywsiu

on O l fi el d and Geothermal Chemstry, Houston,

Texas, 1979.

U. H. Leung, G. I i . Nanco( las, J . l norg. Nucl .

Chem,

vol. 40, p. 1871, 1978,

Ja-ono,H.

Butl.

Chem Sot . Jpn. , Vol . 40, p 11O

1967.

A. E. N elsen, Kinet ics of Precipi tat ion,

Pergamon Press: Oxford, London, 1964.

P. A. Ui l t i ams, R. Harrop, G. O. +hi l ( ips, Chem

Sot . Faraday Trans. 1. , Vol 78, p. 1733. 1982.

M C. wan der Leeden, G. P. van Rosmalen,

~ Inhibit i on of Bariun Sutfate Depait i or, by

Pol ycarboxy[ates of Vari ous Mol ecu(ar Structure

Paper SPE 17914, J ui y 1988.


5/7

SW 206

Tabl e 1 -

Synthetic

Brine Compositions

.

Formation Brine

Seawater

Salt

NaCJ.

mu/L

65,520

Salt

NaCl

*3

.,

Bac12.2H20

1,300

Na2S04

3,919

Table 2 - Static Bottle Test Results

BaSO

t

Inhibition

Inhibl ora MW

Unseeded

Seeded

A

B

c

D

E

F

G

H

:

K

L

M

N

436

710

847

984

1,920

3,840

31,800

159,000

1,660

1,390

492

206

205

275

7

60

49

51

78

57

42

34

71

49 -

0

0

0

0

4

47

37

39

64

79

14

35

2

2

aA-H; homologous series, inc. MW.

E,I,J; homologous series, dec. charge

density.

K,L; typical commercial

phosphonate inhibitors. M,N; other

phosphonate inhibitors.

Table 3

- Thermodynamic Data for Adso~ption Onto BaS04

Inhibitor

AHadS Cal/i:ale ASad~ Cal/mOle~ AGad~ Cal/rnOle

A, pH 4

A, pH 8

B, pH 4

D, pH 4

E, pH 4

F, pH 4

G, pH 4

H, pH 4

I, pH 4

J, pH 4

K, pH 4

2061 t 20G

3139 ? 7

1243 k 663

951 t 162

1224 f 385

492 k 280

1031 t 467

1180 t 366

1866 k 247

1085 t 247

2025 i 240

19.9 5

0.9

24.8 Y 0.1

17.2 k 2.1

16.5 t 0.4

18.0 t 1.5

16.6 t 0.8

17.5 t 1.6

15.7 t 1.0

19.4 i 2.5

15.1 i 1*O

15.8 i 0.1

715

-3818 t 240

-4214 t 48

-3852 f 61

-3921 ? 57

-4112 2 252

-4423 k 151

-4163 t 62

-3468 2 66

-3876 ? 199

-34C0 i 335

-2656 t 250


6/7

100

r

1

0

J

:.50

3.s0

4.50

5.50

10S MW

Figure 1. inhibition as a function of

MW for

unseeded condi ti ons.

1.s0

3.50

4.50

$.5e

Fi ure 3. inhibit on as a function of

MW for wedcd conditions.

z

R

> 41eo

1

3700

,,., ~.~

2. 0

3,50

4.5e

10S MW

Figure 2.

-,\GwdB on BsS04 as a function

MW. T=298 K.

80

60

-

40

1/=

20

0

r-l

.

80

O

40

20

m

MW-7

c

NW-84

33

Mw-l

1

MW-1

J

MW-1

o~-

2.5

3.5

4.3

5.5

6.5

7.5

QH

Figure 4. inhibition m a function of

PH. unseeded conditiotim.

&

/

/

v

/

Ssoo

1.0 2.0 3.0 4,0 $.0 6.0 7.0 8.0

-A

kAw.436

D

uw. n14

-P

UW-3,84Q

-+-- o

Mw-31,800

-H

MW-lj9,000

pH

Figuro 5.

-,jGadm a function of PH.

T=298 K.

716


7/7

t

CORRELATION OF SCALE I NHI BI TOR STRUCTURE WTH ADSORPTION Tti ERkiODYNAMCS

?

ANDPERFORMANCEIN I NHI BITONOF BARIUMSULFATEI NLOUf J HENVI RONMENTS

SPE2068

concentrati on (mg/ L of bari umi n a btankl lsrxmptewhi ch

contai nedno fnhfbi tor. 100%inhi bi ti onwas takent o

be 621 mg/ t barf wn. Percent i rrhfbf tfonoranygfven

fnhfbi torsampl ewas thencal cul atedaccordi ngto

equati on1.

sample -

bl ank)

% I nhi bi ti on=

x 100

(1)

(621 - btank)

Seedei growthbott l etests Mere conductedas

descri bedaboveexcept that 0. 5 g of pouderedbarfum

sul f stewas adci adto the formatfonf>ri nepri or to pH

adjustmant.

B.

I nhi bi torAdsorpti onTest

Adsorpt i onthermodynamcsof scel e i nhi bi torson

bari umsul fatewere determ nedaccordi ngto the

f ol l ow ng procedure. 20 m of i ? 500 Mcol ut i on of

act ive fnhibi tor % defonized water ware placed in a

test tube contai ni ng a precisel y wei ghed mount (5-20g)

of bari umsul fate. A BET surf aceanal ystsr eveal edthe

ba fumsul fate topo$sess a surf aceareaof 2. 994x 10{

5

cmg. The tubewas cappedarw vigoroustyshakenat

regul ar i nterval sover thecourseof a day and al l owed

to aet overnight.

I nhfbf torswera al l owedto absorbat

roomtemperatureand at 85C i n a water bath. The

tubeswere then centri fugedfor 12mnutes. The cl ear

supernatantwas removedand ti tratedfor phosphonete

concentrati on,usi nga Zr (W-arsenezo ti brati on

deveiopedfor thi s purpose.

Fol l owngthemethodsof Naono6 ~ad~ was

cal cul ated

from

(2)Gads = RT1n[(Ci - CfW9CfTl

where Ci=500ppm Cf=f fm phosphonateoncentratt on~

g. gramsof barf~ sul fatei nt he tube, A=bari umsul f rNe

surf acearea par gram T=monol ayerthi cknessandV=vol-

ums of sol uti on. ~Hods W8S

cal cul atedl om

T1T2

cT2ci - cT2cTl

AHad~ ~R [n

. .

T, - T2

cTl ci - cT2cTl

uhereCT1 and CT2 are the f i nal phosphonate

concentrati onsat temperaturesT1 and T2.

&ada was cal cul etadf r0??lA6adsQnd4~Gd~ usf n9

ASods (~Had~

=& ads)/ T .

(4)

Si ncewe haveno i nformati onabout t, tha

monol ayer thi ckness i n equati on 2, wehaveusedfor the

purposeof our cal cul at i ons val ueof lx10-7 cm. Thi s

i a thevol ue gi venby Naono6for sodi umtri pol yphos~ato,

The accuracyof thi s va[ua shoul dhavemnfmal fmpact on

concl usi onsari ai ngf romc~ari sons of AGads for

sim tar typeaof fnf] fbft ors,i ncet i s not expected

to vary si gni fi cantl y.

RESULTSANDDI SCUSSION

Fi gure1 i s a pl ot of percent fnhi bft fonobtai ne

versus l ogmolecul arweight of ahomologousserfesof

phoaphonatei nhi bi tors,for non- sesdodcondi ti onaat

25 qxn of i nhi bi tori n the stati cbottl etest. The da

i s al so l i stedin Tabl e2. As can be seen fn the ffgu

the perf ormancegoes througha maxi nwmw th respectto

mol ecul arwei ght. Thfa ef fectmost l fkel yrefl ects

chengi ngadsorpti oncharacteri st i csas molecul arwefgh

i s vari ed.

Fi gure2 ia a

pl ot of l ogmol ecul erwei ght

for th

samegerfes of inhibitors versus the lnaaSUIWf ad5.

The data fn Fi gure2 i l l ustratethat as I rdecul arwefg

i ncreases @ads b@c~s i ncreasi ngl ynegati ve

suggesti ngthat adsorpti onincreases~i th i ncreasi ng

molecul arwei ght, up to a pofnt. Sucha resul t i s

consi stentw thrrdtf - se~mentalatt achment;as molecu

weight i ncreases,adsorpti oni ncreasesand the

reversi bi l i tyof the adsorpti ondecreasea,due to the

i ncreasi ngnw ber of pofnts of att achment. Counteri n

thi s trend i s a decreasei ndi ff usi onratewft h

i ncreasi ngmol ecul arweight, resul t i ngin fewer

col l i si onsbetween i nhi bi torand bari unsutf atenucl e

The resutt f s that at hfghmol ecul arwei ght, i nhi bi to

ef f i ci encydrops of f , as demonstratedfn Fi gures1 an

I f the prf marymechani smof scal e i nhi bi ti on

i nvol vedthe btockageof act vegrowth sft es on the

crystal surf ace, then i t wou(dbe reasonabl eto expec

corr el ati onbetween~ads atI dPerCent i nhi bi ti on. Su

corr el ati onappears to be absent betweenFfgures1 an

however, si nce themaxi mumi n thesetwo f i guresoccur

for di f ferentmol ecul arwei ghts. An excel l entmatch

occurs, howcvar, betweenFi gure2 and Fi gure3, whi ch

a pl ot of percent i nhi bi ti onobtei nedfor thesame se

of i nhi bi torsunder - growthcondftf ona.

In an

unseededexperi ment,bari umsul f ateparti cl esneed to

exceeda cri ti cal si ze (cri ti cal nucl aus)before thay

thermodynamcal l ytabl e7due to the unfavorabl e

cherni cotpotenti al associ atedw thsurf acesi tesvers

aol vatedi ons. A very smal l crystol embryohas a l ar

rati oof surf aceatoms to bul k atoms, so that at such

staaethere i s an energybarr i ar to hci ncganeous

nucl eati on. I f stabl egrowthsftes exfst, however, s

os on the wal l s of the contai ner,or on the surf aceo

rel ati vel yl argecrystat seeds, then there i s a great

reducadenergybarr i er to crystal l i zati on. Under suc

I l heterogenaousll condi ti ons, bl ockaga of growth sites

expected to be the primarymechani em of i nhi bi ti on, a

tha good corr elati onb@weeT~-&ad$ i n Fi gure2 and

percent i nhi bi ti oni n Fi gure3 support thi s concl usi

Anaddf ti onal mechani smof i nhfbf ti on,ori gi nal

712

Documents

20688 Correlation of Scale Inhibitor Structure of Barium Sul