Chemistry of alkaline scale inhibition in seawater desalination by flocon antiscalant 247

Desalination, 31(1979)289+?98 O~~ScientifiicPublishingCompany,Amstadam-_PrintedinTheNeth~ds

CBEMISTRY SEAWATER

OF ALEALINE

DESALINATION

S. W. Walinsky Pfizer

Central

SCALE

INBIBITION

BY FLOCON

and

Research,

IN

ANIISCALANT

247

B. J. Morton

Groton,

CT,

USA

06340

SUNNARY

Alkaline chemical

scaling

changes

which

FLOCON Antiscalant and

magnesium

and mineral

are

247,

hydroxide

show

that

foulings

247

reducing

seawater's

antiscalant

complexes

disrupts

bicarbonate FLOCON

its

High

clearly

sealant scales

threshold

decomposition

inhibitor, at both

seavater

scale and

of pbysico-

of bicarbonate

suppresses

calcium

the bicarbonate

vbich

bicarbonate/carbouate

alkaline

by a series

ions.

carbonate

decomposition

sequence.

synthetic

interactions

FLOCON

that

the

antiscalant

scale

impedes

provides

alkaline

scaling

calcium

scale

contained

magnesium

14C-sodium

decomposition The

potential.

catalyzed

bicar-

rates,

thereby

formation

of Ca+2/Mg+2-

mechanisms

for accel-

the

scales

14

247

chemical

under

high

calcium carbonate and . experiments using Atlantic

significantly

into

further

the

reduced

incipient

and

of sparingly force

temperature

the

Ocean

the

alkaline

by

in-

of anti-

precipitated earth-autiscalant

incorporation

desalination

hydroxide

seavater

fouling

Codeposition

disperses

soluble, for

magnesium

alkaline

scales.

precipitation

driving

C-radiolabelled maleic anhydride

vith

control

Formation

in the bloudown.

complexes into

of

with

thermal

scale

247 vas synthesized vith

temperature

demonstrate

corporation

the

occurs

decomposition.

Antiscalant

to determine scales.

plants

intervention

the

retards

effectively

erated

by

of

in refluxing

FLOWN

by

threshold

stages

studies

distillation

initiated

a new

deposition

Kinetic bonate

in seavater

of antiscalants

conditions.

INTRODUCTION In support plants, hold

the

scale

mechanistic FLOCON

of research

chemistry inhibition studies,

on new

the

have and

been

247

- a new, seavater

carbonate)

and/or

scaling

reexamined.

describes

the

maleic

brucite

for

threshold‘antiscalantsl

alkaline

operated

Autiscalant Carefully

(calcium

of

process This

chemistry

and

paper

(magnesium

289

are

reports

of alkaline

acid-containing,

evaporators

affected

hydroxide)

seawater

the mechanisms tbe

scale

polymeric primarily scaling.

distillation of

results inhibition

scale by

thresof

these by

inhibitor. aragonite

Recently.

these

wALINSKYANDMOKr~

290

scales have

mineral lant.Such acid

treatments

controlled

eliminate

carbonate 26 reactions-

chemical

+2

by

desalination

4

20B

anhydride

thereby

+ Hz0

co2

4

sodium FLOCON

hazards

E3

+ H*O

frequency

bicarbonate

enabling

scaling

sulfuric

by

the

fol-

(1) (2)

+ + 2ou-

(3)

(brucite)

rates

was

(4)

of reactions

to synthetic 247

with

occurs

antisca-

(aragonite)

relative

Antiscalant

polymeric

co;

*

Mg
the

by

associated

hydroxide

+

+

investigated

conditions.

1,4-14C-maleic

and

co2

+COIj

wg+2+ present study has 14 C-radiolabelled adding

corrosion

B

co;

The

increasing

and magnesium

2Iico; Ca

with

the

Calcium

dosing.

loving

been

brines

synthesized

its mechanisms

(1 and

under from

of action

3)

varied

radiolabelled

to be

determined.

EXPERIWENTAL Synthetic from

reagent

lnmol), and to give

Nuclear) The

sodium

of was

rate

added,

of carbon

in Oxifluor-CO2

was

standard

(1.23

used

NaOH

ing

(1.03

mmol),

for

the

solution

was

sodium the brine

the

samples

FLOCON

conditions

J,4-14C-maleic

anhydride

chemical

and

247, (1.0

properties

the

radioactivity

(10

repeated

a proprietary

brine Mark

for FLOCON Titrator

product,

Amershsm)

into

as desalination

prepared (1.01 water one

England (102 was

was

+

l°C)-

continually

dioxide

was

trapped

radioassayed

I Liquid

in

Scintillation 14 C-internal A

samples.

efficiencies-

in the

mmol! , and

active

Automatic

as well

filtered

(1.39

curves

ntci;

Carbon

of aliquot

ppm

New

to reflux

scintillation

were

sulfate

lo Millipore),

decomposition

Chicago

were

chloride

in distilled

(0.45

assays.

A Nuclear

247

on a Netrohm

Antiscalant

rapidly

bicarbonate

experiments

titrationfcomplexation

filtered

heated

and

magnesium

dissolved

was

to determine

Antiscalant

were

potassium

(10 ng/uCi;

Nuclear),

determining

experiments

mmol),

bicarbonate

scintillation

Nuclear).

decomposition

and

ambient

and

which

(N-E.

and/or

(47.2

mmol),

evolution

(N.E.

decomposition

chloride

(0.31

liquid

to the

mnol)

titrant. 14 C-FLOCON

Physical

dioxide

added

Reported under

then

cocktail

Bicarbonate chloride

and

solution

was

for bicarbonate sodium

bicarbonate

by radiochemical

an Aquafluor System

brines

chemicals,

After solution. 14 C-radiolabelled

50 ml

microcurie

measured

seawater grade

presence magnesium

of calcium chloride

dosage). Antiscalant - Hodel

was

247 were E436

using

synthesized

the polymerization scale

control

by

determined 0.45E

incorporatreaction.

performance

W&INSKp of

AND EfoBTON

14 C-FLCCON

247

Radiochemical minute

per

groups

which

the

stage

flash

standard

Scales

were

analyzed

247

was

was

determined

determined

for by

by

liquid

scanning

(2.44

(503.64

of brine.

Total

dissolved

(2.44

uenol),

sulfate

(28.21

of synthetic

Bicarbonate

10.5

magnesium

mmolar

bicarbonate alkaline plants

represents

by

of

that

catalysis

for

fouling

X-ray

prepared

from

was

and

chloride

(9.92

solids

- 35.10

from

mmol)

presence

measured.

Carrutbers. and

sodium

morphology

mmol),

one

sodium

kilogram

bicarbonate

(555.35

to afford

analyses.

bicarbonate

(25.24

sodium

17

FLCCON

Scale

to make

chloride

the

diffraction

chloride mm011

prepared

sodium

in

absorption,

and

(9.92

was

hr

Ocean conditions.

in a laboratory

(Oxifluor-C02).

magnesium

g/kg.

Atlantic

11.5

by Auerbach

(SDI)

seawater

and

ion

ussol), one

sodium

kilogram

g/kg.

The pR

increases

seawater

vas

flash

magnesium

decomposition

by magnesium

and

ions. which

contained carbon

recycle

rates Calcium

plants,

to assess are

is consistent

the

added

vith

onset

of

14C-sodium

assays.

The

concentration and, their

is markedly previous

in rate-

investigated

factor

seawater

of 2.0, the

Figure in

more

The

.

continually

synthetic

influence. faster

desalination

bicarbonate

in addition,

mmolar,

the maximum

scaling

was

55.4

2.50

in

1) was

evolution

significantly

acceleration

determines

(equation

are

is only

of bicarbonate

dioxide

scintillation

varied

which

controls

preconcentrated,

(HSF)

were

species decomposition

and

seawater

concentration

decomposition

which

liquid

in typical

bicarbonate

thermal

Bicarbonate

experiments

or magnesium

concentrations

whereas

disappearance

multi-stage

bicarbonate

calcium

acid

pressure

conducted

atomic

vas

chemical-limiting

radiochemical

in these

calcium

calcium

the

synthetic

of bicarbonate

simulate

by

- 35.26

dissolved

potential.

decomposition.

in refluxing

used

exchanger

assays

mmol),

for

heat

metals

mnol),

(10.21

refluxed were

chloride

potassium

and

is responsible

monitored

(28.22

respectively,

scaling

limiting

rate

and Total

per

carboxylic

Decomnosition

Since and

anaol),

product.

disintegration

with

or elevated

described

seawater

solids

x 10'

conducted

runs

microscopy

potassium

chloride

brine.

was

been

earth

Synthetic

calcium

were

atmospheric

scintillation

and

Calcium-containing

antiscalant's

in which

has

electron

sulfate

mmol),

the

of

pressure

synthetic

ussol), magnesium

fraction

seavater

(SSFE) SSRE

alkaline

Ragnesi-containing

chloride

the

of the

9.63

under

Elevated

evaporator

operation

commercial

was

experiments

to reflux

ppm).

the unlabelled

atoms.

control

experiments,

to

antiscalant

a small

carbon

scale

(lo-13

identical

isolated

Only

heated

atmospheric

single The

was

247

the

radioactive

temperature

of PMCON

essentially of

(dpm/g).

contained

seawater In

were

activity gram

High

291

the

to

concentrations 1 shows

presence

pronounced 7,g publications.

of than

WALINSKP

292

AND !KnlToN

13 HCOs- (6.15 mmolar) with no polyvalent metal ions 0 HC03‘ (6.15 mm&r) a

0

and Mg+2 (52.5 mmolar)

HCOJ- (6.15 mmolar) and Ca+2 (20.6 mmolar)

10

20

40

30

-< 50

60

Time (min) Figure 1. RATE OF THERMAL

BICARBONATE

DECOMPOSITION

(102OC)

Synthetic Seawater (Concentration Factor = 2.0)

Bicarbonate

decomposition

is reported'

-d(HCO;) -= dt

Direct to

involve

with

interaction a relatively

a double

negative

of

energy

a second

order

reaction.

(5)

k(HCO;)2

two negatively

high

to be

charged

transition

bicarbonate

state,

ions

hypothetical

would

appear

structure

co;

Calcium

and magnesium

Figure

1, reduces

ration

via

In similar and

the

complex

magnesium

catalyzed

overall

formation.

experiments levels,

1 J

charge.

FLOCON

decomposition

activation

energy

as shown

of bicarbonate, for

reaction

(6) by

charge

(6)

in stabili-

2 with 247

synthetic

sezvater

was

to decrease

shown

which the

contained rate

typical

calcium

of bicarbonate/car-

W.AJJNSKf

bonate

AND MORTON

293

decomposition,

duction

in the

Figure

fouling

2.

4.0z 2 ; sz z g

A consequence

of

such

retardation

would

be

a re-

rate.

&

FLOCON 247 (10 $5 m Active) in Synthetic Seawater with HCOi (52.5 mmolar) and Ca+* (20.6 mmolar) (6.15 mm&r). Mg

0

Control reaction without Antiscalant

3_0-

2.0-

x d 1.o-

Time (min) Figure 2. RATE OF CARBONATE DECOMPOSITION OF FLOCON ANTISCALANT 247

(102OC) IN THE PRESENCE

Synthetic Seawater (Concentration Factor = 2.0)

The

importance

desalting high

operations.

temperature

calcium

in solution use

at

with

threshold 2 cannot

A likely complex

which

bonate

calcium

and magnesium

ions

dosages,

disrupts

the

retardation by

is the the

on precipitated

formed.

shown

be explained

mechanism

scale

be

simple

the calcium

recycle

is more

later,

carbonate

may

decomposition

catalyzed

, thereby

by

of FLOCON's observed

in

cations. earth-bicarbonate

decomposition forming

preventing

in mag-

associates

In view

of divalent

function

temperature

resulting

of an antiscalant-alkaline

and magnesium

once-through

rapidly

complexes.

in field

is incomplete,

in high

247

of bicarbonate

antiscalant

and

extensive

FLOCON

to form

displayed

decomposition

Whereas,

sequestration

formation

calcium

is clearly

temperature

bicarbonate

decomposition

As will

rates

where

predominant

scaling.

Alternatively,

carbonate. loidsl'

is the

in low

plants

bicarbonate/carbonate

hydroxide

Figure

decomposition

Qualitatively,

desalination

carbonate

MSF plants, nesium

of bicarbonate

of the bi-

protective

heterogeneous

colbicar-

decomposition.

FLOCON 247

-

Chemical

Ca+2/b++2

Ccqmlexes

interactions

of FLOCON

Antiscalant

247 with

seavater's

major

scale

294

WALINSKY

AND

HORTON

forming cations were investigated. The titration curve in Figure 3 shovs that FLOCON 247 as a carboxylic acid polymer is largely neutralized under the alkaline operating conditions of HSF desalination plants.

When the titration curves were

repeated in the presence of calcium or magnesium ions, the acidity of the polymer was increased.

The titration curve shifts indicate that FLOCON 247 rapidly forms

alkaline earth complexes.

Little difference was noted iu the selectivity of calcium

or magnesium binding.

~Y!ITitration Curve for FLOCON

247

13 Titration Curve for FLOCON 247 in the presenceof Ca** (0.3 mmolar) o

Titration Curve for FLOCON 247 in the presenceof Mg+* (0.3 mmolar)

T&rant fml of O&N Figure 3. TITRATIONCOMPLEXATION

CURVES

NaOH) FOR FLOCON ANTISCALANT 247

Sequestration of alkaline earth metals by carboxylic acid polymers known for some time.

The stoichiometric chelation of calcium

has

been

by

anionic polymers 11 However, the has led to proposals to use these materials as detergent builders. stoichiotuetric use of polymeric sequestrants in detergent formulations or in scale control applications is too expensive.

Threshold scale control treatments use only

very low dosages, parts per million, of sequestrants.

The effectiveness of thres-

hold autiscalants in preventing scale formation is attributed to reduction of the 12 rate of crystal grovth. Nancollas and coworkers have demonstrated that calcium 13 14 15 and calcium sulfate crystal growth can be iucarbonate, magnesium hydroxide, hibited by the adsorption of very small amounts of scale inhibitors on the crystal surfaces.

The question has remsiued as to why other good wuomezic

such as ethylenediaminetetraacetic inhibitors.

chelating agents

(EBTA) do not work effectively as threshold scale

In the present study, a survey of mnaneric

and polymeric chelants

WALINSKY

295

AND NOBTON

such as poly(meth)acrylates,

polyphosphonates,

citrates, sulfonates, aminocarbo-

xylates, and many others indicates that sparingly soluble, aatiscalant-polyvalent metal ion complexes are required for threshold scale inhibition. The limited solu16 bility of these complexes provides the chemical driving force for incorporation of the scale inhibitor into the crystal lattice of the scales.

FLCCON 247 - Alkaline Scale Interactions A series of experiments was conducted with 14C-radiolabelled FLOCON 247 to determine whether the antiscalant is indeed incorporated into the alkaline scales formed.

Table I reports high temperature scale control results from experiments

conducted with authentic Atlantic Ocean seawater which was heated to reflux under both atmospheric and elevated pressures. (SSFE)‘~

A

laboratory single stage flash evaporator

which was designed to simulate field operating conditions was used to eval-

uate heat exchanger fouling.

In all of these experiments the scales were isolated

and then analyzed for calcium, magnesium, and antiscalant content.

Table I FLOCON Anriwalanr 247 - Alkaline Scale lnfcracrions Desalination ScaleControl Experimenrs Using Atlantic Ocean Seawater

The scale control results from the refluxing seawater and

SSFE

experiments

are in very good agreement considering the dissimilar nature of the experiments. Both experiments clearly demonstrate that FLOCON 247 is incorporated into alkaline scales under high temperature, threshold desalting conditions.

FLOCCN 247 intercepts

nucleation or incipient crystal growth at a very early stage since antiscalant/scale

WAUXXYANDHOR!TON

296 ratios

are

blowdown as

fairly

scales

inhibits

high. also

them.

Incorporation

indicates

The

that

of FMCON FLOCON

mechanistic

247

247

into

flash

disperses

implications

of

chamber

alkaline

this

data

and

scales

will

be

brine

as well

discussed

shortly. The was

selectivity

determined

or magnesium marized

in

of FLOCON the

SSFE

alkaline

in Table

247's

using

interactions

synthetic

scale

potential.

Sclrcti~iry

of FLOCON

The

SSFt:

97%

synthetic

of

the

chemical with are

alkaline

but

seawater

in these

of mixed

Ca+2/Mg+2

trol.

The

mixed

the

are

SSFE

not

trials

-FLOCON

double-layer

erals

as dolmite.

a

of antiscalant

amount

was

The

polymer

with

these

scales

either

experiments

calcium

are

sum-

did

not

ions,

complex

FLOCON

Antiscalant

antiscalantfscale

with

magnesium

contain

may

carbonate

investigated

Seawater

high

appears

complexes

Scalelntcracrions

Using Synrhcric

carbonate reports 12,18

any magnesium to enhance

interact or help

SSFE

precipitated,

the

The

with

amount

first,

formation scale the

in the

seawater. of

scale

con-

charged

snore soluble

complexes

synthetic

strong

synthetic

carbonate

to stabilize

with

shows

at

the

ions.

inhibited

interactions

results,

strongly

of Ca +2/Mg+2 -FLOCON in the

The

since

calcium

mre

247 ratio

scales.

The

literature

Precipitation

ions

Alhrlinc

as pronounced.

of calcium

of bicarbonate small

of

and Mg(OW)2

contained

II

-

calcium

complexes

antiscalant

217

scale.

carboxyl

consistent

electrical such

results

Expertments

without

magnesium of

carbonate

unexpected,

Scrle Corrrn~l

seawater

affinity

calcium

CaC03

which

II. T;blr

In

with

seawater

min-

absence Although

inhibitor

WALINSKY AND MOEJ!ON

297

deposited was only two percent alkaline scaling conditions.

incorporation level routinely obtained under

of

Therefore, FIRCON 247 is compatible with seawater at

high temperatures, and its precipitation is regulated by the amount of scale formed. Deposition of PLGCGN 247 into alkaline scales certainly retards mineral crystal growth, but high antiscalant/scale

ratios are not completely consistent with adsor19,20 of scale control, Coprecipitation of

ption-crystal growth inhibition mechanisms

sparingly soluble antiscalant complexes with alkaline scales is mechanistically Antiscalant-scale

more consistent with the data.

codeposition impedes further scaling

and disperses the precipitated scale into a less adhering formIn conclusion, formation of alkaline scale in seawater distillation plants is a sequential chemical-physical of bicarbonate ions. sition

process which is initiated by the decomposition

PLOCON Antiscalant 247 disrupts both the bicarbonate decompo-

scale forming stages of this sequence to inhibit calcium carbonate and

and

magnesium hydroxide

scaling.

ACKNOWLEDGENENl!S Authors

and Bryce

1.

2.

i: 5. 6.

would

Tate

like

for his

to thank helpful

John

O'Neill

discussions

for

and

conducting

review

the

SSFE

experiraents

of the manuscript.

scale inbibitors are additives ubich suppress mineral scale formation at usage levels which are too small to sequester the scale. For initial disclosures see references: E- A. BRBERLEIN, British Patent 223 614, 1923 and A. KIRKALDY, U.S. Patent 1 SO6 306, 1924. W. STDMD ARD J. J. MORGAN, Aquatic Chemistry, John Wiley C Sons, Nev York, 1970; Chapters 2 and 4. H. RILLIER, Proc. Inst. Hech, Eng. (London), Lp, 295 (1952). Threshold

W. F. LANGELIER, D. Il. CALDWELL AND W. 126 (1950). R. DOOLEY AND J. GLATER, Desalinationll, D. A. SKOOG AND D. M. WEST, FL, and Winston, New York, 19633 Rinehart,

B. LAWRRNGE,

Ind.

Eng.

Cbem.,

3,

1 (1972). Bolt, pg.

351.

7.

R. STUMPER, 2. Anorg. Allgem. Chem., 202, 227 (1931). R. STUM?ER~ 2. Anorg. Allgem. Chem., 204, 365 (1932).

9.

B. K. SRDKLA AND D. S. DATAR, Indian J. Appl. Chem., 35, 30 (1972). R. STIJHPER, 2. Anorg. Allgem. Chem., 208, 46 (1932). J. F. SCEAFFER AND R. T. WOODFMMS, Iad. Eng. Chem. s, 3 (1977). J. C. COWAN AND D. 3. WEINTRITT, Water-Formed Scale Deoosits, Gulf Publishing co., Houston, 1976; Chapter 7. M. M. REDDY AND G. H. RARCOLLAS, Desalination, l2, 61 (1973).

a.

10. ::: 13. 14. 15.

16.

S. T. LUI ARD G. H. NANGOLLAS, Desalination, 12, 75 (1973). G. Ii. NANCOLLAS AND J. S. GILL, Proceedings of International Symposium on Society of Oilfield and Geothermal Chemistry, Houston, Texas, Jan., 1979. Petroleum Engineers, SPE 7861. K. FAJANS, Radio Elements and Isotopes. Chemical Forces and Optical Properties of Substances, McGraw-Hill, New York, 1931.

298

17.

18.

19. 20.

WALINSKY AND MORTON

l4.Ii.AUERBACEANDM. S. CARRUTEERS, "Laboratory Applications Testing of Desalination Antiscalants," presented at the International Congress of Desalination and Water Reuse, Nice, October, 1979. M. IL RRDDY AND G. EL NANCOLLAS, J. Crystal Growth 35, 33 (1976). C. H. NESTLER, J- Colloid Interface Sci-, 26, 10 (1968). J. E. CRAWFORD AND B. R. SMITH, J. Colloid Interface Sci., 2l, 623 (1966).