SCALE CONTROL FOR SEA WATER EVAPORATORS USING AN ACRYLIC ACID METHYL ACRYLATE COPOLYMER

SYSTEME DE DETARTRAGE POUR EVAPORATEURS D'EAU DE MER, UTILISANT UN COPOLYMERE D'ACIDE ACRYLIQUE ET D'ACRYLATE DE METHYLE

English Abstract

ABSTRACT OF THE DISCLOSURE
Process for evaporating saline waters comprising treating the
water with from .1 - 3 ppm of an alkali metal or ammonium salt of a
copolymer of acrylic acid and methyl acrylate having a weight ratio
of from 3 - 4:1 and having a molecular weight within the range of
1000 - 3000 and then evaporating said water.

Claims

*
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Process for evaporating saline waters comprising treating the water
with from .1 - 3 ppm of an alkali metal or ammonium salt of a copolymer of
acrylic acid and methyl acrylate having a weight ratio of from 3 - 4:1 and
having a molecular weight within the range of 1000 - 3000 and then evaporat-
ing said water.
2. The method of Claim 1 where the molecular weight of the copolymer
is about 2400.

Description

9~
INTRODUCTION
Evaporation of sea water and other naturally occurring saline
waters gives rise to the formation of scale deposits of low thermal
conductivity on the heat transfer surfaces of the distillation plant. The
heat transfer coefficients are thereby reduced, leading to deterioration of
plant performance and necessitating the eventual shutdown of the plant for
cleaning. Although several methods are in use for the control of alkaline
scales, calcium sulfate and other scaling constituents normally found in
saline waters, scaling considerations still set an upper limit on the brine
boiling temperature and concentration factor, and hence on plant performance.
In evaporators, scale may be formed whenever scale-forming compounds are
present in the feed water, but the type and composition of the scale may
vary. For example, when evaporation of sea water takes place under reduced
pressure at boiling temperatures below about 180F, the principal scaling
phase is calcium carbonate; at higher temperatures it is primarily magnesium
hydroxide in the form of brucite, but calcium sulfate scales may be formed
at all temperatures if the brine concentration is sufficiently high.
THE INVENTION
Process for evaporating saline waters comprising treating the
water with from .1 - 3 ppm of an alkali metal or ammonium salt of a copolymer
of acrylic acid and methyl acrylate having a weight ratio of from 3 - 4:1
and having a molecular weight within the range of 1000 - 3000, preferably
about 2400, and then evaporating said water.
To illustrate the advantage of the invention over other acrylic
acid polymers and copolymers which have been suggested by the prior art as
~cale inhibitors, the following activity test was used.
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Activity Test - CaCO3 Scale Inhibition in Sea Water
A Procedure
1. 500 g. of synthetic sea water ~2) is concentrated to a 1.5 salt
concentration (333.33 g.) in beakers using a magnetic stirrer at 95C and
atmospheric pressure.
2. Concentrated solution is filtered hot through matched weight milli-
pore filters. Filters are dried for 30 min. at 105C and weighed to an ac-
curacy of 0.1 mg. Beakers also are allowed to cool.
3. Deposit on beakers is dissolved in about lO0 g. deionised water and
7 g. 10% by weight HNO3. After mixing to insure dissolution, the solution is
neutralized with 2.5 g. of 10% by weight NaOH (pH 6 - 7) and diluted to 150 g.
with deionised water. The solution is titrated for total dissolved hardness
and dissolved CaCO3 hardness.
4. Precipitate on filter paper is dissolved in ~-200 g. deionised
water and 14 g. 10% by weight HNO3, neutralized with 5.0 g 10% by weight
NaOH and diluted to 250 g. with deionised water. The solution is titrated
for total dissolved hardness and dissolved CaCO3 hardness ~same as Step 3).
Using the above test method, the results of Table I were obtained:
TABLE I
Percent CaCO
DosageInhibition vs.
Composition Peak MW Polymer, ppm Control
M/MA' 5000-9000 077 79
.088 95
. 099 99
AA/MA' _ 2400 .050 99
.070 99
. 090 100
AA ~ 2600 .072 78
.081 70
.090 98
'Weight ratio of acrylic acid to methyl acrylate 3.75:1
Acids are in sodium salt form.

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The significance of Table I shows the 2400 MW copolymer still has
excellent activity at .05 ppm active, whereas, the acrylic and homopolymer
and higher molecular weight copolymer start to lose activity at ~ .08 ppm.
This is ~ 50% increase in activity.