METHODE DE DISPERSION DU CARBONATE DE CALCIUM

METHOD OF DISPERSING CALCIUM CARBONATE

Abrégé anglais

TITLE: COMPOSITION AND ITS USE IN HIGH pH SYSTEMS
Abstract of the Invention
This invention comprises a composition and its use in
dispersing calcium carbonate in high pH systems. By maintaining the
calcium carbonate dispersed, scaling in such systems is alleviated.
The composition consists essentially of a combination of an organo
phosphonate having a specific formula and an amino-organo phosphonate
having a specific formula.
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Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of dispersing calcium carbonate in an aqueous
system having a pH of 9 or greater which comprises adding thereto an
effective amount for the purpose of
(i) an organo phosphonate having the general formula
<IMG>
wherein R1 is a lower alkyl having from 1 to 3 carbon atoms, or a lower
alkyl of 1 to 3 carbon atoms substituted with a member selected from the
group consisting of hydroxyl, lower alkyl of 1 to 3 carbon atoms, or both,
and M is a water soluble cation; and
(ii) an amino-organo phosphonate, having the grouping
-? - CH2 -PO3M2
wherein M is as above defined.
2. A method according to claim 1 wherein the amino-organo
phosphonate has the general formula
<IMG>
wherein R3 is hydrogen or -CH2-PO3M2 and wherein R4, when R3 is
-CH2PO3M2, is also -CH2PO3M2 and wherein R4 is ?(CH2)n-N]m
-(PO3M2)2 when R3 is hydrogen and wherein m is from 1 to 3 and n is from
1 to 6.
3. A method according to claim 2 wherein the pH is in the
range of 10 - 14.
4. A method according to claim 3 wherein the phosphonates
are added in a combined amount of from about 0. 5 to 500 parts per million
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parts of water in said system.
5. A method according to claim 4 wherein the weight ratio
of the organo phosphonate to the amino-organo phosphonate is from about
0.5:4 to 4:0.5.
6. A method according to claim 1 wherein the organo phos-
phonate has the formula
<IMG>
and the amino-organo phosphonate has a formula selected from the group
consisting of N ?CH2PO3M2)3; (M2O3P)2 N-CH2-CH2-
N (PO3M2)2; and (M2O3P)2 N- (CH2)6 - N (PO3M2)2.
7. A method according to claim 6 wherein the pH is in the
range of 10 - 14.
8. A method according to claim 7 wherein the phosphonates
are added in a combined amount of from about 0. 5 to 500 parts per million
parts of water in said system.
9. A method according to claim 8 wherein the weight ratio
of organo phosphonate to the amino-organo phosphonate is from about
0.5:4 to 4:0.5.
10. A method according to claim 9 wherein the weight ratio
is from about 1:6 to 6:1.
11. A method according to claim 10 wherein the aqueous system
is the aqueous medium of a pulp and/or paper mill system.
12. A method according to claim 11 wherein the aqueous system
is the black liquor system.
13. A method according to claim 10 wherein the amino-organo
phosphonate is (M2O3P)2-N-(CH2)6- N- (PO3M2)2.
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14. A method according to claim 13 wherein the aqueous
system is the aqueous medium of a pulp and/or paper mill system.
15. A composition for dispersing calcium carbonate contained
in an aqueous system having a pH of greater than 9 which consists essentially
of
(i) an organo phosphonate having the general formula
<IMG>
wherein R1 is a lower alkyl having from 1 to 3 carbon atoms, or a lower
alkyl of 1 to 3 carbon atoms substituted with a member selected from the
group consisting of hydroxyl, lower alkyl of 1 to 3 carbon atoms, or both,
and M is a water soluble cation; and
(ii) an amino-organo phosphonate having the grouping
-?-CH2-PO3M2, where M is as above defined.
16. A composition according to claim 13 wherein the amino-
organo phosphonate has the general formula
<IMG>
wherein R3 is hydrogen or -CH2-PO3M2 and wherein R4, when R3 is
-CH2PO3M2, is also -CH2PO3M2 and wherein R4 is
?(CH2)n-N]m-(PO3M2)2 when R3 is hydrogen and wherein m is from
1 to 3 and n is from 1 to 6.
17. A composition according to claim 16 wherein the weight
ratio of organo phosphonate to the amino-organo phosphonate is 0.5:4 to
4:0.5
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18. A composition according to claim 17 wherein the organo
phosphonate has the formula
<IMG>
and the amino-organo phosphonate has a formula selected from the group
consisting of N?CH2PO3M2)3; (M2O3P)2N-CH2-CH2-N(PO3M2)2;
and (M2O3P)2N-(CH2)6-N-(PO3M2)2.
19. A composition according to claim 18 wherein the amino-
organo phosphonate is (M2O3P)2-N-(CH2)6-N-(PO3M2)2.
20. A composition according to claim 19 wherein the weight
ratio of the respective phosphonates is from about 1:6 to 6:1.
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Description

13ackground of thc Invcntion
It is well known that many anionic materials such as poly-
acrylates, phosphonic acids and phosphonates and complex phosphates
can inhibit the crystallization, i. e., the formation of calcium carbonate,
in the pH range of 7. 5 to 9. 0 and therefore minimize scaling of the metallic
structure in contact with a potentially scaling environment. It is equally
well known however, that above a pH of 9. 0 the ability of all of these
materials to inhibit calcium carbonate formation and/or to disperse such
is minimal, with the result being that scaling is always encountered.
Accordingly, these materials for either crystallization inhibition or for
dispersion of calcium carbonate in ~igh pH systems normally found in some
pulp and/or paper mills hav-e found little or no use. Black liquor evaporators,
wood pulping digesters using the Kraft process, lime kiIn scrubbers, etc.
have not been treated for scaling with any degree of success. These systems
are merely examples of high pH systems where high calcium carbonate
scaling i8 encountered. The high scaling conditions, together with elevated
temperatures of the system, make the problem more acute, since scaling
i8 accelerated.
In order to illustrate the foregoing, tests were conducted using
complex phosphates, phosphonates and polyacrylates. The phosphonates
are listed in the following Table 1 as a family, since for comparative pur-
poses little differences were observed.
Crystallization Inhibition Test Procedure
The test procedure utilized for measuring the crystallization
inhibition properties of the materials tested was as follows: The primary
goal of the following procedure is to ~leterrrline quantitatively how much a
given treatmcnt will increase the solul~ility of a slightly soluble salt. This
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8~
requires a measurement of the ionic content of either the cationic or the
anionic species. Gener~lly, a measurement of the cationic species is chosen
because of the larger number of instrumental methods which are available
for analysis.
CaCO3 inhibition stu~ies:
The experimental procedure consists of adding
i) D. I. water to a 250 ml beaker
ii) Ca (from standard CaCl2 solution~
iii) Treatment
iv) 1 drop 50% HCl
v) C03-2 (from standard Na2CO3 solution)
vi) Adjust pH to 8. 5 or (10. 5) with NaOH/CHl.
The bealcers are then coverecl and allowed to equilibrate at
the specified temperature (usually 60C) for 1 - 2 hours, The samples are
further allowed to equilibrate overnight at ambient temperatures. The pre-
cipitate is then filtered off through 0. 2 u Nuclepore filter paper, and the
analysis is run on the filtrate. The percent inhibition is calculated as:
[Soluble Ca+2 (treated) - Soluble Ca+2 (control) 3
% Inh, = _ ___ _ X100
[Soluble Ca+Z (theoretical Max. ) - Soluble Ca+;~ (control)]
The soluble Ca+2 is determined by the standard EDTA titration. (See Betz
Handbook of Industrial Water Conditioning, 6th Edition, 1962, page 3d~7),
TA B LE L
Effect of pE~ on the Inhibition of Crystallization of
Calcium Carbonate by Chemical Classes
Conditions: 500 ppm CaCO3
3 ppm Treatrnent level
140 l`emperature
2 ~ours Equilibration Time

69~
Percent Inhibition
~11
7 8 9 1~ 11
Polyacrylates(1 ) 100 95 35 12 8
Polyphosphates (2) 93 87 3717 12
Phosphonates (3) 100 95 55 2519
(1) The average results of two polyacrylates in the molecular weight range
700 - 2, 000.
(2) The average results oI hexametaphosphate, tripolyphosphate, and pyro-
pho sphate .
(3) The average results of AMP, HEDP, HMDTP, and EDTPA.
AMP = Amino tri (~nethylene phosphonic acid)
`HEDP = l-hydroxyethylidene 1, l-diphosphonic acid
~MDTP = Hexamethylene diamine-tetra (methylene phosphonic acid)
EDTPA = Ethylene diamine-tetra (methylene phosphonic acid)
It is evident from the recorded results that the materials
commonly used at pHls lower than 9 and effective at those pH's were not
at all effective when the pH was 9 or above.
In order to illustrate the practical inability of the phosphonates
to function as crystallization inhibitors for calcium carbonate, the individual
phosphonates were tested for their capacity utilizing the afore-described
test procedure. The results derived from these studies are recorded in the
following Table 2.
TABLE 2
~ .
Inhibition of Crvstallization
System: CaCO3

g~
Conditions: 500 ppm CaCO3
Treatment leve] = 3 ppm active
Equilibration Temperature = 140F
Eguilibration Time = 2 hours
Treatment Percent Inhibition
pH
7 8 9 10 11
Amino tri (methylene phosphonic acid ) 100 82 47 22 16
(AMP)
l-hydroxyethylidene 1, l-diphosphonic acid 100 100 50 22 19
(HEDP )
Ethylenediamine tetra (methylene phosphonic lO0 -- - 22 22
acid) (EDTPA~
Hexamethylenediamine tetra (methylene100 100 5d~ 29 19
phosphonic acid) (HMDTA)
The conclusions inherent from the foregoing results are that
at 9 or above the phosphonates are for all practical purposes not effective
as a crystallization inhibitor for calcium carbonate.
Dispersion Ability_of Phosphonates Alone
2 0 Studie s were conducted to a s se s s the capacity of the pho sphonate s
to disperse formed calcium carbonate in aqueous systems at a pH above 9.
The test procèdure utilized was as follows.
Test Procedure for Dispersive Properties: In these studies,
the inorganic precipitate is formed in the presence of treatment, and the
resultant amount of dispersion is measured via light transr~ittance.
CaCO3 dispersion:
The experiInental procedure consists of adding
i ) D. I. Water to 2 5 0 ml beaker
ii) Ca (from standard CaCl2 solution)
--5--

~)6~
iii) TreatInent
iV) C03 2 (frona standard Na2 C03 solution)
v) Adjust pH l;o 11 with NaOH.
The beakers are covered and heated to 60C (140F)
for approximately one hour. Under these conditions CaC03 for~ns quite
. readil~. The contents, after cooling to room temperature, are thoroughly
remi~ed and transferred to a spectrometer where thepercent transmittance
is measured. Those treal:ed systems having the lowest percent transmittance
values are considered to be the most dispersed.
The results of the study are recorded in the following Table 3.
TABLE 3
~ Di sper sion
System: CaCO3
Conditions: 500 ppm CaCO3
Treatment level = 5 ppm active
Equilibration Time = 1/2 hour
Equilibration Temperature = 75F
pH = 1 0.7
- Treatment Perce~t Tlansnaittance
2 0 Control 98
AMP 8 6
HEDP 79
El:)TPA 98
HMDTP 84
It is apparent from the results of this study that individually
the phosphonates were not effective for the purpose of dispersing calcium
carbonate at a pll above 9.
.
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~ ~9
General Description of the Invention
Because there were no treatments which were e~fective or
controlling scaling at pH ' s ab~ve 9 in systems containing the neces-
sary calcium and carbonate ions, the inventors embarked on a research
program with the idea of develcping materials or combination of mat-
erials which would provide the much needed protection.
The inventors discovered that if an aqueous system having
calcium carbonate scaling conditions, i.e., the pH was 9 or above,
was treated with a combination of:
(i) an organo phosphonate having the general formula
o
Il ~
MO P 1 P - OM
OM OM
wherein Rl is a lower alkyl having fxom 1 to 3 carbon atoms, or an al-
kyl of 1 to 3 carbon atoms substituted with a hydroxyl or a lower
alkyl (1 to 3 carbon atoms), or both; and M is a water soluble cation,
preerably hydrogen, sodium, potassium, ammonium; and
(ii) an amino-organo phosphonate hàving the grouping
- N - CH2 PO3 M2, wherein M is as above defined; that effective
dispersion of calcium carbonate could be attained so as to minimize
the scaling normally encountered. The amino-organo phosphonates which
can be utilized in accordance with the present invention are those
set forth in U.SA 3,837,803.
Preferably, the amino-organo phosphonates are those which
possess the general formula:
R3______
4 / N CH~ - P3M2
. ' , ~.
' ' ' ,

~Of~9~0~
whereill R3 is ca hydrogen atom or thc group -- CE~2~PO3M2 and wherein
R,~, when R3 is --CHzPO3Mz~is also CH2PO3Mz~ and wherein R4 is t~e
group ~ (CI-~2)n ~ N ~m --(PO3M2)2 when R3 is hydrogen,' wherein
m is an integer of from about 1 to 3 and n is from about i to 6: and M is
as earlier defined, The specific organo-phosphonates which have been
used with great success are those which contain at least three (3)
- CH2PO3M2 groups. These include l-hydroxyethylidene-l, l-diphosphonic
acid, or water soluble salt having the structure
OH
M203P --CH --PO3M
CH3
The specific amino-organo phosphs~nates which have found particular
efficacy are amino tri (methylene phosphonic acid) or its water soluble
salt having the formula
N ( CEI2PO3M2)3;
ethylene diamine tetra (methylene phosphonic acid) or water soluble salt
having the formula
(M2O3p)2--- N ~ CHz --CHz--N ( PO3M2)2; and
hexamethylene~diamine tetra (methylene phosphonic acid) or water soluble
2 0 salt
(M203P)2 N-- ( CH2 )6--N ( PO3M2 )2 .
The respective phosphonates may be added to the agueous
system either individually or as a mixture consisting essentially of the two
ingredients in a solvent such as water, since the phosphonates are con~patible.
The mixture can be added in any amount effective for the purpose. For
example, if the aqueous system contains a minor amount of calcium car-
bonate, small amounts of the combination can be used. Conversely, if the
~ .
-8-
' " . ` . ' ' ' . , . . ~'' . ' ' ~ '

8~C~
potential of calciuIn carbonatc scaling i~; great, then greater amounts of
the combination should be added. In any event, treatments comprised of
a combined total of the phosphonates of 0. 5 to 500 and preferably 5 to 250
parts per million parts of water in the aqueous system will be effective for
most applications. The weight ratios of the respective phosphonates can be
from about 0, 5: 4 to 4: 0. 5 and preferably from about 1: 6 to 6: 1.
The solecriterionis that at least some of each be present, otherwise the
desired dispersive effect is not achieved.
In systerns which are already heavily scaled with calcium
carbonate, it is recommended that the system be treatecl with acid or base
or combinations to loosen the scale and to permit removal thereof. It has
also been found to be advantageous to pretreat the system before placing
such on-stream with a water system containing from about 10 to 1, 000 ppm
of the combirlation of phosphonates of the invention.
.
Dispersion Testing
In order to stud~ the dispersive chara-teristics of various
combinations including those of the inventive combination, various com-
binations were subjected to the dispersion test earlier described. The
formulations of the combinations are as follows, with the explanatior. matter
2 0 also set forth:
__IngredientsPercent by weight
Combination 1
HMDTP 5
LMW-PAA 10
Water 79
NaOH 6

- 1~6980~
Cor~bination 2
HEOP 1 5
LMW-PAA S
Wate r 8 0
Combination 3
.. HEDP 6. 4
HMDTP 1. 1
KOH 7.3
Water 85 . Z
Combination 4
AMP 3.8
LMW- PAA 5 . 5
Water 88. 0
NaOH 2 . 7
Combination 5
HEDP 2 . 7
LMW- PAA 7 . 5
NaOH 2 . 3
. . Wate r 8 7 . 5
Combination 6
Carboxymethylcellulose 1. 5
LMW - PAA 15 . 0
Wate r 83 . 5
Combination 7
` LMW-PAA 5, 0
; STPP . .7. 5
Water 85. 5
NaOH 2 . 0
.
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. .

- ~o~9~
Combination 8
HMW- P~A 4 . O
STPP ~. O
KOH 3.2 .
water 87. 8
LMW-PAA = Low molecular weight polyacrylic ac:id (~10
EIMW-PAA = High molecular weight polyacrylic acid (~105 )
AMP = (methylene phosphonic acid)
HEDP = 1-hydroxyethylidene 1, l-diphosphonic acid)
HMDTP = Hexamethylenediamirie tetFa (methylen~ phosphonic acid)
STPP = Sodium Tripolyphosphate
The results of the studies are recorded in lable 4 below.
TABLE 4
Dispersion
System: CaCO3
Conditions: 800 ppm CaCO3
Treatment level = 5 ppm total active
Equilibra$ion time = 1 hour
Equilibration temperature = 140F
pH= 11.0
Treatment Percent Transmittance
Combination 1 91
Combination 2 65
Combination 3 44
Combination 4 ~9
Combination 5 47
.
- 1 1 -

~1698~
Combination 6 89
Combination 7 88
Combination 8 91
It is apparent that Combination 3, which lepresents the inven-
tive combination,was superior to all of the other combinations tested~with
Combination 5 not far behind.
Combinations 3 and 5 were tested at a lower dosage level (3
ppm) and the percentage transmittance for Combination 3 decreased to 36%.
indicating enhanced dispersion, while Combination 5 increased to 6~o, indi-
cating poorer dispersion.
The foregoing results conclusively established the effectiveness
for the purposes of the inventive combination and accordingly, because of
the impressive results, field trials were arranged. A description of the
trials is set forth below.
FIE LD T RIA LS
1. A Southwest Pulp Mill Evaporator System
A southwest pulp mill black liquor evaporator system (pH~ 0)
was experiencing severe calcium carbonate scaling which necessitated a hot
watsr boilout every 2 - 3 days. This scaling reduced heat transfer to the
liquor to such an extent that the liquor flow had to be decreased in order to
produce an exit liquor of the desired high solids content. Since the successful
operation of the entire mill depended on the maximum throughput of liquor
through the evaporator system, the decreased flow and downtime for cleaning
proved to be very expensive for the mill.
After cleaning and preconditioning the system at 100 ppm of
Combination 3, the comhination was fed directly to the weak black liquor at
levels Or 15 - 50 ppm. During the three week period during which this
. .
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.
' ~ : : . .. : ' . ' : ' . , ' '

8~0
colnbination was fed, it was found th,-l; hot watcr bc)ilouts were necessary
only every 5 - 8 days and maximum liquor flows were able to be maintained
for allnost twice as long. Both of these results indicated that less calcium
carbonate scale was forming in the evaporator system.
2. ~ Pacific Northwest Pulp Mill Evaporator System
This mill was experiencing similar severe calcium carbonate
scaling in its black liquor evaporator system (pH = 12~. One primary con-
cern of this mill was the amount of steam it must produce to operate the
evaporator system efficiently. The parameter normally measured to
indicate this amount of steam is called the steam economy. The economy
value is the number of pounds of water in the liquor that i9 evaporated per
pound of steam used. VVhen scaling is evident in lhe evaporator system,
the steam econorny decreases. Prior to the addition of Combination 3, this
system operated at a steam economy of 2. 50. After preconditioning in the
usual fashion with this combination and then feeding the combination at
15 - 30 ppm to the weak black liquor over a two month period, the steam
economy was found to average 3. 06. This represented an increase of 20%
in the steam economy and obviously represented a substantial dollar savings
to the mill in better steam utilization.
3. A Midwestern Synthetic Natural Gas Plant
This plant manufactured synethetic natural gas from coal via
a two-step proces 5:
(1) lignite coal + steam ~ CO2+H2 in gasifier reactor
(2) C02+Ca~ (from dolomite) ) CaC03 which was separated
from the coal feed.
When thc hot gas from the gasifier reaction vessel was put through a venturi
scrut)ber. sevc~cCaCO3 scaling occurred. This scaling, occurring at plI
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~6~ 0
greater than l0. resulted in low suCtiOIl pre.ssures in the gasifier, thereby
causing decreased production. In order to keep the units operating efficiently,
this scaling had to be manually l~rodded out1l at least once a shift. When
Combination 3 was fed at 150 - 200 ppm prior to the scaling area (at the
ve.nturi), the pressure across the venturi ceased to drop and stabilized at
3-4 units. In addition, visual inspection of the venturi after the run indicated
a scale build-up of l/16" - l/8". This was noted to be the smallest build-up
of scale after any gasification run.
The field evaluations proved conclusively that the present
invention performed under the severe conditions encountered in normal
operations .
Having thus disclosed the invention, what is claimed is: