CA1069800A

CA1069800A - Method of dispersing calcium carbonate

Info

Publication number: CA1069800A
Application number: CA267,461A
Authority: CA
Inventors: Lewis Volgenau; Philip S. Davis
Original assignee: Betz Laboratories Ltd
Current assignee: GE BetzDearborn Canada Co
Priority date: 1976-06-07
Filing date: 1976-12-08
Publication date: 1980-01-15
Also published as: BE855456A; NL7702952A; DE2725199A1; IT1086672B

Abstract

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.

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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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.

~ .
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

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) ~)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.

~ 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 El:)TPA 98 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.

.

~ ~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 ~

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

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~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 Water 79 NaOH 6 - 1~6980~

Cor~bination 2 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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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.

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 .

~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 . .

.
' ~ : : . .. : ' . ' : ' . , ' ' 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

~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:

Claims

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 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 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 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 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.

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 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 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

18. A composition according to claim 17 wherein the organo phosphonate has the formula 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.