CA2208936A1 - Scale deposit inhibitor for kraft digesters and method for controlling scale deposition in kraft digisters - Google Patents
Scale deposit inhibitor for kraft digesters and method for controlling scale deposition in kraft digistersInfo
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- CA2208936A1 CA2208936A1 CA 2208936 CA2208936A CA2208936A1 CA 2208936 A1 CA2208936 A1 CA 2208936A1 CA 2208936 CA2208936 CA 2208936 CA 2208936 A CA2208936 A CA 2208936A CA 2208936 A1 CA2208936 A1 CA 2208936A1
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Abstract
A scale deposit inhibitor and a method for continuously controlling scale deposition applicable to a digester and its peripheral equipment used in making kraft pulps are disclosed, the scale deposit inhibitor comprising a maleic acid/acrylic acid/2-acrylamido-2-methylpropanesulfonic acid terpolymer having a maleic acid to acrylic acid molar ratio of 10:1 to 10:30, a 2-acrylamido-2-methylpropanesulfonic acid content of 1 to 30 mol%, and a weight-average molecular weight of 500 to 20000. The scale deposit inhibitor is injected to a cooking liquor at concentration of 0.01 to 10 ppm per ppm of a calcium ion in the cooking liquor.
Description
SCALE DEPOSIT INHIBITOR FOR KRAFT DIGESTERS AND
METHOD FOR CONTROLLING SCALE DEPOSITION IN KRAFT DIGESTERS
FIELD OF THE INVENTION
This invention relates to a scale deposit inhibitor for a continuous digester and its peripheral equipment (e.g., piping) used in making kraft pulps and to a method of scale deposit control using the same.
BACKGROUND OF THE INVENTION
Kraft pulp is produced by cooking wood chips in an aqueous cooking liquor mainly comprising sodium hydroxide and sodium sulfide in high temperature under high pressure to remove lignin from the chips. The typical composition of the cooking liquor (white liquor) is 55 to 100 g/Q of sodium hydroxide, 18 to 45 g/Q of sodium sulfide, and 10 to 30 g/Q
of sodium carbonate, each in terms of Na2O, which is sometimes used as partly diluted with a black liquor. The cooking temperature is about 170~C.
Calcium ions leached from wood chips react with carbonate ions in the cooking liquor to form calcium carbonate in the system, which is precipitated and deposited on the inner wall of a digester and subsequent tanks and pipes. The scale deposition, especially at the upper cooking zone, the heat exchangers and the digester screens, causes various operational problems, such as reduction in thermal efficiency, hindrance to the flow of the liquid and pulp, reduction in productivity, non-uniform pulp quality, and unscheduled shutdown of the equipment.
The scale is generally removed by cleaning with an acid solution. This method is, however, disadvantageous in that scale removal itself entails much labor and that suspension of operation for cleaning causes a production loss and an enormous energy loss.
It has therefore been keenly demanded to develop a technique for continuously controlling scale deposition and thereby minimizing the necessity of the scale removal. In this line, it has been proposed to use maleic acid polymers (see JP-B-2-53551, the term "JP-B" as used herein means an "examined published Japanese patent application") or mixtures of polyaminopoly(alkylenephosphonic acids) together with nonionic surfactants (see U.S. Patent 4,799,995) as a scale deposit inhibitor. ~owever, none of the inhibitors proposed gives satisfactory results for controlling the scale deposition, and there still has been a demand for a more effective scale deposit inhibitor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an effective scale deposit inhibitor which can be applied to a digester and its peripheral equipment used in making kraft pulps and a method for continuously controlling scale deposition in the digester using the inhibitor.
As a result of extensive investigations, the present inventors found that a terpolymer comprising maleic acid units, acrylic acid units, and 2-acrylamido-2-methylpropane-sulfonic acid (hereinafter abbreviated as AMPS) units at a specific ratio produces a markedly higher effect on the control of scale formation in the cooking liquor than a maleic acid homopolymer, an acrylic acid homopolymer or a maleic acid/acrylic acid copolymer. The present invention has been completed based on this finding.
The present invention relates to a scale deposit inhibitor for a continuous digester used in making kraft pulps, which comprises a terpolymer comprising (A) maleic acid units, (B) acrylic acid units, and (C) AMPS units and having an (A) to (B) molar ratio of from 10:1 to 10:30, a (C) content of from 1 to 30 mol%, and a weight-average molecular weight of from 500 to 20000.
The present invention also relates to a method for controlling scale deposition in the continuous kraft digester and peripheral equipment thereof. The method comprises injecting the above-mentioned scale deposit inhibitor to the cooking liquor in the digester. The dosage is from 0.01 to 10 ppm per ppm of a calcium ion present in the cooking liquor.
DETAILED DESCRIPTION OF THE INVENTION
The polymer which can be used as the scale deposit inhibitor in the present invention is a terpolymer comprising maleic acid units, acrylic acid units, and AMPS units. The molar ratio of maleic acid to acrylic acid is from 10:1 to 10:30, preferably from 10:2 to 10:15, particularly from 10:3 to 10:10. AMPS in the terpolymer is from 1 to 30 mol%, preferably from 3 to 20 mol%, more preferably 4 to 10 mol%.
The terpolymer has the weight-average molecular weight of from 500 to 20000, preferably from 1000 to 10000, more preferably 3000 to 8000.
The monomer ratio is a~significant factor on the performance. The maleic acid units and acrylic acid units inhibit calcium from the precipitation, while the AMPS units disperse the precipitating calcium particles and inhibit the growth into scale.
Although the terpolymer may be a random terpolymer, a block terpolymer or a mixture thereof, the random terpolymer is preferable.
The method for preparing the terpolymer for use in the present invention is not particularly restricted. For example, to an aqueous solution of maleic acid, acrylic acid, and AMPS, an alkali metal hydroxide (i.e., sodium hydroxide) aqueous solution and then a polymerization initiator solution are dropwise added at a temperature of preferably from 80~ to 110~C. Maleic acid, acrylic acid, and AMPS may be each either free acid or salt of sodium, potassium or ammonium.
Maleic anhydride may also be used.
The polymerization initiator includes peroxides, such as hydrogen peroxide, sodium persulfate, chlorine peroxide, and butyl hydroperoxide, and azo compounds, such as azobisisobutyronitrile, with hydrogen peroxide and a persulfate being preferred. The amount of the initiator used may be generally varied depending on its kind and on the polymerization condition. Hydrogen peroxide, for example, is used in an amount of from 0.5 to 10 mol%, preferably from 1 to 5 mol%, based on the total monomers.
Water is the most preferred solvent for the polymerization. Organic solvents, such as alcohols and dioxane, may also be used.
The polymerization is preferably carried out at a temperature of from 80~ to 110~C.
The scale deposit inhibitor according to the present invention is usually injected to the cooking liquor at concentration of from 0.01 to 10 ppm, preferably from 0.05 to 5 ppm, and particularly preferably from 0.1 to 3 ppm, per ppm of a calcium ion present in the cooking liquor. It is recommended to occasionally measure the calcium ion concentration in the liquor to adjust the dosage of the inhibitor to an optimum level.
The injection method of the scale deposit inhibitor into the liquor is not particularly restricted. It is convenient in practice to inject the inhibitor to the liquor to be supplied to the digester and/or the circulating liquor.
If desired, the inhibitor may be applied in combination with other optional additives as far as it is accomplished as _ purposed.
The scale deposit control mechanism according to the present invention is explained as such that the inhibitor is adsorbed onto the growing crystals to give a crystal distortion or modification, which makes the precipitating crystals mechanically weak. As a result, calcium carbonate is hardly precipitated, and, even if precipitated, the crystals are so grossly distorted not to form scale. The scale deposit inhibitor is also considered to be effective in dispersing the precipitated calcium carbonate in the liquor to prevent the growth into scale.
As described and demonstrated above, scale deposition in the digester in making kraft pulps can be controlled in a continuous manner by applying the scale deposit inhibitor and the scale deposit inhibition method according to the present invention. It follows that the run length of the digester operation can be extended to achieve a great improvement in productivity, a uniformity of pulp, and a reduction in energy loss. Further, troubles arising from the scale deposition are greatly diminished, which makes a valuable contribution to the improvement of the operation.
The present invention will now be illustrated in detail with reference to Examples, but the present invention should not be construed as being limited thereto.
Preparation of Polymer:
Polymers A to M according to the present invention and comparative polymers N to W having the characteristics shown in Table 1 below were prepared.
To take an instance, preparation of polymer F is described below. In a 500 mQ five-necked flask 35.1 g (0.358 mol) of maleic anhydride and 50 g of water were charged, and a 50 wt~ sodium hydroxide aqueous solution was added thereto to adjust to a pH of 6. After the flask was purged with nitrogen, the solution was heated to 90~C and, while stirring, a solution of 4.2 g of sodium persulfate in 50 g of water, 12.9 g (0.179 mol) of acrylic acid, and a solution of 4.7 g (0.023 mol) of AMPS in 50 g of water were separately added thereto through the respective dropping funnels. After the addition, the stirring was continued for an additional 3 hours at 90~C to obtain a polymer aqueous solution. No residual monomers was detected by ion chromatography, which reveals nearly completion of the reaction. The resulting polymer solution was subjected as such to the evaluation of calcium carbonate precipitation.
The molecular weight of the polymer obtained was 4500 by gel-permeation chromatography.
Other polymers were prepared in the same manner as described above, except for changing the monomer ratio as shown in Table 1.
O O
,Y .,_ ~-1 =
H O
C~
4~
O h o o o o o o o o o o O o o o O O o o o o o o o o o o o o o o o o o o O O O o O o o o o o o o U r ;~ t~ ~ o ~ o ~n ~n oo 0 ~~ O O O O ~ o o t~ o ~ ~ co ~, O
O ' ~4 -U~ olP ~1 ~ t~l d~ ~ ~--1 t~ O 1~1 IJ~ t~ O O O O N O CO O
p,,,_~ . . . . . . . . . . . . . . . . . . .
O ~ ~7 r' u~ ~ d' 1' 0 0 O~ t' t' ~ O O O O U~ U~ O C~
-U
.U ~o ~ .~ ~ Ln ~ ~ ~ ~
J O O O O O O O O O O o o o I I O O O O O
~-1 U
U ,_ --I ~ o~p t~ c~ ~Ir') ~ oal o ~DLO d'CO O O O ~ O t~ ~ ~1 N
.,~ . . . . . .. . .. . . . . . . .. . .
O ~ ~ O O O O ~ 7 0 CO
,_ ~ ~ a~ ~ ~ I' ~ ~ o r~ O ~r ~ o o o ~ o 1' a~ -1 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ . . . . . . .
U O r~ ~ ~ U~ I O ~ t~ r o o o o o~ o ~D O ~O O
_ ~ ~ ~ ~ ~ ~ ~ o S~
m c~ ~ ~ ~ ~ :c H 1~ Z O ~ 01 ~ tl~
o Evaluation:
Inhibition of calcium carbonate precipitation in a highly alkaline white liquor was evaluated according to the following test methods.
1) Effect on Inhibition of Calcium Carbonate Precipitation at 100 ~C:
Calcium chloride was added to 200 mQ of a model white liquor (an aqueous solution consisting of 8.0 wt% NaOH, 4.0 wt% Na2S, 3.5 wt% Na2CO3, 0.5 wt% KOH, and 84.0 wt% ion-exchanged water) to a final calcium ion concentration of 100 ppm. Each of the polymers prepared was added to the mixture to a prescribed concentration as a scale deposit inhibitor. The resulting mixture was heated at 100~C to form a uniform solution. After allowing to stand at 100~C for 4 hours, the liquid was filtered by suction through a filter paper for quantitative determination (Filter No. 6, manufactured by Advantec Toyo Kaisha Ltd.). The filter paper was dried, and the calcium carbonate on the filter paper was weighed to obtain the amount of precipitate (A). As a control, the amount of precipitate (B) of the system containing no scale deposit inhibitor was obtained. A
percent inhibition of calcium carbonate precipitation was calculated according to an equation:
Percent Inhibition (%) = (1 - A/B) x 100 The results obtained are shown in Table 2.
Concentration of Scale Deposit Inhibitor Scale 50 ppm 25 ppm10 ppm 5 ppm 1 ppm Deposit (0.50 (0.25(0.10 (0-05 (0.01 Inhibitor ppm)* ppm) ppm) ppm) ppm) Remark Polymer A94.6 93.3 87.415.7 - Invention Polymer B96.4 96.0 94.891.8 85.2 Polymer C97.0 96.5 95.793.1 89.4 "
Polymer D96.5 95.0 93.890.6 50.1 1' Polymer E94.7 93.8 90.838.1 - "
Polymer F98.2 97.5 96.294.0 90.0 "
Polymer G98.5 97.5 97.095.3 91.0 1' Polymer H97.7 96.8 95.193.0 87.7 "
Polymer I96.5 94.8 92.785.3 26.9 "
Polymer J95.0 94.6 90.423.5 - 1' Polymer K98.0 97.0 95.593.4 90.2 "
Polymer L96.0 95.1 92.085.3 20.1 1' Polymer M95.3 94.1 82.07.1 - "
Polymer N72.6 18.8 2.3 - -Comparison Polymer O63.5 19.1 3.5 - - "
Polymer P4.5 Polymer Q4.0 - - - -Polymer R68.2 34.7 4.8 - - "
Polymer S90.1 70.5 8.9 - - "
Polymer T52.6 43.0 6.7 - - "
Polymer U83.2 63.3 8.0 - - "
Polymer V 67.9 46.2 - - - "
Polymer W 54.2 32.3 - - - "
~ote: * Values in the parentheses are concentrations per ppm of Ca2+.
METHOD FOR CONTROLLING SCALE DEPOSITION IN KRAFT DIGESTERS
FIELD OF THE INVENTION
This invention relates to a scale deposit inhibitor for a continuous digester and its peripheral equipment (e.g., piping) used in making kraft pulps and to a method of scale deposit control using the same.
BACKGROUND OF THE INVENTION
Kraft pulp is produced by cooking wood chips in an aqueous cooking liquor mainly comprising sodium hydroxide and sodium sulfide in high temperature under high pressure to remove lignin from the chips. The typical composition of the cooking liquor (white liquor) is 55 to 100 g/Q of sodium hydroxide, 18 to 45 g/Q of sodium sulfide, and 10 to 30 g/Q
of sodium carbonate, each in terms of Na2O, which is sometimes used as partly diluted with a black liquor. The cooking temperature is about 170~C.
Calcium ions leached from wood chips react with carbonate ions in the cooking liquor to form calcium carbonate in the system, which is precipitated and deposited on the inner wall of a digester and subsequent tanks and pipes. The scale deposition, especially at the upper cooking zone, the heat exchangers and the digester screens, causes various operational problems, such as reduction in thermal efficiency, hindrance to the flow of the liquid and pulp, reduction in productivity, non-uniform pulp quality, and unscheduled shutdown of the equipment.
The scale is generally removed by cleaning with an acid solution. This method is, however, disadvantageous in that scale removal itself entails much labor and that suspension of operation for cleaning causes a production loss and an enormous energy loss.
It has therefore been keenly demanded to develop a technique for continuously controlling scale deposition and thereby minimizing the necessity of the scale removal. In this line, it has been proposed to use maleic acid polymers (see JP-B-2-53551, the term "JP-B" as used herein means an "examined published Japanese patent application") or mixtures of polyaminopoly(alkylenephosphonic acids) together with nonionic surfactants (see U.S. Patent 4,799,995) as a scale deposit inhibitor. ~owever, none of the inhibitors proposed gives satisfactory results for controlling the scale deposition, and there still has been a demand for a more effective scale deposit inhibitor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an effective scale deposit inhibitor which can be applied to a digester and its peripheral equipment used in making kraft pulps and a method for continuously controlling scale deposition in the digester using the inhibitor.
As a result of extensive investigations, the present inventors found that a terpolymer comprising maleic acid units, acrylic acid units, and 2-acrylamido-2-methylpropane-sulfonic acid (hereinafter abbreviated as AMPS) units at a specific ratio produces a markedly higher effect on the control of scale formation in the cooking liquor than a maleic acid homopolymer, an acrylic acid homopolymer or a maleic acid/acrylic acid copolymer. The present invention has been completed based on this finding.
The present invention relates to a scale deposit inhibitor for a continuous digester used in making kraft pulps, which comprises a terpolymer comprising (A) maleic acid units, (B) acrylic acid units, and (C) AMPS units and having an (A) to (B) molar ratio of from 10:1 to 10:30, a (C) content of from 1 to 30 mol%, and a weight-average molecular weight of from 500 to 20000.
The present invention also relates to a method for controlling scale deposition in the continuous kraft digester and peripheral equipment thereof. The method comprises injecting the above-mentioned scale deposit inhibitor to the cooking liquor in the digester. The dosage is from 0.01 to 10 ppm per ppm of a calcium ion present in the cooking liquor.
DETAILED DESCRIPTION OF THE INVENTION
The polymer which can be used as the scale deposit inhibitor in the present invention is a terpolymer comprising maleic acid units, acrylic acid units, and AMPS units. The molar ratio of maleic acid to acrylic acid is from 10:1 to 10:30, preferably from 10:2 to 10:15, particularly from 10:3 to 10:10. AMPS in the terpolymer is from 1 to 30 mol%, preferably from 3 to 20 mol%, more preferably 4 to 10 mol%.
The terpolymer has the weight-average molecular weight of from 500 to 20000, preferably from 1000 to 10000, more preferably 3000 to 8000.
The monomer ratio is a~significant factor on the performance. The maleic acid units and acrylic acid units inhibit calcium from the precipitation, while the AMPS units disperse the precipitating calcium particles and inhibit the growth into scale.
Although the terpolymer may be a random terpolymer, a block terpolymer or a mixture thereof, the random terpolymer is preferable.
The method for preparing the terpolymer for use in the present invention is not particularly restricted. For example, to an aqueous solution of maleic acid, acrylic acid, and AMPS, an alkali metal hydroxide (i.e., sodium hydroxide) aqueous solution and then a polymerization initiator solution are dropwise added at a temperature of preferably from 80~ to 110~C. Maleic acid, acrylic acid, and AMPS may be each either free acid or salt of sodium, potassium or ammonium.
Maleic anhydride may also be used.
The polymerization initiator includes peroxides, such as hydrogen peroxide, sodium persulfate, chlorine peroxide, and butyl hydroperoxide, and azo compounds, such as azobisisobutyronitrile, with hydrogen peroxide and a persulfate being preferred. The amount of the initiator used may be generally varied depending on its kind and on the polymerization condition. Hydrogen peroxide, for example, is used in an amount of from 0.5 to 10 mol%, preferably from 1 to 5 mol%, based on the total monomers.
Water is the most preferred solvent for the polymerization. Organic solvents, such as alcohols and dioxane, may also be used.
The polymerization is preferably carried out at a temperature of from 80~ to 110~C.
The scale deposit inhibitor according to the present invention is usually injected to the cooking liquor at concentration of from 0.01 to 10 ppm, preferably from 0.05 to 5 ppm, and particularly preferably from 0.1 to 3 ppm, per ppm of a calcium ion present in the cooking liquor. It is recommended to occasionally measure the calcium ion concentration in the liquor to adjust the dosage of the inhibitor to an optimum level.
The injection method of the scale deposit inhibitor into the liquor is not particularly restricted. It is convenient in practice to inject the inhibitor to the liquor to be supplied to the digester and/or the circulating liquor.
If desired, the inhibitor may be applied in combination with other optional additives as far as it is accomplished as _ purposed.
The scale deposit control mechanism according to the present invention is explained as such that the inhibitor is adsorbed onto the growing crystals to give a crystal distortion or modification, which makes the precipitating crystals mechanically weak. As a result, calcium carbonate is hardly precipitated, and, even if precipitated, the crystals are so grossly distorted not to form scale. The scale deposit inhibitor is also considered to be effective in dispersing the precipitated calcium carbonate in the liquor to prevent the growth into scale.
As described and demonstrated above, scale deposition in the digester in making kraft pulps can be controlled in a continuous manner by applying the scale deposit inhibitor and the scale deposit inhibition method according to the present invention. It follows that the run length of the digester operation can be extended to achieve a great improvement in productivity, a uniformity of pulp, and a reduction in energy loss. Further, troubles arising from the scale deposition are greatly diminished, which makes a valuable contribution to the improvement of the operation.
The present invention will now be illustrated in detail with reference to Examples, but the present invention should not be construed as being limited thereto.
Preparation of Polymer:
Polymers A to M according to the present invention and comparative polymers N to W having the characteristics shown in Table 1 below were prepared.
To take an instance, preparation of polymer F is described below. In a 500 mQ five-necked flask 35.1 g (0.358 mol) of maleic anhydride and 50 g of water were charged, and a 50 wt~ sodium hydroxide aqueous solution was added thereto to adjust to a pH of 6. After the flask was purged with nitrogen, the solution was heated to 90~C and, while stirring, a solution of 4.2 g of sodium persulfate in 50 g of water, 12.9 g (0.179 mol) of acrylic acid, and a solution of 4.7 g (0.023 mol) of AMPS in 50 g of water were separately added thereto through the respective dropping funnels. After the addition, the stirring was continued for an additional 3 hours at 90~C to obtain a polymer aqueous solution. No residual monomers was detected by ion chromatography, which reveals nearly completion of the reaction. The resulting polymer solution was subjected as such to the evaluation of calcium carbonate precipitation.
The molecular weight of the polymer obtained was 4500 by gel-permeation chromatography.
Other polymers were prepared in the same manner as described above, except for changing the monomer ratio as shown in Table 1.
O O
,Y .,_ ~-1 =
H O
C~
4~
O h o o o o o o o o o o O o o o O O o o o o o o o o o o o o o o o o o o O O O o O o o o o o o o U r ;~ t~ ~ o ~ o ~n ~n oo 0 ~~ O O O O ~ o o t~ o ~ ~ co ~, O
O ' ~4 -U~ olP ~1 ~ t~l d~ ~ ~--1 t~ O 1~1 IJ~ t~ O O O O N O CO O
p,,,_~ . . . . . . . . . . . . . . . . . . .
O ~ ~7 r' u~ ~ d' 1' 0 0 O~ t' t' ~ O O O O U~ U~ O C~
-U
.U ~o ~ .~ ~ Ln ~ ~ ~ ~
J O O O O O O O O O O o o o I I O O O O O
~-1 U
U ,_ --I ~ o~p t~ c~ ~Ir') ~ oal o ~DLO d'CO O O O ~ O t~ ~ ~1 N
.,~ . . . . . .. . .. . . . . . . .. . .
O ~ ~ O O O O ~ 7 0 CO
,_ ~ ~ a~ ~ ~ I' ~ ~ o r~ O ~r ~ o o o ~ o 1' a~ -1 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ . . . . . . .
U O r~ ~ ~ U~ I O ~ t~ r o o o o o~ o ~D O ~O O
_ ~ ~ ~ ~ ~ ~ ~ o S~
m c~ ~ ~ ~ ~ :c H 1~ Z O ~ 01 ~ tl~
o Evaluation:
Inhibition of calcium carbonate precipitation in a highly alkaline white liquor was evaluated according to the following test methods.
1) Effect on Inhibition of Calcium Carbonate Precipitation at 100 ~C:
Calcium chloride was added to 200 mQ of a model white liquor (an aqueous solution consisting of 8.0 wt% NaOH, 4.0 wt% Na2S, 3.5 wt% Na2CO3, 0.5 wt% KOH, and 84.0 wt% ion-exchanged water) to a final calcium ion concentration of 100 ppm. Each of the polymers prepared was added to the mixture to a prescribed concentration as a scale deposit inhibitor. The resulting mixture was heated at 100~C to form a uniform solution. After allowing to stand at 100~C for 4 hours, the liquid was filtered by suction through a filter paper for quantitative determination (Filter No. 6, manufactured by Advantec Toyo Kaisha Ltd.). The filter paper was dried, and the calcium carbonate on the filter paper was weighed to obtain the amount of precipitate (A). As a control, the amount of precipitate (B) of the system containing no scale deposit inhibitor was obtained. A
percent inhibition of calcium carbonate precipitation was calculated according to an equation:
Percent Inhibition (%) = (1 - A/B) x 100 The results obtained are shown in Table 2.
Concentration of Scale Deposit Inhibitor Scale 50 ppm 25 ppm10 ppm 5 ppm 1 ppm Deposit (0.50 (0.25(0.10 (0-05 (0.01 Inhibitor ppm)* ppm) ppm) ppm) ppm) Remark Polymer A94.6 93.3 87.415.7 - Invention Polymer B96.4 96.0 94.891.8 85.2 Polymer C97.0 96.5 95.793.1 89.4 "
Polymer D96.5 95.0 93.890.6 50.1 1' Polymer E94.7 93.8 90.838.1 - "
Polymer F98.2 97.5 96.294.0 90.0 "
Polymer G98.5 97.5 97.095.3 91.0 1' Polymer H97.7 96.8 95.193.0 87.7 "
Polymer I96.5 94.8 92.785.3 26.9 "
Polymer J95.0 94.6 90.423.5 - 1' Polymer K98.0 97.0 95.593.4 90.2 "
Polymer L96.0 95.1 92.085.3 20.1 1' Polymer M95.3 94.1 82.07.1 - "
Polymer N72.6 18.8 2.3 - -Comparison Polymer O63.5 19.1 3.5 - - "
Polymer P4.5 Polymer Q4.0 - - - -Polymer R68.2 34.7 4.8 - - "
Polymer S90.1 70.5 8.9 - - "
Polymer T52.6 43.0 6.7 - - "
Polymer U83.2 63.3 8.0 - - "
Polymer V 67.9 46.2 - - - "
Polymer W 54.2 32.3 - - - "
~ote: * Values in the parentheses are concentrations per ppm of Ca2+.
2) Effect on Inhibition of Calcium Carbonate Precipitation at 180~C:
A hundred milliliters of a model white liquor (an aqueous solution consisting of 8.0 wt% NaOH, 3.5 wt% NazCO3, 0.5 wt% KOH, and 88.0 wt% ion-exchanged water) were heated to 100~C, and calcium chloride was added thereto to a final calcium ion concentration of 150 ppm. Each of the scale deposit inhibitors prepared was added to the mixture to a prescribed concentration. The resulting mixture was kept still in an autoclave set at 180~C for 3 hours. The autoclave was rapidly cooled by dipping in tap water, and the liquid was passed through a filter paper for quantitative determination (No. 6) by gravity filtration. The residual calcium ion concentration of the filtrate was determined by atomic-absorption spectroscopy. The results obtained are shown in Table 3 below.
Residual Ca2+ Concentration (ppm) Concentration of Scale Deposit Inhibitor Scale60 ppm 30 ppm 15 ppm Deposit(0.40 (0.20 (0.10 No Inhibitor ppm)* ppm)~' ppm)* Addition Remark Polymer B 50.3 48.9 40.2 Invention Polymer C 51.0 50.2 47.0 "
Polymer F 51.2 50.3 47.5 "
Polymer G 50.8 50.4 42.7 "
Polymer H 50.3 49.4 40.0 7.3 ~
Polymer K 50.7 50.6 43.3 "
Polymer S 23.7 14.4 11.0 Comparison Polymer T 16.5 11.8 9.6 "
Polymer U 20.6 14.8 11.1 "
~ote: * Values in the parentheses are concentrations per ppm of Ca2+.
It is seen from the results in Tables 2 and 3 that the scale deposit inhibitor comprising the polymer according to the present invention exhibits a markedly high inhibitory effect on calcium carbonate precipitation.
While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
A hundred milliliters of a model white liquor (an aqueous solution consisting of 8.0 wt% NaOH, 3.5 wt% NazCO3, 0.5 wt% KOH, and 88.0 wt% ion-exchanged water) were heated to 100~C, and calcium chloride was added thereto to a final calcium ion concentration of 150 ppm. Each of the scale deposit inhibitors prepared was added to the mixture to a prescribed concentration. The resulting mixture was kept still in an autoclave set at 180~C for 3 hours. The autoclave was rapidly cooled by dipping in tap water, and the liquid was passed through a filter paper for quantitative determination (No. 6) by gravity filtration. The residual calcium ion concentration of the filtrate was determined by atomic-absorption spectroscopy. The results obtained are shown in Table 3 below.
Residual Ca2+ Concentration (ppm) Concentration of Scale Deposit Inhibitor Scale60 ppm 30 ppm 15 ppm Deposit(0.40 (0.20 (0.10 No Inhibitor ppm)* ppm)~' ppm)* Addition Remark Polymer B 50.3 48.9 40.2 Invention Polymer C 51.0 50.2 47.0 "
Polymer F 51.2 50.3 47.5 "
Polymer G 50.8 50.4 42.7 "
Polymer H 50.3 49.4 40.0 7.3 ~
Polymer K 50.7 50.6 43.3 "
Polymer S 23.7 14.4 11.0 Comparison Polymer T 16.5 11.8 9.6 "
Polymer U 20.6 14.8 11.1 "
~ote: * Values in the parentheses are concentrations per ppm of Ca2+.
It is seen from the results in Tables 2 and 3 that the scale deposit inhibitor comprising the polymer according to the present invention exhibits a markedly high inhibitory effect on calcium carbonate precipitation.
While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
Claims (5)
1. A scale deposit inhibitor for a continuous digester used in making kraft pulps, which comprises a terpolymer comprising maleic acid units, acrylic acid units, and
2-acrylamido-2-methylpropanesulfonic acid units and having a maleic acid to acrylic acid molar ratio of from 10:1 to 10:30, a 2-acrylamido-2-methylpropanesulfonic acid content of from 1 to 30 mol%, and a weight-average molecular weight of from 500 to 20000.
2. The scale deposit inhibitor as claimed in Claim 1, wherein said terpolymer has the maleic acid to acrylic acid molar ratio of from 10:2 to 10:15, the 2-acrylamido-2-methylpropanesulfonic acid content of from 3 to 20 mol%, and the weight-average molecular weight of from 1000 to 10000.
2. The scale deposit inhibitor as claimed in Claim 1, wherein said terpolymer has the maleic acid to acrylic acid molar ratio of from 10:2 to 10:15, the 2-acrylamido-2-methylpropanesulfonic acid content of from 3 to 20 mol%, and the weight-average molecular weight of from 1000 to 10000.
3. A method for controlling scale deposition in a continuous digester used in making kraft pulps, which comprises injecting a scale deposit inhibitor comprising a terpolymer comprising maleic acid units, acrylic acid units, and 2-acryl-amido-2-methylpropanesulfonic acid units and having a maleic acid to acrylic acid molar ratio of from 10:1 to 10: 30, a 2-acrylamido-2-methylpropanesulfonic acid content of from 1 to 30 mol%, and a weight-average molecular weight of from 500 to 20000 to a cooking liquor in a digester at concentration of from 0.01 to 10 ppm per ppm of a calcium ion present in said cooking liquor.
4. The method for controlling scale deposition as claimed in Claim 3, wherein said concentration is from 0.05 to
5 ppm per ppm of the calcium ion.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8-179067 | 1996-07-09 | ||
| JP17906796A JP3194867B2 (en) | 1996-07-09 | 1996-07-09 | Scale adhesion inhibitor and method for suppressing scale adhesion in pulp digester |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2208936A1 true CA2208936A1 (en) | 1998-01-09 |
Family
ID=16059532
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2208936 Abandoned CA2208936A1 (en) | 1996-07-09 | 1997-06-27 | Scale deposit inhibitor for kraft digesters and method for controlling scale deposition in kraft digisters |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP3194867B2 (en) |
| CA (1) | CA2208936A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110023253A (en) * | 2016-11-25 | 2019-07-16 | 栗田工业株式会社 | Sodium salt scale preventive agent, sodium salt dirt prevention method, water-based viscosity reductant, water-based management method and water-based process for reducing viscosity |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4787433B2 (en) * | 2001-08-24 | 2011-10-05 | オルガノ株式会社 | Water treatment method |
| JP2004293028A (en) * | 2003-03-13 | 2004-10-21 | Hakuto Co Ltd | Scale inhibitor and scale inhibitory method for barium sulfate in water system |
| JP5903953B2 (en) * | 2012-03-15 | 2016-04-13 | 栗田工業株式会社 | Iron scale inhibitor and method for preventing steam generator |
| JP6286819B2 (en) * | 2012-11-02 | 2018-03-07 | 栗田工業株式会社 | How to suppress scale |
| JP6294124B2 (en) * | 2014-03-31 | 2018-03-14 | 株式会社日本触媒 | Copolymer and process for producing the same |
-
1996
- 1996-07-09 JP JP17906796A patent/JP3194867B2/en not_active Expired - Lifetime
-
1997
- 1997-06-27 CA CA 2208936 patent/CA2208936A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110023253A (en) * | 2016-11-25 | 2019-07-16 | 栗田工业株式会社 | Sodium salt scale preventive agent, sodium salt dirt prevention method, water-based viscosity reductant, water-based management method and water-based process for reducing viscosity |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3194867B2 (en) | 2001-08-06 |
| JPH1025684A (en) | 1998-01-27 |
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