GB2061249A - The treatment of aqueous systems to inhibit deposition of solid material - Google Patents
The treatment of aqueous systems to inhibit deposition of solid material Download PDFInfo
- Publication number
- GB2061249A GB2061249A GB8033922A GB8033922A GB2061249A GB 2061249 A GB2061249 A GB 2061249A GB 8033922 A GB8033922 A GB 8033922A GB 8033922 A GB8033922 A GB 8033922A GB 2061249 A GB2061249 A GB 2061249A
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- Prior art keywords
- polymer
- phosphonate
- acid
- water
- hydrogen
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
- C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
- C02F5/10—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents using organic substances
- C02F5/14—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents using organic substances containing phosphorus
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- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
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Abstract
The deposition of solid material in aqueous systems is reduced or prevented by the incorporation in the water of at least one phosphonate which contains at least 3 acid groups which are carboxylic and phosphonic acid groups at least one of which is a carboxylic acid group and at least one of which is a phosphonic acid group, at least the said 3 acid groups being attached to carbon atoms, in the form of free acid or salt, and at least one water soluble polymer possessing carboxylic (including carboxylic anhydride) and sulphonate groups.
Description
SPECIFICATION
The treatment of aqueous systems
The present invention relates to the treatment of aqueous systems, and, more particularly, to reducing or preventing the deposition of solid particles in an aqueous system, especially hard water.
It is well known that particles of solid matter including clay, silt, microbiological debris, ferric oxide and calcium carbonate deposit in aqueous systems and, in particular, in aqueous systems used in heat exchangers, cooling towers and associated equipment. Such deposits greatly retard the transfer of heat not only by limiting the circulation of water but by insulating it from the surface it is intended to cool. A further effect is that serious corrosion may occur under any deposits formed; such corrosion is minimised by keeping the metal surfaces clean. Apart from deposition of hardness salts, particulate matter is introduced into a cooling system, for example by the passage of large volumes of air through the cooling tower, and in the process the finely divided solids are effectively scrubbed out of the air.
A similar but even more severe situation exists in cooling and scrubbing the gases formed during steel making where large amounts of lime and iron oxide particles were carried over into the aqueous cooling and quenching system. This gives rise to a cooling water which is high in hardness-forming cations and particulate solid levels. An extremely efficient dispersant is required to operate under these conditions.
Accordingly, it is highly desirable that some way be found to disperse such particles so as to prevent particle deposition. It is to be appreciated that this is a different problem from the inhibition of scale where certain dissolved salts in the water precipitate or crystallise out or in some cases are deliberately caused to precipitate by the addition of, for example, phosphates and the resulting precipitate or sludge is conditioned so that it can readily be removed rather than adhere to the walls of the vessel.
The use of a variety of polycarboxylates and other low molecular weight polymers, including acrylate polymers, as dispersants in such water systems has been known for many years. It is well recognised, however, that these materials suffer a considerable decrease in effectiveness when used in hard water, for example water containing more than 300 ppm calcium hardness. This is obviously a serious deficiency in attempting to obtain higher concentration factors in cooling systems. The aim of the present invention is to provide a method which is more effective in preventing deposition in hard water than those currently available.
According to the present invention it has surprisingly been found that this can be achieved by the use of a specific combination of certain water-soluble phosphonates and certain water-soluble organic sulphonate polymers. It has been found that the use of this combination of phosphonate and polymer results in a synergistic effect in spite of the fact that the individual components are adversely affected when used in hard water. In addition, the synergistic mixture assists in the prevention of the formation of scale.
Accordingly, the present invention provides a method of treating water, in particular to reduce or prevent the deposition of solid material therein, which comprises incorporating in the water at least one phosphonate as defined below and at least one water soluble organic polymer possessing carboxylic (including carboxylic anhydride) and sulphonate groups.
While it is possible to incorporate the phosphonate and polymer separately it will be appreciated that it will generally be more convenient to incorporate them together in the form of a composition. Accordingly, the present invention also provides a composition suitable for addition to water to reduce or prevent deposition of solid material therein, comprising at least one water-soluble phosphonate as defined below, and at least one of the said water-soluble organic polymers.
The phosphonates for use in the present invention are those which contain at least 3 acid groups which are carboxylic and phosphonic acid groups, such that at least one acid group is a carboxylic acid group and at least one acid group is a phosphonic acid group, at least the said 3 acid groups being attached to carbon atoms.
The preferred phosphonates possess the general formula:
wherein R is hydrogen, alkyl, alkenyl or alkynyl having up to 4 carbon atoms; phenyl; cycloalkyl having 3 to 6 carbon atoms; benzyl; phenethyl or
wherein R' is hydrogen, alkyl having 1 to 4 carbon atoms or carboxyl, R" is hydrogen or methyl and R"' is carboxyl or phosphonate. 2-Phosphonobutane-1 ,2,4-tricarboxylic acid, a commercially available material, is particularly preferred. Another preferred material is 2,4.diphosphonobutane-1,2-dicarboxylic acid. These phosphonates can be obtained by processes well known in the art, for example as described in British
Specification No. 1,282,078.
In general, the polymers used in the present invention are vinyl addition type copolymers possessing recurring units of the formula:
wherein R1 represents hydrogen or lower alkyl, i.e. of 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, or -CH2COOH, R2 represents hydrogen or lower alkyl, X represents -COOH and Z represents hydrogen or -COOH or X and Z together represent -CO-O-CO-, and Y represents -S03H, -C6H5 SO3H (para) or -CONHQ(R3) (R4) SO3H in which Q represents -CH2- or -CH2-CH2- and R3 and R4, independently, represent hydrogen, phenyl, substituted phenyl, C 1-12 linear or branched alkyl or C 3-12 cycloalkyl, especially methyl.Preferred such Y radicals include -CON H -C(CH3)(R3)-CH2-SO3H, especially where R3 represents methyl, and -CONHCH2SO3H.
The phosphonates and polymers are generally used in the form of alkali metal, especially sodium or potassium, ammonium, or lower amine salts although the use of the free acids, zinc or other salts of either or both is not excluded.
The molar proportion of the two types of recurring unit is generally from 5:95 to 95:5, more particularly from 25:75 to 75:25 and especially about 50:50. The polymers generally possess a molecular weight from 500 to 750,000 and in particular from 1,000 to 10,000 and especialyfrom 4,000 to 6,000. It will be appreciated that if the molecular weight of the polymer is too high intends to behave as a flocculating agent but this is not necessarily disadvantageous provided the flocculated material is sufficiently light to remain in suspension.
Preferred copolymers for use in the present invention include a copolymer of methacrylic acid and 2-acrylamido-2-methyl-propane sulphonic acid (AMP#S) in the form of, in particular, the sodium salt, especially in a molar ratio of about 1:1 and having a molecular weight of about 5,000, and a copolymer of styrene sulphonic acid and maleic acid in the form of, in particular, the sodium salt, especially in a molar ratio of about 3:1 and having a molecular weight of about 4,500.
The first units of the copolymers are generally derived from ethylenically unsaturated acids such as maleic acid (or anhydride), acrylic acid and methacrylic acid. The second units of the copolymers are generally derived from ethylenically unsaturated monomers; these monomers may either contain the sulphonate group or this group can be introduced by sulphonation of the copolymer.
The polymers used in the present invention can be obtained from the monomers using conventional polymerisation processes. The styrene sulphonate polymers can be prepared by sulphonating a copolymer of styrene and maleic anhydride with a sulphur trioxide - organic phosphorus compound (see, for example,
U.S. Patent 3,072,618).
In general, the polymer and phosphonate are used in the weight ratios from 10:1 to 1:10, more especially from 4:1 to 1:4 and most especially about 1:1.
The dosage of phosphonate and polymer depends, to some extent, on the nature of the aqueous system to be treated. Thus the phosphonate dosage depends to some extent on the calcium concentration while the polymer dosage depends to some extent on the concentration of suspended solids. In general, however, it can be said that the concentration in the feed is from 0.01 to 500 ppm of additive and, more particularly, from 0.1 to 50 ppm. A particularly preferred concentration is about 2.0 ppm. However the optimum concentration used must depend on the degree of build-up in the system.
It will be appreciated that other ingredients customarily employed in water treatment such as alkali, lignin derivatives, biocides and corrosion inhibitors can also be employed.
The composition of the present invention will normally be in the form of an aqueous solution although other forms such as powders are not excluded.
The following Examples further illustrate the present invention. In these Examples two different types of tests were employed, namely a static test and a circulatory test. The details of these are as follows:
(i) In the static cylinder type test a suspension of graded particle size is allowed to stand for 24 hours in 250 ml measuring cylinders. The height of the solid/liquid interface is noted and the "% Hold Up" is calculated by dividing final height by original height, expressed as a %.
(ii) A laboratory scale recirculating rig consisting of a centrifugal pump, .a 5 litre vessel and a flow through cell for monitoring the optical transmission of a suspension under standard conditions. The light transmission decreases with the better dispersion of the particulate matter in suspension.
Examples 1 to 9 These Examples show the effect of water containing varying degrees of calcium hardness on a number of additives, using the static test.
Suspension of 1,000 ppm China Clay. The results obtained are shown in Table I.
TABLE I
Interface % Hold Up
Example Additive Dose, 100 ppm 300 ppm
No. - ppm Ca2+ water Ca2+water
1 Blank --- 0 0
2 Polymer 1 5 70 0
3 Polymer 2 5 71 0
4 Polymer 3 5 72 0
5 Polymer 4 5 69 0
6 Polymer 5 5 69 30
7 Polymer 6 5 70 37.5
8 Polymer 7 5 68 15
9 Phosphonate 1 5 60 0
Polymer 1 = Sodium polyacrylate M Wt 2,000
2 = Sodium polyacrylate M Wt 5,000
3 = Sodium polymethacrylate M Wt 1,000
4 = Sodium polymethacrylate M Wt 4,500
Polymer 5 = Copolymer of methacrylic acid/2 acrylamido 2 methyl
propane sulfonic acid in 3:2 mole ratio
6 = Copolymer as in 5 but in a 1::1 mole ratio
7 = Sodium polystyrene sulphonate, M Wt 70,000
Phosphonate 1 = Nitrilotrismethylene phosphonic acid
(as sodium salt)
The above results show the serious effect of calcium hardness on the performance of some standard materials currently employed for dispersing particulate matter in cooling water systems. Although the copolymers 5, 6 and 7 give the best results, the deterioration in performance in hard water is still extremely undesirable. This test is severe but does indicate relative strengths and weaknesses on a comparative basis.
Examples 10 to 13
The results in Table II were obtained using the re-circulating rig after 5 hours using water containing 90 ppm China Clay Solids Suspension. They again indicate that the results in Table I are not due to the method of test.
TABLE II
% Transmission in
Example Additive Dose, 100 ppm 300 ppm
No. ppm Ca2+ water Ca2+ water
10 Blank --- 55 60
11 Polymer 6 5 33 36.4
12 Polymer 8 5 36.5 49.0
13 Phosphonate 2 5 34.0 48.0
Polymer 6 = Copolymer of methacrylic acid/2 acrylamido 2-methyl propane sulphonic acid 1:1 mole ratio
Polymer 8 = Sodium polyacrylate M Wt 1,000
Phosphonate 2 = 2-phosphonobutane tricarboxylic acid 1,2,4
Examples 14 to 24
Table Ill gives the results of a number of tests run on the re-circulating rig in order to ascertain the effect of adding a phosphonate to the polymer in question.
TABLE lil Re-circulating rig - 90 ppm China Clay Solids Suspension
Duration of test - 5 hours Dose level of additive 5 ppm in
all cases 300 ppm Ca2+ hardnesswater.
Example Additive
No. Transmission
14 Blank 60
15 Polymer 6 36.3
16 Phosphonate 2 48.0
17 4/1 ratio Polymer6/Phosphonate2 34.0
18 1/1 ratio Poiymer6/Phosphona,;te2 31.5
19 1/4 ratio Polymer 6/Phosphonate 2 34.2
.20 Phosphonate 1 50.0
21 1/1 ratio Polymer6/Phosphonate 1 40.2
22 1/1 ratio Polymer6/Phosphonate2 51.0
23 Polymer 9 40.8
24 1/1 ratio Polymer 9/Phosphonate 2 38.4 Polymer 9 = Copolymer of Styrene sulphonate/Maleic acid in ratio 3:1 Molecular Wt 4,500.
These results show the synergistic effect of using the combination of phosphonates and the polymers; in contrast no such effect is evident when using phosphonate 1. Indeed, experiments with a number of other phosphonates as indicated in the following Examples show the specific nature of the synergistic effect.
Examples 25 to 30
A static cylinder test was conducted using a 100 ppm suspension of China Clay in 300 ppm Ca2+ hardness water. The suspension in 250/ml measuring cylinders was allowed to settle for 2 hours, samples were then withdrawn at a given depth and the turbidity measured by a nephelometer.The efficiency of the additive as a dispersant was calculated from:
Final reading of additive Final reading of blank
x 100= /Oefflclency
Initial reading of blank - Final reading of blank
Test Additive Dose Efficiency
level,
ppm
25 Polymer 6 5 33.1
Phosphonate 2 5 19.2
1:1 ratio Polymer 6/
Phosphonate 2 5 42.6
26 Polymer 6 5 33.0
Phosphonate 3 5 25.0
1:1 ratio Polymer 6/
Phosphonate 3 5 21.0
Phosphonate 1 5 16.6
1:1 ratio Polymer 6/
Phosphonate 1 5 27.1
27 Polymer 6 5 29.2
Phosphonate 4 5 25.2
Phosphonate 5 5 10.4
1:1 ratio Polymer 6/
Phosphonate 4 5 10.6
1:1 ratio Polymer 6/
Phosphonate 5 5 20.8
28 Polymer 6 5 31.8
Phosphonate 6 5 17.3
1:1 ratio Polymer 6/
Phosphonate 6 5 27.3
29 Polymer 6 5 32.7
Phosphonate 7 5 6.0
1:1 ratio Polymer 6/
Phosphonate 7 5 17.7
30 Polymer 6 5 32.4
Phosphonate 8 5 16.2
1: :1 ratio Polymer 6/
Phosphonate 8 5 43.2
Phosphonate 3 = Hexamethylene diamine tetramethylene phosphonic acid.
Phosphonate 4 = N,N-bis(carboxymethyl)imino methylene phosphonic acid.
Phosphonate 5 = N, carboxymethyl imino di(methylene phosphonic acid).
Phosphonate 6 = N, carboxymethyl imino monomethylene phosphonic acid.
Phosphonate 7 = Hydroxyethylidene diphosphonic acid.
Phosphonate 8 = 2,4-Disphosphonobutane-1, 2-dicarboxylic acid.
It can be seen that only phosphonates 2 and 8 give a synergistic effect.
Claims (22)
1. A method of treating water which comprises incorporating in the water at least one phosphonate which contains at least 3 acid groups which are carboxylic and phosphonic acid groups at least one of which is a carboxylic acid group and at least one of which is a phosphonic acid group, at least the said 3 acid groups being attached to carbon atoms, in the form of free acid or salt, and at least one water soluble polymer possessing carboxylic (including carboxylic anhydride).and sulphonate groups.
2. A method according to claim 1 in which the phosphonate has the general formula:
wherein R is hydrogen, alkyl, alkenyl, or alkynyl having up to 4 carbon atoms; phenyl; cycloalkyl having 3 to 6 carbon atoms; benzyl; phenethyl or
wherein R' is hydrogen, alkyl having 1 to4carbonatomsorcarboxyl,R" is hydrogen or methyl and R"' is carboxyl of phosphonate.
3. A method according to claim 2 in which the phosphonate is 2-phosphonobutane-1,2,4-tricarboxylic acid or 2,4-diphosphonobutane-1,2-dicarboxylic acid
4. A method according to any one of claims 1 to 3 ib which the polymer possesses recurring units of the formula::
wherein P1 represents hydrogen or lower alkyl, or -CH2COOH, 92 represents hydrogen or lower alkyl, X represents -COOH and Z represents hydrogen or -COOH or X and Z together represent -CO-O-CO-, and
Y represents -SO3H, -C6H5 SO3H (para) or -CONHQ(R3) (R4) SO3H in which Q represents -CH2- or -CH2-CH2- and R3 and R4 independently represent hydrogen, phenyl, substituted phenyl, C 1-12 linear or branched alkyl or C 3-12 cycloalkyl.
5. A method according to claim 4 in which R1 represents alkyl of 1 to 4 carbon atoms, and Y represents a radical of the formula: -CONH-C(CH3) (R3)-CH2-SO3H or -CONHCH2SO3H.
6. A method according to claim Sin which the polymer is a copolymer of methacrylic acid and 2-acrylamido-2-methyl-propane sulphonic acid.
7. A method according to claim 4 in which the molar ratio of the comonomers is about 1:1.
8. A method according to claim 6 in which the polymer is a copolymer of styrene sulphonic acid and maleic acid.
9. A method according to claim 8 in which the molar ratio of the comonomers is about 3:1, respectively.
10. A method according to any one of the preceding claims in which the polymer is in the form of a sodium salt.
11. A method according to any one of the preceding claims in which the polymer has a molecular weight of 4,000 to 6,000.
12. A method according to any one of the preceding claims in which the phosphonate and polymer are incorporated in a weight ratio from 4:1 to 1:4.
13. A method according to any one of the preceding claims in which the total concentration of phosphonate and polymer is from 0.1 to 50 ppm.
14. A method according to any one of the preceding claims in which the water is hard water.
15. A composition for addition to water to reduce or prevent deposition of solid material therein which comprises at least one phosphonate as defined in claim 1 and at least one polymer as defined in claim 1.
16. A composition according to claim 15 in which the phosphonate is as defined in claim 2 or 3.
17. A composition according to claim 15 or 16 in which the polymer is as defined in any one or more of claims 4 to 11.
18. A composition according to any one of claims 15 to 17 in which the weight ratio of phosphonate to polymer is from 4:1 to 1:4.
19. A composition according to claim 15 substantially as hereinbefore described.
20. A method according to any one of claims 1 to 14 in which the phosphonate and polymer are incorporated by adding to the water a composition as claimed in any one of claims 15 to 19.
21. A method according to claim 1 substantially as hereinbefore described.
22. Water whenever treated by a method as claimed in any one of claims 1 to 14,20 and 21.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8033922A GB2061249B (en) | 1979-10-23 | 1980-10-21 | Treatment of aqueous systems to inhibit deposition of solid material |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7936773 | 1979-10-23 | ||
| GB8033922A GB2061249B (en) | 1979-10-23 | 1980-10-21 | Treatment of aqueous systems to inhibit deposition of solid material |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2061249A true GB2061249A (en) | 1981-05-13 |
| GB2061249B GB2061249B (en) | 1983-05-18 |
Family
ID=26273330
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8033922A Expired GB2061249B (en) | 1979-10-23 | 1980-10-21 | Treatment of aqueous systems to inhibit deposition of solid material |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2061249B (en) |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3230291A1 (en) * | 1981-08-18 | 1983-03-03 | Dearborn Chemicals Ltd., Widnes, Cheshire | COMPOSITION FOR PREVENTING KETTLE IN AQUEOUS SYSTEMS |
| FR2533549A1 (en) * | 1982-09-27 | 1984-03-30 | Dearborn Chemicals Co | COMPOSITION AND METHOD FOR INHIBITING TARTAR FORMATION |
| FR2540855A1 (en) * | 1983-02-16 | 1984-08-17 | Dearborn Chemicals Co | COMPOSITION AND METHOD FOR INHIBITING TARTAR FORMATION |
| US4479878A (en) * | 1982-10-28 | 1984-10-30 | Betz Laboratories, Inc. | High calcium tolerant deposit control method |
| US4556493A (en) * | 1983-02-16 | 1985-12-03 | Dearborn Chemical Company | Composition and method for inhibiting scale |
| US4559156A (en) * | 1980-11-18 | 1985-12-17 | Dearborn Chemicals, Ltd. | Process for dispersing particulate material in aqueous systems |
| US4575425A (en) * | 1984-12-24 | 1986-03-11 | Calgon Corporation | Process for controlling calcium oxalate scale over a wide pH range |
| US4581145A (en) * | 1982-09-27 | 1986-04-08 | Dearborn Chemical Company | Composition and method for inhibiting scale |
| US4600524A (en) * | 1983-12-08 | 1986-07-15 | W. R. Grace & Co. | Composition and method for inhibiting scale |
| US4717542A (en) * | 1987-01-23 | 1988-01-05 | W. R. Grace & Co. | Inhibiting corrosion of iron base metals |
| US4836933A (en) * | 1987-01-16 | 1989-06-06 | National Starch And Chemical Corporation | Water treatment polymer |
| US4936987A (en) * | 1983-03-07 | 1990-06-26 | Calgon Corporation | Synergistic scale and corrosion inhibiting admixtures containing carboxylic acid/sulfonic acid polymers |
-
1980
- 1980-10-21 GB GB8033922A patent/GB2061249B/en not_active Expired
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4559156A (en) * | 1980-11-18 | 1985-12-17 | Dearborn Chemicals, Ltd. | Process for dispersing particulate material in aqueous systems |
| DE3230291A1 (en) * | 1981-08-18 | 1983-03-03 | Dearborn Chemicals Ltd., Widnes, Cheshire | COMPOSITION FOR PREVENTING KETTLE IN AQUEOUS SYSTEMS |
| US4566972A (en) * | 1981-08-18 | 1986-01-28 | Dearborn Chemicals, Ltd. | Treatment of aqueous systems |
| US4581145A (en) * | 1982-09-27 | 1986-04-08 | Dearborn Chemical Company | Composition and method for inhibiting scale |
| FR2533549A1 (en) * | 1982-09-27 | 1984-03-30 | Dearborn Chemicals Co | COMPOSITION AND METHOD FOR INHIBITING TARTAR FORMATION |
| US4479878A (en) * | 1982-10-28 | 1984-10-30 | Betz Laboratories, Inc. | High calcium tolerant deposit control method |
| US4556493A (en) * | 1983-02-16 | 1985-12-03 | Dearborn Chemical Company | Composition and method for inhibiting scale |
| GB2137185A (en) * | 1983-02-16 | 1984-10-03 | Dearborn Chemicals Co | Composition and Method for Inhibiting Scale |
| FR2540855A1 (en) * | 1983-02-16 | 1984-08-17 | Dearborn Chemicals Co | COMPOSITION AND METHOD FOR INHIBITING TARTAR FORMATION |
| US4936987A (en) * | 1983-03-07 | 1990-06-26 | Calgon Corporation | Synergistic scale and corrosion inhibiting admixtures containing carboxylic acid/sulfonic acid polymers |
| US4600524A (en) * | 1983-12-08 | 1986-07-15 | W. R. Grace & Co. | Composition and method for inhibiting scale |
| US4575425A (en) * | 1984-12-24 | 1986-03-11 | Calgon Corporation | Process for controlling calcium oxalate scale over a wide pH range |
| US4836933A (en) * | 1987-01-16 | 1989-06-06 | National Starch And Chemical Corporation | Water treatment polymer |
| US4717542A (en) * | 1987-01-23 | 1988-01-05 | W. R. Grace & Co. | Inhibiting corrosion of iron base metals |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2061249B (en) | 1983-05-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19991021 |