CA2167612C - Method of controlling fluoride scale formation in aqueous systems - Google Patents
Method of controlling fluoride scale formation in aqueous systems Download PDFInfo
- Publication number
- CA2167612C CA2167612C CA002167612A CA2167612A CA2167612C CA 2167612 C CA2167612 C CA 2167612C CA 002167612 A CA002167612 A CA 002167612A CA 2167612 A CA2167612 A CA 2167612A CA 2167612 C CA2167612 C CA 2167612C
- Authority
- CA
- Canada
- Prior art keywords
- recited
- fluoride
- parts per
- spray water
- hydrogen
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/52—Compositions for preventing, limiting or eliminating depositions, e.g. for cleaning
- C09K8/528—Compositions for preventing, limiting or eliminating depositions, e.g. for cleaning inorganic depositions, e.g. sulfates or carbonates
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Hydrology & Water Resources (AREA)
- General Chemical & Material Sciences (AREA)
- Water Supply & Treatment (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Inorganic Chemistry (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Materials Engineering (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
A method of treating water to inhibit the formation of fluoride salt scale is disclosed. The method is particularly effective at inhibiting the formation and deposition of fluoride containing salts in spray water cooling systems such as steel casting systems. The method comprises introducing into the aqueous system an alkyl epoxy carboxylate of the general formula: (see formula I) where n ranges from about 2 to about 11, M is hydrogen or a water soluble cation such as Na+, NH4+ or K+ and R is hydrogen, C1-4 alkyl or C1-4 substituted alkyl.
Description
METHOD OF CONTROLLING FLUORIDE
SCALE FORMATION IN AQUEOUS SYSTEMS
FIELD OF THE INVENTION
The present invention relates to the treatment of water to inhibit the formation of scale. More particularly, the present invention relates to the use of an alkyl epoxy carboxylate to inhibit fluoride salt scale formation in aqueous systems.
BACKGROUND OF THE INVENTION
In an aqueous system such as a steel casting process, molten steel is shaped as it passes through a mold. This mold is coated with powder to prevent the adherence of steel to the sides. Many mold pow-ders contain fluoride salts which dissolve in the spray water used to cool the hot molten slab. These fluoride-containing solutions are splashed on the inside of the enclosure which houses the spray nozzle banks (the spray chamber) and on the outside of the spray nozzles in such a continu-ous caster spray water system. Subsequently, fluorides are deposited in and around the spray nozzles and the piping immediately preceding the ~16 7 6 12 nozzles, particularly in areas of decreased spray water flow and high radi-ant heat. Water to the spray nozzles is from the cooling tower at a pH of about 8. Dissolution of mold powders decreases the pH to about 4.
It would be advantageous to prevent the formation of scale in and around the spray nozzles and chambers, thereby enhancing spray water cooling efficiency by increasing water flow and maintaining the spray pattern, reducing the potential for a breakout which poses serious safety concerns, and reducing production downtime. Such objectives are ac-complished by the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention comprises treating industrial waters with an alkyl epoxy carboxylate (hereinafter Polymer A) of the general formula:
R R
I I
HO --t-i -i -O~H
0 = C C = 0 M M
where n ranges from about 2 to 50, preferably 2 to 25, M is hydrogen or a water soluble cation such as Na+, NH4+ or K+ and R is hydrogen, C1_4 alkyl or C1_4 substituted alkyl (preferably R is hydrogen).
SCALE FORMATION IN AQUEOUS SYSTEMS
FIELD OF THE INVENTION
The present invention relates to the treatment of water to inhibit the formation of scale. More particularly, the present invention relates to the use of an alkyl epoxy carboxylate to inhibit fluoride salt scale formation in aqueous systems.
BACKGROUND OF THE INVENTION
In an aqueous system such as a steel casting process, molten steel is shaped as it passes through a mold. This mold is coated with powder to prevent the adherence of steel to the sides. Many mold pow-ders contain fluoride salts which dissolve in the spray water used to cool the hot molten slab. These fluoride-containing solutions are splashed on the inside of the enclosure which houses the spray nozzle banks (the spray chamber) and on the outside of the spray nozzles in such a continu-ous caster spray water system. Subsequently, fluorides are deposited in and around the spray nozzles and the piping immediately preceding the ~16 7 6 12 nozzles, particularly in areas of decreased spray water flow and high radi-ant heat. Water to the spray nozzles is from the cooling tower at a pH of about 8. Dissolution of mold powders decreases the pH to about 4.
It would be advantageous to prevent the formation of scale in and around the spray nozzles and chambers, thereby enhancing spray water cooling efficiency by increasing water flow and maintaining the spray pattern, reducing the potential for a breakout which poses serious safety concerns, and reducing production downtime. Such objectives are ac-complished by the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention comprises treating industrial waters with an alkyl epoxy carboxylate (hereinafter Polymer A) of the general formula:
R R
I I
HO --t-i -i -O~H
0 = C C = 0 M M
where n ranges from about 2 to 50, preferably 2 to 25, M is hydrogen or a water soluble cation such as Na+, NH4+ or K+ and R is hydrogen, C1_4 alkyl or C1_4 substituted alkyl (preferably R is hydrogen).
A method of preparing an alkyl epoxy carboxylate similar to that employed as a scale control agent in the present invention is described in U.S. Pat. No. 4,654,159, issued March 31, 1987 to Bush et al. The Bush et al. patent describes ether hydroxypolycarboxylate prepared from epoxy succinates by treatment with an alkaline calcium compound. The polyepoxysuccinic acid of a specific molecular weight distribution is described in Bush et al. as a useful detergent builder due to its ability to act as a sequestering agent. The sequestering agent of Bush et al. complexes with hardness cations in water supplies which aids in detergent processes by preventing the cations from adversely effecting the detergents.
In the present invention, the alkyt epoxy carboxylate is added to aqueous systems at substoichiometric levels to inhibit fluoride-containing salt scale formation. The method of the present invention provides effec-tive deposition inhibition in waters having relatively high Langelier satura-tion indexes. The method of the present invention provides such control at relatively low active treatment levels without the use of phosphates or phosphonates.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention pertains to a novel method of inhibiting the formation of fluoride salt scale such as calcium fluoride scale from aque-ous systems. Specifically, the method of the present invention comprises adding to an aqueous system an alkyl epoxy carboxylate (or polyepoxy-succinic acid) of the general formula:
In the present invention, the alkyt epoxy carboxylate is added to aqueous systems at substoichiometric levels to inhibit fluoride-containing salt scale formation. The method of the present invention provides effec-tive deposition inhibition in waters having relatively high Langelier satura-tion indexes. The method of the present invention provides such control at relatively low active treatment levels without the use of phosphates or phosphonates.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention pertains to a novel method of inhibiting the formation of fluoride salt scale such as calcium fluoride scale from aque-ous systems. Specifically, the method of the present invention comprises adding to an aqueous system an alkyl epoxy carboxylate (or polyepoxy-succinic acid) of the general formula:
R R
HO -t- i - i - O}-nH
O= C C= O
M M
where n ranges from about 2 to 50, preferably 2 to 25, M is hydrogen or a water soluble cation such as Na+, NH4+ or K+ and R is hydrogen, C1_4 alkyl or C1_4 substituted alkyl (preferably R is hydrogen).
The polyepoxysuccinic acid material employed in the present in-vention can be obtained by the polymerization of epoxysuccinate in the presence of calcium hydroxide or other alkaline calcium salts. The general reaction can be represented as follows:
Ca(OH)2/H20 R R
0 HO-{-C -C -O}-õH
R-C C- R O= C C O
0=C C=0 O O
M M
A complete description of a method of preparing such a polyepoxy-succinic acid of a specific molecular weight distribution is included in U.S.
Pat. No. 4,654,159, issued March 31, 1987.
HO -t- i - i - O}-nH
O= C C= O
M M
where n ranges from about 2 to 50, preferably 2 to 25, M is hydrogen or a water soluble cation such as Na+, NH4+ or K+ and R is hydrogen, C1_4 alkyl or C1_4 substituted alkyl (preferably R is hydrogen).
The polyepoxysuccinic acid material employed in the present in-vention can be obtained by the polymerization of epoxysuccinate in the presence of calcium hydroxide or other alkaline calcium salts. The general reaction can be represented as follows:
Ca(OH)2/H20 R R
0 HO-{-C -C -O}-õH
R-C C- R O= C C O
0=C C=0 O O
M M
A complete description of a method of preparing such a polyepoxy-succinic acid of a specific molecular weight distribution is included in U.S.
Pat. No. 4,654,159, issued March 31, 1987.
5 The treatment levels of alkyl epoxy carboxylate added to an aque-ous system can range from about 25 parts per billion up to about 500 parts per million. The preferred treatment levels range from about 50 ppm up to about 100 ppm. The concentration of alkyl epoxy carboxylate necessary to provide effective calcium fluoride control will, of course, vary from system to system. The treatment level wi!l vary, in part, with changes in tempera-tures, pH, and LSI. However, in all cases, the concentration of alkyl epoxy carboxylate added to an aqueous water system in accordance with the present invention is at substoichiometric concentrations. That is, the con-centration of alkyl epoxy carboxylate is much lower than the concentration of the scale forming material in the system to be treated.
The treatment of the present invention may be added to a circulating aqueous system such as a once-through cooling system, a recirculating system such as cooling tower where the water is reused or a static/stagnant system such as a stand-by service system. The treatment of the present invention is effective at inhibiting the formation of scale in systems where the water is in motion as well as systems where the water is static or stagnant.
The present invention will now be further described with reference to a number of specific examples which are to be regarded solely as illustrative and not as restricting the scope of the present invention.
The treatment of the present invention may be added to a circulating aqueous system such as a once-through cooling system, a recirculating system such as cooling tower where the water is reused or a static/stagnant system such as a stand-by service system. The treatment of the present invention is effective at inhibiting the formation of scale in systems where the water is in motion as well as systems where the water is static or stagnant.
The present invention will now be further described with reference to a number of specific examples which are to be regarded solely as illustrative and not as restricting the scope of the present invention.
Laboratory experiments were conducted with solutions of pH, Ca2+
and F- levels typical of those in spray water systems and those encoun-tered under more aggravated process upset conditions. Plant water was obtained and spiked with additional calcium and fluoride to resemble con-ditions at the spray nozzles. The concentration of the soluble Ca2+ and calcium inhibition were determined relative to a control under the same conditions. Static beaker and dynamic recirculated tests were conducted.
In the static beaker tests, several sets of varying calcium and fluoride levels were evaluated.
Static Beaker Tests Condition I: (Synthetic Water) 600 ppm Ca2+ as CaCO3, 75 ppm F', 500 ppm Mg2+ as CaCO3, 250 ppm S042-, pH=7, Temperature=50 C, time=18 hours.
Condition II: (Pre-clarifier Plant Water) Spiked to 621 ppm Ca2+ as CaCO3, 253 ppm F-, pH=8, temperature=30 C, time=4 hours.
Calcium fluoride inhibition efficacy results of a commercially available phosphonate and Polymer A under Condition I are found in Table I. Table I shows the relative ability of phosphonate and an alkyl epoxy carboxylate (Polymer A) to inhibit calcium fluoride using synthetic test water as described in Condition I.
and F- levels typical of those in spray water systems and those encoun-tered under more aggravated process upset conditions. Plant water was obtained and spiked with additional calcium and fluoride to resemble con-ditions at the spray nozzles. The concentration of the soluble Ca2+ and calcium inhibition were determined relative to a control under the same conditions. Static beaker and dynamic recirculated tests were conducted.
In the static beaker tests, several sets of varying calcium and fluoride levels were evaluated.
Static Beaker Tests Condition I: (Synthetic Water) 600 ppm Ca2+ as CaCO3, 75 ppm F', 500 ppm Mg2+ as CaCO3, 250 ppm S042-, pH=7, Temperature=50 C, time=18 hours.
Condition II: (Pre-clarifier Plant Water) Spiked to 621 ppm Ca2+ as CaCO3, 253 ppm F-, pH=8, temperature=30 C, time=4 hours.
Calcium fluoride inhibition efficacy results of a commercially available phosphonate and Polymer A under Condition I are found in Table I. Table I shows the relative ability of phosphonate and an alkyl epoxy carboxylate (Polymer A) to inhibit calcium fluoride using synthetic test water as described in Condition I.
TABLE I
Static Beaker Tests - Condition I
Sample ppm, actives % Inhibition Polymer A 1 28 10 Phosphonate 1 16 As shown, the polyepoxysuccinic acid polymer is more effective than the phosphonate under these conditions. Calcium levels in these systems are not typically this elevated. However, this result reflects the calcium tolerance and superior inhibition of Polymer A relative to a phosphonate under process upset conditions.
Calcium fluoride efficacy of phosphonate and Polymer A under Condition II with pre-clarifier water received from the field is summarized in Table II. In Table II, experiments were conducted with pre-clarifier plant water spiked to elevate the calcium and fluoride levels. Note that these particular test conditions are relatively severe and that Polymer A
continued to outperform the phosphonate. Similar results were achieved atapHof4.
Static Beaker Tests - Condition I
Sample ppm, actives % Inhibition Polymer A 1 28 10 Phosphonate 1 16 As shown, the polyepoxysuccinic acid polymer is more effective than the phosphonate under these conditions. Calcium levels in these systems are not typically this elevated. However, this result reflects the calcium tolerance and superior inhibition of Polymer A relative to a phosphonate under process upset conditions.
Calcium fluoride efficacy of phosphonate and Polymer A under Condition II with pre-clarifier water received from the field is summarized in Table II. In Table II, experiments were conducted with pre-clarifier plant water spiked to elevate the calcium and fluoride levels. Note that these particular test conditions are relatively severe and that Polymer A
continued to outperform the phosphonate. Similar results were achieved atapHof4.
TABLE II
Static Beaker Tests - Condition II
Sample ppm, actives % Inhibition Polymer A 5 21 Phosphonate 5 9 12.5 11 Dynamic recirculation tests were conducted to duplicate the nozzle environment, with radiant heat generated from the slab. In these tests, pre-clarifier (or "scale pit") plant water was circulated over a metal sleeve heated to 205 +/- 5 C. Bulk water temperature was maintained at 21 C.
Tests were conducted for 4 hours. Results are summarized in Table III.
Table III shows the ability of Polymer A relative to phosphonate and AA/AHPSE (acrylic acid/allyl hydroxypropyl sulfonate ether sodium salt copolymer) to maintain calcium in solution in scale pit waters of two compositions where CaF2 is expected to precipitate. As shown, Polymer A provided significant benefit over phosphonate and AA/AHPSE.
Static Beaker Tests - Condition II
Sample ppm, actives % Inhibition Polymer A 5 21 Phosphonate 5 9 12.5 11 Dynamic recirculation tests were conducted to duplicate the nozzle environment, with radiant heat generated from the slab. In these tests, pre-clarifier (or "scale pit") plant water was circulated over a metal sleeve heated to 205 +/- 5 C. Bulk water temperature was maintained at 21 C.
Tests were conducted for 4 hours. Results are summarized in Table III.
Table III shows the ability of Polymer A relative to phosphonate and AA/AHPSE (acrylic acid/allyl hydroxypropyl sulfonate ether sodium salt copolymer) to maintain calcium in solution in scale pit waters of two compositions where CaF2 is expected to precipitate. As shown, Polymer A provided significant benefit over phosphonate and AA/AHPSE.
TABLE III
Percent Soluble Calcium Retained in Scale Pit Water Solutions by Selected Inhibitors After Four Hours in a Dynamic Test Scale Pit Water Composition Percent Soluble ppm Ca++ ppm F- Bulk Water Calcium Retained in as CaCO3 as Fluoride pH Temperature Treatment Solution atT=4 hours 138 118 6.8 70 F Control 75 0.5 ppm phosphonate 85 0.5 ppm Polymer A 95 99 135 7.6 70 F Control 40 5 ppm AA/AHPSE 65 4 ppm Polymer A 88 @ T=220 min While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modi-fications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.
Percent Soluble Calcium Retained in Scale Pit Water Solutions by Selected Inhibitors After Four Hours in a Dynamic Test Scale Pit Water Composition Percent Soluble ppm Ca++ ppm F- Bulk Water Calcium Retained in as CaCO3 as Fluoride pH Temperature Treatment Solution atT=4 hours 138 118 6.8 70 F Control 75 0.5 ppm phosphonate 85 0.5 ppm Polymer A 95 99 135 7.6 70 F Control 40 5 ppm AA/AHPSE 65 4 ppm Polymer A 88 @ T=220 min While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modi-fications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.
Claims (12)
1. A method of controlling the formation and deposition of fluoride salt scale in a caster spray water system containing calcium and fluoride ions comprising introducing into said system a substoichiometric amount sufficient for the purpose of a treatment comprising a polyepoxysuccinic acid of the general formula:
wherein n ranges from about 2 to about 50, M is hydrogen or a water soluble cation and R is hydrogen, C1-4 alkyl or C1-4 substituted alkyl.
wherein n ranges from about 2 to about 50, M is hydrogen or a water soluble cation and R is hydrogen, C1-4 alkyl or C1-4 substituted alkyl.
2. The method as recited in claim 1, wherein said fluoride salt is calcium fluoride.
3. The method as recited in claim 1, wherein M is Na+, NH4+, or K+.
4. The method as recited in claim 1, wherein said polyepoxysuccinic acid is added to the caster spray water system at active treatment levels ranging from about 25 parts per billion to about 500 parts per million.
5. The method as recited in claim 4, wherein said polyepoxysuccinic acid is added to the caster spray water system at active treatment levels ranging from about 50 parts per billion to about 100 parts per million.
6. The method as recited in claim 1, wherein n ranges from about 2 to about 25.
7. A method of controlling the formation and deposition of fluoride salt scale in a steel casting spray water system comprising adding to said steel casting spray water system containing calcium and fluoride ions a substoichiometric amount sufficient for the purpose of a treatment comprising a polyepoxysuccinic acid of the general formula:
wherein n ranges from about 2 to about 50, M is hydrogen or a water soluble cation and R is hydrogen, C1-4 alkyl or C1-4 substituted alkyl.
wherein n ranges from about 2 to about 50, M is hydrogen or a water soluble cation and R is hydrogen, C1-4 alkyl or C1-4 substituted alkyl.
8. The method as recited in claim 7, wherein said fluoride salt is calcium fluoride.
9. The method as recited in claim 7, wherein M is Na+, NH4+, or K+.
10. The method as recited in claim 7, wherein said polyepoxysuccinic acid is added to the steel casting spray water system at active treatment levels ranging from about 25 parts per billion to about 500 parts per million.
11. The method as recited in claim 10, wherein said polyepoxysuccinic acid is added to the steel casting spray water system at active treatment levels ranging from about 50 parts per billion to about 100 parts per million.
12. The method as recited in claim 7, wherein n ranges from about 2 to about 25.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002167612A CA2167612C (en) | 1996-01-19 | 1996-01-19 | Method of controlling fluoride scale formation in aqueous systems |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002167612A CA2167612C (en) | 1996-01-19 | 1996-01-19 | Method of controlling fluoride scale formation in aqueous systems |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2167612A1 CA2167612A1 (en) | 1997-07-20 |
| CA2167612C true CA2167612C (en) | 2007-05-29 |
Family
ID=4157387
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002167612A Expired - Lifetime CA2167612C (en) | 1996-01-19 | 1996-01-19 | Method of controlling fluoride scale formation in aqueous systems |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2167612C (en) |
-
1996
- 1996-01-19 CA CA002167612A patent/CA2167612C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2167612A1 (en) | 1997-07-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP0460797B1 (en) | Methods of controlling scale formation in aqueous systems | |
| US4443340A (en) | Control of iron induced fouling in water systems | |
| US4659481A (en) | Water treatment polymers and methods of use thereof | |
| EP1704123B1 (en) | Cooling water scale and corrosion inhibition | |
| US3766077A (en) | Compositions and method for inhibiting scaling in aqueous systems | |
| EP0599485B1 (en) | Method of inhibiting corrosion in aqueous systems | |
| US4732698A (en) | Water treatment polymers and methods of use thereof | |
| US4701262A (en) | Water treatment polymers and methods of use thereof | |
| US4717499A (en) | Water treatment polymers and methods of use thereof | |
| CA1187765A (en) | Control of iron induced fouling in water systems | |
| US4944885A (en) | Water treatment polymers and methods of use thereof | |
| CA2125224C (en) | Methods and composition for controlling scale formation in aqueous systems | |
| US4869845A (en) | Water treatment compositions | |
| EP0277412B1 (en) | Inhibiting corrosion of iron base metals | |
| EP0538969B1 (en) | Composition and method for inhibiting scale and corrosion using naphthylamine polycarboxylic acids | |
| EP0609590A1 (en) | Method for inhibiting corrosion of metals using polytartaric acids | |
| CA2167612C (en) | Method of controlling fluoride scale formation in aqueous systems | |
| US5705077A (en) | Method of controlling fluoride scale formation in aqueous systems | |
| CA2074336A1 (en) | Inhibition of scale formation and corrosion by sulfonated organophosphonates | |
| US4836933A (en) | Water treatment polymer | |
| KR19990016148A (en) | Corrosion and scale prevention water treatment composition of boiler and corrosion and scale suppression method of boiler using same | |
| KR100896518B1 (en) | Composition for preventing corrosion anc scale of boiler and treatment method of water for boiler | |
| CA1324941C (en) | Water treatment polymers and methods of use thereof | |
| JP3427859B2 (en) | Treatment method of direct cooling water system in hot rolling process | |
| KR20040012135A (en) | Water treatmrnt composition, preparation method of the same and water treatment method using the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20160119 |