Liquid purification or separation – Processes – Preventing – decreasing – or delaying precipitation,...
Reexamination Certificate
2001-10-19
2003-12-02
Lovering, Richard D. (Department: 1712)
Liquid purification or separation
Processes
Preventing, decreasing, or delaying precipitation,...
C210S698000, C210S760000, C252S180000, C422S028000
Reexamination Certificate
active
06656365
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preventing formation of scale. More particularly, the present invention relates to a process for preventing formation of scale in accordance with which a polymeric scale inhibitor having an average molecular weight within the optimum range for preventing formation of scale is present in a water system in which ozone is used for disinfection and formation of scale is effectively prevented.
2. Description of Related Art
In cooling water systems and water supply systems, polymers having carboxyl group have been used as scale inhibitors and antifouling agents to prevent attachment of scale on the surface of metals contacting water, deposition of sludge and local corrosion under the fouling. In these water systems, in general, disinfection is conducted to prevent growth of microorganisms and formation of slime. As the process for disinfection, the treatment with chlorine is widely conducted. However, in water systems polluted with organic substances, agents containing chlorine occasionally cause formation of organohalogen compounds which are suspected to be carcinogenic and the use of the agents containing chlorine are being restricted. As the sufficiently safe process for disinfection which can replace the treatment with chlorine, the treatment with ozone is increasing. In the treatment with chlorine, polymeric scale inhibitors are chemically stable and the effect of preventing formation of scale is not adversely affected by the treatment with chlorine. However, in the treatment with ozone, polymeric scale inhibitors are decomposed and the molecular weight of the polymeric scale inhibitors decreases since ozone has stronger oxidizing ability than the agents containing chlorine. The average molecular weight of a polymeric scale inhibitor has an optimum range in order to exhibit the effect of preventing formation of scale. The effect decreases when the average molecular weight is either greater or smaller than the optimum range.
Heretofore, polymeric scale inhibitors having an average molecular weight within the optimum range are added to water without taking the decrease in the molecular weight of the polymeric scale inhibitor due to the decomposition into consideration and prevention of troubles caused by attachment of scale and deposition of sludge has been attempted. For example, in Japanese Patent Application Laid-Open No. Heisei 5(1993)-123698, a process for treatment of recycled cooling water using a homopolymer or a copolymer of acrylic acid or methacrylic acid having a weight-average molecular weight of 1,500 to 35,000 is proposed. However, it was found by the present inventors that, when the above process was applied to a water system in which disinfection was conducted in accordance with the treatment with ozone, the polymeric scale inhibitor was oxidized and decomposed with ozone. The molecular weight decreased and the effect of preventing formation of scale of the polymeric scale inhibitor decreased.
SUMMARY OF THE INVENTION
The present invention has an object of providing a process in accordance with which the polymeric scale inhibitor having an average molecular weight within an optimum range for preventing formation of scale is present in a water system in which ozone is used for disinfection and the formation of scale is effectively prevented.
As the result of extensive studies by the present inventors, it was found that the formation of scale could be effectively prevented in a specific water system in which ozone was used for disinfection when the optimum range of the average molecular weight for preventing formation of scale and the relation between the rate of supply of ozone and the rate of decomposition of the polymeric scale inhibitor were obtained and a polymeric scale inhibitor having the initial average molecular weight which gives an average molecular weight within the optimum range for preventing formation of scale after the polymeric scale inhibitor was decomposed with ozone was added to the water system. The present invention has been completed based on the knowledge.
The present invention provides:
(1) A process for preventing formation of scale which comprises adding, into a water system in which ozone is used for disinfection, a polymeric scale inhibitor having a high molecular weight which gives an average molecular weight within an optimum range for preventing formation of scale after the polymeric scale inhibitor is decomposed with ozone;
(2) A process described in (1), wherein the polymeric scale inhibitor is a polymer selected from homopolymers and copolymers of acrylic acid, methacrylic acid, maleic acid, maleic anhydride and itaconic acid; and
(3) A process described in (1), which comprises (1) obtaining, in accordance with a measurement, the optimum range of the average molecular weight for preventing formation of scale from a relation between an average molecular weight of the polymeric scale inhibitor and an effect of preventing formation of scale; (2) obtaining, in accordance with a measurement, a relation between a rate of supply of ozone and a rate of decomposition of the polymeric scale inhibitor; (3) obtaining an initial average molecular weight of the polymeric scale inhibitor which gives an average molecular weight within the optimum range for preventing formation of scale after the polymeric scale inhibitor is decomposed with ozone from the rate of supply of ozone and a period of time of contact between the polymeric scale inhibitor and ozone; and (4) adding the polymeric scale inhibitor having the obtained initial average molecular weight into the water system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the process for preventing formation of scale, a polymeric scale inhibitor having a high molecular weight which gives an average molecular weight within the optimum range for preventing formation of scale after the polymeric scale inhibitor is decomposed with ozone is added into a water system in which ozone is used for disinfection. The components of the scale to which the process of the present invention can be applied is not particularly limited. Examples of the components of scale include calcium carbonate, calcium sulfate, calcium sulfite, calcium fluoride, calcium silicate, calcium phosphate, calcium oxalate, zinc phosphate, zinc hydroxide, zinc carbonate, zinc silicate, magnesium silicate, magnesium hydroxide, ferric hydroxide, iron oxide, mud and flocks of microorganisms.
It is preferable that the present invention is conducted in accordance with the following steps:
(1) The optimum range of the average molecular weight for preventing formation of scale is obtained from the relation between the average molecular weight of the polymeric scale inhibitor which is used as the scale inhibitor (the dispersant) in the water system and the effect of preventing formation of scale with respect to various types of substances forming scale and suspended substances. In the present invention, the method for measuring the average molecular weight of the polymeric scale inhibitor is not particularly limited as long as the same method is used. Examples of the method include the osmotic pressure method, the solution viscosity method, the light scattering method, the ultracentrifugation method and the gel permeation chromatography (GPC). Among these methods, GPC can be preferably used.
Polymeric scale inhibitors which have the same composition and different average molecular weights can be obtained by synthesizing polymeric scale inhibitors having different average molecular weights by polymerization under varied conditions or, alternatively, by synthesizing a polymeric scale inhibitor having a high molecular weight, which was then decomposed by bringing into contact with ozone in water. To obtain data on the relation between the average molecular weight of the polymeric scale inhibitor and the effect of preventing formation of scale, the decomposition of a polymeric scale inhibitor having a high molecular weight with ozone is advantageous s
Hirano Akihide
Ishikawa Katsuhiro
Kempen Hermann
Shiratani Masahiro
Suzuki Takashi
Frishauf Holtz Goodman & Chick P.C.
Kurita Water Industries Ltd.
Lovering Richard D.
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