Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2001-01-03
2002-08-27
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S911000
Reexamination Certificate
active
06440314
ABSTRACT:
FIELD OF THE INVENTION
The herein disclosed invention finds applicability in the field of water purification and in the field of toxic waste removal; and specifically where residues of chlorite are found in aqueous solutions.
BACKGROUND OF THE INVENTION
There is a need in the field of water purification to remove chlorite ion from water prior to use or disposing of the water in order to make the water non-toxic. No good way of destroying chlorite ion has been found, until now. Methods have been found, which require pH adjustment, produce sludge, or have some other drawback. Ascorbic acid reaction with chlorite is pH independent from 2.5 to 8.2, probably higher, and destruction of chlorite is virtually instantaneous.
Chlorite is toxic to several invertebrates which are important in the food chain. Chlorine dioxide (ClO
2
) in disinfection and other applications results in chlorite ion in the water. When this water flows to a receiving stream or other body of water, chlorite must be reduced to very low levels to meet governnent regulations.
Chlorite removal is difficult. Known chlorite removal chemistries are slow, produce sludge, require precise pH control or produce unwanted by-products.
Current regulations in some locations require chlorite ion to be at or below 0.006 ppm in water entering receiving streams; in other locations the amount of chlorite entering the stream may be higher. When chlorine dioxide (ClO
2
) is used at normal usage levels, typically 0.5-1.0 ppm above demand (which can be higher with 2.0 ppm being typical), a total of 2.5-3.0 ppm ClO
2
is used. Approximately 50-80% of this ClO
2
is converted to chlorite ion. If 3.0 ppm is fed, 1.5-2.4 ppm of chlorite ion can be produced. This amount varies depending upon water conditions. Under certain conditions, depending on the contents of the water, less chlorite will be produced. Therefore, to use ClO
2
for a given application, any reducing chemistry for chlorite destruction must be able to reduce chlorite to chloride ion or some other innocuous species. Since most of these systems are once-through, the water velocity is such that any treatment must act quickly and completely to reduce chlorite before discharge. Therefore, any treatment must reduce chlorite levels to essentially immeasurable levels of innocuous species in a few seconds. The treatment itself must also be innocuous, in the event of over treatment.
REVIEW OF THE PRIOR ART
European Patent 0 196 075
European Patent 0 196 075 describes the preparation of a contact lens cleaning solution wherein ascorbic acid is added to chlorite to accelerate the decomposition of chlorite. In decomposing the chlorite by the use of acid, chlorine dioxide is produced. On page 2 the patent identifies the system as containing a chlorite salt in aqueous solution and an agent for accelerating the decomposition of chlorite. The accelerating agent can be an acid. And on page 5, next to the last line, ascorbic acid is listed as the acid accelerating agent. Note also claim
1
, taken with claim
5
, identify the agent for accelerating the decomposition of chlorite to form free oxygen as ascorbic acid. The inventive concept of the herein disclosed invention is distinct from that of European patent 0 196 075. The herein disclosed invention employs adequate ascorbic acid to completely inactive the chlorite ion and to convert it to chloride. The European patent does not.
Further note that European 0 196 075, page 19, Table 3, discloses adding 0.01 g of ascorbic acid to a 0.06 g solution of sodium chlorite. These amounts are opposite those used in this invention. The herein disclosed invention for example uses approximately five parts ascorbic acid to destroy one part chlorite.
The formulation of 0 196 075 is designed to release free oxygen from chlorite. Two components are needed. They are (A) an aqueous solution chlorite, and (B) another solid component containing, (i) an agent for accelerating the decomposition of the chlorite to form free oxygen, selected from acids, organic acid salts, ion exchange resins, reducing agents and sugars, and (ii) an agent for consuming excess free oxygen from the decomposition of the chlorite after impurities have been removed.
The patent refers ‘forming free oxygen’ appears to actually refer to the formation of ClO
2
. This is the reason acids, organic acid salts, ion exchange resins and sugars are used.
On page 5, paragraph 4, the patent states:
“These agents (acids, organic acid salts, ion exchange resins, reducing agents, and sugars) act as a catalyst for accelerating the decomposition of the chlorite contained in the component A. The agents may function by releasing hydrogen ion, which leads to accelerated decomposition of the chlorite to form free oxygen.”
In paragraph 6 of the same page, they state,
“The acid may be any one as long as it provides the function required in the present invention. Preferred examples of the acids include organic acids such as adipic, stearic, sebacic, oxalic, itaconic, edetic, ascorbic; and inorganic acids such as hydrochloric and sulfuric acids. It is more preferred to use tartaric and/or citric acid . . . .”
The inclusion of mineral acids and citric as the preferred embodiment indicates that it is indeed the formation of chlorine dioxide from chlorite that is being referred to here. Just as found in many other patents, when the inventors find an organic acid that appears to be operative, they include other organic acids.
Further in the text, on page 19, in Table 3, a series of products that include chlorite activated by various organic acids. This indicates that the European patent considered ascorbic acid to be just another organic acid. It does not appear that ascorbic acid was recognized as having special properties and considered to be a distinct acid, unlike other organic acids in its effect.
Based on a review of this patent, it appears that what the authors refer to as decomposition of chlorite to form free oxygen is actually activating chlorite to form ClO
2
. There simply is no recognition in European 0 196 075 of the special reactive nature of ascorbic acid with chlorite to form chloride.
On the other hand, the herein disclosed invention requires substantial amounts of ascorbic acid to destroy the chlorite ion and convert it to chloride. Amounts which are beyond the parameters of the European patent, note as follows: The herein disclosed invention employs approximately 5 ppm ascorbic acid to consume 1 ppm of chlorite ion. This ratio of components is distinct and just the opposite of that of European 0 196 075 which in Table 3, page 19, uses 0.02×3=0.06 g of sodium chlorite with 0.01 g of ascorbic acid. It takes about approximately 5 ppm of ascorbic acid to consume 1 ppm of chlorite ion. The reaction is immediate, pH independent, and results in the formation of the chloride ion. No chlorine dioxide is formed as long as ascorbic acid is in a slight excess.
So far as the
Opflow, American Water Works Association
Vol. 24, No. 12, December 1998, pages 1, 4 and 5 publication is concerned, the reference does not speak of deactivating chlorite. The reference speaks only of reducing chlorine or inactivating “chlorine level”. This is distinct from reducing chlorite levels. Nor are the herein disclosed critical proportions of reactants set forth.
European 0 207 633 does disclose both chlorite and ascorbic acid, however, this disclosure is so broad as to not read on your discovery.
Less pertinent references are noted:
Griese, et al—Chemical Abstracts Vol. 115:166,2229 discloses the use of sodium thiosulfate and sulfites to eliminate chlorine dioxide and chlorite ions, residuals, from drinking water.
May U.S. Pat. No. 4,851,130 teaches the use of erythorbate and ascorbate for oxygen removal.
Reynolds in U.S. Pat. No. 4,609,472 teaches the removal of chlorate ions from brine using acid and hydrazine hydrochloride.
Chvapil et al in U.S. Pat. No. 5,104,660 teach an antimicrobial wound dressing which may comprise sodium chlorite and ascorbic acid along with many other components. There is no suggestion in
Bloom Leonard
Hoey Betsey Morrison
Rosen Sam
Vulcan Chemical Technologies, Inc.
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