U.S. patent application number 10/044511 was filed with the patent office on 2002-05-16 for method of producing chlorine dioxide using a metal chlorite and a water-retaining substance.
Invention is credited to Klatte, Fred.
Application Number | 20020058006 10/044511 |
Document ID | / |
Family ID | 26956822 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020058006 |
Kind Code |
A1 |
Klatte, Fred |
May 16, 2002 |
Method of producing chlorine dioxide using a metal chlorite and a
water-retaining substance
Abstract
A method for producing chlorine dioxide by activating zeolite
crystals (which have been impregnated with metal chlorite such as
sodium chlorite, and optionally also a water-retaining substance
such as magnesium sulfate, potassium chloride, potassium hydroxide,
or calcium chloride) with excess protons, or activating an aqueous
solution of metal chlorite and such a water-retaining substance
with excess protons. Proton generating species useful for the
activation are acids such as acetic, phosphoric, and citric acid,
and metal salts such as ferric chloride, ferric sulfate,
ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2, MnSO.sub.4,
MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, and MgSO.sub.4. The activation
can be performed by causing fluid to flow through a bed of zeolite
crystals impregnated with calcium chloride (or other
water-retaining substance) and sodium chlorite, and a bed of
zeolite crystals impregnated with a proton generating species. The
two beds can be physically mixed together or the fluid can flow
sequentially through separate beds. The activation can also be
performed by immersing impregnated zeolite crystals in (or spraying
them with) acid or another proton generating species. To produce
chlorine dioxide using a sodium chlorite-containing aqueous
solution, the solution can be mixed or otherwise combined with
acid. Other aspects of the invention are impregnated zeolite
crystals (or other carriers) which are useful for producing
chlorine dioxide and are stable until activated with protons.
Presence in a sufficient amount of a water-retaining substance in
the unactivated material reduces the rate of chlorine dioxide
outgassing to no more than a negligible amount prior to
activation.
Inventors: |
Klatte, Fred; (San
Francisco, CA) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Family ID: |
26956822 |
Appl. No.: |
10/044511 |
Filed: |
January 11, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10044511 |
Jan 11, 2002 |
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09714417 |
Nov 16, 2000 |
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09714417 |
Nov 16, 2000 |
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09274455 |
Mar 22, 1999 |
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09274455 |
Mar 22, 1999 |
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08798873 |
Feb 11, 1997 |
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Current U.S.
Class: |
423/477 ; 422/29;
422/37; 502/60 |
Current CPC
Class: |
C01B 11/026 20130101;
C01B 11/023 20130101; C01B 11/024 20130101; C01B 11/025
20130101 |
Class at
Publication: |
423/477 ; 502/60;
422/37; 422/29 |
International
Class: |
C01B 011/02 |
Claims
What is claimed is:
1. A method for producing chlorine dioxide, including the steps of:
(a) providing impregnated zeolite crystals which have been
impregnated with a metal chlorite; and (b) activating the
impregnated zeolite crystals with excess protons, thereby producing
the chlorine dioxide as a result of reaction of the protons with
the impregnated zeolite crystals.
2. The method of claim 1, wherein the metal chlorite is sodium
chlorite.
3. The method of claim 1, wherein the zeolite crystals have also
been impregnated with at least one impregnating agent selected from
the group consisting of calcium chloride, magnesium sulfate,
potassium chloride, and potassium hydroxide.
4. The method of claim 3, wherein the zeolite crystals comprise
1%-6% sodium chlorite, 0.5%-2% calcium chloride, 0%-20% water, and
72%-98.5% zeolite by weight.
5. The method of claim 3, wherein step (b) includes the step of:
exposing the impregnated zeolite crystals to excess protons,
thereby producing the chlorine dioxide as a result of reaction of
the protons with the impregnated zeolite crystals.
6. The method of claim 1, wherein step (b) includes the step of
exposing the impregnated zeolite crystals to a proton generating
species, thereby producing the excess protons and producing the
chlorine dioxide as a result of reaction of the protons with the
impregnated zeolite crystals.
7. The method of claim 6, wherein the proton generating species is
an aqueous acid.
8. The method of claim 1, wherein step (b) includes the step of
activating a proton generating species to produce the excess
protons.
9. The method of claim 8, wherein step (b) includes the step of
exposing the impregnated zeolite crystals to the proton generating
species and then activating the proton generating species to
produce said excess protons.
10. The method of claim 8, wherein the proton generating species
comprises a metal salt, and the step of activating said proton
generating species is accomplished by exposing the metal salt to
water.
11. The method of claim 10, wherein the metal salt is a member of
the group consisting of ferric chloride, ferric sulfate,
ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2, MnSO.sub.4,
MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, and MgSO.sub.4.
12. A method for producing chlorine dioxide, including the steps
of: (a) causing a fluid to flow through a first set of impregnated
zeolite crystals, wherein the impregnated zeolite crystals have
been impregnated with at least one proton generating impregnating
agent; and (b) after step (a), causing the fluid to flow through a
second set of impregnated zeolite crystals, wherein the impregnated
zeolite crystals in the second set have been impregnated with a
metal chlorite and at least one impregnating agent selected from
the group consisting of calcium chloride, magnesium sulfate,
potassium chloride, and potassium hydroxide, wherein chlorine
dioxide is produced as a result of reaction of the second set of
impregnated zeolite crystals with excess protons released from the
at least one proton generating impregnating agent.
13. The method of claim 12, wherein the metal chlorite is sodium
chlorite.
14. The method of claim 12, wherein the second set of impregnated
zeolite crystals consists essentially of zeolite crystals
impregnated with sodium chlorite and calcium chloride.
15. The method of claim 12, wherein said at least one proton
generating impregnating agent is at least one acid.
16. The method of claim 12, wherein the fluid includes water and
said at least one proton generating impregnating agent includes a
metal salt.
17. The method of claim 16, wherein the metal salt is a member of
the group consisting of ferric chloride, ferric sulfate,
ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2, MnSO.sub.4,
MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, and MgSO.sub.4.
18. A method for filtering a fluid containing a contaminant,
including the steps of: (a) moving the fluid through a first bed of
impregnated zeolite crystals which have been impregnated with one
of at least one proton generating impregnating agent and a metal
chlorite; and (b) after step (a), moving the fluid through a second
bed of impregnated zeolite crystals which have been impregnated
with another one of the least one proton generating impregnating
agent and the metal chlorite, wherein chlorine dioxide is produced
as a result of chemical reaction of said at least one proton
generating impregnating agent.
19. The method of claim 18, wherein the fluid is air.
20. The method of claim 18, wherein the fluid includes
microorganisms, and wherein the chlorine dioxide produced in step
(b) kills at least some of the microorganisms.
21. The method of claim 18, wherein the fluid is contaminated with
volatile organic chemicals, and wherein the chlorine dioxide
produced in step (b) oxidizes at least some of the volatile organic
chemicals.
22. The method of claim 18, also including the step of: (c) after
step (b), moving the fluid relative to a third bed of impregnated
zeolite crystals, wherein the impregnated zeolite crystals in the
third bed are impregnated with an impregnating agent selected from
the group consisting of potassium hydroxide, sodium sulfite, sodium
bisulfite, and ferrous sulfate, so that at least some of the
chlorine dioxide is removed by chemical reaction with the third
bed.
23. The method of claim 18, wherein said at least one proton
generating impregnating agent is at least one acid.
24. The method of claim 18, wherein the fluid includes water and
said at least one proton generating impregnating agent includes a
metal salt.
25. The method of claim 24, wherein the metal salt is a member of
the group consisting of ferric chloride, ferric sulfate,
ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2, MnSO.sub.4,
MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, and MgSO.sub.4.
26. The method of claim 18, wherein the first bed of impregnated
zeolite crystals have been impregnated with said at least one
proton generating impregnating agent and the second bed of
impregnated zeolite crystals have been impregnated with said metal
chlorite and at least one impregnating agent selected from the
group consisting of calcium chloride, magnesium sulfate, potassium
chloride, and potassium hydroxide, and wherein the chlorine dioxide
is produced as a result of chemical reaction of at least a portion
of the second bed with at least one of said at least one proton
generating impregnating agent and protons resulting from activation
of said at least one proton generating impregnating agent.
27. The method of claim 26, wherein the metal chlorite is sodium
chlorite.
28. The method of claim 27, wherein the second bed consists
essentially of zeolite crystals impregnated with sodium chlorite
and calcium chloride.
29. The method of claim 26, wherein the second bed consists
essentially of impregnated zeolite crystals comprising 1%-6% sodium
chlorite, 0.5%-2% calcium chloride, 0%-20% water, and 72%-98.5%
zeolite by weight.
30. The method of claim 18, wherein the first bed of impregnated
zeolite crystals have been impregnated with said metal chlorite and
at least one impregnating agent selected from the group consisting
of calcium chloride, magnesium sulfate, potassium chloride, and
potassium hydroxide, and the second bed of impregnated zeolite
crystals have been impregnated with said at least one proton
generating impregnating agent, and wherein the chlorine dioxide is
produced as a result of chemical reaction of at least one substance
released from the first bed with at least one of said at least one
proton generating impregnating agent and protons resulting from
activation of said at least one proton generating impregnating
agent.
31. The method of claim 30, wherein the metal chlorite is sodium
chlorite.
32. The method of claim 31, wherein the first bed consists
essentially of zeolite crystals impregnated with sodium chlorite
and calcium chloride.
33. The method of claim 31, wherein the first bed consists
essentially of impregnated zeolite crystals comprising 1%-6% sodium
chlorite, 0.5%-2% calcium chloride, 0%-20% water, and 72%-98.5%
zeolite by weight.
34. A method for filtering a fluid containing a contaminant,
including the step of: (a) moving the fluid through a bed of
impregnated zeolite crystals comprising a mixture of first zeolite
crystals and second zeolite crystals, wherein the first zeolite
crystals have been impregnated with at least one proton generating
impregnating agent, and the second zeolite crystals have been
impregnated with a metal chlorite and at least one impregnating
agent selected from the group consisting of calcium chloride,
magnesium sulfate, potassium chloride, and potassium hydroxide,
whereby chlorine dioxide is produced as a result of reaction of the
second zeolite crystals with excess protons released from the at
least one proton generating impregnating agent.
35. The method of claim 34, wherein the metal chlorite is sodium
chlorite.
36. The method of claim 35, wherein the second zeolite crystals
consist essentially of zeolite crystals impregnated with sodium
chlorite and calcium chloride.
37. The method of claim 34, wherein the second zeolite crystals
consist essentially of impregnated zeolite crystals comprising
1%-6% sodium chlorite, 0.5%-2% calcium chloride, 0%-20% water, and
72%-98.5% zeolite by weight.
38. The method of claim 34, wherein the fluid is air.
39. The method of claim 34, also including the step of: (b) after
step (a), moving the fluid relative to a second bed of impregnated
zeolite crystals, wherein the impregnated zeolite crystals in the
second bed have been impregnated with an impregnating agent
selected from the group consisting of potassium hydroxide, sodium
sulfite, sodium bisulfite, and ferrous sulfate, so that at least
some of the chlorine dioxide is removed by chemical reaction with
the second bed.
40. The method of claim 34, wherein said at least one proton
generating impregnating agent is at least one acid.
41. The method of claim 34, wherein the fluid includes water and
said at least one proton generating impregnating agent includes a
metal salt.
42. The method of claim 41, wherein the metal salt is a member of
the group consisting of ferric chloride, ferric sulfate,
ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2, MnSO.sub.4,
MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, and MgSO.sub.4.
43. A method for producing chlorine dioxide, including the steps
of: (a) providing an aqueous solution comprising 1%-6% of sodium
chlorite by weight, 0.5%-2% by weight of at least one chemical
selected from the group consisting of calcium chloride, magnesium
sulfate, potassium chloride, and potassium hydroxide, and 92%-98.5%
of water by weight; and (b) combining the aqueous solution with a
proton generating species thereby producing excess protons, and
thereby producing said chlorine dioxide as a result of chemical
reaction of the protons with the aqueous solution.
44. The method of claim 43, wherein the proton generating species
comprises an aqueous acid.
45. The method of claim 43, wherein the proton generating species
comprises at least one metal salt.
46. The method of claim 45, wherein the at least one metal salt is
a member of the group consisting of ferric chloride, ferric
sulfate, ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2,
MnSO.sub.4, MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, and MgSO.sub.4.
47. The method of claim 43, wherein the at least one chemical is
calcium chloride.
48. A composition of matter, carrying sufficient amounts of
chemicals to be capable of releasing chlorine dioxide upon
activation by excess protons, said composition of matter
comprising: a carrier; a metal chlorite carried by the carrier; and
at least one agent carried by the carrier, said at least one agent
having been selected from the group consisting of calcium chloride,
magnesium sulfate, potassium chloride, and potassium hydroxide.
49. The composition of claim 48, wherein the carrier has a size
sufficient for filtration of a fluid.
50. The composition of claim 48, wherein the metal chlorite is
sodium chlorite.
51. The composition of claim 48, wherein the agent is calcium
chloride.
52. The composition of claim 48, wherein the carrier is a plurality
of zeolite crystals, and the metal chlorite is impregnated into at
least some of the zeolite crystals.
53. The composition of claim 52, wherein the metal chlorite is
sodium chlorite, and said composition comprises 1-6% sodium
chlorite by weight, 0.5%-2% calcium chloride by weight, 0%-20%
water by weight, and 72%-98.5% of said zeolite crystals by
weight.
54. The composition of claim 48, also including: a proton
generating species carried by the carrier.
55. The composition of claim 54, wherein the proton generating
species comprises an acid.
56. The composition of claim 54, wherein the proton generating
species comprises a metal salt.
57. The composition of claim 54, wherein the carrier is a plurality
of zeolite crystals, a first subset of the zeolite crystals is
impregnated with the metal chlorite, and a second subset of the
zeolite crystals is impregnated with the proton generating
species.
58. An aqueous solution, capable of releasing chlorine dioxide upon
activation by acid, said solution comprising: 1%-6% sodium chlorite
by weight; and 0.5%-2% by weight of at least one chemical selected
from the group consisting of calcium chloride, magnesium sulfate,
potassium chloride, and potassium hydroxide; and 92%-98.5% water by
weight.
59. The aqueous solution of claim 58, wherein said at least one
chemical is calcium chloride.
60. The aqueous solution of claim 59, comprising: 1%-6% sodium
chlorite by weight; 0.5%-2% calcium chloride by weight; and
92%-98.5% water by weight.
61. A method for producing chlorine dioxide, including the steps
of: (a) providing a zeolite crystal mixture which comprises zeolite
crystals impregnated with sodium chlorate and zeolite crystals
impregnated with an oxidizer; and (b) activating the zeolite
crystal mixture with excess protons, thereby causing the zeolite
crystal mixture to produce the chlorine dioxide.
62. The method of claim 61, wherein step (b) includes the step of
exposing the zeolite crystals impregnated with the sodium chlorate
and the zeolite crystals impregnated with the oxidizer to a proton
generating species.
63. The method of claim 61, wherein the zeolite crystal mixture
also comprises zeolite crystals impregnated with a proton
generating species, and wherein step (b) includes the step of
causing the zeolite crystal mixture to contact a
moisture-containing fluid, whereby the zeolite crystal mixture is
activated to produce the chlorine dioxide.
64. The method of claim 63, wherein the zeolite crystal mixture is
stored in a dry, air-tight container prior to step (b), and wherein
step (b) includes the step of opening said container to expose the
zeolite crystal mixture to the moisture-containing fluid.
65. The method of claim 63, wherein step (b) includes the step of
causing the moisture-containing fluid to flow through the zeolite
crystal mixture, whereby the mixture is activated by water absorbed
from the moisture-containing fluid and as a result said mixture
produces the chlorine dioxide.
66. The method of claim 63, wherein the proton generating species
is sulfuric acid.
67. The method of claim 61, wherein the zeolite crystal mixture
also includes zeolite crystals impregnated with at least one of a
deliquescent and a water absorbing and retaining substance.
68. The method of claim 61, wherein the zeolite crystals
impregnated with said oxidizer are zeolite crystals impregnated
with at least one of hydrogen peroxide, ferric chloride, peracetic
acid, sodium metabisulfite, and sodium bisulfite.
69. The method of claim 61, wherein the zeolite crystal mixture,
the zeolite crystal mixture also comprises zeolite crystals
impregnated with calcium chloride, wherein the oxidizer is at least
one of hydrogen peroxide, ferric chloride, and peracetic acid, and
wherein step (b) includes the step of: causing the zeolite crystal
mixture to come in contact with liquid sulfuric acid, whereby said
zeolite crystal mixture is activated to produce the chlorine
dioxide.
70. A method for producing chlorine dioxide, including the steps
of: (a) providing a zeolite crystal mixture, the zeolite crystal
mixture comprising zeolite crystals impregnated with a proton
generating species and zeolite crystals impregnated with an
oxidizer; and (b) causing the zeolite crystal mixture to come in
contact with sodium chlorate solution, whereby said zeolite crystal
mixture is activated to produce the chlorine dioxide.
71. The method of claim 70, wherein the zeolite crystal mixture
also comprises zeolite crystals impregnated with calcium chloride,
and wherein the proton generating species is sulfuric acid.
72. A method for producing chlorine dioxide, including the steps
of: (a) providing a zeolite crystal mixture, the zeolite crystal
mixture comprising zeolite crystals impregnated with sodium
chlorate and zeolite crystals impregnated with a proton generating
species; and (b) causing the zeolite crystal mixture to come in
contact with an oxidizer, whereby said zeolite crystal mixture is
activated to produce the chlorine dioxide.
73. The method of claim 72, wherein the zeolite crystal mixture
also comprises zeolite crystals impregnated with calcium chloride,
wherein the proton generating species is sulfuric acid, and wherein
step (b) includes the step of causing the zeolite crystal mixture
to come in contact with a solution of at least one of hydrogen
peroxide, ferric chloride, peracetic acid, sodium metabisulfite,
and sodium bisulfite.
74. A zeolite crystal mixture capable of being activated by excess
protons to produce chlorine dioxide, said mixture comprising:
zeolite crystals impregnated with sodium chlorate; and zeolite
crystals impregnated with an oxidizer.
75. The mixture of claim 74, wherein said mixture also comprises
zeolite crystals impregnated with at least one of a deliquescent
and a water absorbing and retaining substance.
76. The mixture of claim 74, wherein the oxidizer is at least one
of hydrogen peroxide, ferric chloride, peracetic acid, sodium
metabisulfite, and sodium bisulfite.
77. The mixture of claim 74, wherein the mixture also comprises:
zeolite crystals impregnated with a proton generating species.
78. A zeolite crystal mixture capable of being activated by an
oxidizer to produce chlorine dioxide, said mixture comprising:
zeolite crystals impregnated with sodium chlorate; and zeolite
crystals impregnated with a proton generating species.
79. The mixture of claim 78, wherein the proton generating species
is sulfuric acid, and wherein said mixture also comprises zeolite
crystals impregnated with at least one of a deliquescent and a
water absorbing and retaining substance.
80. A composition of matter, carrying sufficient amounts of
chemicals to be capable of releasing chlorine dioxide to a target
region upon activation by excess protons, said composition of
matter comprising: a quantity of impregnated zeolite crystals,
wherein said quantity comprises zeolite crystals impregnated with a
metal chlorite and zeolite crystals impregnated with a proton
generating species, and wherein said quantity is capable of being
activated by excess protons to produce chlorine dioxide.
81. The composition of matter of claim 80, also including: a
barrier separating the quantity of impregnated zeolite crystals
from the target region, wherein the barrier is permeable to flow of
an activating fluid from the target region such that the activating
fluid will interact with the quantity of impregnated zeolite
crystals in a manner resulting in production of said excess protons
and production of said chlorine dioxide, wherein the barrier is
also permeable to flow of the chlorine dioxide to the target
region.
82. The composition of matter of claim 81, wherein the barrier is
permeable to flow of the activating fluid from the target region at
up to a predetermined maximum flow rate, so that the barrier limits
to a predetermined maximum level the rate of release of the
chlorine dioxide to the target region.
83. The composition of matter of claim 80, wherein the quantity of
impregnated zeolite crystals also comprises: zeolite crystals
impregnated with at least one of a deliquescent and a water
absorbing and retaining substance in a concentration which limits
to a predetermined maximum level the rate of release of the
chlorine dioxide to the target region.
84. The composition of matter of claim 80, wherein said zeolite
crystals impregnated with at least one of a deliquescent and a
water absorbing and retaining substance are zeolite crystals
impregnated with calcium chloride.
Description
CROSS-REFERENCE TO RELATED-APPLICATION(S)
[0001] This is a continuation-in-part application of pending U.S.
application Ser. No. 08/798,873, filed Feb. 11, 1997, scheduled to
issue as U.S. Pat. No. 5,885,543 on Mar. 23, 1999, and entitled
"Method for Producing Chlorine Dioxide Using Calcium Chloride
Impregnated Zeolite or Aqueous Calcium Chloride", inventor Fred
Klatte.
FIELD OF THE INVENTION
[0002] The invention relates to methods for producing chlorine
dioxide, and to substances used in performing such methods. Each
method produces chlorine dioxide by activating zeolite crystals
(previously impregnated with a mixture of sodium chlorite and a
water-retaining substance such as calcium chloride) with protons
(from an acid or other proton generating species), or by activating
an aqueous solution of a water-retaining substance (such as calcium
chloride) and sodium chlorite with protons (from an acid or other
proton generating species).
BACKGROUND OF THE INVENTION
[0003] Zeolites are hydrated metal aluminosilicate compounds with
well-defined (tetrahedral) crystalline structures. Because zeolite
crystals (both natural and synthetic) have a porous structure with
connected channels extending through them, they have been employed
as molecular sieves for selectively absorbing molecules on the
basis of size, shape, and polarity.
[0004] Volumes packed with zeolite crystals (for example, small
zeolite crystals chosen to have size in the range from 0.2 mm to
one quarter inch) have been employed in air (or other gas) and
water filtration systems to selectively absorb contaminants from a
flowing stream of water or gas.
[0005] U.S. Pat. No. 5,567,405, issued Oct. 22, 1996 (based on U.S.
application Ser. No. 08/445,025, filed May 19, 1995), and U.S. Pat.
No. 5,573,743, issued Nov. 12, 1996 (based on U.S. application Ser.
No. 08/445,076), teach methods for producing zeolite crystals
impregnated with one or more of sodium chlorite, acetic acid,
phosphoric acid, and citric acid, and methods for producing
chlorine dioxide by moving a fluid (e.g., air or water) relative to
a bed of zeolite crystals impregnated with sodium chlorite, and
moving the fluid relative to another bed of zeolite crystals
impregnated with one of the following: phosphoric acid, acetic acid
and citric acid. The two beds can be physically mixed together, or
the fluid can flow sequentially through distinct first and second
beds. These references also teach a method for filtering a fluid by
producing chlorine dioxide in the fluid (in the manner described in
this paragraph) and then absorbing the chlorine dioxide from the
fluid.
[0006] U.S. patent application Ser. No. 08/704,086, filed Aug. 28,
1996, teaches a variation on the chlorine dioxide production method
of U.S. Pat. No. 5,567,405, which includes the steps of moving a
fluid through a first bed of impregnated zeolite crystals
(impregnated with at least one of phosphoric acid, acetic acid, and
citric acid) and then moving the fluid through a second bed of
impregnated zeolite crystals (impregnated with sodium
chlorite).
[0007] Chlorine dioxide (ClO.sub.2) is useful for killing
biological contaminants (such as microorganisms, mold, fungi, yeast
and bacteria) and for oxidizing volatile organic chemicals which
can contaminate fluid.
[0008] It is known to produce chlorine dioxide by: activating a
metal chlorite solution by adding an acid thereto, activating a
powdered composition (or other dry composition) by adding water
thereto, or preparing an activated dry composition which releases
chlorine dioxide over time. U.S. Pat. No. 4,547,381 (issued Oct.
15, 1985) and U.S. Pat. No. 4,689,169 (issued Aug. 25, 1987)
mention these three techniques for producing chlorine dioxide, and
disclose in some detail one type of such an activated dry
composition. They teach that this activated dry composition is a
mixture of a "dry inert diluent," a metal chlorite, and a dry agent
capable of reacting with the metal chlorite in a dry state to
produce chlorine dioxide. The metal chlorite can be sodium
chlorite, and the dry agent can be a "dry acid" such as granular
citric acid. The inert diluent can be diatomaceous earth, sodium
chloride, sodium silicate, disodium sulfate, or magnesium chloride,
or a combination of two or more thereof. The mixture releases
chlorine dioxide over time until the rate of chlorine dioxide
release becomes low, and the patents teach that the mixture can
then be agitated for "renewed generation" of chlorine dioxide.
[0009] However, an activated composition (such as that described in
U.S. Pat. Nos. 4,547,381 and 4,689,169) is subject to undesirable
storage and shipping losses, due to outgassing of chlorine dioxide
before the time of intended use of the composition.
[0010] Similarly, the inventor has found that sodium
chlorite-impregnated zeolite crystals (of the type described in
referenced U.S. Pat. Nos. 5,567,405 and 5,573,743) are also subject
to undesirable storage and shipping losses, due to outgassing of
chlorine dioxide therefrom before the time of their intended use
(e.g., before fluid is caused to flow through both a bed of the
sodium chlorite-impregnated zeolite crystals and a bed of
acid-impregnated zeolite crystals). Also, efforts to activate
sodium chlorite-impregnated zeolite crystals (of the type described
in referenced U.S. Pat. Nos. 5,567,405 and 5,573,743) with acid at
low temperature (below 40 degrees Fahrenheit) may fail in the sense
that they will not result in release of sufficient amounts of
chlorine dioxide.
[0011] There are also disadvantages to use of conventional metal
chlorite solutions (of the type mentioned in U.S. Pat. Nos.
4,547,381 and 4,689,169) to produce chlorine dioxide. For example,
when such a conventional solution is activated (by adding an acid
thereto) to release chlorine dioxide gas, it is difficult or
impossible to control the rate of release of the chlorine dioxide
gas. Overproduction of chlorine dioxide often results.
[0012] There are also disadvantages to use of conventional powdered
or dry compositions of the type activated by adding water thereto
to release chlorine dioxide (as mentioned, for example, in U.S.
Pat. Nos. 4,547,381 and 4,689,169). Masschelein, in the book
Chlorine Dioxide-Chemistry and Environmental Impact of Oxychlorine
Compounds (published 1979 by Ann Arbor Science Publishers Inc., Ann
Arbor, Mich.) at page 140, describes one such dry mixture
comprising sodium chlorite, and a solid organic anhydride
containing 2 to 20% of a desiccating product such as calcium
chloride. When such a conventional dry composition is activated (by
adding water thereto) to release chlorine dioxide gas, it is
typically difficult or impossible to control the rate of release of
the chlorine dioxide to achieve chlorine dioxide release rates
useful for such applications as air or water filtration.
Overproduction of chlorine dioxide often results.
[0013] Until the present invention, it was not known how to produce
a stable, unactivated substance (either in liquid or dry form)
which does not release significant amounts of chlorine dioxide
until activated by exposure to an acid, and which releases chlorine
dioxide at a useful (and controllable) rate when exposed to an acid
(even at temperatures below 40 degrees Fahrenheit). Nor had it been
known to use such a stable, unactivated substance to produce
controlled release of chlorine dioxide for filtering air or
water.
SUMMARY OF THE INVENTION
[0014] In some embodiments, the invention is a method for producing
chlorine dioxide by activating zeolite crystals (previously
impregnated with sodium chlorite and calcium chloride) with excess
protons or activating an aqueous solution of sodium chlorite and
calcium chloride with excess protons. Typically, the excess protons
are produced by exposing the crystals to an acid (or other proton
generating species), or exposing the aqueous solution of sodium
chlorite and calcium chloride to an acid (or other proton
generating species). Examples of proton generating species useful
for such activation are acids such as acetic acid, phosphoric acid,
citric acid, HCl, propionic acid, and sulfuric acid, and metal
salts such as ferric chloride, ferric sulfate, ZnSO.sub.4,
ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2, MnSO.sub.4, MnCl.sub.2,
CuSO.sub.4, CuCl.sub.2, and MgSO.sub.4. In some embodiments the
proton generating species releases excess protons upon exposure to
the impregnated zeolite crystals themselves. In other embodiments
the proton generating species must itself be activated to cause it
release excess protons, so that the protons can in turn activate
the impregnated zeolite crystals.
[0015] In accordance with the invention, the step of activating
zeolite crystals with excess protons can be performed by causing a
fluid (e.g., air, another oxygen-containing fluid, or water) to
flow through a bed of zeolite crystals impregnated with sodium
chlorite and calcium chloride, and a bed of zeolite crystals
impregnated with the proton generating species. The two beds can be
physically mixed together, or the fluid can be caused to flow
sequentially through distinct first and second beds (preferably
first through the bed containing proton generating
species-impregnated zeolite, but alternatively first through the
bed containing sodium chlorite and calcium chloride-impregnated
zeolite). Alternatively, chlorine dioxide is produced using sodium
chlorite and calcium chloride-impregnated zeolite crystals by
immersing the impregnated zeolite in (or spraying the impregnated
zeolite with) acid or another proton generating species, or
otherwise exposing the impregnated zeolite to acid (preferably
aqueous acetic, phosphoric, citric acid, HCl, sulfuric acid,
propionic acid, or another acid, with a concentration of 0.025% to
0.5%, in the sense that the acid comprises 0.025% to 0.5% by weight
of the combined impregnated zeolite and acid) or another proton
generating species.
[0016] To produce chlorine dioxide using the inventive aqueous
solution of sodium chlorite and calcium chloride, the solution can
be mixed (or otherwise combined) with acid. The liquid mixture can
then be sprayed or coated on a surface (or the liquid mixture can
be absorbed in a material such as a sponge, pad, mat, or the like,
or simply placed in a reservoir, container, box, or the like) from
which chlorine dioxide gas can escape at a desired rate.
[0017] In any of the embodiments, the rate of chlorine dioxide
release (following activation) can be controlled in any of several
ways, including by appropriately selecting the concentration and
amount of the activating acid (or other proton generating species),
and using impregnated zeolite having appropriately selected weight
ratios of metal chlorite (e.g., sodium chlorite) or sodium chlorate
to zeolite, and deliquescent or water absorbing and retaining
substance (e.g., calcium chloride) to zeolite.
[0018] Other embodiments of the invention are substances useful for
producing chlorine dioxide, which are stable until activated with
excess protons (in the sense that they do not release chlorine
dioxide gas in significant amounts until so activated with
protons). One such embodiment is one or more zeolite crystals
impregnated with sodium chlorite and calcium chloride. Preferably,
the zeolite crystals are small (each of size in a range from 0.2 mm
to one quarter inch). Also preferably, the crystals comprise 1%-6%
sodium chlorite, 0.5%-2% calcium chloride, 0%-20% (48-8% in some
preferred embodiments) water, and 72%-98.5% (8%-94.5% in some
preferred embodiments) zeolite by weight. Another such embodiment
is an aqueous solution of sodium chlorite and at least one chemical
selected from the group consisting of magnesium sulfate, potassium
chloride, potassium hydroxide, and calcium chloride, preferably
comprising 1%-6% of sodium chlorite, 0.5%-2% of said at least one
chemical, and 92%-98.5% of water (by weight). Preferably, the
solution comprises 1%-6% sodium chlorite, 0.5%-2% calcium chloride,
and 92%-98.5% water (by weight).
[0019] In variations on any embodiment of the invention, a
water-retaining substance other than calcium chloride, such as
magnesium sulfate (MgSO.sub.4), potassium chloride, or potassium
hydroxide, is substituted for calcium chloride. For example,
zeolite crystals impregnated with sodium chlorite and magnesium
sulfate are within the scope of the invention. For another example,
a method of producing chlorine dioxide by activating an aqueous
solution of sodium chlorite and magnesium sulfate with an acid is
also within the scope of the invention.
[0020] In other variations on any embodiment of the invention, a
metal chlorite other than sodium chlorite is substituted for sodium
chlorite. For example, zeolite crystals impregnated with calcium
chloride (or magnesium sulfate) and a metal chlorite other than
sodium chlorite are within the scope of the invention.
[0021] The inventor has found that the-presence (in a sufficient
amount) of calcium chloride (or another water-retaining substance
such as magnesium sulfate, potassium chloride, or potassium
hydroxide) in the unactivated composition of the invention reduces
the rate of chlorine dioxide outgassing to no more than a
negligible amount at times prior to activation of the composition
with protons, and yet allows release of chlorine dioxide at a
desired rate following activation of the composition with protons.
One of the reasons for chlorine dioxide outgassing (prior to
activation with excess protons) from zeolite impregnated with metal
chlorite (but not impregnated with a water-retaining substance such
as calcium chloride) is migration of protons in the
aluminosilicates comprising the zeolite.
[0022] In other embodiments, the invention is a method for
producing chlorine dioxide, including the steps of providing a
zeolite crystal mixture, wherein the mixture comprises zeolite
crystals impregnated with sodium chlorate and zeolite crystals
impregnated with an oxidizer, and activating the mixture with
excess protons, and a zeolite crystal mixture for use in performing
such method. In other embodiments, the invention is a method for
producing chlorine dioxide, including the steps of providing a
zeolite crystal mixture, wherein the mixture comprises zeolite
crystals impregnated with a proton generating species and zeolite
crystals impregnated with an oxidizer (or sodium chlorate), and
causing the zeolite crystal mixture to come in contact with sodium
chlorate solution (or an oxidizer, where the mixture includes
zeolite crystals impregnated with sodium chlorate but not an
oxidizer), and a zeolite crystal mixture for use in performing such
method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a cross-sectional view of a zeolite crystal
impregnated with a metal chlorite, and one of calcium chloride (or
other deliquescent or water absorbing and retaining substance),
magnesium sulfate, potassium chloride, and potassium hydroxide.
[0024] FIG. 2 is a cross-sectional view of a zeolite crystal
impregnated with a proton generating species, or another substance
or mixture of substances in accordance with any of the embodiments
of the invention.
[0025] FIG. 3 is a cross-sectional view of a mixture of impregnated
zeolite crystals (prepared in accordance with any embodiment of the
invention) in a sealed container.
[0026] FIG. 4 is a cross-sectional view of a mixture of impregnated
zeolite crystals (prepared in accordance with the invention)
surrounded by a barrier permeable to chlorine dioxide gas.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] In one class of embodiments, the invention is a process for
impregnating zeolite crystals with sodium chlorite and calcium
chloride, and the product of such process. The zeolite crystals can
have size (i.e., largest dimension) equal (or approximately equal)
to 0.125 inch, 0.25 inch, 0.50 inch, or 0.75 inch, or size in the
range from 0.2 mm to several millimeters, or size in the range from
0.2 mm to 0.25 inch, or the zeolite crystals can have dimensions
equal or substantially equal to 0.25 inch.times.0.167 inch, 0.125
inch.times.0.10 inch, 0.25 inch.times.0.125 inch, 0.125
inch.times.0.50 inch, or 0.50 inch.times.0.75 inch. The
impregnation process produces zeolite crystals uniformly
impregnated (throughout the volume of each crystal) with sodium
chlorite and calcium chloride.
[0028] Preferred embodiments of this impregnation process employ,
as input material, zeolite crystals whose moisture content has been
reduced (substantially below an initial moisture content) to a low
level (preferably about 5%). Such input material is preferably
produced by mining zeolite, crushing the mined mineral into
appropriately sized zeolite crystals (having a natural moisture
content substantially above 5%), and then dehydrating the zeolite
crystals until their moisture content is reduced to about 5%.
[0029] The dehydrated zeolite crystals are then immersed in (or
sprayed with) an aqueous solution of sodium chlorite and calcium
chloride at high temperature (e.g., in the range from 120.degree.
F. to 190.degree. F.), and the resulting slurry is thoroughly
mixed. Then, the mixed slurry is air dried (or allowed to
equilibrate) to the desired moisture level (typically 0-20%) to
produce impregnated zeolite crystals. Alternatively, the air drying
step can be avoided by calculating the amount of aqueous
impregnating material needed to achieve the desired final moisture
level (e.g., 15%) and adding this amount to the dehydrated zeolite
at the time of impregnation.
[0030] Alternatively, the dehydrated zeolite crystals are immersed
in (or sprayed with) an aqueous solution of sodium chlorite at high
temperature (e.g., at least 190.degree. F.), and the resulting
slurry is thoroughly mixed. Then, the mixed slurry is air dried (or
allowed to equilibrate) to the desired moisture level to produce
sodium chlorite-impregnated zeolite crystals. Alternatively, one
calculates the amount of aqueous sodium chlorite needed to achieve
the desired moisture level (e.g., a desired level in the range
15%-20%) and adds this amount to the dehydrated zeolite at the time
of impregnation. Then, the sodium chlorite-impregnated zeolite
crystals are immersed in (or sprayed with) an aqueous solution of
calcium chloride at high temperature, and the resulting slurry is
thoroughly mixed. Then, the mixed slurry is air dried (or allowed
to equilibrate) to the desired final moisture level (typically
0-20%) to produce zeolite crystals impregnated with both sodium
chlorite and calcium chloride. Alternatively, air drying is avoided
by calculating the amount of aqueous calcium chloride needed to
achieve the desired final moisture level (e.g., a desired level in
the range 15%-20%) and adding this amount to the sodium
chlorite-impregnated zeolite at the time of calcium chloride
impregnation.
[0031] In variations of any of the described zeolite impregnation
processes, a water-retaining substance such as magnesium sulfate
(MgSO.sub.4), potassium chloride, or potassium hydroxide is
substituted for calcium chloride as an impregnating agent.
[0032] In other variations on the described zeolite impregnation
processes, a metal chlorite other than sodium chlorite is
substituted for sodium chlorite.
[0033] FIG. 1 represents one impregnated zeolite crystal, having
channels uniformly impregnated with mixture 2 of metal chlorite and
a water-retaining substance. The water-retaining substance is
preferably calcium chloride, but alternatively is magnesium
sulfate, potassium chloride, potassium hydroxide, or another
water-retaining substance. The metal chlorite is preferably sodium
chlorite.
[0034] The rate at which impregnated zeolite crystals of the type
shown in FIG. 1 (e.g., zeolite crystals uniformly impregnated
sodium chlorite and calcium chloride) react with in the presence of
excess protons to release chlorine dioxide can be controlled
(reduced or increased to a desired level) by varying the relative
amounts (by weight) of the different impregnating agents
therein.
[0035] In some embodiments of the invention, the proton generating
species is in the form of zeolite crystals impregnated with one or
more metal salts (preferably one or more of ferric chloride, ferric
sulfate, ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2,
MnSO.sub.4, MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, and MgSO.sub.4).
Upon exposure of the metal salt or salts to water (either liquid
water or a moisture-containing gas, e.g. atmospheric moisture),
excess protons are generated.
[0036] In other embodiments of the invention, the proton generating
species is activated (other than by exposure to water) to release
excess protons. The proton generating species is activated in such
a manner that impregnated zeolite crystals are exposed to excess
protons, thereby initiating a reaction resulting in release of
chlorine dioxide gas. In some embodiments, the proton generating
species releases excess protons upon exposure to the impregnated
zeolite crystals themselves (the impregnated zeolite crystals
together with the proton generating species does not need to be
further activated to cause the proton generating species to release
excess protons).
[0037] In some embodiments of the invention, the proton generating
species is in the form of zeolite crystals impregnated with at
lease one acid (preferably one or more of acetic acid, citric acid,
phosphoric acid, HCl, propionic acid, and sulfuric acid).
Above-referenced U.S. Pat. Nos. 5,567,405 and 5,573,743 disclose
methods for producing such acid-impregnated zeolite crystals.
Briefly, the acid impregnation step is preferably performed by
immersing dehydrated zeolite crystals in (or spraying zeolite
crystals with) an aqueous solution of one or more of the acids at
high temperature, thoroughly mixing the resulting slurry, and
finally air drying (or allowing the slurry to equilibrate) to the
desired moisture level (e.g. 0%-20%) the mixed slurry to produce
the acid-impregnated zeolite crystals. FIG. 2 represents one such
impregnated crystal, having channels uniformly impregnated
(throughout the volume of the crystal) with chemical 10, where
chemical 10 is acetic acid, citric acid, phosphoric acid, HCl,
propionic acid, or sulfuric acid (or another acid), or a mixture of
two or more of such acids, or another proton generating species, or
another substance or mixture of substances in accordance with any
of the embodiments of the invention.
[0038] In general, the acid or acids employed (for activation of
impregnated zeolite crystals) in accordance with the invention can
be impregnated in zeolite crystals, mixed in an aqueous solution
(including a metal chlorite and a water-retaining substance such as
calcium chloride), or added to (e.g., sprayed on) zeolite crystals
that have been impregnated with a metal chlorite and a
water-retaining substance such as calcium chloride.
[0039] With reference again to zeolite crystals that have been
impregnated in accordance with the invention with sodium chlorite
and calcium chloride, such crystals are preferably small (each of
size in a range from 0.2 mm to one quarter inch), and each crystal
preferably comprises 1-6% sodium chlorite, 0.5%-2% calcium
chloride, 0%-20% (4%-8% in some preferred embodiments) water, and
72%-98.5% (84%-94.5% in some preferred embodiments) zeolite by
weight. The inventor has found that the presence of calcium
chloride (preferably in the preferred amount noted above) in the
unactivated impregnated zeolite reduces the rate of chlorine
dioxide outgassing to no more than a negligible amount until
activation of the composition with acid, and yet allows release of
chlorine dioxide at a desired rate following activation of the
composition with acid. This finding was unexpected, since mixing of
sodium chlorite and calcium chloride with water would have been
expected to produce chlorine dioxide as a result of the following
sequence of reactions:
[0040] 1. 2NaClO.sub.2+2H.sub.2O+CaCl.sub.2.fwdarw.
[0041] 2. Ca(OH).sub.2+2HCL+2NaClO.sub.2.fwdarw.
[0042] 3. HCL+NaClO.sub.2+NaCl+ClO.sub.2.Arrow-up bold.protons.
[0043] Instead, the unexpected finding that the rate of chlorine
dioxide outgassing is substantially reduced is believed to result
from the following reaction:
[0044] 1. 2NaClO.sub.2+H.sub.2O+CaCl.sub.2.fwdarw.
[0045] 2. H.sub.2O+CaClO.sub.2+2NaCl.
[0046] The products of this reaction, when activated with excess
protons (e.g., by exposure to acid or a metal salt) are converted
to ClO.sub.2.Arrow-up bold. and other substances including excess
protons. In another embodiment, when sodium chlorite and ferric
chloride react with water to produce chlorine dioxide gas, it is
believed that the chlorine dioxide is produced as a result of the
following reaction:
3NaClO.sub.2+3H.sub.2O+FeCl.sub.3.fwdarw.3ClO.sub.2+(Fe)(OH).sub.3+3NaCl.
[0047] In another class of embodiments, the invention is an aqueous
solution of sodium chlorite and calcium chloride (or sodium
chlorite and a water-retaining substance other than calcium
chloride). This solution can be activated by exposure to protons
(e.g., as a result of exposure to a proton generating species such
as acetic acid, phosphoric acid, citric acid, or another acid) so
as to release chlorine dioxide in a controlled manner. Preferably,
the solution comprises 1%-6% sodium chlorite, 0.5%-2% calcium
chloride, and 92%-98.5% water (by weight). Also preferably, the
solution is activated by being mixed (or otherwise combined) with
aqueous acetic acid, phosphoric acid, citric acid, HCl, propionic
acid, or sulfuric acid (or another acid) having a concentration of
0.025% to 0.5% (by weight of the total mixture). An example of such
an aqueous acid is produced by adding 1% (by weight of the total
mixture) of a 3% aqueous acetic acid solution. The activated liquid
mixture (of aqueous sodium chlorite, calcium chloride, and acid)
can then be sprayed or coated on a surface (or the liquid mixture
can be absorbed in a material such as a sponge, pad, mat, or the
like, or simply placed in a reservoir) from which chlorine dioxide
gas can escape at a desired rate.
[0048] The inventor has found that the presence of diluted calcium
chloride or one of the alternative water-retaining substances
(preferably in the above-noted preferred amount of 0.5%-2% by
weight) in the unactivated solution reduces the rate of chlorine
dioxide outgassing to no more than a negligible amount at times
prior to activation with an acid, and yet allows release of
chlorine dioxide at a desired rate upon activation of the solution
with acid. The unexpected finding that the rate of chlorine dioxide
outgassing (prior to activation) is substantially reduced is
believed to result from the following reaction in the unactivated
solution:
[0049] 1. 2NaClO.sub.2+H.sub.2O+CaCl.sub.2.fwdarw.
[0050] 2. H.sub.2O+CaClO.sub.2+2NaCl. The products of this
reaction, when activated with excess protons (e.g., by addition of
acid) are converted to ClO.sub.2.Arrow-up bold. and other
substances including excess protons.
[0051] The impregnated zeolite crystals of the invention (crystals
impregnated with a metal chlorite and calcium chloride, or a metal
chlorite and a water-retaining substance other than calcium
chloride) are useful in a class of methods for producing chlorine
dioxide (ClO.sub.2). Such methods will be described in preferred
embodiments in which calcium chloride is an impregnating agent and
the metal chlorite is sodium chlorite, but it should be understood
that a water-retaining substance (such as magnesium sulfate,
potassium chloride, or potassium hydroxide) can be substituted for
calcium chloride as an impregnating agent in the methods (and that
a metal chlorite other than sodium chlorite can be substituted for
sodium chlorite).
[0052] In one chlorine dioxide-producing method in accordance with
the invention, a fluid (preferably a fluid containing oxygen, such
as air or water) is caused to move relative to a first bed (i.e.,
the fluid flows through the first bed or the crystals comprising
the first bed move through the fluid) of zeolite crystals
impregnated with: (1) phosphoric acid (H.sub.3PO.sub.4), (2) acetic
acid (CH.sub.3COOH), (3) citric acid, (4) ferric chloride
(FeCl.sub.3), (5) ferric sulfate, or (6) another metal salt, such
as ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2, MnSO.sub.4,
MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, or MgSO.sub.4, or (7) an acid
other than phosphoric, acetic, or citric acid, or another proton
generating species suitable for the particular application. Then,
the fluid is caused to move relative to a second bed (i.e., the
fluid flows through the second bed, or the crystals comprising the
second bed move through the fluid) of zeolite crystals which are
impregnated with a mixture of sodium chlorite (NaClO.sub.2) and
calcium chloride (CaCl.sub.2). Upon moving the fluid relative to
the second bed, chlorine dioxide is released (due to contact with
acid or other proton generating substance transferred from the
first bed). It is believed that the chlorine dioxide release occurs
as a result of the following reaction, in the case of a first bed
impregnated with acetic acid:
CH.sub.3COOH+CaClO.sub.2+2NaCl+H.sub.2O.fwdarw.ClO.sub.2.Arrow-up
bold.+Ca(CH.sub.3COO).sub.2+excess protons,
[0053] where Ca(CH.sub.3COO).sub.2 is calcium acetate.
[0054] As discussed above, CaClO.sub.2, 2NaCl, and H.sub.2O are
believed to be present in the channels of the zeolite crystals of
the first bed as a result of reaction of the impregnating agents
NaClO.sub.2 and CaCl.sub.2, and H.sub.2O, in the channels of the
zeolite crystals of the first bed.
[0055] In variations on this chlorine dioxide production method,
the first bed can include a mixture of phosphoric acid-impregnated
zeolite crystals and acetic acid-impregnated zeolite crystals, or a
mixture of phosphoric acid-impregnated zeolite crystals and citric
acid-impregnated zeolite crystals, or a mixture of acetic
acid-impregnated zeolite crystals and citric acid-impregnated
zeolite crystals, or a mixture of all three types of
acid-impregnated zeolite crystals, or a mixture of zeolite crystals
impregnated with one of these three types of acids and zeolite
crystals impregnated with another acid (e.g., HCl or
H.sub.2SO.sub.4).
[0056] It is preferable for the fluid to flow through a first bed
of proton generating species-impregnated (e.g., acid-impregnated)
zeolite crystals before the fluid flows through a second bed
containing sodium chlorite and calcium chloride-impregnated zeolite
crystals, since this sequence will result in protons entering the
fluid (due to interaction of the fluid with the acid or other
proton generating species in the crystals of the first bed), and
since the presence of the hydrogen ions in the fluid will enhance
chlorine dioxide production when the hydrogen ion-containing fluid
interacts with the impregnating chemical in the crystals of the
second bed.
[0057] While the foregoing process for producing ClO.sub.2 has been
described with reference to two distinct (first and second) beds of
impregnated zeolite crystals, a single bed containing a mixture of
crystals can be used as long as the mixed bed contains both
impregnated zeolite crystals from the first bed described above and
zeolite crystals from the second bed described above. As an
example, a mixed bed of zeolite crystals (zeolite crystals
impregnated with sodium chlorite and calcium chloride mixed with
zeolite crystals impregnated with phosphoric acid) can be used to
produce chlorine dioxide (e.g., by flowing a fluid through the
mixed bed).
[0058] Alternatively, chlorine dioxide can be produced by adding
aqueous acid to a bed of zeolite crystals impregnated with a metal
chlorite (e.g., sodium chlorite) and a water-retaining substance
(e.g., calcium chloride). In these alternative embodiments, the
rate of release of chlorine dioxide can be controlled by varying
the amount and concentration of the added acid.
[0059] In alternative embodiments, chlorine dioxide is produced
with a reversed sequence of distinct first and second beds, as
follows. A fluid (preferably a fluid containing oxygen such as air)
is caused to move relative to a first bed (i.e., the fluid flows
through the first bed, or the crystals comprising the first bed
move through the fluid). The first bed comprises zeolite crystals
impregnated with sodium chlorite (NaClO.sub.2) and calcium chloride
(CaCl.sub.2). Then, the fluid is caused to move relative to a
second bed (i.e., the fluid flows through the second bed, or the
crystals comprising the second bed move through the fluid) of
zeolite crystals which are impregnated with: (1) phosphoric acid,
(2) acetic acid, (3) citric acid, (4) ferric chloride (FeCl.sub.3),
(5) ferric sulfate, or (6) another metal salt, such as ZnSO.sub.4,
ZnCl.sub.2, CoSO.sub.4, CoCl.sub.2, MnSO.sub.4, MnCl.sub.2,
CuSO.sub.4, CuCl.sub.2, or MgSO.sub.4, or (7) an acid other than
phosphoric, acetic, or citric acid, or another proton generating
species suitable for the particular application. Upon moving the
fluid relative to the second bed, chlorine dioxide is released. As
with other embodiments described herein, a water-retaining
substance such as magnesium sulfate, potassium chloride, or
potassium hydroxide can be substituted for the calcium chloride
(and a metal chlorite other than sodium chlorite can be substituted
for the sodium chlorite).
[0060] In another class of embodiments of the inventive chlorine
dioxide production method, zeolite crystals impregnated with sodium
chlorite and calcium chloride are activated by being immersed in
(or sprayed with) aqueous acetic acid, phosphoric acid, citric
acid, HCl, or sulfuric acid, with a concentration of 0.025% to 0.5%
(in the sense that the acid comprises 0.025% to 0.5% by weight of
the combined impregnated zeolite and acid). Alternatively, another
acid or other proton generating species suitable for the particular
application can be used to immerse (or spray) the impregnated
zeolite crystals as a substitute for the aqueous acetic acid,
phosphoric acid, citric acid, HCl, or sulfuric acid.
[0061] While chlorine dioxide can kill microorganisms in the fluid
undergoing treatment, and can oxidize volatile organic chemicals
which contaminate the fluid undergoing treatment (as described
above), chlorine dioxide itself is a contaminant. Therefore, it is
sometimes desirable to remove chlorine dioxide from the fluid
stream after the chlorine dioxide has performed purification
(including biological purification) of the fluid stream. Another
aspect of the present invention relates to a multi-step filtration
process in which chlorine dioxide is first produced in a fluid
stream and, subsequently, removed from the fluid stream.
[0062] First, a fluid is caused to be moved relative to a primary
bed (or primary beds) of zeolite crystals (i.e., the described
first and second beds, or the described mixed bed) which will cause
chlorine dioxide to be released, as described above. While the
fluid moves relative to (e.g., while the fluid flows through) the
primary bed or beds, chlorine dioxide is released (generally as a
gas). The released chlorine dioxide will kill biological
contaminants in the fluid and will oxidize volatile organic
chemicals which contaminate the fluid.
[0063] Then, the fluid is moved relative to a secondary bed
(filter) of zeolite crystals impregnated with one of the following:
(1) potassium hydroxide (KOH), (2) sodium sulfite, (3) sodium
bisulfite, and (4) ferrous sulfate (i.e., the fluid flows through
the secondary bed or the crystals comprising the secondary bed move
through the fluid). The zeolite crystals of the secondary bed react
with the chlorine dioxide to remove the chlorine dioxide from the
fluid. Some chemical equations describing possible reactions in the
secondary bed follow.
[0064] For a secondary bed of potassium hydroxide:
2KOH+2ClO.sub.2.fwdarw.KClO.sub.2+KCLO.sub.4+H.sub.2O
[0065] For a secondary bed of sodium sulfite:
ClO.sub.2+Na.sub.2SO.sub.3.fwdarw.H.sub.2O+S.sub.2O.sub.5+H.sup.+.sub.3ClO-
.sub.3
[0066] Note that H.sup.++ from the acids involved in the previous
reactions cancel this reaction.
[0067] For a secondary bed of sodium bisulfite:
ClO.sub.2+Na.sub.2SO.sub.5.fwdarw.H.sub.2O+S.sub.2O.sub.5+H.sup.+.sub.3ClO-
.sub.3
[0068] Note that H.sup.++ from the acids involved in the previous
reactions cancel this reaction.
[0069] The preferred composition of the secondary bed is ferrous
sulfate. For a secondary bed of ferrous sulfate:
ClO.sub.2+Fe.sup.++SO.sub.4.fwdarw.Fe.sup.++++Cl.sup.-+ClO.sub.2.fwdarw.Fe-
Cl.sub.3 (primarily).
[0070] When using a secondary bed of ferrous sulfate a color
change, from white to brown, takes place. This is an indicator of
neutralization.
[0071] Various modifications and variations of the described
methods and compositions of the invention will be apparent to those
skilled in the art without departing from the scope and spirit of
the invention. For example, a carrier other than zeolite crystals
or water (e.g., pumice, diatomaceous earth, bentonite, or clay) can
be used to carry the metal chlorite and water-retaining substance
(and optionally also the acid or other proton generating species)
of the invention.
[0072] We next describe other classes of embodiments of the
invention.
[0073] In one such class of embodiments, the invention is a method
for producing chlorine dioxide by activating a mixture comprising
zeolite crystals impregnated with sulfuric acid (or other proton
generating species), zeolite crystals impregnated with sodium
chlorate, zeolite crystals impregnated with an oxidizer, and
optionally also zeolite crystals impregnated with calcium chloride
(or another deliquescent or water absorbing and retaining
substance). The oxidizer is a substance (or mixture of substances)
which reacts (in the presence of water absorbed by the deliquescent
or water absorbing substance) to release another substance which in
turn reacts with one or more of the other impregnating substances
to produce chlorine dioxide. In some of these embodiments, the
oxidizer is ferric chloride or ferric sulfate, or a mixture of
ferric chloride and ferric sulfate. Although each of these iron
salts desirably absorbs water in addition to functioning as an
oxidizer, ferric chloride is preferably used (rather than ferric
sulfate, or a mixture of ferric chloride and ferric sulfate) since
it is the most reactive during performance of the inventive method.
Where sodium chlorate, ferric chloride, and sulfuric acid are
present upon activation, the chlorine dioxide-producing reaction is
believed to be: 2Na(ClO.sub.3)+FeCl.sub.3+H-
.sub.2SO.sub.4+3H.sub.2O.fwdarw.Na.sub.2SO.sub.4+Fe(OH).sub.3+3HCl+2H.sub.-
2O+2ClO.sub.2.Arrow-up bold.. In any of this class of embodiments,
the activation can be accomplished by exposing the mixture to a
moisture-containing gas (e.g., air including water vapor), or (to
achieve a higher chlorine dioxide production rate) causing water or
a moisture-containing gas to flow through the mixture (or by
causing the mixture to move through the gas). When activation is
accomplished using a flowing fluid, all the impregnated zeolite
crystals can be physically mixed together in a single bed, or the
gas can be caused to flow sequentially through distinct beds of
subsets of the zeolite crystals.
[0074] In other embodiments, chlorine dioxide is produced by
activating (with excess protons) a zeolite crystal mixture
comprising zeolite crystals impregnated with sodium chlorate,
zeolite crystals impregnated with at least one oxidizer (e.g.,
hydrogen peroxide, ferric chloride, or peracetic acid), and
optionally also zeolite crystals impregnated with calcium chloride.
Preferably, the mixture comprises equal (or substantially equal)
amounts of crystals impregnated with each of the four species. The
activation can be accomplished by exposing the mixture to a
moisture-containing gas (e.g., air including water vapor), or (to
increase the chlorine dioxide production rate) causing water or a
moisture-containing gas (e.g., air including water vapor) to flow
through the mixture. When activation is accomplished using flowing
fluid, all impregnated zeolite crystals can be physically mixed
together in a single bed, or the fluid can be caused to flow
sequentially through distinct beds of subsets of the zeolite
crystals. In embodiments in which the impregnated crystal mixture
comprises distinct beds of different subsets of zeolite crystals
(e.g., a bed of crystals impregnated with a first substance, and
another bed of crystals impregnated with a second substance mixed
with crystals impregnated with a third substance), the fluid must
flow sequentially through the beds to accomplish activation.
[0075] Where sodium chlorate, hydrogen peroxide, and sulfuric acid
are present upon activation, the chlorine dioxide-producing
reaction is believed to be
2Na(ClO.sub.3)+H.sub.2O.sub.2+H.sub.2SO.sub.4.fwdarw.2ClO.-
sub.2.Arrow-up bold.+Na.sub.2SO.sub.4+H.sub.2O.
[0076] In variations on the embodiments described in the previous
paragraph, zeolite crystals impregnated with sodium metabisulfite
(or sodium bisulfite) are used rather than zeolite crystals
impregnated with at least one of hydrogen peroxide, ferric
chloride, and peracetic acid. Activation of the mixture by absorbed
water (water absorbed by the deliquescent or water absorbing and
retaining substance) causes a reaction of the sodium metabisulfite
(or sodium bisulfite) which releases sulfur dioxide (SO.sub.2). The
SO.sub.2 then reacts to form chlorine dioxide gas. Each of sodium
metabisulfite and sodium bisulfite is considered an "oxidizer" in
the sense that the latter expression is used herein, since each
reacts (in the presence of the absorbed water) to release sulfur
dioxide which in turn reacts with one or more of the other
impregnating substances to produce chlorine dioxide.
[0077] In other embodiments, chlorine dioxide is produced by
activating a zeolite crystal mixture comprising zeolite crystals
impregnated with sodium chlorate, zeolite crystals impregnated with
sulfuric acid (or another proton generating species, such as ferric
chloride, ferric sulfate, ZnSO.sub.4, ZnCl.sub.2, CoSO.sub.4,
CoCl.sub.2, MnSO.sub.4, MnCl.sub.2, CuSO.sub.4, CuCl.sub.2, and
MgSO.sub.4 or another metal salt), zeolite crystals impregnated
with an oxidizer, and optionally also zeolite crystals impregnated
with a deliquescent (or water absorbing and retaining substance).
As in other embodiments, activation of the zeolite crystal mixture
can be accomplished by exposing the mixture to a
moisture-containing gas (e.g., air including water vapor), or (in
order to increase the chlorine dioxide production rate) by causing
water or a moisture-containing gas to flow through the mixture (or
causing the mixture to move through such fluid). When activation is
accomplished using flowing fluid, the impregnated zeolite crystals
can be physically mixed together in a single bed or the fluid can
be caused to flow sequentially through distinct beds of subsets of
the zeolite crystals. In some of these embodiments, the
deliquescent (or water absorbing and retaining substance) is
magnesium sulfate (MgSO.sub.4), potassium chloride, or magnesium
chloride (MgCl).
[0078] In other embodiments, the invention is a method for
producing chlorine dioxide by activating an impregnated zeolite
crystal mixture with an oxidizer (such as ferric chloride solution
(preferably) or liquid hydrogen peroxide or liquid peracetic acid).
The zeolite crystal mixture comprises zeolite crystals impregnated
with sodium chlorate, zeolite crystals impregnated with sulfuric
acid (or another proton generating species), and optionally also
zeolite crystals impregnated with calcium chloride (or another
deliquescent or water absorbing and retaining substance).
[0079] In other embodiments, the invention is a method for
producing chlorine dioxide by activating an impregnated zeolite
crystal mixture with excess protons, such as by exposing it to
liquid sulfuric acid (or another proton generating species). The
zeolite mixture comprises zeolite crystals impregnated with sodium
chlorate, zeolite crystals impregnated with an oxidizer (e.g., at
least one of hydrogen peroxide, ferric chloride, and peracetic
acid), and optionally also zeolite crystals impregnated with
calcium chloride (or another deliquescent or water absorbing and
retaining substance).
[0080] In other embodiments, the invention is a method for
producing chlorine dioxide by activating an impregnated zeolite
crystal mixture with sodium chlorate solution. The zeolite mixture
comprises zeolite crystals impregnated with sulfuric acid (or
another proton generating species), zeolite crystals impregnated
with an oxidizer (e.g., at least one of hydrogen peroxide, ferric
chloride, and peracetic acid), and optionally also zeolite crystals
impregnated with calcium chloride (or another deliquescent or water
absorbing and retaining substance).
[0081] Also within the scope of the invention are methods in which
mixtures of two or more of the above-described impregnated zeolite
mixtures are activated to produce chlorine dioxide. An example is a
method for producing chlorine dioxide by activating a zeolite
crystal mixture comprising zeolite crystals impregnated with
sulfuric acid, zeolite crystals impregnated with sodium chlorate,
zeolite crystals impregnated with at least one of hydrogen
peroxide, ferric chloride, and peracetic acid, zeolite crystals
impregnated with calcium chloride, and zeolite crystals impregnated
with sodium metabisulfite (or sodium bisulfite).
[0082] In any embodiment of the invention, the rate of chlorine
dioxide release (upon activation of the zeolite crystal mixture)
can be controlled in any of several ways, including by
appropriately selecting the concentration and amount of an
activating liquid (e.g., where the activating liquid is sodium
chlorate solution or liquid sulfuric acid), using impregnated
zeolite crystals having an appropriately selected weight ratio of
one or more of the impregnating substances (e.g., iron salt) to
zeolite, and selecting an appropriate method for activating the
mixture. For example, activation by exposing the mixture to
moisture-containing gas typically results in a low chlorine dioxide
release rate, and activation by flowing water or
moisture-containing gas through the mixture typically results in a
higher chlorine dioxide release rate. Prior to activation, the
mixture of impregnated crystals should be as dry as possible.
Preferably, the mixture (e.g., mixture of impregnated zeolite
crystals 40 of FIG. 3) is sealed within a dry, air-tight capsule or
other container (e.g., container 41 of FIG. 3), and the container
is unsealed to expose the mixture to the activating fluid shortly
before activation.
[0083] In yet another class of embodiments, the invention is a
mixture of impregnated zeolite crystals which can be activated (by
any of the above-described liquids or by water or
moisture-containing gas in accordance with the invention) to
perform any embodiment of the inventive chlorine dioxide production
method.
[0084] The chlorine dioxide produced in accordance with the
invention can be used to kill microorganisms in the
moisture-containing gas which activates the crystal mixture, and
can oxidize volatile organic chemicals which contaminate the
moisture-containing gas.
[0085] In another class of embodiments, the invention is
composition of matter which carries sufficient amounts of chemicals
to be capable of releasing chlorine dioxide to a target region upon
activation by excess protons, said composition of matter comprising
a quantity of impregnated zeolite crystals including zeolite
crystals impregnated with a metal chlorite and zeolite crystals
impregnated with a proton generating species, wherein the quantity
is capable of being activated by excess protons to produce chlorine
dioxide. Zeolite crystals 30 of FIG. 4 are such a quantity of
impregnated zeolite crystals. Preferably, those of crystals 30
which are impregnated with a metal chlorite are also impregnated
with at least one of a deliquescent and a water absorbing and
retaining substance (e.g., they are impregnated with calcium
chloride) in a concentration which limits (to a predetermined
maximum level) the rate of release of chlorine dioxide to the
target region in response to activation of the quantity of crystals
with excess protons. For example, zeolite crystals 30 can include
zeolite crystals impregnated with metal chlorite, a water absorbing
and retaining substance, and an acid (or other proton generating
species). Such crystals will be activated by liquid water or
atmospheric moisture (which will cause production of excess
protons, which in turn will cause chlorine dioxide production). The
relative concentrations of impregnating chemicals will control the
rate at which excess protons are produced (and thus the rate at
which chlorine dioxide is produced) in response to a specific
amount of water.
[0086] For some applications, the quantity of crystals is separated
by a barrier (e.g., barrier 50 of FIG. 4) from the target region.
The barrier should be permeable to flow of an activating fluid
(e.g., water) from the target region such that the activating fluid
will interact with the quantity of impregnated zeolite crystals in
a manner resulting in production of excess protons (which in turn
results in production of chlorine dioxide). The barrier should also
be permeable to flow of the chlorine dioxide to the target region.
Preferably, the permeability of the barrier is such that the
quantity of zeolite crystals is exposed to no more than
predetermined maximum flow rate of the activating fluid (e.g., the
barrier is permeable to flow of the activating fluid from the
target region at up to a predetermined maximum flow rate), so that
the barrier limits to a predetermined maximum level the rate of
release of chlorine dioxide to the target region.
[0087] Although the invention has been described in connection with
specific preferred embodiments, it should be understood that the
invention as claimed should not be unduly limited to such specific
embodiments.
* * * * *