Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Organic
Reexamination Certificate
2001-07-03
2004-01-06
Phasge, Arun S. (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Organic
C205S703000, C205S746000, C205S753000, C205S758000, C205S759000, C205S760000, C204S257000, C204S263000, C204S265000, C204S269000, C204S270000
Reexamination Certificate
active
06673229
ABSTRACT:
The present invention relates to an electrochemical method and apparatus for purifying fluids, especially waste water or air, e.g. for the purposes of decontamination and/or disinfection. Current methods for treating organic, inorganic and microbiological pollutants in air, water and soil include so-called “advanced oxidation processes”. These advanced oxidation processes create a highly reactive oxidizing agent that can readily convert organic waste to carbon dioxide and water, while mineralizing inorganic constituents for easy removal. One of the agents considered in this context is the OH radical, which can be created by the Fenton reaction
Fe
2+
+H
2
O
2
+H
+
→Fe
3+
+.OH+H
2
O. (1)
The Fe
3+
-ion is subsequently reduced by hydrogen peroxide via the reaction
Fe
3+
+H
2
O
2
→Fe
2+
+.O
2
H+H
+
(2)
Various ways of providing H
2
O
2
and Fe
2+
for process (1) were proposed in the past.
J. S. Do and C. P. Chen, J. Electrochem. Soc. 140 (1993), 1632 proposed to create H
2
O
2
by the reaction
O
2
+2H
+
+2
e
−
→H
2
O
2
on a graphite, reticulated carbon or carbon-PTFE cathode. Fe
2+
was added externally.
K. Pratap, A. T. Lemley, J. Agric. Food Chem 42 (1994), 209 proposed to generate Fe
2+
by a sacrificial iron anode and to add H
2
O
2
externally.
It was also proposed by E. Brillas et al., Electrochem. Solid-State Lett. 1 (1998), 168 to combine these two approaches, i.e. to produce H
2
O
2
on a carbon cathode, as indicated above, and to generate Fe
2+
by a sacrificial iron anode.
EP 0 694 501 A1 discloses an electrochemical cell for purification of contaminated water using OH radicals. In this document it is proposed to enable the Fenton reaction by adding FeSO
4
to a liquid electrolyte. Although this electrochemical cell was shown to be effective in destroying pollutants, it requires the continuous addition of FeSO
4
when purifying a continuous fluid flow. Furthermore, the classical Fenton reaction, as employed according to this document, has several intrinsic limitations in that it requires H
2
O
2
to be created, which consumes hydroxyl radicals. Furthermore, the regeneration of Fe
2+
according to reaction (2) is relatively slow so that Fe
3+
accumulates in the system, which slows down the reaction rate and leads to precipitation of colloidal solids containing Fe(OH)
3
, the so-called Fenton-sludge.
U.S. Pat. No. 5,645,700 discloses an electrolytic cell for generation of hydrogen peroxide, wherein a catalyst for a reaction for creating hydrogen peroxide is used which may be a complex of group VIII metals with porphyrines and phthalocyanines as ligands. These ligands prohibit the creation of OH radicals.
John E. Biaglov and Alexander V. Kachur, Radiation Research 148 (1997), 181 and Alexander V. Kachur, Stephen W. Tuttle and John E. Biaglov, Radiation Research 150 (1998), 475 consider the role of Fe-complexes in creating the hydroxyl radical in biological system. They found that a class of Fe-complexes having polyphosphates or acetic derivatives of ethyleneamine as ligands promote the generation of the OH radical. These complexes were considered for modelling biological processes. A relation of this effect to the purification of fluids, for example waste water, was not considered.
All previously mentioned Fenton-type processes require the addition of an iron salt or an Fe complex to a liquid, or the provision of a sacrificial iron anode.
It is the object of the present invention to provide a basically self-sustained apparatus for purifying fluids employing an electrochemical cell and a related method for purifying fluids.
This object is accomplished according to the invention by an apparatus for purifying fluids comprising at least one electrochemical cell having a cathode, an anode and an electrolyte between cathode and anode, said cell comprising a metal complex, ML, immobilized at or in a solid at the cathode side of the electrolyte, as opposed to the anode side, wherein M represents a metal, L represents an organic or inorganic ligand, said complex being capable of forming the hydroxyl radical by a reaction wherein the metal in the complex is oxidised and acquires an additional positive charge, said anode creating positive ions and electrons, said electrolyte allowing the transfer of positive charges, said solid being arranged such that the fluid to be purified can come into contact with the metal complex.
Said oxidation of said metal may especially involve oxygen and/or H
+
ions
According to a preferred embodiment, the metal complex is an iron complex, FeL, wherein the FeL complex may allow for the iron having two different oxidation states Fe
2+
L and Fe
3+
L.
The solid may especially be the cathode or the electrolyte. According to the invention, the metal complex may be deposited, attached or incorporated into the cathode or into a solid electrolyte at the cathode side thereof. In the latter case, the cathode may be bonded, deposited or otherwise attached to said cathode side of the electrolyte in a way allowing the reduction of the metal in the complex by providing an electron, e.g. from Fe
3+
to Fe
2+
.
The anode and cathode are connected or connectable to a power source which may or may not be part of the apparatus.
Usually, the apparatus according to the invention will comprise means for guiding the fluid to be purified to the cathode and/or means for guiding purified fluid away from the cathode.
The invention may also provide that said Fe complex FeL is capable of undergoing the net reaction
3Fe
2+
L+O
2
+3H
+
→3Fe
3+
L+.OH+H
2
O. (3)
Fe complexes enabling other reactions involving agents that readily produce oxygen, e.g. H
2
O
2
,.O
2
H etc., may also be considered in order to produce the hydroxyl radical. Especially, the Fe complex may be capable of undergoing the reaction.
Fe
2+
L+H
2
O
2
+H
+
→FeL
3+
+.OH+H
2
O,
wherein H
2
O
2
may be externally provided from an H
2
O
2
source or produced in situ.
Preferably said anode enables a reaction creating H
+
ions and electrons and said electrolyte allows the migration of H
+
ions, although other ways of providing H
+
ions may be contemplated.
The invention may also provide that said anode comprises a catalyst for promoting the reaction.
H
2
O→½O
2
+2H
+
+2e
−
. (4)
Said catalyst may be a metal oxide or a mixture of metal oxides containing at least one transition metal and often including one of the precious metals, such as Ru, Rh, Pd, Os, Ir, Pt.
Said catalyst may especially be ruthenium dioxide, iridium dioxide and mixed oxides of ruthenium and manganese, ruthenium and titanium, or nickel and cobalt.
Chelating agents suitable for forming a Fe complex are generally suitable ligands L.
The invention may provide that the ligand L is selected from the group comprising polyphosphates, pyrophosphates, bisphosphonates, polyaminocarboxylates, citrates, ethylene amines and derivatives thereof and further comprising analogues of said substances and derivatives which allow covalent attachment to the cathode.
The ethyleneamines mentioned above especially comprise ethylenediamine and ethylenediaminetetraacetic acid (EDTA).
The invention may also provide that said ligand is selected from the group comprising acetic derivatives of ethylene amine, polyphosphates or bisphosphonates and analogues thereof.
The ligand may be coupled directly to the surface of the electrode via a functional moiety selected from the group comprising an amino group, a hydroxyl group and a carbonyl group. In one embodiment the amino group may form part of 3-aminopropylsilanol or of derivatives thereof, wherein the attachment to the electrode surface occurs through the silanol moiety.
The invention may especially provide that the ligands are of the general form
R—(NX
2
)
p
,
wherein X is selected from the group compr
Ford William
Vossmeyer Tobias
Wessels Jurina
Frommer William S.
Frommer & Lawrence & Haug LLP
Megerditchian Samuel H.
Phasge Arun S,.
Sony International (Europe) GmbH
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