Note: Descriptions are shown in the official language in which they were submitted.
PERMIONIC ~EMBRANE ELECTROLYTIC CELL CURRE~T DISTRIBUTION MEANS
DESCRIPTION OF T~E INVENTION
Permionic membrane electrolytic cells, including zero gap permi-
onic membrane electrolytic cells, have a ca~ion s~lective permionic membrane.
The cation selective permionic membrane separates the anolyte compartment,
with an anode therein, Erom the catholyte compartment, with a cathode
therein. In a ~ero gap permionic membrane electrolytic cell the anodic
electrocatalyst and the cathodic electrocatalyst are in contact with the
respective faces of the permionic membrane. In a solid polymer electrolyte
electrolytic cell the anodic electrocatalyst and cathodic electrocatalyst
ure bonded to and embedded in the permionic membrane.
The zero gap permionic membrane electrolytic cell offers the
advantage of ready removability of the electrocatalyst. That i8, the
n~odic and cathodic electrocatalyst can be removed from contact with the
permionic membrane without destruction or degradation of the permionic
membrane. Another advantage offered by æero gap pe~mionic membrane elec- -
trolytic cell~ over solid polymer electrolyte electrolytic cells i~ the
higher current efficiency of the zero gap permionic membrane electrolytic
cell. Ho~ever, the higher current efficiency com2s at a penalty of a
higher cell voltage.
According to the invention herein contemplated, it has now been
found that the v~ltage of a zero gap permionic membranç electrolytic cell
may be reduced if there is present in and on the cathodic surface of the
~~
permionic membrane, ~uitable current distribution mPan6~ ~h~r~by to enhance
electronic conduction across the cathodic surface of the permionic membrane.
A~ herein conte~plated, the cathode contact~ the permionic membrane with
the cathode ~urface of the permionic membrane having curreDt distribution
msterial, i.e~, conductive, substantislly non-catalytic materials, dis-
persed acro83 the cathodic surface of the permionic membrane. The non-
ca~alytic ~aterial may be bonded ~o and embedded in the ca~hodic surface of
the per~ionie m~brane.
DETAILED DESCRIPTION OF THF, INVENTION
_
~ erein contemplated is an electrolytic cell having an anolyte
comp~rtment with an snode therein, a catholyte compartment with a caehode
therein, and a permionic membrane ther~between, with at le~st the cathode
contacting the permionic ~embrane. The per~ionic me~brane i~ characterized
by its cathodic surface having electrically cond~ctive, substantially non-
electrocataly~ic material in contact therewith, and either adherent thereto
or adherent to the cathodic electroc~taly~t. By sub~tantially non-catalytic
material it ic meant that the material serve~ the purpose of an electronic
current distributor, having a metallic e'Lectrical conductivity, but havin~
8 high hydrogen evolution overvoltage, i.e., at least ~bout 0.1 volt higher
than the hydrogen evolution overvoltage of the cathodic electro~atalyst
used in combination therewith.
More particularly, the invention provides
a method of electrolyzing an alkali metal chloride
br~ne in an electrolytic cell having an anolyte compartment with an
anode therein, a catholyte compartment with a cathode therein, and a
o~rmioni~ membran~ therebetween, said cathode contacting Lhe permionic
membrane, ~hich method comprises passing an electrical current from the
anode to the cathode, evolving chlorine at the anode and hydroxyl ion at
the cathode; the improvement wherein said cathode comprises a Group VIII
transition metal as the electrocatalyst, said permionlc membrane has an
anodic surface and a cathodic surface, the cathodic surface thereof havinr
electrically conductive, substantially non-electrocatalytic particles of
material chosen from the group consisting of Group IB metals and corrosion
resistant, electrically conductive compounds thereof bonded thereto, the
- 2 -
7~2
particles havlng a hydrogen evolution overvoltage at least 0.1 volt higher
than tha hydrogen overvoltage of the electrocatalyst.
Preferably, the elec~ricslly conductive, Rub~tantially non-
catslytic material i~ chosen Erom the group con3isting of Group IB metals
ant corrosion re6i~ant, electrically conductive, but ~ub~tantially non-
electrocatalytic compounds thereof. These ~sterials include copper,
silv~r, and gold, as well as those oxides thereof that are seable in the
aqueous, slkali ~e~al hydroxide envison~ent. Especially preferred, for
reu~ons of co~t, availabili~y, and lo~ electrocatalytic ac~iviey, are
silver oxide, silver, and copper.
- 2a
The electrically conductive~ substantially non-electrocatalytic
material may be a particulate material, for example, particles having a
particle size of ~rom about 0.1 micron ~o about minus 2~0 me~h and prefera-
bly from about 0.5 micron to about minus 325 mesh. The substantially non-
electrocatalytic, electrically conductive material is preferably adherent
to the permionic membrane. That i8, it i6 preferably bondsd to and embedded
in the permionic membrane, and substantially non-removable therefrom with-
out degradation, partial destruction, or de~truction of either the material
or the permionic membrane, or both. Alternatively, especially when the
non-catalytic material is of a finer mesh si~e than the electrocatalyst, it
may be adherent to either the electrocatalyst or to the substrate carrying
the electrocataLyst, as where the electrocatalyst i8 a particulate electro-
catalyst bonded to a metallic substrate, with particulate conductor material
on the substrate, and between and on the e'Lectrocatalyst particles.
Typicfllly, the cathode electrocal:alyst of the electrolytic cell
is a Group VIII transition metal, having a lower hydrogen evolution over-
voltage than ~he electrically conductive, l3ubstsntially non-electrocatalytic
material. Typical cathodic electrocatalysts include iron, cobalt, nickel
and the platinum group metals, especially electrocPlly catalytic forms such
as Raney nickel, platini~ed platinum, and platinum black.
According to an alternative exemplification of the method of this
invention, there i8 provided a method of electrolyzing an alkali metal
chloride brine in an electrolytic cell having an anolyte compartment with
an anode therein, a catholyte compartment with a cathode therein, and a
permionic mambrane therebetween. The cathode contacts the permionic
membrane, preferably and removably, that is readily removable without
destruction or degradation of either the cathodlc electrocatalyst or the
7~2
permionic membrane. As herein contempla~e~, the process comprises passing
an electrical current from the anode to the cathode, whereby to evolve
chlorine at the anode and hydroxyl ion at the cathode. The method is
characteri~ed in that the permionic membrane has on its cathodic aurface
electrically conductive, sub~tantially non-electrocatalytic material either
adherent thereto or in contac therewith J as descrihed ~bove.
Accordin~ to one exemplification herein contemplated, the current
distributor may be bonded to the cathodic surface of the permionic membrane
alone, that i8, without electrocatalyst being present thereon. In this way,
the electrocatalyst is readily removable from the surface, and i9 present
on a separate electrode structure, i.e., a metallic screen, mesh, shee,
plate, or the like, having a coating, surface, or film of electrocatalyst
n~ herein described.
According to an alternative exemplification, the electrocatalyst
i~ present as a bilayer, i.e., a~ a second layer, atop the layer, sur- -
face, or film of particulate, electrically conductive, substantially
non-electrocatalytic ~aterial which is bonded to and embedded in the
permionic mernbrane. According to this exemplification, the ~ubstantially
non-electrocatalytic, electrically conductive material is applied first
to the permionic membrane, and thereafter the electrocatalyst i8 applied
thereto, both above and between particles of ~he conductive, non-catalytic
material.
According to a 3ill further exemplification of the method of
this invention, electrocatalyst may be present on the ~urface of the per-
mionic membrane, in admi~ture with the electrically conducti~e, substan-
tially non-catalytic material wnich i5 also adherent to the permionic
membrane surface.
According to a still further exemplification, the electrocatalyst
and the non-catalytic material may bo~h be present on and adherent to an
electroconductive subetrate, and removable from the permionic membrane.
Generally the loading of the electronically conductive, current
distributor i6 from about 1 milligram per square centimeter to about 100
milligrams per square, and generally from about 2 to about 20 milligrams
per square centimeter. Amounts lower than about 1 milligram per gquare
centimeter do not provide significant amount~ of current distribution,
~hile amounts greater than about 100 milligrams per square centimeter may
~uhstantially interfere with the electrochemical process, providing an
impermeable barrier, sheet, or film on the cathodic surface of the permi-
onic membrane.
The permionic membrane interposed between the-anolyte and the
porou~ matrix is fabricated of a polymeric fluorocarbon copolymer having
immobile, cation selective ion exchange group~ on a halocarbon backbone.
The membrane may b~ from about 2 to about ~S mils thick, although thicker
or thinner permionic membranes may be utilized. The permionic membrane
may be a laminate of two or more membrane ~heet~. It may, additionally,
have internal reinforcing fibers.
The permionic membrane may be a copolymer of (I) a fluorovinyl
polyether having pendant ion exchange groups and having the formula
(I) CF2~CF-Oa-[(CX'X'')C (CFX')d (CF2-0-(XIX")e (CX"X'0-CF2)~-A
w~ere a is 0 or 1, b i8 0 to 6, c iB 0 to 6, d is 0 to 6, e i8 0 to 6, f i8
0 to 6; X, X', and X" are ~ Cl, -F, and -(CF2)gCF3; g i8 1 to 5, [ ] i8
a discretionary arrangement of the moieties therein; and A is the pendant
functional group as will be described hereinbelow. Preferably a i8 1, and
X, X' ~nd X" are -F and (CF2)gCF3.
7~
The fluorovinyl polyether may be copolymerized with a (II) fluoro-
vinyl compound
(II) CF2 = CF~a~(CF~ d) A
and a (III) perfluorinated olefin
(III) CF2 - CXX',
or (I) may be copolymerized with only a (III~ perfluorinated olefin, or
(I) may be copolymerized with only a (II) perfluorovinyl compound.
The functional group is a cation selective group. It may be a
sulfonic group, a phosphoric group, a phosphonic group, a carboxylic group,
~ a precursor thereof, or a reaction product thereof, e.g., an ester thereof.
Carboxylic groups, precursor~ thereof, and reactions products thereof are
preferred. Thus, as herein contemplated, A is preferably chosen from the
group consisting of
-COOH,
-COOR l,
-COOM,
-GOF,
-COCl,
-CN,
-CONR2R3 ~
-S03H,
-S03M,
-S02F, and
-S02Cl
where Rl is a Cl to Clo alkyl group, R2 and R3 are hydrogen or Cl to Clo
alkyl groups, and M i~ an alkali metal or a quaternary ammonium group.
According to a particularly preerrPd exemplification, A is
~7fl~
-COCl,
-COO~I,
-COORl,
-S02F, or
-S02Cl
where Rl i8 a Cl to Cs alkyl.
As herein contemplated, the permionic membrane i~ preferably a
copolymer which may have:
~I) fluorovinyl ether acid moieties derived from
CF2=cF-o-lcF2btcxlx~)ctcFx~)tcF2-o-cx~x~i)etcx~x~-o~cF2)f~-A~ -
exemplified by
CF2=CFOCF2CFtCF30CF3CF2CF2COOOCH3,
CF2=CFO(CF2)30CFCOOCH3,
CF3
CF2=CFotCF2)40CIFCoc~cH3,
CF3
CF2=CFOCF2CFCF2COOCH3, and
CF3
CF2=CFOCF2CF(CF3)0CF(COOC~3)CF3, inter alia;
(II) fluorovinyl moieties derived from
CF2~CF-to)~,-(CFX' )d-A,
exemplified by
CF2-CF(CF2)2_4COOCH3
CF2-CF ( CF2 ) 2-4COOCH3 ~
CF~=CFotCF2)2_4CooCH3,
CF2 = CFotCF2)2_4CooC2H5~ and
CF2 = CFO(CF2)2-4CoOcH3, inter alia;
7~L;~
(III) fluorinated olefin moieties derived from
CF = CXX'
as exenplified by tetrafluoroethylene, trichlorofluoroethylene,
hexafluoropropylene, trifluoroethylene, vinylidene, fluorlde, and the
like; and
(IV) vinyl ethers derived from
CF2 = CFOR4
The permionic membrane herein contemplated has an ion exchange
capacity of from about 0.5 to about 2.0 milliequivalentspergram of dry
polymer, preferably from about 0.9 to about 1.8 milliequivalents per gram
of dry polymer, and in a particularly preferred exemplification, from
about 1.0 to about 1.6 milliequivalents per gram of dry polymer. The
permionic membrane herein contemplated has a volumetric flow rate of 100
cubic millimeters per second at a temperature of 150 to 300 degrees
Centlgrade, and preferably at a temperature between 160 to 250 degrees
Centigrade. The glass transition temperature of the permionic membrane
polymer is below 70C, and preferably below about 50C.
The permionic membrane herein contemplated may be prepared by
the methods described in U.S. Patent 4,126,588.
Most commonly the ion exchange resins will be in a thermoplastic
form, i.e., a carboxylic acid ester, e.g., a carboxylic acid ester of
methyl, ethyl, propyl, isopropyl, or butyl alcohol, or a sulfonyl halide,
e.g., sulfonyl chloride or sulfonyl fluoride, during the fabrication herein
contemplated9 and will thereafter be hydrolyzed.
According to one exemplification of this invention, an electro-
lytic cell may be assembled having an anode bearing upon the anodic surface
of the permionic membrane, and platinum black and silver oxide, Ag2O bonded
to the cathodic side of the permionlc membrane. According to this
exempliEicatlon, a perfluorocarbon polymer having pendant carboxylic acid
ester groups, l.e.~ being in the thermoplastic form, may be coated with a
plasticizer, i.e., bis(2-ethyl hexyl) isophthalate, one part platinum
black and 4 parts silver oxide, whereby to provide a loading of about
12 milligrams per square centimeter of silver oxide and about 3 milligrams
per square centimeter of platinum black. The coated permionic membrane
may ~hen be hot pressed, for example from about 180C to about 225C and
at a pressure o~ about 100 to lS00 pounds per square inch for about 2 to
10 minutes whereby to provide a cathodic solid polymer electrolyte
surface. Thereafter an electrolytic cell may be assembled having coated
tltanium anode bearing upon the anodic surface of the permionic membrane,
and a nickel current collector bearing upon the cathodic, solid polymer
electrolyte surface of the permionic membrane.
According to a still further exemplification of this invention,
a permionic membrane electrolytic cell may be prepared having an anode
bearing upon the surface of the permionic membrane and a multiple layer
of silver oxide and platinum black deposit:ed on the cathodic surface of the
permionic membrane. As herein contemplated, a sheet of perfluorocarbon
copolymer having pendant carboxyllc acid ester groups may be coated with a
suitable plasticizer as dioctylphthalate plasticizer to which 1 micron
diameter silver oxide particles are applied. Thereafter, minus 325 mesh
platinum black particles may be applied, and the resulting bilayer pressed
at a temperature of about 180 to about 225C, and a pressure from about 800
to about 1500 pounds per square inch for about 2 to 10 minutes so as to
obtain a solid polymer electrolyte cathodic surface having silver oxide
particles in intimate contact with the permionic membrane and e~ternal
particles of platinum blackO
_ 9 _
7~
According to a still further exemplification of this invention,
an ~ mil thick permionic membrane fabricated of a perfluorocarbon copolymer
having pendant carboxylic acid ester groups may be coated with dodecyl-
phthalate and minus 325 mesh copper particles. Thereafter the permionic
membrane may be hot pressed at a temperature of abou~ 180C to 220 C and a
pressure of about 700 to 1500 pounds per square inch for about 2 to about
10 mlnutes. The cathode may be a screen having abou~ 20 mesh per inch by
30 mesh per inch and a thickness of about 0.005 of an inch with an electro-
deposited coating of platinum thereon. In this way there is provided a
zero gap permionic membrane cell having copper particles as electrical
distributors on the surface thereof.
The use of plasticizQrs, for example, phthalates, phosphates,
and fatty acid esters is particularly advantageous in the method of this
invention in order to enhance the adherence of the electronic current
dlstribotor to the permionic membrane, e4pecially at reduced temperatures,
presaures, and times of hot pressing.
The following examples are illustrative:
EXAMPLE 1
A permionic membrane electrolytic cell was assembled having a
ruthenium dioxide coated anode bearing upon the anodic side of the
permionic membrane, and platinum black and silver oxide, Ag2O, bonded to
the cathodic side of the permionic membrane.
An eleven mil thick by 5 inch by 5 inch Asahi Glass Co., Ltd.
FLEMION~ HB permionic membrane fabricated of a perfluorocarbon copolymer
having pendant carboxylic acid ester groups was coated with bis(2 ethyl
hexyl) isophthalate plasticiæer to which was added 0.2 grams of minus 325
-- 10 --
74~;2
mesh platinum black and 0.8 grams of minus 325 mesh silver oxide, A~2~,
providing 3.4 milligrams per sguare centimeter of platinum and 12.8 grams
per square centimeter of silver oxide. The coated permionic membr~ne was
hot pressed at 200 degrees Centigrade and 20 tons force for 5 minutes.
Thereafter the electrolytic cell was assembled, with a ruthenium
dioxide coated 40 mesh to the inch by 40 mesh to the inch, 3 inch by 3
inch~ titanium anode pressed against the anodic surface of the permionic
membrane hy a 2.5 mesh to the inch by 5 mesh to the inch, 3 inch by 3 inch,
ruthenium dioxide coated titanium screen. The cathode current collector
was a 2.5 mesh to the inch by 5 mesh to the inch, 3 inch by 3 inch, nickel
screen.
After 14 days of electrolysis the cell voltage was 3.36 volts
at 400 Ampere3 per square foot with 86 percent cathode current efficiency.
EXAMPLE II
A permionic membrane electrolytic cell was assembled having a
ruthenium dioxide coated titanium screen bearing upon the anodic surface of
the permionic membrane and a bilayer of silver oxide, Ag20, and platinum
black deposited on the cathode surface of the permionic membrane.
An eleven mil thick by 5 inch by 5 inch Asahi Glass Co., Ltd.
FLEMION~ HB permionic membrane formed of perfluorocarbo~ cop~lymer having
pendant carboxylic acid ester groups was coated with bis(2 ethyl hexyl)
isophthlate plasticizer. Silver oxide particles, 1 micron in diameter,
were applied atop the plasticizer to provide a silver oxide loading oE 12
milligrams per ~quare centimeter. Atop the silver oxide, minus 325 mesh
platinum black was applied to provide a platinum loading Gf 3.4 milligrams
per square ~entimeter. The coated permionic membrane wss hot pressed at
200 degrees Centigrade and 20 tons force for 5 minutes.
~L8~
ThereaEter the electrolytic cell ~as as~embled, with a ruthenium
dioxide coated, 40 mesh to the inch by 40 mesh to the inch, 3 inch by 3
inch ~itanium anode pressed ~gainst the anodic surface of the permionic
membrane by a ruthenium dioxide coated, 2.5 mesh to the inch by 5 mesh to
the inch, 3 inch by 3 inch titanium screen.
After 31 days of electrolysis the cell voltage ~as 3.56 volts at
396 Amperes per square foot and the cathode current efficiency was 87 percent.
EXAMPLE III
A permionic membrane electrolytic cell wa~ assembled having a
ruthenium dioxide coated titanium anode screen bearing upon the anodic
surface of the permionic membrane, and a platinum coated nickel cathode
bearin~ upon the silver oxide coated, cathodic surface of the permionic
membrane.
An 11 mil thick by 5 inch by 5 inch Asahi Gl~s~ Co., Ltd. FLEMION3
type HB permionic membrane fabricated of a perfluorocarbon copolymer having
pendant carboxylic acid ester groups was coated with bis(2-ethyl hexyl)
, o~
isophthlPte plasticizer. To this membrane was added 0.8 grsms of 1 micron
silver oxide, Ag20. The membrane was then hot pressed at 200 degrees
Centigrade and 20 tons force for 5 minutes.
The cathode was prepared by electrolytic&lly depositin~ platinum
black onto a 40 mesh to the inch by 4~ mesh ~D the inch, 3 inch by 3 ineh,
0.005 ineh thiek expanded mesh niekel screen. The electrolytic cell was
assembled ~ith a ruthenium dioxide coated, 40 me~h to the inch by the 40
mesh to the inch, 3 inch by 3 inch titanium screen anode bearing against
the anodic surface of the permionic membr~ne, nd the platinum black coated
nickel screen bearing against the silver oxide coated cathodic surfAce of
the permionic membrane.
- 12 -
~8~
After 22 days of electroly~is the cell voltage was 3.41 volts at
396 Amperes per square foot, and the cathode current efficiency was 83.7
percent.
EXAMPLE IV
A ~ermionic membrane electrolyeic cell was assembled having a
ruthenium dioxide coated titanium anode screen bearin8 against the anodic
surface of the permionic membrane and a nickel screen cathode bearing
against the silver oxide coated, cathodic surface of the permionic membrane.
An 11 mil thick hy 5 inch by 5 inch Asahi Glass Co., Ltd.
FLEMION~ type HB permionic me~brane fabricated of a ~erfluorocarbon copoly- -
mer having pendant carboxylic acid eRter gro~ps was coated with bis(2-ethyl
a,
hexyl) isophthlate plasticizer. To this Membrane was added 0.8 grams of 1
micron silver oxide, Ag2O, powder. The membrane was then hot pressed at
200 degrees Centigrade and 20 tons force for 5 minutes.
The cathode was fln uncoated, 20 mesh to the inch by 30 mesh to
the inch, 3 inch by 3 inch, 0.005 inch thick nickel screen. The electro-
lytic cell was assembled with a ruthenium dioxide coated, 40 mesh to the
inch, 3 inch by 3 inch, titanium screen anode against the anodic surface of
the permionic membrane, and the nickel cathode pressed agninst the silver
oxide coated, cathodic surface of the permionic membrane.
After 29 days of electrolysis the cell voltage ~as 3.31 volt~
at 396 Amperes per square foot, and the cathode current efficiency was
87.1 percent.
EXAMPLE V
A permionic membrane electrolytic cell was prepared by depositing
cathodic electrocatalyst into the cathodic side of the permionic membrane
by utilizing a plasticizer in conjunction wi~h the electrocatalyst prior to
hot pressing the cathodic electrocatalyst into the permionic membrane.
An ll mil ~hick by 5 inch by 5 inch A~Phi Glass CompPny, Ltd.
FI.EMIO~ type ~ permionic membrane fabricated of a perfluorocarbon copoly-
mer having pendant carboxylic acid ester groups was coated with bi~(2-ethyl
hexyl) isopthalate plas~icizer. To the pla~tici~er coated surface of the
permionic membrane was added 0.8 gram of minus 325 mesh platinum black.
The pla~inum black was added by air brushing.
l~ereafter the permionic mem~rane was hot pressed at 200 degrees
Centigrade and 20 tons orce for 5 minutes. The cell was then assembled
by pressing a ~0 mesh to the inch by 40 mesh to the inch, 3 inch by 3 inch,
ruthenium dioxide coated titanium mesh screen against the anodic surface
of the permionic membrane, and a 20 me~h to the inch by 30 mesh to the
inch, 3 inch by 3 inch, cathode current collector against the platinum
black coated, cathodic surface of the permionic membrane.
After 31 days of electrolysis the cell vol~age wa~ 3.86 volts
at 396 Amperes per square foot, and the cathode current efficiency was
87.0 percent.
XA~PL~ VI
A permionic membrane electrolytic cell was prepared by depositing
cathodic electrocatalyst into the cathodic surface of the permionic mem-
brane utili~ing a plastici~er in conjunction ~ith particulate cathodic
electrocataly~t.
A 5 mil thick by 3 inch by 3 inch Asahi Glass CGmpany Co., Ltd.
FLEMION~ type ~ permionic membrane fabricated of a perfluorocarbon copoly- -
mer having pendant carbo~ylic acid ester groups was coated with bi~(2-ethyl
hexyl) isophthlate plPsticizer. To the plasticizer coated surface of the
permionic membrane was air brushed 0.4 gram~ of platinum black. The mem-
brane wa8 then hot pressed at 200 degrees Centigrade and 20 eOns force
for 5 minutes to adhere the catalyst to the membrane.
The cell was then assembled by pressing a 40 me~h to the inch by
40 mesh to the inch, 3 inch by 3 inch ruthenium dioxide coated titanium
mesh screen againæt the anodic surface of èhe permionic membrane, and 20
mesh to the inch by 30 meæh to the inch, 3 inch by 3 inch cathode current
collQctor against the platinum black coated, cathodic 3urface of the
permionic membrane.
After 13 days of electrolyæi~ the cell voltage was 3.79 volts
at 396 Amperæ per square foot, and ehe cathode current efficiency wa~
75.2 percent.
While the invention has been described with respect to certain
preerred exemplifications and em~odimentsl the æcope of protection i~ not
intended to be limited thereby, but only by the claima appended hereto.
