CA1179631A - Hc1 electrolyzer with unitary membrane-electrode structure with discrete anode projections - Google Patents
Hc1 electrolyzer with unitary membrane-electrode structure with discrete anode projectionsInfo
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Abstract
HCl ELECTROLYZER WITH UNITARY MEMBRANE-ELECTRODE STRUCTURE WITH DISCRETE ANODE PROJECTIONS
ABSTRACT OF THE DISCLOSURE
An HCl electrolyzer utilizing a membrane with catalytic electrodes physically bonded to the surfaces of the membrane is provided with an electron current conducting structure which comprises an array of individual current conducting elements contacting the electrode. The cell is operated at high temperatures (60° - 90°C) to take advantage of the reduction of electrode overpotential at these temperatures but with low feed acid concentrations (?9M) to minimize hydrogen chloride in the chlorine, i.e., HCl vapor pressure is below 0.1 atmospheres - 76 Torr. There is also a large decrease in membrane resistance as temperature is increased. Simultaneously O2 evolution is suppressed to maintain O2 content in the chlorine at 0.1% or less.
ABSTRACT OF THE DISCLOSURE
An HCl electrolyzer utilizing a membrane with catalytic electrodes physically bonded to the surfaces of the membrane is provided with an electron current conducting structure which comprises an array of individual current conducting elements contacting the electrode. The cell is operated at high temperatures (60° - 90°C) to take advantage of the reduction of electrode overpotential at these temperatures but with low feed acid concentrations (?9M) to minimize hydrogen chloride in the chlorine, i.e., HCl vapor pressure is below 0.1 atmospheres - 76 Torr. There is also a large decrease in membrane resistance as temperature is increased. Simultaneously O2 evolution is suppressed to maintain O2 content in the chlorine at 0.1% or less.
Description
~ 31 ~2EE 317/312 The instant invention relates to a process and appara~us for the electrolytic production of halogens from aqueous halide solutions. More particularly, it relates to the electrolysis o~
aqueous HCl solutions at high temperatues and low feed acid concentrations.
The production of chlorine by the elec-trolysis of aqueous solutions of halides in a cell comprising a~ermselective membrane having a conductive, catalytic electrode permanently affixed to the surface thereof and in physical contact with an external electron current distributor is described in Canadian Application Serial Number 315,516, filed October 31, 1978, in the name of Russell Mason Dempsey et al assigned to General Electric Company, the assignee of the present invention. Cells of this type include a graphite electron current distrlbutor which contacts the surface of the catalytic electrode bonded to the membrane. 5uch electron cwrrent collectors have a plurality o~ elongated, continuous, parallel ribs extending from a conducti~e base. The elongated ribs contact the catalytic electrode to distribute current while the channels formed between the ribs provide fluid distribution channels for the anolyte entering the cell as well as for gases evelved at the electrode. Continuo~s ribs may have the disadvantage of obstructing a relatively large area of the electrode thereby limiting access of the aqueous anolyte to the electrode at these locations.
Because of the obstruction or l'blinding" of areas of the bonded electrode, chloride ion s-tarvation under these areas can result in electrolysis of water and the evolution of oxygen.
~ 63~ 52EE 317/31~
Coevolution o~ oxygen at a chlorine anode has a number of practical consequences, all of them undesirable. The evolution of oxygen, of course, represents a process inefficiency and increases the electrical cost necessary for producing chlorine, i.e., increases the production cost of chlorine.
High oxygen levels also result in severe corrosion of graphite cell components. As pointed out previously, in an HCl electrolysis cell having anode electrodes bonded directly to an ion exchanging membrane, the preferred current collector fluid distributor is a molded graphite-polymer-aggregate having a plurality of parallel grooves which contact the electrode in order to provide current to the electrodes while distributing the anolyte and the electrolysis product at the anode.
If the oxygen level in the chlorine remains below 0.1%
(V/V) very little corrosion of the graphite is observed whereas levels in exce~s of 1~ (V/V) lead to severe corrosion in a matter of days. It is therefore highly desirable to maintain the oxygen level at or below 0.1%.
The discharge potential of oxygen, i.e., the standard electrode potential for 2' is actually lower than that o~ chlorine (1.23 vol-ts v. 1.36 volts).
~Iowever, the great irreversibility of oxygen electrodes (i.e. the overpotential for oxygen) permits preFerential evolution of chlorine despite these thermodynamic considerations. Thus, normally, chlorine is evolved prefercntially although oxygen evolution is no-t entirely suppressed. The oxygen evolution reaction can be inhibited by maintaining a high acid concentra-tion at the electro reaction site. By maintaining the ~63~ 52EE 317/312 chloride ion concen-tration suf~iciently high, chlorine di.scharge at the anode is facilitate,d.
The concentration of hydrochloria acid at any reaction si-te can be defi,ned by the expression:
R S FD
where i = the cell current density F = FARADAY
D = the HCl diffusion coefficient CS = the HCl concentration of the feed CR = the HCl concentration at the discharge site underneath the contact point between the electrode and the current collector l = the true diffusion path length for the HCl to the discharge site.
Thus, it may be seen the acid concentration at the reaction site, and hence the 2 :in C12 l~vel, is a function of both the diEfusion path length and the feed stock acid concentration.
The discharge site below a contact element of the current collector has a longer diffusion path than do the sites below the li~uid flow channel because the acid must diffuse laterally underneath the contact element and within and across the anode thickness to reach the electrode reaction site below a contact element, while the acid need only be diffused across the anode thickness to reach the discharge site below the flow channel. Because of the greater path length, the acid concenkration below the contact element is reduced and the rate of 2 evolution tends to increase.
~ 52EE 317/312 sy increasiny the acid concentration of the ~eed, (Cs) the chloride ion content beneath the contact element is maintained sufficiently high to minimize oxygen evolution even though the area is partially obstructed or "blinded". Thus, it is customary to operate with anolyte acid feed concentration in exess of 10M, preferably between 10 and 12~i to maintain the oxygen content in the chlorine at 0.1% or less.
While malntaining the feed stock acid concentration at very high levels is effective in reducing the oxygen evolution reaction, it has been found that it does have a number of shortcomings which make it less than on optimum solution. The problem is that the vapor pressure of hydrogen chloride, which is a gaseous material, is both a function of temperature and concentration. Its solubility in water is a logarithmic function of temperature. Operation of the cell at temperatures of 60C and above (which is desirable to minimize internal resistance, and electrode overpotential and maximize eleckrical efficiency) results in high hydrogen chloride partial pressures and impure chlorine product which must be purified. Thls expense is, of course, in addition to the undesirable corrosive effects of the hydrogen chloride orl the cell and downstream equipment. If the operating temperature of the cell is reduced (i.e., to 30-40 C) in order to maintain the hydrogen chloride vapor pressure at a reasonable level, the overpotential of the electrodes and internal ohmic loss increase~
and the power efficiency of the system decreases also resulting in hic~her chlorine production costs.
~ 52EE 317/312 Thus, presently known ~echniques to minimize oxygen evolution in chlorine cells by increasing the acid feed stock concentration result in high hydrogen chloride vapor pressures; in an impure chlorine product, in added expense due to purification costs and in potential-corrosion of equipment. Attempts to control the hydrogen chloride vapor pressure when operating with a high feed acid concentration by reducing the temperature do reduce the vapor pressure, but result in a substantial penalty in cell voltage because internal resistance and the electrode overpotential increase as the temperature is reduced.
~ pplicant has found now that it is possible to electrolyze aqueous hydrogen chloride with low oxygen evolution levels (less than 0.1%), at high te~peratures (60-80C) with low hydroyen chloride vapor pressures (less than 0.1 of an atmos~here, i.e. 76 Torr) by maintaining high chloride ion concentrations at the membrane electrode current collector contact area even with low feed acid concentration, i.e. acid concentration of less than 9M and preferably 8.5 or 8M or less.
Applicant has found that this may be achieved by minimizing the obstruction or "blinded" areas of the electrode and by maximizing diffusion of chloride to the "blinded" areas. To this end, a novel current collector construction is provided in which an array of contact elements is utilized in place of continuous parallel contact elements to establish a planar array of individual, unconnected current trans~er areas, preferably in the plane of the electrode. The incoming ~ ' 52EE 317/312 anolyte is broken up into a plurality vf intersecting anolyte streams which flow across the electrode surace.
The turbulent flow due to the intersecting skreams surround~the point contact elements, and the increased ~e}n~e~ exposed to anolyte permi ~ diffusion of the acid anolyte to take place ~r~ all sides of the contact elements. This reduces the diffusion path length so that the -i~ chloride~concentration beneath the ~ f~ l"
contact~may be maintained at a sufficiently high level to reduce oxygen evolution below 0.1% with feed acid concentrations of less than 9 molar. Because the cell is operated with lower feed acid concentrations, ` the cell may be operated at a much higher temperature ; (60C), without raising the hydrogen chloride vapor pressure to an undesirable level, (i.e. the vapor pressure is maintained at 0.1 atmosphere - 76 torr or less)~ By operating at temperatures o 60 and above the cell voltage is substantially reduced because at these temperatures the electrode over-potential and ohmic losses are substantially reduced.
It is thereore a principal objective of this invention to provide a method and apparatus for electrolyzing aqueous halides in which coevolution of oxygen at the anode is minimized while operating at temperatures which maximize the cell efficiency.
Yet another objective of the invention is to provide a process for generating halogen from an aqueous hydrogen halide in whiçh the vapor pressure of the halide is minimized at temperatures at which the cell is most efficient;
Yet another objective of the invention is to provide a process for generating chlorine from a ~6--~ ~ ~ 52E~ 317/312 hydrogen chloride with minimal coevolution of oxygen at low concentrations o~ the hydrogen halide anol~te.
Still another objective of the invention is to provide a cell for generating chlorine from aqueous hydrogen chloride in which the oxygen content of the chlorine is 0.1~ or less and the hydrogen ahloride vapor pressure is very low at cell operating temperatures o 60C or more.
Other objectives and advantages of the invention will become apparent as the description thereof proceeds.
In accordance with the invention, halogens such a chlorine, bromine and etc. are generated by the electrolysis of aqueous hydrogen halides at the anode of an electrolysis cell which includes an ion exchange membrane separaking a cell lnto catholyte and anolyte chambers. A thin, porous, gas permeable catalytic anode is rnaintained in intimate contack with the ion exchange membrane so as to bond it to the surface o~ the ion exchange membrane. A graphite electron current conducting distributor which includes a planar array of conductive projections contacts the bonded electrode at a plurality of points either directly or through the medium of an interposed conductive screen. By virtue of the multipoint contact array configuration, turbulent flow is established over the electrode as the incoming anolyte is divided into in a plurality of intersecting streams. The multiple anolyte streams surround the 0 con~act elements and maximize diffusion of the e ~ ~ r anolyte beneath the ~ urface and into contact with the chlorine evolving bonded electrode. In effect the ~ 5ZEE 317/312 diffusion path o the current conductor is decreased ; therehy maintaining the chloride ion concentration beneath the contacting element such that coevolution ; o~ oxygen is held at 0.1% by volume or less with low feed acid concentrations. The vapor pressure of the hydrogen chloride above the fluid is kept very low (less than 0.1 atmospheres) while operating the cell at 60C or above so that the overpotential of the electrode for chlorine evolution and separator resistance are minimized.
The novel features which are believed to be characteristic of the invention are set for with particularity in the appended claims. The invention itsel~, however, both as to its organization and - method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
Figure l is an exploded perspective view o~
an electrolyæer cell utilizing a novel current collector in which the processes to be described herein can be performed.
Figure 2 is partial sectional view showing the membrane, electrode and a plurality of contact elements of the current collector.
Figure 3 is a plan view of the current collector and its planar array of contact elements illustrating the flow fields for the anolyte with the multiple contact array construction of the current collector.
The cell assembly of Figure 1 includes an ion transporting permselectlve mer~rane lO, preferably a i :~31 52EE 317/31~
cation permselective membrane, that separates the cell into anode and cathode chambers. A yas permeable cathode electrode 11, pre~erably in the form of a layer of electrocatalytic particles and particles of a polymeric binder such as polytetrafluorethylene, is bonded to the upper surface of ion transporting membrane 10. A gas and liquid permeable anode, not shown, which may similarly be a mass of catalytic and polymeric particles, is bonded to and in intimate contact with the other side of membrane 10. The cell assembly is clamped between cathode current collecting end plate 12 and current collector 13 which are respectively connected to the terminals of the cell power cupply. Although a single cell unit is shown for convenience, current collec-tor 13 may be bipolar and used as a current conducting separator element between cell units. Niobium current distributing screen elements 1~ and 15 are optionally positioned between membrane 10 cln~ ano~ curren~ collector fluid distributing element 13 and endplate 12 respectively.
Collector 13 which is a molded graphite and fluorocarbon composite consists of a main body 16, a chamber 17 within the main body, and of an array of conductive contact elements 18 which contact either screen 15 or the anode electrode bonded to the underside of membrane 10. An inlet manifold 19 comrnunicates with anode chamber 17 and a suitable inlet conduit to permit introduction of hydrochloric acid. An outlet conduit 20 also comrnunicates with the anode chamber to permit the removal o~ spent anolyte as well as the gaseouselectrolysis product~ Anode current collector/fluid distributor 13 serves two purposes, ~ ~ 1 52EE ~:L7/312 it provides a path for electrical current to reach the anode electrode bonded to the underside o membrane 10, and it forms the ~luid containing and distributiny path to hold the aqueous hydrochloric feed stack and the chlorine gas.
Electrical contact to the bonded anode is made through the array of contact elements 18.
As may be readily seen in Figure 2, membrane lO has a cathode electrode 11 bonded to one side and an anode electrode 21 bonded to the other. These electrodes are physically bonded to membranes so as to form a unitary membrane electrode construction. That is, the electrode is physically part of the membrane and conforms dimensionally and physically to the membrane during operation of the cell. The membrane is preferably a permselective cation transporting membrane such as those sold by the Dupont Company under trade desiynation Nafion. Nafion is a sulfonated perfluorinated membrane (i.e., hydrated copolymers of polytetrafluoroethylene and polysulfonyl fluoride vinyl e~her with pendant sulfonic acid yroups) and i3 readily available in various equivalent weights and thicknesses. ~ ten mil thick Nafion 120 membrane, which has an equivalent weight of 1200, is perfectly adequate for use in the cell. The anode electrode is preferably a bonded agglomerate of catalytic particles, such as oxides of the platinum group metals i.e., ruthenium, iridium, palladium, etc., and a thermoplastic fluoropolymer such as Teflon* to form a liquid and a yas permeable electrode structure. The preferred catalytic particles are reduced, temperatures skabilized o~ides of a platinum group metal such as ruthenium or ruthenium *Trademark ~ ~ 52EB 3L7/312 and iridium in a suitable mixture. Reference is hereby made to U.S. Patent No. 4,191,618, issued March 4, 1980, Cooker et al, and assigned to General Electric Company, the assignee of the present invention, for a complete description of the manner of producing the catalytic electrode and a-ttaching it to the membrane. Contact elements 18 are pressed firmly against screens 14 and 15 which are interposed between the contact elements and the bonded electrodes. The cathode and anode screens shown in Figures 1 and 2 are optional and contact elements 18 may be positioned directly against the electrodes.
Screebs are slnetunes oreferred becayse tget distribute the current more evenly and also distribute the physical pressure on the electrodes more evenly so as to avoid corrugation or distortion of the membrane.
As may be seeIl in Figure 2 the anoly-te shown by the arrows 22 diffuses undernea-th contact surfaces 23 ~rom a~l aides so that the anolyte diffuses rapidly to the sur~ace of the anode electrode to maintain the desired chloride ion concentration so as to favor chlorine evolution.
Each contact element, as may be seen in Figure 2 and in Figure 1 consists of a square pedestal 24 which extends from the base of the anode chamber.
The top of the pedestal is chamfered to form a truncated pyramid 25 which has the flat contact surface 23 which presses against the screen or against -the electrode. Alternatively, the pedestal may be eliminated and the entire contact element may be in the form of a truncated pyramid.
The current collector i5 preferably a molded 3~
52EE 31'7/~12 aggregate, of conductive graphite particles and a thermoplastic fluoropolymer such as polyvinylidene fluoride which is available from the Pennwalt Corpora-tion under its trade mark Kynar. Okher fluoropolymer resins such as tetrafluoroethylene, etc. may be utilized with equal facility although polyvinylidene fluoride is preferable as it is a low cast material and has a lower molding temperature (T = 590 - 630) than most other fluoropolymers.
The conductive and resin particles in the agglomerate may be present in a weight ratio of between 2.5:1 and 16:1 which results in a structure having a bulk resistivity of 1 - 3.5 x 10 3 ohm inches.
Figure 3 shows a partially broken away plan view of the bipolar current collector and 1uid distributor. In let manifold 19 allows introduction of an anolyte, such as hydrochloric acid, into anode chamber 17. The array of conductive elements 18 projects frorn the base o e the anode chamber, and as may be seen the contact surfaces 23 of elemen-ts 18 form a planar array. The incominy anolyte stream shown by arrows 26 is broken up into a plurality intersecting fluid streams. Turbulent flow is established in the fluld paths and the anolyke flows on all four sides of contact elements 18 so that diffusion paths are established around the entire perimeter. This in eEfect, reduces the dlffusion path length of the anolyte and produces the desired chloride ion concentration a-t the electrode even with anolyte concentrations or less than 9M.
The geometry of the contact elements is such that the perimeter to area ratio is hiyh and ~ 52EE 317/312 preferably in excess o~ a 100:1 ~or areas for which the contact area is 0.25 mils or less. The larger the ratio the more readily the anolyte is transported underneath the contact area thereby increasing the diffusive transport of HCl into the contact area and in effect reducing the diffusion path. A further advantage to an array of individual contact collectors i5 a greater degree of turbulence within the anode chamber. With a continuous rib geometry, flow of liquid and gas ~n constrained within the channels formed by the ribs and is essentially laminar flow;
with the contact desi~n such as shown in Figure l and 3 where there is an array of contac-ting elements, discontinuous in nature, a very large number of stream intersections are present which promote turbulent mixing and cavitation and result in a plurality of non-parallel i.e. intersectiny streams whi.ch consequently minimize HCl depletion at the electrocle surface directly beneath the contact elements.
EXAMPLES
Two cells were constructed which incorporated ion exchange membraneshaving catodes and anodes bonded thereto. The cells were operated to electrolyze aqueous hydrogen chloride, to determine the effect of a multiple current conductor array in terms of oxygen centent, hydrogen chloride vapor pressure~ and cell voltage at various temperatures and feedstock concentra-tions. The cells were constructed with a lO
mil Nafion 120 membrane. The anode was a 100 micron thick particulate mass of temperature stabilized, reduced oxides of platinum group metals, specifically 52~ 317/312 1~3~
ruthenium (47 5~ by weight) and iridium (5~ by weight), mixed with the Teflon* polytetrafluorethylene particles.
The anode had an active area of 0.05 ft2 and the loading was 4 milligrams/per cm2 of the platinum group catalyst and 1.3 milligrams per cm2 of Teflon*. The cathode was a platinum black Teflon* mixture. Both cells were fitted with 5 Mil niobium anode collector screens. A current collector with an array of individual contact elements was incorporated in Cell #1. The current collector was a compression molded graphite and 25~ polyvinylidene -fluoride (Kynar*) structure with 506 elements spaced at 60 mil intervals. Each element had a 20 mils square contact area (0.02 x 0.02 in.). The pedestal was 60 mils by 60 mils and the overall height was 60 mills.
A second cell was then constructed identical to Cell #1 except that 17 continuous parallel ribs were employed as the contact element of the current collector. The ribs were beveled at the top to a ~0 mil (0.020 inch) width with the ribs being 2614 mils (2.614 in.) in length. The cells were operated at a current density of 400 ASF with varying feed stock concentrations and at various temperatures to determine the oxygen content of the chlorine, the vapor pressures as well as the cell voltages. Table I
illustrates the effect of ~arying temperature and concentration on the oxygen content, vapor pressure and cell voltage for Cell #2 utilizing the continuous parallel rib configuration for the current collector.
*Trademarks ~; - 14 -~ 3~ 52EE 317/312 Feed Conc. Temp Cell Volkaye 2 Content HCl press (Molar~ (C) (volts) (Vol. %) (Torr.) ll.9 35 1.98 0.1 246 (.450 atmos) 10.5 60 1.78 0.013 450 (0.6 atmos) 7.9 60 1.78 0.41 30 (0.04 atmos) As may be seen from Table I, a high HCl concentration 10.5 M and a high cell temperature, 60C, results in a low 2 content (less than 0.1%) and a cell voltage of 1.78. However, -the vapor pressure of the hydrogen chloride under these conditions is 450 Torr or 0.6 of an atmosphere. It should be pointed out, khat continuous boiling o~f o~ the hydrogen chloride also results in a reduction in the concentration and ultimately in an increa~e in -the oxyyen content.
Mainkaining the temperature constant at 60C' but reducing the concentration to 7.9M resulted in an increase in the voltage to 1.86 volts due to a concentration polarization potential at the contact points as chloride ions are depleted and water is electrolyzed. Furthermore, the oxygen content in the chlorine increased to 0.41%. Thus, while the vapor pressure was reduced by reducing the concentration of the feed stock, a penalty is paid in increases in the oxygen content as well as in the cell voltage because of the concentration polarization as the chloride ion content is depleted. Operating the cell at 35C
using an 11.9M hydrochloric acid feed stock reduces the oxygen content, but the vapor pressure even at - ~ 52EE 317/312 ~i6~3~
this low temperature i5 in excess of 200 Torr and the cell voltage is increased to 1.98 volts. Thus, it can be seen that with a continuous rib configuration it is not possible to operate simultaneously with very low oxygen (less than 0.1%), high temperature (60-80C) and with low hydrogen chloride vapor pressures (i.e. less than 0.1 atmosphere).
Cell #l was then tested under various conditions to determine its operational characteristics at various oncentrations, and temperatures to ascertain effects on cell voltage, oxygen content, and vapor pressure.
Table II shows the results.
TABLE II
Feed Conc Temp Cell Voltage 2 Content HCl vapor Press.
(~olar) (OC) (vol-ts) (~ol. ~) (Torr) 10~3M 36 1.~0 0.1% 60 (0.08 atmos.) ~.4 60 1.75 0.01~ 55 (0.08 atmos) At 60C and with an anolyte feed concentration of 8.4M the cell voltage was 1.75V, the oxygen content-0~01% and the hydrogen chloride vapor pressure - 55 Torr (i.e. 0.08 atmospheres). Even at higher concentration and lower temperature performance is better than that of cell #1. Thus, it can be seen that with the point contact configuration the l'blinding" of the electrode in minimized, oxygen evolution is reduced even with feed acid concentrations less than 9M and even 8M or less. Thus, it is possible to minimize oxygen content in the chlorine stream, (below 0.1%) at high temperatures l~ g639L' 60~C or more with the atkendant improvemen-t in cell voltage, while at the same time malntaining lowe hydrogen chloride vapor pressures (less than 0.1 atmosphere). The latter, of course, minimizes the cost associated with purification of the chlorine as well as avoiding or minimizing the corrosive action of the gaseous hydroyen chloride on the cell as well as equipment downstream from the cell.
It is apparent from the foregoing that at current densities up to 400 ASF, the oxygen content may be held below 0.1~ (an 2 level at which there is no observable corrosion at the graphite cell compon~nts);
the cell temperature is 60C or greater and the HCl vapor pressure is at 76 Torr or less with a~ueous HCl concentrations oE less than 9M and preferably 8M or less. ~t will be obvious to the man skilled in the art that for any given current density above ~00 MAF, the feed acid concentration must be such that chloride ion conc~entrakion is adequate t~ support the current density so that oxygen being evolved does not exceed 1~ and preferably does not exceed 0.1% and without increasing hydrogen chloride vapor pressure excessively~
It will be obvious from the foregoing that an improved process and apparatus for electrolyzing halides such as hydroch]oric acid, has been described which minimizes oxygen coevolution with the chlorine, optimizes the cell voltage and minimizes boil off of hydrogen chloride gas by utilizing low concentration of the acid feed stock.
While the instant invention has been shown with certain preferred embodiments thereof, the ~11 ~ J 1 5~EE 3~7/312 invention is by no means limited thereto since other modifications of the instrumentalities employed and the steps of the process may be made and still fall within the scope of the invention. It is contemplated by the appended claims to cover any such modifications that fall within the true scope and spirit of this invention.
aqueous HCl solutions at high temperatues and low feed acid concentrations.
The production of chlorine by the elec-trolysis of aqueous solutions of halides in a cell comprising a~ermselective membrane having a conductive, catalytic electrode permanently affixed to the surface thereof and in physical contact with an external electron current distributor is described in Canadian Application Serial Number 315,516, filed October 31, 1978, in the name of Russell Mason Dempsey et al assigned to General Electric Company, the assignee of the present invention. Cells of this type include a graphite electron current distrlbutor which contacts the surface of the catalytic electrode bonded to the membrane. 5uch electron cwrrent collectors have a plurality o~ elongated, continuous, parallel ribs extending from a conducti~e base. The elongated ribs contact the catalytic electrode to distribute current while the channels formed between the ribs provide fluid distribution channels for the anolyte entering the cell as well as for gases evelved at the electrode. Continuo~s ribs may have the disadvantage of obstructing a relatively large area of the electrode thereby limiting access of the aqueous anolyte to the electrode at these locations.
Because of the obstruction or l'blinding" of areas of the bonded electrode, chloride ion s-tarvation under these areas can result in electrolysis of water and the evolution of oxygen.
~ 63~ 52EE 317/31~
Coevolution o~ oxygen at a chlorine anode has a number of practical consequences, all of them undesirable. The evolution of oxygen, of course, represents a process inefficiency and increases the electrical cost necessary for producing chlorine, i.e., increases the production cost of chlorine.
High oxygen levels also result in severe corrosion of graphite cell components. As pointed out previously, in an HCl electrolysis cell having anode electrodes bonded directly to an ion exchanging membrane, the preferred current collector fluid distributor is a molded graphite-polymer-aggregate having a plurality of parallel grooves which contact the electrode in order to provide current to the electrodes while distributing the anolyte and the electrolysis product at the anode.
If the oxygen level in the chlorine remains below 0.1%
(V/V) very little corrosion of the graphite is observed whereas levels in exce~s of 1~ (V/V) lead to severe corrosion in a matter of days. It is therefore highly desirable to maintain the oxygen level at or below 0.1%.
The discharge potential of oxygen, i.e., the standard electrode potential for 2' is actually lower than that o~ chlorine (1.23 vol-ts v. 1.36 volts).
~Iowever, the great irreversibility of oxygen electrodes (i.e. the overpotential for oxygen) permits preFerential evolution of chlorine despite these thermodynamic considerations. Thus, normally, chlorine is evolved prefercntially although oxygen evolution is no-t entirely suppressed. The oxygen evolution reaction can be inhibited by maintaining a high acid concentra-tion at the electro reaction site. By maintaining the ~63~ 52EE 317/312 chloride ion concen-tration suf~iciently high, chlorine di.scharge at the anode is facilitate,d.
The concentration of hydrochloria acid at any reaction si-te can be defi,ned by the expression:
R S FD
where i = the cell current density F = FARADAY
D = the HCl diffusion coefficient CS = the HCl concentration of the feed CR = the HCl concentration at the discharge site underneath the contact point between the electrode and the current collector l = the true diffusion path length for the HCl to the discharge site.
Thus, it may be seen the acid concentration at the reaction site, and hence the 2 :in C12 l~vel, is a function of both the diEfusion path length and the feed stock acid concentration.
The discharge site below a contact element of the current collector has a longer diffusion path than do the sites below the li~uid flow channel because the acid must diffuse laterally underneath the contact element and within and across the anode thickness to reach the electrode reaction site below a contact element, while the acid need only be diffused across the anode thickness to reach the discharge site below the flow channel. Because of the greater path length, the acid concenkration below the contact element is reduced and the rate of 2 evolution tends to increase.
~ 52EE 317/312 sy increasiny the acid concentration of the ~eed, (Cs) the chloride ion content beneath the contact element is maintained sufficiently high to minimize oxygen evolution even though the area is partially obstructed or "blinded". Thus, it is customary to operate with anolyte acid feed concentration in exess of 10M, preferably between 10 and 12~i to maintain the oxygen content in the chlorine at 0.1% or less.
While malntaining the feed stock acid concentration at very high levels is effective in reducing the oxygen evolution reaction, it has been found that it does have a number of shortcomings which make it less than on optimum solution. The problem is that the vapor pressure of hydrogen chloride, which is a gaseous material, is both a function of temperature and concentration. Its solubility in water is a logarithmic function of temperature. Operation of the cell at temperatures of 60C and above (which is desirable to minimize internal resistance, and electrode overpotential and maximize eleckrical efficiency) results in high hydrogen chloride partial pressures and impure chlorine product which must be purified. Thls expense is, of course, in addition to the undesirable corrosive effects of the hydrogen chloride orl the cell and downstream equipment. If the operating temperature of the cell is reduced (i.e., to 30-40 C) in order to maintain the hydrogen chloride vapor pressure at a reasonable level, the overpotential of the electrodes and internal ohmic loss increase~
and the power efficiency of the system decreases also resulting in hic~her chlorine production costs.
~ 52EE 317/312 Thus, presently known ~echniques to minimize oxygen evolution in chlorine cells by increasing the acid feed stock concentration result in high hydrogen chloride vapor pressures; in an impure chlorine product, in added expense due to purification costs and in potential-corrosion of equipment. Attempts to control the hydrogen chloride vapor pressure when operating with a high feed acid concentration by reducing the temperature do reduce the vapor pressure, but result in a substantial penalty in cell voltage because internal resistance and the electrode overpotential increase as the temperature is reduced.
~ pplicant has found now that it is possible to electrolyze aqueous hydrogen chloride with low oxygen evolution levels (less than 0.1%), at high te~peratures (60-80C) with low hydroyen chloride vapor pressures (less than 0.1 of an atmos~here, i.e. 76 Torr) by maintaining high chloride ion concentrations at the membrane electrode current collector contact area even with low feed acid concentration, i.e. acid concentration of less than 9M and preferably 8.5 or 8M or less.
Applicant has found that this may be achieved by minimizing the obstruction or "blinded" areas of the electrode and by maximizing diffusion of chloride to the "blinded" areas. To this end, a novel current collector construction is provided in which an array of contact elements is utilized in place of continuous parallel contact elements to establish a planar array of individual, unconnected current trans~er areas, preferably in the plane of the electrode. The incoming ~ ' 52EE 317/312 anolyte is broken up into a plurality vf intersecting anolyte streams which flow across the electrode surace.
The turbulent flow due to the intersecting skreams surround~the point contact elements, and the increased ~e}n~e~ exposed to anolyte permi ~ diffusion of the acid anolyte to take place ~r~ all sides of the contact elements. This reduces the diffusion path length so that the -i~ chloride~concentration beneath the ~ f~ l"
contact~may be maintained at a sufficiently high level to reduce oxygen evolution below 0.1% with feed acid concentrations of less than 9 molar. Because the cell is operated with lower feed acid concentrations, ` the cell may be operated at a much higher temperature ; (60C), without raising the hydrogen chloride vapor pressure to an undesirable level, (i.e. the vapor pressure is maintained at 0.1 atmosphere - 76 torr or less)~ By operating at temperatures o 60 and above the cell voltage is substantially reduced because at these temperatures the electrode over-potential and ohmic losses are substantially reduced.
It is thereore a principal objective of this invention to provide a method and apparatus for electrolyzing aqueous halides in which coevolution of oxygen at the anode is minimized while operating at temperatures which maximize the cell efficiency.
Yet another objective of the invention is to provide a process for generating halogen from an aqueous hydrogen halide in whiçh the vapor pressure of the halide is minimized at temperatures at which the cell is most efficient;
Yet another objective of the invention is to provide a process for generating chlorine from a ~6--~ ~ ~ 52E~ 317/312 hydrogen chloride with minimal coevolution of oxygen at low concentrations o~ the hydrogen halide anol~te.
Still another objective of the invention is to provide a cell for generating chlorine from aqueous hydrogen chloride in which the oxygen content of the chlorine is 0.1~ or less and the hydrogen ahloride vapor pressure is very low at cell operating temperatures o 60C or more.
Other objectives and advantages of the invention will become apparent as the description thereof proceeds.
In accordance with the invention, halogens such a chlorine, bromine and etc. are generated by the electrolysis of aqueous hydrogen halides at the anode of an electrolysis cell which includes an ion exchange membrane separaking a cell lnto catholyte and anolyte chambers. A thin, porous, gas permeable catalytic anode is rnaintained in intimate contack with the ion exchange membrane so as to bond it to the surface o~ the ion exchange membrane. A graphite electron current conducting distributor which includes a planar array of conductive projections contacts the bonded electrode at a plurality of points either directly or through the medium of an interposed conductive screen. By virtue of the multipoint contact array configuration, turbulent flow is established over the electrode as the incoming anolyte is divided into in a plurality of intersecting streams. The multiple anolyte streams surround the 0 con~act elements and maximize diffusion of the e ~ ~ r anolyte beneath the ~ urface and into contact with the chlorine evolving bonded electrode. In effect the ~ 5ZEE 317/312 diffusion path o the current conductor is decreased ; therehy maintaining the chloride ion concentration beneath the contacting element such that coevolution ; o~ oxygen is held at 0.1% by volume or less with low feed acid concentrations. The vapor pressure of the hydrogen chloride above the fluid is kept very low (less than 0.1 atmospheres) while operating the cell at 60C or above so that the overpotential of the electrode for chlorine evolution and separator resistance are minimized.
The novel features which are believed to be characteristic of the invention are set for with particularity in the appended claims. The invention itsel~, however, both as to its organization and - method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
Figure l is an exploded perspective view o~
an electrolyæer cell utilizing a novel current collector in which the processes to be described herein can be performed.
Figure 2 is partial sectional view showing the membrane, electrode and a plurality of contact elements of the current collector.
Figure 3 is a plan view of the current collector and its planar array of contact elements illustrating the flow fields for the anolyte with the multiple contact array construction of the current collector.
The cell assembly of Figure 1 includes an ion transporting permselectlve mer~rane lO, preferably a i :~31 52EE 317/31~
cation permselective membrane, that separates the cell into anode and cathode chambers. A yas permeable cathode electrode 11, pre~erably in the form of a layer of electrocatalytic particles and particles of a polymeric binder such as polytetrafluorethylene, is bonded to the upper surface of ion transporting membrane 10. A gas and liquid permeable anode, not shown, which may similarly be a mass of catalytic and polymeric particles, is bonded to and in intimate contact with the other side of membrane 10. The cell assembly is clamped between cathode current collecting end plate 12 and current collector 13 which are respectively connected to the terminals of the cell power cupply. Although a single cell unit is shown for convenience, current collec-tor 13 may be bipolar and used as a current conducting separator element between cell units. Niobium current distributing screen elements 1~ and 15 are optionally positioned between membrane 10 cln~ ano~ curren~ collector fluid distributing element 13 and endplate 12 respectively.
Collector 13 which is a molded graphite and fluorocarbon composite consists of a main body 16, a chamber 17 within the main body, and of an array of conductive contact elements 18 which contact either screen 15 or the anode electrode bonded to the underside of membrane 10. An inlet manifold 19 comrnunicates with anode chamber 17 and a suitable inlet conduit to permit introduction of hydrochloric acid. An outlet conduit 20 also comrnunicates with the anode chamber to permit the removal o~ spent anolyte as well as the gaseouselectrolysis product~ Anode current collector/fluid distributor 13 serves two purposes, ~ ~ 1 52EE ~:L7/312 it provides a path for electrical current to reach the anode electrode bonded to the underside o membrane 10, and it forms the ~luid containing and distributiny path to hold the aqueous hydrochloric feed stack and the chlorine gas.
Electrical contact to the bonded anode is made through the array of contact elements 18.
As may be readily seen in Figure 2, membrane lO has a cathode electrode 11 bonded to one side and an anode electrode 21 bonded to the other. These electrodes are physically bonded to membranes so as to form a unitary membrane electrode construction. That is, the electrode is physically part of the membrane and conforms dimensionally and physically to the membrane during operation of the cell. The membrane is preferably a permselective cation transporting membrane such as those sold by the Dupont Company under trade desiynation Nafion. Nafion is a sulfonated perfluorinated membrane (i.e., hydrated copolymers of polytetrafluoroethylene and polysulfonyl fluoride vinyl e~her with pendant sulfonic acid yroups) and i3 readily available in various equivalent weights and thicknesses. ~ ten mil thick Nafion 120 membrane, which has an equivalent weight of 1200, is perfectly adequate for use in the cell. The anode electrode is preferably a bonded agglomerate of catalytic particles, such as oxides of the platinum group metals i.e., ruthenium, iridium, palladium, etc., and a thermoplastic fluoropolymer such as Teflon* to form a liquid and a yas permeable electrode structure. The preferred catalytic particles are reduced, temperatures skabilized o~ides of a platinum group metal such as ruthenium or ruthenium *Trademark ~ ~ 52EB 3L7/312 and iridium in a suitable mixture. Reference is hereby made to U.S. Patent No. 4,191,618, issued March 4, 1980, Cooker et al, and assigned to General Electric Company, the assignee of the present invention, for a complete description of the manner of producing the catalytic electrode and a-ttaching it to the membrane. Contact elements 18 are pressed firmly against screens 14 and 15 which are interposed between the contact elements and the bonded electrodes. The cathode and anode screens shown in Figures 1 and 2 are optional and contact elements 18 may be positioned directly against the electrodes.
Screebs are slnetunes oreferred becayse tget distribute the current more evenly and also distribute the physical pressure on the electrodes more evenly so as to avoid corrugation or distortion of the membrane.
As may be seeIl in Figure 2 the anoly-te shown by the arrows 22 diffuses undernea-th contact surfaces 23 ~rom a~l aides so that the anolyte diffuses rapidly to the sur~ace of the anode electrode to maintain the desired chloride ion concentration so as to favor chlorine evolution.
Each contact element, as may be seen in Figure 2 and in Figure 1 consists of a square pedestal 24 which extends from the base of the anode chamber.
The top of the pedestal is chamfered to form a truncated pyramid 25 which has the flat contact surface 23 which presses against the screen or against -the electrode. Alternatively, the pedestal may be eliminated and the entire contact element may be in the form of a truncated pyramid.
The current collector i5 preferably a molded 3~
52EE 31'7/~12 aggregate, of conductive graphite particles and a thermoplastic fluoropolymer such as polyvinylidene fluoride which is available from the Pennwalt Corpora-tion under its trade mark Kynar. Okher fluoropolymer resins such as tetrafluoroethylene, etc. may be utilized with equal facility although polyvinylidene fluoride is preferable as it is a low cast material and has a lower molding temperature (T = 590 - 630) than most other fluoropolymers.
The conductive and resin particles in the agglomerate may be present in a weight ratio of between 2.5:1 and 16:1 which results in a structure having a bulk resistivity of 1 - 3.5 x 10 3 ohm inches.
Figure 3 shows a partially broken away plan view of the bipolar current collector and 1uid distributor. In let manifold 19 allows introduction of an anolyte, such as hydrochloric acid, into anode chamber 17. The array of conductive elements 18 projects frorn the base o e the anode chamber, and as may be seen the contact surfaces 23 of elemen-ts 18 form a planar array. The incominy anolyte stream shown by arrows 26 is broken up into a plurality intersecting fluid streams. Turbulent flow is established in the fluld paths and the anolyke flows on all four sides of contact elements 18 so that diffusion paths are established around the entire perimeter. This in eEfect, reduces the dlffusion path length of the anolyte and produces the desired chloride ion concentration a-t the electrode even with anolyte concentrations or less than 9M.
The geometry of the contact elements is such that the perimeter to area ratio is hiyh and ~ 52EE 317/312 preferably in excess o~ a 100:1 ~or areas for which the contact area is 0.25 mils or less. The larger the ratio the more readily the anolyte is transported underneath the contact area thereby increasing the diffusive transport of HCl into the contact area and in effect reducing the diffusion path. A further advantage to an array of individual contact collectors i5 a greater degree of turbulence within the anode chamber. With a continuous rib geometry, flow of liquid and gas ~n constrained within the channels formed by the ribs and is essentially laminar flow;
with the contact desi~n such as shown in Figure l and 3 where there is an array of contac-ting elements, discontinuous in nature, a very large number of stream intersections are present which promote turbulent mixing and cavitation and result in a plurality of non-parallel i.e. intersectiny streams whi.ch consequently minimize HCl depletion at the electrocle surface directly beneath the contact elements.
EXAMPLES
Two cells were constructed which incorporated ion exchange membraneshaving catodes and anodes bonded thereto. The cells were operated to electrolyze aqueous hydrogen chloride, to determine the effect of a multiple current conductor array in terms of oxygen centent, hydrogen chloride vapor pressure~ and cell voltage at various temperatures and feedstock concentra-tions. The cells were constructed with a lO
mil Nafion 120 membrane. The anode was a 100 micron thick particulate mass of temperature stabilized, reduced oxides of platinum group metals, specifically 52~ 317/312 1~3~
ruthenium (47 5~ by weight) and iridium (5~ by weight), mixed with the Teflon* polytetrafluorethylene particles.
The anode had an active area of 0.05 ft2 and the loading was 4 milligrams/per cm2 of the platinum group catalyst and 1.3 milligrams per cm2 of Teflon*. The cathode was a platinum black Teflon* mixture. Both cells were fitted with 5 Mil niobium anode collector screens. A current collector with an array of individual contact elements was incorporated in Cell #1. The current collector was a compression molded graphite and 25~ polyvinylidene -fluoride (Kynar*) structure with 506 elements spaced at 60 mil intervals. Each element had a 20 mils square contact area (0.02 x 0.02 in.). The pedestal was 60 mils by 60 mils and the overall height was 60 mills.
A second cell was then constructed identical to Cell #1 except that 17 continuous parallel ribs were employed as the contact element of the current collector. The ribs were beveled at the top to a ~0 mil (0.020 inch) width with the ribs being 2614 mils (2.614 in.) in length. The cells were operated at a current density of 400 ASF with varying feed stock concentrations and at various temperatures to determine the oxygen content of the chlorine, the vapor pressures as well as the cell voltages. Table I
illustrates the effect of ~arying temperature and concentration on the oxygen content, vapor pressure and cell voltage for Cell #2 utilizing the continuous parallel rib configuration for the current collector.
*Trademarks ~; - 14 -~ 3~ 52EE 317/312 Feed Conc. Temp Cell Volkaye 2 Content HCl press (Molar~ (C) (volts) (Vol. %) (Torr.) ll.9 35 1.98 0.1 246 (.450 atmos) 10.5 60 1.78 0.013 450 (0.6 atmos) 7.9 60 1.78 0.41 30 (0.04 atmos) As may be seen from Table I, a high HCl concentration 10.5 M and a high cell temperature, 60C, results in a low 2 content (less than 0.1%) and a cell voltage of 1.78. However, -the vapor pressure of the hydrogen chloride under these conditions is 450 Torr or 0.6 of an atmosphere. It should be pointed out, khat continuous boiling o~f o~ the hydrogen chloride also results in a reduction in the concentration and ultimately in an increa~e in -the oxyyen content.
Mainkaining the temperature constant at 60C' but reducing the concentration to 7.9M resulted in an increase in the voltage to 1.86 volts due to a concentration polarization potential at the contact points as chloride ions are depleted and water is electrolyzed. Furthermore, the oxygen content in the chlorine increased to 0.41%. Thus, while the vapor pressure was reduced by reducing the concentration of the feed stock, a penalty is paid in increases in the oxygen content as well as in the cell voltage because of the concentration polarization as the chloride ion content is depleted. Operating the cell at 35C
using an 11.9M hydrochloric acid feed stock reduces the oxygen content, but the vapor pressure even at - ~ 52EE 317/312 ~i6~3~
this low temperature i5 in excess of 200 Torr and the cell voltage is increased to 1.98 volts. Thus, it can be seen that with a continuous rib configuration it is not possible to operate simultaneously with very low oxygen (less than 0.1%), high temperature (60-80C) and with low hydrogen chloride vapor pressures (i.e. less than 0.1 atmosphere).
Cell #l was then tested under various conditions to determine its operational characteristics at various oncentrations, and temperatures to ascertain effects on cell voltage, oxygen content, and vapor pressure.
Table II shows the results.
TABLE II
Feed Conc Temp Cell Voltage 2 Content HCl vapor Press.
(~olar) (OC) (vol-ts) (~ol. ~) (Torr) 10~3M 36 1.~0 0.1% 60 (0.08 atmos.) ~.4 60 1.75 0.01~ 55 (0.08 atmos) At 60C and with an anolyte feed concentration of 8.4M the cell voltage was 1.75V, the oxygen content-0~01% and the hydrogen chloride vapor pressure - 55 Torr (i.e. 0.08 atmospheres). Even at higher concentration and lower temperature performance is better than that of cell #1. Thus, it can be seen that with the point contact configuration the l'blinding" of the electrode in minimized, oxygen evolution is reduced even with feed acid concentrations less than 9M and even 8M or less. Thus, it is possible to minimize oxygen content in the chlorine stream, (below 0.1%) at high temperatures l~ g639L' 60~C or more with the atkendant improvemen-t in cell voltage, while at the same time malntaining lowe hydrogen chloride vapor pressures (less than 0.1 atmosphere). The latter, of course, minimizes the cost associated with purification of the chlorine as well as avoiding or minimizing the corrosive action of the gaseous hydroyen chloride on the cell as well as equipment downstream from the cell.
It is apparent from the foregoing that at current densities up to 400 ASF, the oxygen content may be held below 0.1~ (an 2 level at which there is no observable corrosion at the graphite cell compon~nts);
the cell temperature is 60C or greater and the HCl vapor pressure is at 76 Torr or less with a~ueous HCl concentrations oE less than 9M and preferably 8M or less. ~t will be obvious to the man skilled in the art that for any given current density above ~00 MAF, the feed acid concentration must be such that chloride ion conc~entrakion is adequate t~ support the current density so that oxygen being evolved does not exceed 1~ and preferably does not exceed 0.1% and without increasing hydrogen chloride vapor pressure excessively~
It will be obvious from the foregoing that an improved process and apparatus for electrolyzing halides such as hydroch]oric acid, has been described which minimizes oxygen coevolution with the chlorine, optimizes the cell voltage and minimizes boil off of hydrogen chloride gas by utilizing low concentration of the acid feed stock.
While the instant invention has been shown with certain preferred embodiments thereof, the ~11 ~ J 1 5~EE 3~7/312 invention is by no means limited thereto since other modifications of the instrumentalities employed and the steps of the process may be made and still fall within the scope of the invention. It is contemplated by the appended claims to cover any such modifications that fall within the true scope and spirit of this invention.
Claims (13)
1. A process of generating halogens which comprises, a) electrolyzing an aqueous halide between an anode and a cathode electrode separated by a permselective, liquid and gas impervious ion exchanging membrane, said anode being bonded to the membrane to provide a gas and liquid permeable electrode which forms part of a unitary electrode-membrane structure, b) applying potential to the anode through a separate electron current conducting structure to introduce electron current flow to the bonded anode at a plurality of discrete areas on the surface of the anode, c) establishing turbulent anolyte flow conditions over the surface of the anode to maintain the chloride ion concentration at the discrete areas of the anode at a level to minimize chloride ion starvation and oxygen evolution at the operating current density to maintain the oxygen content of the evolved halogen below 1%.
2. The process according to Claim 1 wherein the oxygen content of the evolved halogen is maintained below 0.1%.
3. The process according to Claim 1 wherein the aqueous halide anolyte is brought into contact with the anode over a plurality of intersecting fluid paths defined by the elements for introducing current to the anode to maximize the chloride ion concentration between the said elements and the discrete areas of the anode surface.
4. The process according to Claim 3 wherein the oxygen content of the evolved halogen is maintained below 0.1% and the cell is operated at temperatures in excess of 60°C.
5. The process according to Claim 4 wherein the halide vapor pressure in the evolved halogen is less than 0.1 atmosphere (76 Torr).
6. A process of generating chlorine which comprises, a) electrolyzing aqueous hydrogen chloride between an anode and a cathode separated by liquid and gas impervious cation exchange membrane, with the anode being gas and liquid permeable and bonded to the membrane to form a unitary membrane and electrode structure.
b) applying potential to the cell and introducing electron current flow to the anode at a plurality of discrete, areas on the surface thereof through discrete conductive elements of a separate electron current conducting structure, c) flowing the aqueous hydrogen chloride anolyte through said current conducting structure to establish a plurality of intersecting anolyte streams flowing on all sides of the discrete elements to maximize diffusion of anolyte between the discrete elements to minimize oxygen evolution and maintain the oxygen content below 1%.
b) applying potential to the cell and introducing electron current flow to the anode at a plurality of discrete, areas on the surface thereof through discrete conductive elements of a separate electron current conducting structure, c) flowing the aqueous hydrogen chloride anolyte through said current conducting structure to establish a plurality of intersecting anolyte streams flowing on all sides of the discrete elements to maximize diffusion of anolyte between the discrete elements to minimize oxygen evolution and maintain the oxygen content below 1%.
7. The process according to Claim 6 wherein the oxygen content is maintained below 0.1% with the hydrogen chloride concentration less than 9 molar and the operating temperature in excess of 60°C.
8. The process according to Claim 6 wherein the hydrogen chloride concentration is adequate to maintain the oxygen content below 0.1 percent and the vapor pressure below 0.1 atmospheres (76 Torr) at cell temperature of 60°C or greater.
9. A halogen electrolysis unit comprising a) an anode and cathode chamber divided by an ion transporting membrane, b) anode and cathode electrodes in the anode and cathode chambers with the anode bonded to the membrane to form a unitary anode-membrane structure, c) a flow distributing, current collector positioned in the anode chamber, said current collector comprising a conductor plate, an array of discrete, conductive elements projecting from said plate to said anode to define a plurality of intersecting fluid flow paths, each of said conductive elements having contact surfaces to thereby form a planar array of contact surfaces for current conduction to the bonded anode, d) means for establishing an electrical potential between the cathode and the anode through said current collector, e) means to introduce an aqueous anolyte into the chamber to produce flow through said collector to break the anolyte into a plruality of intersecting streams which surround the conductive projections to maximize anolyte diffusion between the planar array of contact surfaces and the adjacent anode electrode areas and minimize oxygen evolution.
10. The cell according to Claim 9 wherein the current collector is a molded graphite-polymer aggregate.
11. The cell according to Claim 9 wherein a conductive element is interposed between the discrete, individual conductive projections and the anode bonded to the membrane.
12. The cell according to Claim 9 wherein the ratio of perimeter to area of the contact area of each projection is at least 100 to 1.
13. The cell according to Claim 10 wherein the planar contact area of each projection is the top of a truncated pyramid.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000382438A CA1179631A (en) | 1981-07-24 | 1981-07-24 | Hc1 electrolyzer with unitary membrane-electrode structure with discrete anode projections |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000382438A CA1179631A (en) | 1981-07-24 | 1981-07-24 | Hc1 electrolyzer with unitary membrane-electrode structure with discrete anode projections |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1179631A true CA1179631A (en) | 1984-12-18 |
Family
ID=4120521
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000382438A Expired CA1179631A (en) | 1981-07-24 | 1981-07-24 | Hc1 electrolyzer with unitary membrane-electrode structure with discrete anode projections |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1179631A (en) |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5411641A (en) * | 1993-11-22 | 1995-05-02 | E. I. Du Pont De Nemours And Company | Electrochemical conversion of anhydrous hydrogen halide to halogen gas using a cation-transporting membrane |
| US5798036A (en) * | 1993-11-22 | 1998-08-25 | E. I. Du Pont De Nemours And Company | Electrochemical conversion of anhydrous hydrogen halide to halogens gas using a membrane-electrode assembly or gas diffusion electrodes |
| US5824199A (en) * | 1993-11-22 | 1998-10-20 | E. I. Du Pont De Nemours And Company | Electrochemical cell having an inflatable member |
| US5855759A (en) * | 1993-11-22 | 1999-01-05 | E. I. Du Pont De Nemours And Company | Electrochemical cell and process for splitting a sulfate solution and producing a hyroxide solution sulfuric acid and a halogen gas |
| US5855748A (en) * | 1993-11-22 | 1999-01-05 | E. I. Du Pont De Nemours And Company | Electrochemical cell having a mass flow field made of glassy carbon |
| US5863395A (en) * | 1993-11-22 | 1999-01-26 | E. I. Du Pont De Nemours And Company | Electrochemical cell having a self-regulating gas diffusion layer |
| US5868912A (en) * | 1993-11-22 | 1999-02-09 | E. I. Du Pont De Nemours And Company | Electrochemical cell having an oxide growth resistant current distributor |
| US5961795A (en) * | 1993-11-22 | 1999-10-05 | E. I. Du Pont De Nemours And Company | Electrochemical cell having a resilient flow field |
| US5976346A (en) * | 1993-11-22 | 1999-11-02 | E. I. Du Pont De Nemours And Company | Membrane hydration in electrochemical conversion of anhydrous hydrogen halide to halogen gas |
| US6042702A (en) * | 1993-11-22 | 2000-03-28 | E.I. Du Pont De Nemours And Company | Electrochemical cell having a current distributor comprising a conductive polymer composite material |
| US6180163B1 (en) | 1993-11-22 | 2001-01-30 | E. I. Du Pont De Nemours And Company | Method of making a membrane-electrode assembly |
| USRE37433E1 (en) | 1993-11-22 | 2001-11-06 | E. I. Du Pont De Nemours And Company | Electrochemical conversion of anhydrous hydrogen halide to halogen gas using a membrane-electrode assembly or gas diffusion electrodes |
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1981
- 1981-07-24 CA CA000382438A patent/CA1179631A/en not_active Expired
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US5411641A (en) * | 1993-11-22 | 1995-05-02 | E. I. Du Pont De Nemours And Company | Electrochemical conversion of anhydrous hydrogen halide to halogen gas using a cation-transporting membrane |
| US5580437A (en) * | 1993-11-22 | 1996-12-03 | E. I. Du Pont De Nemours And Company | Anode useful for electrochemical conversion of anhydrous hydrogen halide to halogen gas |
| US5798036A (en) * | 1993-11-22 | 1998-08-25 | E. I. Du Pont De Nemours And Company | Electrochemical conversion of anhydrous hydrogen halide to halogens gas using a membrane-electrode assembly or gas diffusion electrodes |
| US5824199A (en) * | 1993-11-22 | 1998-10-20 | E. I. Du Pont De Nemours And Company | Electrochemical cell having an inflatable member |
| US5855759A (en) * | 1993-11-22 | 1999-01-05 | E. I. Du Pont De Nemours And Company | Electrochemical cell and process for splitting a sulfate solution and producing a hyroxide solution sulfuric acid and a halogen gas |
| US5855748A (en) * | 1993-11-22 | 1999-01-05 | E. I. Du Pont De Nemours And Company | Electrochemical cell having a mass flow field made of glassy carbon |
| US5863395A (en) * | 1993-11-22 | 1999-01-26 | E. I. Du Pont De Nemours And Company | Electrochemical cell having a self-regulating gas diffusion layer |
| US5868912A (en) * | 1993-11-22 | 1999-02-09 | E. I. Du Pont De Nemours And Company | Electrochemical cell having an oxide growth resistant current distributor |
| US5961795A (en) * | 1993-11-22 | 1999-10-05 | E. I. Du Pont De Nemours And Company | Electrochemical cell having a resilient flow field |
| US5976346A (en) * | 1993-11-22 | 1999-11-02 | E. I. Du Pont De Nemours And Company | Membrane hydration in electrochemical conversion of anhydrous hydrogen halide to halogen gas |
| US6042702A (en) * | 1993-11-22 | 2000-03-28 | E.I. Du Pont De Nemours And Company | Electrochemical cell having a current distributor comprising a conductive polymer composite material |
| USRE36985E (en) * | 1993-11-22 | 2000-12-12 | E. I. Du Pont De Nemours And Company | Anode useful for electrochemical conversion of anhydrous hydrogen halide to halogen gas |
| US6180163B1 (en) | 1993-11-22 | 2001-01-30 | E. I. Du Pont De Nemours And Company | Method of making a membrane-electrode assembly |
| USRE37042E1 (en) * | 1993-11-22 | 2001-02-06 | E. I. Du Pont De Nemours And Company | Electrochemical conversion of anhydrous hydrogen halide to halogen gas using a cation-transporting membrane |
| US6203675B1 (en) | 1993-11-22 | 2001-03-20 | E. I. Du Pont De Nemours And Company | Electrochemical conversion of anhydrous hydrogen halide to halogen gas using an electrochemical cell |
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