Abstract
This invention is a method and apparatus for operating electrochemical reactors with multi-phase feeds, in which a liquid feed stream is dispersed in a second fluid to form a spray, mist or emulsion before entering the reaction zone. The invention is applicable to both electro-synthesis and fuel cell reactors, with particular utility in mixed-reactant fuel cells.
Claims
1. A method of operating a continuous mixed reactant fuel cell reactor or a continuous Swiss roll mixed reactant fuel cell reactor, having an electrochemical reaction zone, the method comprising the step of dispersing a liquid reactant in a gas or liquid as it enters said electrochemical reaction zone of the reactor.
2. The method of claim 1 wherein said method comprising dispersing said liquid reactant in said gas to form a spray or mist, said spray or mist entering said electrochemical reaction zone of the reactor.
3. The method of claim 1 wherein said reactor comprises a continuous Swiss-roll mixed reactant fuel cell reactor, the method comprising the step of dispersing said liquid reactant in said gas to form a spray or mist, said spray or mist entering said electrochemical reaction zone of said reactor.
4. The method of claim 3 in which the volumetric gas to liquid feed ratio of said gas and said liquid reactant is in the range of 10 to 1000.
5. The method of claim 1 wherein said reactor comprises a continuous Swiss-roll mixed reactant fuel cell reactor, and wherein said gas and said liquid are immiscible with said liquid reactant such that when said liquid reactant is dispersed in said gas or said liquid an emulsion is formed, said emulsion entering said electrochemical reaction zone of said reactor.
6. The method of claim 1 wherein said electrochemical reactor is a multi-cell reactor.
7. The method of claim 6 wherein said multi-cell reactor comprises either single cells, monopolar cell stacks, or bipolar cell stacks with adjacent single cells, monopolar cell stacks or bipolar cell stacks respectively.
8. The method of claim 6 wherein said multi-cell reactor has an electrode arrangement comprising: at least two sandwich arrangements, each sandwich arrangement comprising at least two deformable electrodes, first insulating means for preventing electronic contact between said at least two electrodes and second insulating means for preventing electronic contact between one of said at least two deformable electrodes and other conducting parts of said reactor, said at least two sandwich arrangements being rolled around an axis in spaced separation from one another inside an electronically conductive cylinder; and wherein said axis and said cylinder are both longitudinally segmented by electronic insulators to allow for bipolar operation of cells of said reactor.
9. An apparatus for operating a continuous mixed reactant fuel cell reactor or a continuous Swiss roll mixed reactant fuel cell reactor that includes a dispersal device for dispersing a liquid reactant in either a gas to form a spray or mist, or in a liquid to form an emulsion, said spray, mist or emulsion being fed into an electrochemical reaction zone of said reactor.
10. The apparatus of claim 9 wherein said dispersal device comprises a spray nozzle, a mixing nozzle or an in-line mixer.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings and wherein:
(2) FIG. 1 shows a conventional continuous single-cell electrochemical reactor with separate anode and cathode compartments, fed with a liquid reactant dispersed in a non-reactive gas.
(3) FIG. 2 shows a continuous electrochemical reactor with multiple parallel plate cells operating in series with respect to fluid flow. In this case a reactant liquid is dispersed into gas in the mixed feed stream entering the reactor and flows through porous fluid distributors that provide the electronic contact between adjacent bipolar cells.
(4) FIG. 3 shows a continuous cylindrical Swiss-roll electrochemical reactor, where a reactant liquid is dispersed into the top of the reactor body, using a spray nozzle driven by a reactant gas. The reactant fluids (liquid and gas) then flow in parallel through the fluid distributor(s) of a single cell or of multiple bipolar cells wound on a central mandrel.
(5) FIG. 4 shows a variation of FIG. 3 in which both reactants are fed to the reactor as liquids that are mutually immiscible.
(6) FIG. 5 shows a combination of FIGS. 3 and 4 involving a three-phase fluid (L/L/G) system. Here the immiscible liquid reactant(s), optionally with a non-reactive liquid carrier, are premixed to form a L/L dispersion (e.g. an emulsion) then flow to a gas/liquid nozzle for delivery as a spray to the electrochemical reactor.
(7) FIG. 6 shows the experimental set up for a Swiss-roll mixed reactant fuel cell electrochemical reactor.
(8) FIG. 7 is a graph showing the effect of temperature (A) and oxidant (B) on the Swiss-roll mixed reactant fuel cell electrochemical reactor without a feed sprayer nozzle.
(9) FIG. 8 is a graph showing the effect of temperature (A) and oxidant (B) on the Swiss-roll mixed reactant fuel cell electrochemical reactor with a feed sprayer nozzle.
(10) FIG. 9 is a graph showing the polarization and superficial power density for a Swiss-roll mixed reactant fuel cell electrochemical reactor with and without the presence of a sprayer nozzle.
(11) FIG. 10 is a graph showing the polarization and superficial power density for a Swiss-roll mixed reactant fuel cell electrochemical reactor with a sprayer nozzle.
(12) FIG. 11 shows the configuration of the bipolar Swiss-roll mixed reactant fuel cell electrochemical reactor with 3 cell rolls in series. In this case each cell roll may be a single cell (as in FIG. 1) or a multi-cell stack (as in FIG. 2) with electrodes and counter electrodes in electronic contact respectively with an electronically conductive mandrel and an electronically conductive external pipe which function as current collectors. Additionally, the reactor may be fed by a single fluid dispersion device (e.g. spray nozzle) or by multiple such devices, as required to distribute the reactants within the reactor.
(13) FIG. 12 is a graph showing the polarization and superficial power density for a bipolar Swiss-roll mixed reactant fuel cell electrochemical reactor with sprayer feed nozzle.
DETAILED DESCRIPTION OF THE INVENTION
(14) The preferred embodiments relate to continuous electrochemical reactors used to generate electricityso-called fuel cells and to continuous electrochemical reactors used for the electro-synthesis of chemicals.
(15) In fuel cell applications the fuel and oxidant reactants are in separate phases, with fuel in a liquid phase and oxidant in a gas phase, or vice-versa, or with fuel and oxidant respectively in immiscible liquid phases.
(16) Liquid phase fuels may be water soluble inorganic compounds such as ammonia, hydrazine and sodium borohydride, as well as organics, such as methanol, ethanol, propanol, ethylene glycol, glycerol, formic acid, sodium formate, formaldehyde, urea, dimethyl ether and the C4 to C8 alkanes and aliphatic alcohols. In general the fuels should have an electrochemical redox potential below about 0.5 Volt relative to a corresponding oxidant and preferably an electro-oxidation standard exchange current density above about 1E-3 A/m.sup.2 at 25 C. on an appropriate electrocatalyst.
(17) Liquid phase oxidants may be water soluble inorganic compounds such as hydrogen peroxide, persalts and metal ions in high valence state such as Fe(III), V(IV) and Cr(VI), as well as organics such as dimethyl dioxyrane and organo-peracids and peroxides that are soluble in water and/or non-aqueous solvents. Liquid phase oxidants can include solutions of gas phase oxidants in organic solvents such as octane and perfluorinated hydr(oxy)carbons. In general the oxidants should have an electrochemical redox potential above about 0.5 Volt, relative to a corresponding fuel and preferably an electro-reduction standard exchange current density above about 1E-3 A/m.sup.2at 25 C. on an appropriate electrocatalyst.
(18) In the case of liquid reactants the terms reactant fuel and oxidant are intended here to apply to both the pure reactants and to their solutions in aqueous or non-aqueous media, which may also contain non-reactive electrolytes.
(19) Gas phase fuels may be gases or vapours such as hydrogen, ammonia, hydrocarbons such as methane, ethane, and the like, sulphur dioxide and volatile organics such as those listed above for liquid fuels.
(20) Exemplary gas phase oxidants are chlorine, nitrous oxide, nitrogen dioxide, oxygen and ozone.
(21) In general a gas phase fuel or oxidant should have an electrochemical redox potential respectively below 0.5 Volt and above 0.5 Volt relative to a corresponding counter reactant, preferably with a standard exchange current density for electrooxidation or electro-reduction on an appropriate electrocatalyst above about 1E-3 A/m.sup.2 at 25 C.
(22) Non-reactive gases can be, for example, nitrogen, carbon dioxide or in some cases, air.
(23) Appropriate electrocatalysts include those well known in the prior art, for example: for fuelsplatinum, ruthenium, palladium, osmium, nickel and perovskites with associated transition metals. for oxidantsplatinum, gold, silver, transition metal oxides, perovskites and macrocyclic organo-metal compounds such as cobalt and iron porphyrins and phthalocyanines.
(24) Considering the application of this invention to fuel cell (continuous) electrochemical reactors:
(25) FIG. 1 shows a conventional fuel cell [1] in which the liquid fuel or oxidant [2] is contacted with a non-reactive gas [3] in spray nozzle [4] to form a gas/liquid dispersion [5] that enters (respectively) the anode or cathode chamber [6] and leaves in product stream [7]. The anode or cathode chamber [6] is electronically isolated from the corresponding cathode or anode chamber [8] by an ion conducting separator [9], positioned to prevent contact between the supporting oxidant or fuel [10], which leaves in product stream [11].
(26) FIG. 2 shows an unconventional mixed-reactant fuel cell [12] such as that described in Oloman, C., Mixed-reactant flow-by fuel cell, GB2474202B 18 Jul. 2012. Here the liquid fuel or oxidant [13] is contacted with a complimentary gas oxidant or fuel [14] in a spray nozzle [15] and the gas/liquid dispersion [16] enters and passes through the fuel cell [12] via a porous fluid distributor [17] providing electronic contact between electrodes [18] and counter-electrodes [19] in adjacent electrochemical cells. In each electrochemical cell the electrode (anode or cathode) [18] is electronically isolated from the corresponding counter-electrode (cathode or anode) by an ionically conducting separator [20] and the mixed reaction products leave the reactor in the product stream [21].
(27) FIG. 3 illustrates an unconventional cylindrical Swiss-roll mixed-reactant fuel cell [22] such as that described in Aziznia, A., Oloman, C., Gyenge, E., A Swiss-roll mixed-reactant fuel cell, J.Power Sources, 212,(2012),154-160. Here the liquid fuel or oxidant [23] is contacted with a complimentary gas oxidant or fuel [24] in a spray nozzle [25] and the gas/liquid dispersion [26] enters and passes through the fuel cell spool [27] to leave the reactor as a mixed reaction product in the product stream [28]. The gas to liquid volumetric ratio of the gas to liquid dispersion [26] may be in the range of about 10 to 1000. The spooled cells have flexible components that are assembled as in FIG. 1 or FIG. 2, with an electrode, counter-electrode, electronically conductive porous fluid distributor and ionically conductive separator. Electric current is drawn from the reactor by the electronically conductive outer tube wall [29] and central mandrel [30], respectively in contact with the electrode and counter-electrode.
(28) FIG. 4 shows a Swiss-roll mixed-reactant fuel cell [31] where the liquid fuel or oxidant [32] is contacted with a complimentary immiscible (immiscible means mutually insoluble) liquid oxidant or fuel [33] in a spray nozzle [34] and the liquid/liquid dispersion [35] enters and passes through the fuel cell spool [36] to leave the reactor in the product stream [37]. The spooled cells have flexible components that are assembled as in FIG. 1 or FIG. 2, with an electrode, counter-electrode, electronically conductive porous fluid distributor and ionically conductive separator. Electric current is drawn from the reactor by the electronically conductive outer tube wall [38] and central mandrel [39], respectively in contact with the electrode and counter-electrode.
(29) FIG. 5 represents a Swiss-roll mixed-reactant fuel cell [40] where a liquid fuel or oxidant [41] is contacted with an immiscible liquid oxidant or fuel [42] in a liquid/liquid contacting device [43] to form a liquid/liquid dispersion [44] which is subsequently contacted with a reactive or non-reactive gas [45] in spray nozzle [46] to form a gas/liquid dispersion [47] that enters and passes through the fuel cell spool [48] to leave the reactor in the product stream [49]. The spooled cells have flexible components that are assembled as in FIG. 1 or FIG. 2, with an electrode, counter-electrode, electronically conductive porous fluid distributor and ionically conductive separator. Electric current is drawn from the reactor by the electronically conductive outer tube wall [50] and central mandrel [51], respectively in contact with the electrode and counter-electrode.
(30) In electro-synthesis applications FIGS. 1 to 5 illustrate how the appropriate dispersion of the reactor feed(s) may be used in processes with multi-phase reactants.
(31) FIG. 1 shows a divided cell electro-synthesis reactor [1], where the liquid anode or cathode reactant [2] is contacted with a reactive or non-reactive gas [3] in a spray nozzle [4] to give a gas/liquid dispersion [5] that is fed to the anode or cathode [6] which is electronically isolated from the counter catholyte or anolyte [8] by an ionically conductive separator [9] and discharged in product stream [7]. The complimentary cathode or anode reactant feed [10] is discharged in product stream [11]. Such an arrangement may apply, for example, to the electro-reduction of sulphur dioxide (gas) to aqueous dithionite and to the electro-reduction of carbon dioxide (gas) to aqueous formate.
(32) FIGS. 2 and 3 illustrate respectively parallel plate and Swiss-roll electrochemical reactors [12],[22] with undivided cells, where liquid reactants [13],[23] are contacted with reactant or non-reactant gases [14],[24] in spray nozzles [15],[25] to give gas/liquid dispersions [16],[26] that enter and pass through the reactors via porous fluid distributors [17] providing electronic contact between electrodes [18] and counter-electrodes [19] in adjacent electrochemical cells. In each electrochemical cell the electrode (anode or cathode) [18] is electronically isolated from the corresponding counter-electrode (cathode or anode) by an ionically conducting separator [20] and the mixed reaction products leave the reactors in the product streams [21],[28]. Electric current is fed to the reactors via electronically conductive contacts with the terminal electrodes [12],[29] and counter-electrodes [19],[30]. Such an arrangement may apply, for example, to operation with a single electrolyte in electro-synthesis reactors with undivided cells, such as in the production of adiponitrile from acrylonitrile and of peroxide by electro-reduction of oxygen.
(33) FIGS. 4 and 5 represent the application of the present invention to electro-synthesis in liquid/liquid (L/L) systems.
(34) FIG. 4 shows a Swiss-roll electrochemical reactor [31] where liquid reactant [32] is contacted with an immiscible liquid reactant or non-reactant [33] in a mixing nozzle and the consequent L/L dispersion [35] passes into and through coiled electrochemical cell(s) [36] into the product stream [37]. Electric current is fed to the reactor via electronically conductive contacts with the terminal electrode [38] and counter-electrode [39].
(35) FIG. 5 shows a Swiss-roll electrochemical reactor [40] where a liquid reactant [41] is contacted with an immiscible liquid reactant or non-reactant [42] in mixing nozzle [43] and the consequent L/L dispersion [44] flows to spray nozzle [45] where it is contacted with a reactive or non-reactive gas [46]. The consequent gas/liquid/liquid (G/L/L) dispersion [47] passes into and through coiled electrochemical cell(s) [48] into the product stream [49]. Electric current is fed to the reactor via electronically conductive contacts with the terminal electrode [50] and counter-electrode [51].
(36) The arrangements of FIGS. 4 and 5 may be applied, for example, in electro-synthetic processes such as the direct electro-reduction or electro-oxidation of organics (e.g. nitro-alkanes or aromatics) in aqueous acid, electrochemical organic halogenations and electrochemically mediated oxidation or reduction of organics, such as the oxidation of naphthalene to naphthaquinone via the Ce(IV)/Ce(III)(aq) redox couple. These reactions are carried out in L/L emulsions, generated, for example, by the L/L mixing nozzles in FIGS. 4 and 5. In some situations fine L/L emulsions are counterproductive due to the difficulty of the subsequent phase separation, but this problem may be relieved by the mixing nozzle design, respecting the drop size and phase/volume ratio.
(37) The arrangements of FIGS. 4 and 5 may also be applied to electrochemical field-assisted separations; for example, in the separation of salty water from liquid organics by electrodialysis.
(38) A bipolar Swiss-roll mixed reactant fuel cell electrochemical reactor with 3 cell rolls in series is illustrated in FIG. 11. Each cell roll may be a single cell (as in FIG. 1) or a multi-cell stack (as in FIG. 2) with electrodes and counter electrodes in electronic contact respectively with an electronically conductive mandrel and an electronically conductive external pipe which function as current collectors. Additionally, the reactor may be fed by a single fluid dispersion device (e.g. spray nozzle) or by multiple such devices, as required to distribute the reactants within the reactor. The anodes of the individual [cells/stacks/bipolar stacks] are electronically connected to but ionically separated from the cathodes of adjacent [cells/stacks/bipolar stacks], as exemplified in FIG. 11. In Figure lithe ionic separation is done by the gaps between the cells 1, 2 and 3, in which the ionic conductor (i.e. electrolyte) should be discontinuous to prevent ionic conduction between the cells. That discontinuity is given by the 2-phase flow in which 1 phase (e.g. a gas) is an ionic insulator. Each cell in FIG. 11 can be a single cell roll (FIG. 1) or a multi-cell roll of bipolar cells (FIG. 2). The electronic insulators in FIG. 11 force the electric current to flow in series through the 3 cells, to set up the bipolar operation in which the total voltage between the external anode (bottom mandrel) and cathode (top pipe) is theoretically the sum of the individual cell voltages.
EXAMPLES
(39) As detailed in Aziznia et al., a continuous Swiss-roll mixed-reactant fuel cell (SRMRFC) reactor was set up as in FIG. 6, with a single monopolar cell having electrodes 20 mm wide by 100 mm long rolled onto a 10 mm diameter stainless steel mandrel and inserted in a 250 mm ID gold plated (inside) SS pipe. This reactor was operated with feed of liquid fuel [1 M NaBH.sub.4(aq)+2 M NaOH(aq)], mixed with a gas oxidant (O.sub.2(g)). Experimental results from this apparatus are given below in Examples 1, 2 and 3 (FIGS.7,8,9 and 10). In another set of trials the SRMRFC was used in a multi-cell bipolar reactor, as described in Example 4 and shown in FIGS. 11 and 12.
Example 1
(40) Here the flowing liquid fuel and gas oxidant were mixed at a T junction and passed directly into the top of the reactor as a two-phase stream in a 3mm ID stainless steel tube protruding to about 50 mm above the top face (inlet) of the coiled cell. FIG. 7 shows performance curves for this reactor over a range of temperatures, using Pt/C anode catalysts coupled with an MnO.sub.2/C cathode catalyst. The peak superficial power density measured here was about 871 W/m.sup.2, at 323 K.
Example 2
(41) As in Example 1 the flowing liquid fuel and gas oxidant were mixed at a T junction, but in this case the two-phase mixture was passed through a spray nozzle inside the reactor, with its outlet located about 2 cm above the top face (inlet) of the coiled cell. Again a Pt/C anode catalyst was coupled with an MnO.sub.2/C cathode catalyst, and operated under the same conditions as in Example 1. FIG. 8 shows performance curves for this reactor at 323 K, giving a maximum superficial power density of about 2250 W/m.sup.2.
(42) The performance of SRMRFC with and without utilizing the feed sprayer nozzle is compared in FIG. 9. As shown in FIG. 9, higher open circuit potential and also the 3 fold increase in maximum superficial power density from Example 1 to Example 2 is attributed to the use of the feed spray nozzle, which distributes the fuel more uniformly over the anode and facilitates access of the oxidant gas to the cathode of the SRMRFC. This uniform distribution of fuel and oxidant also suppresses flooding and mixed-potential on the cathode. Except for the presence and absence of the sprayer feed nozzle, all other operating and reactor conditions were kept constant for FIG. 9.
Example 3
(43) A SRMRFC reactor was set up and operated with a feed sprayer nozzle as in Example 2, except that in this case the fuel and oxidant were respectively a solution of [1M methanol with 2 M NaOH] and nitrous oxide (N.sub.2O) gas. FIG. 10 shows the reactor performance curves for Example 3, with a peak superficial power density of 22 Wm.sup.2 at 200 Am.sup.2.
(44) Example 4
(45) A SRMRFC reactor was set up as in FIG. 11, for bipolar operation with both 2 and 3 of the single cells of Examples 1 and 2 connected in series with respect to both electric current and fluid flow. As shown in FIG. 11 and discussed above, an important aspect of this bipolar configuration is that the individual cells 1, 2 and 3 are connected electronically to each other via the central mandrel and outer pipe, but are ionically insulated from each other by an open space in which the ionically conductive electrolyte liquid is present as a discontinuous dispersion in the flowing (non-conductive) gas.
(46) Note also that while the three cells of Example 4 were spooled single cells (as in FIG. 1), the cells in FIG. 11 may be either spooled single cells or spooled bipolar cell stacks (as in FIG. 2).
(47) In the present case the fuel and oxidant were respectively [0.5 M NaBH.sub.4 with 2 M NaOH] liquid solution and oxygen gas. FIG. 12 shows the bipolar reactor performance with spooled single cells, in which 3 cells in series gave a peak power output of about 2 W.
(48) While specific examples are provided above, it is understood that the teachings of the invention apply to other reactors as discussed above. In its practical application an important aspect of the invention concerns the design of the integrated system of the dispersion device with a given electrochemical reactor. This is due to the fact that the conditions of the reactant dispersion affect the performance of the reactor. Hence one skilled in the art will understand that the design of a given reactor incorporating a dispersion device should account for such factors as the reactant flow rate(s), phase volume ratio, interfacial tension and droplet diameter(s), along with the pressure and temperature change across the dispersion device, distance of the dispersing device from the reaction zone and the suppression of droplet coalescence in relation to the path of the reactant dispersion through the reactor. These things are relevant with respect to the reactant distribution, mass transfer rates, temperature profile, parasitic power consumption and other factors that determine the performance of continuous electrochemical reactors.
(49) While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention.
