Abstract:
Systems are described for the “on-site” production of substantial amounts of carbon dioxide and hydrogen. The systems include a stack of multiple electrochemical cells, which decompose organic carboxylated compounds into CO 2  and H 2  without leaving any residue. From a bench-top small generator, producing about 1 lb of CO 2  per day to a large-scale generator producing 1 ton of CO 2  per day, the process is essentially identical. 
     Oxalic acid, either anhydrous or in its dihydrate form, is used to efficiently generate the gases. The energy required is less than 0.3 Kilowatt-hours per lb of CO 2  generated. Individual cells operate at less than 1.2 volts at current densities in excess of 0.75 amps/cm 2 . CO 2  production rates can be controlled either through voltage or current regulation. Metering is not required since the current sets the gas production rate. These systems can competitively replace conventional compressed CO 2  gas cylinders.

Description:
[0001]    This application claims the priority of U.S. Provisional Patent Application No. 60/765,392 filed Feb. 3, 2006. 
     
    
     TECHNICAL FIELD  
       [0002]    Commercial carbon dioxide (CO 2 ) is generally manufactured by separation and purification from CO 2 -rich gases produced by combustion or biological processes. It is also found in underground formations in some U.S. states. 
         [0003]    CO 2  is commercially available as high-pressure cylinder gas (about 300 psig), refrigerated liquid or as a solid (dry ice). 
         [0004]    Common uses of CO 2  include fire extinguishing systems, carbonation of soft drinks and beer; freezing of food products, refrigeration and maintenance of environmental conditions during transportation of food products, enhancement of oil recovery from wells, materials production (plastics, rubber), treatment of alkaline water, etc. 
       Applications Include: 
       [0000]    
       
         
           
             shield during welding where it protects the weld against oxidation 
             dry ice pellets for sand blasting surfaces, without leaving residues 
             in the chemical processing industry, such as methanol production 
             priming oil wells to maintain pressure in the oil formation 
             removing flash from rubber or plastic objects by tumbling with dry ice 
             creation of inert blankets or environments 
             carbonation of soft drinks, beers and wine 
             preventing fungal and bacterial growth 
             as an additive to oxygen for medical use—as a propellant in aerosol cans 
             maintaining a level of 1000 ppm in green houses to increase production yields of vegetables, flowers, etc. 
           
         
       
     
         [0015]    To meet the needs of these various applications, requiring from small quantities of CO 2  (less than a pound/day) to extremely large quantities (tons/day), CO 2  is available as:
       a compressed gas requiring heavy cylinders, or a liquid under pressure available from tube or liquid trailers, or as solid dry ice.       
 
         [0017]    Very small users rely on high pressure cylinders. Their distribution is generally conducted by locally-focused businesses that buy the gas in bulk liquid form and package it at their facilities. 
         [0018]    Small to medium size customers truck-in bulk liquid products that are then processed through evaporation to produce the gas. 
         [0019]    Larger customers&#39; needs are often met with “tube trailers”, i.e. bundles of high-pressure cylinders mounted on wheeled platforms. 
         [0020]    “Onsite” plants are usually installed by customers consuming more than 10 tons/day of the gas. 
         [0021]    There is an increasing interest in user-owned, small, non-cryogenic gas generators, in many markets. Such generators are available for oxygen, hydrogen and nitrogen, but not for carbon dioxide. 
         [0022]    For example, small to medium size users of oxygen or nitrogen may find an economical supply alternative in pressure-swing-adsorption (PSA) plants. Or again, hydrogen and oxygen may be produced through electrolysis of water. High purity hydrogen may then be produced by purification of the stream by using palladium foil diffusers. 
         [0023]    The benefits of these “on-site” generators are multiple: generation on demand, as needed independence from suppliers and possible supply interruptions cost-insensitivity to supply issues no need for pressure vessels, their storage and recycling Etc. 
         [0024]    To-date, “on-site” economical carbon dioxide generators, such as are available for hydrogen and oxygen, do not exist, although the demand for carbon dioxide is substantial 
       SUMMARY AND OBJECTS OF THE INVENTION  
       [0025]    It is the primary object of this invention to provide for an “on-site” generator of carbon dioxide which can controllably generate substantial quantities of carbon dioxide, that does not require a combustion or biological process, while producing carbon dioxide on demand in an economical manner. 
         [0026]    It is another object of this invention to provide “on-site” systems capable of generating mixed CO 2  and H 2  streams or streams of the purified gases. 
         [0027]    The applicant has invented an electrolytic process and method to produce carbon dioxide from organic acids that were originally described in U.S. Pat. Nos. 6,780,304 B1 and 6,387,228 B1. He has pursued the development of that generation technology by developing multiple electrochemical cells assembled in stacks to achieve production rates and volumes much larger than those described in these patents. 
     
    
     
       DESCRIPTION OF THE DRAWINGS  
         [0028]      FIG. 1  is a schematic front perspective view of a multi-cell generator stack for producing carbon dioxide and hydrogen from oxalic acid, an organic acid; 
           [0029]      FIG. 2A  is an exploded perspective view of the various components that make up individual cells; 
           [0030]      FIG. 2B  is an enlarged schematic front elevation view of an electrochemical cell; 
           [0031]      FIG. 3  is a side elevation view of the principal components of a self-contained carbon dioxide generation system; 
           [0032]      FIGS. 4A  is a schematic cross sectional view of a first version of a multi-cell stack inter-cell connection that generates a mixture of carbon dioxide and hydrogen; 
           [0033]      FIG. 4B  is a schematic cross sectional view of a second version of a multi-cell stack inter-cell connection that (separately) generates carbon dioxide and hydrogen streams; 
           [0034]      FIG. 5  is a schematic cross sectional view of a carbon dioxide generation system in which the hydrogen is allowed to electrochemically react with air within the generator, thereby decreasing the energy required to operate the system; 
           [0035]      FIG. 6  is a schematic illustration of a carbon dioxide generator producing mixed carbon dioxide and hydrogen and where the mixture is processed externally to the system to generate pure carbon dioxide and pure hydrogen; 
           [0036]      FIGS. 7A  is a schematic illustration of a first single cell generator releasing CO 2  and H 2  separately; 
           [0037]      FIGS. 7B  is a schematic illustration of a second single cell generator releasing CO 2  and H 2  separately; 
           [0038]      FIG. 8  is a schematic view of a multi-cell CO 2  generator where one of the generated gases, CO 2  or H 2 , is collected separately from the other; 
           [0039]      FIG. 9  is a partially exploded schematic view showing the assembly steps of a generator allowing for gas separation; and 
           [0040]      FIG. 10  is an exploded schematic perspective view of the individual components used to assemble a gas collection chamber. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0041]    The novel multi-cell generators will now be described by referring to  FIGS. 1-10  of the drawings. The same structural members in the various embodiments will be identified by the same numerals. 
         [0042]    The multi-cell generator  15  of  FIG. 1  consists of five individual electrochemical cells  17  kept under compression and alignment by means of four separators  18 . Two stack end plates  20  are placed at opposite ends of the stack and put under compression by means of four compression rods  21 . End plates  20  are perforated plates (plastic or metal) to allow access of the organic acid to, and gas evolution from, the electrode surfaces of the electrochemical cells. Each individual cell  17  has current collectors  23  with flaps  24 . Flaps  24  of appropriate length, provide means to interconnect the various current collectors  23 . The complete stack is immersed in a (super-saturated) solution of an organic carboxylated acid such as oxalic acid. 
         [0043]      FIG. 2A  is a schematic representation of single electrochemical cell  17  that includes an ionic conductor  26  “sandwiched” between two electrodes  27  (see  FIG. 2B ) and two current collectors  23 . Ionic conductor  26  has a left outer surface  22  and a right outer surface  25 . Separators  18  consisting of four arms  28  are interlocked by means of grooves  29  and tongues  30 , which provides for a rigid structure similar to a human vertebral column and disks. Electrodes  27  can either be situated on each side of ionic conductor  26  or can be integrated within the current collectors  23 . If the organic solution is an adequate proton carrier it becomes its own ionic conductor and integral electrode/current collectors can be used. In all instances described herein, the ionic conductor is a proton exchange membrane conducting protons from electrode to electrode. Proton exchange membranes of this type are available as Nafion films from DuPont &amp; Co. 
         [0044]    The size of electrochemical cells  17  can vary from sub-cm 2  areas, as described in a co-pending patent application, to m 2  as used for brine electrolysis. The examples discussed later in the description make use of this wide range of sizes. 
         [0045]    Current collectors  23  are open-mesh structures that allow easy access of the carboxylated acid solution to the electrodes and they provide for a low resistance path for electron transfer from the external circuit. In some instances a dual current collector is used, i.e. a thin screen is embedded in the electrode and a thicker current collector is maintained in tight contact with the screen. 
         [0046]      FIG. 3  is a side view of a multi-cell generator stack  32  attached to a container lid  34 . Means of attachment to the lid are bent collector flaps  24  which are connected to terminals  36  The lid  34  is securely attached to the container body  37  by means of four lid attachment screws  38 . Lid  34  also holds seal  40  that ensures a gas tight container. Inter-cell connections  42  are achieved by using short threaded rods  43  and nuts  44  and these combinations provide for low inter-cell connection resistance. A gas exit line  46  and port  47  allow for gas generated within the container  37  to exit the sealed system. During operation the stack is completely immersed in the acid solution. 
         [0047]      FIGS. 4A and 4B  illustrate different interconnections between electrodes to achieve either mixing of gases or gas separation In  FIG. 4A  adjacent current collectors  23  from two cells  17  are interconnected at  42  and the counter current collectors  23  become cathode C and anode A. Both cells are immersed in solution  49  in chamber  45  of container  48  with the liquid level  50  preferably completely covering the electrodes. A source of electrical current  51  (usually a battery) is connected to an electrical circuit  54  having a switch  58 . Electrical circuit  54  is connected between cathode C and anode A. 
         [0048]    In  FIG. 4B  alternate current collectors  23  are connected at  52  resulting in H 2  gas being generated at adjacent electrodes. In this arrangement H 2  evolves at facing electrodes and is evacuated through gas exit port  53 . Since H 2  evolution does not require the presence of the organic acid solution, the chamber  55  between the electrodes can be sealed off by top wall  56  and bottom wall  57  to create a watertight secondary container  59 . This embodiment has an electrical circuit  60 . 
         [0049]      FIG. 5  is a modification of  FIG. 4B . In this instance, port  62  is provided to allow air to be injected into the H 2  generation chamber  55 . Two of the alternate current collectors  23  are connected at  64 . The other two current collectors are connected at  66 . Electrical circuit  68  is connected between cathode C and anode A. The oxygen from the air acts as a depolarizer (see equation  3 ) thereby preventing the formation of H 2 . Air injected in the hydrogen evolution cavity  55  will react electrochemically with protons, thereby reducing the energy (voltage) required to perform the electrolytic process. 
         [0050]      FIG. 6  is a schematic representation of a complete system, including the DC power source  51 , acid feeder sub-system  70  (hopper) to feed carboxylic acid to the generator  72  and external processing unit  74 . The hopper is filled either with solid oxalic acid or oxalic acid contained in water permeable bags from which the acid can be dissolved and moved into the generator container by means of conduit and feed port  73  placed below the liquid level  50  of the aqueous oxalic acid solution  49 . By maintaining the liquid level  50  above the feed port the acid is progressively dissolved and can migrate to the electrochemical generator  72 . 
         [0051]    When the DC power supply  51  is connected to the electrochemical stack by means of switch  58  and power lines  75 , CO 2  and H 2  are generated and transported by means of conduit  77  to gas processing unit  74  where the gases are separated and released as H 2  through conduit  78  and CO 2  through conduit  79 . Water entrained by the gas stream is recovered by means of condenser/scrubber  80  and recycled to the generator  72  by means of conduit  81 . 
         [0052]      FIGS. 7A and 7B  illustrate the concept of a single-cell electrolyzer allowing for separate recovery of CO 2  and H 2 . In  FIG. 7A , a single electrochemical cell  17 , incorporated in partition  82  forms two distinct chambers  84 A and  84 B, is immersed in oxalic acid solution  49 . Partition  82  does not filly extend to the bottom of container  85  to allow for liquid motion between compartments without allowing gases to escape into adjacent chambers. Two separate gas exit ports  87 A and  87 B are provided to allow separate exits for CO 2  and H 2 . In  FIG. 7B , partition  89  completely separates container  85 . Since the H 2  evolution does not require the presence of oxalic acid solution, the solution is only provided in compartment  84 A, partially defined by the oxalic acid decomposition electrode. In this instance also the gases are released through two different exit lines  87 A and  87 B. 
         [0053]    In  FIG. 8  one of the gases can be collected in a separate collection chamber within the multi-cell electrolyzer  90 . Either CO 2  or H 2  can be collected separately. For the sake of this description, we have assumed that H 2  is the separated gas while CO 2  is allowed to bubble freely in, and from, the solution. The generator  90  consists of five separate H 2  collection chambers  92  (and therefore 10 electrochemical cells), releasing H 2  from evacuation lines  93 , merging into a single H 2  gas exhaust line  94 . Each individual H 2  chamber assembly  91  is bolted together by means of nuts and bolts  96 , as a single subassembly. These subassemblies are separated from each other by means of perforated separators  97 . The separators are perforated to allow gas to freely move upward from the solution. The complete generator structure  90  is bolted together by means of compression rods  21 , nuts  44  and end plates  20 . The compression rods and separators are used to maintain good electrical contact between current collectors  23  and the electrode surfaces. This is particularly important when cells operate at high current densities, i.e. 2 amps/cm 2 . Current collectors  23  (four for each H 2  chamber) are electrically connected in a manner such that each individual cell in the chambers releases H 2  whereas each individual counter-electrode releases CO 2 . In operation, the complete structure is submerged into the oxalic acid solution. 
         [0054]      FIG. 9  shows that each H 2  chamber assembly  91  is an autonomous unit progressively stacked between end plates  20 . Each separator  97  fits within a cavity of the H 2  chamber end plates  99 . 
         [0055]    In  FIG. 10 , the H 2  compartment  92  consists of two end plates  99  and  100  and an elastomeric center plate  102 , all of which are perforated with 8 holes  103 , four of which are used for the compression rods and four of which are used to bolt the individual chambers together. End plates  99  have cavities or central apertures  98 . Center plate  102  is further provided with a gas exit line  93 . To assemble the unit, first separator  105 , provided with perforated arms  106  to allow free flow of H 2  in the chamber, is located within the cavity  108  of the center plate  102 . Then current collectors  23  are placed on both sides of the separator, their perforated flaps  24  fitting within the groove  110  of the center plate  102 . Current collectors  23  can be either a perforated metal or a metal screen that allows free flow of gases away from the electrodes  112  of electrochemical cells  17 . The electrochemical cells are placed against the current collectors  23 . A H 2  chamber  92  is thereby defined by two electrochemical cells and a center plate  102 . Finally, current collectors  23  are placed on top of cells  17 , respectively. All components are bolted together to form a H 2  collection chamber  92 . An internal seal is achieved by using end plates  99  and  100  to compress the outer ring of electrochemical cells  17  against the elastomeric center plate  102 . Simultaneously, the end plates  99  and  100  also compress the flaps  24  of current collectors  23  against the elastomeric center plate  102 . Separators  97  fit within the cavity  98  of end plates  100 . When compressed with compression rods  21  the end plates apply a load onto current collectors  23  to achieve a good electrical contact with the electrodes of the electrochemical cell. The function of separator  97  is to prevent the cells from bending, an action which would increase the internal resistance. Since the generator may be required to operate under high current loads it is essential that internal resistances be kept at a minimum to reduce the generator voltage. 
         [0056]    The ease and simplicity of controlling the process was illustrated by an experiment with an AC/DC converter, rated at 3.3 amps, maximum, (input 100-240 volts AC, 47-63 Hz, 0.7 amps), that was directly connected to the generator terminals, without additional current and/or voltage regulation. A steady-state operating condition of 2.85 amps, 4.94 volts and a generator temperature of 55 degree Celsius were observed. This type of “desk-top” generator is capable of producing over 300 liters of CO 2  per day (more than 1 lb/day). 
         [0057]    Oxalic acid is the preferred carboxylic acid for the generation of CO 2 . Either anhydrous oxalic acid (COOH) 2  or the dihydrate (COOH) 2 .2H 2 O can be used for the generator. 
         [0058]    By activating switch  33 , a current is applied to the electrochemical stack immersed in the aqueous oxalic acid solution. 
         [0000]      The anode reaction is: (COOH) 2 →2CO 2 +2H + +2 e   −   Eqn. 1 
         [0000]      The cathode reaction is: 2H + +2 e   − →H 2    Eqn. 2 
         [0059]    The generation of H 2  can be beneficially used as an independent gas stream, or evolve simultaneously with CO 2  to create an anaerobic gas mixture of 66.7% CO 2  and 33.3% of H 2 . 
         [0060]    Whenever H 2  is not beneficially used, the cathode reaction can be mitigated by using an air depolarized cathode, i.e. supplying oxygen or air to the cathode chamber such that reaction of eqn. 2 now becomes: 
         [0000]      2H + +2 e   − +½O 2 →H 2 O   Eqn. 3 
         [0000]    and the electrochemical decomposition process results solely in the production of CO 2  and water.
 
The following materials compositions options are available:
 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Organic Acid 
                 A. H2 recovery 
                 B. H2 Consumption 
               
               
                   
               
             
             
               
                 1. Oxalic acid anhydrous 
                 2 CO 2  + H 2   
                 2 CO 2  + H 2 O 
               
               
                 2. Oxalic acid dihydrate 
                 2 CO 2  + H 2  + 2H 2 O 
                 2 CO 2  + 3 H 2 O 
               
               
                   
               
             
          
         
       
     
       Processes  1 A and  2 A allow for H 2  recovery 
     Processes  1 B and  2 B allow for oxidation of H 2  to water to reduce process energy needs. 
       [0061]    In instances where water is a rare commodity, oxalic acid dihydrate can be substituted for anhydrous oxalic acid. The dihydrate (COOH) 2 .2H 2 O contains about 28.5% of water by weight that is released during the electrolytic process. The generation of CO 2  does not require any additional water, except possibly when immediate full rated output is required. However, even then, only a minimum of water is required to solubilize the oxalic acid to allow access of the solution to the generation electrodes. 
         [0062]    Since heating of the acid solution or slurry increases the oxalic acid solubility, it is beneficial to insulate the generator to allow its operation at higher temperatures, which results in a substantial reduction of the specific power requirements, i.e. kilowatts/(lb of CO 2 /hr). 
         [0063]    The electrolytic process can also be conducted under pressure, which can be beneficial for the recovery of water and the separation of CO 2  from H 2 . 
         [0064]    The generator systems described so far produce CO 2  and H 2 . In some instances the streams do not need separation, in others it is essential to generate high purities of each constituent. 
         [0065]    Whenever separation is desired, multiple processes are available to achieve that result. 
         [0000]    Some of these are briefly described in the following:
       compression with the possible result that liquid or solid CO 2  is produced, while H 2  is released as a gas;   absorption by a solution where CO 2  is preferentially extracted and H 2  is released; then through a secondary process CO 2  is released;   adsorption by a material such as metal powders that preferentially produce a metal hydride which can be recovered by heating the metal;   membrane separation where a passive process based on a partition coefficient either preferential to CO 2  or H 2  is used to enrich the gas streams;   thin metal (Palladium) foil separation of hydrogen;   electrochemical extraction of H 2  from the gas stream, releasing nearly pure CO 2  and H 2 .   Hydrogen-hydrogen cells are extremely efficient and able to carry loads in excess of 5 amps/cm 2 . Such an electrochemical H 2 -H 2  cell has been described by Maget in U.S. Pat. No. 3,489,670.       
 
         [0073]    If H 2  is undesirable either in the CO 2  gas stream or as a by-product, H 2  can be converted into thermal energy in the following manners:
       catalytic combustion of hydrogen to produce water, or   electrochemical oxidation of H 2  to water in presence of air. The by-product of his process is   the generation of power that can be used to reduce the energy needed to generate CO 2 . This process is illustrated in example 5.       
 
         [0077]    The electrochemical process is DC driven. Power sources can be either AC-DC converters, batteries or solar photovoltaic cells, that are well suited for this process since they also operate at low voltages and high currents. 
       EXAMPLE 1 
       [0078]    A single cell is placed in a container holding supersaturated oxalic acid dihydrate in form of a slurry. The cell, having a surface area of 8.3 cm 2  is connected to a DC power supply. The following table summarizes some observed currents and voltages displayed by the cell, at 25° C.: 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Production 
                   
               
               
                   
                 Rate of CO 2   
               
             
          
           
               
                 Cell current, amps 
                 Cell voltage, volts 
                 Liters/hr 
                 lbs/day 
               
               
                   
               
               
                 1.5 
                 1.06 
                 1.3 
                 0.13 
               
               
                 3.0 
                 1.20 
                 2.7 
                 0.26 
               
               
                 4.0 
                 1.30 
                 3.6 
                 0.35 
               
               
                 5.0 
                 1.44 
                 4.5 
                 0.44 
               
               
                 6.0 
                 1.64 
                 5.5 
                 0.53 
               
               
                   
               
             
          
         
       
     
       A single cell would be adequate to satisfy the needs of the small, occasional user. 
       [0079]    The limiting current is in excess of 6 amps (0.75 amp/cm 2 ). The current limits are caused by diffusion polarization of the slurry to the electrode surface. By mixing the slurry higher currents can be achieved. The second parameter affecting the performance of the stack is the slurry temperature. At room temperature the oxalic acid solubility in water is approximately 10 wt %, increasing rapidly as temperature increases, thus decreasing diffusion polarization, an observation readily noticeable when the generator, operating at fixed current, is allowed to heat up, resulting in a decrease in cell voltage. 
         [0080]    Experiments were conducted with the 5-cell stack of example 2, thermally insulated to allow operation at elevated temperatures, without the need for additional heat source. We have, generally observed that the stack voltage decreases by 43 millivolts for each degree Celsius of temperature rise. 
         [0000]    At an operating temperature of 60 degrees Celsius, the following conditions were recorded: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Stack current 
                 Stack voltage 
               
               
                   
                 Amps 
                 volts 
               
               
                   
                   
               
             
             
               
                   
                 1.0 
                 2.37 
               
               
                   
                 2.0 
                 3.50 
               
               
                   
                 3.0 
                 4.20 
               
               
                   
                 4.0 
                 4.60 
               
               
                   
                 5.0 
                 5.00 
               
               
                   
                 6.0 
                 5.33 
               
               
                   
                   
               
             
          
         
       
     
       These results represent about 27% power consumption reduction over room temperature operation. 
     EXAMPLE 2 
       [0081]    A 5-cell stack, essentially in the form of  FIG. 3 , is placed in a container holding supersaturated oxalic acid, in form of a slurry. The cells having a surface area of 8.3 cm 2  each, are inter-connected in series and then connected to a DC power supply. The following results are obtained: 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Cell 
                   
                 Carbon dioxide 
                   
               
               
                 current 
                 Stack voltage 
                 generation 
                 Power consumption 
               
             
          
           
               
                 Amps 
                 volts 
                 rate, Liters/hr 
                 lbs/day 
                 kilowatt/(lbCO 2 /hr) 
               
               
                   
               
             
          
           
               
                 1.16 
                 4.10 
                 5.2 
                 0.5 
                 0.24 
               
               
                 1.82 
                 4.73 
                 8.2 
                 0.8 
                 0.26 
               
               
                 2.18 
                 4.95 
                 9.8 
                 1.0 
                 0.27 
               
               
                 2.65 
                 5.20 
                 12.0 
                 1.2 
                 0.28 
               
               
                 3.00 
                 5.35 
                 13.7 
                 1.3 
                 0.29 
               
               
                 4.00 
                 5.80 
                 18.2 
                 1.8 
                 0.31 
               
               
                 5.00 
                 6.37 
                 22.8 
                 2.3 
                 0.34 
               
               
                   
               
             
          
         
       
     
         [0082]    A small 5-cell stack would be adequate to satisfy he needs of small users consuming less than 2.5 lbs of CO 2 /day. 
         [0000]    Note that by a current adjustment the production rate is changed over a substantial dynamic range. Therefore a simple potentiometer would be adequate as a means of control of the generator output. In addition, the change in current results in an instantaneous change in carbon dioxide production rate. 
       EXAMPLE 3 
       [0083]    Based on these experimental results and a reduction in cell resistance the following stack capabilities are possible: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Single cell size, cm 2   
                 100 
               
               
                   
                 Number of cells: 
                 50 
               
               
                   
                 Current/cell, amps 
                 50 
               
               
                   
                 Single cell voltage, volts: 
                 1.12 
               
               
                   
                 Stack voltage, volts 
                 56 
               
               
                   
                 Stack power, Kilowatts: 
                 2.8 
               
               
                   
                 CO 2  production rate, lbs/hr or (Ton/day): 
                 9.3 (0.1) 
               
               
                   
                 Energy consumption, kilowatt-hr/lb CO 2 : 
                 0.3 
               
               
                   
                 Oxalic acid consumption/day, Tons: 
                 ca. 0.1 
               
               
                   
                   
               
             
          
         
       
     
         [0084]    This analysis shows that the electrolytic process is compatible with “on-site” generator capabilities as needed by small to medium-size users. 
       EXAMPLE 4 
       [0085]    Based on the previously described stack performance, the following capabilities are possible: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Single cell size, cm 2 : 
                 1,000 
               
               
                   
                 Number of cells: 
                 50 
               
               
                   
                 Current/cell, amps: 
                 500 
               
               
                   
                 Stack voltage, VDC: 
                 56 
               
               
                   
                 Stack power requirement, Kilowatt: 
                 28 
               
               
                   
                 CO 2  production rate, Ton/day 
                 1 
               
               
                   
                 Acid consumption rate, ton/day 
               
               
                   
                 Anhydrous oxalic acid: 
                 1 
               
               
                   
                 Dihydrate oxalic acid: 
                 1.4 
               
               
                   
                   
               
             
          
         
       
     
       EXAMPLE 5 
     Two 8.3 cm 2  cells of the type described in this application, placed back-to-back (anodes facing each other) with cathodes exposed to air, are used to extract H 2  from a gas stream generated from a 5-cell CO 2  generator stack, described previously. 
       [0086]    The voltage at a current of 400 milliamps is 0.5 volts; the limiting current, limited by the air cathode, is about 3 amps. This stack is capable of removing 1.5 liters/hour of hydrogen gas from the gas stream. 
         [0087]    Four pairs of cells would be adequate to remove the hydrogen generated from a 12 liters/hour (1.2 lbs/day) CO 2  generator. 
         [0088]    Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention. For example, equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and the number and configuration of various components described above may be altered, all without departing from the spirit or scope of the invention as defined in the appended Claims.