Carbon dioxide-generating electrode apparatus

Abstract: The present invention provides a carbon dioxide-generating electrode apparatus comprising an anode carbon, the upper end part thereof being fixed to a terminal part, and a cathode placed in a non-contact state so as to face the anode carbon, characterized in that a distance between the anode carbon and the cathode is broadened relatively and continuously from the lower part toward the upper part. The distances between the anode carbon and the cathode are set to an equal distance in the positions on the same horizontal cross section, and the difference (W₁ - W₂) of a distance (W₁) between the side face at the upper end part of the anode carbon and the inner face of the cathode from a distance (W₂) between the side face at the lower end part of the anode carbon and the inner face of the cathode is preferably set to a range of 1.0 to 5.0 mm. A carbon dioxide-generating electrode apparatus according to the present invention secures the always stable generation of carbon dioxide over the long period of time by an electrolytic operation with a fixed current.

Description: FIELD OF THE INVENTION The present invention relates to a carbon dioxide-generating electrode apparatus, comprising a carbon anode, the upper end part thereof being fixed to a terminal part, and cathode placed in a non-contact state so as to face the carbon anode. BACKGROUND OF THE INVENTION In carrying out rearing of water grasses and synthetic culture of algae in a water tank, carbon dioxide necessary for photosynthesis has to be supplied to dissolve it in water. In general, carbon dioxide is supplied to a water tank via a carbon dioxide bomb installed outside, and it is difficult in this method to supply carbon dioxide evenly at a slow flow rate of 10 ml/minute or less. In order to rear ornamental water grasses, employed is a method in which carbon dioxide is filled in a diffusion cylinder with the one end thereof opened in water, and gas-liquid contact at the open end causes carbon dioxide to be dissolved in water. However, the above method has the defect that supply/stop and a supplying speed can not be controlled. In order to solve such problems, one of the present inventors developed an apparatus for supplying dissolved carbon dioxide in which water is electrolyzed with carbon used as an anode in liquid to which dissolved carbon dioxide is supplied as a mechanism for automatically supplying carbon dioxide without relying upon the supply of carbon dioxide from an external supply source such as a bomb, and has already filed patent (JP-A-6-154760). In this invention, a concrete embodiment is comprising a cathode member formed by a perforated pipe made of cylindrical stainless steel, a carbon rod anode inserted in the cathode member in a non-contact state, and a terminal fixed on the cathode member at the upper part thereof. According to the above structure, since not only the carbon anode can be compactly integrated with the cathode but also dissolved carbon dioxide and gaseous hydrogen resulting on the cathode is emitted to liquid from holes formed on the cathode member, it becomes possible to dissolve carbon dioxide into liquid safely and efficiently. However, continuing an electrolytic operation at a fixed current using the carbon dioxide-generating electrode apparatus with the structure described above has gradually increased the voltage between both electrodes while a considerable amount of anode carbon remains and has sometimes resulted in causing the situation that current does not flow eventually between the electrodes and electrolysis is stopped. Investigations repeatedly made by the present inventors in order to solve the cause of this problem have resulted in clarifying that the problem originates in the phenomenon that since in the existing structure described above, a cylindrical carbon anode having the same diameter throughout the rod is inserted in a cylindrical cathode pipe having the same inner diameter in a longitudinal direction in such a parallel non-contact state that a distance between the electrodes becomes fixed, the consumption of the anode carbon particularly in the vicinity of the upper part thereof connected directly to the terminal proceeds dominantly to increase locally an insulation degree, and the carbon anode at the lower part thereof remains unreacted. SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems described above in the current carbon dioxide-generating electrode apparatus. It is an object of the present invention to provide a carbon dioxide-generating electrode apparatus in which an electrolytic operation with a fixed current secures the always stable generation of carbon dioxide over the extended period of time. It is an another object of the present invention to provide a carbon dioxide-generating electrode apparatus in which a carbon anode can be uniformly consumed to the last without causing trouble such as stopping of an electrolytic operation. The object of the present invention is achieved by the carbon dioxide-generating electrode apparatus comprising a carbon anode, the upper end part thereof being fixed to a terminal part and a cathode placed in a non-contact state as so to face the carbon anode, characterized in that a distance between the carbon anode and the cathode is broadened relatively and continuously from the lower part toward the upper part, the distance between the carbon anode and the cathode are set to an equal distance in the positions on the same horizontal cross section, and the difference (W 1 - W 2 ) of a distance (W 1 ) between a side face at the upper end part of the carbon anode and the inner face of the cathode from a distance (W 2 ) between a side face at the lower end part of the carbon anode and the inner face of the cathode is set to a range of 1.0 mm to 5.0 mm. In the present invention, the arrangement of the carbon anode and the cathode placed in a non-contact state includes the electrode structure wherein the cathode surrounds the circumference of the carbon anode, the cathodes face both sides of the carbon anode and the carbon anode and the cathode face each other at predetermined intervals. The invention is suitably used in the fields in which carbon dioxide is required to be dissolved in water, such as, for example, rearing of water grasses and culture of algae utilizing photosynthesis in water, or culture of animal cell and plant cells controlling pH of water by dissolving carbon dioxide. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially notched side cross-sectional drawing illustrating the carbon dioxide-generating apparatus according to the present invention. Fig. 2 is A-A line cross-sectional drawing of Fig. 1 in the case a cylindrical carbon anode is used. Fig. 3 is A-A line cross-sectional drawing of Fig. 1 in the case a prismatic carbon anode is used. Fig. 4 is an external drawing of the carbon dioxide-generating apparatus according to the present invention in which the cathode having an aperture part which is divided lengthwise into two pieces is provided. Fig. 5 is an external drawing of the carbon dioxide-generating apparatus according to the present invention in which the cathode having a slit-shaped aperture part is provided. Fig. 6 is an external drawing of the carbon dioxide-generating apparatus according to the present invention in which the cathode having an aperture part formed in the horizontal positions of the upper part and the lower part in the form of a row of circular perforations is provided. Fig. 7 is a side cross-sectional drawing in case a plate-like carbon anode is used. Fig. 8 is A-A line cross-sectional drawing of Fig. 7. Fig. 9 is a side cross-sectional drawing in case the anode and the cathode formed in same plate-like shape are used. Fig. 10 is A-A line cross-sectional drawing of Fig. 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 (partially-notched side cross-sectional drawing) illustrates the carbon dioxide-generating electrode apparatus according to the present invention, wherein 1 is an carbon anode, and 2 is a cathode provided so as to surround the circumference of the carbon anode 1 in a non-contact state and having an aperture part on the side face. The upper end part of the carbon anode 1 is connected to a covered lead wire 5 for passing current via a terminal part 4, and a part including the terminal part 4 is covered tightly with a rubber-made waterproof cover 6. A plastic-made insulating spacer 7 is provided between the lower part of the carbon anode 1 and the bottom of the cathode, and the upper positions of the carbon anode 1 and the cathode 2 in which the anode-cathode distance is longer are fixed with a plastic-made fixing member 8. The numeral 9 is a lead wire fixed on the upper part of the cathode member 2. The shape of the anode carbon 1 in the apparatus illustrated in Fig. 1 may be cylindrical or square or rectangular. However, when the carbon anode 1 is cylindrical, the cathode 2 is made tubular as illustrated in Fig. 2 (A-A line cross-sectional drawing in Fig. 1). When the anode carbon is prismatic, the cathode is molded to the same square or rectangular tubular shape as illustrated in Fig. 3 (A-A- line cross-sectional drawing in Fig. 1), and the distances between the carbon anode 1 and the cathode 2 in the positions of the same horizontal cross section are designed in an equal distance. The aperture part 3 formed at the side face of the cathode 2 can be formed by dividing lengthwise the cathode 2 into two pieces as shown in Fig. 4, or can be formed as plural circular holes as shown in Fig. 1 or plural slits as shown in Fig. 5, or can be formed in combination thereof. Accordingly, metal plates in which numberless perforations are formed on the whole face such as wire gauze and punching metal can naturally be used as well. In case a cylindrical, square or rectangular shaped rod is used as the anode, the most effective shape of the aperture part 3 is designed so that a plurality of the perforations as the aperture part 3 are provided in the horizontal positions at the upper part and the lower part of the cylindrical cathode 2 as shown in Fig. 6. According to this shape, since dissolved carbon dioxide resulting on an anode face and hydrogen gas resulting on a cathode face flow out smoothly from upper holes by natural convention, further smooth electrolysis can be carried out. In case a plate-like carbon rod anode and a plate shaped cathode are used, as illustrated in Fig. 7 and Fig. 8, a carbon anode 1 is perpendicularly placed, and a cathode 2 is arranged in order that a distance between the anode carbon 1 and the cathode 2 is broadened continuously from a lower part toward an upper part, and the side part is in an open state, except the existence of the cathodes. Fig. 9 and Fig. 10 illustrates a carbon dioxide-generating electrode apparatus in which the carbon anode 1 and the cathode 2 are made of same material and are formed in same plate-like shape. A carbon anode 1 and a cathode 2 are arranged on the inner face of non-conductive mesh cage such as a plastic cage 10 so as to face each other and in order that the distance (W 1 ) between a side face at the upper end part of the carbon anode 1 and the inner face of the cathode 2 becomes larger than the distance (W 2 ) between a side face at the lower end part of the carbon anode 1 and the inner face of the cathode 2. An embodiment in which the distance between the carbon anode 1 and the cathode 2 is broadened relatively and continuously from the lower part toward the upper part includes a structure in which as shown in Fig. 2, or Fig. 3, the carbon anode 1 is a circular cylinder, or square or rectangular rod having the same diameter and inserted in the cylindrical, square or rectangular cathode 2 molded to a reverse conical trapezoidal shape. In addition thereto, there can be employed a structure in which the tapered cylindrical carbon anode 1 in which the upper part has a smaller diameter and the diameter is increased gradually toward the lower part is inserted in the tubular cathode having the same inner diameter. However, in order to generate continuously stable carbon dioxide, it is effective to employ the former structure. In particular, it is preferable than the distances between the carbon anode 1 and the cathode 2 are set to an equal distance in the positions on the same cross section and that an inclined face is provided so that the difference (W 1 - W 2 ) of a distance (W 1 ) between the side face at the upper end part of the carbon anode 1 and the inner face of the cathode 2 from a distance (W 2 ) between the side face at the lower end part of the carbon anode 1 and the inner face of the cathode 2 falls in a range of 1.0 to 5.0 mm. Deviating from the distance difference range described above prevents the consumption rate of the carbon anode from proceeding uniformly from the bottom end of the carbon anode, and an electrical resistance of the top end of the carbon anode increases and the utilization efficiency of the carbon tends to decrease. The distance (W 2 ) between the side face at the lower end part of the carbon anode 1 and the inner face of the cathode 2 is preferably set to a range of 0.5 to 4.5 mm. Coke, activated carbon, carbon black, graphite materials using thermosetting resins as carbon sources, vitreous carbon, and other various carbonaceous materials are applied to the carbon anode 1 used in the present invention, but the materials thereof are not specifically restricted. However, preferably used for the object of the present invention is the carbonaceous material which is produced by blending 35 to 70 weight % of activated carbon, 15 to 50 weight % of kaolin series clay, 5 to 10 % of graphite, and 3 to 5 % of carboxymethyl cellulose and kneading it together with water to mold the blend to a prescribed shape, followed by subjecting it to a burning carbonization treatment in a temperature region of 900 to 1200°C in a non-oxidizing atmosphere. On the other hand, metallic plate such as copper, steel or nickel plate is applied to the cathode in the apparatus illustrated in Fig. 1 or Fig. 7, and stainless steel plate having an excellent corrosion resistance is preferably used for a metal material constituting the cathode 2. In the apparatus illustrated in Fig. 9, the cathode is preferably formed by carbon plate as well as the anode. The structure described above makes it possible to use the anode and the cathode changing their polarity at a predetermined interval of time. The structure also makes it possible to use the reverse sides of the anode and/or the cathode by turning inside out. It results in an effective use of carbon plate forming the anode and the cathode. The carbon dioxide-generating electrode apparatus of the present invention comprises fundamentally a compact structure in which the circumference of a carbon anode in which the upper end part thereof is fixed to a terminal part faces a cathode in a non-contact state to integrate them. It is suspended and set in, for example, a water tank for aquarium fishes in which water grasses and algae grow, and operated by passing a prescribed current between the anode and the cathode. In this case, in a conventional structure in which a cylindrical carbon anode having the same diameter throughout the rod is inserted in a cylindrical cathode pipe having the same inner diameter in a longitudinal direction in such a parallel non-contact state that a distance between the electrodes becomes fixed, the consumption of the carbon anode in the vicinity of the upper part thereof connected directly to the terminal proceeds dominantly to increase an insulation degree, and the electrolysis ceases while the anode at the lower part is scarcely consumed, which brings about a reduction in the utilization efficiency of the anode. In contrast to the above, since the electrode apparatus according to the present invention is designed to the structure in which the distance between the carbon anode and the cathode is broadened relatively and continuously from the lower part toward the upper part, the anode-cathode distance between the carbon anode and the cathode in the vicinity of the upper part connected directly to the terminal is longer as compared with the distance at the lower part. Since this causes the consumption of the carbon anode at the lower part in which the anode-cathode distance is shorter to proceed most rapidly and allows a continuously inclined consumption degree to be given in which the consumption of the carbon anode decreases gradually from the lower part toward the upper part, the consumption proceeds keeping very good balance on the whole from the bottom end of the anode. This action allows electrolysis to go on stably over the extended time of period and causes an always fixed amount of carbon dioxide to generate continuously. In particular, in the case where the anode-cathode distances between the carbon anode and the cathode are set to an equal distance in the positions on the same cross section, and the difference (W 1 - W 2 ) of a distance (W 1 ) between the side face at the upper end part of the carbon anode and the inner face of the cathode from a distance (W 2 ) between the side face at the lower end part of the carbon anode and the inner face of the cathode is set to a range of 1.0 to 5.0 mm, the function described above is exhibited more effectively. Further, providing the perforations of the aperture part formed on the surface of the cylindrical cathode in the horizontal positions of the upper part and the lower part prevents hydrogen and carbon dioxide from staying in the cylindrical cathode member by a convectional action and makes it possible to promote the efficient dissolution of carbon dioxide. In the apparatus having the anode and the cathode formed by carbon plate, it becomes possible to perform a uniform consumption of the electrodes, an effective use of the electrodes and simplification of the electrode structure by changing the polarity of the anode and the cathode at a predetermined interval of time and using the reverse sides of the anode and/or the cathode. EXAMPLE The examples of the present invention will be explained below in detail based on illustrated examples. However, the present invention is not restricted to these examples. Example 1 As shown in Fig. 1, produced was a carbon dioxide-generating electrode apparatus having a structure in which a cylindrical carbon anode 1 having the same diameter is inserted in the center of a reverse conical trapezoidal cathode 2 made of a stainless steel plate and having an aperture part 3 where a lot of perforations were bored on the side face thereof in a non-contact state. The upper end part of the carbon anode 1 was connected to a covered lead wire 5 for passing current via a terminal part 4, and a part including the terminal part 4 was covered tightly with a rubber-made waterproof cover 6. A plastic-made insulating spacer 7 was provided between the lower part of the carbon anode 1 and the cathode 2. The anode-cathode distances between the carbon anode 1 and the cathode 2 were set to an equal distance on the same cross section, and the design was made so that the difference (W 1 - W 2 ) of a distance (W 1 ) between the side face at the upper end part of the carbon anode 1 and the inner face of the cathode 2 from a distance (W 2 ) between the side face at the lower end part of the carbon anode 1 and the inner face of the cathode 2 became 2.0 mm, and the upper positions of the anode carbon 1 and the cathode 2 in which the anode-cathode distance was longer were fixed with a plastic-made fixing member 8. The carbon anode 1 was produced in the following manner. Blended were 60 weight % of coconut husk activated carbon ("Diasorp" manufactured by Mitsubishi Chemical Co., Ltd.) having a particle diameter of 53 to 140 µm, a specific surface area of 1570 m 2 /g, and an iron content of 0.1 weight % or less, 25 weight % of kaolin clay (manufactured by Kyoritsu Yogyo Genryo Co., Ltd.), 10 weight % of graphite powder, and 5 weight % of carboxymethyl cellulose, and water of 80 weight parts based on 100 weight parts of the above blend was added and kneaded sufficiently. The kneaded product was extrusion-molded in a cylindrical form with a plunger type extrusion-molding machine and dried at a temperature of 50°C to cure a binder component. Then, the molding was transferred in a kiln maintained in argon gas atmosphere, and the temperature was raised up to 1000°C at a temperature-raising speed of 100°C/hour. The molding was burned at this temperature for 10 hours to subject it to carbonization treatment. This carbon rod was surface-treated, whereby the carbon anode 1 having a diameter of 15 mm and a length of 100 mm was obtained. Each carbon dioxide-generating electrode apparatus described above was set in a water grass water tank filled with fresh water in a suspending state so that it was dipped therein, and a lead wire at the cathode was connected to a constant-current generator to carry out an electrolytic operation on the conditions of a current of 120 mA and an anode current density of 2.8 mA/cm 2 , until the voltage between the both electrodes increases to 10 V. After starting the electrolysis, measurement was made with a commercially available dissolved carbon dioxide reagent for fresh water (manufactured by Tetra Co., Ltd.) to confirm that carbon dioxide was stably generated. In this case, after electrolysis of 38 days, a current flow amount was 398 x 10 3 coulomb and stabilized without having variation with the passage of time. Example 2 The carbon rod prepared from the same material as that used in Example 1 was processed to prepare a cylindrical carbon anode having a diameter of 15 mm and a length of 100 mm and an carbon anode having a rectangular cross section (thickness 5 mm and width 15 mm) and a length of 150 mm. These carbon anodes were used to fabricate the carbon dioxide-generating electrode apparatuses having the same structure as that employed in Example 1. When the rectangular shaped carbon anode was used, a cathode was formed as well in a rectangular tubular shape. The distances between the carbon anode 1 and the cathode 2 were set to an equal distance on the same cross section, and the difference (W 1 - W 2 ) of a distance (W 1 ) between the side face at the upper end part of the carbon anode 1 and the inner face of the cathode from a distance (W 2 ) between the side face at the lower end part of the carbon anode 1 and the inner face of the cathode 2 was varied in a range of 0.5 to 7.0 mm to carry out an electrolytic operation in the same conditions as those employed in Example 1. In this case, a current flow amount was measured, and the result thereof is shown in Table 1 in contrast with the difference (W 1 - W 2 ). It was confirmed from the results summarized in Table 1 that when the differences (W 1 - W 2 ) were 0.5 mm and 7.0 mm, the current flow amount was reduced but in the ranges of 1.0 to 5.0 mm, the current flow amount was stabilized at a high level and that an electrolytic operation proceeded effectively and the anode carbon was consumed uniformly. Difference (W 1 - W 2 ) Current flow amount (x 10 3 coulomb) carbon Anode rod Cylinder length 100 mm Cylinder length 150 mm Plate length 150 mm 0.5 261 391 402 1.0 336 514 524 1.5 350 547 562 2.0 398 590 587 3.0 392 586 583 4.0 384 572 576 5.0 367 558 561 7.0 280 423 425 Example 3 In Example 1, the aperture part 3 of the cathode 2 was formed in the horizontal positions of the upper part and the lower part in the form of a row of circular perforations. A carbon dioxide-generating electrode apparatus was fabricated in the same manner as that in Example 1, except that this cathode member was used. Then, an electrolytic operation was carried out, and it was visually observed that the generation efficiency of carbon dioxide was enhanced and the life of the carbon anode becomes long as compared with the case where a lot of perforations were formed on the whole side face of the cathode. Example 4 The carbon rod prepared from the same material as that used in Example 1 was processed to prepare an carbon anode and a cathode of a carbon plate having a rectangular cross section (thickness 5 mm and width 15 mm) and a length of 150 mm. The carbon anode 1 and the cathode 2 are arranged, as shown in Fig. 9, on an opposite side of non-conductive mesh cage 10 comprising a synthetic resinous material. The difference (W 1 - W 2 ) of the distance (W 1 ) between the top end of the both carbon plates and the distance (W 2 ) between the bottom end of the both carbon plates is set to 2.0 mm. In the above apparatus, an electrolytic operation was carried out using an electric current of 100 mA on condition that the polarity of an anode and a cathode is changed in an interval of 30 minutes. After starting the electrolytic operation, measurement was made with a commercially available dissolved carbon dioxide reagent for fresh water (manufactured by Tetra Co., Ltd.), and it was confirmed that carbon dioxide was stably generated. At the time when voltage between both electrodes exceeds 10 V, the both carbon plate forming the anode and the cathode were turned over in order that the back sides of the anode and the cathode face each other. Electrolytic operation was performed thereafter and voltage between the both electrodes decreased down to 5 V. The surface conditions of the both electrodes were observed after voltage between the both electrodes increased over 10 V. As its result, a uniform consumption on the whole surfaces of the both carbon plate was observed. As described above, the carbon dioxide-generating electrode apparatus according to the present invention causes electrolysis to go on stably over the extended time of period and makes it possible to generate continuously an always fixed amount of carbon dioxide. Accordingly, a carbon anode can be uniformly consumed to the last without causing troubles such as stopping of an electrolytic operation, and the use efficiency thereof can be notably improved.

Claims: A carbon dioxide-generating electrode apparatus comprising a carbon anode, the upper end part thereof being fixed to a terminal part, and cathode placed in a non-contact state so as to face the carbon anode, characterized in that a distance between the carbon anode and the cathode is broadened relatively and continuously from a lower part toward an upper part, the distance between the carbon anode and the cathode are set to an equal distance in the positions on the same horizontal cross section, and the difference (W 1 - W 2 ) of a distance (W 1 ) between a side face at the upper end part of the carbon anode and the inner face of the cathode from a distance (W 2 ) between a side face at the lower end part of the carbon anode and the inner face of the cathode is set to a range of 1.0 mm to 5.0 mm. A carbon dioxide-generating electrode apparatus as claimed in claim 1, wherein the carbon anode is a cylindrical shaped rod and the cathode is formed in tubular shape arranged so as to surround the circumference of the carbon anode. A carbon dioxide-generating electrode apparatus as claimed in claim 1, wherein the carbon anode is a square or rectangular shaped rod and the cathode is formed in square or rectangular tubular shape arran ed so as to surround the circumference of the carbon anode. A carbon dioxide-generating electrode apparatus as claimed in claim 1, wherein the carbon anode is a platelike rod and the cathode is formed in plate shape, the cathode being arranged so as to face one side or both sides of the carbon anode. A carbon dioxide-generating electrode apparatus as claimed in claim 1, wherein the carbon anode and the cathode are made of same material and are formed in same plate-like shape, and the carbon anode being placed in a non-contact state so as to face the cathode. A carbon dioxide-generating electrode apparatus as claimed in claim 1, wherein the length between the upper end part of the carbon anode and the lower end part of the carbon anode is 100 mm to 150 mm. A carbon dioxide-generating electrode apparatus as claimed in claim 1, wherein the cathode is formed by plate-like electrical conductive metal having an aperture part. A carbon dioxide-generating electrode apparatus as claimed in claim 7, wherein the aperature is part is formed by dividing the cathode plate lengthwise into two pieces and/or boring a plurality of perforations in the cathode plate.

Inventors: ISHIKAWA YOICHI, OZAWA SANJI, YOKOSE CHIKARA, ISHIKAWA, YOICHI, OZAWA, SANJI, YOKOSE, CHIKARA
Applicants: ABLE CORP, ORIENTAL SANGYO CO LTD, ABLE CORPORATION, ORIENTAL SANGYO CO. LTD.
Application year: 1995
Main classification: C25B11
IPC codes: C25B9, C02F1, B01F3, A01G7