Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Water – sewage – or other waste water
Reexamination Certificate
1994-12-09
2001-05-22
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Water, sewage, or other waste water
C205S751000, C205S759000
Reexamination Certificate
active
06235189
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is concerned with an apparatus and method of supplying carbon dioxide dissolved in water. More particularly, the invention is concerned with the supply to plants in water, cultivating mediums for cells of animals and plants, potable water, etc., with carbon dioxide dissolved in water.
Systems which should be continuously supplied with a dissolved carbon dioxide in water include those involved with photosynthesis in plants and cultivation of cells of animals. For this purpose, conventionally, a gas source from outside, such as a bomb of carbon dioxide, is used and contacting of the gas with a liquid forms dissolved carbon dioxide therein. In this method, however, the gas-feeding rate can be controlled only by the contacting area of gas and liquid and the partial pressure of the carbon dioxide gas. Moreover, the bombs must constantly be replaced when they become empty. Maintenance is troublesome.
Aquatic plants living with ornamental fish are supplied with carbon dioxide gas by introducing carbon dioxide into a tube having the upper end closed and the lower end opening in the water so that water entering through the open end of the tube is brought into contact with the carbon dioxide gas contained in the tube, thus dissolving carbon dioxide gas in the water. The carbon dioxide gas must be introduced as frequently as about once per day, which is laborious. Furthermore, the carbon dioxide gas continues to be supplied even when there is no light to give rise to photosynthesis. Controlling the supply of carbon dioxide in this way is very difficult.
SUMMARY OF THE INVENTION
It is known that electrolysis of water using a positive carbon electrode produces oxygen gas which reacts with the carbon electrode and erodes it. For this reason, carbon electrodes are not used as anodes in the electrolysis of water. The present invention utilizes this disadvantage to provide an apparatus and method for supplying a controlled amount of dissolved carbon dioxide to an aqueous medium.
The invention provides an apparatus for supplying a controlled amount of carbon dioxide dissolved in water comprising supply means for supplying carbon dioxide and contact means for contacting the supplied carbon dioxide with water to effect dissolution of the carbon dioxide in the water, characterized in that the supply means together with the contact means are comprised of a carbon electrode in contact with the water and adapted, when connected together with a second electrode, also in contact with the water, to a source of direct electric current, to function as a positive electrode and in that control means are provided controlling the current density fed to the electrodes at or below the level at which no or substantially no oxygen gas is formed at said carbon electrode.
In a further embodiment, the invention provides an apparatus for supplying carbon dioxide gas dissolved in water in which the positive carbon electrode is covered with a hydrophilic water-permeable cover, which prevents carbon particles from dropping from the electrode during electrolysis and diffusing into the water.
The carbon electrode may be solid carbon, e.g., in the form of a rod. Preferably, the carbon electrode is a composite which comprises 30 to 70 percent by weight carbon and 70 to 30 percent of a material such as a ceramic, glass wool or a synthetic resin which is inert to carbon and electrolysis products. The inert material may be in the form of a skeleton or framework support which maintains the form of the electrode during use. The carbon may be in the form of particles, e.g., a powder, or may be in the form of granules preferably having a size of 2 mm or below. The electrode may also comprise a collecting member around which the electrode is formed.
The invention also provides a method of supplying dissolved carbon dioxide to an aqueous medium characterized by electrolyzing the water in the aqueous medium by means of electrodes disposed in the aqueous medium and supplied with electric current, at least one of the electrodes being a carbon electrode which acts as a positive electrode, and maintaining the current density supplied to the electrodes at or below the level at which no or substantially no gaseous oxygen is formed at the positive carbon electrode.
Oxygen is generated at the positive electrode by electrolysis of the water and then at least a part of the oxygen reacts with the carbon of the positive electrode to generate carbon dioxide. It has now been found that not only the amount of carbon dioxide generated but also the dissolved carbon dioxide supply rate can be controlled by adjusting the current density supplied to the electrodes for the electrolysis.
Hydrogen gas is generated at the negative electrode. In the event a cation in the aqueous medium happens to deposit on the negative electrode, it may be removed by reversing the polarity of the electrodes for a period from time to time.
Carbon is resistant to steam sterilization. Accordingly, it can be used in the cultivation of animal and plant cells in a culture.
The supply of dissolved carbon dioxide gas to an aqueous system effects a decrease in the pH value existing in the aqueous system. The invention can therefore be applied to control the pH in a culture during cell cultivation. Potable water also may be supplied with carbon dioxide gas.
The supply rate of the dissolved carbon dioxide is controlled by adjusting the current density supplied to the electrodes. At low current densities, the range of generation of oxygen at the carbon anode is also low so that substantially all the oxygen produced by electrolysis is able to react with the carbon of the anode to form carbon dioxide. As the current density is increased, the rate of generation of oxygen is also increased so that a point is reached when only a part of the oxygen generated at the carbon anode is able to react with the carbon of the electrode to form carbon dioxide. Under these circumstances, both dissolved carbon dioxide and oxygen gas are released from the carbon anode. The apparatus and method of the present invention do not contemplate an electrolysis in which substantial quantities of oxygen gas are produced at the carbon electrode.
Although, like the bomb of carbon dioxide gas used in the prior art, the carbon electrode is consumed, it can easily be replaced by fresh electrodes. Water plants in a 200 liter ornamental water tank require to be supplied with, in general, about 50 to 500 ml a day of carbon dioxide. This amount corresponds to 0.03 to 0.3 grams of carbon. In providing such a supply rate in the manner of the invention, it, therefore, will take more than 100 days to consume 30 g of carbon. This means that the rate of replacement of carbon anodes is much less than that necessary in the conventional case where bombs have to be replaced. Furthermore, the danger inherent in using high pressure equipment like a bomb, is not present.
The rate of generation of carbon dioxide depends in part on the current density and also depends on the form and type of carbon which is used to form the electrode. For a given form of carbon, the efficiency of carbon dioxide production increases to a maximum as the current density increases and then falls off somewhat as the current density is further increased. Thus, in the case of carbon black, the efficiency rises from a level of about 35 percent, at a current density of 1 mA, to a maximum of about 80 percent, at a current density of 6 mA, and falls again to about 60 percent, at a current density of 10 mA per sq. cm. of electrode surface. In general, amorphous forms of carbon, such as active carbon, are preferred.
The water is preferably circulated so as to constantly flow past the surface of the carbon electrode and convey dissolved carbon dioxide away from the surface of the carbon electrode.
REFERENCES:
patent: 4360417 (1982-11-01), Reger et al.
patent: 4369104 (1983-01-01), Beckley
patent: 5256268 (1993-10-01), Goto et al.
patent: 1 578 756 (1980-11-01), None
Grant, Hackh's Chemical Dictionary, 4th editi
Able Corporation
Flynn ,Thiel, Boutell & Tanis, P.C.
Gorgos Kathryn
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