F.G.Lepekhin - Electrolysis of water.The possibility of implementing an energetically favorable method for producing hydrogen in low-voltage electrolysis of water is being considered. At the same time, the estimated amount of heat that can be obtained after the combustion of hydrogen may be even greater than the energy taken from the network to carry out the hydrogen production process. In this process, hydrogen becomes not just “fuel”, but is actually the working fluid of the heat pump, since the energy required for the dissociation of water molecules into hydrogen and oxygen is obtained by reducing internal energy environment. And this is the energy of the Sun, accumulated by the Earth over millions of years of its existence. By human standards, its reserves are limitless. It is shown that such a possibility does not contradict any well-established laws of physics, and, therefore, can be technically realized.

1. Introduction

Problems of hydrogen energy in last years are discussed in the media, and at different levels - from US President D. Bush to the Presidium of the Russian Academy of Sciences. There are cars and planes that use hydrogen as fuel. Most often, the environmental purity of hydrogen as a fuel is pointed out - during combustion, water is formed, from which it, in principle, can be obtained, and is obtained, in large quantities in industrial electrolysers. Of course, it can be obtained, for example, from methane, but you need methane, or another gas that burns without extracting hydrogen from it. And in industrial electrolyzers, the energy consumption to produce hydrogen is one and a half to two times more than the heat that can be produced by burning this hydrogen. But the electricity already obtained from the combustion of hydrocarbon fuels can be converted into either heat or work, but the heat obtained from the combustion of hydrogen cannot be completely converted into either electricity or work. Producing hydrogen as a fuel, not as a raw material chemical industry for the production of another product is not economically profitable. Expensive. This is the main problem with using hydrogen as a fuel. It cannot be said that they were not looking for a solution. But the fact is that it has not yet been resolved. Is it possible to find it at all, what prevents this from happening, and in what direction should this solution be sought - all these questions will be considered in this work.

2. Physics and electrochemistry

Since the subject of consideration is the electrolysis of water, and the discovery and its main principles were studied in physics, we will start with physics. In the fundamental “Course of Physics” by O. D. Khvolson we read: “The phenomenon that occurs in an electrolyte introduced into a closed circuit is called electrolysis.” It also defines what “electrolyte”, “anion” and “cation” are. And further, in the same place: "With outside anion and cation appear to be products of decomposition of the electrolyte, and, moreover, decomposition produced by a current passing through the electrolyte." During the electrolysis of some acids and alkalis, oxygen and hydrogen are released. We see that "the current decomposes water." So we took this for granted and obvious until the second half of the 19th century.

However, in the works of Clausius (1857), Helmholtz (1880) and Arrhenius (1894), the mechanism of electrolysis was established and the foundations of the theory of electrolytic dissociation were created, which are not outdated today. Clausus already pointed out that if we proceed from the idea that electrical forces “decompose” the electrolyte, overcoming the force of chemical affinity, then for each chemical compound some specific electric force to overcome this affinity. "In fact, even the weakest electromotive force causes electrolysis in any electrolyte" - page 564, .

Helmholtz's main merit is that he accurately pointed out the role of electric current, found out where the energy that is obviously consumed during electrolysis comes from, and which is numerically equal to the energy released during the chemical combination of electrolysis products. In the electrolysis of water, this is the energy released when hydrogen burns and produces water. According to Helmholtz, the decomposition of water during electrolysis is carried out due to the internal energy of the electrolyte, and not at all “the current decomposes the water.” This is precisely the basis for the idea of ​​using hydrogen as the working fluid of a heat pump under certain conditions for electrolysis of water. But more about this below, but for now let’s turn to electrochemistry.

She defines electrolysis as “the process of reduction or oxidation of substances on electrodes, accompanied by the acquisition or loss of electrons by particles of the substance as a result of an electrochemical reaction” (see A.I. Levin). And this is significantly different from what physics understands by electrolysis. If the goal of physics is to understand the laws of Nature, then electrochemistry solves the problem of “intensifying the production of non-ferrous, rare, noble and trace metals.” In physics: “In a circuit in which an electrolyte is included, there cannot be a current without electrolysis, i.e., the appearance of ions on the electrodes in contact with the electrolyte. For example, Oswald and Nernst (1889) showed that when passing discharge of a Leyden jar, containing only 5 * 10 -6 coulombs, through a solution of sulfuric acid, a hydrogen bubble was obtained at the cathode, the dimensions of which turned out to be quite consistent with the first law of electrolysis." And further, in the same place - “The experiments of A.P. Sokolov, who managed to prove the existence of polarization at an EMF equal to 0.001 volts, were of decisive importance here. There is no reason to assume that this has reached the limit below which polarization stops.” And the phenomenon of electrode polarization, which will be discussed later, arises as a consequence of electrolysis. Thus, in physics, electrolysis occurs at an arbitrarily low voltage on the electrodes. This is understandable - the component of the speed of chaotic movement of ions in the electrolyte under the influence electric field, after applying voltage to the electrodes, is not quantized. It can change by an infinitesimal amount. Note that, in contrast, the energy required, for example, to dissociate one molecule of water into oxygen and hydrogen (about 1.228 eV) is quantized. It cannot be communicated to the molecule in parts, in one collision and then in another. This must be done immediately, in one inelastic interaction.

And in electrochemistry, where the practical result is important, for example, the decomposition voltage during the electrolysis of water is understood as the voltage at which hydrogen bubbles appear on the neutral electrodes on the cathode. This concept, of course, is important in practice, but today it “...does not have a definite physical meaning.” Since this issue is important in practical terms when producing hydrogen by electrolysis, we will consider it in more detail.

3. Hydrogen evolution overvoltage

The processes that occur when current passes through an electrolyte, both in the electrolyte itself and on both electrodes, are very complex and diverse. For this reason, the results of electrolysis are often practically not reproducible. Once electrolysis has begun, and has been going on for some time, it is no longer possible to return to the original state after it has stopped. Changes will occur both in the electrolyte and on the electrodes, which will not be restored even after an arbitrarily long wait. And the beginning of electrolysis is not reproducible - this process depends on the material and condition of the electrode surface, the presence of minor impurities in it, etc. Almost the same applies to chemical composition electrolyte. Therefore, even despite the fact that in connection with the widespread industrial use of electrochemical processes, studies of the phenomenon of electrolysis as electrochemistry understands it have been and are being carried out by many special institutions, there is still no complete clarity of understanding of what happens during electrolysis. All the numerous electrolysis details are out of scope fundamental science. She doesn't deal with details.

But what can we say about electrolysis, when we don’t know everything about water. Thus, “There is a point of view according to which water is a mixture of various kinds associated molecules, for example, 8(H 2 O), 4(H 2 O)... and “simple” molecules H 2 O." This is trying to explain some of the anomalous properties of water. In this light, discussions about the mechanism of movement of H + ions or H 3 O + in electrolysis, about processes in the double layer between the electrode and the electrolyte. It is clear that it exists even between gas and solid body, and even more so between a liquid and a solid. Of course, its role in the electrolysis process is great. But accurate quantitative description this role is hardly possible, and maybe not necessary. “It’s worthless” from the point of view of fundamental science, as our outstanding theorist Ya. I. Frenkel said on another occasion.

Of course, there is a potential jump between the electrode and the electrolyte even without any externally applied voltage. And when it is there, and even a weak current appears, and we do not see the evolution of hydrogen at the cathode, changes begin on the electrodes in the material of the electrode, the structure of its surface, and the composition of the electrolyte near the electrode. Everything changes over time and never comes back. According to the well-known laws of physics, all processes that begin in the first moments after voltage is applied to the electrodes will be directed against the causes that caused them, i.e., against the already ongoing electrolysis process. This is Le Chatelier's principle. Will begin complex processes polarization of electrodes. This is how we describe this process of counteracting the electrolysis process. An EMF appears directed against the applied voltage. The electrolysis process that has begun will almost stop. In order for it to move stationary and at the speed we need, we need to increase the external voltage. And this is “overvoltage”. But its value is not related to the “decomposition potential” or “decomposition voltage” of water, which is 1.228 volts. It depends on the current strength, on the nature of the electrodes, the state of their surface, etc. So, for tungsten, at a current density of 5 mA per square meter. see this is 0.33 volts.

It is not difficult to find the amount of energy required to decompose a water molecule into hydrogen and oxygen, knowing how much energy is released during the combustion of one gram-mole of hydrogen. But this does not have any evidentiary force that this energy is wasted precisely by current. If electrolysis occurs at a voltage on the electrodes of more than 1.228 volts, this does not mean that it is the current that consumes the energy of 1.228 eV to destroy water molecules. Yes, nowhere, except implicitly in , is this stated. But this is not a scientific, but a “...production and technical...” monograph, as stated in its abstract. Let us consider in more detail how the internal energy of the electrolyte is spent on the decomposition of water molecules into oxygen and hydrogen during the process of electrolysis. What is the mechanism of this phenomenon.

4. Mechanism of water dissociation during electrolysis

The question of how exactly “current decomposes water” and in what elementary act this occurs is not considered in electrochemistry. A.I. Levin, for example, writes: “It can be assumed that one of the following processes will take place at the anode...”, and then three processes are given in which a neutral water molecule gives 4, or 2 of its electrons to the anode, turning into H + and OH - ions. This “one can assume” is wonderful. But like a neutral molecule, it suddenly gives up its electrons. After all, she needs a “payment” for this - 1.228, 1.776 or 2.42 eV in each of the three above processes. And all at once, and not in parts. Who has this energy near the anode and can spend it on destroying the water molecule.

Further, A.I. Levin writes: “...the decrease in water observed during electrolysis... in the anolyte indicates the occurrence of its decomposition. This can apparently occur through the reaction
2H 2 O - 4 e - = O 2 + 2H +." (1)

“Apparently” - but how? Electrochemistry does not answer these questions. Yes, in fact, she does not insist that this is actually what happens. But in physics all this is available. We read from O. D. Khvolson: “A reaction occurs at the anode
SO 4 + H 2 O = H 2 SO 4 + O..." (2)

And the neutral residue of sulfuric acid is obtained from a negative ion, which is neutralized at the anode. The resulting sulfuric acid molecule immediately breaks down into ions, replenishing their loss at the anode and cathode. According to this scenario, the concentration of water molecules in the “anolyte” actually decreases. Water decomposes. But according to a different reaction. Discharge negative ions SO 4 2- at the anode seems quite natural. True, O. D. Khvolson lists a whole bunch of chemical reactions that take place in the electrolyte. But what is important to us is the general line, not the details.

Now where does this minimum energy of 1.228 eV come from, which still needs to be spent in one act? Physics knows the answer to this question too. At normal pressure, and a temperature of 2000 degrees, without any electrolysis, 0.081% of all water molecules are dissociated. At 5000 degrees, 95.4% of all water molecules already disintegrate. This occurs in acts of inelastic interaction between two neutral water molecules. Such processes are well known to us in particle physics.

The reaction probability is equal to the product of this phase volume and the matrix element. In the absence of particle resonances in this system, it is usually set to unity. As the energy increases above the threshold, the probability of a reaction increases sharply - the impulse part of the phase volume grows like the cube of the impulse in the SDH system. In our case, the greater the energy of two water molecules in their SCI, i.e., the greater the relative and absolute velocities of the colliding molecules, the greater the probability of one of them decaying into hydrogen and oxygen in the act inelastic collision two particles. This is observed as the temperature increases. The distribution of molecular speeds is described by the Maxwell distribution. It always contains a “tail” of high-energy molecules. It is they who will be eliminated during the “self-disintegration” of water at any temperature. The same happens during electrolysis in reaction (2). The removal of molecules with high speeds from the velocity distribution leads to a decrease in the average speed of all molecules. The average speed is proportional to the temperature. Both during the “self-disintegration” of water molecules and during the electrolysis of water, the energy for the dissociation of water molecules is obtained by reducing the internal energy of the liquid, i.e. due to its cooling in these processes.

Of course, the work of the current in the electrolyte, as in any conductor, is also spent on heating it. The ions, coming into accelerated motion in the direction of the electric field, elastically interact with neutral water molecules and transfer part of their energy to them, heating the electrolyte. If this change in the internal energy of the electrolyte due to its heating by current is equal to or greater than the decrease in the internal energy of the electrolyte spent on the decomposition of water molecules, then its temperature will be constant, or it will heat up. This is what happens in industrial electrolysers. An illusion is created: “the current decomposes the water.” If in fact this is not the case, it is not the “current decomposes the ox”, and it is not the magnitude of the “decomposition voltage” that prevents the electrolysis process at low voltage, when the electrolyte must be cooled, then how can this be accomplished? What reasons actually prevent this?

5. Heat pump

The most interesting and effective of all attempts to implement low-voltage electrolysis so far can be considered the electric-hydrogen generator (EVG) of V.V. Studennikov. His proposal is based on the work of R. Colley (1873), who discovered a new source of EMF. It was shown that if the electrodes in the electrolyzer are not placed vertically, at the same height, when the ions move horizontally, but are spaced apart in height, then due to the difference in the masses of the positive and negative ions, now moving up and down in the Earth’s gravitational field, EMF will occur. The artificial gravitational field generated by rotation gives the Tolman-Stewart effect. They have a link to the work of R. Colley. In patents, this effect is used in the design of electrolyzers with electrolyte rotation. It was patented in the USA in 1929 and 1964. A quantitative study of the effect of reducing the anode and cathode potential differences obtained by rotating the electrolyzer was published in.

As V.V. Studennikov claimed, he managed to obtain “... intense self-cooling of the solution, providing conditions for absorbing heat from the environment... i.e., operating in the mode... of a heat pump.” Unfortunately, this statement was contained in a message posted on the Internet by V.V. Studennikov himself, but its scientific publication never appeared. However, the fact of indicating the possibility of using hydrogen as the working fluid of a heat pump belongs to V.V. Studennikov. The possibility of a cheaper way to produce hydrogen as a fuel looks rather pale in comparison. Of course, the processes taking place in EVG can be even more complex than in the classical electrolysis scheme. Two facts seem important. Firstly, during rotation, the electrolyte constantly rubs against the electrodes, “renewing” them. This leads to a decrease in polarization emf. And secondly, no external source EMF. Electrolysis occurs due to the internal voltage drop of the EMF source. And the electrolyte resistance is low. This means that the voltage drop is also small. Hence the self-cooling of the electrolyte. The fatal drawback of EVG is the very expensive method of generating EMF using the energy of the gravitational field. It cannot be compared in any way with the generation of EMF when a conductor moves in a magnetic field. At least, there is no evidence that in EVG the EMF is not really generated simply by rotating the electrolyte in the Earth’s magnetic field. Well, the statement that in addition to hydrogen, there is also a source of constant voltage in the external circuit looks completely strange. We need to decide - either we get hydrogen by cooling the environment, or we design a new machine for generating electricity.

6. Prospects

Research in the field of hydrogen energy in Russia alone is carried out by 20 institutes of the Russian Academy of Sciences. Some of them have been doing this for 20 years. Created fuel cells, used in space research. But it will most likely not come to their widespread production and introduction into our everyday life for a long time. The scientific value of the contribution of RAS institutes in this area is, to put it mildly, not great. The main problem of hydrogen energy, which was mentioned in the introduction, is not solved by them, and will not be solved. There is no customer. Improving industrial electrolyzers using traditional electrolysis is also futile.

Only unconventional methods its solutions, which are the lot of individual inventors. But among them there are quite a few dubious, and often simply illiterate, proposals and statements. An example of this is "Kazakova's Eternal Energy" from Alma-Ata. This is what a correspondent writes about this work, who perhaps simply did not understand Kazakov’s work well. Kazakov uses infrasound, and claims that with enormous speed"self-electrolysis of water" is taking place. This phenomenon is unknown in physics. In one second, 9 cubic meters of hydrogen are obtained, i.e., about 7 liters of water per second “self-disintegrates” into hydrogen and oxygen. If this is true, then the installation capacity is 95 MW. If there were about 200 liters of water in the tank, then in 2-3 seconds it should have frozen. True, the author only needed 100 thousand dollars to release an industrial design and make humanity happy. As a rule, there are no scientific publications by such craftsmen on this topic. Often they scold the conservative " official science"Checks of such applicants always reveal that, out of simplicity or ignorance, they are wishful thinking.

It is possible that from all that has been said, only Studennikov’s EVG may have some prospects if it works in tandem with a conventional compression heat pump. Then it will utilize the heat of the environment with a conventional heat pump and produce hydrogen with a conversion coefficient common to both it and the heat pump, even slightly greater than one. But all this still needs to be done and done. The main thing that I wanted to show here is that there are no fundamental obstacles, including the need to overcome the “water decomposition potential” by increasing the voltage applied to the electrodes.

Literature

1. O. D. Khvolson, Course of Physics, RSFSR, Gosizdat, Berlin, 1923, vol. 4.
2. A. I. Levin, Theoretical foundations of electrochemistry, State. Scientific and technical Publishing house, Moscow, 1963.
3. A. P. Sokolov, ZhRFKhO, vol. 28, p. 129, 1896.
4. Phys. Encycl. Slov., ed. "Soviet Encyclopedia", Moscow, 1960, vol. 1, p. 288.
5. L. M. Yakimenko et al., Electrolysis of water, ed. "chemistry", Moscow, 1970.
6. Stanley Meyer Cell
7. EVG Studennikov
8. R. Colley, Journal of the Russian Chemical Society and the Physical Society at St. Petersburg University, vol. 7, Physical Part, St. Petersburg, 1873, p. 333.
9. R. C. Tolman, T. D. Stsward, Phys. Rev. 8, 97, 1916.
10. E. Thomson, U.S. Pat. 1, 701.346(1929).
11. T. B. Hoover, U. S. Pat. 3, 119, 759(1964).
12. H. Cheng at al., Jorn. Of the Electrochemical Society, 149(11), D172-D177(2002).

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1. Properties, production and use of hydrogen

Basic concepts about hydrogen energy

There is a direction in technology called “hydrogen energy”. In hydrogen energy, hydrogen is considered not only as a chemical reagent, but also as an energy carrier. Hydrogen energy covers the production, storage, transport and use of hydrogen.

There are several reasons why hydrogen has potential for use as an energy carrier:

§ the most common element (0.01% mass earth's crust is hydrogen, atomic fraction - 17% (at.));

§ hydrogen can be obtained from water; when hydrogen is burned, water is formed, which is returned to the circulation;

§ hydrogen is not toxic; its combustion produces fewer harmful components than the combustion of natural organic fuel;

§ Using hydrogen, it is possible to accumulate energy generated by power plants, as well as energy from renewable sources.

Hydrogen as a technical product is widely used in many industries National economy- in technological processes of oil refining, production of ammonia, methanol, in the metallurgical industry, in many branches of science and technology. The use of hydrogen as a fuel in vehicles(road and air transport, aerospace objects) due to its high calorific value and significant cooling capacity. Of particular interest is hydrogen as an energy accumulator - a secondary energy carrier that can be effectively used, for example, in power plants to cover peak loads. In addition, the use of hydrogen as an energy carrier makes it possible to transfer energy to long distances with higher efficiency than modern systems provide.

Physical and chemical properties of hydrogen

Under normal conditions, molecular hydrogen is a colorless and odorless gas, easily flammable and burns with a bluish, dim flame. It is very rare in the free state (volcanic and natural gases). Hydrogen is found in water, coal, oil, natural gas and many mineral and organic matter, as well as in animal organisms and plants.

The hydrogen atom has one valence electron, which is within the range of the atomic nucleus. Therefore, hydrogen forms only diatomic molecules. Hydrogen molecules are characterized by high strength and low polarizability, have small sizes and low mass. This causes high mobility of hydrogen molecules, low melting point (- 259.1? C) and boiling point (- 252.6? C). Hydrogen is slightly soluble in water and organic solvents.

Some physical properties hydrogen are given in the table.

Physical properties of hydrogen at ambient conditions

The hydrogen included in the water molecule is a mixture of three isotopes: protium H with atomic mass 1, deuterium D with atomic mass 2 and tritium T with atomic mass 3.

Heavy water (deuterium oxide) D 2 O is an isotopic variety of water, the molecules of which contain deuterium atoms instead of 1 H atoms. In natural water, there are 6500 - 7200 atoms of 1 N per one deuterium atom.

Molecular weight of D 2 O - 20.09; boiling point - 101.43? C; melting point - 3.81? C; liquid phase density - 1.104 kg/m3.

Heavy water slows down biological processes and has a depressing effect on living organisms.

Electrolysis of water is the main method for producing heavy water. The process is based on the property of heavy water to concentrate in the electrolyte due to the lower rate of electrochemical decomposition of D 2 O.

Heavy water is used in nuclear reactors as a neutron moderator and coolant, used as a fuel component of thermonuclear reactors.

The chemical properties of hydrogen are determined by its single electron. The amount of energy required to remove this electron is greater than any known chemical oxidizing agent can provide. That's why chemical bond hydrogen with other atoms is closer to covalent than to ionic. To initiate most reactions, it is necessary to break or weaken a strong H-H bond; this requires a lot of energy. The rate of hydrogen reactions is increased using catalysts (platinum group metals, transition or heavy metal oxides), by exciting the hydrogen molecule using light, electrical discharge or electric arc at high temperature. Under such conditions, hydrogen reacts with almost any element except noble gases.

Hydrogen is the lightest element. Its density is approximately 14 times less than that of air. It spreads quickly in the surrounding air, diffusing through leaks and small openings. This makes it difficult to store. Hydrogen atoms are easily incorporated into the molecular lattice of many metals (especially at elevated temperatures and pressures), which is the cause of “hydrogen embrittlement” of metals. When burned, hydrogen produces approximately 3 times more heat than gasoline and almost 2.5 times more heat than natural gas (per unit weight). It ignites in a wide range of concentrations (from 4 to 74%), which is significantly greater than that of other energy carriers - natural gas, gasoline and propane-butane mixture. When interacting with oxygen in combustion processes or electrochemical transformations, water vapor is obtained.

The chemical properties of hydrogen have been well studied. It is a good reducer. At ordinary temperatures it practically does not react with oxygen and chlorine. On the surface of the catalyst, with increasing pressure and temperature, the process accelerates sharply. Hydrogen, when heated, reduces metal oxides, easily attaches to carbon atoms with a multiple bond, therefore it is used for the hydrogenation of fats and unsaturated hydrocarbons. In alkaline hydrides and alkaline earth metals hydrogen is in the form of the H - ion.

Basic industrial methodsPproductionhydrogen

There are several main industrial methods for producing hydrogen.

Hydrogen production by steam reforming of methane is the main industrial method of hydrogen production. The primary product of methane conversion is synthesis gas (m CO+ n H 2). Steam catalytic reforming of methane in a tube furnace (primary reforming) consists of the oxidation of methane with water vapor. In the reaction tubes of a tubular furnace on a nickel catalyst, the process of steam conversion of natural gas with steam is carried out according to the reactions:

CH 4 + H 2 O = CO + 3H 2 - Q; (1)

CH 2n + 2n H 2 O = nCO + (2n + 1) H 2 - Q; (2)

CH 4 + 2H 2 O = CO 2 + 4H 2 - Q; (3)

CO + H 2 O = CO 2 + H 2 + Q; (4)

Steam-air catalytic conversion of methane in a shaft converter (secondary reforming) is carried out on a nickel catalyst according to the reactions:

CH 4 +0.5O 2 = CO + 2H 2 + Q; (5)

CO + H 2 O = CO 2 + H 2 + Q. (6)

CH 4 + H 2 O = CO + 3H 2 - Q; (7)

CH 4 + CO 2 = 2CO + 2H 2 - Q; (8)

The conversion of carbon monoxide with water vapor occurs according to the reaction:

CO + H 2 O = CO 2 + H 2 + Q (9)

In industry, hydrogen is also produced in other ways:

§ by treating hot coal with water steam in special devices - gas generators. As a result of the interaction of water vapor with carbon, the so-called water gas is formed, consisting of hydrogen and carbon monoxide:

C + H 2 O = CO + H 2. (10)

When water gas is treated with water vapor in the presence of an iron catalyst, carbon monoxide is converted into dioxide, which easily dissolves in water at high blood pressure or in alkali solutions:

CO + H 2 O = CO 2 + H 2; (eleven)

This process takes place at a temperature of about 1000°C in the presence of a nickel-based catalyst with the addition of oxides of magnesium, aluminum and other metals. The resulting mixture can be used as a raw material for the production of various organic substances (methanol, aldehydes, hydrocarbons, etc.) or the production of hydrogen (the mixture is treated with water steam, as shown above);

§ as a by-product of the production of chlorine and alkali metal hydroxides by electrolysis of solutions of their chlorides.

Producing hydrogen from biomass. Hydrogen is obtained from biomass by thermochemical or biochemical methods. With the thermochemical method, biomass is heated without oxygen to a temperature of 500 - 800°C (for wood waste), which is much lower than the temperature of the coal gasification process. As a result of the process, H 2, CO and CH 4 are released. In a chemical process, hydrogen is produced by various bacteria.

The purest hydrogen in industry is produced by electrolysis of water. Electrolysis of water is one of the most well-known and well-researched methods for producing hydrogen. The economics of the process mainly depend on the cost of electricity. In the production costs of producing hydrogen, the cost of electrical energy is approximately 85%. This method has been used in a number of countries with significant hydropower resources. The largest electrochemical complexes are located in Canada, India, Egypt, Norway, but more than a thousand small installations have been created and operate in many countries. This method is also important because it is the most universal in relation to the use of primary energy sources. In connection with the development of nuclear energy, a new flourishing of water electrolysis based on cheap energy from nuclear power plants is possible. The electrochemical method of producing hydrogen from water has the following positive qualities:

1) high purity of the produced hydrogen - up to 99.9%;

2) simplicity of the technological process, its continuity, the possibility of the most complete automation, the absence of moving parts in the electrolytic cell;

3) the possibility of obtaining the most valuable by-products - heavy water and oxygen;

4) publicly available raw material - water;

5) process flexibility and the ability to produce hydrogen directly under pressure;

6) physical separation of hydrogen and oxygen during the electrolysis process itself.

If you create a constant electrical voltage, which exceeds the decomposition voltage of water, then a current will appear in the circuit and oxygen will begin to be released at the anode, and hydrogen at the cathode, in volumetrically 1:2.

The hydrogen and oxygen produced by electrolysis of water are of high purity. Their composition is standardized by GOSTs. Hydrogen obtained by electrolysis of water must meet the requirements of GOST 3022-80 (technical hydrogen grade B).

Obtaining heavy water

Electrochemical methods for producing heavy water are based on the fractionation of hydrogen isotopes in the process of electrochemical hydrogen discharge. As a result of the difference in the release potentials of light protium and heavy deuterium, protium is released at a higher rate than deuterium. This leads to the accumulation of deuterium in the electrolyte.

The main stage in the production of heavy water is the electrolysis of water. During electrolysis, water and D 2 O decompose with at different speeds. As a result, the electrolyte is enriched with heavy water. This occurs because the equilibrium potentials during the release of deuterium are more electronegative than for protium, and the overvoltage is higher. The hydrogen produced by electrolysis contains less deuterium than the original water.

Concentration of heavy water is carried out using a batch method and a continuous technological scheme.

If you carry out electrolysis in a periodic mode by loading a portion of natural water, you can obtain heavy water of any concentration in the electrolyte. To produce 1 g of heavy water with a concentration of the main substance of 99.8%, it is necessary to spend 100 kg of natural water. In this case, 5% of the deuterium contained in the source water will pass into the finished product. The rest of the deuterium will be carried away with hydrogen. In a batch process, the heavy water content in the electrolyte gradually increases. There comes a moment when the relative content of deuterium in the cathode gas exceeds its content in the original electrolyte. In this case, it becomes advisable to return the cathode gas to the process.

In industrial production, a continuous process is used, in which the energy costs for producing heavy water are significantly lower than in a batch process. Various options for a continuous process have been developed that make it possible to return deuterium-enriched hydrogen to the process by enriching one of the phases with heavy water. All methods for the continuous process of producing heavy water are based on the use of a stepped cascade of electrolyzers.

The first stage of the cascade includes filter-fresh electrolyzers, in which KOH (C = 26%) is used as an electrolyte. During the electrolysis process, oxygen and hydrogen are released from the electrolyzers and water enriched with D 2 O evaporates. This water is condensed and sent to the electrolyzers of the second stage of the cascade. The second stage of the cascade includes smaller number electrolysers, since only water carried away with electrolytic gases from the first stage of the cascade is used to power them. The third stage of the cascade includes the smallest number of electrolyzers. To power the electrolysers of this stage, condensate from the second stage is used.

Modern continuous technological schemes for the production of heavy water are designed using the processes of electrolysis, recovery, catalytic isotope exchange, and phase isotope exchange.

Catalytic isotope exchange consists of the fact that when water vapor comes into contact with hydrogen containing an increased amount of deuterium, the following reactions occur sequentially:

H 2 O + HD = HDO + H 2 (12)

HDO + D 2 = D 2 O + HD (13)

The equilibrium in these reactions is shifted to the right.

The basic design of the installation for concentrating heavy water is shown in the figure.

The basic design of a heavy water concentration plant:

1 - electrolysis stages;

2 - refrigerators;

3 - stages of phase catalytic exchange.

Steam enriched with heavy water condenses, and the condensate is separated from the vapor phase. Deuterium passes from the gas phase into the liquid phase. The distribution of deuterium between the gas and liquid phases is characterized by the separation coefficient:

where, C and are the concentrations of deuterium in the electrolyte solution and in the gas phase, molar fractions.

The value of the separation coefficient is influenced by factors: cathode materials and the state of their surface, cathode potential, process temperature.

Dependence on cathode material at a temperature of 75? C

In the case of phase isotope exchange upon contact liquid water with hydrogen containing an increased amount of gaseous deuterium, the reaction takes place:

H 2 O + HD = HDO + H 2 (15)

The equilibrium in this reaction is shifted to the right. Based on isotope exchange, a countercurrent process can be constructed in which deuterium is systematically transferred from the gas phase to the liquid phase.

During the recovery process, hydrogen containing an increased amount of deuterium is burned in a recovery furnace in a stoichiometric amount of oxygen, and water enriched with deuterium is fed to an earlier stage of electrolysis.

Modern continuous process flows for the production of heavy water are designed using electrolysis, recovery, catalytic isotope exchange and phase isotope exchange. In this case, a cascade of electrolyzers and furnaces is used to recover gases. The degree of water enrichment with deuterium in each electrolyzer of the cascade depends on the relationship between the strength of the electrolysis current and the supply of water for electrolysis. Using this scheme, it is possible to convert 25 - 40% of the deuterium contained in the source water into heavy water.

2 . Hydrogen productionelectrolysisohmwater

The concept and essence of electrolysis

Electrolysis is the redox process that occurs on the electrodes under the influence of an electric current supplied from an external source. Electrolysis converts electrical energy into chemical energy.

The electrolysis cell is called an electrolyser and consists of two electrodes and an electrolyte. The electrode on which the reduction reaction occurs (cathode) in the electrolyzer is connected to the negative pole of an external current source. The electrode on which the oxidation reaction occurs (anode) is connected to the positive pole of the current source. The nature and course of electrode processes are greatly influenced by the electrolyte composition, solvent, electrode material and electrolysis mode (voltage, current density, temperature, etc.).

The total voltage that must be applied to the electrolytic cell for the electrolysis process to begin is called the decomposition voltage - E decomposition. .

Overvoltage during electrolysis - h. Cathode overvoltage is an additional voltage applied to the cathode to shift its potential to the negative side, and anodic overvoltage is applied to the anode to shift its potential to the positive side. The voltage can be reduced by decreasing the resistance of the electrodes and electrolyte, as well as the polarization of the electrodes. The internal resistance of the electrolyser can be reduced by using an electrolyte with high electrical conductivity, increasing the temperature and reducing the distance between the electrodes.

Polarization can be reduced by increasing the surface of the electrodes, temperature, reagent concentration, stirring, as well as decreasing the current and using catalyst electrodes.

Sequence of electrode processes. Often, several types of cations and anions and undissociated molecules are present in the electrolyte, so several electrode reactions can occur.

Cathode processes. Since a reduction reaction occurs at the cathode, i.e. When electrons are accepted by an oxidizing agent, the strongest oxidizing agents must react first. At the cathode, the reaction with the most positive potential occurs first. For cathodic reduction during electrolysis of an aqueous electrolyte solution, all oxidizing agents can be divided into three groups. Metal ions whose potential is more negative than the potential of the hydrogen electrode. These include metal ions in the voltage range up to and including aluminum. In aqueous solutions, the discharge of these ions at the cathode practically does not occur; instead, hydrogen is released:

2H 2 O + 2e = H 2 + 2OH - (2H + + 2e = H 2). (16)

Anodic processes. Oxidation reactions of reducing agents take place at the anode, i.e. donation of electrons. Therefore, at the anode, substances with the most negative potential are oxidized first. The nature of the reactions at the anode also depends on the electrode material. There are insoluble and soluble anodes. Insoluble anodes are made from coal, graphite, and platinum. During electrolysis, insoluble anodes themselves do not send electrons to the external circuit; electrons are sent as a result of the oxidation of anions and water molecules.

Theoretical basis of the water electrolysis process

The process of electrolytic decomposition of water is described by the following overall chemical equation:

H 2 O = H 2 + 1/2 O 2 (17)

To produce gases separately, electrolyzers with diaphragms or membranes separating the cathode and anode spaces are used.

The specific conductivity of purified water is insignificant: at 18°C ​​it is 4.41·10 -6 Ohm -1 m -1 . Therefore, the electrolytic decomposition of water is carried out in the presence of a background electrolyte. Due to the significant corrosion problems encountered during the electrolysis of acids, almost all electrolyzers today use aqueous solutions based on potassium and sodium hydroxides with a concentration of 350-400 g/l. KOH solutions have advantages over NaOH due to the greater conductivity of the K + ion against the Na + ion. The KOH concentration corresponds to the optimal current densities. Small impurities in KOH are not an obstacle to its use. To prevent or reduce corrosion of electrolyzer parts, only pure KOH and NaOH are used when preparing the electrolyte.

To produce hydrogen by electrolysis of water, distilled or desalted water is used. natural water, which avoids the accumulation of various impurities in the electrolyte.

The electrolyte solution used in water electrolysis plants contains 16-20% NaOH or 25-30% KOH.

EtcOprocesses on electrodes

The cathodic process can be described by summary equations:

2H + + 2e = H 2 (in acidic medium) (18)

2H 2 O + 2e = H 2 + 2OH - (in alkaline environment) (19)

Let us consider the mechanism of cathodic hydrogen evolution from alkaline solutions. A direct discharge of water molecules occurs with the formation of hydrogen atoms and hydroxide ions adsorbed on the electrode. Next, the so-called electrochemical desorption reaction occurs. In total, these two processes give the cathodic reaction of hydrogen evolution.

The anodic process also depends on the acidity of the medium:

H 2 O = 2H + + 0.5O 2 + 2e (in acidic medium) (20)

2OH- = H2O + 0.5O2 + 2e (in an alkaline medium) (21)

In an alkaline environment, the flow of hydroxide ions to the anode surface is not hindered and direct oxidation of OH- occurs with the formation of oxygen and water (figure).

Electrolysis circuit

electrolysis hydrogen chemical

Electrolyzer designs

Industrial electrolysers for hydrogen production come in two types:

Monopolar - electrodes are powered in parallel in the same container;

Bipolar - electrodes are fed in series (an electrode on one side of the surface is an anode, and on the other - a cathode) and form a cell stack. Schemes of such electrolyzers are presented in Figure 1.3.

When connecting electrodes monopolarly, all electrodes of the same sign are connected to a bus coming from the corresponding pole of the source direct current. When the electrodes are connected bipolarly, current is supplied only to the outermost electrodes 1 and 2, which are monopolar electrodes. All other electrodes do not have a current supply and operate bipolarly.

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The relationship between current and voltage in electrolyzers

The lower the voltage on the electrolyzer cell, the less power it consumes. As the temperature of the electrolyte increases, the voltage of the electrolyzer decreases; therefore, it would be energetically beneficial to operate electrolyzers at elevated temperatures (when operating under pressure - with a temperature of 100°C and even higher). However, with increasing electrolyte temperature, corrosion processes intensify and the aging of the paronite gasket material is significantly accelerated. Therefore, for small electrolysis installations at power plants, the main importance is the reliability of the equipment and the duration of operation between repairs; the electrolyte temperature should be maintained at 60-75 ° C, and in cases where the operation of the electrolyzer at full load is not required, it is advisable to maintain 40-50 ° C. At the same time, to maintain the desired performance of the electrolyzer, the voltage should be increased.

In order for the current to pass through an electrolyzer with bipolar connection of electrodes, the voltage across the electrolyzer (U) must be equal to:

U= U 1 ·n, (22)

n - number of cells.

The voltage on a monopolar electrolyzer is equal to the voltage between a pair of electrodes (on one cell U= U 1).

The current (I) supplied to a monopolar electrolyzer branches out to all electrodes in accordance with the laws parallel connection. Therefore, the current flowing through a pair of electrodes I 1 =I/n.

In a bipolar electrolyzer, the current flowing through each pair of electrodes is equal to the current through the entire electrolyzer (I 1 = I) - the law of series connection.

Thus, with the same current load on the monopolar and bipolar electrolyzers, the amount of the resulting substance in the bipolar electrolyzer is n times greater. Therefore, for a bipolar electrolyzer there are concepts of linear and equivalent current. The equivalent current is equal to the linear current passing through the electrolyser multiplied by the number of cells:

I eq =I n. (23)

Monopolar electrolysers are not designed for current loads higher than 200 - 300 kA; bipolar electrolysers operate at an equivalent current load of up to 2000 kA. Consequently, bipolar electrolysers are more powerful and more productive.

Another advantage of bipolar electrolyzers is the reduction in voltage drop in the electrolyzer busbar and in the contacts by reducing their number (see Fig. 3).

In addition, the level of automation of bipolar electrolysers is higher than monopolar ones, which reduces costs work force for their service.

All modern designs of electrolysers for water electrolysis are of the filter-press type with bipolar inclusion of electrodes.

Diagram of a filter-press electrolyzer

The diagram of a filter-press electrolyzer for producing hydrogen and oxygen is shown in Figure 1.4.

Such electrolysers do not have a body, but are assembled from individual cells (the number of cells can be more than 100), which are rigidly fastened into a single filter-press structure using tie plates (6) and bolts (7). The side walls of the cells are the main sheets (3) of the electrodes, to which the remote perforated electrodes (1) are attached. The remaining four walls of the cell are a diaphragm frame (8), to which a diaphragm (5) is attached, separating the anode and cathode spaces of the cell. The diaphragm is asbestos, reinforced with nickel wire. Sealing of the electrolyzer is facilitated by gaskets (9). The electrolyte is supplied to the cells through the supply channel (10) through the fitting (11). To remove hydrogen and oxygen from the cells together with the electrolyte, fittings (12) and channels (13) and (14) are used. Gas is separated from the electrolyte in special traps. Thus, all cells of the filter-press bipolar electrolyzer communicate with each other through the supply and removal systems of the circulating electrolyte.

Small thicknesses of electrolysis cells (5 - 6 cm) and their extremely close mutual arrangement, as well as the high overall voltage on the electrolyzer contribute to the occurrence of current leaks.

There are two ways for current leakage from cells through fittings (11, 12) and channels (10, 13, 14):

1) by electrolyte in fittings and channels;

2) along the walls of fittings and channels.

There may be current leakage from the main electrode to the diaphragm frame. To reduce current leakage through the electrolyte, increase its resistance in the fittings:

where R is the electrolyte resistance (Ohm);

With - resistivity electrolyte (Ohm?m);

l - channel length (m);

S - channel cross-section (m2).

In accordance with formula (24), to increase the resistance of the electrolyte in the fittings, it is necessary to increase their length and reduce the cross-section.

Current leakage through the electrolyzer parts (fittings, diaphragm frames, etc.) bypassing the internal bipolar electrodes reduces the current passing through them and, accordingly, the amount of products obtained (hydrogen and oxygen). In addition, current leaks can include electrolyzer parts (fittings and diaphragm frames) in the electrolysis as bipolar electrodes, due to which mutual contamination of gases occurs. To reduce current leakage along the walls of fittings and supply channels, they are made of dielectrics or insulating inserts are used. To reduce current leakage along the diaphragm frame, insulating paronite gaskets (9) are placed between the main sheet of the electrode and the diaphragm frame, and the diaphragm frame is lined.

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Diagram of a bipolar filter-press electrolyzer:

1 - remote electrode; 2 - monopolar electrode (anode); 3 - bipolar electrode; 4 - monopolar electrode (cathode); 5 - diaphragm; 6 - tie plate; 7 - coupling bolt; 8 - diaphragm frame; 9 - paronite gasket; 10 - channel for electrolyte supply; 11 - fitting for electrolyte supply; 12 - fitting for draining the gas-liquid mixture; 13 - channel for collecting hydrogen; 14 - channel for collecting oxygen

Bipolar electrodes, when passing through a direct current electrolyzer, produce hydrogen on one side (cathode) and oxygen on the other (anode). Bipolar electrodes are made of carbon steel, with the anodes additionally coated with a layer of nickel.

The gases released at the electrodes are separated by an asbestos diaphragm attached to the diaphragm frames. The electrolyzer has three collectors: the upper ones are designed to remove gases and electrolyte, the lower one is for returning the cooling electrolyte to the cells. All elements of the electrolyzer are connected into a common package and tightened with four coupling bolts. To compensate for thermal expansion of the apparatus, disc springs are installed at the ends of the bolts. The tie bolts are isolated from the end plates using special bushings.

3 . Description of the technological process and diagrams of electrolysis plants

The process of producing hydrogen and oxygen by electrolysis of water for all types of electrolysis consists of the following operations:

Preparation of distilled water;

Electrolyte preparation;

Carrying out the process of electrolysis of water.

The first two operations are carried out periodically, according to the need for distilled water and electrolyte, the third operation is carried out continuously.

The production of feed water - distillate - is carried out in steam or electric distillers. For electrolysers operating under pressure, the distillates of the electrolysers are fed by dosing pumps.

The electrolyte is prepared in special boxes with false bottoms, on which drums with caustic sodium are placed with previously removed lids and heating coils for faster dissolution. The prepared solution of sodium hydroxide in distilled water is pumped into tanks, the capacity of which should be slightly larger than the capacity of one electrolyzer. Electrolyzers are replenished with electrolyte periodically through electrolyte filters if the concentration of sodium hydroxide in the electrolyzer decreases below the permissible level.

The process of producing hydrogen by electrolysis of water

When water is exposed to direct electric current, water decomposes into hydrogen and oxygen H 2 O = H 2 + 0.5 O 2 with the release of hydrogen at the cathode and oxygen at the anode. Chemically pure sodium hydroxide (NaOH) or potassium hydroxide (KOH) is added to the water. The voltage between the electrodes is 1.6 - 2.3 V, which is enough to decompose water, but not enough to decompose alkali.

The processes of water electrolysis are negatively affected by the presence of chlorine, sulfuric, carbonic acid, and iron ions in the electrolyte. Iron can accumulate at the cathode, forming bridges towards the anode, causing oxygen to become contaminated with hydrogen. To eliminate this process, potassium bichromate K 2 Cr 2 O 7 or sodium bichromate Na 2 Cr 2 O 7 is added to the electrolyte.

The hydrogen production workshop includes:

The electrolysis department, where the main technological process- electrolysis of water;

Preparatory department;

Gas analyzer;

Converter substation (for converting alternating current to permanent);

Open transformer substation;

Domestic premises.

Hydrogen and oxygen are produced in an electrolyzer by decomposing water using direct current. Pure water has very low electrical conductivity, so KOH (potassium oxide hydrate) solution is used as an electrolyte. Alkali in solution is in the form of charged particles - ions. Water dissociates into ions slightly. When an electric field is applied to a solution, the following processes occur at the cathode and anode:

4H 2 O + 4e- > 2H 2 - 4OH-

4OH- + 4e- > O 2 + 2H 2 O

2H 2 O > 2H 2 + O 2

The potassium ion is not discharged at the cathode, being only a carrier of electric current. From the electrolyzers, gases enter the separation columns along with the electrolyte. The electrolyte is cooled and returned to the electrolyzers. Hydrogen from the columns goes to the hydrogen pressure regulators, oxygen from the columns goes to the oxygen pressure regulators. The regulators are connected to each other at the bottom. Above the pressure regulators, equalization tanks are installed, from which water flows by gravity into the liquid system of pressure regulators when the water in the hydrogen pressure regulator is lowered to the fitting, which is connected to the upper zone of the equalization tanks. The electrolyte is prepared in a tank and pumped into the electrolyzer. During operation of the electrolysis unit, hydrogen is supplied to drying through a refrigerator; During startup, hydrogen is released into the atmosphere through a fire arrester, oxygen through a water seal. When the surge tanks are filled with water, hydrogen is released into the atmosphere through an expander.

Scheme of the process for producing hydrogen and oxygen by electrolysis of water

Production capacity and main technologicalequipment

Production capacity is determined by the productivity of the electrolyzer in m 3 /hour of hydrogen production.

The main technological equipment are:

Electrolyzers

Power transformers and rectifiers

Distillers

Tanks for preparing and storing electrolyte

Distilled water storage tanks

Feed pumps for electrolyte and distillate.

Technical characteristics of electrolysers

The technical characteristics of electrolyzers are given according to the technical documentation of the manufacturing plants in the table.

Characteristics of electrolysers

A schematic diagram of water electrolysis is shown in the figure.

Schematic diagram of water electrolysis

Technological scheme for producing hydrogen by electrolysis inOyes

To electrolyze water, you need a set of devices. They are connected into a technological scheme. The main apparatus of the circuit is an electrolyzer. In it, under the influence of direct electric current, part of the water is decomposed into hydrogen and oxygen, and the electrolyte continuously circulates, passing through electrolytic cells and then through the refrigerator. The circulating electrolyte carries with it the released hydrogen and oxygen. Gases are separated from it and collected separately. Next, the gases pass through devices for separating electrolyte splashes, washers and refrigerators (condensers).

The technological scheme of water electrolysis includes the following main components and stages:

- electrolyte preparation unit;

- stage of water purification using mechanical and ion exchange filters;

- the electrolysis stage with cooling and electrolyte circulation systems, regulating the electrolyte level and maintaining equal gas pressure in the cell; stages of gas drying and purification.

On rice Section 1.7 shows a technological scheme for producing hydrogen and oxygen by electrolysis of water.

The working electrolyte solution is prepared by dissolving solid alkali from the drums 1 in solvent tank 2. The resulting solution is sent to tank 3 for adjustment and fed into electrolyzer 21. To suppress steel corrosion, 2-3 kg/m 3 K 2 Cr 2 O 7 is introduced into the electrolyte.

Water, purified from mechanical impurities on the filter 4, is sent sequentially to columns 6, 7, filled with cation and anion exchange resins, respectively, where deep purification from impurities is carried out, and by gravity flows into the collection 9, from where it is pumped into the feed tank 10 and through the washer gas is supplied to electrolyzer 21.

Hydrogen and oxygen obtained during the electrolysis process are separated from the circulating electrolyte solution in columns 20 and supplied to washers - gas pressure regulators 18 and 19, in which the gases are cooled and washed from alkali.

From the washers, gases are sent through valve pressure regulators 17 to the consumer. If necessary, electrolysis gases are subjected to additional purification. On attachment filters 11 filled with glass wool, gases are purified from alkaline fog. Hydrogen is purified from oxygen impurities in contact apparatus 12 on nickel-aluminum or nickel-chromium catalysts at 100-130°C. Oxygen is purified from hydrogen impurities in a contact apparatus 13 filled with platinized asbestos, platinum deposited on aluminum oxide, or hopcalite.

Purified gases are supplied to refrigerators 14 and, after cooling, transferred for drying to drying columns 15 filled with silica gel or aluminum gel. The dried gases are sent to consumers through receivers 16.

Technological scheme for producing hydrogen by electrolysis of water

1 - drums with alkali; 2 - solvent tank; 3 - containers; 4 - filter for removing mechanical impurities from water; 5 - container for acid regeneration solution; 6 , 7 - ion exchange columns; 8 - container for alkaline regeneration solution; 9 - purified water collections; 10 - nutrient tank; 11 - filters for purifying gases from alkaline fog; 12 - apparatus for catalytic purification of hydrogen; 13 - apparatus for afterburning hydrogen and oxygen impurities; 14 - gas refrigerators; 15 - gas dryers; 16 - hydrogen and oxygen receivers; 17 - valve gas pressure regulators; 18, 19 - oxygen and hydrogen gas scrubber - gas pressure differential regulators; 20 - separation columns; 21 - electrolyzer; 22 - nitrogen cylinders for purging the electrolyzer; 23 - current converter

These devices are mounted as one unit and interact in the following order. From the oxygen and hydrogen parts of each electrolytic cell, the gas-filled electrolyte is carried into the gas collection channels of the electrolyzer separately into the oxygen and hydrogen channels. These channels end in the hydrogen and oxygen compartments of the middle chamber, respectively. In the middle chamber, gases are separated from the electrolyte and cooled. Due to the difference in weight of the column of gas-filled electrolyte (in the electrolytic cell) and free of gas (in the middle chamber), the electrolyte circulates. In the middle chamber it moves downwards, washing the tubes through which cooling water is pumped. In the lower part of the middle chamber, the electrolyte from both its compartments (hydrogen and oxygen) is mixed, passes through the filter and enters the channel for distributing the electrolyte among the electrolytic cells.

A schematic diagram of a device for equalizing gas pressure is shown in the figure.

Schematic diagram of the gas pressure regulator device

1.13 - float regulators; 2.12 - hydraulic regulators-washers; 3.11 - phase separators-capacitors; 4 - electrolytic cell; 5 - cathode space; 6 - nutrient channel; 7 - diaphragm; 8,9 - gas outlet channels; 14,15 - receivers; 10 - anode space.

Regulators act as intermediate hydraulic valves between the receivers and the cavities of the electrolyser. The pressure of hydrogen and oxygen in all cavities of the electrolyzer up to these gates is the same and higher than in receivers by the weight of the columns of water through which gases bubble in the oxygen and hydrogen compartments of the regulator. The height of the pillars is self-adjusting depending on the difference in gas pressure in the receivers. In electrolyzers operating under pressure significantly higher than atmospheric pressure, it is not possible to create hydraulic regulators required in height. Then the hydraulic regulators are supplemented with float valves. If necessary, gases from the electrolyzer are subjected to additional purification from electrolyte mist, oxygen from hydrogen impurities, and hydrogen from oxygen impurities. Gases are purified from electrolyte mist in packed filters filled with glass wool. Drops of fog are caught by cotton wool, the liquid flows into bottom part filter, from where it is periodically removed.

Hydrogen is purified from oxygen impurities by afterburning oxygen in contact devices. The hydrogen is then cooled in a refrigerator and dried in a column filled with silica gel. Oxygen is also purified from hydrogen impurities by afterburning, after which the gas is cooled and dried.

The production of hydrogen and oxygen is fully automated. The current strength is adjusted depending on the specified performance by correspondingly changing the voltage. The voltage is continuously monitored with a voltmeter. Voltage drops between the cathode and frame, as well as the anode and frame, are periodically checked to monitor short circuits and current leaks. The amount of supplied water is regulated based on the liquid level in the gas collector.

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On a negatively charged electrode - cathode is happening electrochemical reduction particles (atoms, molecules, cations), and on a positively charged electrode - anode coming electrochemical oxidation particles (atoms, molecules, anions). Below are classic formulas electrolysis

1.Salt of active metal and oxygen-containing acid

Na 2 SO 4 ↔2Na + +SO 4 2−

A(+): 2H 2 O - 4e = O 2 + 4H +

Conclusion: 2H 2 O (electrolysis) → H 2 + O 2

2. Hydroxide: active metal and hydroxide ion

NaOH ↔ Na + + OH −

K(-): 2H 2 O + 2e = H 2 + 2OH −

A(+): 2H 2 O - 4e = O 2 + 4H +

Conclusion: 2H 2 O (electrolysis) → 2H 2 + O 2

During the electrolysis of water, Oxygen () is released at the anode, and Hydrogen () at the cathode

We will conduct the first experiment to obtain hydrogen and oxygen.
Make an electrolyte from a baking soda solution (you can use soda ash), lower the electrodes there and turn on the power source. As soon as the current flows through the solution, gas bubbles that form at the electrodes will immediately become noticeable: oxygen will be released at “+”, hydrogen at “-”. It is this distribution of gases that occurs due to the fact that near the anode “+” there is an accumulation of negative OH- ions and reduction of oxygen, and near the cathode “-” ions accumulate alkali metal, which are contained in soda ash(Na2CO3) having a positive charge (Na+) and at the same time hydrogen reduction occurs. The reduction of sodium ions to pure metal Na does not occur, since the metal sodium is in the series of metal voltages to the left of hydrogen
Li< K < Rb < Cs < Ba < Ca < Na < Mg < Al < Mn < Cr < Zn < Fe < Cd < Co < Ni < Sn < Pb < H2 < Cu < Ag < Hg < Pt < Au

Traditionally, so-called dry electrolysers are used to produce hydrogen and oxygen from water in cars. They are also called NGO Generators

Hydrogen and oxygen produced in the engine, through the HHO generator through electrolysis, will significantly accelerate the ignition of the fuel mixture in the cylinders of your engine, increasing the power output of the gasoline or diesel internal combustion engine (Engine). internal combustion). Hydrogen ignites 1000 times faster than evaporated liquid fuel, thereby igniting the evaporated liquid fuel and increasing the work of the explosive force of the piston in the first phase of its operation. The benefits of adding NHO to the fuel mixture of internal combustion engines, including diesel engines, have been well studied and documented by both the US and foreign governments and many major universities and research centers around the world.

ELECTROLYSIS

set of electrochemical oxidation-reduction processes occurring during the passage of electricity. current through an electrolyte with electrodes immersed in it. At the cathode, cations are reduced into ions of a lower oxidation state or into atoms, for example: Fe 3+ + eFe 2+, Cu 2+ + 2e Cu (e - electron). Neutral molecules can participate in transformations at the cathode directly or react with the products of the cathodic process, which are considered in this case as intermediates. in-va E. At the anode, oxidation of ions or molecules coming from the electrolyte volume or belonging to the anode material occurs; in the latter case, the anode dissolves or oxidizes (see. Anodic dissolution). Eg:

E. includes two processes: migration of reacting particles under the influence of electricity. fields to the surface of the electrode and the transfer of charge from particle to electrode or from electrode to particle. The migration of ions is determined by their mobility and transport numbers (see. Electrical conductivity of electrolytes). The transfer process is several. electric charges are carried out, as a rule, in the form of a sequence of one-electron reactions, i.e. step by step, with the formation of intermediates. particles (ions or radicals), which sometimes exist for some time on the electrode in the adsorbir. condition.
The speeds of the electrode circuits depend on the composition and concentration of the electrolyte, the material of the electrodes, electrode potential, t-ry, hydrodynamic. conditions (see Electrochemical kinetics). The measure of speed is the current density - the number of transferred electric currents. charges through a unit area of ​​the electrode surface per unit time. The number of products formed during E. is determined Faraday's laws. The day of release of 1 gram equivalent of a substance on the electrode requires an amount of electricity equal to 26.8 A* hours. If several are simultaneously formed on each of the electrodes. products as a result of a number of electrochemical r-tions, the share of current (in %) going to the formation of the product of one of the r-tions, called. current output of this product.
The electrode process involves substances that require the least amount of electricity to transfer charge. potential; this might be not those substances that determine the transfer of electricity in the volume of the solution. For example, during the emission of an aqueous solution of NaCl, Na + and Cl + ions participate in migration, however, on solid cathodes, Na + ions are not discharged, but an energetically more favorable process of discharge of protonated water molecules occurs: H 3 O + + e - > 1/2H 2 + H 2 O.

Application of E. Obtaining target products by electrolysis makes it possible to relatively simply (by adjusting the current strength) control the speed and direction of the process, thanks to which it is possible to carry out processes both in the “softest” and in the extremely “hard” conditions of oxidation or reduction, obtaining the strongest oxidizing agents and reducing agents. By E., H 2 and O 2 are produced from water, C1 2 from aqueous solutions of NaCl, F 2 from the KF melt in KH 2 F 3.
Hydroelectrometallurgy is an important branch of non-ferrous metallurgy (Cu, Bi, Sb, Sn, Pb, Ni, Co, Cd, Zn); it is also used to obtain noble and trace metals, Mn, Cr. E. is used directly for cathodic separation of metal after it has been transferred from ore to solution, and the solution has been purified. This process is called electroextraction. E. is also used for cleaning metal - electrolytic. refining (electrorefining). This process consists of anodic dissolution of the contaminated metal and its subsequent cathodic deposition. Refining and electroextraction are carried out with liquid electrodes made of mercury and amalgams (amalgam metallurgy) and with electrodes made of solid metals.
E. electrolyte melts are an important method for the production of many. metals So, for example, raw aluminum is obtained by E. cryolite-alumina melt (Na 3 AlF 6 + A1 2 O 3), the raw material is purified electrolytically. refining. In this case, the anode is melt A1, containing up to 35% Cu (for weighting) and therefore located at the bottom of the electrolyzer bath. The middle liquid layer of the bath contains BaCl 2, AlF 3 and NaF, and the upper one contains molten refiner. A1 serves as the cathode.
E. melt of magnesium chloride or dehydrated carnallite - max. a common method for obtaining Mg. In prom. scale E. melts are used to obtain alkaline and alkaline-earth. metals, Be, Ti, W, Mo, Zr, U, etc.
To electrolytic Methods for producing metals also include the reduction of metal ions to other, more electron-negative ones. metal. The isolation of metals by their reduction with hydrogen also often includes the stages of electrochemical reactions. ionization of hydrogen and deposition of metal ions due to the electrons released during this process. Important role processes of joint isolation or dissolution of several play. metals, joint release of metals and mol. hydrogen on the cathode and adsorption of solution components on the electrodes. E. is used for the preparation of metallic. powders with specified characteristics.
Other important applications of E.- electroplating, electrosynthesis, electrochemical metal processing, corrosion protection (see Electrochemical protection).

Electrolyzers. Industrial design devices for carrying out electrolytic processes is determined by the nature of the process. In hydrometallurgy and electroplating they use preim. so-called box electrolysers, which are an open container with electrolyte, in which alternating cathodes and anodes are placed, connected accordingly. with negative and put it down. poles of a direct current source. For the manufacture of anodes, graphite, carbon-graphite materials, platinum, oxides of iron, lead, nickel, lead and its alloys are used; They use low-wear titanium anodes with an active coating made from a mixture of ruthenium and titanium oxides (ruthenium-titanium oxide anodes, or ORTA), as well as from platinum and its alloys. For cathodes in most electrolyzers, steel is used, including decomp. protective coatings taking into account the aggressiveness of the electrolyte and electrolyte products, t-ry and other process conditions. Some electrolyzers operate under high pressure conditions, for example, water decomposition is carried out under pressure up to 4 MPa; Electrolyzers are also being developed for higher pressures. In modern Plastics are widely used in electrolyzers. masses, glass and fiberglass, ceramics.
In plural electrochemical production requires separation of the cathode and anode spaces, which is done using diaphragms that are permeable to ions, but impede the flow. mixing and diffusion. This achieves separation of liquid and gaseous products, formed on the electrodes or in the volume of the solution, the participation of the original, intermediate ones is prevented. and final products of electrolysis in areas on the electrode of the opposite sign and in the near-electrode space. In porous diaphragms, both cations and anions are transferred through micropores in quantities corresponding to the transfer numbers. In ion exchange diaphragms (membranes), either only cations or anions are transferred, depending on the nature of the ionogenic groups included in their composition. When synthesizing strong oxidizing agents, diaphragm-less electrolyzers are usually used, but K 2 Cr 2 O 7 is added to the electrolyte solution. During the electromagnetic process, a porous chromite-chromate film is formed on the cathode, which performs the functions of a diaphragm. When producing chlorine, a cathode in the form of a steel mesh is used, on which a layer of asbestos is applied, which acts as a diaphragm. In the E. process, brine is fed into the anode chamber, and NaOH solution is removed from the anode chamber.
Electrolyzer used for the production of magnesium, aluminum, alkaline and alkali-earth. metals, is a bath lined with refractory material, at the bottom there is a molten metal that serves as a cathode, while anodes in the form of blocks are placed above a layer of liquid metal. In the processes of membrane production of chlorine, in electrosynthesis, filter-press type electrolyzers are used, assembled from separate. frames, between which ion-exchange membranes are placed.
Based on the nature of the connection to the power source, monopolar and bipolar electrolysers are distinguished (Fig.). A monopolar electrolyzer consists of one electrolytic cell. cells with electrodes of the same polarity, each of which can consist of several. elements connected in parallel to a current circuit. A bipolar electrolyzer has a large number of cells (up to 100-160) connected in series to the current circuit, and each electrode, with the exception of the two outer ones, works on one side as a cathode and the other as an anode. Monopolar electrolysers are usually designed for high current and low voltage, bipolar - for relatively low current and high voltage. Modern electrolysers allow a high current load: monopolar up to 400-500 kA, bipolar equivalent to 1600 kA.

Electrolysis of water- This is a well-known electrolysis process for everyone who is familiar with technology, in which water is used as an electrolyte.

However, it should be noted that water is always present during electrolysis. First, let's look at what the electrolysis process is in general.

Electrolysis

Electrolysis is electrochemical process, which is carried out by placing two electrodes in the electrolyte and connecting direct current to them.

Electrolytes are called liquid conductors, which belong to the second type of conductors. Liquid conductors mean liquids/solutions that have electrical conductivity.

For reference, we add that the vessels into which electrolytes are poured are called galvanic baths.

During the electrolysis process, ions, under the influence of an electromagnetic field generated in the electrolyte by a direct electric current, begin to move towards the electrodes. Ions with positive charge, in accordance with the laws of physics, move towards the electrode with negative charge, which is called CATHODE, and the negatively charged ions accordingly move to another electrode called ANODE. Electrolysis is accompanied by the release of substances on the electrodes, which indicates the movement of atoms in electrolytes. For example, metals and hydrogen are typically released at the CATHODE.

The electrolysis process is influenced by several factors:

• current strength connected to the electrodes;
• ion potential;
• electrolyte composition;
• the material from which the electrodes are made - CATHODE and ANODE.

Electrolysis of water

As we noted above, electrolysis of water involves the use of water as an electrolyte.

As a rule, when electrolysis of water, for a better process, a little of some substance is added to the water, for example baking soda, but this is not necessary, since ordinary water almost always already contains impurities.

As a result of the electrolysis of water, hydrogen and oxygen are released. Oxygen will be released at the ANODE, and hydrogen at the CATHODE.

Application of water electrolysis

Water electrolysis technology is used:

• in water purification systems from all kinds of impurities;
• to produce hydrogen. Hydrogen, for example, is used in a very promising industry - hydrogen energy. We have already written about this in more detail in our material.

As we see, water electrolysis, despite its apparent simplicity, is used in very important areas - in areas on which the development and prosperity of our entire civilization depends.

Electrolysis of water is called physical-chemical process, in which, under the influence of a direct electric current, water decomposes into oxygen and hydrogen. The DC voltage for the cell is usually obtained by rectifying the three-phase alternating current. In an electrolytic cell, distilled water undergoes electrolysis, while chemical reaction goes according to the following well-known scheme: 2H2O + energy -> 2H2+O2.

As a result of dividing water molecules into parts, the volume of hydrogen produced is twice that of oxygen. Before use, the gases in the installation are dehydrated and cooled. The outlet pipes of the installation are always protected by check valves to prevent fires.

The frame of the structure itself is made of steel pipes and thick sheets of steel, which gives the entire structure high rigidity and mechanical strength. Gas tanks must be tested under pressure.

The electronic unit of the device controls all stages of the production process, and allows the operator to monitor the parameters on the panel and pressure gauges, which ensures safety. The efficiency of electrolysis is such that from 500 ml of water about a cubic meter of both gases is obtained with a cost of about 4 kW/h of electrical energy.

Compared to other methods of producing hydrogen, electrolysis of water has a number of advantages. Firstly, available raw materials are used - demineralized water and electricity. Secondly, there are no polluting emissions during production. Thirdly, the process is completely automated. Finally, the output is a fairly pure (99.99%) product.

Therefore, electrolysis plants and the hydrogen produced from them are used today in many industries: in chemical synthesis, in the heat treatment of metals, in the production of vegetable oils, in the glass industry, in electronics, in cooling systems in the energy sector, etc.

The electrolysis installation is installed in the following way. The control panel for the hydrogen generator is located outside. Next, a rectifier, transformer, switchgear, demineralized water system and a unit for replenishing it are installed.

In an electrolytic cell, hydrogen is produced on the cathode plate side, and oxygen is produced on the anode plate side. This is where the gases leave the cell. They are separated and fed into a separator, then cooled with demineralized water, after which they are separated from the liquid phase by gravity. Hydrogen is sent to the washer, where drops of liquor are removed from the gas and cooling occurs in the coil.

Finally, the hydrogen passes through filtration (a filter on the top of the separator), where water droplets are completely eliminated, and enters the drying chamber. Oxygen is usually released into the atmosphere. Demineralized water is supplied to the washer by a pump.

Lye is used here to increase the electrical conductivity of water. If the operation of the electrolyzer is normal, then the liquor is replenished once a year in a small amount. Solid caustic potassium is placed in a lye tank two-thirds filled with demineralized water, after which a pump stirs it into solution.

The water cooling system of the electrolyser serves two purposes: it cools the liquor to 80-90°C and cools the resulting gases to 40°C.

The gas analysis system accepts hydrogen samples. Drops of liquor in the separator are separated, the gas is supplied to the analyzer, the pressure is reduced, and the oxygen content of hydrogen is checked. Before the hydrogen is sent to the tank, the dew point will be measured in the moisture meter. A signal will be sent to the operator or PC to decide whether the resulting hydrogen is suitable for sending to the storage tank and whether the gas meets the receiving conditions.

The operating pressure of the installation is regulated using an automatic control system. The sensor receives information about the pressure inside the electrolyzer, then the data is sent to a PC, where it is compared with the specified parameters. Next, the result is converted into a signal of about 10 mA, and the operating pressure is maintained at a given level.

The operating temperature of the unit is controlled by a pneumatic diaphragm valve. The computer will similarly compare the temperature with the set temperature, and the difference will be converted into an appropriate signal for .

The safety of the electrolyzer is ensured by a locking and alarm system. In case of hydrogen leakage, detection occurs automatically by detectors. The program immediately turns off the generation and starts the fan to ventilate the room. The operator must have a portable leak detector. All these measures make it possible to achieve a high degree of safety during the operation of electrolysers.