SU1000390A1 - Method for purifying hydrogen - Google Patents

Description

The invention relates to methods for purifying hydrogen by diffusion, in particular by diffusion through metal or alloy membranes.

A known method of purification of hydrogen by filtering gas filters on palladium and its alloys with silver, with the highest permeability to hydrogen of Le 100 or more times higher than that of other metals) at relatively low operating temperatures. The hydrogen to be purified from gas impurities is heated to 200 700 ° C and is fed under pressure up to 200 atm into a chamber, one or several of which is made of a thin palladium membrane. On the opposite side of the membrane, a low pressure chamber is installed, into which the hydrogen that has diffused through the membrane penetrates. For npej, .-. repulsing the pushing of the membrane from the low pressure side is supported by a porous metal or ceramic liner, which takes on mechanical loads tl.

The disadvantage of this method is low filtration performance (no more than 1 In addition /

The working surface of the membrane is sometimes covered with a layer of impurities adsorbed on it, which are contained in hydrogen, as a result of which the surface activity decreases, the hydrogen molecules are difficult to access and the filtration performance decreases. To restore the surface activity of the membranes, they are periodically cleaned and rinsed with solvents jt, which does not lead to a complete restoration of the filtering properties. Therefore, after several applications, the membranes have to be replaced.

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The closest to the proposed technical essence and the achieved result is the method of hydrogen purification by filtration through a metal membrane, the surface of which is activated by a glowing glow, constantly burning in the filtered gas. For this, the membrane is attached to the negative pole of the voltage source, and at some

25, the distance from the membrane in the high-pressure chamber installs an electrode connected to the positive pole of the voltage source (.1000-1200 V K. At gas pressure in

A high-pressure chamber of a few mm Hg between the electrode and the membrane ignites a self-sustaining volumetric discharge with a current density of 10 mA / cm. At the discharge discharge part of the gas molecules occurs, in the cathode region Glow discharge positive ions are accelerated by an electric field and bombard the surface of the cathode, which is a membrane. Under the action of ion bombardment, oxide films and contaminants are sputtered onto the metal surface. As a result, the surface is gradually cleaned and activated. On the activated areas of the membrane surface, chemisorption of part of the hydrogen molecules that hit the surface during thermal motion in the gas occurs. And with the fastest speed, I chemisorb with the excited hydrogen molecules with the discharge. As a result of chemisorption, the hydrogen molecules dissociate into atoms, the atoms transfer their electrons to the metal and, in the form of protons, are introduced into the metal and diffuse in it. On the opposite side of the membrane, protons are again bonded to electrons and in the form of hydrogen atoms are released on the metal surface. Then, the atoms join into hydrogen molecules and leave the membrane surface on the side of the low pressure chamber, where there is no electrical discharge in the gas. During the time of activation of the membrane surface with 200 minutes glowing with the specified parameters, the rate of hydrogen penetration through the steel membrane 1 mm thick gradually increased from 0 at the initial moment to 1 - / s-cm-2. The disadvantage of the known method is the low performance of hydrogen filtration , due to the fact that the glow discharge exists only at gas pressures Hummer. At higher pressures, this discharge ceases to be volumetric. As a result, at such low gas pressures, the cleaning capacity hydrogen does not exceed 1-cm cm-sm. The purpose of the invention is to increase the productivity of the cleaning process. The goal is achieved according to the hydrogen purification method, which includes filtering it through a metal membrane, activating the surface of the membrane by volumetric electric discharge in the gas to be filtered, removing the purified hydrogen, in which the activation of the membrane surface is carried out by a non-self-ionizing discharge. This method allows to increase the productivity of the process by 10 1 times from 3-10 to 5-10. A device for carrying out the proposed method consists of a metal body into which a porous gas-permeable insert is inserted, which has sufficiently high mechanical strength, electrical conductivity and thermal conductivity. A metal membrane with a thickness of 10 to 100 microns is pressed or attached to the insert. It can be made from any metal or alloy,; but palladium, nickel, niobium, titanium and stainless steel are preferred. The membrane is sealed with copper rings between the casing and the ceramic insulator. The metal casing of the working chamber is pressed to the opposite end of the insulator or the pressure tube is pressed through the seal. hydrogen. Inside the working chamber there is an electrode made of metal mesh or foil attached to the body and installed parallel to the membrane. The distance between the electrode and the membrane should be chosen to be minimal, but sufficient to withstand without self-test the potential difference applied to the electrode and the membrane from an external voltage source. In addition, the electrode should be fixed so that there is free gas access to the membrane surface, but that the gas flow through the chamber does not displace the electrode, there is a window in the work chamber housing covered with a titanium or beryllium foil 30-50 µm thick that serves through it into the working chamber of the electron beam from an external source of electrons. On the outside, the foil is tucked in a grid that helps to withstand high gas pressures on the foil. The grille is attached to the flange that presses the foil through a seal to the body. The back side of the metal casing, forming a low pressure chamber, is closed with a lid with a pipe attached to it to drain clean (filtered) hydrogen. The metal housing of the low pressure chamber is electrically connected to the negative pole of the voltage source, and the housing of the high pressure chamber to the positive pole. A pipe with cooling fluid circulating through it is welded to the housing of the low pressure chamber. Example 1 Pure hydrogen is obtained by filtration of a nitric mixture obtained by dissociating technical ammonia. For this purpose, the nitric mixture under pressure up to 1 atm is supplied to the device. Membrane

made of metal listed in table 1, has a thickness of 50 microns and an area of 10-100 cm. The pure liner is made of powder-coated metallurgy of stainless steel powder and has pores of 50 microns. The foil is made of titanium with a thickness of 50 microns and has an area of 5 "100 cm. The electrode is made of titanium foil with a thickness of 50 microns, mounted on a steel grid. The distance from the membrane to the electrode foil is 2 mm, from the electrode foil to the window foil - 50 mm. The flow rate of the source gas through the device is 100. Through the window, covered with foil, an electron beam from the ELITA-500 miniature accelerator is fed into the working chamber. The accelerator generates pulses of an electron beam with a duration of 5 µs, repeated at a frequency of 300 Hz. The electron energy is 0.4 MeV, the beam current per pulse is 0.25A. The time average power of the beam is 100 watts. In the exhaust system of the accelerator, the electron beam is attached with the help of magnetic lenses to the shape of an ellipse in cross section with semiaxes 5 and 100 cm. On the foil closing the entrance to the canal. the high pressure measure, the electron beam is scattered with the rms scattering angle of the aura and passing through the gas in the high pressure chamber, irradiates the electrode foil more or less evenly throughout its area. Passing through the foil, the electron beam will ionize the gas between the electrode and the membrane. The beam current density in a pulse on a membrane is 0.2 A / cm. A potential difference of 7 kV from an external rectifier is applied to the electrode and the membrane. During the pulses of the electron beam between the electrode and the membrane, a non-self-sustaining (electro-ionization) ignites, the discharge with a current pulse duration equal to the beam pulse duration (-5 μs). The amplitude of the discharge current pulses reaches 4 kA. The current density is 4 A / cm. With a pulse repetition frequency of 300 Hz, the average discharge power consumed from the rectifier reaches 42 kW, and the average power density in the discharge of 42 W / CM - In a discharge gap, the gas is heated by electric discharges and at the output of The device has a tempo of 400 to 400. In order to recover heat, the HOT gas coming out of the device is fed through a pipe to a heat exchanger, where it heats the cold nitrogen-hydrogen mixture up to 200-300 0 entering the discharge device. The pure hydrogen that diffuses the membrane collects in the low pressure chamber and under pressure up to 1 The pipeline is delivered to the consumer. Clean water and 99.999% by volume. The capacity of the device and the specific productivity of filtration (nl / h-cm measured during the operation of the device for 4 hours, depend on the metal of the membrane and are listed in Table 1.

Example 2. The clearing is carried out. ku technical hydrogen with a purity of 98 vol%. All operations are carried out in the same manner as in Example 1, with the difference that

Gargon in the amount of 5 o6L%. Ib result at camera exit

low pressure, hydrogen is obtained with a purity of 99.999% by volume, and

leaving the high pressure chamber is a mixture enriched in argon.

Table 1 shows the comparative data of hydrogen filtration according to the prototype method, known spjco6y and proposed.

The introduction of the proposed invention would not allow to obtain a significant economic effect due to the replacement of the palladium filter with a nickel filter, which saves about 12 kg of palladium per year only on a TV-e installation.

Claims (2)

1. Stezhenskiy A.I. et al. Production of high-purity hydrogen in diffusion plants. K., Naukova Dumka, 1970, p. 35. 2.R R.A. And others. Hydrogen penetration into metals under gas discharge conditions. Lime universities of the USSR, sir. Physics, 3, 1969, p. 136-138 (prototype).