LABORATORY SETUP FOR PRODUCING HYDROGEN BY WATER ELECTROLYSIS

S. I. SMOLYANINOV

(Presented by Prof., Doctor of Technical Sciences I. V. Gebler)

Hydrogen is used in the laboratory for a wide variety of purposes. Relatively small quantities of it are easily and simply obtained by the action of metals on acids. However, systematic consumption of hydrogen, and especially of substantial quantities of it, is less convenient by this method and is associated with a considerable expenditure of reagents. In this case, the production of hydrogen by the electrolysis of water proves more convenient. Despite the comparatively complicated apparatus, this method is good in that it requires almost no expenditure of any reagents; the apparatus can always be ready for operation; and, finally, the hydrogen obtained is of high purity. In addition, oxygen is obtained as a by-product, which can also be used.

Described below is a simple-to-manufacture and sufficiently productive apparatus for producing hydrogen that we have constructed. The design of the electrolyzer is shown in Fig. 1.

Fig. 1. Electrolyzer.

The device consists of a series of cells connected in sequence. A cell is a U-shaped glass tube 1 with an internal diameter of about 10–12 mm, filled almost to the top with electrolyte. Electrodes 2, made of nickel wire 0.5–1.0 mm in diameter, wound in the form of a spiral with an outside diameter slightly smaller than the diameter of the glass tube, are lowered into both knees of the tube. The length of the wire in the spiral is about 0.5–0.8 m. The electrodes are made in pairs, so that one of them is the anode of one cell and the other the cathode of another—

cell. The section of nickel wire connecting them is insulated along its entire length outside the U-shaped tubes with a polyvinyl chloride tube 3, into which water is poured to create a hydraulic seal. The U-shaped tubes are installed in special sockets 4 so that one and the same pole is in a single row for all the tubes. A comb manifold 5 with tees for the electrolyzer cells is connected to each of these rows. Glass tubes 7 are attached to the tees by means of pieces of rubber tubing 6; the upper edge of these tubes is set at the same level as the upper edge of the U-shaped tubes; hydrogen and oxygen are collected in these manifolds—each on the corresponding side. In order to ensure the collection of these gases, the entire system is lowered into a vessel with running water, with the water level not reaching the edge of the U-shaped tubes by approximately 1 cm, and each arm of the latter, together with the glass tube for gas collection 7 and part of the connecting section of the electrodes 3, is covered from above by a glass bell 8. The water hermetically seals the rubber connections and, in addition, cools the electrolyzer cells. The ends of the collecting manifold, installed with a slight incline, are led out through the walls of the vessel (Fig. 2).

Fig. 2.

General diagram of an apparatus for producing hydrogen by electrolysis of water.

During electrolysis, as is known, the concentration of electrolyte at the cathode increases and decreases at the anode, which leads to an increase in the electrical resistance of the cell and a drop in the current. It is therefore necessary periodically to stir the electrolyte in the cells. For this purpose the glass caps are removed from the anode side, and a piece of glass tubing 6 mm in diameter, having a bulb-shaped enlargement in its upper part and fitted with a rubber bulb, is lowered into the U-shaped tubes to the bottom. With the aid of such a device, stirring is carried out easily and quickly.

In addition, distilled water must be added to the cells from time to time, as well as electrolyte, since during operation some of it is carried away in the form of mist.

Such an electrolyzer, consisting of two parallel branches of seventeen series-connected cells, gives 15 liters of hydrogen per hour at a current passing through one cell of 1 ampere and a voltage drop per cell of about 15 volts. A 15-percent solution of caustic soda is used as the electrolyte. The normal operating temperature of the bath is about 60°C.

The output of the electrolyzer can be increased by increasing the current load to 1.5 amperes per cell. A further increase in the load is associated with severe contamination of the hydrogen, since under these conditions the gas evolution from the electrolyte does not have time to be fully completed, and

some of the oxygen bubbles may be carried by the convective flow of the liquid into the cathode half of the cell.

The general layout of the apparatus for producing hydrogen is shown in Fig. 2. Direct current is obtained with the aid of a gasotron 1 (VG-237). The anode voltage is regulated by autotransformer 2. Hydrogen and oxygen from electrolyzer 3 pass through the system of hydraulic seals 4 into pressure regulator 5, which maintains the same pressure in the cathode and anode compartments. The oxygen is then discharged into the atmosphere or collected in a separate vessel. The hydrogen passes through a section of glass tube 6 with electric heating, filled with palladized asbestos. Here it is purified of the oxygen impurity.

Then the hydrogen, after passing through the line of the hydraulic-seal safety device 7, is fed by gas blower 8 into the gas holder.

The pumping rate is regulated by float relay 9.

Such an apparatus has already been in operation for several years and has proved itself reliable in operation, convenient to service, and sufficiently safe.