Laboratory Gas Generator
Abstract Generated abstract
A simple laboratory generator is described for producing water gas or carbon monoxide by passing steam or carbon dioxide through an electrically heated bed of carbonaceous material. The design uses two electrodes, a quartz tube, a water seal, and an adjustable fuel layer, avoiding joints in the high-temperature zone and allowing relatively easy charging, disassembly, and replacement of parts. The author notes both the attainable high temperatures and the difficulty of maintaining a constant regime typical of cryptol-type furnaces, and reports that a unit operating on charcoal at 1100 to 1300°C produced more than 100 liters of carbon monoxide per hour from carbon dioxide.
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LABORATORY GAS GENERATOR
S. I. SMOLYANINOV
(Presented by the scientific seminar of the Chemical-Technology Faculty)
In the laboratory one often has to deal with water gas or carbon dioxide, which may be required both for carrying out various kinds of syntheses (for example, the synthesis of hydrocarbons) and for other purposes.
Below is described a simple design of a laboratory gas generator suitable for obtaining the indicated gases.
In principle, the generator consists of two electrodes, between which is placed a layer of electrically conducting carbonaceous material (coke, charcoal) heated by an electric current to the required temperature; steam or carbon dioxide is passed through it.
The construction of the generator is shown in Fig. 1. In the center of cup 1, made of roofing iron or another suitable material, a one-inch gas pipe 2 is soldered in. The lower electrode 3, rolled without a seam from a piece of roofing iron, is fitted onto the pipe with sufficient friction. A quartz tube 4, about 40 mm in diameter and 500 mm high, is freely placed over this electrode and the pipe. The tube rests on the bottom of the cup. From above, the upper electrode 5, made of roofing iron in the form of a funnel, is inserted into tube 4. A conductor 7 is attached to this electrode by means of screw 6; along its entire length it is insulated by a porcelain tube 8. The conductor, on rubber stopper 9, is introduced through metal tube 10 (about 10 mm in diameter), soldered into the bottom of cup 1. The area of the electrodes must correspond to a current density of \(0.1\ a/\text{cm}^2\). Pipe 2 is closed from below with rubber stopper 11, through which the sheath of thermocouple 12 is passed. The electrodes and the quartz tube are covered from above by cap 13, having a somewhat smaller diameter than the cup. The cap is made of roofing iron, and the seams
Fig. 1.
are soldered with hard solder or welded. Onto the upper edge of the funnel of electrode 5, with the aid of pieces of wire, several sections of porcelain tube may be fitted in order to prevent a short circuit in the event of possible contact between cap 13 and electrode 5 (not shown in Fig. 1).
The carbonaceous material is poured into the funnel of the upper electrode and fills the space inside tube 2, quartz tube 4, and the funnel. The latter serves as a reserve hopper.
To charge the generator it is sufficient to remove cap 13. The generator can be discharged (carefully, so as not to break the thermocouple sheaths) by pulling out plug 11.
Voltage, through a rheostat—or, better, an autotransformer—is applied on one side to conductor 7 and through it to the upper electrode, and on the other side to the generator body and through it to the lower electrode.
Water is poured into cup 1 to form a hydraulic seal; in addition, it protects the rubber stoppers and the soldering of the cup from overheating.
Carbon dioxide or steam is fed into the lower part of the generator through nipple 14, rises through the quartz tube, passes through the layer of incandescent fuel between the electrodes, enters through the funnel under the cap, and descends beneath it. The reacted mixture is withdrawn through metal tube 15, 8–10 mm in diameter, soldered into the bottom of the cup. If necessary, the jacket of a condenser is fitted onto the outer end of this tube. For removal of condensate accumulating during operation with steam in the lower part of tube 2, a soldered-in small tube 16 is provided. A piece of rubber tubing with a clamp is fitted onto it.
Thus, in the high-temperature zone there are no joints whose tightness might be a cause for concern.
Assembly and disassembly of the generator, as well as replacement, when necessary, of faulty parts (this chiefly concerns the electrodes and the quartz tube), are carried out easily and quickly.
By moving the lower electrode 3, the height of the fuel layer between the electrodes can be changed, and thereby (if necessary) the electrical resistance of the layer can be regulated.
The temperature of the process can be very high and is limited only by the refractoriness of the material of the electrodes and of tube 4. Attainment of this temperature is not associated with the difficulties that arise when electric coils are used, which, moreover, can often burn out.
Among the disadvantages of this design should be mentioned the known difficulties of maintaining a constant temperature regime, associated with the negative temperature coefficient of resistance of the heater; these, however, are usual for any cryptol-type furnace.
Such a generator, with the dimensions indicated in Fig. 1 (it is understood that, if desired, these dimensions may be altered accordingly), operating on charcoal (piece size 2–7 mm) at temperatures of 1100–1300°C, produced over the course of an hour more than 100 liters of carbon monoxide from carbon dioxide. In this case the current passing through the layer of charcoal did not exceed 7 A at a voltage of 200–250 V.
Note. Charcoal, which is especially desirable in producing pure gases for synthesis purposes, often requires preliminary calcination to about 800° in order to give it the necessary electrical conductivity.