* OUT
IN
-0
Figure 2.
Schematic diagram of switching circuit
R
=
100 K
c, = Cf = apf
Harbor, Mich.) operating in the follower configuration was observed to introduce negligible drain on the charged ~
capacitors and was used between the capacitor system and the readout meter. The balance potentiometer of the voltage follower was used as the source of zeroing voltage.
performed manually in this work; The system has been tested for however, it should be a simple matter to linearly . . varying voltages from a utilize a servo mechanism to automate standard voltage source and real chemical systems. Results demonstrate rethese operations. This possibility is Droducibilitv and accuracy for the being investigated. method in the range of 1 t i 2%. D ~ tails of applications and results are LITERATURE CITED being prepared for publication. The (1) Park, B., IND.ENG. CHEM.,ANAL. zeroing and calibration operations were ED.8, 32 (1936).
Ultrapure Hydrogen Generator for Gas Chromatography J. K. Jacobsen, Milton Roy Co., St. Petersburg 33, Flo. HYDROGEN
is generally considered
to be the best carrier gas for gas chromatography. However, it is not widely used because of the danger involved in the storing and handling of cylinder hydrogen, particularly in enclosed spaces. There is also a problem of impurities in cylinder gases. The hydrogen generator described avoids both the danger involved with storing hydrogen and the impurity problem. Because no hydrogen is stored, the unit simply generating the hydrogen demanded by the chromatograph (which is normally less than 85 ml. per minute), the danger involved with its use is practically eliminated. At the same time, the hydrogen from
the generator has passed through a palladium metal membrane and, because only hydrogen can diffuse through palladium metal, it is ultrapure (6). This eliminates the need to purify the gas before it is used as a carrier. The hydrogen is supplied under 60 psig of pressure, although the electrolytic cell operates a t atmospheric pressure. Hzpressure is developed as described by the Nernst equation which relates the hydrogen pressure developed on the cathode wall and the voltage applied to the cathode. The pressures that can be generated are extremely high; pressures well over 1000 psi have been obtained with no significant reduction in flow rate. The maximum pressure
obtainable appears to be limited only by the strength of the cathode tubes. Some preliminary data on the electrolytic transmission of H1 through a pure Pd cathode were reported by Wahlin in 1951 (3). In 1956 he obtained a patent on a method of hydrogenation using a pure Pd cathode (4). In 1960 Achey (1) reported on the development of a practical generator and recently Darling described a prototype Hz generator utilizing this principle (2). Description of Unit. To make a practical source, most of the hydrogen generated at the cathode should enter the tube and be recovered. The hydrogen that does not enter the VOL. 37, NO. 2, FEBRUARY 1965
319
L
FIRECHECK VALVE
S.S. WOOL LOW PRESSURE LIGHT HI PRESS. CUT OFF WITCHWENS @ 60 #
-
PRESSURE REGULATOR FLOAT LEVEL VMVE 120-V.A.C. SOURCE
120 VA TRANS L -
THERMOSWITCH I
I
Figure 1.
I
Cell and connections for hydrogen generation
cathode collects as bubbles on the outside surface of the tube and is not recovered. I n some cases little hydrogen enters the cathode. The percentage of hydrogen absorbed can be increased if the surface of the tube is coated with palladium black to increase its activity. A tube activated in this manner normally will absorb at least 60% of the hydrogen generated when run a t 90" C. and a current density of 60 amperes per sq. foot. Recent work indicates that with a special activation of the cathode tubes, 100% recovery of the Hz can be achieved. However, tests of the long
term stability of this activation have not been completed. Because hydrogen can cause expansion and cracking of pure palladium, the cathode is normally constructed from a 75% palladium-25yo silver alloy. The cell consists of a series of 1/8-inch 0.d. palladium-silver tubes with &mil walls. Nickel anodes are located between the cathode tubes. The anodes and cathodes are cast into an epoxy header and the assembly is placed in an epoxy cylinder. Teflon spacers are used to keep the electrodes separated. The electrolyte is a 15y0 NaOH solution.
Figure 1 shows a layout of the cell and its connections. The cell is maintained a t its operating temperature of 90" C. by a combination of self-heating and a thermostatically controlled heater. Approximately 2 volts d.c. are supplied by a full wave rectifier. Two pressureoperated switches are used to give a warning of low pressure and to shut off the power when the operating pressure is reached. A float valve is used to maintain the liquid level in the cell; distilled or demineralized water is used for makeup. A pressure regulator and control valve are located on the output. Figure 2 shows the variation of output with temperature a t various current levels. The curves indicate that operating a t higher temperatures greatly increases the transmission efficiency. Operation. A prototype cell has been operating with a Beckman GC2A chromatograph in our laboratory for 10 months and has proved to be a very convenient setup. The generator is normally left on at all times as this allows the unit to be used a t any time with much less base-line drift than when the carrier gas is shut off. This is especially true with the molecular sieve column we normally use. The generator described appears to be a practical source of hydrogen gas for gas chromatographs and for any oth'er system requiring moderate amounts of hydrogen under pressure. LITERATURE CITED
(1) Achey, F. A., report to Milton Roy
Co., June 1960.
7 1 7 1 7 7 0
36
Figure 2.
70
101
140
fAI~ER~S-lo
176 PI0 2 4 1 -CURRENT
2IO
,
311 V O
DEN I T
a
1;
3L1
1;
YO)-
IA/?7
l i
1,4
4 1 1 490
1;
1,8
616
M O
Variation of output with temperature at various current levels Cathode area = .029 rq. foot
320
( 2 ) Darling, A. S., Platinum Metals Reu. 7, 126 (1963). (3) Wahlin, H. B., A p p l . Phys. 22, 1503
ANALYTICAL CHEMISTRY
(1901). (4) Wahlin, H. B., U. S. Patent 2,749,293 (1956). (5)-Young, J. R., Rev. Sci. Instr. 34, h o . 8, 891 (1963). Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., 1964.
