AIDS FOR ANALYTICAL CHEMISTS Gas Purification and Pressure Control System for Inert Atmosphere Boxes I. Dwaine Eubanks and Floyd J. Abbott Department of Chemistry, Oklahoma State University, Stillwater, Okla. 74074 GLOVE BOXES have come to be widely used for the handling of moisture and oxygen-sensitive materials in the laboratory. A circulating system is generally used for gas handling in preference to a static system because more efficient use is made of gas-purification reagents. Several drying agents have been used with good success, but suitable agents for oxygen removal have been more difficult to find (1). Excellent inert atmosphere boxes have been commercially available for several years, but no adequate gas handling system designed for general laboratory use is as yet available. This paper describes a simple, relatively inexpensive system designed to remove moisture and oxygen, provide sensitive pressure control, permit in-line monitoring of moisture and oxygen concentration, and permit regeneration of the purification agents without interruption of the box operation. EXPERIMENTAL
Recirculation. (Figure 1). Gas is removed from the box and pushed through the gas purification columns using a diaphragm pump having a stainless steel pump housing and a neoprene diaphragm (Dyna-Vac Model 7064). The box volume used is 345 l., and the gas is recycled at a flow rate of 1.1 l./min. When materials are being brought into the box, a portion of the recirculating gas is used to back-fill the entry port after evacuation. Partial evacuation of the box itself is prevented by the pressure control system described below. Gas Purification. Oxygen and moisture are removed using reduced BTS-Catalyst (BASF Colors and Chemicals, Inc., New York) and molecular sieves, respectively. The BTSCatalyst contains finely divided copper on an inert carrier and has a capacity of >20 l.On/kg catalyst at 150 ‘C., according to the manufacturer’s literature. Catalysts of this type
have been known for some time (2,3), but knowledge of their virtues for oxygen removal from gas streams has become widespread only recently (4). The BTS-Catalyst and molecular sieves are placed in a two-compartment U-shaped column which is attached to the gas recirculating system via double end shut off quick-connects C (Swagelok). This permits column replacement without interrupting the operation of the glove box. The molecular sieves and catalyst are regenerated by passing dry hydrogen through the molecular sieves at 250 “C and through the oxidized catalyst at 150 “C. Performance Measurement. Although excellent electrolytic moisture meters are commercially available, the dewpoint meter described by Tyree (5) was quite satisfactory and it is quite inexpensive to construct. The polished copper mirror was coated with Hypalon to prevent its corrosion in the gas stream. The dew point can be easily converted to water content using Caplan’s nomograph (6). Both polarographic and paramagnetic oxygen analyzers are commercially available, and an oxygen meter based on a galvanic cell has been described by Bomyer and Hutt (7). We found an even simpler method for measuring oxygen concentration which gives entirely satisfactory results. The lifetime of a light bulb filament in the recirculating gas stream is a function of the oxygen concentration. The filaments are calibrated at the flow rate of the recirculating gas, the same (2) M. Schutze, Angew. Chem., 70, 697 (1958). (3) R. F. Meyer and G. Ronge, ibid., 52,637 (1939). (4) A. D. Broadbent, J. Chem. Educ., 44,145 (1967). ( 5 ) S. Y . Tyree, Jr., ibid., 31, 603 (1954). (6) F. Caplan, Chem. Eng., 68 (9), 154 (1961). (7) P. Bomyer and E. C. Hutt, UKAEA Report AWRE-0-14/54, 1954.
104 (1) C. J. Barton in “Technique of Inorganic Chemistry,” Vol. 111,
H. B. Jonassen and A. Weissberger, Eds., Interscience, New York, 1963, pp 259-333.
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Figure 1. Recirculation and pressure control system 1708
ANALYTICAL CHEMISTRY
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potential is applied for each reading, and all bulbs of the same manufacture are used to ensure reproducible results. The results of two calibration runs are shown in Figure 2. The filaments of A/C No. 63 bulbs were used at an applied potential of 10 V and a gas flow rate of 1.1 l./min. The filament assembly is connected to the recirculating system via double end shut off quick-connects. The assembly is removed from the gas stream after each performance test and replaced with a jumper tube. The filament is replaced and the assembly purged with nitrogen before returning it to the recirculating system. Pressure Control. The fully automatic pressure control system is based on a differential switch-gauge having both high and low pressure limit switches. (Photohelic Series 3000, F. W. Dwyer Manufacturing Co., Inc., Michigan City, Ind.). The box pressure is maintained within the desired range (typically between 0.2 in. HzO and 0.6 in. above atmospheric pressure) as follows: The recirculating pump is discharged to the atmosphere through solenoid valve B when an over-pressure is created (as when the hands are inserted into the gloves). Additional gas is supplied from the cylinder through solenoid valve A when an under-pressure is created (when the hands are withdrawn from the gloves and when the entry port is being back-filled or purged). An iso-
lating seal consisting of a 2.5- X 0.002-in. polyethylene bag in a 2- X 12-in. Lucite tube is used to protect the Photohelic gauge from corrosion (8). RESULTS
The dry box was initially purged without recirculation to reduce the oxygen concentration to -1000 ppm. This procedure lengthens the life of the BTS-Catalyst before regeneration is needed and also reduces the heating of the catalyst. Water and oxygen content were measured as a function of box throughputs. Under the conditions employed (0.19 box throughput/hour using a 25-mm X 60-cm catalyst column and a 25-mm X 45-cm molecular sieve column) impurity concentrations were reduced to
