US 3368329 A
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Feb. 13, 1968 TAl (ASHI EGUCHI ET AL 3,368,329
HYDROGEN PURIFICATION APPARATUS Original Filed April 26, 1965 HYDROGEN PURE I HYDROGEN 4 I MIXTURE GAS 'fiyi Lil United States Patent 3,368,329 HYDROGEN PURIFICATION APPARATUS Takashi Eguchi, 12 330-1 Kamijikken, Sakashita, Chigasaki, Chigasaki-shi, Kanagawa-ken, Japan, and Ryosuke Goto, 282 Karasuyama-cho, Setagaya-ku, Tokyo, Japan Continuation of application Ser. No. 450,787, Apr. 26, 1965. This application Aug. 10, 1965, Ser. No. 479,057 Claims. (Cl. 55158) This application is a continuation of our copending application Ser. No. 450,787, filed on Apr. 26, 1965, now abandoned.
This invention relates to the purification of hydrogen by diffusion through palladium or palladium alloys at elevated temperature, and particularly to apparatus for such hydrogen purification.
The diffusion of hydrogen through palladium and its alloys follows the common diffusion laws. The rate of diffusion increases with the pressure differential between the two sides of a palladium diaphragm, and decreases with the thickness of the diaphragm. The mechanical strength of palladium alloys is relatively low and makes it necessary to seek a compromise between diaphragm thickness and pressure differential. It has been established in this art that cylindrical capillary tubes of palladium offer the best compromise of mechanical strength and wall thickness. At equal tube wall thickness, a substantially greater pressure differential is permissible if the gas pressure within the tube is greater than the external pressure,
A purification process relying on outward diffusion through a palladium tube requires provisions to be made for feeding an impure gas to the tube, and for withdrawing the impurities therefrom. If the process is to be continuous, a feed conduit and a discharge conduit must communicate with axially spaced portions of the palladium tube, the latter term being understood to include tubes made from palladium alloys.
The operating temperature required for economically purifying hydrogen by diffusion is about 500 C. The axial expansion of a palladium tube between'room temperature and a temperature of 500 C. is so great that a straight diffusion tube connected to fixedly mounted feed and discharge conduits would be subjected to stresses too great to be withstood by a tube having a wall thickness small enough for rapid hydrogen diffusion.
It has therefore been proposed heretofore to avoid the use of straight diffusion tubes, and to employ palladium diffusion tubes of at least partly arcuate configuration which are flexed during thermal expansion and contraction. Coiled capillary palladium tubing has been disclosed in Patent No. 2,911,057, and U-shaped tubing in the application Ser. No. 35,299. Coils and U-shapes, however, are difficult to produce from palladium tubing having the preferred wall thickness of 0.05 mm. or less, and an outer diameter of about 1.5 mm. to 3 mm. The repeated deformation of the arcuately shaped tubes under thermal stresses, moreover, significantly reduces the useful life of the tubes.
The primary object of this invention thus is the provision of a hydrogen purification apparatus in which a feed conduit supplies a gas mixture to one end of a straight palladium diffusion tube, hydrogen in the mixture diffuses outward through the tube wall, and the remainder of the mixture is withdrawn through a discharge conduit communicating with the other end of the straight palladium tube, and in which the tube is fully protected from deformation under thermal stresses.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments when considered in connect-ion with the accompanying drawing in which:
FIG. 1 shows a hydrogen purification apparatus of the invention in elevational section;
FIG. 2 illustrates a modified purification apparatus in a View analogous to that of FIG. 1; and
FIG. 3 shows a detail of the apparatus of FIG. 1 on an enlarged scale.
Referring initially to FIGS. 1 and 3, there is seen a bundle of about thin-walled, straight, capillary palladium tubes 1. The open ends of the tubes 1 are sealed in parallel, radially spaced relationship into a short, flanged pipe 2 and a cup-shaped receptacle 11 respectively which function as manifolds. The pipe 2 and the receptacle 11, as well as all other parts of the apparatus yet to be described are made of heat resistant stainless steel having a wall thickness many times greater than that of the palladium alloy tubes 1.
The flange portion of the pipe 2 is secured between corresponding flanges on a tubular shell 5 and a cover 8 which closes one axial end of the shell. Another flangedly attached cover 5 closes the other axial end of the shell 5 so that the shell and its covers enclose a chamber which is divided into two sealed compartments by the tubes 1 and associated elements.
The latter include a coil 3 of stainless steel tubing one end of which is attached to the bottom of the receptacle 11, whereas the other end 4 forms a discharge conduit fixedly attached to the cover 5 and passes outward through the cover. Another length of tubing 9 is coaxially attached to the cover 8 to communicate with one of the compartments in the diffusion chamber, whereas a nipple 7 attached to the shell 5 communicates with the other compartment.
The dimensions of the apparatus illustrated are chosen in such a manner that the coil 3 is under axial tensile stress when the apparatus is at room temperature, and is substantially relaxed at the normal operating temperature of the apparatus which is about 500 C.
1 In operating the device, a hydrogen-bearing hot gas mixture is fed to the diffusion chamber under pressure, through the tubing 9, pure hydrogen is withdrawn through the nipple 7, and the remainder of the gas mixture is exhausted through the discharge conduit 4.
The tensile stresses initially present in the coil 3 at room temperature (approximately 20 C.) are distributed over the large number of capillary tubes 1, and cannot cause significant strain in the tubes. The magnitude of the stress in each tube 1 decreases as the temperature is raised, and becomes zero or practically zero at the operating temperature at which the tube would be most adversely affected by applied forces.
The stainless steel coil 3 can withstand axial expansion and contraction over a long period of operation. Moreover, it can be replaced quickly and at minimal expense if needed. The palladium tubes 1 in the hydrogen apparatus of the invention have a useful service life substantially longer than similar tubes in any other comparable device that we are aware of.
In the absence of significant axial compressive stresses in the tubes 1 under any operative condition, the tubes 1 may be made as long as desired without any need for basic changes in the very simple apparatus illustrated. There is no relative movement of abuttingly engaged structural elements and no frictional wear. Palladium tubes 1,000 mm. long expand 6.5 mm. when heated to 500 C. A relatively short helical stainless steel tube 3 can readily absorb such expansion.
High melting solder or brazing alloy is employed for sealing the tubes 1 into the pipe 2 and the receptacle 11,
and such sealing materials are well known in this art and commercially available. Metallic gaskets are employed between engaged flanges, and welded joints are preferred where steel conduits make sealing connections with other stainless steel elements.
While stainless steel is a preferred material of construction for all elements of the diffusion apparatus other than the tubes 1, other heat resistant materials of construction impervious to hydrogen at a temperature near 500 C. may obviously be employed.
The modified hydrogen purification apparatus shown in FIG. 2 differs from the first-described embodiment of the invention by the resilient manifold connection between the lower ends of the palladium alloy tubes 1 and the discharge conduit 4.
The lower tube ends are sealed in the afore-described manner into a short pipe 10 connected to the conduit 4 by bellows 3 analogous to the coil 3.
In assembling the apparatus of FIG. 1 r 2, the conduit 4 is initially left free to slide axially in the cover 5', so that the coil 3 or the bellows 3' are in the relaxed condition. The conduit 4 is then pulled outward until the desired pre-stress is produced in the resilient connecting element 3, 3 whereupon the conduit 4 is fixedly sealed to the cover 5 by high-temperature solder or welding.
The following examples are further illustrative of this invention, and it will be understood that the invention is not limited thereto.
Example 1 An apparatus of the type illustrated in FIGS. 1 and 3 was constructed from 115 pieces of cylindrical palladium tubing, each piece having a length of 1,000 mm., a. bore of 2 mm., and a wall thickness of 0.06 mm. The coil 3 was made from stainless steel tubing having a bore of 7 mm. and a wall thickness of 0.3 mm. The coil had a diameter of 30 mm. and consisted of turns. The exposed combined surface area of the palladium tubes was 7,130 cm.
Electrolytically produced crude hydrogen was compressed to a gage pressure of 10 kg./cm. (147 lbs/sq. in.) and heated to 500 C. prior to being fed to the diffusion tubes. Ten cubic meters of purified hydrogen were withdrawn from the apparatus per hour.
The dew point of the purified gas was 80 C. and the total amount of impurities, including nitrogen, oxygen, and hydrocarbons was less than 0.1 ppm.
The apparatus was in continuous use for 30 months without requiring repair or replacement of the diffusion tubes.
Example 2 A gas mixture consisting of nitrogen and 75% hydrogen was produced by dissociating ammonia, and was introduced into the apparatus described in Example 1 at a gage pressure of 10 kg./cm. Pure hydrogen was obtained in a single pass at a rate of 6 cubic meters per hour, corresponding to a hydrogen recovery of 80%.
It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.
What is claimed is:
1. A hydrogen purification apparatus comprising, in combination:
(a) a diffusion chamber enclosing a cavity;
(b) a plurality of elongated palladium tubes in said cavity;
(1) each tube having an axis, a first axial end portion, and a second axial end portion,
(2) the axes of said tubes being substantially straight and parallel;
(c) a first and a second manifold fixedly fastened in said chamber to said first and second end portions respectively for communication therewith;
(d) a feed conduit communicating with said first manifold;
(e) a discharge conduit communicating with said second manifold, said conduits being fixedly fastened to said chamber;
(f) a resiliently expandable tubular member interposed between one of said conduits and the corresponding manifold,
(3) said tubular member having two terminal portions respectively fastened to said one conduit and said corresponding manifold,
(4) said terminal portions being spaced in the direction of said axes, and
(5) said conduits being fastened to said chamber in such a manner that said tubular member is stressed in an axial direction when said apparatus is at room temperature and is substantially relaxed when said apparatus is at a temperature of approximately 500 C.; and
(g) means for withdrawing a gas from said chamber.
2. An apparatus as set forth in claim 1, wherein said tubular member has a coil-shaped portion.
3. An apparatus as set forth in claim 1, wherein said tubular member has a bellows-shaped portion.
4. An apparatus as set forth in claim 1, wherein the wall thickness of said tubular member is substantially greater than the wall thickness of each of said tubes.
5. An apparatus as set forth in claim 1, wherein said tubular member is of stainless steel.
References Cited UNITED STATES PATENTS 2,961,062 11/1960 Hunter et a1 55158 3,022,858 2/1962 Tillyer et a]. 55158 X 3,210,162 10/1965 Rudd 55158 X 3,279,154 10/1964 Emerson et al 55l58 3,251,173 5/1966 Ehlers et al 55158 3,274,754 9/1966 Rubin 55158 FOREIGN PATENTS 1,178,480 12/1958 France.
SAMIH N. ZAHARNA, Primary Examiner.
REUBEN FRIEDMAN, Examiner.
.T. ADEE, Assistant Examiner.