Rejuvenable ambient temperature purifier

Details Rejuvenable ambient temperature purifier Rejuvenable ambient temperature purifier

1999-08-06

2003-02-18

Tran, Hien (Department: 1764)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Waste gas purifier

C422S168000, C422S171000

Reexamination Certificate

active

06521192

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to gas purification and more particularly to gas purifiers containing dispersed impurity-sorbing materials.
2. Description of the Related Art
Ultra-high purity (UHP) gases are used for the manufacture of semiconductor devices, laboratory research, mass spectrometer instruments and other industries and applications. UHP gases are typically defined as at least 99.9999999% pure gas by volume. There are several methods of producing UHP gases. Purifiers are widely used based on the use of solid materials that can bond impurities in the stream of a main gas, by interacting with the impurity molecules according to a variety of mechanisms.
An important class of gas purifiers exploits the properties of getter alloys, which include Zr, Ti, Nb, Ta, and V based alloys as active elements. Examples of commonly used alloys are an alloy of weight percent composition Zr 70%-V 24.6%-Fe 5.4%, under the trademark St 707; an alloy of composition Zr 76.5%-Fe 23.5%, under the trademark St 198; an alloy of composition Zr 84%-Al 16%, under the trademark St 101; and certain Ti—Ni alloys, all of which are produced and sold in conjunction with gas purifiers by SAES Pure Gas, Inc. of San Luis Obispo, Calif.
The working principle of getter alloys is chemisorption of species such as O
2
, H
2
O, CO, CO
2
and CH
4
, through surface adsorption followed by dissociation and diffusion in the bulk of the getter material of the atoms making up the impurity molecules. Some getter alloys may also fix N
2
according to the same mechanism. The result is the formation of oxides, carbides or nitrides of the metals of the alloy. Because the species formed are very stable, the sorption of the above mentioned gases by getter alloys is essentially irreversible.
Because getter alloys do not react with noble or inert gases, they are well suited for purification of these gases. By using these alloys it is possible to remove traces of reactive gases from inert gases. Examples of gases that may be purified by means of getter alloys include noble gases, chloroflourocarbons, which are used in the semiconductor industry, and nitrogen N
2
). For example, N
2
may be purified by the St 198 alloy, which has a negligible sorption capability for the gas. Examples of purifiers based on the use of getter alloys are disclosed in UK Patents GB 2,177,079 and GB 2,177,080, in European Patent EP 365490, and in U.S. Pat. No. 5,194,233 and 5,294,422.
FIG. 1A
is a schematic illustration of a getter purifier
10
of the prior art during process gas purification at an elevated temperature. Getter purifier
10
includes a chamber
12
, which is coupled to an inlet
14
and an outlet
16
. Chamber
12
is partially filled with getter material particles
18
. A heater
20
heats getter purifier
10
to at least about 300 degrees Celsius. A process gas with gaseous impurities such as water or carbon oxide is introduced into chamber
12
through inlet
14
where getter material particles
18
absorb the traces of water and carbon oxide. A purified process gas then exits chamber
12
through outlet
16
.
While getter materials show essentially irreversible gettering for impurities (e.g. oxygen, water, carbon monoxide, carbon dioxide, methane) normally present in noble or relatively inert gases (such as argon, helium and nitrogen) for semiconductor industry, getter materials behave very differently towards hydrogen. In fact, getter materials show reversible gettering for hydrogen, which undergoes an equilibrium reaction with most getter materials. At about room temperature, the pressure of “free” gas at is very low, but the pressure increases with increasing temperature.
FIG. 1B
is a schematic illustration of a getter purifier
10
of the prior art during the removal of hydrogen from a process gas. Getter purifier
10
is operational at ambient temperatures (0 to 40 degrees Celsius) to remove traces of hydrogen from process gases. If a process gas with hydrogen is introduced into chamber
12
through inlet
14
, getter material particles
18
will absorb the hydrogen, leaving a purified process gas to exit chamber
12
through outlet
16
.
Getter based purifiers are highly efficient in removing impurities as shown in
FIG. 1A
, but they are costly and need to be kept at about 300 to about 450° C. for operation. Therefore, in some circumstances other kinds of purifiers are preferred. An example of lower cost purifiers is the so-called nickel purifiers, which operate at around room temperature. These purifiers include as the active material, metallic nickel, generally supported on a porous substrate such as silica.
FIG. 2A
is a schematic illustration of a nickel purifier
22
of the prior art during process gas purification. Nickel purifier
22
includes a chamber
24
, which is coupled to an inlet
26
and an outlet
28
. Chamber
24
is partially filled with nickel material particles
30
. Nickel is typically present in metallic form for at least 5% of the overall amount of nickel material particles
30
, with the remainder generally being present as nickel oxide, NiO. Nickel is generally present in a particulate or “dispersed” form, so as to have a high specific area of at least 100 m
2
/g and preferably between about 100 and 200 m
2
/g, but the overall amount of nickel is limited. By “dispersed” it is meant that the material is formed by discrete particles, such as powders, granules, pellets, etc.
Nickel purifiers often also contain physical water sorbers, such as molecular sieves, to help remove water vapor and leave nickel material available for removal of oxygen and carbon oxides. As shown, a process gas, water, and trace amounts of oxygen and carbon oxide enter chamber
24
through inlet
26
. During operation of nickel purifier
10
, nickel material particles
18
react with oxygen or water and with CO or CO
2
. The product of the Ni and oxygen or water reaction is NiO. Once the sorbing capacity of nickel material particles
18
has reached its limits, the purifier may be regenerated.
FIG. 2B
is a schematic illustration of a nickel purifier
22
of the prior art during the process of regeneration. Nickel material particles
30
are regenerated by passing a flow of hydrogen-containing inert gas over the nickel material particles
30
maintained at a temperature of about 200° C. by heater
20
. The inert gas is preferably nitrogen, the amount of hydrogen is preferably below about 20% by volume, and more preferably between about 2 and about 5% by volume of the flowing gas, and the regeneration process is preferably continued for about 14-20 hours. In these conditions NiO and the product of the reaction of Ni and CO/CO
2
are reduced to metallic nickel. Nickel purifiers are disclosed, e.g., in U.S. Pat. No. 4,713,224.
Because water and CO are produced during the regeneration step, the operation must be performed with the purifier disconnected from the pure gas line, in order not to pollute the system. A wide range of nickel-based purifiers is sold by Aeronex Inc. of San Diego, Calif. under the name GATEKEEPER®. Further to the application indicated above, another important use of nickel-based purifiers is in gas cabinets, for the purification of gas (generally nitrogen) used to purge gas pipelines during process gas cylinders change out.
FIG. 3
illustrates another nickel purifier unit
32
of the prior art. Nickel purifier unit
32
includes a body or enclosure
33
defining a chamber
34
, which is generally made of stainless steel into an essentially cylindrical shape. Chamber
34
is preferably electropolished to at least 10 Ra. At the two opposing bases of nickel purifier unit
32
, a gas inlet
36
and an outlet opening
38
are provided. Gas inlet
36
and outlet opening
38
are typically equipped with suitable fittings
40
for connection to a set of gas lines. Fittings
40
shown are male face seal fittings, but as is well known in the art, compression fittings may also be used. Nickel purifier unit
32
is preferably equipped with particle filt

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