# Patent

## Title
Purification of H2Se

## Abstract

Methods of purifying H2Se by removing H2S and/or H2O are disclosed. The amount of H2S in the H2Se-containing gas is reduced below 10 ppmv by passing the H2Se-containing gas through an AW-500 molecular sieve. H2S and H2O are removed by passing H2Se through a 4 A molecular sieve and subsequently passing H2Se through an AW-500 molecular sieve.

## Background
BACKGROUND
Hydrogen selenide (H2Se) is a gas currently used in the photovoltaic industry for Copper Indium Gallium Selenide (CIGS) and Copper Indium Gallium Selenide Sulfide (CIGSS) thin film solar cells. Impurities in the H2Se gas may negatively affect the deposition process of the Se-containing films. Two such impurities include H2O and H2S. H2O may contribute oxygen to the metals being added to the film and hinder proper deposition. H2S may be added in a controlled manner later in the process. However, sulfur is known to change the bandgap structure of the selenium-containing adsorber layer, thus impurities such as H2S in H2Se may affect the film performance. The combination of H2S and H2O is known to cause corrosion of distribution systems and their components, leading to component/system failure as well as introduction of metal impurities during the deposition process resulting from corrosion of the distribution system.
Prior art gas purifiers are known in the art. See, e.g., the Nanochem® C/CL-series gas purifiers from Matheson Tri-Gas, the Mini Gaskleen® gas purifier from Pall Microelectronics, and the MC-190 and HP-190 MicroTorr purifiers from SAES Pure Gas, Inc. However, none of these purifiers identify H2Se as the gas to be purified and H2O and H2S as the impurities to be removed.
U.S. Pat. No. 4,797,227 to Tom et al. discloses a process and composition for purifying H2Se and H2Te to remove moisture and oxidant impurities therefrom. Tom et al. note that H2Se and H2Te are extremely difficult to purify because of their high reactivity and toxicity (col. 1, lines 35-37). Tom et al. utilize aluminum-containing compounds to remove water and oxidants from H2Se or H2Te (claim 1). The water and oxidants react with the aluminum-containing compounds (col. 5, lines 25-30). Tom et al. do not address the removal of H2S from H2Se.
JP2007-246342 to Taiyo Nippon Sanso Corp discloses a method for producing H2Se which has high purity and in which the water content and the amount of H2S are made particularly small. Taiyo Nippon Sanso Corp discloses the reaction of high purity H2 with metallic Se and liquefies or solidifies the resulting H2Se product. This process requires a lot of energy for both the reaction and the subsequent liquefaction/solidification.
A need remains for an efficient method to remove both H2O and H2S from available H2Se supplies.
SUMMARY
Disclosed are methods of purifying a H2Se-containing gas. The amount of H2S in the H2Se-containing gas is reduced below 10 ppmv by passing the H2Se-containing gas through an AW-500 molecular sieve. The disclosed methods may further include one or more of the following aspects:

    
    
        the purified H2Se-containing gas containing less than 5 ppmv H2S;
        reducing an amount of H2O in the H2Se-containing gas below 20 ppmv by passing the H2Se-containing gas through a 4 A molecular sieve;
        the purified H2Se-containing gas containing less than 1 ppm H2O;
        passing the H2Se-containing gas through the 4 A molecular sieve prior to passing it through the AW-500 molecular sieve; and
        receiving the purified H2Se-containing gas in a cylinder cooled to a temperature ranging from approximately −20° C. to approximately −60° C.
    
    


Also disclosed are methods of purifying H2Se by passing H2Se through a 4 A molecular sieve and subsequently passing H2Se through an AW-500 molecular sieve. The disclosed methods may further include one or more of the following aspects:

    
    
        the purified H2Se containing less than 10 ppmv H2S;
        the purified H2Se containing less than 5 ppmv H2S;
        the purified H2Se containing less than 20 ppmv H2O;
        the purified H2Se containing less than 1 ppm H2O; and
        receiving the purified H2Se in a cylinder cooled to a temperature ranging from approximately −20° C. to approximately −60° C.
    
    





BRIEF DESCRIPTION OF THE FIGURES
For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying figure wherein:
FIG. 1a is an illustration of an exemplary purification container;
FIG. 1b is an illustration of an alternate purification container;
FIG. 2 is an illustration of an exemplary purification system; and
FIG. 3 is an illustration of a second purification system.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Disclosed are methods of purifying H2Se-containing gases, such as “pure” H2Se gas. Applicants have discovered that the quantities of impurities in H2Se may change during use or over time. For example, a H2Se cylinder initially containing 25 ppm H2O contained 600 ppm H2O when the cylinder was nearly empty. Of course, these changes will affect the quality of the resulting photovoltaic product. Therefore, H2Se used for CIGS or CIGSS deposition should have as high a purity as possible.
Due to the reactivity of H2Se and H2Se-containing gases, the disclosed purification methods and any subsequent storage should be performed in systems and stored in vessels through which inert gas previously flowed to remove air and moisture. Exemplary inert gases include N2, Ar, He, and combinations thereof. In the following examples, N2 was used. The stainless steel components of the purification system should undergo complete electro polish and drying.
In order to prevent generation of additional impurities in the purified H2Se gas, it should be stored in cylinders having surfaces with which the H2Se does not react. Suitable surfaces include steel, carbon steel with Ni coating, aluminum, stainless steel, glass, quartz, nylon, metal alloys sold under the trademark Monel®, metal alloys sold under the trademark Hastelloy®, fluorine-containing resins sold under the trademark Teflon®, synthetic rubber sold under the trademark Kalrez®, synthetic rubber sold under the trademark Viton®, and/or glassware sold under the trademark Pyrex®. Preferably, the purified H2Se is stored in cylinders made of aluminum or carbon steel with Ni coating.
H2Se-containing gas is commercially available. H2Se is most often produced in a high temperature reaction of H2 with molten Se [H2 (g)+Se (molten)→H2Se (g)]. The reaction produces a H2Se-containing gas comprising approximately 95% v/v to approximately 99.9% v/v H2Se, and typically comprising approximately 99.5% v/v to approximately 99.99% v/v H2Se. H2S impurities in the H2Se-containing gas are produced from sulfur impurities in the selenium used to produce the gas. While low-sulfur selenium is commercially available, it is very expensive to remove sufficient sulfur to produce low H2S in the H2Se-containing gas.
Applicants have surprisingly found that H2S in the H2Se-containing gas is adsorbed by AW-500 when flowing the H2Se-containing gas through AW-500 molecular sieve. This result is unexpected because a different molecular sieve having the same pore size as the AW-500 molecular sieve did not remove H2O or H2S from the H2Se-containing gas.
H2Se has a critical diameter of approximately 4 angstrom. The critical diameter is the approximate molecular diameter of a molecule. H2S has a critical diameter of 3.6 angstroms. H2O has a critical diameter of 3.2 angstroms. Based on these sizes, one of ordinary skill in the art would expect the best molecular sieve that would capture H2O and H2S without capturing H2Se to have a pore size of approximately 4 angstroms. However, the AW-500 molecular sieve has a pore size of 5 angstroms, but still effectively removes H2S (3.6 angstroms/134 pm) from H2Se (4 angstroms/146 pm), notwithstanding that both molecules are smaller than the pore size of the AW-500 molecular sieve. Additionally, the polarities of the three molecules are similar: H2Se (0.59 D), H2S (0.97 D), and H2O (1.85 D), making separation by adsorption techniques difficult (D=debyes; 1 coulomb-meter=2.9979×1029 D).
The H2Se-containing gas contacts the AW-500 molecular sieve by flowing through a container of the AW-500 molecular sieve. The AW-500 molecular sieve is commercially available. Currently, AW-500 is supplied as 1/16′′ or 1⁄8′′ pellets. Either size may be used in the disclosed methods. The AW-500 molecular sieve may be placed in a container made of stainless steel. Alternatively, the AW-500 molecular sieve may be placed in a container made of aluminum, stainless steel passivated by SiH4, or nickel plated carbon steel. The container should have an inlet and outlet. In one alternative, depicted in FIG. 1A, the inlet 10 and outlet 20 are located on opposite ends of the container 1 in order to minimize dead flow zones within the molecular sieve. The arrows in FIG. 1A depict the direction of gas flow through the container 1. However, alternative inlet and outlet locations may also be desired, such as the inlet 10 being located on one end of a cylindrical container 1 with the outlet 20 located on the cylindrical surface of the container 1 at the other end of the container 1. One of ordinary skill in the art will recognize that the shape of the container 1 is not limited to a cylinder, but may also include spherical, cubic, or other polyhedric shapes.
The commercially available AW-500 molecular sieve is provided in its activated state by the manufacturer. Applicants, however, re-activate the AW-500 molecular sieve prior to use in order to remove any contaminants that may have been adsorbed during transport from the manufacturer, during transport from its original container to the purification container, or from the purification container itself. Applicants activate the AW-500 molecular sieve by heating it to a temperature ranging from approximately 150° C. to approximately 250° C. under an inert gas for approximately 10 to approximately 24 hours. The inert gas may be N2, Ar, He, or combinations thereof. One of ordinary skill in the art will recognize that the amount of molecular sieve to be activated will determine the activation time and temperature, with larger quantities requiring either longer times or higher temperatures and smaller quantities requiring less time or lower temperatures. The AW-500 may be activated by heating to temperatures as high as 600° C. However, heating the AW-500 to such temperatures will require the remaining components in the purification system, such as valves, to become more expensive because they will be engineered to withstand exposure to such temperatures. As a result, activation at temperatures below 300° C. permits the use of less expensive valves in the purification system.
The initial reaction between the H2Se-containing gas and the AW-500 molecular sieve produces CO2. Therefore, after activation of the AW-500 molecular sieve, the initial H2Se-containing gas flowing through the AW-500 molecular sieve is vented. Applicants have not calculated the time required to reduce the CO2 levels resulting from initial contact between the H2Se-containing gas and the AW-500 molecular sieve with relation to the amount of molecular sieve. However, the initial reaction causes the temperature of the AW-500 molecular sieve to rise. In order to produce high purity H2Se gas (i.e., containing low quantities of CO2), Applicants have allowed the H2Se gas to flow through the AW-500 molecular sieve until the temperature of the AW-500 molecular sieve returned to room temperature (approximately 15° C. to approximately 30° C.). For approximately 10 kg of AW-500 molecular sieve and a H2Se-containing gas flow rate of approximately 100 cc/min to approximately 1,000 cc/min, the average time to reach room temperature has been approximately 2 hours. The purified H2Se gas contained less than approximately 3 ppm CO2. One of ordinary skill in the art will recognize that different amounts of AW-500 may require longer or shorter venting periods. Additionally, one of ordinary skill will recognize that higher concentrations of CO2 may be acceptable for some H2Se applications and, as a result, the disclosed purification process may require little or no venting time.
In order to reduce the amount of H2S in the H2Se-containing gas, the H2Se-containing gas flows through the AW-500 molecular sieve that has been prepared in accordance with the paragraphs above. The H2Se-containing gas should remain in contact with the AW-500 molecular sieve for approximately 0.5 seconds to approximately 100 seconds, and preferably from approximately 2 seconds to approximately 40 seconds. The process may take place at room temperature (approximately 15° C. to approximately 30° C.). Alternatively, the process may take place at a temperature ranging from approximately 0° C. to approximately 35° C. However, as shown in the Examples that follow, more H2S is adsorbed on the AW-500 molecular sieve during the room temperature process than during the lower temperature processes.
The resulting H2Se-containing gas has less than 10 ppmv H2S, and preferably less than 5 ppmv H2S, and contains between approximately 99.995% v/v and approximately 99.999% v/v H2Se.
Water (H2O) is also preferably removed from the H2Se-containing gas. The presence of moisture may contribute to the corrosion of piping and gas distribution systems even at very low concentrations. H2O may be removed by flowing the H2Se-containing gas through 4 A molecular sieve. The 4 A molecular sieve is commercially available. Currently, 4 A molecular sieve is supplied as 14×30 granular, 10×20 beads, 8×12 beads, 4×8 beads, 1/16′′ pellets, and 1⁄8′′ pellets. Any of these sizes may be used in the disclosed methods. Like the AW-500 molecular sieve, the 4 A molecular sieve may be stored in a stainless steel container. Alternatively, the 4 A molecular sieve may be placed in a container made of aluminum, stainless steel passivated with SiH4, or nickel plated carbon steel. Like the container for the AW-500 molecular sieve, the container for the 4 A molecular sieve should have an inlet and outlet. In one alternative, depicted in FIG. 1A, the inlet 10 and outlet 20 are located on opposite ends of the container 1 in order to minimize dead flow zones within the molecular sieve. The arrows in FIG. 1A depict the direction of gas flow through the container 1. However, alternative inlet and outlet locations may also be desired, such as the inlet 10 being located on one end of a cylindrical container 1 with the outlet 20 located on the cylindrical surface of the container 1 at the other end of the container 1 as depicted in FIG. 1B. One of ordinary skill in the art will recognize that the shape of the container 1 is not limited to a cylinder, but may also include spherical, cubic, or other polyhedric shapes.
Prior to use, the 4 A molecular sieve is activated by heating it under an inert gas to a temperature ranging from approximately 150° C. to approximately 250° C. for approximately 10 to approximately 24 hours. The inert gas may be N2, Ar, He, or combinations thereof. N2 is adsorbed on the 4 A molecular sieve at these temperatures. Therefore, a He purge should follow activation of the 4 A molecular sieve under a N2 atmosphere in order to produce a purified H2Se gas having low quantities of N2. For each 500 g of 4 A molecular sieve, the flow of the inert gas should be proportional to approximately 100 cc/min (i.e. 500 g=100 cc/min; 1 kg=200 cc/min, etc.). After approximately 8 hours of He purge, purification of the H2Se-containing gas may begin. One of ordinary skill in the art will recognize that different amounts of 4 A may require a longer or shorter activation period.
In order to reduce the amount of H2O in the H2Se-containing gas, the H2Se-containing gas is passed through the 4 A molecular sieve that has been prepared in accordance with the paragraph above. The H2Se-containing gas should remain in contact with the 4 A molecular sieve for approximately 0.5 seconds to approximately 100 seconds, and preferably from approximately 2 seconds to approximately 40 seconds. The process may take place at room temperature (approximately 15° C. to approximately 30° C.). Alternatively, the process may take place at a temperature ranging from approximately 0° C. to approximately 35° C.
The resulting H2Se-containing gas has less than 20 ppmv H2O, and preferably less than 1 ppmv H2O, and contains between approximately 99.995% v/v and approximately 99.999% v/v H2Se.
The water removal step using the 4 A molecular sieve may occur before or after the H2S removal step using the AW-500 molecular sieve. When the water removal step follows the H2S removal step, Applicants believe that the 4 A molecular sieve helps to reduce the CO2 produced from the reaction of H2Se and the AW-500 molecular sieve. When the H2S removal step follows the water removal, Applicants believe that the water content in the H2Se-containing gas will be reduced so that little to no CO2 will be produced by the reaction of H2Se and the AW-500 molecular sieve. In another alternative, both the AW-500 molecular sieve and the 4 A molecular sieve may be stored in the same container to simultaneously remove H2S, H2O, and CO2.
After purification, the purified gas may be transferred to suitable cylinders at a temperature ranging from approximately −20° C. to approximately −60° C. The cylinder may be located on a scale to assure that the cylinder is not overfilled with H2Se.
One exemplary purification system is depicted in FIG. 2. The H2Se-containing gas is contained in the cylinder labeled H2Se Source. The cylinder valve (not shown) and valve V1 are opened allowing the H2Se-containing gas to flow into Vessel-1 containing one of the disclosed molecular sieves in order to remove either H2O or H2S from the H2Se-containing gas. Pressure sensor P1 indicates the H2Se Source cylinder pressure. Pressure sensor P1 may be a pressure gauge or a pressure transducer. Valve V2 is opened to allow the H2Se-containing gas to flow to Vessel-2 containing a different molecular sieve than contained in Vessel-1. For example, if Vessel-1 contains AW-500, Vessel-2 contains 4 A. Alternatively if Vessel-1 contains 4 A, Vessel-2 contains AW-500. In another alternative, both Vessel-1 and Vessel-2 may contain both AW-500 and 4 A. The purified H2Se then flows through valve V3 into the cylinder labeled H2Se Purified (when the cylinder valve, not shown, is open). Pressure sensor P2 will give an indication of any unexpected pressure drop across Vessel-1 or Vessel-2. Pressure sensor P2 also gives an indication H2Se gas is flowing to the H2Se Purified product cylinder. Pressure sensor P2 may also be a pressure gauge or pressure transducer. Valves V1 and V2 may be closed if service to Vessel-1 becomes necessary. Valves V2 and V3 may be closed if service to Vessel-2 becomes necessary.
A second exemplary purification system is depicted in FIG. 3. The H2Se-containing gas is contained in the cylinder labeled H2Se Source. Valve V9 is used to assure the entire system is properly purged of any contaminants by cycling between (a) pressurized purge gas (e.g., N2, He, Ar, or other inert gas) and (b) pulling a vacuum on the system. Whenever the source or product cylinder is connected or disconnected from the system, the purge/vacuum cycling would be used to maintain the purity of the H2Se purification system. This procedure will also prevent any H2Se exiting the system to expose the operator and prevent the entrance of air and other impurities into the system.
Before operation of the purification system all valves would be closed. The H2Se Source cylinder valve (not shown) would be opened, followed by valves V1, V2, V4, V5, V6, V7, and V8. Vessel 1 may contain molecular sieve 4 A and Vessel 2 may contain molecular sieve AW-500. Alternatively, Vessel 1 may contain molecular sieve AW-500 and Vessel 2 may contain molecular sieve 4 A. In another alternative, both Vessel 1 and Vessel 2 may include both molecular sieve AW-500 and 4 A. Pressures sensor P1 indicates the H2Se Source cylinder pressure. Filter 1 and Filter 2 are used to prevent particulates from coming out of Vessel 1 and Vessel 2 and going into the purified H2Se Product cylinder. Pressure sensor P2 will give an indication of any unexpected pressure drop across Vessel 1, Vessel 2, Filter 1 or Filter 2. Pressure sensor P2 also gives an indication that H2Se gas is flowing to the H2Se Product cylinder.
V10 may be used to send an H2Se sample to analysis instrumentation to determine if the H2Se is the proper quality to fill in the H2Se Product cylinder. If the H2Se quality is at the required level, cooling means together with the thermocouple TC may be used on H2Se Product cylinder to reduce the pressure of the cylinder maintain a pressure differential between the source cylinder and the product cylinder. Suitable cooling means include liquid baths capable of cooling the H2Se Product cylinder to temperatures as low as −60° C., such as liquid nitrogen, dry ice, acetone, isoproponal, and other known heat transfer liquids. The cooling means and TC act as a temperature controller to cool the product cylinder. This creates a pressure difference that enables flow of H2Se from the H2Se Source to the H2Se Product. Once the H2Se Product cylinder valve (not shown) is opened, high purity H2Se will flow from the H2Se Source cylinder to the H2Se Product cylinder. Scale 1 will be able to indicate the amount of product that has left H2Se Source cylinder and scale 2 will indicate the amount of product that has been filled into the H2Se Product cylinder. Valves V4 and V5 may be closed if service to Purifier 1 and/or Filter 1 becomes necessary. Valves V6 and V7 may be closed when service to Purifier 2 and/or Filter 2 becomes necessary. Filter 3 is a final filter used to assure no particles enter the H2Se product. If purification of the H2Se source is not necessary, valves V2 and V8 may be closed and valves V1 and V3 opened.
EXAMPLES
The following non-limiting examples are provided to further illustrate embodiments of the invention. However, the examples are not intended to be all inclusive and are not intended to limit the scope of the inventions described herein.
Example 1
The following series of molecular sieves and catalysts were screened.

















H2O 
H2O 
H2S 
H2S 



Purifiers
challenge
removal
challenge
removal




















A
AW-300
60
0%
39.2
25%


B
AW-500 25C
—
NT
39.2
85%


B
AW-500 3C
—
NT
33.8
30%


B
AW500 -15C
690
0%
38.2
22%


C
5A
690
0%
38.2
0%


D
4A Pt—Si
—
NT
38.2
13%


E
ZnO
690
0%
38.2
61%


F
R3-12 3 × 5 mm
690
10%
38.2
38%


G
R3-12 0.5-1.0 mm
75
30%
45
47%


H
BASF COS
75
0%
45
28%


J
4A
75
95%
45
36%





NT—Not Tested






The H2O and H2S challenge levels in the table represent the amounts of H2O and H2S in ppmv that were in the H2Se source. The H2O and H2S removal columns provide the % v/v of each that were removed from H2Se.
The H2O challenge and H2O removal analysis was performed by a Meeco Aquavolt+ with a P2O5 electrolyte H2O analyzer. However, Se deposited on the P2O5 electrolyte. Additionally, the response time was very slow. As a result, H2O analysis was not performed in all of the tests in the table above. Additional H2O analysis was performed with a HALO H2O analyzer.
The H2S challenge and the H2S removal analysis was performed by GC HP 5890/PDHID. A Restek GC column capable of detecting N2, O2, CO2, CH4, and H2S in the H2Se-containing gas was utilized. The GC was calibrated using a gas standard containing 30 and 100 ppm of each of these impurities. The detection limits were  ̃0.1 ppm (3×S/N).
In addition to measuring the removal of the H2S and H2O impurities, the generation of other impurities due to contact with H2Se was analyzed.
While ZnO successfully removed H2S, it seemed to produce another impurity that has not yet been identified.
Molecular sieve 5 A did not remove H2O or H2S. This may be the result of H2Se adsorption in the 5 angstrom pores.
AW-500 removed H2S while releasing some CO2. Surprisingly, AW-500 removed H2S from H2Se, even though AW-500 has the same 5 angstrom pore size as molecular sieve 5 A. Capacity of the AW-500 molecular sieve for H2S in H2Se was found to be >1% g H2S/g AW-500.
The capacity of the 4 A molecular sieve for H2O in H2Se was found to be 2.4% g H2O/g 4 A.
Example 2
One vessel containing 4 A molecular sieve was used specifically to remove H2O from H2Se at  ̃110 psig @ 72° F. The second vessel containing AW-500 molecular sieve, and in series with the first vessel, was used to remove H2S from H2Se at  ̃110 psig @ 72° F. Analytical equipment capable of measuring both H2S and H2O concentrations in H2Se was located downstream of the vessels. Measurement of the level of H2O in H2Se was below 1 ppm, and H2S in H2Se was below 5 ppm. At these levels the chance for reaction with H2O or H2S in the process is quite low.
It will be understood that many additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above and/or the attached drawings.

## Claims

1. A method of purifying a H2Se-containing gas, the method comprising reducing an amount of H2S in the H2Se-containing gas below 10 ppmv by passing the H2Se-containing gas through an AW-500 molecular sieve.

2. The method of claim 1, wherein the purified H2Se-containing gas contains less than 5 ppmv H2S.

3. The method of claim 1, further comprising reducing an amount of H2O in the H2Se-containing gas below 20 ppmv by passing the H2Se-containing gas through a 4 A molecular sieve.

4. The method of claim 3, wherein the purified H2Se-containing gas contains less than 1 ppm H2O.

5. The method of claim 3, wherein the H2Se-containing gas is passed through the 4 A molecular sieve prior to being passed through the AW-500 molecular sieve.

6. The method of claim 3, further comprising receiving the purified H2Se-containing gas in a cylinder cooled to a temperature ranging from approximately −20° C. to approximately −60° C.

7. The method of claim 1, further comprising receiving the purified H2Se-containing gas in a cylinder cooled to a temperature ranging from approximately −20° C. to approximately −60° C.

8. A purification method for H2Se, the method comprising:
passing H2Se through a 4 A molecular sieve; and
subsequently passing H2Se through an AW-500 molecular sieve.

9. The method of claim 8, wherein the purified H2Se contains less than 10 ppmv H2S.

10. The method of claim 9, wherein the purified H2Se contains less than 5 ppmv H2S.

11. The method of claim 8, wherein the purified H2Se contains less than 20 ppmv H2O.

12. The method of claim 11, wherein the purified H2Se contains less than 1 ppm H2O.

13. The method of claim 8, further comprising receiving the purified H2Se in a cylinder cooled to a temperature ranging from approximately −20° C. to approximately −60° C.