Patent Application
20090028781
The present invention relates to a catalytic reactor apparatus and a method for producing high purity water vapor by reacting hydrogen and oxygen.
High purity water vapor with very low impurity levels is required in a variety of industrial and scientific applications. For example, in the production of semiconductors, high purity water vapor is used in the silicon oxide film coating step by the moisture oxidation method. High purity water vapor for this process step can be produced by reacting purified hydrogen and oxygen together in the presence of a catalyst to form high purity water. The catalyst reduces the temperature needed to sustain the reaction, thus improving the safety and controllability of the reaction step. U.S. Pat. Nos. 6,093,662 and 6,180,067, granted to Ohmi et al., describe a method and a reactor for generating water by reacting hydrogen and oxygen within a reaction chamber having an interior coating of platinum to act as a catalyst. While these previous patents represent a significant advance in this technical area, continued research has been directed toward further improvements of such a process, in particular toward the goals of improved safety, reliability and control of the process and improved purity of the water vapor produced.
In keeping with the foregoing discussion, the present invention takes the form of a catalytic reactor apparatus and a method for producing high purity water vapor by reacting hydrogen and oxygen together within a catalytic reaction chamber. The reactants and an inert gas, such as argon gas or nitrogen, are supplied to the catalytic reaction chamber in a controlled fashion by a gas panel. The cylindrical catalytic reaction chamber is preferably constructed of titanium or stainless steel. The catalytic reaction chamber is filled with high purity pellets of a nonreactive material coated with a catalyst, such a noble metal catalyst. Screens at each end of the reaction chamber prevent the catalyst pellets from being transported outside reaction chamber. The interior of the reaction chamber has two perpendicular baffle plates traversing the length to increase contact area with the catalytic pellets for electrical charge and thermal transport during the reaction. The temperature of the reaction chamber is maintained below 350 C during operation.
The catalytic reactor apparatus of the present invention has a number of distinct advantages over the prior art. In particular, the catalytic reactor apparatus has a lower thermal budget in that it does not require heating to initiate or sustain the reaction. The catalytic reactor apparatus allows the reaction temperature to be more precisely controlled for improved safety and reliability. Prior art water vapor generators generally operate at a temperature of approximately 460 C, whereas the operating temperature of the catalytic reactor apparatus of the present invention can be reliably maintained at less than 350 C. Furthermore, the catalytic reactor apparatus of the present invention. The configuration of the catalytic reactor apparatus provides improved flexibility of gas flows to allow adjustability of the flow rate and the concentration of water vapor, hydrogen, oxygen and inert gas in the output of the reactor. The configuration also allows the ability to easily change and recharge the catalyst in the reactor. Additional advantages of the invention include more reliable operation, lower cost of manufacturing and smaller footprint of the reactor compared with prior moisture generator systems.
The Ar gas connection 102 is connected to an Ar purge valve assembly 108, which is used for purging the lines for the reactive gases with Ar gas. Within the Ar purge valve assembly 108, the Ar gas line branches off to a first solenoid operated valve 1 that is configured to deliver Ar gas to the O2 and H2 branches of the gas panel 150 via Ar line 114 and to a second solenoid operated valve 2 that is configured to deliver Ar gas through a first mass flow controller MFC 1 to a third solenoid operated valve, the Ar control valve 3.
The O2 gas connection 104 is connected to an O2 valve assembly 110. The O2 gas enters the O2 valve assembly 110 through a fourth solenoid operated valve 4. A first branch of the Ar line 114 from the Ar purge valve assembly 108 enters the O2 valve assembly 110 through a fifth solenoid operated valve 5 just downstream of the fourth solenoid operated valve 4. The fourth and fifth solenoid operated valves 4, 5 can be operated to allow the O2 valve assembly 110 to deliver O2 or Ar gas through a second mass flow controller MFC 2 to a sixth solenoid operated valve, the O2 control valve 6. The Ar gas is typically used to purge the O2 valve assembly 110, the O2 control valve 6 and the O2 gas lines.
The H2 gas connection 106 is connected to an H2 valve assembly 112. The H2 gas enters the H2 valve assembly 112 through a seventh solenoid operated valve 7. A second branch of the Ar line 114 from the Ar purge valve assembly 108 enters the H2 valve assembly 112 through an eighth solenoid operated valve 8 just downstream of the seventh solenoid operated valve 7. The seventh and eighth solenoid operated valves 7, 8 can be operated to allow the H2 valve assembly 112 to deliver H2 and/or Ar gas through a third mass flow controller MFC 3 to a ninth solenoid operated valve, the H2 control valve 9. The H2 valve assembly 112 can deliver H2 and Ar gas mixed in different ratios. The hydrogen concentration can range from 0% to 100%, with concentrations of 1% to 50% being typical for many applications. This gas mixture is the feed reactant gas used in the catalytic reaction chamber 120. The Ar gas can be used separately to purge the H2 valve assembly 112, the H2 control valve 9 and the H2 gas lines.
The outlet of the Ar control valve 3, the O2 control valve 6 and the H2 control valve 9 are all connected to a common line 116, which is in turn connected to the inlet 224 of the catalytic reaction chamber 120. A water vapor outlet tube 118 is connected to the outlet 222 at the opposite end of the catalytic reaction chamber 120. The water vapor outlet tube 118 has a titanium connection and, optionally, includes a hydrogen sensor to detect unreacted hydrogen gas.
The gas panel enclosure 138 has a removable front panel 142 and top panel 160. The front panel 142 is made with one or more cooling air inlets 146 and an access panel 144. For the convenience of the operator, a schematic diagram 164, similar to that shown in
On the top of the enclosure 170 between the top panel 160 of the gas panel enclosure 138 and the top panel 162 of the reaction chamber enclosure 140 is a control panel 136 where the operating controls of the catalytic reactor apparatus 100 are located. The operating controls located on the control panel 136 include a purge enable switch 122, an Ar enable switch 124, an Ar on/off switch 126, an O2 enable/purge switch 128, an O2 on/off switch 130, an H2 enable/purge switch 132 and an H2 on/off switch 134.
The isolation panel 166, which separates the gas panel enclosure 138 and the reaction chamber enclosure 140, can be seen on the interior of the enclosure 170. The isolation panel 166 has one or more internal vents 182 to allow circulation of cooling air from the gas panel enclosure 138 to the reaction chamber enclosure 140. Preferably, one or more cooling fans 186 direct cooling air through the internal vents 182 toward the catalytic reaction chamber 120.
The gas lines upstream of the catalytic reaction chamber 120 are preferably constructed of stainless steel tubing, typically ¼ inch diameter, with 5-10 Ra surface roughness. Optionally, the water vapor outlet tube 118 downstream of the catalytic reaction chamber 120 may be made of titanium and optionally may be welded to the reactor vessel 200.
The purity of the materials used in the reactor are such that the analysis of the steam produced shows extremely low or no metallic impurities. TRXRE analysis data show the levels of Fe, Ni, Cr and other metals in the steam generated by this reactor to be acceptable for stringent semiconductor manufacturing requirements.
To begin operation, the purge enable switch 122 is turned on, which activates solenoid operated valve 1 to supply Ar gas to the O2 valve assembly 110 and the H2 valve assembly 112. The Ar enable switch 124 is turned on to open solenoid operated valve 2 and the O2 enable/purge switch 128 and the H2 enable/purge switch 132 are moved from the neutral position to the purge position to open solenoid operated valves 5 and 8. Then, the Ar on/off switch 126, the O2 on/off switch 130 and the H2 on/off switch 134 are turned on to open solenoid operated valves 3, 6 and 9 to purge the system with Ar gas, typically for a period of approximately 1-5 minutes, to flush out impurities in the system.
After the system has been sufficiently purged with Ar, the Ar is shut off. The reaction is initiated by moving the O2 enable/purge switch 128 from the purge position to the ON position to close solenoid operated valve 5 and open solenoid operated valve 4. Next, the H2 enable/purge switch 132 is moved from the purge position to the ON position to close solenoid operated valve 8 and open solenoid operated valve 7. The O2 and the H2/Ar mixture flow into the catalytic reaction chamber 120. The H2 and O2 contact the catalyst and react to form water vapor at a temperature below the autoignition temperature of 560 C. In many applications, it is preferred to have the H2 and O2 in an approximately stoichiometric ratio of 2:1 or with the O2 slightly in excess of stoichiometric with the H2 in order to assure complete reaction of the hydrogen. For example, the H2:O2 ratio may be in the range of approximately 2:1.1 to 2:1.2, most preferably approximately 2:1.15. In some applications, it is preferable to have the O2 in excess of stoichiometric with the H2, to provide oxygen rich water vapor for processes requiring an oxidizing atmosphere. For these applications, the H2:O2 ratio can range as low as 2:1.45 or even lower. In other applications, it is preferable to have the H2 in excess of stoichiometric with the O2 to provide hydrogen rich water vapor for processes requiring a reducing atmosphere. For these applications, the H2:O2 ratio can range as high as 2.9:1 or even higher. The O2:H2 ratio can be adjusted using the O2 and H2 mass flow controllers MFC 2, MFC 3.
The Ar on/off switch 126 may be turned off or it may remain on depending on the ratio of water vapor to inert gas that is desired for the output of the reactor. The H2O to Ar ratio can be adjusted from approximately 1 to 100% by adjusting the H2 to Ar ratio in the feed gas.
Water vapor, or water vapor mixed with Ar gas, flows out of the water vapor outlet tube 118. A filter 190 connected to the water vapor outlet tube 118 removes impurities from the water vapor produced. Particles in excess of approximately 0.0003 μm size are filtered out.
As the exothermic reaction proceeds, there is a temperature rise. Air flow cooling is employed using fans 186 that work to lower the skin temperature of the catalytic reaction chamber 120. The temperature increases at a predetermined rate and the temperature sensor feedback loop is used to detect anomalies and warn the user appropriately. If the temperature sensor senses a temperature greater than 350 C, the reaction is automatically shut off by shutting down the H2 flow and/or the mixed gas flow in the common line 116. One or more thermal fuses may be placed at various points in the control circuit as a safety shutdown in case the catalytic reaction chamber 120 exceeds the maximum allowable temperature. Alternatively, if the temperature sensor senses a temperature less than 50 C after 2 minutes, the same automatic shutdown sequence occurs to check the catalytic reactor apparatus 100 for malfunction.
To shut the catalytic reactor apparatus 100 down after use, the H2 is shut off first, then the Ar is shut off and finally the catalytic reaction chamber 120 is purged with O2, which is then shut off.
The catalytic reactor apparatus 100, in the configuration shown, is capable of delivering from approximately 100 sccm (standard cubic centimeters per minute) to 1 slm (standard liters per minute) of high purity water vapor. The catalytic reactor apparatus 100 is also scalable to deliver any desired rate of high purity water vapor. In a preferred method, the capacity of the catalytic reactor apparatus 100 can be increased in a modular fashion by connecting multiple catalytic reaction chambers 120 in parallel, with each catalytic reaction chamber 120 providing up to 1 slm of high purity water vapor. This modular approach is advantageous because the thermal characteristics-of the catalytic reaction chambers 120 are already known and would not need to be reengineered for safety and thermal equilibrium.
While the present invention has been described herein with respect to the exemplary embodiments and the best mode for practicing the invention, it will be apparent to one of ordinary skill in the art that many modifications, improvements and subcombinations of the various embodiments, adaptations and variations can be made to the invention without departing from the spirit and scope thereof.
This application claims the benefit of U.S. Provisional Application, Ser. No. 60/311,887, filed on Aug. 13, 2001, the disclosure of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10219988 | Aug 2002 | US |
| Child | 12240763 | US |
