CN1668780A

CN1668780A - Apparatus and method for fluorine production

Info

Publication number: CN1668780A
Application number: CNA038168847A
Authority: CN
Inventors: G·赫德森; R·达森
Original assignee: BOC Group Inc
Current assignee: Messer LLC
Priority date: 2002-07-19
Filing date: 2003-07-11
Publication date: 2005-09-14
Anticipated expiration: 2023-07-11
Also published as: TWI265147B; JP2005533925A; GB0216828D0; ATE312212T1; US20050224366A1; AU2003244866A1; DE60302669T2; CN100378248C; TW200403187A; DE60302669D1; WO2004009873A1; EP1523587B1; EP1523587A1; KR20050042751A

Abstract

Apparatus and a method for the generation of fluorine by the electrolysis of hydrogen fluoride are described. The apparatus comprises: a plurality of individual fuorine generating cassettes; said individual fluorine generating cassettes being operably connected to a fluorine gas distribution system for the remote use and consumption of said fluorine gas; said fluorine generating cassettes being individually isolatable from said gas distribution system and removable from the apparatus for remote maintenance.

Description

Apparatus and method for producing fluorine

Technical Field

The present invention relates to an apparatus for producing fluorine and a method for producing fluorine using the same.

Background

Semiconductor devices are typically produced by forming multiple layers of silicon in a vacuum chamber by a Chemical Vapor Deposition (CVD) process. During the manufacturing process, the desired pattern may also be formed on the device by etching the material layers that make up the device. Over time, such vacuum chamber etching processes can result in the deposition of certain etched substrate materials, such as silicon, silicon oxide, silicon nitride, etc., on the surfaces of the vacuum chamber. Most of the unused reagents and byproducts of the deposition or etching process are exhausted from the chamber during each production step, but there are always some unwanted reagents and byproducts that inevitably deposit on the interior walls and surfaces of the process chamber as potential contaminants. For example, some of these deposited materials may fall off the chamber walls and add to the device, making them waste. Such undesirable deposits and residues must be periodically cleaned from the chamber surfaces to avoid accumulating to the extent that they may be harmful.

Although semiconductor devices are mentioned specifically above, CVD techniques are very widely used for producing numerous types of electronic devices. For example, CVD is used in the production of Thin Film Transistor (TFT) flat panel displays by depositing films of materials on large substrates, such as glass plates, for example in the production of Liquid Crystal Displays (LCDs).

Traditionally, the removal of unwanted materials from the surfaces of CVD chambers has been accomplished by the use of cleaning gases such as nitrogen trifluoride, hexafluoroethane, and sulfur hexafluoride. While these gases work well to remove contaminants from the process chamber, they have the disadvantage of causing global warming upon entry into the atmosphere. If these gases are used, they decompose under the action of the plasma, releasing atomic fluorine in the chamber, which is an active cleaning component.

It has been recently reported that molecular fluorine can be used to replace the conventional gaseous compounds described above, either directly for cleaning a CVD chamber or after treating molecular fluorine in a plasma chamber to generate fluorine atoms. Another advantage of molecular fluorine is that it does not contribute to global warming. EP-A-1138802 describes the use of molecular fluorine for removing contaminants from CVD chambers.

However, although the above-discussed EP-A-1138802 clearly shows that molecular fluorine itself or fluorine atoms generated by treatment can effectively clean CVD chambers, it does not describe how such fluorine gas is generated in order to build commercial CVD plants.

However, the electronics manufacturing industry is not well equipped to maintain or cope with the equipment of conventional chemical plants to generate fluorine in sufficient quantities for cleaning the large number of CVD chambers that are present in typical modern chemical plants that produce electronic devices. The industry requires a reliable, easily scalable in-situ production process and means of delivery of high purity fluorine gas streams. It is desirable that maintenance and upgrading of a fluorine gas production plant be accomplished quickly and easily with minimal or no chemical poisoning, and more importantly, without loss of production during maintenance or upgrading. The ability to upgrade is very important because some users may require that the ability to produce fluorine be expanded as the capacity of electronic devices increases, as the CVD chamber is also increased substantially.

Compressed fluorine gas in cylinders is of no practical value for large scale CVD applications due to safety considerations and the maximum fluorine gas storage of 28 bar gauge in a typical 50 liter cylinder is only 1.4 kg. Therefore, the amount of compressed fluorine gas required by a conventional plant means that it is not environmentally or safely satisfactory because the reactivity of fluorine gas after compression is greatly improved. Furthermore, the cost of providing large amounts of fluorine gas in this manner is also prohibitive.

In situ generation of fluorine gas currently exists in certain industries, but fluorine generating devices are designed to meet chemical standards related to fluorine production, require relatively high on-site maintenance, and require constant operator intervention, often involving chemical processing or sampling, such as the electrolyte from which the fluorine gas is produced. This procedure is common in the chemical industry, but requires the personnel to wear appropriate protective clothing, use breathing equipment, etc., to avoid injury from the toxic fluorine gas released into the atmosphere when the chamber connections are broken or the chambers are opened. However, this method is not feasible in the electronics industry because it is desirable that the personnel do not have to rely on protective clothing or the like, and that any toxic gases should be confined at any time and not released into the atmosphere in any case.

In the absence of particular process advantages for cleaning CVD tools with molecular fluorine, it is claimed that changes to existing methods and cleaning chemicals can save at least 30% of the expense for the industry. Therefore, it has been considered to provide each CVD processing apparatus with a conventional fluorine generating cell. One obvious advantage of this approach is that the output port of the fluorine chamber can be matched to the fluorine requirements of the particular apparatus being the subject of the fluorine supply. This method also minimizes the piping required to carry fluorine gas. Another significant advantage is that failure of one fluorine generator does not cause a plant-wide shutdown, but only a shutdown of one CVD apparatus. However,the practical and economic disadvantages of this method are covered by the excellent attractiveness of a CVD apparatus with a fluorine generator. Because each fluorine generator must have the same processing module, it takes an extra large amount of money to duplicate and process many components, including: anhydrous hydrogen fluoride supply, downstream purification of fluorine gas, gas compression and storage, and treatment of generator effluent. Thus, this process involves many relatively hazardous chemical processes, including large scale production of hydrogen fluoride and storage of fluorine gas throughout the production plant. As a result, all fluorine generating operations and maintenance activities are relatively dispersed throughout the plant and pose a threat to plant safety.

Furthermore, fluorine gas quality is extremely important in CVD cleaning applications, but gas quality control is very difficult because continuous in situ analysis is prohibitively expensive when several devices are required, and periodic sampling of fluorine gas from multiple devices presents many practical difficulties and is not safe.

Unlike the above-described method of supplying a fluorine generator to a large number of CVD apparatuses from a single large conventional generator through a plurality of supply routes, there is a significant drawback in that when the generator is out of order or stopped for repair or maintenance, the entire production line must be shut down until the generator is returned to operation.

In a first aspect, the present invention relates to a method for generating fluorine gas by electrolyzing hydrogen fluoride, the apparatus comprising: a plurality of individual fluorine generating units; the single fluorine generating unit is connected with a fluorine gas conveying system so as to meet the utilization and consumption of the fluorine gasby remote equipment; the fluorine generation unit is distributively removable from the fluorine gas delivery system and removable from the apparatus for servicing elsewhere.

The term "maintenance" referred to above includes removal of the individual fluorine generating units from the apparatus for any reason. In the present invention, the term "maintenance" may include regular maintenance, servicing, or repair of the chamber, and the like. It also includes the removal of such maintenance-requiring chambers from the apparatus to a location remote from the fluorine-consuming plant, thereby eliminating inconvenience, contamination or safety concerns to the plant or workers.

In this specification, the plant is referred to as a "kit" of fluorine generating plants. The term "kit" refers to a plant or the like that is constructed and assembled at a fluorine plant supply company, tested to ensure efficient operation of the plant, shut down and packaged, shipped as a separate plant to a customer site or the like so that the customer can utilize the fluorine gas in production. Generally, the equipment can be completely independent and can operate without the need of a customer to provide power, water, compressed gas or nitrogen and the like; it can be installed in land or sea containers that can be used directly at the customer's site, as well as holding equipment.

The fluorine generating workshop or equipment can generate 0-2.7kg F according to the total fluorine gas generation amount₂There are several categories of/. There are also conventional large-scale fluorine gas generation plants used in chemical plants which generate thousands of tons of fluorine gas per year, wherein the fluorine production per chamber is usually not less than 4kg F₂These plants can have many individual rooms which can be taken off by a person wearing and using suitable protective equipment. The various rooms and fixtures of these plants are built in situ and pulled to the operating site for assembly. Such plants are used in the nuclear industry and the like to produce nuclear fuel precursors such as uranium hexafluoride and the like. This plant is very different from a "complete" plant which can be used as a unit fluorine gas generating device, the latter being the subject of the present invention. In the present invention, the apparatus may be contained in a container, the container having an integral scaleThe dimensions do not substantially exceed standard ISO containers, nor are they smaller than the dimensions described in detail below.

In this specification, an apparatus comprises a plurality of self-contained fluorine gas generating units. The cells may be formed from a single chamber such that each cell effectively contains one cathode and one anode. Alternatively, the cell may comprise a set of chambers, such that there may be more than one cathode and anode in the cell. Thus, the apparatus of the present invention comprises a plurality of fluorine generators which are separable from each other and from the apparatus as a whole, each unit being removable from the apparatus independently of each other without interrupting the supply of fluorine gas to the entire apparatus. For ease of description, the individual fluorine generating units are hereinafter referred to as "fluorine cassettes". Similarly, other devices in a fluorine production facility, such as fluorine purification units and fluorine compression and storage units are also referred to as "cassettes," e.g., "purification cassettes" and "compression and storage cassettes. The term "cassette" means an individual package having the aforementioned features or means that is easily removed from the apparatus for maintenance or repair and can be replaced with the same package without harm to people or affecting the continuous production of fluorine.

In the fluorine production industry, a fluorine "cell" is a common term used to refer to a metal container but which has a number of anodes (the container itself typically constitutes the cathode). Prior art fluorine chambers typically have up to 36 individual anodes. Thus, in the present invention, each fluorine chamber or cassette may contain 6, 12 or 24 anodes depending on the customer's fluorine requirements.

The removed fluorine cassette is preferably replaced with another substantially identical fluorine cassette so that the amount of fluorine generated by the apparatus is not significantly affected.

The apparatus of the present invention provides a self-contained fluorine generating system that allows the plant to have a sufficient amount of fluorine generated, for example, as a cleaning gas for CVD chambers or tools to which the fluorine generating system is connected, such that fewer than the total number of individual fluorine cassettes in the apparatus are required to meet the total fluorine demand. Thus, if a fluorine cassette requires repair or maintenance or service, the apparatus can continue to generate fluorine gas to meet the overall fluorine demand without shutting down the fluorine generating apparatus of the present invention and without other downtime. As described above, the removed fluorine cassette can be immediately replaced with a substantially identical (referring to the primary feedstock and size) fluorine cassette so that the overall potential for fluorine generation is not radically compromised. For example, for a plant containing three fluorine generating cassettes, the conventional average output of the three cassettes is less than 66% of the output per peak at peak demand. Thus, if for some reason it is desired to remove one cassette, the remaining two cassettes can meet the total demand for peak fluorine for the shop application.

Thus, a single point failure of the fluorine cassette of the apparatus of the present invention will not cause the entire apparatus to shut down and will not reduce the ability to meet the peak fluorine demand.

As mentioned above, when a fluorine generating cell is conventionally maintained, maintained or repaired in situ, the cell must be shut down and removed in situ, which means that all but those wearing suitable protective clothing must be removed from the site where the work is to be performed, due to the extreme toxicity of the fluorine gas and the electrolyte used. The down time to accomplish this is typically several days. This means that the plant supplying fluorine gas with the fluorine plant is interrupted and production time is lost.

The fluorine cassettes to be treated for the apparatus of the invention are preferably electrically isolated and isolated by valve means when fluorine gas is involved, removed from the apparatus, transported by truck or the like to a remote location for repair. However, replacement fluorine cassettes that are ready for use in situ may be installed in the facility on-the-fly. Thus, there is no time limit as to when the chamber is reused for removal; the chamber may be sent for maintenance to a location having a suitable location for performing maintenance; people who work in the workshop after taking off the fluorine box are not injured; the time of workshop production is not lost.

The overall size of the apparatus of the present invention is small. For example, as noted above, the size may approach standard ISO containers, which are widely used internationally for shipping and transporting many types of cargo. The overall dimensions of such a container are about 2.44m wide by 2.44m high by 6.5m long (or about 8 ' wide by 8 ' high by 20 ' long). Thus, the fluorine generating apparatus of the present invention can have a small footprint (footprint) and be easily installed at a convenient location in a customer's production facility.

The apparatus of the invention comprises a self-contained integrated fluorine generating unit which can be transported as a unit, either by land or by sea. The apparatus of the present invention, when based on ISO type vessels, may comprise up to three fluorine cassettes, at least one fluorine purification cassette and at least one fluorine compression and storage/buffer cassette.

One embodiment of the present invention comprises a fluorine generating apparatus comprising three fluorine cassettes, two fluorine purification cassettes, a fluorine compression and storage cassette and other associated equipment, all enclosed within the outer dimensions of a standard ISO container. However, another aspect of shipping is shipping a backup or replacement fluorine cassette; a standard ISO container can hold up to 8 fluorine cassettes of about 0.74m width, but this is only an example and the manufacturing dimensions of each fluorine cassette can vary within certain limits. The boxes of the apparatus of the invention are individually transportable packages because their periphery is completely panel-like, which allows the boxes to form a closed unit that does not require additional packaging or protection for transportation.

Although the fluorine cassette used in a particular apparatus of the present invention may be formed into an apparatus set having particular peripheral dimensions and having service connections, fluorine gas outlets, hydrogen gas outlets, etc. at predetermined locations to ensure reciprocity, the actual fluorine chamber in the fluorine cassette may be altered to suit the fluorine gas requirements of the customer. For example, the initial fluorine generating capacity of the fluorine cell may be 0-385g/h, and as demand increases, the output capacity of the fluorine cell may be varied to 0-700 or 0-1400g/h, etc. Thus, the apparatus of the present invention can be upgraded with increasing fluorine demand.

The fluorine cassettes may be installed in an overwrap of the overall apparatus, in which all of the fluorine cassettes may be routinely operated. Such conventional operations may include the routing of fluid conduits, the burying of electrical cables, and the routing of electrical/instrumentation.

And an isolation valve is arranged on a toxic fluid connecting line with the fluorine box. Preferably, a double isolation valve is installed on the toxic fluid connection line with the fluorine cassette, and a vacuum connection is formed between the two isolation valves. Thus, the two isolation valves can be closed, the toxic substances can be evacuated by vacuum, the connection between the fluorine cassette and the connecting lines can then be broken, and only then can the fluorine cassette be removed from the apparatus. The vacuum extraction system for removing toxic substances is preferably connected to a scrubbing system for removing and neutralizing toxic substances.

The non-toxic fluid line may be provided by, for example, a quick connect coupling or the like.

Once the fluorine cassette is disconnected from the apparatus, it is immediately completely isolated from the environment and poses no danger to humans. Similarly, a new replacement fluorine cassette is also harmless until it is connected to the equipment and the isolation valve is opened to allow toxic fluids to pass.

The spare fluorine cassettes may be stored in-situ for quick replacement. Similarly, replacement cassettes can be safely stored in situ until they are removed for transport to a remote location for repair or for off-site maintenance, etc.

The fluorine cassette may be provided with means to facilitate removal and insertion of the cassette from the apparatus packaging. Suitable tools may include wheels and the like.

In a preferred embodiment of the invention, the fluorine cassette itself has a separate enclosure along one or more of the fluorine gas generation chambers so that leakage of fluorine gas occurs while still confined within the enclosure. The cassette enclosure is preferably connected to a vacuum extraction system which is equipped with a scrubber to remove harmful chemicals.

In the apparatus of the present invention, each cassette has its own outer packaging, which is a strong metal frame and plate. When installed in the plant, the package is connected to extraction and scrubbing units to cope with any possible leakage, thus providing a sealed protective outer package. The overwrapping provides the dual benefit of not only eliminating the need for repackaging during shipping, but also providing protection for the cassette and protection for the person handling the cassette when the cassette is removed from the apparatus.

In a preferred embodiment of the apparatus of the present invention, there is also provided at least one, and preferably two, fluorine purification cassettes through which the fluorine gas exits to remove unwanted particulate matter and undesirable gaseous contaminants before the fluorine gas reaches the intended processing apparatus. The purpose of having two such cassettes is to allow one cassette to be repaired or replaced during the fluorine production process. Such unwanted substances may include hydrogen fluoride, etc., which is carried from the electrolyte into the fluorine gas stream, which may pass through a sodium fluoride trap, etc. The carbon tetrafluoride formed by the reaction of fluorine with the carbon anode may be removed by a suitable known absorption system.

The fluorine purification cassette is also isolatable and can be easily removed from the apparatus for repair and maintenance in a manner similar to the fluorine cassette. Therefore, this isolation is preferably accomplished by means of a double isolation valve, as in the case of a fluorine cassette, with the vacuum extraction system involved.

In another preferred embodiment of the apparatus of the invention, a fluorine buffer cassette may also be provided, which is connected to the fluorine line downstream of the fluorine purification cassette. The buffer box has the function of collecting the generated purified fluorine, concentrating it in a tank, constituting a fluorine gas reservoir, reducing the fluctuation of the fluorine gas flow so as to supply the fluorine gas at a constant pressure.

The apparatus of the invention may be wholly housed in a main enclosure frame which is fitted with suitable panels to provide an effective enclosure to the environment. In addition, the main overwrap is preferably provided with a vent passage to remove any leakage and prevent contamination of the surrounding area. The exhaust system may be connected to a suitable scrubber for safely removing any harmful substances.

The main enclosure is also preferably equipped with all necessary power and electrical control systems in known manner to allow for efficient electrolysis of the hydrogen fluoride electrolyte to generate fluorine gas.

According to a preferred embodiment of the apparatus of the invention, the frame of the fluorine cassette can be used as a cathode connection for the fluorine cell in the cassette, so that the cassette must be installed in the main enclosure for cathode connection to the electrolytic cell in the cassette.

The apparatus of the invention is also preferably provided with purging means to remove reactive fluids, such as water vapour and the like, which may be present, from the conduit prior to introduction of the fluorine gas. Such a purge means may comprise a valve connected to the plant line for introducing nitrogen or the like for purging oxygen or the like from the line.

In another embodiment of the apparatus of the present invention, each individual fluorine cassette may be provided with the requisite equipment to continue operation even in the event of failure of certain "core" components. In this alternative embodiment, the separate cassette enclosure may also be equipped with a dc power supply for electrolysis, fluorine purification and compression, and fluorine storage/buffering. The cassette is relatively bulky and the fluorine generating unit is located in the lower portion of the cassette enclosure, leaving sufficient space for other devices. The connection of the storage tank/buffer device can also be realized by means of a double isolating valve. In this alternative embodiment, the cassette can be disconnected from the output of the fluorine tank/buffer unit from the apparatus enclosure because the fluorine cassette itself, the purification and compression device, is upstream thereof.

In a second aspect, the present invention provides a method of operating and maintaining an apparatus for the electrolytic production of fluorine gas from hydrogen fluoride, the method comprising the steps of: providing a plurality of fluorine generating units connected to a fluorine gas delivery system for remote customer use and consumption of said fluorine; providing means for isolating individual fluorine generating units from said fluorine gas delivery system and from each other; means are provided for removing said separate fluorine generating units from said apparatus without interrupting the supply of fluorine gas to the remaining fluorine generating units.

The same definitions apply in respect of the fluorine generating units in the apparatus according to the first aspect of the invention for the process according to the invention.

In order that the invention may be more fully understood, some embodiments will now be described, by way of example only, with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of a prior art fluorine generating cell;

FIG. 2A shows a front view (without a panel) of a first embodiment of the apparatus of the present invention;

FIG. 2B is a rear view of the apparatus shown in FIG. 2A;

FIG. 3 is a side view of the fluorine cassette shown in FIG. 2 without the packaging board;

FIG. 4 is a front view of the fluorine cassette shown in FIG. 3 without the packaging panel;

FIG. 5 is a side view of the fluorine purification unit of the apparatus of FIG. 2 without the packaging plate;

FIG. 6 is a front view of the purification unit of FIG. 5;

FIG. 7 is a side view of the buffer unit of the apparatus of FIG. 2, without the wrapper plate;

FIG. 8 is a front view of the buffer unit of FIG. 7;

fig. 9 shows a perspective view of a second embodiment of the apparatus of the present invention, but without the main and other packaging sheets for clarity.

Referring now to FIG. 1, this is merely to explain the basic principles of the electrolytic production of fluorine gas. The fluorine generating cell is shown at 10. The fluorine generating cell comprises a safety container 12 which may or may not constitute the cathode of the fluorine generating cell; in the latter case, reference numeral 14 indicates a separate cathode. The top 16 of the vessel 12 is closed, leaving only

outlets

18, 20 for fluorine andhydrogen, respectively, with valve means thereon. The container 12 contains an electrolyte 22 of hydrogen fluoride in molten potassium fluoride salt. A separate sleeve 24 is suspended from the vessel top wall 16 with its lower end 30 extending below the electrolyte surface 32 to effectively divide the space above the electrolyte surface into two separate hydrogen and

fluorine chambers

34 and 36. The anode 38 is typically constructed of high density isotropic carbon that extends into the electrolyte 22, typically below the lowermost end of the sleeve 24, but not in all cases. The container 12 is typically provided with means (not shown) for heating and melting the electrolyte, since this electrolyte is solid at room temperature. Typically, the temperature of the electrolyte is maintained at 80-100 ℃ by a heating device while the fluorine generating cell is in a quiescent state. Heat is generated during the electrolysis process and the electrolyte must generally be cooled by suitable cooling means. Any suitable heating means may be used, including, for example, a tubular heater extending into the container and through the electrolyte, and an electrical heating blanket or steam jacket wrapped around the container. A suitable power source 40 is provided to cause electrolysis of the electrolyte. Typically, the voltage is lower, about 6-9 volts, but the current is higher, about 500-2400 amps, depending on the number of anodes in the cartridge.

The electrolytic reaction is as follows:

the amount of fluorine generated is proportional to the applied current. Fluorine and hydrogen rise almost perpendicular to the anode and cathode surfaces, respectively, into the collection chamber above the electrolyte surface 32. The electrolyte temperature was adjusted as described above and the composition and content were controlled by the addition of anhydrous hydrogen fluoride.

Referring now to fig. 2-8, wherein like features are represented by like reference numerals. An apparatus according to a first embodiment of the invention is indicated at 100; the apparatus comprises a main package frame 102 having removable panels (not shown) which in use form a main sealed package 104, the sealed package being connected to an evacuation system (not shown) via a manifold 124 which in turn is connected to a scrubbing system (not shown) to neutralise hazardous chemicals. Three

fluorine cassettes

106, 108, 110 are contained in the

master packaging

102, 104 and are substantially identical, meaning that each fluorine cassette can be replaced by another fluorine cassette and the connection fittings, such as valves, piping, plumbing fittings, electrical components, etc., are located identically. The fluorine cassette is connected to a fluorine gas manifold 114 that collects the fluorine gas generated in the fluorine cassette and is connected to the fluorine gas chamber of the electrolysis cell in the fluorine cassette by a fluorine gas standpipe 116 (see figure 1 above and the following more detailed description of the fluorine cassette). Standpipe 116 is connected to manifold 114 via

double isolation valves

118, 120, the crossover space between which is connected to an evacuated fluorine manifold 124, which in turn is connected to a scrubbing system (not shown) for neutralizing any harmful gases. Hydrogen gas generated during electrolysis is vented through a standpipe 130 on each cassette and is connected by a flanged connection 132 to a standpipe of a hydrogen manifold 134 which delivers the hydrogen gas for further processing or for combustion as required. All of the piping through which the fluorine gas flows are connected to a source of purge gas (not shown), such as nitrogen, through suitable valves (not shown) to purge oxygen and/or moisture from the piping prior to introduction of the fluorine gas.

Each

fluorine cassette

106, 108, 110 includes a fluorine cassette packaging frame 140, which may be horizontally divided into 2 sections: a lower portion 142 in which a fluorine generating cell 144 is disposed; an upper portion 146, in which a power source is installed, for electrolysis, etc. The cassette packaging is separated so that the fluorine generating cell is readily accessible when the cassette is removed from the

main packaging

102, 104. To increase mobility, wheels 148 may be provided on the fluorine cassette to facilitate removal from the

main package

102, 104. The cassette shown in figures 3 and 4 has a fluorine generating cell but the cell may contain 6, 12 or 24 anodes depending on the amount of fluorine production required, as explained above. The total output of fluorine from each cassette is directed internally to a single fluorine collection tube 116 having

dual isolation valves

118, 120. Similarly, all hydrogen produced by electrolysis is directed to a single collection standpipe 130. The fluorine generating cell 144 has a common safety container 150 of steel forming the cell cathode, welded to the lower portion 142 of the encasement frame 140. The encasement frame thus forms the cathode connection of the entire cassette. Each box may have its own dc power supply 152 and control system 154, but all box power supplies and control systems may be located centrally in the main package 104. The upper portion 160 of the main package 102,104 houses the bus and main power supply (not shown) etc. to which each fluorine cassette is connected when installed in the main package, and is connected to the junction box 158 by a plug and play type plug (not shown).

As mentioned above, the encasement frame can form the cathode connection of the apparatus of the present invention. Since the frame is a cathode, which is also charged, the current on the 24 anode cell can be up to about 2400 amps. The frame is therefore substantially made of a profile in order to preventexcessive temperatures due to thermal resistance. The cathode connection is set at 0 volts relative to ground and the anode connection is 6-9 volts. The use of a packing frame for the cathode connection and current carrier makes the device more economical to manufacture and stronger because the profile is thicker and the cathode connection does not have to be made of copper wire. Since the frame is 0 volts with respect to ground, the device is electrically safe.

The fluorine cassettes 106,108, 110 are connected at their total fluorine output to a fluorine purification cassette 170, which allows the fluorine gas to pass through the purification cassette for removal of certain substances, such as hydrogen fluoride or other electrolyte components carried by the fluorine gas stream, as well as contaminants formed during the electrolysis process. The purification cassette is described in more detail in figures 5 and 6. The purification cassette includes a container 172 which contains chemical traps and filters (not shown) to remove unwanted materials from the fluorine gas stream by known methods. The purification cassette 170 has a packaging frame 174 that encloses the container 172 and, like the fluorine cassette, has

dual isolation valves

178, 180 to allow installation and removal of the purification cassette from the apparatus when desired. The unit is fitted with wheels 180 to facilitate movement.

The purified fluorine gas passes from the cassette 170 to a fluorine compression cassette 190, as shown in fig. 7 and 8. In this embodiment, the compression cassette contains three vapor collection tanks 192 having a total capacity of 650 liters that can safely withstand a fluorine pressure of 5 bar, but fluorine gas at such a pressure is not generally used from a safety standpoint. Purified fluorine gas from the purification cassette 170 is fed to a compression cassette pump 194 and through a compression controller 196 to a vapor collection tank 192. The compression box 190 stores fluorine gas. When it is desired for some reason to shut down the apparatus, shut down the process for a period of time, in order to replace the purification cassette 170, the fluorine inventory continues to meet process requirements until fluorine production is resumed. The compression box also reduces fluctuations in fluorine gas production, allowing fluorine gas to be delivered to the process plant at a steady pressure. Similar to the fluorine cassette and the purification cassette, the compression cassette also has a packing frame 200 and wheels 202. The compression cassette is again connected to the fluorine manifold 114 by a double isolation valve (not shown) as are the fluorine cassette and the purification cassette. The output fluorine gas is fed through a second pressure controller 198 to the fluorine gas manifold 114 and then to the plant where the fluorine gas is to be used.

As can be seen in fig. 2A, 2B, 3 and 4, the fluorine cassette 106, etc. can be installed and removed from the

main packaging

102, 104 without interfering with the other two

cassettes

108, 110, which can continue to provide the desired fluorine gas for processes occurring outside the apparatus. The fluorine generating capacity of the apparatus 100 can be calculated so that any two of the three cassettes on the apparatus can meet the overall process requirements of the gas supply plant, thus allowing one cassette to be damaged, removed, or replaced as needed.

In the above described embodiment, the length of the apparatus 100 is substantially less than the length of the ISO container and is therefore easily transportable by land or sea. The container may be sized slightly larger, but still within the dimensions of a standard ISO container, which is empty and may accommodate additional fluorine cassettes and the like, to expand the fluorine generation capacity as demand increases. The space is provided withthe necessary valving and tubing connections to the manifold etc. so that additional fluorine cassettes can only be connected to the system as would already be the case.

The main enclosure frame 102 is provided with removable panels to seal, in use, the fluorine outlet or the like. The package is connected to an in situ vacuum and scrubbing system to remove harmful chemicals. Furthermore, each of the fluorine cassettes, purification cassettes and compression cassettes are similarly equipped with panels in use on the

frames

140, 174 and 200 to form substantially sealed secondary packages within the

primary packages

102, 104, which are also connected to the in situ vacuum and scrubbing system.

Figure 9 shows a single perspective view of a fluorine gas generation plant 300 in accordance with a second embodiment of the present invention. The apparatus of figure 9 is similar to that described in figures 2 to 8 of the first embodiment with respect to the capacity and ability to produce, process, control and store fluorine gas. Apparatus 300 also includes a main package frame 302 that is provided with panels (not shown) to form a substantially sealed outer package. Three

fluorine cassettes

304, 306 and 308 are provided, each having its

own overwrap frame

310, 312, 314 with plates (not shown), each of which can be independently isolated and removed using valves (not shown), as in the first embodiment. The fluorine gas passes through a purification cassette comprising a main purifier 320 and a back-up purification cassette 324, then through main and back-up

compressors

328, 330 into a compression cassette comprising a plurality of storage tanks 326. The fluorine gas is then transported to a CVD apparatus or the like through a pipe and utilized. Tank 332 contains liquid hydrogen fluoride. The hydrogen fluoride vaporizer 334 vaporizes the liquid hydrogen fluoride in the tank 332 and supplies it to the

cartridges

304, 306, 308 to maintain a constant electrolyte concentration. The fluorine abatement cassette 340 is provided to remove solids from the fluorine gas, to remove fluorine from piping when the cassette is replaced for maintenance or repair, etc., and to remove fluorine gas that is not available to the customer. The apparatus shown in figure 9 has a full tube purge system, a safety bleed and scrubber system as in the first embodiment.

Claims

1. An apparatus for generating fluorine gas by electrolysis of hydrogen fluoride, the apparatus comprising: a plurality of individual fluorine generating cassettes; the single fluorine generating box is connected with a fluorine gas conveying system so as to meet the requirements of remote equipment on utilization and consumption of the fluorine gas; the fluorine generation cassettes are each separable from the fluorine gas delivery system and are removable from the apparatus for remote maintenance.

2. The apparatus of claim 1 wherein the fluorine generating cassette is connected to the apparatus by a valve for isolating and disconnecting said fluorine generating cassette from the apparatus.

3. The apparatus of claim 2, wherein the valves are double isolation valves, the space between which is connected to a gas withdrawal and scrubbing system.

4. The apparatus of any of the preceding claims, wherein the fluorine generating cassettes are housed in a common housing.

5. The apparatus of any of the preceding claims, wherein all of the fluorine generating cassettes are substantially identical.

6. The apparatus of any of the preceding claims, wherein the fluorine generating cassette is provided with wheels.

7. The apparatus of any of the preceding claims wherein each fluorine generating cassette is provided with an overwrap.

8. The apparatus of claim 4, wherein the main enclosure is connected to an extraction system and a scrubbing system.

9. The apparatus of claim 7 wherein each fluorine generating cassette enclosure is connected to a gas extraction system and a scrubbing system.

10. The apparatus of any one of the preceding claims further comprising at least one fluorine purification cassette through which the fluorine gas exiting the fluorine generation cassette passes.

11. The apparatus of any one of the preceding claims further comprising at least one fluorine buffer cassette connected to the fluorine line downstream of the at least one fluorine purification cassette.

12. The apparatus of claim 11 wherein the buffer box contains compressed fluorine gas.

13. The apparatus of any of claims 7 to 12, wherein the fluorine generating cells in the fluorine generating cassette are secured to the outer packaging such that the outer packaging provides a cathode connection for the fluorine generating cells.

14. The apparatus of claim 13, wherein the outer package comprises a frame having panels.

15. An apparatus as claimed in claim 13 or 14, wherein the cathode connection is at 0 volts to earth.

16. Apparatus according to any one of the preceding claims, further comprising purging means to purge any reactive fluid that may be present before fluorine enters the conduit.

17. The apparatus of any one of claims 1 to 16, wherein the apparatus is transportable by land or sea as an integral unit.

18. The apparatus of claim 17, wherein the overall dimensions of the apparatus are up to the dimensions of a standard ISO container.

19. The apparatus of any one of claims 1 to 9, wherein each fluorine generating unit is further provided with a power supply for at least one of electrolysis, fluorine purification, fluorine compression and fluorine storage tank/buffer means.

20. A method of operating and maintaining an apparatus for the electrolytic production of fluorine gas from hydrogen fluoride, the method comprising the steps of: providing a plurality of fluorine generating cassettes connected to a fluorine gas delivery system for remote use and consumption; providing means for isolating any individual fluorine generating unit from said fluorine gas delivery system and from each other; means are provided for removing and removing the separate fluorine generating units from the apparatus without interrupting the supply of fluorine gas to the remaining fluorine generating cassettes.

21. The method of claim 20, wherein a plurality of fluorine generating cassettesare provided with sufficient fluorine generating capacity such that the total demand for fluorine gas is met by less than the total number of fluorine generating cassettes in the apparatus.

22. The method of claim 20 or 21, wherein a single fluorine generating cassette is removable from the apparatus and can be taken to a remote location for maintenance while still maintaining the output of fluorine gas to meet demand.

23. The method of any one of claims 20 to 22, further comprising the step of providing power to each fluorine generating cassette for at least electrolysis, fluorine purification, fluorine compression and fluorine storage/buffer means.