SELECTIVELY SEPARATING REACTIVE SPECIES

Cross Reference to Related Applications

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 61/667,134, filed on July 2nd, 2012, which is incorporated herewith by reference in its entirety.

Background of the Invention

1. Field of the Invention

[0002] The instant invention generally relates to an apparatus for facilitating an equilibrium reaction. More specifically, the apparatus enables reactive species from the equilibrium reaction to be selectively separated to drive the equilibrium reaction in a desired direction.

2. Description of the Related Art

[0003] In reversible chemical reactions, equilibrium generally exists when the rate of the forward reaction equals the rate of the reverse reaction, the result being that concentration of reactive species involved in the equilibrium reaction does not change over time. Temperature and pressure are common levers used to influence the reactant and product compositions at equilibrium. Independent of temperature and pressure, removing one or more reactive species may also be used to impact equilibrium compositions; however it can be challenging to selectively separate the desired reactive species from the equilibrium reaction while leaving the other reactive species for further reaction.

[0004] As one example of an equilibrium reaction that has significant industrial applicability, reactions conducted between halides of semiconductors and elemental metal have numerous industrial applications, mainly for purposes of producing high purity semiconductor. High purity semiconductors, such as silicon and germanium, have wide-ranging uses from electronics applications including use in computer processors to use in solar energy applications such as use in solar cells. One method for the production of high purity semiconductors involves reaction of a halide of the semiconductor with elemental metal to produce high purity semiconductor and a metal halide. For example, when the halide of the semiconductor is silicon tetrachloride, elemental metal such as zinc and the silicon tetrachloride can be reacted at elevated temperatures to produce silicon through the following equilibrium reaction:

SiCl ₄ + 2Zn ^ Si + 2ZnCl ₂ [0005] While producing silicon through the above reaction may present industrial advantages, there is a desire to recover elemental zinc from the zinc chloride to both reduce product waste streams and to recycle the relatively valuable elemental zinc within the process. However, current methods for recovery of zinc from the zinc chloride can be the source of process difficulties and high costs themselves (e.g. ZnCl ₂ electrolysis). Reverse reacting elemental silicon and zinc chloride can be limited by the presence of the resulting elemental zinc and silicon tetrachloride as the elemental zinc and silicon tetrachloride will not allow conversions to exceed the concentrations dictated by thermodynamic equilibrium.

[0006] In view of the foregoing, there is a desire to provide an apparatus for facilitating an equilibrium reaction, such as the equilibrium reaction between elemental silicon and zinc chloride to produce elemental zinc and silicon tetrachloride, with the apparatus enabling selective separation of the reactive species to drive yield of reactive species in a desired direction.

Summary of the Invention and Advantages

[0007] An apparatus is provided for facilitating an equilibrium reaction and selectively separating reactive species. The apparatus includes a heating zone, an overhead temperature modulation zone in fluid communication with the heating zone, and an overhead cooling zone in fluid communication with the overhead temperature modulation zone. The heating zone includes a solid reactant support and a reactant gas input. The heating zone defines a space between the support and the reactant gas input. During operation of the apparatus, the solid reactant retained by the support is in fluid communication with reactant gas provided by the reactant gas input. The heating zone also includes a heater for heating reactants contained in the heating zone to produce a gaseous stream from the solid and gaseous reactants. The overhead temperature modulation zone includes a temperature regulator for modifying the temperature of the overhead temperature modulation zone relative to the heating zone and for condensing a portion of the gaseous stream from the heating zone. The overhead temperature modulation zone also includes an overhead gas outlet for conveying remaining gaseous stream out of the overhead temperature modulation zone after condensing the portion of the gaseous stream. The overhead temperature modulation zone also provides a reflux flow path for the condensate to return to the heating zone. The overhead cooling zone receives the gaseous stream from the overhead gas outlet of the overhead temperature modulation zone and has a chiller for cooling the temperature of the overhead cooling zone relative to the overhead temperature modulation zone. The chiller also condenses at least a second portion of the gaseous stream. The overhead cooling zone provides a barrier to separate the second condensate from the overhead temperature modulation zone. The apparatus further includes an apparatus wall that defines an interior chamber of the apparatus between the zones for facilitating the fluid communication between the zones.

[0008] By providing the apparatus as described with the various zones having the respective heater, temperature regulator, and chiller, and with the zones configured in relation to each other as described, separation of reactive species in the equilibrium reaction is made possible to drive yield of reactive species in one direction of the equilibrium reaction while minimizing conditions that promote reaction in the reverse direction of the equilibrium reaction. As a result, the equilibrium reaction can theoretically be driven toward near complete yield of reactive species in one direction or another of the equilibrium reaction.

Description of the Drawings

[0009] Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0010] Figure 1 is a cross-sectional schematic representation of an apparatus for facilitating an equilibrium reaction and selectively separating reactive species, with the apparatus including a heating zone, an overhead temperature modulation zone, and an overhead cooling zone; and

[0011] Figure 2 is a cross-sectional schematic representation of another embodiment of an apparatus for facilitating an equilibrium reaction and selectively separating reactive species, with the apparatus including a heating zone, an overhead temperature modulation zone, and an overhead cooling zone.

Detailed Description of the Invention

[0012] Referring to the Figures, wherein like numerals indicate like or corresponding parts, an apparatus for facilitating an equilibrium reaction and selectively separating reactive species is generally shown at 10 in Figure 1. The apparatus 10 described herein is particularly suitable for use in conducting equilibrium reactions and enables reactive species that participate in the equilibrium reaction to be selectively separated. By enabling the reactive species to be selectively separated, shifting of thermodynamic equilibrium of the reaction is enabled to thereby maximize yield of the reaction in a desired direction while minimizing yield of reactive species resulting from the reverse reaction in the undesired direction. Essentially, by selectively separating reactive species, the thermodynamic equilibrium of the reaction can be shifted to drive the equilibrium reaction in one direction or the other, i.e., to either a product side or a reactant side of the equilibrium reaction.

[0013] The apparatus 10 is typically sealed from the ambient environment. It is to be appreciated that the apparatus 10 may be unsealed for purposes of inserting or removing reactive species; however, during the reaction, the apparatus 10 is sealable to prevent contaminants from entering the apparatus 10, to avoid detrimental environmental effects on the reaction, and to control thermodynamics of the equilibrium reaction.

[0014] As shown in Figure 1, the apparatus 10 includes a heating zone 12, an overhead temperature modulation zone 14 in fluid communication with the heating zone 12, and an overhead cooling zone 16 in fluid communication with the overhead temperature modulation zone 14. In particular, by "fluid communication", it is meant that liquids and/or gases from one zone may flow between the zones without unsealing the apparatus 10 (although valves, gates or other intervening structures or devices may be disposed between the various zones to control flow of apparatus 10 contents between the zones).

[0015] In one embodiment, as shown in Figure 1, the heating zone 12, overhead temperature modulation zone 14, and overhead cooling zone 16 are in direct gaseous communication, i.e., no physical barriers to gas flow are present between the various zones (although the configurations of the apparatus 10 that is shown in Figure 1 provides a barrier 38 to liquid flow between the overhead cooling zone 16 and the other zones due to the angle at which the overhead cooling zone 16 extends relative to the overhead temperature modulation zone 14). Furthermore, by being in direct gaseous communication, the apparatus 10 is typically free from other zones that are not described herein and that could add additional reactive species, remove reactive species, or otherwise process the reactive species through control of environmental conditions. The overhead temperature modulation zone 14 and the heating zone 12 are typically in direct liquid communication, meaning that liquid can freely flow from the overhead temperature modulation zone 14 back to the heating zone 12, thereby establishing a reflux flow path as described in further detail below.

[0016] The temperature of each zone is typically independently controlled, in relation to other zones in the apparatus 10, to enable thermodynamic equilibrium of the equilibrium reaction to be shifted in the various zones of the apparatus 10, thereby enabling the physical state of the reactive species in the various zones to be controlled (e.g. between solid, liquid, and/or gas states) and enabling separation of reactive species based upon physical state under the environmental conditions in the respective zones. In this regard, the various zones are defined primarily by features that enable control of the temperature therein. By separation of the reactive species based upon physical state, and by including the zones specified above, equilibrium reactions can be driven in one direction or another as described in further detail below. While temperature in each of the zones is independently controlled, it is to be appreciated that the zones are not necessarily isolated from each other and conditions from one zone may affect conditions in other zones. In this regard, the apparatus 10 may have integral zones contained therein, such as the reactor shown in Figure 1, with temperature in one zone possibly affecting conditions in adjacent zones.

[0017] The apparatus 10 includes an apparatus wall 32 that defines an interior chamber 20 of the apparatus 10 between the zones for facilitating the fluid communication between the zones. The apparatus wall 32 enables the interior chamber 20 of the apparatus 10 to be sealed from the ambient environment. While the apparatus wall 32 may generally be continuous between the various zones, it is to be appreciated that portions of the apparatus 10 may be separable and the apparatus wall 32 may be configured in a way to enable such separation. For example, to enable access into the interior chamber 20 of the apparatus 10, the apparatus 10 may comprise various separate parts that are connectable e.g., through threaded screw connections, male/female connections, flanged connections, or the like, with the apparatus wall 32 extending through the connected parts. Figures 1 and 2 illustrate the apparatus wall 32 that is separable at the line indicated by numeral 52.

[0018] The apparatus wall 32 is typically formed from a material that has high thermal and chemical resistance, and that minimizes introduction of contaminants into the equilibrium reaction and intermingling of contaminants with reactive species that are to be separated through operation of the apparatus 10. For example, in one embodiment, the apparatus wall 32 is formed from quartz. It is to be appreciated that in some embodiments, the entire apparatus wall 32 may be formed from quartz, while in other embodiments at least a portion of the apparatus wall 32 is formed from quartz. For example, other features (e.g., seals, connection tubes, etc.) may form part of the apparatus wall 32 and may be formed of material other than quartz.

[0019] The heating zone 12 of the apparatus 10 has a solid reactant support 18. The solid reaction support 18 supports solid reactant 28 that remains solid in the heating zone 12 during operation of the apparatus 10. In one embodiment, the solid reactant support 18 may be further defined as a dish or a suspended tray 18 that defines perforations 22 for enabling reactant gas to flow upwardly through the perforations 22 and contact solid reactant 28 retained by the support 18, and/or unreacted refluxed liquid reactants to flow downwardly through the perforations 22 and back into the heating zone 12 to be re- vaporized.

[0020] The suspended tray or dish 18 may be supported by the apparatus wall 32 in the heating zone 12 (as shown in Figures 1 and 2), or may otherwise be suspended in the heating zone 12 through other features of the apparatus 10. For example, the solid reactant support 18 could alternatively be a suspension cage or similar device (not shown) for suspending the solid reactant 28 in the flow of the reactant gas. Like the apparatus walls 32, the suspended tray or dish 18 is typically formed from quartz.

[0021] The heating zone 12 further includes a reactant gas input 46. In one embodiment, as shown in Figure 2, the reactant gas input 46 may be further defined as a gas inlet 46 for introducing reactant gas into the heating zone 12. In another embodiment, the reactant gas input 46 may be further defined as a retention vessel 46 that retains a solid or liquid reactant 26, which solid or liquid reactant 26 is vaporized during operation of the heating zone 12 to provide reactant gas into the heating zone 12. As shown in Figures 1 and 2, the heating zone 12 defines a space between the solid reactant support 18 and the reactant gas input 46. In operation of the apparatus 10, the solid reactant 28 retained by the solid reactant support 18 is in fluid communication with reactant gas provided by the reactant gas input 46, e.g., through travel of the reactant gas through the perforations 22 in the solid reactant support tray or dish 18, with a reaction occurring between reactant gas provided by the reactant gas input 46 and solid reactant 28 retained by the solid reactant support 18.

[0022] The heating zone 12 further includes a heater 30 for heating reactants contained in the heating zone 12. The heater 30 is typically capable of operating at temperatures that are as hot as the materials of construction of the apparatus 10 allow without compromising the structural integrity thereof, i.e., typically at a temperature of at least about 1000°C, e.g. from about 1000 to about 1200°C. In one embodiment, as shown in Figures 1 and 2, the heater 30 is further defined as an external furnace 30, although it is to be appreciated that an internal heater (not shown) disposed in the interior chamber 20 in the heating zone 12 could be used. The external furnace 30 may be disposed outside of the interior chamber 20 and heats the apparatus wall 32 in the heating zone 12. In this embodiment, heating of the apparatus wall 32 in the heating zone 12 influences temperature within the interior chamber 20 of the apparatus 10 in the heating zone 12. In one embodiment, the external furnace 30 surrounds the apparatus wall 32 in the heating zone 12. More specifically, the external furnace 30 may be disposed around all sides of the heating zone 12. In one specific example of this embodiment, the external furnace 30 may define a hole through a furnace wall thereof (not shown), with the apparatus wall 32 in the heating zone 12 inserted into the hole through the furnace wall of the external furnace 30. Alternatively, the external furnace 30 may be exposed to only a portion of the apparatus wall 32 in the heating zone 12, although such configuration could result in non-uniform heating of the interior chamber 20 in the apparatus 10, which may result in control difficulties.

[0023] In certain embodiments, a carrier (or diluent) gas is introduced into the heating zone 12 of the reactor 10 to strip one or more components from the reactants in the heating zone 12. The gas is typically inert, but may also be reactive towards another compound. Examples of such gases include noble gases, e.g. argon gas, and/or process gases, such as silicon tetrachloride (STC) gas, hydrogen gas (H ₂ ), etc. As an example, the gas can be passed (e.g. bubbled) through the reactants when in a molten/liquid state to remove unwanted species therefrom, such as volatiles. Such a process may be referred to in the art as gas stripping of the reactants.

[0024] As set forth above, the apparatus 10 further includes the overhead temperature modulation zone 14 that is in fluid communication with the heating zone 12. More specifically, the overhead temperature modulation zone 14 is typically in direct gaseous and liquid communication with the heating zone 12 such that a gaseous stream traveling from the heating zone 12 typically flows directly into the overhead temperature modulation zone 14 without intervening treatment, supplementation, or removal of reactive species from the gaseous stream. Further, as described in further detail below, condensate formed in the overhead temperature modulation zone 14 typically flows directly back into the heating zone 12, either through gravitational-induced flow, pumping, or other reflux methods. In this regard, the overhead temperature modulation zone 14 provides a reflux flow path for condensate formed therein to return to the heating zone 12. The overhead temperature modulation zone 14 is included in the apparatus 10 for selectively removing some reactive species that are present in the gaseous stream that is produced by the heating zone 12, thereby selectively condensing certain reactive species, while maintaining environmental conditions (e.g., temperature and/or pressure) sufficiently elevated in relation to ambient conditions to maintain other reactive species in the gaseous stream without condensing such that the reactive species can be forwarded on to the overhead cooling zone 16 where the reactive species are isolated and thus separated from the heating zone 12. As such, the overhead temperature modulation zone 14 is typically operated at lower temperature and/or pressure than the heating zone 12, but is also typically operated at temperatures and/or pressures that are substantially higher than ambient conditions. While some reactive species may exist (e.g. be formed due to the reverse reaction and/or be present due to an incomplete reaction), such reactive species are typically condensed in the overhead temperature modulation zone 14 and refluxed to the heating zone 12. Through such operation, equilibrium reactions conducted in the apparatus 10 can theoretically be driven to near complete yield of reactive species in one direction or another as described in further detail below.

[0025] The overhead temperature modulation zone 14 has a temperature regulator 33 for modifying the temperature of the overhead temperature modulation zone 14 relative to the heating zone 12 and for condensing a portion of the gaseous stream from the heating zone 12. As with the heater 30 in the heating zone 12, the temperature regulator 33 can regulate temperature by externally heating the apparatus wall 32, or by internally heating the interior chamber 20 of the apparatus 10. In any event, the temperature regulator 33 typically provides heat to the overhead temperature modulation zone 14, instead of cooling the overhead temperature modulation zone 14. In certain embodiments, the temperature regulator 33 comprises heat tape 34 that is disposed on the apparatus wall 32 outside of the interior chamber 20. In this embodiment, the heat tape 34 is directly disposed on the apparatus wall 32 outside of the interior chamber 20, which enables precise control of the temperature within the interior chamber 20 in the overhead temperature modulation zone 14. To further enable such precise control of temperature in the overhead temperature modulation zone 14, the temperature regulator 33 typically further comprises a temperature controller 36 connected to the heat tape 34. Other than heat tape 34, various other types of heater means (not shown) may be used for heating (in addition or alternate to the heat tape 34), such as heat lamps, another furnace, another independent zone with the furnace use for the main reactor body, a susceptor, etc. A temperature sensor 44 may be inserted into the interior chamber 20 of the apparatus 10 in the overhead temperature modulation zone 14 to monitor the temperature therein. Various types of temperature sensors 44 may be utilized, such as a thermocouple, a resistance temperature detector (RTD), etc.

[0026] The overhead temperature modulation zone 14 further includes an overhead gas outlet 39 for conveying remaining gaseous stream out of the overhead temperature modulation zone 14 after condensing the portion of the gaseous stream. During operation of the apparatus 10, the temperature in the overhead temperature modulation zone 14 is controlled in such a way so as to maintain at least some reactive species from the equilibrium reaction in the gaseous stream, with the gaseous stream then routed out of the overhead temperature modulation zone 14 and into the overhead cooling zone 16 through the overhead gas outlet 39. By maintaining at least some reactive species from the equilibrium reaction in the gaseous stream, physical separation can be maintained between the reactive species that are condensed in the overhead temperature modulation zone 14 and reactive species that remain in the gaseous stream and that are routed out of the overhead temperature modulation zone 14 to thereby minimize yield in the reverse direction of the equilibrium reaction.

[0027] As set forth above, the apparatus 10 further includes the overhead cooling zone 16 for receiving the gaseous stream from the overhead gas outlet 39 of the overhead temperature modulation zone 14. The overhead cooling zone 16 has a chiller 40 (e.g. a coil 40) for cooling the temperature of the overhead cooling zone 16 relative to the overhead temperature modulation zone 14 and for condensing at least a second portion of the gaseous stream to form a second condensate. The chiller 40 is typically capable of establishing temperatures in the overhead cooling zone 16 that are below ambient temperatures. Various types of cooling means can be utilized. As set forth above, the overhead cooling zone 16 is in fluid communication with the overhead temperature modulation zone 14. As also set forth above, the overhead cooling zone 16 is typically in direct gaseous communication with the overhead temperature modulation zone 14, with the gaseous stream freely flowable between the overhead temperature modulation zone 14 and the overhead cooling zone 16. However, as alluded to above, the overhead cooling zone 16 provides a barrier 38 to separate the second condensate that is formed in the overhead cooling zone 16 from flowing back into the overhead temperature modulation zone 14. The barrier 38 is not particularly limited to any specific feature so long as the barrier 38 is capable of hindering flow of the second condensate from the overhead cooling zone 16 to the overhead temperature modulation zone 14.

[0028] In one embodiment, as shown in Figures 1 and 2, the overhead cooling zone 16 extends transverse to the overhead temperature modulation zone 14 to provide the barrier 38 that separates the second condensate from the overhead temperature modulation zone 14. As an alternative or in addition to the angle at which the overhead cooling zone 16 extends relative to the overhead temperature modulation zone 14 _s and as shown in Figure 2, a oneway valve 42 (or "check" or "non-return" valve) may be disposed between the overhead cooling zone 16 and the overhead temperature modulation zone 14 to prevent flow of the second condensate from the overhead cooling zone 14 back into the overhead temperature modulation zone 14. The second condensate produced in the overhead cooling zone 16 may be collected in a collection chamber 24, as shown in Figures 1 and 2, and utilized in other processes or may be properly disposed of. The collection chamber 24 may be chilled using, e.g., a chilling bath 48 to maintain the second condensate in liquid form (since the second condensate may be in the gaseous state under ambient conditions). The overhead cooling zone 16 is typically operated at temperatures and/or pressures that are sufficient to condense all reactive species that participate in the equilibrium reaction. Nonetheless, uncondensed portions of the gaseous stream that may remain even under the temperatures and pressures present in the overhead cooling zone 16 may be drawn out through a vent 50.

[0029] As alluded to above, external or internal heaters 30, temperature regulators 33, or chillers 40 can be employed in the respective zones and the configuration thereof may be coordinated in the overall apparatus 10. For example, at least one of the heater 30 in the heating zone 12, the temperature regulator 33 in the overhead temperature modulation zone 14, or the chiller 40 in the overhead cooling zone 16 may externally influence the temperature of the respective zone from outside of the interior chamber 20. Alternatively, it is to be appreciated that the heater 30, temperature regulator 33, and/or chiller 40 may be disposed in the interior chamber 20 of the apparatus 10, although such configurations may be undesirable (at least for the heater 30 and temperature regulator 33) due to possible deposition of condensate thereon. Typically, as described above, the external furnace 30 is employed and serves to define the heating zone 12, with the overhead temperature modulation zone 14 and the overhead cooling zone 16 disposed outside of the external furnace 30. Further, the heat tape 34 is typically employed to externally influence the temperature in the interior chamber 20 of the apparatus 10 in the overhead temperature modulation zone 14. Such external heating is generally advantageous for the heating zone 12 and the overhead temperature modulation zone 14 to minimize deposition of reactive species onto the heater 30 and temperature regulator 33, which may simplify and promote transfer and/or removal of condensate between or from the various zones. However, the chiller 40 in the overhead cooling zone 16 typically internally cools the interior chamber 20 of the apparatus 10 in the overhead cooling zone 16, where deposition of reactive species on the chiller 40 may be less of a concern than in other zones. Internal cooling within the overhead cooling zone 16 may also enable more efficient cooling in view of the fact that differences in temperatures between the overhead temperature modulation zone 14 and the overhead cooling zone 16 may be significant. [0030] As one example of an equilibrium reaction that can be conducted using the apparatus 10 described herein, a metal halide and an elemental semiconductor (i.e., semiconductor atoms present in a source of the semiconductor and that are available for reaction) can be reacted to produce a halide of the semiconductor and elemental metal (i.e., metal atoms separated from the halogen atoms of the halide), which benefits from driving the equilibrium reaction in one direction or the other for purposes of recovering the elemental metal. In particular, the elemental semiconductor may be provided in a relatively impure source of the semiconductor that includes impurities in addition to the elemental semiconductor, and the reaction of the elemental semiconductor and metal halide may be exploited to effectively separate the elemental semiconductor from some of the impurities in the source of the elemental semiconductor, with the resulting halide of the semiconductor possibly subjected to further processing to further purify and separate the elemental semiconductor from the halogen atoms in the halide.

[0031] It is to be appreciated that the apparatus 10 described herein may be used to conduct any equilibrium reaction and is not particularly limited to use in conducting an equilibrium reaction that involves reaction of the metal halide and elemental semiconductor to produce the halide of the semiconductor and elemental metal. However, for exemplary purposes, only equilibrium reactions that involve reaction of a metal halide and elemental semiconductor to produce a halide of the semiconductor and elemental metal are described herein. Additional details regarding such equilibrium reactions are described in co-pending PCT Application

No. , which claims priority to U.S. Application Serial No. 61/667,138 filed on July 2nd 2012, and is entitled "METHOD OF CONDUCTING AN EQUILIBRIUM REACTION AND SELECTIVELY SEPARATING REACTIVE SPECIES OF THE EQUILIBRIUM REACTION" (Docket No.: DC11237PSP1), filed on even date herein, the entirety of which is hereby incorporated by reference.

[0032] In accordance with the exemplary equilibrium reaction, a first composition comprising the metal halide, e.g., zinc chloride, in substantially pure form (i.e., at least 90%, at least about 92.5%, at least about 95%, at least about 98%, at least about 99%, at least about 99.5%, at least about 99.9%, or at least about 99.99%, by weight) may be introduced into the heating zone 12 of the apparatus 10 through the reactant gas input 46. A source of the elemental semiconductor that is reactive with the metal halide is also introduced into the heating zone 12 of the apparatus 10 and is placed in the suspended tray or dish 18. The reactant gas input 46 introduces the first composition into the heating zone 12 beneath the suspended tray or dish 18 to promote flow of the first composition (once in gaseous form) toward the source of the elemental semiconductor that is disposed in the suspended tray or dish 18. The metal halide from the first composition and the elemental semiconductor from the source of the elemental semiconductor are reacted through a gas/solid phase reaction in the heating zone 12 of the apparatus 10 to produce a gaseous stream comprising a halide of the semiconductor, unreacted metal halide, and, optionally, elemental metal. The reaction may leave impurities that may be present in the source of the semiconductor behind in solid form in the suspended tray or dish 18, thereby effectively separating the semiconductor from some impurities that may be present in the source of the semiconductor. The temperature and pressure of the heating zone 12 may be controlled so as to avoid melting of the source of the semiconductor and to avoid condensation of the halide of the semiconductor and unreacted metal halide. The elemental metal may have a boiling point that is greater than environmental conditions, i.e., temperature and pressure, in the heating zone 12 such that the elemental metal may condense in the heating zone 12 upon reaction of the metal halide and the elemental semiconductor. In this regard, the temperature and pressure in the heating zone 12 may be controlled so as to promote condensation of the elemental metal within the heating zone 12, in which case a collector (not shown) may be provided in the heating zone 12 to collect the condensed elemental metal separate from the source of the elemental semiconductor. For example, when the suspended tray or dish 18 is present in the heating zone 12 and defines perforations 22, the collector may be disposed beneath the suspended tray or dish 18 and may collect liquid elemental metal that flows downward through the perforations 22. Alternatively, the elemental metal may have a boiling point that is lower than the environmental conditions in the heating zone 12 such that the gaseous stream produced by reaction of the metal halide and elemental semiconductor includes the elemental metal, which may result in greater conversion efficiency of the semiconductor to the halide of the semiconductor.

[0033] In one specific example of the equilibrium reaction in which the elemental metal is condensed in liquid form in the heating zone 12, the elemental semiconductor is silicon, the metal halide is zinc chloride, the elemental metal is zinc, and the halide of the semiconductor is silicon tetrachloride. In this example, the silicon and zinc chloride may be reacted in the heating zone 12 at a temperature of from about 756 up to about 910°C, which conditions are sufficient to condense zinc in liquid form in the heating zone 12 while maintaining the temperature in the heating zone 12 above the boiling point of zinc halide. [0034] All temperatures referred to herein are internal temperatures of the specified zones unless indicated otherwise (as opposed to temperatures of walls, heating elements, or other features of the apparatus 10). For example, a jacket disposed around the heating zone 12 may be set at a temperature of about 1000°C which imparts the heating zone 12 with a temperature of from about 756 to about 910°C. It is expected that at least some amount of heat is lost between such heating elements and the heating zone 12. The same logic applies to the other zones of the reactor, e.g. the cooling zone 16 where the cooling means may be at a temperature lower than that of the cooling zone 16 itself. It is to be appreciated that some zinc can still be present in the gaseous stream under such conditions, even though some zinc may condense in the heating zone 12. It is also to be appreciated that features present within the heating zone 12 may be too hot to allow for the condensation of the elemental zinc thereon such that the elemental zinc may remain in the gaseous stream.

[0035] The gaseous stream including the unreacted metal halide and, optionally, elemental metal is fed into the overhead temperature modulation zone 14, and the unreacted metal halide and any elemental metal present in the gaseous stream is condensed in the overhead temperature modulation zone 14 that is in fluid communication with the heating zone 12. Because the temperature in the overhead temperature modulation zone 14 is independently controlled in relation to the heating zone 12, the temperature in the overhead temperature modulation zone 14 can be established to selectively condense the unreacted metal halide and the elemental metal (when present) while maintaining the halide of the semiconductor in the gaseous stream. Because the elemental metal and metal halide typically have different melting points, the elemental metal and the metal halide can be further separated depending upon the temperature at which the overhead temperature modulation zone 14 is operated. For example, it may be possible to solidify the elemental metal while condensing the metal halide into liquid form (with the liquid being less viscous than the elemental metal). The condensed metal halide may be returned from the overhead temperature modulation zone 14 to the heating zone 12 to participate in the reactions conducted therein with the elemental semiconductor, thereby effectively recovering the unreacted metal halide and increasing the conversion of metal halide to the elemental metal. The unreacted metal halide can be recovered through the above- summarized mechanism until the gaseous stream is free of unreacted metal halide. In this regard, excess semiconductor can be employed in the equilibrium reaction such that this cycle may be repeated until the metal halide is depleted. [0036] In one specific embodiment, the elemental semiconductor is silicon, the metal halide is zinc chloride, the elemental metal is zinc, and the halide of the semiconductor is silicon tetrachloride. The silicon and zinc chloride may be reacted in the heating zone 12 at a temperature of at least about 910°C at ambient pressure, at which conditions zinc is present in the gaseous stream. The zinc is condensed in liquid or solid form in the overhead temperature modulation zone 14. In particular, the unreacted zinc chloride and zinc may be condensed and/or solidified from the gaseous stream at a temperature of from about 275 up to about 756°C at ambient pressure in the overhead temperature modulation zone 14, which conditions are less than a boiling point yet above the melting point of the zinc chloride and enable condensation thereof. Alternatively, the unreacted zinc chloride and zinc may be condensed from the gaseous stream at a temperature of from about 275 up to about 420°C at ambient pressure, under which conditions the zinc is solid and the zinc chloride is liquid, which may enable easier separation of the zinc chloride and zinc. Alternatively, the unreacted zinc chloride and zinc may be condensed from the gaseous stream at a temperature of from about 420 up to about 756°C at ambient pressure. Under such conditions, the zinc is condensed in liquid form, and the presence of the zinc in liquid form could promote reaction in the headspace between silicon tetrachloride and zinc to a greater degree than when the zinc is in solid form.

[0037] For purposes of driving the equilibrium reaction toward yield of halide of the semiconductor and elemental metal, at least a portion of the gaseous stream including the halide of the semiconductor is isolated from the condensed metal halide and elemental metal after condensing the metal halide and, when present, elemental metal from the gaseous stream. By isolating at least a portion of the gaseous stream that includes the halide of the semiconductor after the condensing step described above, at least a portion of the halide of the semiconductor is effectively removed from the equilibrium reaction to drive yield of the equilibrium reaction toward production of the halide of the semiconductor and the elemental metal. Ultimately, such isolation can possibly shift the equilibrium reaction to much higher yields such as at least about 90% by mole conversion and even approaching 100% by mole conversion.

[0038] To isolate at least a portion of the gaseous stream including the halide of the semiconductor from the condensed metal halide and elemental metal after condensing the metal halide and, when present, elemental metal from the gaseous stream, the gaseous stream remaining after condensation in the overhead temperature modulation zone 14 is fed to the overhead cooling zone 16, with at least a portion of the gaseous stream condensed in the overhead cooling zone 16. More specifically, conditions in the overhead cooling zone 16 may be such that the halide of the semiconductor is condensed therein to form a second condensate, while conditions in the overhead temperature modulation zone 14 maintain the halide of the semiconductor in gaseous form. The barrier 38 in the apparatus 10 separates or isolates the second condensate in the overhead cooling zone 16 from the overhead temperature modulation zone 14. The overhead cooling zone 16 prevents intermingling of the condensate produced therein and other condensate, gaseous stream, or other reactive species that are present in the other zones of the apparatus, thereby effectively isolating the condensate that is produced in the overhead cooling zone 16 from reactive species that are present in other zones of the apparatus 10. The condensate produced in the overhead cooling zone 16 may be collected in the collection chamber 24, as shown in Figure 1, and utilized in other processes or may be properly disposed of.

[0039] Many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described within the scope of the appended claims. It is to be understood that the appended claims are not limited to express and particular compounds, compositions, or methods described in the detailed description, which may vary between particular embodiments which fall within the scope of the appended claims. The subject matter of all combinations of independent and dependent claims, both single and multiple dependent, is herein expressly contemplated. With respect to any Markush groups relied upon herein for describing particular features or aspects of various embodiments, it is to be appreciated that different, special, and/or unexpected results may be obtained from each member of the respective Markush group independent from all other Markush members. Each member of a Markush group may be relied upon individually and or in combination and provides adequate support for specific embodiments within the scope of the appended claims.

[0040] It is also to be understood that any ranges and subranges relied upon in describing various embodiments of the present invention independently and collectively fall within the scope of the appended claims, and are understood to describe and contemplate all ranges including whole and/or fractional values therein, even if such values are not expressly written herein. One of skill in the art readily recognizes that the enumerated ranges and subranges sufficiently describe and enable various embodiments of the present invention, and such ranges and subranges may be further delineated into relevant halves, thirds, quarters, fifths, and so on. As just one example, a range "of from 0.1 to 0.9" may be further delineated into a lower third, i.e., from 0.1 to 0.3, a middle third, i.e., from 0.4 to 0.6, and an upper third, i.e., from 0.7 to 0.9, which individually and collectively are within the scope of the appended claims, and may be relied upon individually and/or collectively and provide adequate support for specific embodiments within the scope of the appended claims. In addition, with respect to the language which defines or modifies a range, such as "at least," "greater than," "less than," "no more than," and the like, it is to be understood that such language includes subranges and/or an upper or lower limit. As another example, a range of "at least 10" inherently includes a subrange of from at least 10 to 35, a subrange of from at least 10 to 25, a subrange of from 25 to 35, and so on, and each subrange may be relied upon individually and/or collectively and provides adequate support for specific embodiments within the scope of the appended claims. Finally, an individual number within a disclosed range may be relied upon and provides adequate support for specific embodiments within the scope of the appended claims. For example, a range "of from 1 to 9" includes various individual integers, such as 3, as well as individual numbers including a decimal point (or fraction), such as 4.1, which may be relied upon and provide adequate support for specific embodiments within the scope of the appended claims.