Abstract:
An improved reaction tube having an interior configured for bifurcated chambers. The present device has an inert chamber and a catalyst chamber where the materials contained therein are decoupled from one another. This improved tube is especially beneficial as it provides for greater working efficiency, preservation of catalytic materials, straightforward maintenance and replacement procedures, and effective isolation of unwanted particles.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an improved high temperature combustion tube generally used within a Total Organic Carbon Analyzer. More specifically, the present invention provides for a combustion tube with distinct inert and catalytic chambers; as such, inert (energy-absorbing) materials are decoupled from catalytic materials. 
     2. Background Information 
     Conventionally, the oxidative furnaces utilized in high temperature carbon-oxidative combustion contains an inner assembly tube that is fabricated from quartz. This tube is in turn packed with various layers of materials that provide a profile to ensure combustion of the carbon within the furnace. 
     Typical packing of the tube starts furthest from the inlet region of the tube, where the tube is loaded with catalytically active materials (such as platinum on an alumina, zirconia, or titania substrate, or platinum as a solid pellet, or platinum as a porous pellet). Above the catalytically active materials, rests an inert section of quartz wool, upon which quartz chips or quartz beads are loaded. 
     A sample is introduced in the top via a small injection needle. Upon impact of the sample on the top layer of either the quartz or catalyst, the sample is vaporized, generating a significant expansion pulse or shock front. The energy of the expansion pulse is transferred in both the gas phase as well as by direct solid-to-solid contact between the quartz chips or beads to the very bottom of the reactor tube. This mode of energy transfer results in chipping or flaking of the platinum catalyst, decreasing the activity and subsequent efficiency of the platinum to convert the carbon in the sample to carbon dioxide. Moreover, the fine platinum, quartz, and platinum support particles that flake off are transferred by gravity and transport gas flow, out of the active (hot) reactive zone, down to the exit vent of the reaction tube. The vent section of the reactor tube is typically at temperatures below 200 C to allow conventional coupling of the reactor tube to Teflon or other inert tubing for transport to the bulk water condenser element and/or other high-efficiency drying element. 
     The purported reason for the upper quartz layer (either as quartz wool, or as quartz chips, or beads) is to absorb the shock of vaporization of water contained in the sample transferred for combustion to the reaction tube. However, since the quartz chips/beads are in direct (or after multiple injections come to be in direct) contact with the catalyst, the shock of expansion is directly coupled to the platinum catalyst. The resulting impact causes the catalyst to crack and flake off of the ceramic substrate. The platinum that flakes off, or the beads that have cracks or chips typically have reduced catalytic activity. Moreover, these catalyst particles (microscopic flakes of platinum) migrate to the bottom of the furnace tube. Since this region of the furnace tube is generally of reduced temperature, the “free” catalyst particles loose their effectiveness. These free catalyst particles inadvertently increase the back pressure of the system due to blockage of the exit vent. 
     Another effect that occurs upon addition of sample into the reactor tube is the deposit and transport of salts and other inorganic oxides onto the initial quartz body. With time, these salts migrate or are “channeled” by various means into the catalytic body immediately below the upper quartz or other ceramic elements in the upper packing layer. These salts or inorganic oxides coat the catalyst, severely limiting the catalyst from oxidizing the organic species present in the gaseous stream. As a function of time, these salts tend to increase the back pressure, and contribute to additional coupling of shock wave energy by direct contact with the platinum substrate (i.e. the inorganic salts and oxides further accelerate the deterioration of the platinum catalyst). 
     Finally, instruments known in the art require the user to make and break connections to the combustion tube from both the top and bottom of that tube. This makes servicing the instrument a very difficult procedure. 
     In view of the limitations of combustion tubes known in the art, a great need exists for improvement with respect to these tubes. Applicant&#39;s invention provides novel solutions to the problems mentioned above. By employment of a unique interior tube configuration, Applicant&#39;s invention provides a means to decouple the shock wave propagated by direct contact between the top-layer quartz (or other energy absorbing media) and the catalytic surface. Resulting advantages of the present invention include: (1) decreased rate of deterioration of the catalytic bed, (2) uniform thermal geometry in the base of the furnace and elimination of cold regions within the catalyst bed, (3) non transport of inorganic salts and inorganic oxides onto the surface of the catalyst, (4) easier servicing of the reactor tube, and (5) reduction in the amount of catalyst required. 
     Applicant&#39;s invention provides for uniform thermal geometry in the base of the tube. That is, the upper section of the tube is ‘cold’ and the bottom surface of the tube is maintained at the same temperature as the main body of the surrounding furnace. This ensures that moisture present in the system does not condense in the combustor tube after it enters the system. Consequently, there is no regeneration of a second shock wave as the superheated gas moves from the inlet (gas expansion side) into the outlet (catalytic reaction) side of the reactor tube. Moreover, because the gas is not allowed to cool, cold regions in the catalytic volume are not established. This greatly increases the efficiency of the reaction process. Summarily, in view of the prior art, the bifurcated-chamber design of the present invention permits less catalyst to be used—primarily because uniform thermal gradients maintain efficient reaction rates, and eliminate direct coupling of the expansion shock wave energy. 
     While incorporation of a bifurcated-chamber design may appear to be a subtle distinction at first glance, its effects completely change the operation and maintenance of these tubes and their overall combustion systems. For instance, prior art designs require excess loading of catalyst to account for decreased efficiency and catalyst degradation. However, the present invention eliminates the requirement to load the combustion tube with an excessive amount of catalyst. 
     The present system prevents degraded or dislodged inert particles, and inorganic salts and oxides deposited on the inert quartz body, from being transported to the catalyst side of the reactor tube. Rather, such particles are trapped along the bottom surface of the tube. As such, these unwanted particles cannot obstruct gas flow or attach to the catalyst materials. Again, as the catalyst remains free from interfering matter, its working efficiency is preserved. 
     The present invention allows complete service of the combustion tube from only the top-side, making replacement or service of the combustion tube more “user” friendly. Since the platinum catalyst does not rapidly degrade, servicing of the combustion tube allows the user to reuse the platinum catalyst. This feature alone results in a substantial reduction in the cost of servicing the combustion system. 
     Finally, the present invention eliminates the requirement of humidification of the oxidant. In prior art designs, the catalyst limits the sorption of carbon dioxide (or degradation products containing carbon). The sorption is due to the degradation of the catalyst—caused by exposure to inorganic salts and/or oxides and the resulting “barrier” coating of the catalyst, exposure of chemically active sites, or crevices and fissures within the support phase of the catalyst. In the prior art, humidification of the catalyst serves to hydrate the inorganic salts and/or oxides, converting them into a form in which the carbon dioxide or degradation products of the oxidation process are not as strongly sorbed. As such, devices in the prior art are much more complex with regard to plumbing and servicing, as humidification reservoirs are required. Applicant&#39;s invention, however, presents a very straightforward plumbing mechanism and eliminates the need for a humidification reservoirs. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide an improved combustion tube where inert materials are decoupled from catalyst materials. 
     It is another object of the present invention to provide an improved combustion tube where degraded inert particles do not interfere with, or coat catalytic material. 
     It is another object of the present invention to provide an improved combustion tube where catalytic material is preserved throughout the combustion/oxidation process. 
     It is another object of the present invention to provide an improved combustion tube where catalytic material is held at a constant temperature throughout the combustion/oxidation process. 
     It is another object of the present invention to provide an improved combustion tube that eliminates the need for catalytic material humidification. 
     It is another object of the present invention to provide an improved combustion tube that is easily cleaned. 
     It is another object of the present invention to provide an improved combustion tube where replacement of component pieces is easily achieved. 
     It is yet another object of the present invention to provide an improved combustion tube where catalytic material is preserved throughout the combustion process. 
     In satisfaction of these and other related objectives, Applicant&#39;s present invention provides an improved combustion tube characterized by bifurcated inert and catalyst chambers. That is, an inert (energy absorbing) material of the tube is decoupled from the catalyst material. Further, the novel design of the present invention decreases the amount of catalyst utilized and greatly increases the working efficiency of the overall combustion system. Gas flow within the improved combustion tube is of a general “U-shape.” This design allows for uniform thermal gradients within the flow and promotes the deposit of unwanted matter along the bottom surface of the tube. 
     In the present device, as in the case of instruments known in the art, upon impact of the sample on the top layer of the quartz chips, quartz beads, or other inert particles (beads, rods, tubes, or crushed pieces of the same), the energy of the liquid being converted to steam, and the corresponding rapid expansion of the resulting gas, is transferred to the very bottom of the reactor tube. This energy transfer occurs both in the gas phase as well as by direct solid-to-solid contact between the quartz chips or beads. 
     However at this point, a difference in energy transfer is observed. Since the catalyst chamber, and the catalyst material contained therein, are no longer in direct contact with the energy absorbing layer of quartz (or other inert material), energy transfer by direct contact between particles does not occur. As such, the pressure pulse is severely attenuated by the quartz particles and the resulting gas expansion energy (due to physically increasing the flow rate through the reactor tube) does not result in significant chipping or flaking of the platinum catalyst. 
     An alternative embodiment of the present invention is characterized by a concentric tube design where an inner tube lies within an outer catalyst tube. In this design, the sample is injected in the inner inlet chamber. The inlet chamber is packed as described above, with quartz chips, beads, or other inert materials. The packing in the inlet serves (as described above) to absorb the thermal shock and dissipate the energy without the direct particle to particle transfer of this energy to the catalyst. The catalyst is located in the space between the outer wall of the catalyst tube and the outer wall of the inert tube. An aperture that allows air flow is located at the base of the combustion tube. This feature allows inert particles to lodge along the bottom surface of the combustion tube without blocking gas flow through the tube. This mechanism virtually eliminates the contamination of the catalytic surface. 
     Because of the bifurcated chamber configuration, the catalyst chamber is located in a region of maximum thermal stability, i.e. next to the furnace wall. Although the inner tube “cools” due to the heat of vaporization of the aqueous sample, the catalyst itself remains at constant temperature. This feature is extremely beneficial as the temperature at which the sample is vaporized is not a critical parameter; however, the temperature of the catalyst for ensuring complete oxidative combustion is critical. Moreover, thermal energy will not transfer to the center tube by conduction until after the oxidative combustion of the sample has been completed. 
     After a sufficient number of samples have been injected, the build-up of inorganic salts and/or oxides can eventually begin to plug the inlet chamber. However, since the inlet chamber consists of a simple tube, removal of the tube, packing material, and inorganic salts and/or oxides that have been deposited in the inlet tube are easily replaced with another tube containing the inert packing material. The inexpensive quartz chips can be readily replaced while the catalyst can be reinstalled without any additional conditioning or user preparation required. The reuse of the catalyst is of economic importance to the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Applicant&#39;s invention may be further understood from a description of the accompanying drawings, wherein unless otherwise specified, like referenced numerals are intended to depict like components in the various views. 
         FIG. 1  is a cross sectional view of the preferred embodiment of the improved combustion tube of the present invention. 
         FIG. 2  is a cross sectional view of the preferred embodiment of the improved combustion tube of the present invention, wherein its inner constituents are further depicted. 
         FIG. 3  is a cross sectional view of an alternative embodiment of the improved combustion tube of the present invention. 
         FIG. 4  is a cross sectional view of an alternative embodiment of the improved combustion tube of the present invention, wherein its inner constituents are further depicted. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , the preferred embodiment of the apparatus of the present invention is generally designated by numeral  10 . In the preferred embodiment, apparatus  10  is primarily composed of an inert, non-catalytic material, such as quartz. However, other suitable materials having sufficient characteristics will be apparent to those skilled in the art. 
     Apparatus  10  is characterized by inlet port  12 , whereby an analyte sample is inserted or injected into apparatus  10 . Injection port  12  is primarily defined by first outer surface  16  and separation wall  14 . In the preferred embodiment, an analyte sample may be injected into apparatus  10  by automated or manual means, as known in the art. As such, injection port  12  may be configured in such a manner so as to allow for proper injection by any such means known in the art. 
     As best seen in  FIG. 1 , inert chamber  20  is defined as first outer surface  16  and separation wall  14  extend, in adjacent fashion, from injection port  12  toward bottom surface  18 . That is, inert chamber  20  lies below injection port  12  and above bottom surface  18 , demarcated by first outer surface  16  and separation wall  14 . Inert chamber  20 , in the preferred embodiment, contains inert materials  40 . 
     Referring now to  FIG. 2 , inert material  40  is positioned within inert chamber  20 . In the preferred embodiment, inert material  40  primarily consists of material such as quartz beads or quartz chips. As previously discussed, these materials are meant to bear the brunt of the induced shock from the sample vaporization (expansion) as it enters the combustion tube. Again, as these materials absorb the shock wave energy, some degradation is unavoidable. However, apparatus  10 , through incorporation of separation wall  14 , and other novel attributes to be fully discussed, eliminates the problems previously associated with such degradation. 
     Specifically, the unique configuration of device  10  allows broken/chipped material to fall onto bottom surface  18  without obstructing gas flow to catalytic chamber  32  of apparatus  10 . Also, the dual-chamber nature of apparatus  10  prevents the inert materials of inert chamber  20  from contacting with the catalytic materials of catalytic chamber  32 . 
     Apparatus  10 , in the preferred embodiment, is further characterized by outlet port  34 , whereby an analyte sample egresses from apparatus  10 . Outlet port  34  is primarily defined by second outer surface  30  and separation wall  14 . In the preferred embodiment, outlet port  34  is typically at temperatures below 200 C, and may be configured to allow conventional coupling of the reactor tube to Teflon or other inert tubing for transport to a bulk water condenser element and/or high efficiency drying element. A high efficiency drying element may be chemical or be composed of a single or several ‘nation’ type driers. The initial nafion drier being heated to temperatures above 100 C (nominally between 150 and 120 C), and the secondary nafion drier being held at or near room temperature. Such devices are available from PermaPure, as either single (initial drier heated, and is then coupled to a second device which is not heated, or coupled (contains both the heated and non heated regions on a single device) element. 
     In addition, as second outer surface  30  and separation wall  14  extend, in adjacent fashion, from outlet port  34  towards bottoms surface  18 , catalytic chamber  32  is defined. That is, catalytic chamber  32  lies below outlet port  34  and above bottom surface  18 , demarcated by second outer surface  30  and separation wall  14 . 
     Referring again to  FIG. 2 , catalytic chamber  32 , in the preferred embodiment, contains catalytically active materials  38 . In the preferred embodiment, catalytically active materials  38  are generally materials such as platinum on an alumina, zirconia, or titania substrate. As previously discussed, catalytic materials  38  are primarily responsible for the high efficiency of the oxidative process. By virtue of novel configuration of apparatus  10  the integrity of catalytic materials  38  is maintained. Also, such configuration provides for constant catalyst temperature. As such, apparatus  10  is more effective, requires less maintenance, and provides for easier component material replacement in view of the prior art. Further, this design facilitates easy service and removal of inert materials as the tube need only be opened from the injection port  32 . Importantly, during this process catalytically active materials  38  are left undisturbed. This is simply not possible with prior art devices. 
     A plurality of detents  42  rest just above bottom surface  18  and are positioned along each respective chamber. Detents  42  are attached within both inert chamber  20  and catalytic chamber  32 , and are configured so that each detent  42  extends toward the other. The resulting arrangement formed by the combination of detents  42  is a “bottleneck” within each chamber. Detents  42  aid in the support of inert material  40  and catalytic material  38 , and help hold the respective materials fixed with respect to one another. 
     As best seen in  FIG. 1 , separation wall  14  extends, along the interior defined by the combination of first outer surface  16 , bottom surface  18 , and second outer surface  30 . However, separation wall  14  does not span the entire length of the interior, so that an aperture exists between separation wall  14  and bottom surface  18 . The interior shape defined by the combination of first outer surface  16 , bottom surface  18 , second outer surface  30 , and separation wall  14  causes a “U-shaped” flow path for the sample as it traverses through apparatus  10 . Specifically, an analyte enters through injection port  12 , is pushed through inert chamber  20 , toward bottom surface  18 , and around separation wall  14 , up through catalyst chamber  32  and out through outlet port  34 . 
     Referring to  FIG. 3 , an alternative embodiment of the present invention is generally designated by the numeral  100 . In this alternative embodiment, apparatus  100  is primarily distinguished by an inner cylinder lying within an outer cylinder, rather than distinct chambers being partition by a separation wall as in the preferred embodiment. 
     Apparatus  100  is characterized by inlet port  112 , whereby an analyte sample is inserted or injected into apparatus  100 . Injection port  112  is primarily defined by inner cylinder wall  114 . In the preferred embodiment, an analyte sample may be injected into apparatus  100  by automated or manual means, as known in the art. As such, injection port  112  may be configured in such a manner so as to allow for proper injection by any such means known in the art. 
     As best seen in  FIG. 3 , as inner cylinder surface  114  extends toward bottom surface  118 , inert chamber  120  is defined. That is, inert chamber  120  lies below injection port  112  and above bottom surface  118 , demarcated within inner cylinder surface  114 . Inert chamber  120 , in this embodiment, contains inert materials  140 . 
     Referring now to  FIG. 4 , inert material  140  is positioned within inert chamber  120 . In this embodiment, inert material  140  primarily consists of material such as quartz beads or quartz chips. As previously discussed, these materials are meant to bear the brunt of the induced shock wave from the sample vaporization process as it enters the combustion tube. Again, as these materials absorb the shock wave energy, some degradation is unavoidable. However, apparatus  100 , through incorporation of inner cylinder surface  114 , and other novel attributes to be fully discussed, eliminates the problems previously associated with such degradation. 
     Specifically, the unique configuration of device  100  allows broken/chipped material to fall onto bottom surface  118  without obstructing gas flow to catalytic chamber  132  of apparatus  100 . Also, the dual-chamber nature of apparatus  100  prevents inert material  140  of inert chamber  120  from contacting with the catalytic material  138  of catalytic chamber  132 . 
     Apparatus  100 , in this embodiment, is further characterized by outlet port  134 , whereby an analyte sample egresses from apparatus  100 . Outlet port  134  extends as an aperture from outer cylinder surface  116 . In the preferred embodiment, outlet port  134  is typically at temperatures below 200 C, and may be configured to allow conventional coupling of the reactor tube to Teflon or other inert tubing for transport to a bulk water condenser element and/or high efficiency drying element (as described above). 
     In addition, as outer cylinder surface  116  and inner cylinder surface  114  extend, in adjacent fashion, towards bottoms surface  118 , catalytic chamber  132  is defined. That is, catalytic chamber  132  lies below outlet port  134  and above bottom surface  118 , bound within second outer cylinder  116  and outside of cylinder surface  114 . 
     Referring again to  FIG. 4 , catalytic chamber  132 , in the preferred embodiment, contains catalytically active materials  138 . In this embodiment, catalytically active materials  138  are generally materials such as platinum on an alumina, zirconia, or titania substrate, or platinum as a solid or porous pellet. As previously discussed, catalytic materials  138  are responsible for the oxidative process. By virtue of novel configuration of apparatus  100  the integrity of catalytic materials  138  is maintained. As such, apparatus  100  is more effective, requires less maintenance, and provides for easier component material replacement in view of the prior art. 
     A plurality of detents  142  rest just above bottom surface  118  and are positioned along each respective chamber. Detents  142  are attached within both inert chamber  120  and catalytic chamber  132 , and are configured so that each detent extends toward the other. The resulting arrangement formed by the combination of detents  142  is a “bottleneck” within each chamber. Detents  142  aid in the support inert material  140  or catalytic material  38 , and help hold the materials fixed with respect to one another. 
     As best seen in  FIG. 4 , inner cylinder  114  extends, in adjacent fashion, along the interior defined by outer cylinder  116 , towards bottom surface  118 . However, inner cylinder  114  does not span the entire length of the interior, so that an aperture lies between inner cylinder  114  and bottom surface  18 . The interior shape defined by the combination of outer cylinder  116 , interior cylinder  114 , and bottom surface  118 , causes a “semi-circular” flow path for the sample as it traverses through apparatus  10 . Specifically, an analyte enters through injection port  112 , is pushed through inert chamber  120 , towards bottom surface  118 , and around inner cylinder  114 , up through catalyst chamber  132  and out through outlet port  134 . 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.