Combustion Extraction Probe for Sulfur Chemiluminescence Detection

Abstract

This disclosure is directed to an improved extraction probe and method of operation for sampling combustion gases from a furnace or burner for sulfur selective detection. The extraction probe is comprised of at least one constrained reduction zone with at least one discontinuous sampling conduit made from at least one smooth refractory material. The configured assembly allows for controlled formation of species that facilitate transport of sulfur monoxide or its equivalent for enhanced detection and system performance of sulfur chemiluminescence detectors.

Claims

1. An improved method for sulfur chemiluminescence detection comprising a multicomponent combustion gas extraction probe for collection and transfer of reactive species for their detection, whereby an inner component of the probe consists of an inert refractory and an outer component is a refractory material.

2. An apparatus for sulfur chemiluminescence detection comprising: a. a dual combustion zone burner; b. a chemiluminescence reaction cell; c. a vacuum pump; and d. a multicomponent combustion gas extraction probe for collection and transfer of reactive species for their detection, whereby an inner component of the probe consists of an inert refractory and an outer component is a refractory material.

3. The improved method of claim 1, further comprising: a. a dual combustion zone burner; b. a chemiluminescence reaction cell; and c. a vacuum pump.

4. The apparatus according to claim 2, whereby the inner component contains wool, beads, or other features to induce turbulence and pressure drop.

5. A apparatus according to claim 2, whereby a change in inner dimensions of the probe induces turbulence.

6. The method of claim 3, further comprising a quartz probe and components to increase sample signal and reduce background noise.

7. The method of claim 6, further characterized by improving the analysis of sulfur compounds in a sample.

8. The method in claim 3 wherein the active species from a flame or plasma utilizing a quartz probe and components to eliminate interfering background chemiluminescence by means of surfaces to allow some survival of an active species (SiO) to facilitate high transport efficiency of SO.

9. The method in claim 3 wherein operating conditions are adjusted to maintain a consistent low level of background noise commensurate with high detector sensitivity and stability.

10. The method in claim 3 wherein a silicone-based transfer line is used from the burner to the chemiluminescence reaction cell.

11. The method in claim 3 wherein an ozone destruction catalyst assembly with lower pressure drop and improved means for trapping particulates is used between the chemiluminescence reaction cell and the vacuum pump.

12. The method in claim 3 wherein the dual combustion zone burner is operated with two hydrogen-rich reducing-zones.

13. The method in claim 3 wherein burner gas flows to the dual combustion zone burner are cyclically pulsed or modulated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:

[0030] FIG. 1 is a representative drawing illustrating an embodiments of a quartz probe;

[0031] FIG. 2 illustrates a transfer line of silicone tubing with sheath and boot to exclude light;

[0032] FIG. 3 illustrates an adapter that allows simultaneous FID and sulfur detection by SCD incorporating embodiments of this invention;

[0033] FIG. 4 illustrates a filtering assembly for placement within an ozone destruction device.

[0034] FIG. 5 is an illustrative chromatogram example of sensitivity and selectivity obtained from an inventive quartz probe vs. a conventional ceramic probe.

DETAILED DESCRIPTION

[0035] This disclosure describes an improved method and extraction probe apparatus for sampling sample reactive product gas from an externally heated combustion furnace. It also describes a silicone transfer line used to efficiently transfer the combustion product gas to an ozone induced chemiluminescent reaction cell, and it describes an improvement in construction of an ozone destruction device. More particularly, it describes their implementation for sensitive and selective chromatographic detection of sulfur compounds by ozone induced chemiluminescence in which interferences are eliminated by their conversion to non-responding species, such as carbon dioxide and water, and it describes an adapter for coupling an FID to a burner using a heated transfer line.

[0036] FIG. 1 is a generalized drawing of the improved extraction probe assembly 15 consisting of a quartz tube 10; and internal components 20, which in a preferred embodiment are comprised of quartz beads. The dimensions of the quartz tube are partially chosen to be accommodated within a commercial Agilent SCD burner. Most importantly, however, is the need to maintain a stable flame like structure within the immediately prior combustion zone, thus within these constraints the inventive extraction probe is readily adaptable to other dimensions for use in other manufacturers' burners.

[0037] The tube 10 has dimensions of typically ca. 110 mm length with ca. 0.5-0.7 mm internal diameter and 1.2-1.3 mm outer diameter. Longer and shorter lengths are readily accommodated and if desired the tube could be coiled, for example to aid fabrication of a smaller lower power consuming burner or if a furnace is of sufficient length to accommodate longer lengths. The fused quartz beads consisted of particles within the diameter range of 0.2 to ca. 0.4 mm that were fused into an internal bed of about 4-5 mm long bed using a hydrogen/oxygen torch using standard quartz blowing techniques. The bed 20 completely fills the space from inner wall to inner wall so as to avoid channeling. Ends are fire polished to remove sharp edges. Other embodiments utilized quartz wool held into place by dimples made within the quartz tube and silicon carbide held in place with quartz wool and still others require no internals. Relatively inert refractory materials, such as alumina, translucent alumina, sapphire, zirconia, titania and other ceramics, and refractories could be packed in place of or in combinations, e.g., with quartz to provide turbulence and pressure drop. The availability of fused silica (quartz) of various shapes and dimensions provides for greater flexibility in pressure drop across the probe compared to the availability of ceramic tubing, resulting in a more robust system of detection. Installation of the inventive probe into existing commercial furnaces or burners requires little or no modification of existing systems. Where needed, a fitting or ferrule can be drilled out to accommodate a slightly large outer diameter of the inventive probe. Seals of the probe to furnaces and burners are made conventionally with soft ferrules or o-rings. Those skilled in the art can readily optimize these dimensions and materials according to desired applications. It was found that quartz could be sealed within a protective ceramic sheath for mechanical protection at the exit of the burner, provided that the sealant of high-temperature silicone or epoxy was not exposed to temperatures exceeding about 350-400° C. This seal also serves to provide strain relief toward thermal expansion of different materials.

[0038] Some embodiments used quartz tubing by itself, blown to produce an hour glass shape or other shapes, with and without other internal components, to impart flow turbulence. It should be noted that an abrupt change in tube dimension from one size to another also introduces turbulence. The use of quartz beads, however, lends itself to relatively reproducible configurations from a manufacturing perspective. The use of removable quartz or ceramic wool against a fixed internally placed stop allows for facile testing of experimental materials. A small dead volume is created from the annular space between the inner and outer materials of the inventive probe. A small quartz capillary with dimensions of approximately 100 microns outer diameter and 7 microns inner diameter, for example, can also be inserted into this annular space to act as a shunt for sweeping this dead volume, if so desired.

[0039] FIG. 2 illustrates a transfer line made of silicone tubing 30; with sheath 40 and boot 50 to exclude ambient light from being detected in the chemiluminescence reaction cell 60, which is comprised of machined aluminum. The sheath 40 is preferably comprised of black heat shrink tubing placed on the outside of 30, nearest 60. A length of about 25 cm is adequate when used in combination with a boot 50 that fully covers the tube connector into 60 and overlaps 40. The wall and diameter are chosen to reduce pressure drop and to resist collapse under operating vacuum. Effective outer and inner diameters are 6 mm and 3 mm, respectively.

[0040] FIG. 3 is a drawing of an adapter that allows the coupling on an Agilent/Hewlett Packard FID with a burner. Components of the interface include an exhaust gas probe 70 that in embodiments is between approximately 10 and 150 cm and which is maintained at elevated temperature of about 65-100° C. by an electrically heated transfer line 80. In embodiments, the length of 70 and 80 are about 60 cm and controlled to about 90° C. and 70 is comprised of fused silica capillary or fused silica lined metal capillary with an internal diameter of 0.53 mm (a standard dimension for fused silica capillary tubing). The capillary has a deactivation layer consisting of polydimethylsiloxane polymer, for example with a 7 μm thickness. Exhaust gas probe 70 is positioned approximately in the center and perpendicularly within the gas flow exhaust of the FID collector 100 through with the combusted gases exit from the chimney 90 that originate at jet 110 of the FID. The adapter housing 120, fastens to the FID chimney 90. The flow collected is a fraction of the FID flow rate, from about 20-40% depending on the total flow through the FID and the length of the 70.

[0041] Particulates consisting of ozone destruction catalyst fines are formed through normal abrasion processes. They must be trapped to prevent them from damaging the detector's vacuum pump. FIG. 4 is a drawing of a cylindrical filter assembly 200 that consists of an open cylinder upon which a downstream cylindrical wedge elliptical screen 210 and an upstream perpendicular circular screen 220. The body of the cylinder is comprised of any material that is stable to ozone exposure over a long period, such as stainless steel, copper, PVC, and upon which screens are readily affixed using an adhesive. The upstream screen 220 is more open (lower mesh) and the downstream screen 210 is less open (higher mesh). Pressure drop is minimized because the elliptical screen has a greater surface area than a circular cross section. The acute angle formed by the elliptical screen and the cylinder body provides a volume for collection of particulates that pass through the larger spaces of the perpendicular screen and settle in corners or where space velocity is low.

EXAMPLES

[0042] Combustion extraction probes were produced within the ranges of dimensions and materials of composition as described in the foregoing. Results from the extraction probe embodiments of this invention were compared against those obtained from conventional, commercial ceramic tubes. Consistent with the literature, it was found that all quartz tubular probe construction was ineffective because of a large background signal that grew over time and they exhibited unstable response. In fact, with all quartz single straight tubes tested, in only a few minutes the background noise because so high (off-scale) so as the render the signal unusable, even though in the first minute or few minutes response to sulfur was also high. Embodiments of this invention in which internals were added to quartz tubes or another tube was used to surround the inner tube were found to be available commercial burner inner ceramic tubes. Owing to several desirable properties in terms of inertness, low surface area, low thermal expansion and ease with which its shape is modified, quartz tubing is deemed a preferred embodiment for this invention. Deposition of an inert surface, such as silica by way of chemical vapor means, may provide similar benefit provided that the surface is mechanically and chemically sound.

[0043] Probes were tested with and without silicone transfer lines and with an improved ozone destruction device. Since silicone transfer lines and improved ozone destruction devices led to equal or improved performance for all extraction probes, this reduced the number of combinations of experiments required for investigation. For heated transfer line control from the FID adapter, a variable transformer was used to conveniently apply voltage to a Watlow flexible tube heater. Little or no advantage was found for heating the silicone transfer line to the chemiluminescent cell, at least for sulfur detection.

Example 1

[0044] An extraction probe was prepared using a 100 mm length with ca. 0.5-0.7 mm internal diameter and 1.2-1.3 mm outer diameter, ID alumina ceramic tube of 118 mm length. A Hewlett Packard model 5890 Series II Gas Chromatograph was used for this work throughout. The SCD was a Sievers model 350B with a modified Agilent Dual Plasma burner and controller. Air was used for the ozone generation with its inlet pressure set to 3 psig. The column was a 15 m, 0.32 mm ID, SPB-1 with a 4 μm film thickness. The head pressure was 7 psig with nitrogen carrier with a split ratio of 1:10 and oven temperature program of 40° C. for 1 minute to 120° C. at 10° C./min, hold 1 minute. The SCD furnace was operated at 800° C. with hydrogen and air flows of 130 and 5 mL/min, respectively. Prior to operation, the average peak to peak noise was arbitrarily set to 0.0 mvolt. After stabilization for several minutes, with oxygen flowing to the ozone generator, the average peak to peak noise was measured at 0.1 mVolt and with the ozone generator energized it measured 0.6 mVolt. This indicates the presence of SiO, which chemiluminesces with ground-state oxygen. The system using the inventive probe exhibited fast start-up times capable of generating qualitative and semi-quantitative results in a manner of minutes, faster than conventional probes.

Example 2

[0045] Probes were examined under conditions of hydrogen flow to the burner about 80 mL/min and air flow rate about 90 mL/min. The SCD furnace was operated at 800° C. and a 30 m, 0.32 mm ID, DB-1 with a 2 μm film thickness was used. The head pressure was 12 psig (nitrogen) with a split ratio of 1:10 and oven temperature program of 50° C. for 0.5 minutes to 280° C. at 12° C./min, hold 1 minute. The column and conditions used generated significant bleed (siloxanes). Superior performance of the inventive extraction probe was observed by comparison to other constructions as shown by results summarized in Table 1 (qualified by sensitivity, selectivity and stability). Excellent results obtained from the invention described herein were unexpected. The combination of a treated ceramic tube at the point of flame/plasma formation and in the nearby quench zone, along with a liner as described are capable of producing superior performance. The inventive extraction probe is also resistant to hydrogen poisoning, whereas the conventional commercial probe is not.

TABLE-US-00001 TABLE 1 Example Sensitivity Selectivity Stability Inventive Quartz Probe* Good Good Good Quartz Probe - By Good** Fair Poor itself with Internals Commercial Probe Good Good Fair *Quartz tube(s) with internals and/or outer protection **Unusable almost immediately due to high noise

Example 3

[0046] Using conditions typical of convention dual plasma SCD, FIG. 5 is an example chromatogram of sensitivity and selectivity obtained from an inventive quartz probe vs. conventional commercial ceramic probe, showing improved performance for the inventive probe. Peak shape obtained is excellent and no difference in shape was observed using a shunt to sweep any annular space dead volume.

Example 4

[0047] Using the conditions typical of a single plasma SCD, for example, operating at 780° C. with an initial hydrogen flow rate of 60 mL/min and oxygen flow rate of 8 mL/min. Following ignition of the burner, as evidenced by a sudden rise in the baseline, then a gradual fall was observed over about 5 minutes, the detector baseline began to rise continuously from about 0.3 mV to over 50 mV, at which point the hydrogen flow rate was lowered to 30 mL/min with an immediate fall in the baseline to about 2 mV. The baseline signal was monitored and the hydrogen flow rate was adjusted up to 34 mL/min in multiple steps so that the baseline signal was steady. Alternatively, a solenoid valve was placed on the hydrogen line to the burner with hydrogen flow rate set to 60 mL/min and oxygen flow rate of 8 mL/min. A cyclic timer was used to actuate the solenoid valve continuously at nominally 10 Hz, a rate faster than the signal peak width by at least a factor of 2 or 3. Because the hydrogen flow is momentarily interrupted at each cycle, total hydrogen consumption was reduced but surprisingly a factor of 2 improvement in signal is observed with slight improvement in peak shape because surface reactivity is diminished. Addition of a low flow rate of gas, for example air or oxygen from about 1 to 15 mL/min, preferably closer to 1 mL/min, provided an even slightly better peak shape without significant loss in signal.

[0048] While preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, and the like.

[0049] Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent they provide exemplary, procedural or other details supplementary to those set forth herein.