Title:
Method for the measurement of the reactive molecular species in liquid petroleum and liquid petroleum products
Kind Code:
A1


Abstract:
An apparatus and method for the direct measurement of corrosive sulfur and other corrosive compounds is provided. The method and apparatus of the current invention provides a rapid, reliable and cost effective method to directly measure the content of corrosive compounds in various fluids, and in particular liquid petroleum and liquid petroleum products such as gasoline. The apparatus can be retrofit to existing analyzers where they exist, or easily installed in locations that require such analysis.



Inventors:
Falkiner, Robert J. (Mississauga, CA)
Lau, Tian C. (Whitby, CA)
Application Number:
11/701485
Publication Date:
12/27/2007
Filing Date:
02/02/2007
Assignee:
ExxonMobil Research and Engineering Company (Annandale, NJ, US)
Primary Class:
International Classes:
C10G29/06
View Patent Images:



Primary Examiner:
BOYER, RANDY
Attorney, Agent or Firm:
ExxonMobil Research & Engineering Company (Annandale, NJ, US)
Claims:
1. An apparatus for the on-line measurement of reactive molecular species of a chemical element present within a liquid that can react with a target material comprising: an analyzer capable of measuring the total content of the chemical element; a flow splitting device positioned upstream from the analyzer that splits on-line flow of the liquid into a first stream and a second stream that both flow to the analyzer, wherein the first stream flows untreated to the analyzer; and a pre-treatment device positioned in the second stream prior to the analyzer, wherein the pre-treatment device selectively removes the reactive molecular species of the element from the liquid that would react with a target material, whereby a measurement of the total content of the chemical element is taken from each stream.

2. The apparatus of claim 1 where the target material comprises a metal.

3. The apparatus of claim 1 where the pre-treatment means comprises a sacrificial reactant that removes the reactive molecular species.

4. The apparatus of claim 3 wherein the pre-treatment means is a plug flow packed bed reactor comprising the sacrificial reactant.

5. The apparatus of claim 3 where the sacrificial reactant comprises a metal.

6. The apparatus of claim 3 where the target material comprises a metal, where the sacrificial reactant comprises metal and where the target material and the sacrificial reactant both comprise the same type of metal.

7. The apparatus of claim 1 where the reactive molecular species of a chemical element are reactive sulfur species.

8. The apparatus of claim 1 where the target material comprises silver, where the sacrificial reactant comprises silver and where the reactive molecular species of a chemical element are silver reactive sulfur species.

9. The apparatus of claim 8 where the silver reactive sulfur species comprise elemental sulfur and hydrogen sulfide.

10. The apparatus of claim 8 where the pre-treatment means is a plug flow packed bed reactor containing a sacrificial reactant that removes reactive species.

11. The apparatus of claim 1 wherein the liquid is selected from liquid petroleum and liquid petroleum products.

12. The apparatus of claim 11 wherein the liquid is an automotive fuel.

13. The apparatus of claim 12 where the liquid is gasoline.

14. The apparatus of claim 1 wherein the analyzer is a monochromatic wavelength-dispersive X-ray fluorescence spectrometer.

15. The apparatus of claim 1 where the target material comprises silver, where the sacrificial reactant comprises silver, where the reactive molecular species of a chemical element are silver reactive sulfur species, and where the liquid is an automotive fuel.

16. The apparatus of claim 1 comprising a computer program that automatically receives and compares the total content of the chemical element in each stream and calculates a difference that represents the content of reactive compounds in the liquid.

17. A method for measuring the content of reactive molecular species of a chemical element present in a liquid that can react with a target material comprising the steps of: (i) measuring the total content of the chemical element in a non-treated first sample of liquid; (ii) removing reactive molecular species of the chemical element that can react with the target material from a second sample of the liquid to form a treated sample; (iii) measuring the total content of the chemical element in the treated sample; (iv) determining the total content of the reactive molecular species of the chemical element in the liquid by calculating the difference in the total content of the chemical element in the non-treated sample and the treated sample. (v) optionally repeating steps i) through iv) one or more times.

18. The method of claim 17 where the target material comprises a metal.

19. The method of claim 18 where the removing step uses a sacrificial reactant that removes the reactive molecular species.

20. The method of claim 19 wherein the sacrificial reactant is configured in a plug flow packed bed reactor.

21. The method of claim 20 where the sacrificial reactant comprises a metal.

22. The method of claim 21 where the sacrificial reactant and the target material both comprise the same metal.

23. The method of claim 17 wherein the element is sulfur and the reactive molecular species of the element are reactive sulfur species.

24. The method of claim 23 wherein the step for removing the reactive sulfur species is performed by exposing the second sample to a plug flow packed bed reactor containing a sacrificial reactant that removes reactive sulfur species.

25. The method of claim 24 where the target material is silver and the sacrificial reactant comprises one or more of the following metals: silver, copper, brass, sodium and alloys thereof.

26. The method of claim 25 wherein the sacrificial reactant is silver.

27. The method of claim 17 wherein the liquid is selected from liquid petroleum and liquid petroleum products.

28. The method of claim 27 wherein the liquid is gasoline.

29. A method for measuring the content of silver reactive sulfur species present in an automotive fuel comprising the steps of: (i) measuring the total content of sulfur in a first non-treated sample of fuel; (ii) removing silver reactive sulfur species from a second sample of the fuel to form a treated sample; (iii) measuring the total content of sulfur in the treated sample; (iv) determining the total content of the sulfur reactive molecular species in the fuel by calculating the difference in the total sulfur content in the non-treated sample and the treated sample. (v) optionally repeating steps i) through iv) to obtain more than one determination of the total content of the reactive species in the liquid.

30. The method of claim 29 wherein the steps for measuring the total content of the sulfur are performed using a monochromatic wavelength-dispersive X-ray fluorescence spectrometer.

31. The method of claim 27 wherein an amount of corrosion inhibitor additive is added to the fuel depending on the amount of reactive sulfur species detected.

Description:

1.0 CROSS REFERENCE TO RELATED APPLICATION

This invention relates and claims priority to U.S. Provisional Patent Application No. 60/815,843, filed on Jun. 23, 2006, entitled “Method For The Measurement Of Reactive Molecular Species In Liquid Petroleum And Liquid Petroleum Products”.

2.0 BACKGROUND OF THE INVENTION

2.1 Field of the Invention

This invention relates to the detection of reactive molecular species of a chemical element in liquids. More particularly the invention relates to a method and apparatus to detect and quantify reactive molecular species containing a chemical element, such as reactive molecular species containing sulfur, that are potentially present in a liquid, such as gasoline, and react with a material to which the liquid may be exposed, such as silver.

2.2 Description of Related Art

Copper, silver, brass and other “soft metal” alloys are susceptible to corrosion from reactive sulfur molecules. The occasional presence of reactive sulfur molecules in gasoline has caused and continues to cause serious problems for automobile drivers due to sulfiding (formation of metal sulfides) of silver fuel level sensors. On some vehicles, these sensors have failed due to sulfidation of the silver electrical contact points. This can lead to the fuel gauge indicating more or less fuel than is actually in the vehicle tank. The sulfiding of fuel level sensors can result in unexpected and sudden run-out-of-fuel incidents with the dashboard fuel gauge still indicating sufficient fuel. A vehicle, unexpectedly running out of fuel, experiences a loss of engine power that may result in rapid deceleration from full engine braking, and abrupt loss of power steering. Different vehicles exhibit different failure symptoms depending on their design. For example, electronic fuel injected vehicles tend to run out of gas suddenly, without prior warning. The National Transportation Safety Board (“NTSB”) considers sudden power loss to be a consumer safety issue, as it can result in stalled vehicles in traffic.

As a result, distribution of gasoline with even low trace levels of reactive sulfur can expose the gasoline manufacturer, distributor and marketer to significant liability and adverse publicity. Some jurisdictions have mandated that the IP 227 silver corrosion test used for aviation fuel be used for gasoline. ASTM International is currently developing an adaptation of the copper strip (ASTM D130) copper corrosion test method for gasoline using a silver coupon.

ASTM DI30, and other tests such as mercaptan tests (D4952 and D3227), however, are not designed to detect very low levels of H2S and elemental sulfur. The D130 test is a “static” coupon test, and may over-predict durability for more easily corroded alloys such as silver, or for rubbing, rolling or heated soft alloy fuel system components. Therefore, any test method derived from these tests, such as the static silver coupon test being adapted from ASTM D130, may fail to provide the sensitivity necessary to address the problem. In fact, a static silver corrosion coupon test is dependant on sampling, sample storage, testing variability and on the subjective visual inspection of the user. The user soaks silver coupons in a test sample of gasoline for a defined period of time and quantifies the reactive sulfur molecules in the test sample by visually comparing the corroded coupons with pictures of coupons corroded with a known amount of reactive sulfur. There is no reliable field correlation between the test and silver fuel sensor sulfiding on a silver fuel level sensor.

Field problems have been experienced with some copper fuel pump commutators, silver alloy fuel sender unit resister arrays and silver plated crankcase bearing cages with gasoline that passes ASTM D130. Direct measurement of reactive molecular species of sulfur such as elemental sulfur and hydrogen sulfide with a low enough detection limit is needed to provide a more reliable means of ensuring adequate field performance. In addition, a method that enables accurate measurement of the aforementioned compounds on-line and in-situ as fuel travels through a production and/or distribution pipeline would be beneficial.

3.0 BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are for illustrative purposes only and are not intended to limit the scope of the present invention in any way:

FIG. 1 illustrates an example of a measurement device of the present invention.

FIG. 2 illustrates a block diagram of a method of the present invention.

4.0 SUMMARY OF THE INVENTION

The method and apparatus of the current invention provide a rapid, reliable and cost effective means to directly measure reactive molecular species of a chemical element contained in a defined liquid that will react with a defined target material. Suitable reactive molecular species include, in particular, reactive molecular species of sulfur such as elemental sulfur and hydrogen sulfide. Suitable liquids include, in particular, liquid petroleum and liquid petroleum products. Suitable target materials include, in particular, metals such as silver.

The method and apparatus are particularly well suited to on-line measurement of reactive molecular species of sulfur, that react with metals contained in fuels such as ultra low sulfur gasoline and diesel fuel, at sites that practice simultaneous blending and release (SBR). However, neither the method nor the apparatus are solely limited to measuring reactive sulfur species in fuels and both can easily be adapted to measure different reactive molecular species in any number of liquids.

In one embodiment, the invention comprises an apparatus for the on-line measurement of reactive molecular species of a chemical element present within a liquid that can react with a target material. The apparatus comprises: (i) an analyzer capable of measuring the total content of the chemical element in a sample of the liquid, including content that is part of compounds formed with the chemical element; (ii) a flow splitting device positioned upstream from the analyzer that splits on-line flow of the liquid into a first stream and a second stream that both flow to the analyzer, wherein the first stream flows untreated to the analyzer; and (iii) a pre-treatment device positioned in the second stream prior to the analyzer, wherein the pre-treatment device selectively removes the reactive molecular species of an element from the liquid that would react with a target material, whereby the analyzer provides a measurement of the total content of the chemical element in each stream. The difference between the total content of the chemical element in the two streams is indicative of the total content of reactive molecular species of the chemical element present in the liquid.

In another embodiment, the invention comprises a method for measuring the content of reactive molecular species of a chemical element present in a liquid that can react with a target material. The method comprises the following steps: (i) measuring the total content of a chemical element in a non-treated first sample of liquid; (ii) removing reactive molecular species of the chemical element that react with the target material from a second sample of the liquid to form a treated sample; (iii) measuring the total content of the chemical element in the treated sample; (iv) determining the total content of reactive molecular species of the chemical element in the liquid by calculating the difference in the total content of the chemical element in the non-treated sample and the treated sample; and (v) optionally repeating steps i) through iv) one or more times.

5.0 DETAILED DESCRIPTION

5.1 Definitions

The following definitions apply throughout the application unless otherwise noted:

“Molecular Species,” relative to a chemical element, refers to any molecular compound containing the element including single atom molecules of the element and molecules with multiple atoms where at least one atom is the element. For example, the molecular species for the element sulfur (i.e., the “sulfur species”) consist of elemental sulfur and any molecule containing sulfur including hydrogen sulfide, mercaptans, etc.

“Reactive molecular species,” is a subset of a molecular species that refers to any molecule comprising the chemical element that is reactive with a defined target material. For example, if the element is sulfur and the target material is silver, then the reactive molecular species (i.e., the “silver reactive sulfur species”) consist of any molecules that contain sulfur, including elemental sulfur, and react with silver. If the target material is changed to a different metal, such as copper, the specific sulfur molecules that form the copper reactive sulfur species may or may not be the same as those that form the silver reactive sulfur species.

“Non-reactive molecular species,” is a subset of molecular species that refers to any molecule, comprising the chemical element that is not reactive with a defined target material. For example, if the element is sulfur and the target material is silver, then the non-reactive molecular species (i.e., the “silver non-reactive sulfur species”) consist of any molecules that contain sulfur but do not react with silver.

“Target Material” refers to any substance that reacts with one or more molecules of a molecular species that may be present in a liquid. Typically, the target material is a metal, such as silver, that is or may be exposed to the liquid, thereby exposing any reactive molecular species present in the liquid to the target material. In some instances the reaction between the reactive molecular species and the target material adversely affects the target material, such as when silver reactive sulfur species present in gasoline corrodes silver fuel level sensors.

“Sacrificial reactant,” refers to a chemical substance that is incorporated into a pre-treatment device to react with and retain, absorb, adsorb, scavenge or otherwise selectively remove one or more members of a reactive molecular species from a sample aliquot exposed to the pre-treatment device.

“Simultaneous blending and release” (SBR) refers to when a fuel such as gasoline or diesel is being continuously blended (manufactured) at the manufacturing site and released into an external transportation conveyance such as a pipeline, tanker, truck, railcar without stoppage of the blending (manufacturing) process.

“Total content of a chemical element” refers to a quantitative measurement that is proportional to the total number of the chemical element atoms present in a sample, including those that are part of compounds formed with the chemical element;

5.2 Overview

A method and apparatus for measuring the quantity in a liquid of molecular species of a chemical element that react with a given target material, is provided. The method may be performed on-line, e.g., in-situ during manufacture and/or distribution of the liquid via a pipeline. The method can also be performed off-line, e.g., through batch testing.

The on-line apparatus has a flow-splitter that splits liquid from a supply line into two streams. Each stream leads to an analyzer that is capable of measuring the total content of the chemical element in the samples. Samples from the first stream are untreated and measured for the total content of the chemical element. The total quantity of the chemical element in the samples taken from the first stream is attributable to both reactive molecular species of the chemical element and non-reactive molecular species of the chemical element. Samples from the second stream are also taken, but only after the stream is treated by being exposed to a sacrificial reactant to selectively remove the reactive molecular species. The sacrificial reactant may or may not be the same as the target material. The treated samples are then measured for the total content of the chemical element. The content of reactive molecular species in the liquid is then determined by subtracting the total content of the chemical element in the treated samples from the total content of the element in the non-treated samples. The determination of this difference can be done manually or automatically. If the determination is done automatically, the determination is typically performed by a processor integrated with the analyzer and the total amount of reactive molecular species in the liquid is provided as an output in the form of a screen display and/or printout to a local user in direct communication with the processor or a remote user communicating with the processor through an internet or intranet, or other data telemetry means.

The concept of measuring the quantity of a reactive molecular species of a chemical element in a liquid by selectively removing reactive molecular species from one or more samples and comparing the total quantity of element remaining therein to an untreated sample can also be applied off-line. The steps of the method essentially parallel the operation of the apparatus. One or more samples of the liquid are treated to selectively remove the reactive molecular species of interest. One or more samples of liquid are also untreated. The two sets of samples are then tested quantitatively by an analyzer for the total amount of the particular chemical element present. Again, the total content of reactive molecular species of the element in the liquid is determined by subtracting the total content of the chemical element in the treated samples from the total content of the chemical element in the non-treated samples.

5.3 On-Line Apparatus and Method

FIG. 1 provides an illustration of one embodiment of the configuration of the inventive apparatus in an on-line system. Other on-line configurations may be implemented that are within the spirit and scope of the invention. The apparatus 1 is positioned on-line in a distribution stream of a liquid at some point between upstream 10 and downstream 100. The apparatus 1 can be positioned at any point in the distribution stream and its specific placement depends on the requirements and characteristics of the specific distribution stream.

The liquid is supplied from upstream 10 by supply line 15, which leads to a flow splitting device 25 through supply line 20. Supply line 20 is typically an offshoot of a main line 15 of the distribution stream, and typically only a relatively small portion of the liquid flowing downstream in the main line 15 enters supply line 20. The arrows of the diagram indicate the direction of the flow of the liquid inside the lines. The flow splitting device 25 splits the flow from the supply line 20 into two separate streams in two separate lines 30 and 40 at a user selectable ratio. A portion of the stream in line 30 continues into line 35, while the remainder continues to a disposal point A. The configuration of the disposal points are not critically important and essentially receive spent or excess liquid not delivered to analyze 60 through selection device 55. The stream in line 40 is passed through a pre-treatment device 45 (alternatively referred to herein as a “trap”), and exit into stream 42. A portion of stream 42 continues into line 50 towards stream selection device 55, while the remainder continues on to disposal point A′. Spent or otherwise unneeded sample from pre-treatment device 45 may be disposed of through disposal point A′.

Analyzer 60 is positioned to receive a sample of the liquid from the stream in line 30 via line 35, or a sample of the liquid from the stream in line 42 via line 50, through a stream selection device 55 which, preferably, alternates in taking samples from the two streams. As one embodiment is for taking on-line measurements, it is contemplated that much of the liquid flowing in the distribution stream will not be analyzed by the analyzer 60, but merely continue to flow downstream through line 15. Spent sample from analyzer 60 is disposed of through disposal point A″.

In one embodiment, the apparatus is used to measure the amount of reactive molecular species of sulfur (i.e., “reactive sulfur species”) in gasoline towards silver. Silver is a material commonly used in automotive gas gauge components. In this embodiment gasoline is the liquid in supply line 15. The analyzer 60 measures the total sulfur content in the liquid from the stream in line 35 or the stream in line 50, as determined by the stream selection device 55. The preferred technique for analyzing the total sulfur content is monochromatic wavelength-dispersive X-ray fluorescence (“MWDXRF”) spectrometry, such as that described in ASTM D7039, which is hereby incorporated by reference. Other techniques can be used, however, including but not limited to ultra-violet fluorescence, chemiluminescence, and oxidative microcoulometry.

More specifically, in this embodiment, a sample of the gasoline flowing through supply line 20 is delivered untreated to the analyzer 60 via line splitter 25, lines 30 and 35 and stream selection device 55, and is tested for total sulfur content. The total sulfur content of this sample includes both reactive sulfur and non-reactive sulfur species; to the extent either type is present in the gasoline. An aliquot of the gasoline flowing in supply line 20 is also diverted to line 40 by the flow splitter 25. This aliquot is treated by the pre-treatment device 45, before being delivered and similarly tested for total sulfur content by the sulfur analyzer 60 via lines 40 and 50 and selection device 55. Thus, the analyzer 60 is alternately analyzing for total sulfur content of the untreated and treated liquid from streams in line 35 and line 50 in a sequential fashion. The duration of analysis for each stream, and the frequency of stream switching by stream selection device 55, is optimized for each application. The aliquot may be any volume so long as the volume is known. The pretreatment device 45, in this embodiment, is packed with material that will selectively scavenge, and thereby remove, the reactive sulfur species for silver from the liquid stream. The total content of the reactive sulfur species in the liquid is then obtained by calculating the difference between the measured total sulfur content in the non-treated sample and the treated sample.

The specific type of reactive sulfur in this embodiment will primarily be elemental sulfur and hydrogen sulfide, both of which are highly reactive with silver. However, other forms of reactive sulfur, such as carbonyl sulfide for example, may be present. In practice, the specific type of reactive sulfur species is not important to the analysis as any sulfur molecule that reacts with silver is being quantified.

The pre-treatment device 45 can be any device that removes reactive sulfur species for silver from the aliquot of gasoline. In one embodiment, the pre-treatment device 45 is a plug flow packed bed reactor containing a sacrificial reactant. The amount of sacrificial reactant employed will vary depending on the volume of gasoline to be treated before switching out used sacrificial reactant with a fresh supply. The reactive sulfur species present in the gasoline react or otherwise interact with the sacrificial reactant and are retained in the packed bed. The treated aliquot is then flushed from the bed and introduced to the total sulfur analyzer 60. The sulfur measurement of the treated sample consists of non-reactive sulfur species only as all of the reactive sulfur species in the aliquot were retained in the packed bed. The amount of reactive sulfur species in the gasoline stream is provided by the difference between the total sulfur measured in the treated and non-treated samples.

The aliquot that is treated by the pre-treatment device 45 remains in residence in the pre-treatment device 45 for a time (“residence time”) that is as long as necessary for all of the reactive sulfur species to react with the sacrificial reactant in the trap (and thereby be removed from the liquid). The exact amount of residence time necessary for all the reactive sulfur species to be retained will vary as the required time is dependent on a variety of factors. These factors include the temperature inside the pre-treatment device and the surface area of sacrificial reactant inside the trap relative to the amount of reactive sulfur in the aliquot.

For example, the sulfidation rate of the three principle reactive sulfur species for silver is dependent upon temperature and so increasing the temperature of the device 45 will speed up the reaction and reduce the time necessary for the aliquot to remain in residence. Preferably, the temperature of the device 45 is kept in the range of 40° C.-60° C., as a wide variety of low energy heaters and hot water sleeves can be used to maintain the temperature. Those skilled in the art will readily be able to approximate a residence time that will ensure that the sulfidation reaction is complete. In one embodiment the apparatus has a continuously flowing stream going through the fixed bed of the trap 45, where it has a residence time in the trap that allows all the reactive sulfur species to react. In another preferred embodiment, the device uses a static stopped flow approach, in which some fixed quantity of gasoline is diverted into the trap and held for some amount of time, and optionally heated, to allow the sulfidation reaction to go to completion. Optionally, sulfidation reaction completion can be determined inferentially by adding a known amount of reactive species into stream 20, and then varying the residence time and/or temperature such that the calculated reactive molecular species as obtained by this embodiment equals the known added amount.

It is important the sulfidation reaction be complete or the results of the analysis will be falsely low. In practice, it may be preferable to err on the side of allowing the aliquot to remain in the pre-treatment device 45 longer than may be necessary. There are no negative effects on the results, for example, by over exposing the aliquot to a sacrificial reactant in a pre-treatment device 45.

Any sacrificial reactant that reacts with, absorbs, adsorbs or otherwise removes silver reactive sulfur species may be used Examples of typical sacrificial reactants for silver reactive sulfur species include (i) metals such as silver, copper, brass, soft metal alloys and sodium that remove reactive sulfur species of various types and concentrations (e.g., H2S, COS, mercaptans, polysulfides), (ii) mole sieves or stripping gas that remove H2S, and (iii) liquid, solid or polymer supported reagents such as triphenyl phosphine that remove elemental sulfur. Any sacrificial reactant that selectively removes one or more types of silver reactive sulfur species, and preferably all silver reactive sulfur species, can be used. More generally, any substance may be used as a sacrificial reactant so long as the substance selectively reacts with, or otherwise retains, the particular molecular species that is being quantified.

In general, the preferred sacrificial reactant is identical or similar to the target material. Therefore, where, as here, the target material is silver, the preferred sacrificial reactant is a metal and the most preferred metal is silver. The sacrificial reactant can take any form—such as balls, mesh, foil, pellets, particles, etc . . . —that can be placed into the pretreatment device,

The exact configuration of the plug flow packed bed reactor is not critically important to the functioning of the apparatus so long as there is sufficient exposure so that all of the reactive sulfur species in the aliquot are retained. However, the amount of reactive sulfur species that can be removed at any given time is dependent upon the amount of sacrificial reactant surface area that is exposed. Accordingly, materials with higher exposed surface area (e.g., foils, balls, pellets, particles, etc.) are preferred. In one embodiment, silver spheres (like ball bearings or bee-bees) are used to pack the bed, but other materials such as silver wool or foil may be used. The use of ball bearings or other such pellets or coated beads with a precise geometry is preferred since it permits the determination of the surface area of the sacrificial silver reactant. Knowing the surface area of sacrificial reactant permits the determination of how much reactive species that bed can consume. In this way, the user can predict when the sacrificial reactant in the bed will need regenerating or replacing. Specifically, if the user knows the total capacity available in the bed to react and retain reactive sulfur species, and the user keeps track of the cumulative amount of reactive sulfur species that the bed has removed, then the user can determine when the bed needs to be replaced or regenerated. Alternatively, other strategies can be used such as a lead-guard system or a semi-batch type of a system to determine when the bed is in need of replacing or regenerating.

It is important that the sacrificial reactant maintain its ability to consume the desired reactive molecular species. Therefore, the sacrificial reactant must be periodically replaced or regenerated. For example, if the surface of silver sacrificial reactant in a bed is completely consumed, then the reactive sulfur species in the gasoline will not be retained in the bed, and the final total reactive sulfur species determination will be falsely low. The sacrificial reactant may be regenerated chemically, or electrochemically, or may simply be replaced with a new load of sacrificial reactant.

Although the apparatus has been discussed in detail with respect to removing silver reactive sulfur species from gasoline, the invention is not so limited. The apparatus can easily be adapted to measure molecular sulfur species that react with other materials, especially other metals. For example, copper corrosion from fuels is also of concern for some automotive applications and so the apparatus can be easily modified to test for sulfur species that react with copper. Naturally, in this instance, one preferred choice for the sacrificial reactant in the packed bed would comprise copper. Similarly, the presence of sulfur species that react with iron or steel can be tested and a preferred choice for the sacrificial reactant would comprise iron or steel, respectively. Basically, molecular sulfur species that are reactive with any metal may be detected using the inventive apparatus by, for example, using a metal that reacts similarly to, and preferably is or contains a metal that is identical to, the target metal, as a sacrificial reactant in the packed bed.

The invention is also not limited to measuring for reactive sulfur species. The method and apparatus of the invention may be applied to measuring any reactive molecular species using any pre-treatment device or technique that selectively removes that type of reactive molecular species. However, to analyze for a reactive molecular species other than reactive sulfur species, the analyzer 60 must be changed or adapted to be suitable for measuring the new element. For example, in one embodiment hydrofluoric acid content is the reactive species of interest. In this embodiment, the pre-treatment device 45 is packed with material that selectively removes hydrofluoric acid. The analyzer 60 used is then a total-fluoride analyzer. The content of hydrofluoric acid in the stream or batch is the difference between the fluoride content in an untreated sample and a treated sample.

Finally, the method and apparatus are not limited to use with any particular fluid. Although the method and apparatus are particularly well suited to on-line measurement of silver reactive sulfur species in ultra low sulfur gasoline and diesel fuel at sites that practice simultaneous blending and release (SBR), the method and apparatus may also be applied to analyzing for reactive species for other target materials in other liquids. The method and apparatus can be applied to any fluid, and especially any liquid petroleum or liquid petroleum product, in which the measurement of a total reactive species of a chemical element toward a defined target is sought.

The method and apparatus can be easily retrofit to work with existing analyzers, such as total sulfur analyzers, where they exist. In one embodiment the method and apparatus can be used to monitor and control reactive sulfur content in the fuel being manufactured, or to determine the amount of suitable corrosion inhibitor additives required based on the amount of reactive sulfur detected. The analyzer 60 can be interfaced with a computer with a program that automatically receives and compares the total content of the chemical element in each stream and calculates a difference that represents the content of reactive compounds in the liquid. Additionally the computer can be programmed to take certain corrective or other actions upon obtaining data outside of certain predefined limits.

5.4 Off Line and Alternative On Line Methods

In another embodiment, an off-line method for measuring reactive species (e.g., reactive sulfur species) for a target material (e.g., silver) is provided. In the method the flow-splitting device, pre-treatment device and analyzer are not necessarily incorporated into an on-line apparatus. Referring to FIG. 2, the core tenets of the on line concept are applied off line to a static batch 115 or group of batches of gasoline or some other test sample liquid. In this off line method an untreated sample 130 from the batch 115 is tested for the total content of a chemical element (e.g., total sulfur content) in an analyzer 60. Because it is a static batch, a flow splitter 25 is not necessary. Instead, a second sample 140 is drawn from the same batch 115 and exposed to a pre-treatment device 45 for a time and at a temperature sufficient to react all the reactive species (e.g., silver reactive sulfur species) with the sacrificial reactant (e.g., silver) in the pre-treatment device 45—thereby removing the reactive species only from the sample. The second sample 140 is subsequently tested for the total content of the element (e.g., the total sulfur content) in analyzer 60. The amount of reactive species of the element in the sample is then determined by subtracting the element content in the treated sample from the element content in the untreated example. Alternatively, the method can be applied to an on-line situation where instead of a flow splitter 25, separate samples are simply siphoned off by a valve or other means.

As with the apparatus, the method of the present invention may be applied to measure a variety of reactive species in addition to reactive sulfur simply by changing the nature of the sacrificial reactant in the pretreatment device 45 and/or changing the analyzer 60. Similarly, a variety of sacrificial reactants in addition to silver can be utilized and a variety of fluids beyond gasoline may be tested, such as those previously discussed.

5.5 Measurement Sensitivity

When the reaction in the pre-treatment device 45 goes to completion, the sensitivity and precision of the method and apparatus of the present invention are a function only of the limits of the analyzer 60. Therefore, the results of a single test on a single treated aliquot may or may not provide sufficient information for a particular purpose. Various analytical methodologies can be implemented to obtain data that will allow the user to draw a useful conclusion for a particular application. For example, a single aliquot can be subjected to multiple analyses by the analyzer 60 to obtain a data set, and then one or more various statistical treatments (such as a one-sample t-test, analysis of variance) can be applied to the data set to increase the detection power of the apparatus. Alternatively, multiple aliquots can be treated in the pre-treatment device 45 over a given period of time and each aliquot analyzed one or more times to obtain a data set, which can then be subjected to various statistical treatments including times series analysis to ascertain the behavior of the supply line reactive sulfur species over time. Additionally a quality control material containing a known amount of reactive species may be used to validate the performance of an apparatus using classical statistical quality control charting techniques such as those described in ASTM D6299.

5.6 On-Line Versus Off-Line

The apparatus can be placed anywhere on-line where the measurement of a reactive species is desired. In practice, where repeated measurements over time are desired at a specific location in a distribution stream, it may be preferable to set up the apparatus on-line. In the instance where only a single measurement is desired, it may be preferable to apply the method to a sample from the distribution stream without specifically incorporating the apparatus on-line. In such an instance, samples can be drawn or siphoned from the distribution stream and analyzed by the method of the invention without fitting the distribution stream with an on-line apparatus. On-line systems are typically deployed at: a) manufacturing site such as gasoline or diesel fuel blenders at the refineries; b) where blending of fuel occurs (e.g. terminals); and/or c) transportation conveyances such as pipeline receipt and discharge locations.

5.7 Closing

There will be various modifications, adjustments, and applications of the disclosed invention that will be apparent to those of skill in the art, and the present application is intended to cover such embodiments. Although the present invention has been described in the context of certain preferred embodiments, it is intended that the full scope of these be measured by reference to the scope of the following claims.

The disclosures of various publications, patents and patent applications that are cited herein are incorporated by reference in their entireties.