Published on January 23, 2008
Total Sulfur and Speciated Halides (Fluorine, Chlorine, Bromine) in Liquid and Gaseous Hydrocarbons by Combustion Ion Chromatography : Total Sulfur and Speciated Halides (Fluorine, Chlorine, Bromine) in Liquid and Gaseous Hydrocarbons by Combustion Ion Chromatography Mark Manahan - Cosa Instruments, Norwood, NJ Kirk Chassaniol – Dionex Corporation, Houston, TX Presented by: Introduction: Introduction The measurement of total fluoride, chloride and sulfur have historically been important parameters in the refinery process. The concentration of both inorganic and organic chlorine and sulfur compounds are routinely measured throughout the entire refinery, from the initial crude feeds to intermediate feedstock's to final products. Introduction: Introduction Total chloride and sulfur are well documented and known poisons of the many catalysts used for the wide variety of applications in the petroleum industry Catalysts based on nickel, copper and palladium are very susceptible to rapid deactivation by chloride ions The lowering of sulfur levels by the EPA for diesel and gasoline has occupied the majority of refineries process engineers attention. Concerns for measuring chloride levels to prevent both the poisoning of new, expensive catalysts and to minimize corrosion has recently gained renewed interest in measuring fluoride and chlorides. Introduction: Introduction Total fluoride, chloride and sulfur all contribute to corrosion problems in today’s refineries The total cost of corrosion control in the USA in 2000 was estimated to be 3.692 billion with: $1.767 billion - for maintenance-related expenses $1.425 billion - for vessel turnaround expenses $0.500 billion - for fouling costs The costs associated with corrosion control in refineries include both petroleum processing and water handling. Flowchart of a typical refining process: Flowchart of a typical refining process Sources of Chloride : Sources of Chloride Crude feedstock Non-extractable (Organic) chlorides are not naturally occurring in crude oil. Crude oils can become contaminated with non-extractable chlorides in a number of ways: From chemicals used in enhanced oil recovery processes From chlorinated solvents used in crude oil production, transportation and storage (though use of these solvents for down hole paraffin control is no longer permitted) From chlorinated additives used in production, transportation and storage (possibilities include wax crystal modifiers, biocides, corrosion inhibitors, flocculation additives, emulsion breakers) Sources of Chloride: Sources of Chloride Crude feedstock (Continued) From unmonitored disposal of various chlorinated compounds into crude oil storage tanks, pipelines, or refinery slop systems From leaded gasoline (organic lead additives contain 2 moles chloride plus 2 moles of bromide per mole of lead) that is recycled into crude oil or slop Asphaltene-chloride salts (salts of basic functions on asphaltenes with HCl) Oil-coated inorganic salt crystals Extractable (In-Organic) Chlorides Predominantly from calcium and magnesium chlorides which hydrolyze and form HCl during the desalting process Sources of Chloride: Sources of Chloride Typical Crude Concentrations Most crudes contain 0.2-2.0 ppm organic chlorides An east coast refinery developed a list of crude oils containing organic chloride concentrations in the range of 30-50 ppm 20-50 ppm organic chlorides were found in Orient crude 30-50 ppm organic chlorides were found in North Slope crude Concentrations as high as 2000 ppm have been reported Sources of Chloride: Sources of Chloride Problems Caused by Non-extractable Chlorides High caustic consumption to control atmospheric column overhead chloride levels (when organic chlorides hydrolyze in the atmospheric heater) Preheat fouling problems from caustic overfeed while processing high organic chloride crude oils Higher levels of chloride in overhead systems (assuming caustic addition is unable to maintain levels), causing increased neutralizer demand and potentially higher rates of corrosion. High levels of chlorides in naphtha and distillate hydrotreater feed stocks (when organic chlorides distil), causing fouling and corrosion problems in the reactor effluent system Sources of Chloride: Sources of Chloride Introduction of Organic Chloride to Reformer Catalysts Organic chloride used for dosing reformer catalyst breaks down to HCl. The chloride is not irreversibly bonded to the catalyst surface and therefore needs continuous dosing. Eventually, chloride is inevitably found in the product streams leaving the catalytic reforming reactors at low ppm levels. These chloride species are known to cause a number of problems in the separation section of the catalytic reformer and in downstream equipment and units. Examples of the problems include ammonium chloride formation and deposition, corrosion, poisoning of downstream catalysts and product specification issues. Sources of Chloride: Sources of Chloride By-product formation in Guard Beds To remove inorganic chlorides, alumina guard beds have been routinely used in refineries A secondary reaction of HCl with organics form organic chlorides n the guard beds which tend not to be removed and slip from the bed contaminating the product downstream. The acidic surface of the guard columns also offers the possibility of acid-catalyzed polymerization of the unsaturated organic chlorides, thus creating higher molecular weight chains on the alumina surface. These condensation/polymerization reactions can occur repeatedly and build up a high molecular weight hydrocarbons commonly referred to as “green oil” and will cause fouling, blocking of equipment and seepage through valve flanges. green oil can also foul the absorbent bed itself. Common Perception: Common Perception Until a few years ago, a prevalent view was that the chloride was predominantly HCl or that the problems experienced were dominated by the HCl component of the chlorides. One factor in this may have been the relative difficulty in accurately detecting organic chloride compounds at the low levels (0.5 - 5 ppm) that are present. Comparatively, HCl is easier to measure and may have been detected more reliably. Sampling of Current ASTM Methods for Fluoride, Chloride and Sulfur Analysis: Sampling of Current ASTM Methods for Fluoride, Chloride and Sulfur Analysis Need for reliable method: Need for reliable method The review of the available methods and their scope revealed a need for a reliable technique to measure Fluoride and Chloride at or below 1 ppm. Presently, the only ASTM methods for chloride uses microcoulometry. Difficulties with microcoulometry regarding cell stability, cumbersome maintenance and robustness of the method is well know in the industry. In addition, at this time there is no ASTM method for the measurement of fluoride in petrochemical products. ASTM D5453 is routinely used for total sulfur but it’s scope is limited to 1 ppm ASTM D6290 recent scope also does not go below 1ppm as It is obvious there is a need for an automated method which can measure all three elements simultaneously. The new technique of combustion Ion Chromatography was therefore developed Combustion IC Flow Diagram: Combustion IC Flow Diagram DIA AQF/GA-100 & the Dionex ICS90 Ion Chromatogaph): DIA AQF/GA-100 & the Dionex ICS90 Ion Chromatogaph) Ion Chromatograph Furnace & Absorption Unit Parameters: Furnace & Absorption Unit Parameters Operating Parameters Furnace temperature; 1000 oC Ar flow; 200 mL/min O2 flow; 500mL/min Absorbing solution - water / 10ppm H2O2/ 0.5 ppm P (as PO4) AQF/GA-100 Combustion IC System: AQF-100 Furnace, GA-100 Absorption Unit, Automatic Boat Controller & Solid/Liquid Autosampler Configuration of the Reagent Free™ IC System.: Configuration of the Reagent Free™ IC System. DX-320 with EG40 AS11HC (4x250mm) Eluent: 25mM KOH @ 1.3 mL/min ASRS-Ultra 100mA Recycle 200uL sample loop PeakNet 6.4 Calibrated with 0.5 to 5 ppm solutions F, Cl, Br & Sulfur Internal standard 0.5 ppm P as PO4 Why Use Reagent Free IC: Why Use Reagent Free IC Fluoride is an important analyte – Minimal Water Dip Consistent - Auto eluent generation provides extremely low baseline and significantly improves performance Technician Independent - Composition and concentration of the eluent mobile phase is independent of operator Ease to use -Just add water! Tradition Calibration Overview: Tradition Calibration Overview Traditional Calibration Procedure Prepare a series of standards to cover the calibration range of samples Solvent Blank, 0.5ppm, 1.0 ppm, 2.5 ppm & 5 ppm Standards Analyze the standards to generate the calibration curve by combusting the standards through the combustion IC (20 – 240 ul of sample) Analyze unknown samples in the same manner as the standards Organic Standards Used: Organic Standards Used For S: Dibenzothiophene For F: Fluorobenzoic Acid For Br: Bromoacetanilide For Cl: 1,3,5 Trichlorophenol All standards were prepared in iso-octane Traditional Calibration Curve for Fluoride: Traditional Calibration Curve for Fluoride Traditional Calibration Curve for Chloride: Traditional Calibration Curve for Chloride Traditional Calibration Curve for Bromide: Traditional Calibration Curve for Bromide Traditional Calibration Curve for Sulfur: Traditional Calibration Curve for Sulfur Precision and Recovery Data: Precision and Recovery Data Comparison CIC vs. ASTM Methods on Low Level Sulfur Round Robin Samples: Comparison CIC vs. ASTM Methods on Low Level Sulfur Round Robin Samples All Samples Concentrations in ppm wt./vol Iso-Octane Blank: Iso-Octane Blank 0.0 2.0 4.0 6.0 8.0 10.0 12.0 13.5 -0.50 1.00 2.00 3.00 4.00 µS min Fluoride Chloride Sulfate Phosphate 80 ul sample size / iso-octane 1.0 ppm Standard run: 1.0 ppm Standard run 0.0 2.0 4.0 6.0 8.0 10.0 13.0 -0.50 1.00 2.00 3.00 4.00 5.00 6.00 µS min Fluoride Chloride Sulfate Phosphate 80 ul sample size / iso-octane Repeatability and Stability (Drift) Study: Repeatability and Stability (Drift) Study - 3 + 3 Ave Ave 51.586 SD 0.840 %RSD 1.629 80 ul sample size / iso-octane MDL Study by USEPA Method 40 CFR, Part 136, Appendix B : MDL Study by USEPA Method 40 CFR, Part 136, Appendix B 0.96 ppm Standard n = 8 t-value = 2.998 2.34 ppm Standard n = 8 t-value = 2.998 MDL = SD x t-value Observations & Conclusions: Observations & Conclusions Difficulties with Traditional Direct Calibration Procedure For samples below 1.0 ppm, many solvents routinely used for the preparation of standards have concentrations, especially for chloride which are 10-20% of the lowest standards value, typically 0.1 – 0.3 ppm The desire to measure ACCURATELY and with HIGH PRECISION at values under 0.5 ppm necessitated a new approach. In-Direct Calibration of CIC: In-Direct Calibration of CIC Logic of In-direct Calibration Procedure The final concentrations injected into the IC for samples under 1.0 ppm range from 5 to 50 ppb for a 240 ul sample Aqueous IC standards and can easily and accurately prepared in this range Therefore, the calibration of the IC as a detector is performed by generating calibration curves with aqueous IC standards in this range ~ DI Blank, 25 ppb, 50 ppb & 100 ppb In-Direct Calibration of CIC: In-Direct Calibration of CIC Logic of In-direct Calibration Procedure (Continued) The system or matrix blank is calculated using the same volume as the samples to determine the value in ppm The system blank is subtracted from samples and the concentration of sub-ppm samples is measured. New Approach to Calibration CIC: New Approach to Calibration CIC New Approach to Calibration CIC: New Approach to Calibration CIC New Approach to Calibration CIC: New Approach to Calibration CIC New Approach to Calibration CIC: New Approach to Calibration CIC New Approach to Calibration CIC: New Approach to Calibration CIC CIC Analysis on Hydrocarbons: CIC Analysis on Hydrocarbons CIC Analysis on Hydrocarbons: CIC Analysis on Hydrocarbons Conclusions: Conclusions The Combustion IC Technique is capable of determining halogens and sulfur levels from % levels down to 0.200 ppm by traditional Direct Calibration Technique. The Combustion IC Technique is capable of determining halogens and sulfur levels down to 50 ppb by In-direct Calibration Technique with %RSD under 25%!
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