Analysis and Chromatographic Separation of Oxygenates in Hydrocarbon Matrices

Transcription

1 Analysis and Chromatographic Separation of Oxygenates in Hydrocarbon Matrices GC Application Chemist March 3rd, 2008 Pittcon 2008, New Orleans, LA

2 Presentation Outline WCOT vs. PLOT columns OxyPLOT A highly selective phase for oxygenates Proposed ASTM methods Trace oxygenates in reformulated gasoline Oxygenates in C1-C5 hydrocarbon matrices Applications beyond oxygenates Summary Take away message acknowledgements

3 WCOT vs. PLOT Type Stationary Phase Chromatographic Process Stationary Phases WCOT Liquid or gum Gas / Liquid partition Polysiloxanes PEG PLOT Solid Gas solid adsorption Porous Polymers, Al 2 O 3, Zeolites, etc.

4 WCOT Ethylene Analysis

5 PLOT Ethylene Analysis

6 Capillary Column Types Porous Layer Layer Open Open Tube Tubular (PLOT) Carrier Gas Solid Particles Wall Coated Open Tube (WCOT) Carrier Gas Liquid Phase

7 PLOT Columns "Solid" Porous Layer Fused Silica Tubing Ideal for the analysis of gases due to their increased retention (k) and unique selectivity (α) compared to WCOT

8 Surface Interactions in PLOT Columns Gas Flow δ - δ- δ + neutral δ Vapor pressure always plays a leading role in solute interactions

9 Considerations for PLOT Column Analysis Inlet issues split versus direct injection gas sampling valves low dead volume Detector issues particle generation or spiking ; particle traps column ID and flow rate

10 Considerations for PLOT Column Analysis Column issues selectivity capacity; overloaded peaks inertness temperature limits Elution order of major peak Column contamination efficiency loss; ghost peaks ; increase in bleed water, CO 2, high molecular weight hydrocarbons? Carrier gas purifiers

11 Oxygenates Applications Petrochemical and Chemical companies have a need to quantitatively measure low level oxygenates in petroleum products Gas Oil Fields Shipping Ctrs Crude Oil Refineries Light HCs Gas Jet Fuel Diesel Fuel Oil Distribution Centers Diesel Fuel Oil

12 Need for Low Level Analyses Petrochemical and Chemical companies have a need to quantitatively measure low level oxygenates in petroleum products Gas Oil Fields Shipping Ctrs Crude Oil Refineries Light HCs Gas Jet Fuel Diesel Fuel Oil The need to measure trace oxygenates from 10 to 1000 ppm in Gasoline Distribution Centers Diesel Fuel Oil Problems with MTBE in reformulated gasoline MTBE causing groundwater contamination Desire to use ethanol as a renewable, green fuel additive

13 Oxygenates in Gasoline and Naphtha Why are these measurements needed Oxygenated additives in reformulated gasoline Needed for clean air regulations and petroleum fuel extenders Problems with groundwater contamination Ethers in gasoline (MTBE, ETBE, TAME) in underground tanks Greater toxicity than alcohol additives Move toward biofuels Fuels derived from renewable agricultural products Ethanol from fermentation of biomass Lower toxicity than other alcohols Improve quality of feedstocks Gasoline and naphtha used as feedstock for other HPI products Traces of oxygenates poison catalyst lower production yields lower product quality

14 Traditional Oxygenates Methods ASTM D4815 Valve based using TCEP packed/ DB-1 capillary column Used to measure oxygenated additives (0.1 wt% to 15 wt%) ASTM study shows that D4815 has interference problems TCEP column cannot separate trace oxygenates from trace olefins ASTM D5599 Single column method using oxygen selective detector (OFID) Expensive system that is dedicated to only one application Selectivity and sensitivity may not be good enough for low ppm

15 New Method Under Development by ASTM D2 Method Scope Trace oxygenates in finished gasoline from 10 ppm to 1000 ppm (wt/wt) Oxygenates include: methanol, n-propanol, i-propanol, n-butanol, s-butanol, t-butanol, s-butanol, t-pentanol MTBE, ETBE, DIPE, TAME Ethanol additive from 1 to 15 wt% Internal standard: 1,2-dimethoxyethane (DME) Other capabilities can measure other oxygenate contaminants ketones and other alcohols and ethers can be used for naphthas sensitivity range can be lowered to 1 ppm with no changes in method conditions

16 New Proposed ASTM Method Instrumentation Configuration Uses valve switching 2-D GC DB-1 column separates oxygenates/light hydrocarbons from heavy hydrocarbons Agilent GS-OxyPLOT column separates light hydrocarbons from oxygenates

17 Proposed ASTM Methods Uses 2-D GC with Oxygenate Selective PLOT column Vent 4 1. Sample introduction of gasoline onto DB-1 pre-column. Flow Source S/SL DB-1 30m x 0.53mmid x 5um GS-OxyPLOT 10m x 0.53mmid FID Aux EPC Vent Flow Source S/SL DB-1 30m x 0.53mmid x 5um Oxygenates and light hydrocarbons transfer to GS-OxyPlot. Heavy hydrocarbons remain on DB-1 precolumn. GS-OxyPLOT 10m x 0.53mmid FID Aux EPC Vent 3. Heavy hydrocarbons vented from DB-1 pre-column. Oxygenates resolved on GS-OxyPlot column. Flow Source S/SL DB-1 30m x 0.53mmid x 5um GS-OxyPLOT 10m x 0.53mmid FID Aux EPC

18 What Is GS-OxyPLOT? A 10 m x 0.53 mm I.D., 10 µm film thickness, Porous Layer Open Tubular (PLOT) Capillary Column. Agilent p/n The stationary phase is a proprietary salt based adsorbent. Key characteristics are: Strong selectivity to oxygenated hydrocarbons. Methanol (BP 65 C) elutes after Tetradecane (BP 254 C) Solute RI* MTBE 1236 Iso- Butylaldehyde 1368 Methanol 1418 Acetone 1450 *150 C Upper temperature limit 350 C with no column bleed Stabilized phase coating, minimizing particle generation and detector spiking

19 GS-Oxy-PLOT Electronic Selective Interactions Distinct Advantages Adsorption interactions are much stronger than the polar/nonpolar interactions in liquid stationary phases. Oxygenated hydrocarbons, un-retained in a WCOT column even at sub-ambient temperatures can exhibit high retention in a PLOT column at GC oven temperatures above ambient Non-polar solutes are essentially un-retained except for their vapor pressure interaction at a given oven temperature. Ideal column for selective solute-value cut applications Column phase is surprisingly inert to the polar compounds it so strongly interacts with. Good for low concentration, quantitative GC analysis

20 GS-OxyPLOT Column Separation of Trace Oxygenates and Ethanol Additive in Reformulated Gasoline Light Hydrocarbons Ethanol Ethers Methanol C3 to C5 Alcohols min. ETBE MTBE DIPE TAME MeOH i,n-propanol t,s,i-butanol n-butanol t-pentanol 1,2-DME(IS) min min

21 Ethanol Influenced Retention Time Shifts 12 wt% ethanol 1 wt% ethanol min. ETBE MTBE DIPE TAME MeOH min

22 Excellent Quantitative Precision High Concentration QA/QC Check Sample Expected Avg Std Dev RSD (ppm)* (ppm)* (ppm)* ETBE % MTBE % DIPE % TAME % Methanol % Ethanol* 12.0% 11.3% % i,n-propanol % t,s,i-butanol % n-butanol % t-pentanol % Low Concentration QA/QC Check Sample Expected Avg Std Dev RSD (ppm)* (ppm)* (ppm)* ETBE % MTBE % DIPE % TAME % Methanol % Ethanol* 1.0% 0.9% % i,n-propanol % t,s,i-butanol % n-butanol % t-pentanol % *ethanol results are in wt% Each QA/QC sample prepared in reformulated gasoline Five consecutive runs of each sample

23 New Method Under Development by ASTM D2 for Analysis of Oxygenates in Ethene, Propene, C4 and C5 Hydrocarbon Matrices Method Scope Oxygenates in these light hydrocarbon matrices from 500 ppb to 100 ppm (wt/wt) Oxygenates include 25 alcohols, ketones, aldehydes and ethers (e.g.): methanol, ethanol, n-propanol, n-butanol, s-butanol, t-butanol, s-butanol DME, MTBE, DIPE, TAME Acetone, acetaldehyde Liquid Sample Gas Sample Similar in principle to the oxygenates in gasoline method 2 µl 1 ml Fused Silica Restrictor DB-1 25 m X 0.53mm I.D., 1.0 µm GS-OxyPLOT 10 m X 0.53mm I.D., 10 µm

24 Hydrocarbons and Oxygenates Separation using DB-1 Stripper Column and GS-OxyPLOT Separation Column Benzene Isooctane Column 1: DB1, 25 m x 0.53 mm x 1 um 1. Dimethyl ether P/N J 2. Diethyl ether Column 2: GS-Oxy-PLOT, 10 m x 0.53 mm 3. Acetaldehyde P/N Ethyl t-butyl ether Carrier gas: Helium, C Injection volume: 1 ul 5. Methyl t-butyl ether Inlet: Split, Diisopropyl ether Temperature: 225 o C 7. Propionaldehyde Split Ratio: 10:1 Column flow: 11 ml/min 8. Tert-amyl methyl ether 9. Propyl ether Isobutylaldehyde n-octane Butylaldehyde 12. Methanol 21,22, Backflush occurs here Acetone 14. Isovaleraldehyde 15. Valeraldehyde 16. MEK 17. Ethanol Propanol 19. Isopropyl Alcohol 20. Allyl Alcohol 21. Isobutyl Alcohol 22. t-butyl Alcohol 23. s-butyl Alcohol 24. n-butyl Alcohol Methyl-2-pentanol Oven Initial temp 50 o C Initial hold 5 min Ramp rate: 10 o C/min Final temp 240 o C

25 GS-OxyPLOT and ASTM A New Proposed ASTM Method for Trace Oxygenates in Reformulated Gasoline designed to measure 10 to 1000 ppm oxygenates in gasoline with 1 to 15 wt% ethanol additive Agilent 7890A GC System with GS-OxyPlot Column meets method requirements excellent separation of oxygenates from light hydrocarbons resolves all ethers (ETBE, MTBE, DIPE, and TAME) high quantitative precision for both high and low concentrations in the presence of percent ethanol A New Proposed ASTM Method for Trace Oxygenates in Light Hydrocarbon Matrices designed to measure 500 ppb to 100 ppm oxygenates in matrices with BPts less than 200 C

26 Is GS-OxyPLOT also Selective for Sulfur Species? Oxygen and Sulfur same group on periodic chart Similar chemistries Some sulfur species added deliberately to gaseous fuels Both are found in hydrocarbon fuels and feed stocks Sulfur species and oxygenates levels need to be controlled

27 GS-OxyPLOT C5-16 Carbon Ladder/Spectrum Mix Comparison Norm. FID1 B, (021508A\021508A \002B0302.D) min Norm. FID1 B, (021908B\021908B \013B0402.D) min

28 Spectrum Mix GS-OxyPLOT GC: Agilent 6890 Oven: 60% (0.5 min),10% C/min to 120, then 25% C/min to 310% (3min) Injection: 1 µl 25:1 split 250%C, gas saver on at 2 min Carrier: He 30 cm/sec at 60%C constant flow mode Column: GS-OxyPLOT 10 m x 0.53mm x 10 µm Detection: FID 350%C H2 40 ml/min, air 450 ml/min N2 makeup 30 ml/min Norm. FID1 B, (021908B\021908B \013B0402.D) min

29 DB-1 C5-16 Carbon Ladder/Spectrum Mix Comparison pa FID1 A, Front Signal (021508A\021508A \002F0302.D) min pa 24 FID1 A, Front Signal (021908A\021908A \011F0202.D) min

30 DB-1 Spectrum Mix GC: Agilent 7890 Oven: 60% (0.5 min),10% C/min to 120, then 25% C/min to 310% (3min) Injection: 1 µl 25:1 split 250%C, gas saver on at 2 min Carrier: He 30 cm/sec at 60%C constant flow mode Column: DB-1 30 m x 0.25mm x 1.0 µm Detection: FID 350%C H2 40 ml/min, air 450 ml/min N2 makeup 30 ml/min pa FID1 A, Front Signal (021908A\021908A \011F0202.D) min

31 Observed Retention Times on DB-1 and GS- OxyPLOT for C5-C16 alkanes and sulfur species Compound Ret. Time Ret. Time DB-1 OxyPLOT n-pentane n-hexane n-heptane trimethyl pentane n-octane n-nonane n-decane n-undecane n-dodecane n-tridecane n-tetradecane n-pentadecane n-hexadecane toluene Alkanes less retained BP Coumpound Ret. Time Ret. Time BP DB-1 OxyPLOT 1-propanethiol ethyl methyl sulfide methyl thiophene methyl thiophene ethyl disulfide methyl disulfide thianaphthene thiophene ,3,4 trimethyl benzo thiophene ,3,6 trimethyl benzo thiophene ,5,7 trimethyl benzo thiophene Sulfur species more retained

32 Interesting Observations Sulfur species are retained on GS-OxyPLOT high selectivity for some sulfur species more relative retention for lower boiling sulfur species vs. methyl silicone column shift in retention may be useful for shifting sulfur species away from hydrocarbon interferences preliminary results are encouraging

33 Spectrum Mix Composition Speturm Mix Composition methanaethiol ethanethiol dimethyl suldide 1-propanethiol 1-butanethiol 2-propanethiol thiophene diethyl suflide t-butanethiol diethyl disuflide thiophenol bromothiophene phenyl sulfide benzothiophene Level 98.4 ppm 99.3 ppm 99.6 ppm 88.9 ppm 100 ppm 101 ppm 99.9 ppm 100 ppm 100 ppm 100 ppm 100 ppm 101 ppm 100 ppm 99.7 ppm Next steps Follow up on initial study Look at gaseous sulfurs Evaluate using FPD Evaluate dual column approach similar to oxygenates Base Fuel Components isootane 40% 40% hexane 40% 40% toluene 20 % 20%

34 Summary Attributes of a PLOT Column GS-OxyPLOT s characteristics Proposed ASTM methods for oxygenates Reformulated gasoline C1-C5 hydrocarbon matrices GS-OxyPLOT highly selective for oxygenates and indications are for sulfur species

35 Colleague Acknowledgements Abby Folk Simon Jones John J. Harland James D. McCurry Mark Sinnot Bruce Quimby Allen K. Vickers

36 Thank you! TECHNICAL SUPPORT Agilent #4, #1