Presentation Transcript

1. Determination of Short-Chain Branching Distribution of Polyethylene via IR5-GPC

   Youlu Yu* and Paul J. DesLauriers Chevron Phillips Chemical Company LP Bartlesville Research & Technology Center Bartlesville, Oklahoma 74006 February 27 – March 2, 2011 International Polyolefins Conference 2011 Hilton Houston North, Houston, Texas
2. Outline Introduction Instrumentation Methodology Data handling/processing Calibration Error analysis Practical Aspects Comparison with Other Techniques Conclusions
3. Conventional Techniques for PE SCB Distributional Determination SGF-NMR Classic method SGF Fractionation + NMR Off-line technique Tedious & labor intensive Limited resolution Large quantity of solvent/waste On-line SEC-FTIR Pioneered by DesLauriers et al. (DesLauriers, Rohlfing, Hsieh, 2002, Polymer, 43, 159) On-line technique Fast turn-around Chemometrics for data analysis Liquid nitrogen needed Batch mode
4. SGF-NMR vs. Online SEC-FTIR SGF-NMR takes days of operation for one sample SEC-FTIR takes hours of operation for one sample DesLauriers, Rohlfing, Hsieh, Polymer, 43, 2002, 159
5. Desired Improvements in Online SCB Determination Technique With today’s PE business environment where safer, faster, and cheaper operations are required, there are still rooms for improvements with the Online SEC-FTIR SCB determination technique in the following areas: Eliminating liquid nitrogen usage Less human intervention Less system upsets Easier operation System suitable for continuous operations Reduced human intervention Improved productivity Easy/straight forward data processing
6. IR5 Detector Manufactured by Polymer Characterization, S.A. Spain (J. Montesinos, R. Tarin, A. Ortin, B. Monrabal, 1stInternantional Conference of Polyolefins Characterization, 2006, Houston) A fixed-band IR spectrometer with five optical filters for detection of adsorbance in five different mid-IR bands Thermoelectrically-cooled MCT detector Advanced optics to achieve high energy throughput High temperature capability Specifically designed for polyolefins characterization Minimal mixing in cell (cell volume 11.3 uL) No liquid N2 needed Suitable for continuous GPC and high-throughput GPC applications
7. Waste IR5-GPC Instrumentation Computer A Computer B Solvent Reservoir Data Box Pump Injector Columns IR5
8. SCB Calibration and Calculation SCB calculation based on intensity ratios Two intensity ratios tested: ICH3/ICH2 and ICH3/Iall C-H Chain-end effect correction based on polymer chemistry (# CE/molecule) Calibration curve (i.e. intensity ratio as a function of SCB content) needed Polymers of known SCB contents and with flat SCB distribution employed Data points influenced by chain-end effect excluded from the calibration MW/MWD determined by the relative method using the integral calibration method and broad MWD PE standard Both the “compensate” and “un-compensate” modes explored All data processing performed using in-house developed software
9. SCB Calibration and Calculation (E/H Copolymers)
10. Error Analysis Uncertainty defined by signal to noise ratio (S/N)
11. Simulated SCB Error Map 28% 5% Detection limit @ 0.5 – 1 SCB/1,000 TC if CH2 S/N at 2,000 – 3,000
12. SCB Distributional Profile via IR5-GPC(4 columns; flowrate=1.0 mL/min; conc. =1.5 mg/mL; injvol=400 uL) Error bars significantly larger at the two ends where S/N poorer
13. Reducing Determination Uncertainty Minimize low-frequency noise Stable power voltage Good environmental control Room temperature affecting results significantly Increase signal intensity Increase sample concentration Increase injection volume Increase flow rate Reduce number of columns  Increase injection volume Increase flow rate Reduce number of columns
14. Concentration Effect Separation efficiency and signal S/N trade-off Too high a polymer concentration causing MWD and SCBD distortion
15. PracticalAspects Environment control Both detection accuracy and precision affected by environment temperature Chain ends effect Imperfect separation at the low MW end causing significant errors in SCB contents
16. Comparison with NMR IR5-GPC results generally in very good agreement with NMR results Calibration less accommodating to branching types than Chemometrics
17. Comparison with SEC-FTIR IR5-GPC 4 columns; 1.0 mL/min; 0.4 mL; 1.5 mg/mL SEC-FTIR 2 columns; 1.0 mL/min, 0.5 mL; 2.0 mg/mL IR5-GPC results in very good agreement with SEC-FTIR
18. Conclusions IR5-GPC a robust SCB distribution determination technique No liquid N2 needed Continuous process No human intervention between samples Easy operation and simple data processing SCB precision determined by IR5 signal S/N ICH3/ICH2 gives better results GPC column fractionation efficiency and SCB precision trade off Too high a polymer concentration can cause MWD and SCBD distortion No significant difference found between the “compensate” mode and the “un-compensate” mode Results in good agreement with NMR and SEC-FTIR SCB at LMW end significantly affected by column separation efficiency and the presence of impurity/contamination Maintaining stable instrument environment essential for data accuracy and precision