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Determination of Short-Chain Branching Distribution of Polyethylene via IR5-GPC Youlu Yu* and Paul J. DesLauriers Chevron Phillips Chemical Company LP.

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Presentation on theme: "Determination of Short-Chain Branching Distribution of Polyethylene via IR5-GPC Youlu Yu* and Paul J. DesLauriers Chevron Phillips Chemical Company LP."— 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 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 DesLauriers, Rohlfing, Hsieh, Polymer, 43, 2002, 159 SGF-NMR takes days of operation for one sample SEC-FTIR takes hours of operation for one sample

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, 1 st Internantional 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 N 2 needed  Suitable for continuous GPC and high-throughput GPC applications

7 IR5-GPC Instrumentation IR5PumpColumnsInjector Solvent Reservoir Waste Computer AComputer B Data Box

8 SCB Calibration and Calculation  SCB calculation based on intensity ratios –Two intensity ratios tested: I CH3 /I CH2 and I CH3 /I all 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 0.5 – 1 SCB/1,000 TC if CH 2 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; inj vol=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 Practical Aspects  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 N 2 needed –Continuous process No human intervention between samples –Easy operation and simple data processing  SCB precision determined by IR5 signal S/N –I CH3 /I CH2 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


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