UOP 997-2013 Hydrogen Content of Hydrocarbons by Low-Resolution Pulsed Nuclear Magnetic Resonance Spectrometry.pdf

1、 IT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TO DETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH AND SAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS PROCEDURE IN THE MANNER PRESCRIB

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4、 PHONE. Hydrogen Content of Hydrocarbons by Low-Resolution Pulsed Nuclear Magnetic Resonance Spectrometry UOP Method 997-13 Scope This method is for determining the hydrogen content of light and middle distillates boiling in the range of approximately 15C to 350C on an as received basis, and hydroca

5、rbons boiling above 350C by dilution, using low resolution pulsed nuclear magnetic resonance (NMR). The range of quantitation is from 9.5 to 15.4 mass-% hydrogen. The concentration limits of the method may be extended if appropriate pure compounds are obtained as reference standards. Outline of Meth

6、od A sample is analyzed in a pulsed NMR spectrometer with a 20MHz permanent magnet maintained at 40C. The sample must be at the same temperature as the magnet for accuracy, which may require an equalization period in the magnet prior to analysis. The sample must be weighed accurately, be homogenous

7、at 40C, be free of solids or particulate matter, and the entire sample must be within the measuring region of the magnet in order to receive the full hydrogen-NMR (H-NMR) signal. The analyzer records in a non-destructive fashion the total electromagnetic pulse generated NMR signal representing the a

8、bsolute amount of hydrogen atoms in the sample. The pulse is cycled several times allowing the signal to reach equilibrium between each pulse. The delay between pulses must be adequate to aquire quantitative signal intensity. The average hydrogen signal intensity is divided by the sample mass and ca

9、librated with a set of reference standards to determine hydrogen content. The linear range of quantitation can be extended below 9.5 mass-% H or above 15.4 mass-% H by including additional pure reference standards of known hydrogen contents. Samples that are not liquid at 40C are diluted by a standa

10、rd factor in a hydrogen free solvent (tetrachloroethylene) to ensure that the sample is a homogenous liquid. The diluted sample is analyzed against a set of reference standards prepared using the same solvent dilution factor. Homogeneity is critical because the signal decay of solid material is very

11、 different from liquids. Interferences include any ferrous or magnetic material in the samples. Apparatus Balance, readable to 0.001 g 2 of 7 997-13 Hot plate, Fisher Scientific, Cat. No. 11-100-16H Hydrogen-NMR spectrometer, Minispec mq20 (20 MHz) Percent Hydrogen Analyzer comprised of a permanent

12、magnet, magnet temperature control (operating temperature between 35-45C), 18-mm probe assembly, autosampler for 18-mm sample tubes, sample rack for autosampler, dri-block temperature controller, and daily check sample (rapeseed). Bruker Biospin Corp. This method was developed and validated using th

13、is Minispec analyzer. The procedure for analysis maybe different for other instruments and other instruments need to be validated before using for this method. Pipetter, automatic pipetter able to deliver a set amount of 3.5 mL, Finnpipette Novus single-channel pipetter (0.5-5 mL), Fisher Scientific

14、, Cat. No. 21-377-017 Teflon caps, threaded cap able to fit 13mm screw cap vial, Bruker Biospin Corp., Cat. No. mq-tub 18vptcap Test tubes, glass 18x150 mm, VWR Int., Cat. No. 47729-583 Reagents and Materials Acetone, Burdick and Jackson, Cat. No. AH010-4PC Cyclohexane, anhydrous, Aldrich, Cat. No.

15、227048-1L n-Dodecane, Fisher Scientific, Cat. No. 02666-500 Ethyl heptanoate, 99%, Aldrich, Cat. No. 112364-100 2-Nonanone, 99%, Fisher Scientific, Cat. No. AC14878-100 Pipets, transfer, disposable, Fisher Scientific, Cat. No 13-711-9CM Pipette tips, 5 mL, Finntip, VWR Int., Cat. No. 53515-980 Septa

16、, white virgin PTFE septa for 13-425 cap, VWR Int., Cat. No. 66030-388 Tetrachloroethylene, 99.9+%, HPLC Grade, Aldrich, Cat. No. 270393-1L Tetradecane, reagent grade, Fisher Scientific, Cat. No. 04595-500 Toluene, Burdick and Jackson, Cat. No. AH347-4PC Vials, 15 x 45 clear, with 13mm screw top, Fi

17、sher Scientific, Cat. No. NC9802082 Vials, with polyseal caps, 15 mL, VWR Int., Cat. No. 16087-062 Wipes, Kimwipes, Ex-L, Fisher Scientific, Cat. No. 06-666A m-Xylene, Aldrich, Cat. No. 185566-1L Procedure The analyst is expected to be familiar with general laboratory practices, the technique of ana

18、lysis by H-NMR, and the equipment being used. Dispose of used reagents, materials, and samples in an environmentally safe manner according to local regulations. Instrument Setup and Preparation 1. Set up the instrument and applications according to the manufacturers specifications. Suggested operati

19、ng conditions for the Minispec mq20 are listed in Table 1. These conditions may be optimized to meet the users specific requirements. 3 of 7 997-13 2. Insert the daily check sample into the spectrometer and analyze. The check sample is analyzed daily to verify instrument functions. The sample consis

20、ts of rapeseeds supplied with the instrument in a standard test tube. The daily check is not a calibration standard. The calibration should be checked with a quality control sample as specified under Validation Standard. If an error occurs during the analysis of the daily check sample, corrective ac

21、tion should be taken as specified in the manual. Table 1 Suggested Operating Conditions for Bruker Optics Minispec mq20 90 Pulse length s approx. 15 180 Pulse length s approx. 30 Analog/digital det. filter broad (1MHz/Unfiltered) Bandwidth (broad) kHz 20000 Desired magnet temp C 40C Temperature cont

22、rol rack 40C Scans 8 Recycle delay s 20 Gain dB is set by sample size and concentration as per manufacturers specifications 3. Proceed with Part A: Light and Middle Distillates or Part B: Heavy Oils Part A: Light and Middle Distillates Calibration 1. Tare a clean, dry 15 x 45 mm vial on a balance. 2

23、. Pipette 3.5 mL of the dodecane standard into the vial. Record the weight and the hydrogen content of the standard. Suggested standards to be used are listed in Table 2. The highest hydrogen content standard should be measured first followed by the remaining standards in order of decreasing hydroge

24、n content value. Table 2 Hydrogen Content of Suggested Reference Standards Dodecane 15.386% Cyclohexane 14.372% 2-Nonanone 12.756% Ethyl Heptanoate 11.466% m-Xylene 9.494% 3. Seal the vial with a Teflon cap containing two Teflon septa. Teflon caps should be cleaned with toluene followed by acetone.

25、The caps must be dry prior to use. 4. Wipe the outside of the vial with a Kimwipe. 5. Place the capped vial containing the standard into a test tube. The test tube should be tilted slightly to ensure smooth entry of the vial. 6. Place the test tube in the designated sample changer position. Sample p

26、ositions are defined in the application by the user. 7. Repeat Steps 1 through 6 for the remaining standards. 4 of 7 997-13 8. Initiate analysis of the standards. The process allows the sample changer to move each standard into the heating block/system. The time required to reach the temperature of

27、40C is 30 minutes before the next measurement begins. This parameter is programmed into the software of the instrument. 9. The calibration line will be created by the instrument software. Evaluate the data and ensure that the resulting calibration line has a correlation value of greater than 0.999.

28、If the correlation value is lower than the specified value, repeat calibration measurements. Sample Analysis 1. Tare a clean, dry 15 x 45 mm vial on a balance. 2. Pipette 3.5 mL of the sample into the vial. Record the weight of the sample. 3. Seal the vial with a Teflon cap containing two Teflon sep

29、ta. Teflon caps should be cleaned with toluene followed by acetone. The caps must be dry prior to use. 4. Wipe the outside of the vial with a Kimwipe. 5. Place the capped vial containing the sample into a test tube. The test tube should be tilted slightly to ensure smooth entry of the vial. 6. Place

30、 the test tube in the designated sample changer position. Sample positions are defined in the application by the user. 7. Repeat Steps 1 - 6 for the remaining samples. 8. Initiate analysis of the samples. The process allows the sample changer to move each standard into the heating block/system. The

31、time required to reach the temperature of 40C is 30 minutes before the next measurement begins. This parameter is programmed into the software of the instrument. Validation Standard Verify the performance of the instrument by following Steps 1 - 6, under Sample Analysis, using tetradecane as the val

32、idation sample. Ensure that the validation sample is measured in frequent intervals during the analysis of a sample batch. If the determined hydrogen concentration is not within 0.1 mass-% of the theoretical value, corrective action should be taken as per manufacturer recommendations. Part B: Heavy

33、Oils Standard Preparation 1. Tare a clean, dry 15 mL vial on a balance. 2. Weigh 2 g of the dodecane standard into the vial using a transfer pipette. Record the weight of the standard. 3. Add 6 g of tetrachloroethylene to the vial. Record the total weight. This will result in a 1+3 weight/weight sam

34、ple dilution. The dilution of each standard needs to be maintained within 2% of the dilution factor to ensure a proper calibration range. 4. Calculate and record the dilution factor. The instrument software will calculate the total hydrogen concentration of each of the standards using the dilution f

35、actor. 5 of 7 997-13 5. Repeat Steps 1 - 4 for the remaining standards. Suggested standards to be used are listed in Table 2. Calibration 1. Tare a clean, dry 15 x 45 mm vial on a balance. 2. Pipette 3.5 mL of the diluted dodecane standard into the vial. Enter the weight, hydrogen content and the di

36、lution factor from Step 4 under Standard Preparation. The highest hydrogen content standard should be measured first followed by the remaining standards in order of decreasing hydrogen content value. 3. Seal the vial with a Teflon cap containing two Teflon septa. Teflon caps should be cleaned with t

37、oluene followed by acetone. The caps must be dry prior to use. 4. Wipe the outside of the vial with a Kimwipe. 5. Place the capped vial containing the standard into a test tube. The test tube should be tilted slightly to ensure smooth entry of the vial. 6. Place the test tube in the designated sampl

38、e changer position. Sample positions are defined in the application by the user. 7. Repeat Steps 1 - 6 for the remaining standards. 8. Initiate analysis of the standards. The process allows the sample changer to move each standard into the heating block/system. The time required to reach the tempera

39、ture of 40C is 30 minutes before the next measurement begins. This parameter is programmed into the software of the instrument. 9. The calibration line will be created by the instrument software. Evaluate the data and ensure that the resulting calibration line has a correlation value of greater than

40、 0.999. If the correlation value is lower than the specified value, repeat calibration measurements. Sample Preparation 1. Heat samples on a hot plate until the samples have completely liquefied. Most samples applicable to this method will become homogenous liquids at approximately 40C. Some samples

41、 may require a higher temperature to melt, which should be accommodated by a separate hot plate. The diluted sample must remain liquid at 40C in order to be applicable for analysis. 2. Tare a clean, dry 15 mL vial on a balance. 3. Weigh 2 g of a sample into the vial using a transfer pipette. Record

42、the weight of the sample. 4. Add 6 g of tetrachloroethylene to the vial. Record the total weight. This will result in a 1+3 weight/weight sample dilution The dilution of each standard needs to be maintained within 2% of the dilution factor to ensure a proper calibration range. 5. Calculate and recor

43、d the dilution factor. The instrument software will calculate the total hydrogen concentration of each of the samples using the dilution factor. 6. Place the diluted sample onto a hot plate at 40C to ensure that the sample is fully dissolved in the solvent and is a homogenous liquid. 6 of 7 997-13 T

44、he diluted sample must remain liquid at 40C in order to be applicable for analysis. 7. Repeat Steps 1 - 6 for the remaining samples. Sample Analysis 1. Tare a clean, dry 15 x 45 mm vial on a balance. 2. Pipette 3.5 mL of the diluted sample into the vial. Enter the weight and the dilution factor from

45、 Step 5 under Sample Preparation. 3. Seal the vial with a Teflon cap containing two Teflon septa. Teflon caps should be cleaned with toluene followed by acetone. The caps must be dry prior to use. 4. Wipe the outside of the vial with a Kimwipe. 5. Place the capped vial containing the sample into a t

46、est tube. The test tube should be tilted slightly to ensure smooth entry of the vial. 6. Place the test tube in the designated sample changer position. Sample positions are defined in the application by the user. 7. Repeat Steps 1 - 6 for the remaining samples. 8. Initiate analysis of the samples. T

47、he process allows the sample changer to move each standard into the heating block/system. The time required to reach the temperature of 40C is 30 minutes before the next measurement begins. This parameter is programmed into the software of the instrument. Validation Standard Verify the performance o

48、f the instrument by following Sample Preparation, Steps 2 5, and Sample Analysis, Steps 1 - 6, using tetradecane as the validation sample. Ensure that the validation sample is measured in frequent intervals during the analysis of a sample batch. If the determined hydrogen concentration is not within

49、 0.1 mass-% of the theoretical value, corrective action should be taken as per manufacturer recommendations. Calculations All calculations are performed by the instrument software, and results are displayed and printed in mass-%. Report results to the nearest 0.01 mass-%. Precision Repeatability and Site Precision A nested design was carried out for determining hydrogen by NMR on light hydrocarbons and heavy hydrocarbons. Four samples were analyzed by two analysts, with ea