UOP 910-2007 Total Chloride in LPG and Gaseous Hydrocarbons by Microcoulometry.pdf

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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

2、ED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS (MSDS) OR EXPERIMENTAL MATERIAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE). COPYRIGHT 1992, 1997, 2007 UOP LLC. All rights r

3、eserved. Nonconfidential UOP Methods are available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, USA. The UOP Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at serviceastm.org, 610.832.9555 FAX, or

4、610.832.9585 PHONE. Total Chloride in LPG and Gaseous Hydrocarbons by Microcoulometry UOP Method 910-07 Scope This method is for determining total chloride in gaseous hydrocarbons or liquefied petroleum gas (LPG) at concentrations ranging from approximately 1 to 1000 ng/mL for gas or mass-ppm (g/g)

5、for LPG. Except for fluoride, other halogens present are calculated as chloride. Chloride cannot be determined quantitatively if sulfur is present at concentrations greater than approximately 1 mass-%, see Note 1. References Perrys Chemical Engineering Handbook UOP Method 516, “Sampling of Gasolines

6、, Distillate Fuels and C3- C4Fractions”, www.astm.org Outline of Method A commercial microcoulometer is set up according to the manufacturers specifications. Gaseous and LPG samples are collected in stainless steel cylinders. Measured volumes of the LPG or gaseous samples are analyzed by injecting t

7、hem into a heated combustion tube containing oxygen blended with argon. The organic halides are converted quantitatively to hydrogen halide, hydrogen oxyhalide, carbon dioxide and water. The gaseous combustion products are passed through a dryer and then pass into a coulometric cell containing a buf

8、fer, in which the halide ions are dissolved. The instrument automatically titrates the halide ions to a coulometric endpoint and calculates the number of equivalents of halide in the sample. The halide is reported as the equivalent number of chloride ions, given in nanograms. The concentration of ch

9、loride in the sample is then calculated in g/g for LPG or in ng/mL for gases. Any HCl content is non-quantitative because of losses to the vessel walls, especially in the presence of water, and special care must be exercised to determine the HCl content quantitatively (see Note 2). The other halogen

10、s that respond are bromine and iodine. Fluorine does not react with silver so it is not detected. In the case of bromine and iodine, only the HX form titrates with silver, while for chlorine, both HCl and HOCl react with silver. All chlorine is determined, but only approximately 50% of the bromine a

11、nd iodine is detected. In the chlorine mode, the apparent response to bromine and iodine is 2 of 9 910-07 further reduced to 25 and 15% of the chloride response, respectively, due to the differences in their atomic weights. Apparatus References to catalog numbers and suppliers are included as a conv

12、enience to the method user. Other suppliers may be used. Additional items may be required depending on the specific instrument used. Bottle, Teflon, 1000-mL, Fisher Scientific, Cat. No. 02-923-30D Cylinder, graduated, 500-mL, borosilicate glass, Fisher Scientific, Cat. No. 08-552-4E Flask, Erlenmeye

13、r, 1000-mL, borosilicate glass, Fisher Scientific, Cat. No. 10-041C Flowmeter, digital, soap film, range 0.50- to 500-mL/min, Alltech Associates, Cat. No. 4068 Gauge, pressure, 0 to 2760 kPa gauge (0 to 400 psig), Matheson Tri-Gas, Cat. No. 63-2242 Microcoulometer, with attached furnace, cell, gas/L

14、PG module, controls and computer; a printer is optional, but recommended, Mitsubishi TCL-100 (Cosa Instruments), Thermo ECS-3000, or Analytik Jena Multi EA 3100. A Dohrmann MCTS-120, no longer manufactured, may also be used. Follow the manufacturers recommendations for maintaining a supply of spare

15、parts and consumables. Regulator, argon, two-stage, high purity, with stainless steel diaphragm, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3122-580 Regulator, nitrogen, two-stage, high purity, with stainless steel diaphragm, delivery pressure range 35-2400 kPa (5-350

16、 psi), Matheson Tri-Gas, Cat. No. 3128-580, only needed for analysis of LPG Regulator, oxygen, two-stage, high purity, with stainless steel diaphragm, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3122-540 Reagents and Materials References to catalog numbers and supplier

17、s are included as a convenience to the method user. Other suppliers may be used. References to water mean deionized or distilled water. The following items are required to perform the analysis. Additional reagents and materials may be required depending on the specific microcoulometer utilized. Wher

18、e different reagents are specified in the instrument manual, follow the manufacturer recommendations. Argon, compressed gas, 99.99% minimum purity 2-Chlorobutane in isobutane, (LPG and Gas Reference Standard, see Note 3). Liquefied Petroleum Gas and Gas Reference Standards are available by special o

19、rder from most gas suppliers. Request preparation on a mass/mass basis at a concentration similar to that expected for the sample of LPG or on a nominal volume/volume basis at a concentration similar to that expected for the sample of gas. In addition, request that the LPG cylinder be supplied with

20、a full length dip tube to deliver the liquefied gas from the bottom of the cylinder and under 250 psig (1750 kPa) of nitrogen pressure. This will keep the LPG liquefied for instrumental loop-sampling, free of bubbles. The material is certified by the supplier to be stable for at least six months. Ma

21、theson Tri-Gas or local supply. Inorganic chloride standard (NaCl or HCl Solution), prepared to meet manufacturers recommendations, if needed Isobutane, (LPG and Gas Blank). Liquefied Petroleum Gas and Gas Reference Blanks are available on special order from a gas supplier and should be ordered when

22、 the Reference Standards are 3 of 9 910-07 ordered. Request that the LPG cylinder be supplied with a full length dip tube to deliver the liquefied gas from the bottom of the cylinder and under 250 psig (1750 kPa) of nitrogen pressure. This will keep the LPG liquefied for instrumental loop-sampling,

23、free of bubbles. Matheson Tri-Gas or local supply. Leak detector, liquid solution, Matheson Tri-Gas, Cat. No. BUBL-01 Nitrogen, compressed gas, 99.98% minimum purity, only needed for analysis of LPG Oxygen, compressed gas, 99.98% minimum purity Quartz combustion tube, replacement, as supplied for th

24、e instrument used Sulfuric acid, concentrated, Fisher Scientific, Cat. No. A300-212 Sulfuric acid, 90%, for drying combustion exit gases. Pour 50 mL of water into a 1000-mL Erlenmeyer flask cooled in an ice bath. Slowly and carefully add, from a 500-mL graduated cylinder, 450 mL of concentrated sulf

25、uric acid, mix, allow to cool to ambient temperature, and store in a stoppered or capped, air-tight, glass or Teflon bottle. Calibration of Apparatus The analyst is expected to be familiar with general laboratory practices, with the technique of microcoulometry, and with the equipment being used. Se

26、t up the instrument according to the instrument manufacturers instructions and perform any required tests prior to calibrating and analyzing samples (see the instrument manual for any instructions). See the Figure for an example of a setup. Alternative configurations, as recommended by the manufactu

27、rer of the microcoulometer, may be used. The instrument should be calibrated using standards made from an appropriate matrix (LPG calibration should use LPG standards; gas calibration should use gas phase standards). The best calibration is obtained when multiple standard injections are used to buil

28、d a calibration line. This can be obtained by using standards of varying concentrations or by using multiple injections of a single standard, for example calibrating with 1, 2 and 4 injections of a standard. If the sample is analyzed with 2 injections, then the calibrated range is half the standard

29、concentration to twice the standard concentration. This process can be extended to more than 4 injections if needed, but the injection volume of a single portion of LPG into the combustion tube should be 25 L or less. Some instrument software may use only single or two point calibrations. The blank

30、is assumed to be zero for the single point calibration. This calibration mode can be used for LPG samples above 10 mass-ppm and gas samples above 10 ng/mL where the blank is insignificant. The two point calibration uses both a solvent blank and a standard to generate a linear calibration curve. This

31、 curve is useful for LPG samples at or below 10 mass-ppm and gas samples at or below 10 ng/mL where the blank is significant. The level where the blank becomes significant depends on such factors as the system condition, inlet mode, gas purity used and accuracy desired. Calibration for LPG Samples 1

32、. Select calibration standard that covers the range expected in the sample(s). A stainless steel loop of 10 to 25 L is used for LPG samples. Multiple injections of a single standard can be used to extend the range of calibration (for single point calibration) or to build a linear calibration with a

33、single LPG standard. The LPG reference standard concentration can be converted from g Cl/g (mass-ppm) to g Cl/mL by multiplying by the density (g/mL) (Table 1 and Note 3) of the liquefied LPG. 4 of 9 910-07 2. Assemble the instrument and LPG sampling system according to manufacturer instructions. Re

34、place the coulometric cell solution and sulfuric acid scrubber solution each day the instrument is used. Start the flow of oxygen and argon through the instrument. 3. Allow the instrument sufficient time to stabilize before beginning the calibration. 4. Connect the LPG reference standard cylinder to

35、 the Gas/LPG module. It is important to sample the LPG in a liquid state. To keep it as a liquid, the LPG cylinder must be sampled from the bottom and at an elevated pressure. This pressure may be applied by an internal or external high pressure gas source 1750 kPa gauge (250 psig) of nitrogen. 5. C

36、lose the needle valve used to control sample flow through the LPG sampling module. 6. Open the LPG cylinder valve slowly to allow the sample into the inlet module. Use a leak checking solution to check the system for leaks. 7. Watch the viewer located behind the window on the front of the Gas/LPG mo

37、dule. Slowly open the needle valve just enough so that the LPG sample flows continuously through the sample loop, up the viewer tube and out to vent. Be sure that the sample moves at such a speed that no bubbles are visible in the viewer. 8. Let the LPG sample flow through the system for one minute.

38、 9. Start the analysis in the instrument software. Turn the valve to inject LPG into the combustion tube. Wait until the analysis has completed before proceeding to Step 10. If multiple injections of the standard will be done, wait until the flame stops, then refill the loop and repeat the injection

39、. For a system blank measurement, do not inject during data collection. If an LPG blank has been obtained, inject the volume (number of injections) which will be used for the sample. 10. Repeat the analysis of the standard until the average from the last three injections is within 5% of the certifie

40、d value and the relative standard deviation is within 5% (for single point calibration) or until enough different sample concentrations/volumes have been run to create the calibration line. Experience has shown that, especially on low Cl concentrations, it takes 3 repeat injections before the analys

41、is is reliable, so that only injection Nos. 3, 4 and 5 can be used to average the results with acceptable precision. 11. Depending on the instrument model and software, either the instrument will calculate the calibration or provide the ng of Cl measured for use externally. 12. Proceed as described

42、for the Analysis of LPG, under Procedure. Calibration for Gas Samples The use of a gas standard is the most accurate means of analysis of gas samples. The gas standard is passed through the gas port of the Gas/LPG module. A glass or stainless steel loop ranging from 5 to 20 mL is used for gas sample

43、s. 1. Select a calibration standard that covers the range expected in the sample(s). The gas calibration standard concentration can be converted from vol-ppm to ng/mL, see Note 4. 2. Assemble the instrument and gas sampling system according to manufacturer instructions. Replace the coulometric cell

44、solution and sulfuric acid scrubber solution each day the instrument is used. Start the flow of oxygen and argon through the instrument. 3. Allow the instrument sufficient time to stabilize before beginning the calibration. 5 of 9 910-07 4. Connect the gas reference standard cylinder to the Gas/LPG-

45、module. 5. Close the valve used to control sample flow through the gas sampling module. 6. Open the gas cylinder valve slowly to allow the sample into the inlet module. Use a leak checking solution to check the system for leaks. 7. Open fully the gas flow valve. If the gas sampling module has a ball

46、 flowmeter, the ball in the flowmeter should be halfway up the scale. Allow the gas to purge through the port for about 1 minute. 8. Close the valve on the sample cylinder or gas line and allow the ball in the flowmeter to drop to zero. Wait 20 seconds. This is done in order to allow the gas sample

47、to equilibrate to atmospheric pressure. 9. Start the analysis using the instrument software. Inject the sample into the combustion tube. Wait until the analysis has completed before proceeding to Step 10. For a system blank measurement, do not inject during data collection. If an LPG blank has been

48、obtained, inject the volume (number of injections) which will be used for the sample. 10. Repeat the analysis of the standard until the average from the last three injections is within 5% of the certified value and the relative standard deviation is within 5% (for single point calibration) or until

49、enough different sample concentrations/volumes have been run to create the calibration line. Experience has shown that, especially on low Cl concentrations, it takes 3 repeat injections before the analysis is reliable, so that only injection Nos. 3, 4 and 5 can be used to average the results with acceptable precision. 11. Depending on the instrument model and software, either the instrument will calculate the calibration or provide the ng of Cl measured for use externally. 12. Proceed as described for the Analysis of Gas Sample, under Procedure. Pro