UOP291 Chloride Test Method [PDF]

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TOTAL CHLORIDE IN ALUMINA AND SILICA-ALUMINA CATALYSTS BY POTENTIOMETRIC TITRATION UOP Method 291-02 SCOPE This method is for determining the total inorganic chloride content of fresh or spent alumina and silica-alumina catalysts or catalyst supports. The range of quantitation is 0.01 to 10 mass-%.



OUTLINE OF METHOD The as-received sample is weighed into a beaker and digested with hot dilute sulfuric acid. Promoter metals, if present, are reduced with magnesium. Chloride is determined potentiometrically by titration with a silver nitrate solution using a silver-silver chloride indicating electrode system. An alternative digestion procedure, using a microwave oven, is described in the APPENDIX.



APPARATUS References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Balance, readabi1ity 0.1-mg Beaker, electrolytic, extra high form, without spout, 250-mL, Reliance Glass Works, Cat. No. G9906-002 Bottle, washing 500-mL, polyethylene, Fisher Scientific, Cat. No. 03-409-10E Condenser, acorn type (see Figure), Reliance Glass Works, Cat. No. G-9906-002C IT IS THE USER'S 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 PRESCRIBED 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 1963, 1965, 1976, 1986, 1989, 2002 UOP LLC ALL RIGHTS RESERVED Marks of other proprietors may appear incidentally in this method for purposes such as product or service identification, but no claim is made to any other proprietor’s mark used. UOP Methods are available through ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194428-2959, United States. The Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at [email protected], 610.832.9555 FAX, or 610.832.9585 PHONE.



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Cylinders, graduated, standard Class B borosilicate glass, 100- and 250-mL, Fisher Scientific, Cat. Nos. 08-08-550E and –550F, respectively Electrode, combination glass/silver TitrodeTM, MetrohmTM 6.0430.100, Brinkmann Instruments, Cat. No. 20 94 850-7. The electrode should be dedicated to chloride analysis. Hot plate, electric Oven, drying Scotchbrite cleaning pads, or equivalent, local supply Stir bar, magnetic, 38-mm length, Fisher Scientific, Cat. No. 14-511-64 Titrator, potentiometric, recording, 2000-mV range, 1-mV resolution with dispenser having a volume readout of 0.00-99.99 mL and 0.01-mL resolution, Metrohm 751GPD or 736GP TitrinoTM system with optional 730 sample changer, and two 20-mL burets, one for each titrant, Brinkmann Instruments Tongs, TefzelTM, 250-mm long, Cole-Parmer Instrument, Cat. No. U-06442-00 Watch glass, borosilicate glass, 65-mm diameter, Cole-Parmer, Cat. No. U-34507-01



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Figure Condenser-Beaker Assembly



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REAGENTS AND MATERIALS References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Boiling chips, silicon carbide, Thomas Scientific, Cat. No. 1590-D33 Congo red test strips, Fisher Scientific, Cat. No. 14-861 Magnesium, metal turnings, Fisher Scientific, Cat. No. M11 Potassium chloride, primary standard, oven dried at 105ºC for 2.5 hours, Fisher Scientific, Cat. No. P217-500 Potassium chloride solution, saturated, Fisher Scientific, Cat. No. SP138-500 Silver nitrate, 0.10-M standard aqueous solution, Fisher Scientific, Cat. No. SS72-500. If the 0.01-M silver nitrate solution is purchased with a Certificate of Analysis, the Silver Nitrate Standardization step under PROCEDURE may be eliminated. Silver nitrate, 0.01-M standard aqueous solution. Dilute one part of the 0.10-M aqueous solution with 9 parts of water. Sulfuric acid, concentrated, Fisher Scientific, Cat. No. A300-500 Sulfuric acid, approximately 3.5-M. Dilute 200 mL of concentrated acid to one liter with water. The diluted acid should never be stronger than 4-M. Add the concentrated acid cautiously to the cold water while stirring. The 3.5-M sulfuric acid may also be purchased, Fisher Scientific, Cat. No. SX-350. Sulfuric acid, 1:1 dilution. Mix equal volumes of concentrated sulfuric acid and water. Add the concentrated acid cautiously to the cold water while stirring. Water, distilled Wipers, Kimwipes Ex-L, Fisher Scientific, Cat. No. 06-666A



PROCEDURE Silver–Silver Chloride Electrode Preparation and Reconditioning Proper electrode preparation is essential to obtain reproducible and noise-free titration curves having good endpoints. The electrode must be reconditioned prior to running samples. An electrode should be dedicated to chloride analysis. Prepare and recondition the silver-silver chloride electrode as follows: 1.



Clean the silver surface with a Scotchbrite pad. Rinse with water and dry.



2.



Weigh approximately 0.1 g of potassium chloride and place in a beaker. Using a graduated cylinder, add 20 mL of 3.5-M sulfuric acid and 80 mL of water to the beaker. Immerse the electrode; and titrate to the endpoint with 0.10-M silver nitrate.



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3.



Remove the electrode from the solution and rinse with water.



4.



Wipe the excess silver chloride from the electrode with a wiper. •



The electrode should be cleaned after each titration by rinsing with water.



The freshly coated silver-silver chloride electrode may be stored in water or carefully dried using wipers and stored for future use. It is necessary to repeat the electrode preparation when the AgCl begins to peel from the surface. Silver Nitrate Standardization Standardize the 0.1-M silver nitrate solution with potassium chloride as follows: 1. Weigh between 0.09 and 0.10 g of dried potassium chloride to the nearest 0.1 mg into a clean, dry 250-mL electrolytic beaker. 2. Using a graduated cylinder, add 100 mL of water. Add a stirring bar. Acidify to congo red with 1:1 sulfuric acid. 3. While stirring at a moderate rate, titrate with 0.1-M silver nitrate solution. Calculate the molarity of the silver nitrate to 3 significant figures using Eq. 1: AgNO3, M =



A 0.07455B



(1)



where: A = mass of potassium chloride weighed into beaker, g B = volume of silver nitrate solution used in titration, mL 0.07455 = molecular weight of the potassium chloride multiplied by 0.001, the factor to convert milliliters to liters Sample Analysis Sample digestion/reduction can be accomplished by conventional heating, as follows, or by microwave heating (see NOTE and APPENDIX). Samples of fresh or spent catalyst that contain promoter (usually noble) metals must be reduced as described under Reduction, after Digestion, before Titration. Catalyst bases do not require reduction. Digestion 1. Weigh approximately 2 g of the as-received catalyst or catalyst base to the nearest 0.1 mg into a 250-mL electrolytic beaker. When results are to be reported on a volatile-free basis, weigh out a separate portion of the sample for the determination of LOI, as directed in UOP Method 275, at the same time the sample is weighed for chloride. 2. Using a graduated cylinder, add 75 mL of 3.5-M sulfuric acid to the beaker containing the sample for chloride determination. Add several boiling chips. 291-02



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3. Place the beaker on a cool hot plate, located in a hood or well-ventilated area, and place an acorn condenser in the top of the beaker. 4. Start cold tap water running through the condenser and turn on the hot plate. Heat the sample to just below the boiling point (do not allow to boil) until the catalyst is completely digested, or for a maximum of 6 hours. Fresh alumina catalyst or base will usually require about 2 hours for complete digestion, while used alumina catalyst or any silica-alumina catalyst may not completely dissolve, even after 6 hours. 5. Remove the beaker from the hot plate with the acorn condenser in place and allow it to cool so that it can be handled comfortably. 6. Lift off the acorn condenser and rinse it with water, catching the rinsings in the beaker. Cover with a watch glass. •



For some installations, especially those with multiple hot plates and acorn condensers, the water line connections to the acorn condenser may not permit removal of the beaker from the hot plate with the condenser in place. In this case, it is permissible to quickly lift the condenser, rinse it, cover the beaker with a watch glass, and remove the beaker from the hot plate.



7. Reduce the promoter metals, if present, as described in Reduction. 8. Continue the sample analysis as described under Titration. Reduction 1. Add a small stirring bar to each beaker and start the magnetic stirrer. 2. Add approximately 0.6 g of magnesium turnings and cover with the watch glass 3. When the magnesium has completely dissolved, rinse the watch glass catching the rinsings in the beaker. 4. Continue the sample analysis as described under Titration. Titration 1. Condition the electrodes prior to running samples as described in Silver–Silver Chloride Electrode Preparation and Reconditioning. 2. Prior to titration, add sufficient water to ensure complete electrode immersion, typically to about 100 mL total volume. 3. Titrate the sample with 0.10-M silver nitrate at a titration rate of about 2.5 mL/min using a moderately fast stirring rate (no vortex or splashing). As the endpoint is approached, reduce the titration rate to approximately 0.1 mL/min. For chloride levels below 0.05 mass-%, titrate with 0.01-M silver nitrate. The endpoint of the titration corresponds to that volume of titrant at which the rate of change of potential, ∆ EMF/∆ mL, reaches a maximum. If a recording titrator is used, a plot is automatically generated. Alternatively, EMF vs. milliliters of titrant added can be manually plotted and the endpoint determined from the inflection point of the titration curve. 291-02



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Obtain a reagent blank (3.5-M sulfuric acid) each time that fresh reagent is used. Follow the same titration procedure used in the sample analysis. If the titration of the blank requires more than 0.10 mL of 0.10-M silver nitrate, the reagents are not acceptable.



CALCULATION Calculate the chloride content of the sample to the nearest 0.01 % as follows: A) As-received basis: Chloride, mass-% =



3.545(C − D)M W



(2)



B) Volatile-free basis: Chloride, mass-% =



3.545(C − D)M 100 − V W( ) 100



(3)



where: C= D= M= V= W= 3.545 =



volume of silver nitrate to reach the chloride endpoint, mL volume of silver nitrate required for reagent blank, mL molarity of silver nitrate loss on ignition determined by UOP Method 275, mass-% sample mass, g 0.03545 times 100, factor combining the millimolar weight of chlorine and the factor to convert mass fraction to mass-%



NOTE An alternative digestion procedure using a microwave heating technique is described in the APPENDIX. Data from a comparative study has shown that conventional or microwave heating produce equivalent results. If microwave heating is used, the condenser and hot plate under APPARATUS are not required.



PRECISION The precision statements were determined using UOP Method 999. ASTM and UOP Repeatability A nested design was carried out for determining chloride in oxidized and reduced catalysts with two analysts in each of five laboratories. Each analyst carried out tests on two separate days, performing two tests each day. The total number of tests performed was 120. The precision data are summarized in Table 1. Two tests performed by the same analyst on the same day should not differ by more than the ASTM allowable difference with 95% confidence. Two tests performed in one laboratory by different analysts on different days should not differ by more than the UOP allowable difference with 95% confidence.



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The data in Table 1 are a short-term estimate of repeatability. When the test is run routinely, a control standard and chart should be used to develop a better estimate of the long-term repeatability. Table 1 ASTM and UOP Repeatability and Reproducibility, Mass-% ASTM Repeatability



UOP Repeatability



Reproducibility



Catalyst Sample



Mean Chloride Conc.



WithinDay esd



Allowable Difference



WithinLab esd



Allowable Difference



WithinLab and BetweenLab esd



Oxidized Oxidized Reduced



1.18 1.10 1.05



0.012 0.016 0.015



0.04 0.05 0.05



0.014 0.016 0.014



0.04 0.05 0.04



0.017 0.020 0.023



Allowable Difference



0.05 0.06 0.08



Reproducibility A nested design was carried out for determining chloride in oxidized and reduced catalysts with two analysts in five laboratories. Each analyst carried out tests on two separate days, performing two tests each day. The total number of tests performed was 120. The precision data are summarized in Table 1. Two tests performed by different analysts in different laboratories on different days should not differ by more than the allowable difference shown in Table 1 with 95% confidence.



TIME FOR ANALYSIS The total elapsed time for an analysis is 7 hours. The labor requirement per analysis is 1.6 hours when done singly or 0.8 hour when done in groups of 6 or more.



REFERENCE UOP Method 275, www.astm.org SUGGESTED SUPPLIERS Aldrich Chemical Co., Inc., 1000 West Saint Paul Avenue, Milwaukee, WI 53233 (414-273-3850) www.sigma-aldrich.com Brinkmann Instruments Co., One Cantiague Rd., Westbury, NY 11590 (516-334-7500) www.brinkmann.com Cole-Parmer, 625 East Bunker Court, Vernon Hills, IL 60061-1844 (847-549-7600) www.coleparmer.com Fisher Scientific Co., 711 Forbes Ave., Pittsburgh, PA 15219-4785 (412-490-8300) www.fishersci.com Reliance Glass Works, 220 Gateway Road, Bensenville, IL 60106 (630-766-1816) www.relianceglass.com Thomas Scientific, P.O. Box 99, Swedesboro, NJ 08085-0090 (856-467-2000) www.thomassci.com



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APPENDIX



Microwave Digestion of Catalyst SCOPE This appendix describes an alternative catalyst digestion procedure using a microwave heating technique. Data from a comparative study has shown that conventional or microwave heating produce equivalent results. If microwave heating is used, the condenser and hot plate under APPARATUS in the body of the method are not required.



OUTLINE OF METHOD The as-received sample is weighed into a TeflonTM vessel and dilute sulfuric acid is added. The vessel is placed in a specially configured microwave oven and heated for several minutes. The sample is then titrated as described in the body of the method.



APPARATUS References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. The following apparatus is an addition or substitution to that listed in the body of the method: Capping station, CEM, Cat. No. 920030 Carousel (turntable), 12-position. Teflon, CEM Cat. No. 221049 Cylinder, graduated, 50-mL, Fisher Scientific, Cat. No. 08-552D Microwave, 600 watt, CEM, Model MARS 5 Tube, transfer, Teflon, CEM, Cat. No. 324360 Vessel, 120-mL, Teflon, with cap and pressure seal, CEM, Cat, No. 221000



REAGENTS AND MATERIALS References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. The following reagents and materials are an addition or substitution to those listed in the body of the method: Sulfuric acid, 20 vol/vol-%, To prepare, slowly add 200 mL of concentrated sulfuric acid to 800 mL of water and mix thoroughly.



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PROCEDURE 1. Weigh approximately 2 g of the as-received catalyst or catalyst support to the nearest 0.1 mg into a 120-mL Teflon vessel. When results are to be reported on a volatile-free basis, weigh out a separate portion of the sample for the determination of LOI as directed in UOP Method 275, at the same time the sample is weighed for chloride. 2. Using a graduated cylinder, add 30 mL of 20% sulfuric acid to the Teflon vessel. 3. Place a pressure seal on the vessel with the flat side down. Screw the cap onto the vessel until finger tight. Place the vessel in the capping station and press the toggle switch to tighten the cap. Use of the capping station is required to ensure proper torque and sealing of the vent seal. Remove the capped vessel from the capping station and place it on the carousel. 4. Insert a Teflon transfer tube into the fitting on the top of the cap and hand tighten the connection. Insert the other end of the tube into the center catch vessel. The transfer tube is a safety precaution to vent excessive pressure buildup in the vessel. If any liquid is vented from a sample during the digestion, as indicated by the presence of droplets in the transfer tube, the sample must be rerun. 5. Repeat the above procedure with additional samples until the carousel contains either 6 sample vessels (distributed around the carousel) or 12 sample vessels. If it is necessary to run a fewer number of samples, fill the remaining vessels with blanks containing 30 mL of sulfuric acid. Place the carousel in the microwave. Set the switches for power and turntable to the "on" position and fan to "full power.” Set the power and time program for the appropriate number of samples as shown in Table A1. Include at the end of the timing sequence a 20-minute period at 0% power for cooling. Table A1 Number of Samples



Time, Minutes



Power Setting, Watts



12 6



17 8



600 600



6. Remove the carousel from the microwave. Loosen the fittings on the transfer tubes and remove them from the vessels. Place a vessel in the capping station and press the toggle switch to loosen the cap. Remove the vessel from the station and complete removal of the cap by hand. 7. Carefully rinse the seal and the inside of the cap with water, catching the rinsings in the vessel. If any aluminum sulfate crystals form in the sample solution, warm slightly in the microwave. 8. Quantitatively transfer the solution with water to a 250-mL electrolytic beaker. 9. Add a small stirring bar to each beaker and start the magnetic stirrer. Add approximately 0.6 g of magnesium turnings and cover with a watch glass. When the magnesium has completely dissolved, rinse the watch glass catching the rinsings in the beaker. 10. Titrate the sample as described in the body of the method.



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PRECISION The precision statements were determined using UOP Method 999. ASTM and UOP Repeatability A nested design was carried out to compare conventional and microwave digestion with two analysts in one laboratory. Each analyst carried out tests on two separate days, performing two tests each day. The total number of tests performed was 48. The precision data are summarized in Table A2. Two tests performed by the same analyst on the same day should not differ by more than the ASTM allowable difference with 95% confidence. Two tests performed in one laboratory by different analysts on different days should not differ by more than the UOP allowable difference with 95% confidence. Reproducibility There is insufficient data to calculate the reproducibility of the digestion at this time. Table A2 ASTM and UOP Repeatability, Mass-% ASTM Repeatability



UOP Repeatability



Digestion



Mean Chloride Conc.



WithinDay esd



Allowable Difference



WithinLab esd



Allowable Difference



Oxidized



Conventional Microwave



1.19 1.19



0.017 0.013



0.05 0.04



0.019 0.012



0.06 0.04



Oxidized



Conventional Microwave



1.08 1.07



0.033 0.025



0.10 0.07



0.026 0.019



0.08 0.06



Reduced



Conventional Microwave



1.11 1.10



0.029 0



0.08 0



0.022 0.007



0.06 0.02



Catalyst Sample



TIME FOR ANALYSIS The elapsed time for an analysis is one hour. The labor requirement is 0.8 hour.



SUGGESTED SUPPLIERS CEM Corporation, PO Box 200, Matthews, NC 28106-0200 (704-821-7015) www.cem.com Fisher Scientific Co., 711 Forbes Ave., Pittsburgh, PA 15219-4785 (412-490-8300) www.fishersci.com



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