UOP 248-1992 ALKALINITY AND FLUORIDE IN ALKALINE SOLUTIONS.pdf

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1、 COPYRIGHT 1958, 1992 UOP LLCALL RIGHTS RESERVEDUOP Methods are available through ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken PA 19428-2959,United States. The Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service atserviceastm

2、.org, 610.832.9555 FAX, or 610.832.9585 PHONE.ALKALINITY AND FLUORIDE IN ALKALINE SOLUTIONSUOP Method 248-92SCOPEThis method is for determining the alkalinity and fluoride content of alkaline solutions used forneutralization of HF in alkylation plants. Two procedures are included. The first procedur

3、e determines thealkalinity of the sample by colorimetric titration. The second procedure determines fluoride concentrationusing a fluoride ion-selective electrode. Fluoride, as mass-% KOH required for neutralization, is determinedover a range of 0.016 to approximately 50 mass-%.OUTLINE OF METHODIn t

4、he first procedure, A, the sample is titrated with hydrochloric acid to a phenolphthalein endpoint. Thealkalinity, free base plus the basic carbonate, is calculated as mass-% KOH.In the second procedure, B, the sample is diluted to a specific volume with water and mixed with an ionicstrength activit

5、y buffer. The fluoride concentration is determined potentiometrically by comparison tostandard fluoride solutions using a high sensitivity pH meter and a fluoride ion-selective electrode andcalculated as mass-% KOH required for neutralization.APPARATUSReferences to catalog numbers and suppliers are

6、included as a convenience to the method user. Othersuppliers may be used.Balance, readability 0.1-mgBeaker, graduated, 150-mL, polypropylene, Fisher Scientific, Cat. No. 02-591-10CBuret, 25-mL, Class A, Fisher Scientific, Cat. No. 03-700-22BBuret support, clamp with support stand, Fisher Scientific,

7、 Cat. No. 14-688Crucible, porcelain, high form, 10-mL, Fisher Scientific, Cat. No. 07-965CIT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TODETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH ANDSAFETY PRACTICES ARE TO BE FOLLOWED

8、WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THISPROCEDURE 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 INTHIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE P

9、ERSONAL PROTECTIONEQUIPMENT (PPE).2 of 8248-92Cylinder, graduated, 50-mL, borosilicate glass, Fisher Scientific, Cat. No. 08-549-5DDesiccator, with plate, Fisher Scientific, Cat. No. 08-615AElectrode, combination fluoride, ion-selective, Orion, Model 96-09, available from Fisher Scientific, Cat.No.

10、13-641-904Flasks, Erlenmeyer, glass, 125- and 250-mL, Fisher Scientific, Cat. Nos. 10-040D and F, respectivelyFlasks, volumetric, Class B, polypropylene 100-, 200-, 250- and 500-mL, Fisher Scientific, Cat. Nos. 10-198-50B, C, D and E, respectivelyHot plate, Fisher Scientific, Cat. No. 11-496-16Meter

11、, ion analyzer, Orion, Model EA 940, available from Fisher Scientific, Cat. No. 13-641-741Mortar, porcelain, 130-mm OD, Fisher Scientific, Cat. No. 12-961COven, drying, Fisher Scientific, Cat. No. 13-245-506GPestle, porcelain, Fisher Scientific, Cat. No. 12-961-5CPipet, transfer, polyethylene, dispo

12、sable, Fisher Scientific, Cat. No. 13-711-5APipet, volumetric, Class A, 50-mL, Fisher Scientific, Cat. No. 13-660KPipets, volumetric, polypropylene, 1-, 5- and 10-mL, Fisher Scientific, Cat. Nos. 13-662-10A, C and D,respectivelySpatula, micro-, Fisher Scientific, Cat. No. 21-401-15Stir bar, magnetic

13、, 8- x 32-mm, Teflon, Fisher Scientific, Cat. No. 14-511-94Stirrer, magnetic, Fisher Scientific, Cat. No. 14-493-120MRTongs, crucible, 230-mm long, Fisher Scientific, Cat. No. 15-186Tongs, flask, Fisher Scientific, Cat. No. 10-062REAGENTS AND MATERIALSAll reagents shall conform to the specifications

14、 established by the Committee on Analytical Reagents ofthe American Chemical Society, when such specifications are available, unless otherwise specified.References to water mean deionized or distilled.References to catalog numbers and suppliers are included as a convenience to the method user. Other

15、suppliers may be used.Bromocresol green, indicator, Fisher Scientific, Cat. No. B383Bromocresol green, indicator solution. Weigh 0.1 0.01 g of the indicator into a 250-mL volumetricflask. Add approximately 14 mL of 0.01-M NaOH with a graduated cylinder and dilute to the markwith water.Desiccant, 8-m

16、esh, indicating, Fisher Scientific, Cat. No. 07-578-3AElectrode filling solution, fluoride combination electrode, Fisher Scientific, Cat. No. 13-641-899Ethyl alcohol, denatured, Fisher Scientific, Cat. No. A407Hydrochloric acid, 0.1-M, certified standard, Fisher Scientific, Cat. No. SA543 of 8248-92

17、Hydrochloric acid, 0.025-M. Pipet 50 mL of 0.1-M hydrochloric acid standard into a 200-mLpolypropylene volumetric flask and fill to the mark with water. Invert several times to mix.Phenolphthalein, solid indicator, Fisher Scientific, Cat. No. P79Phenolphthalein, indicator solution. Weigh 1.0 0.01 g

18、of the solid indicator into a 100-mLpolypropylene volumetric flask. Dilute with 100 mL of ethyl alcohol to the mark.Sodium fluoride, 99.99% purity, Aldrich Chemical, Cat. No. 20,485-4Sodium hydroxide, 0.01-M solution, Fisher Scientific, Cat. No. SS284TISAB II (total ionic strength activity buffer),

19、fluoride electrode activity standard, Fisher Scientific, Cat.No. 13-641-873Toothpaste, non-gel type, fluorinatedPROCEDUREProcedure AStandardization of Hydrochloric Acid1. Crush approximately 1 g of sodium carbonate using a mortar and pestle.2. Transfer the sodium carbonate to a clean crucible and dr

20、y at 110C for one hour in a drying oven.3. Remove the crucible from the oven using tongs, place it in a desiccator and allow the crucible to cool.4. Weigh approximately 0.05 g of dried sodium carbonate to the nearest 0.1 mg into each of three tared125-mL Erlenmeyer flasks and record the mass in each

21、 flask. The standardization is performed in triplicate.5. Add, by graduated cylinder, 100 mL of water and a stirring bar to each flask.6. Add 3 drops of bromocresol green indicator to each flask.7. Set up the buret and fill it with the 0.025-M hydrochloric acid solution.8. Titrate the sodium carbona

22、te solution with the 0.025-M hydrochloric acid until the solution turns fromblue to green.9. Place the Erlenmeyer flask on a hot plate and boil 5 to 6 minutes. Boiling expels carbon dioxide. The solution will return to a blue color.10. Remove the flask from the hot plate using tongs.11. Return the f

23、lask to the titration stand and continue the titration of the hot solution. Titration is complete when the solution becomes green.12. Calculate the molarity of the hydrochloric acid to three significant figures as follows:310 B=105.98 CM (1)4 of 8248-92where:B = mass of potassium hydrogen phthalate

24、weighed into beaker, gC = volume of hydrochloric acid solution used to reach the endpoint, mLM = molarity of the hydrochloric acid105.98 = relative molecular mass of sodium carbonate, g/mol103= factor to convert moles per milliliter to moles per liter13. Average the results of the three determinatio

25、ns to three significant figures.Sample Analysis1. Weigh approximately 10 g of the sample to the nearest 0.1 mg into a 100-mL polypropylenevolumetric flask, weighed to the nearest 0.1 mg. Polypropylene pipets and volumetric flasks should be used.2. Dilute the sample with water to the mark, weigh to t

26、he nearest 0.1 mg and thoroughly mix byinverting several times.3. Transfer approximately 10 g of the sample solution, weighed to the nearest 0.1 mg, into a tared 250-mL Erlenmeyer flask with a polyethylene transfer pipet.4. Add approximately 50 mL of water, 2 drops of phenolphthalein indicator and a

27、 stirring bar to the flaskand place it on the magnetic stirrer. Stir the solution at a moderate rate.5. Set up the buret and fill it with the standardized 0.025-M hydrochloric acid.6. Titrate the sample solution to the equivalence point. The solution at the equivalence point becomes colorless.7. Pla

28、ce the Erlenmeyer flask on a hot plate and boil for 5 to 6 minutes. Boiling expels carbon dioxide, which contributes to alkalinity. The solution will become light pink.8. Remove the flask from the hot plate with flask tongs.9. Return the flask to the magnetic stirrer and continue the titration of th

29、e hot solution. Titration is complete when the solution again becomes colorless.10. Record the volume of titrant required for the titration.Procedure BPreparation of Fluoride StandardsFluoride Primary Standard, Approximately 1000-g/g F1. Place approximately 2 g of sodium fluoride into a clean crucib

30、le and dry at 100C for 2 hours in adrying oven.2. Remove the crucible from the oven using tongs and place it in a desiccator to cool.5 of 8248-923. Weigh approximately 0.22 g, weighed to the nearest 0.1 mg, of the dried sodium fluoride into a tared100-mL polypropylene volumetric flask.4. Dilute to t

31、he mark with water, weigh to the nearest 0.1 mg and invert several times to mix.5. Calculate the concentration of the fluoride in the primary standard as follows:=(10 )(0.4525)NFluoride, g/gV6(2)where:N = mass of sodium fluoride weighed into the flask, gV = mass of solution, g0.4525 = relative molec

32、ular mass of fluoride (19.00) divided by the relative molecular mass ofthe sodium fluoride (41.99)106= factor to convert g to gFluoride Working Standard, 100 g/g F1. Weigh approximately 10 g of the 1000-g/g fluoride standard to the nearest 0.1 mg into a tared 100-mL polypropylene volumetric flask.2.

33、 Fill to the mark with water, weigh to the nearest 0.1 mg and mix by inverting several times.Fluoride Working Standard, 10-g/g F1. Weigh approximately 10 g of the 100-g/g fluoride standard to the nearest 0.1 mg into a tared 100-mLpolypropylene volumetric flask.2. Fill to the mark with water, weigh t

34、o the nearest 0.1 mg and mix by inverting several times.Fluoride Working Standard, 1-g/g F1. Weigh approximately 10 g of the 10-g/g fluoride standard to the nearest 0.1 mg into a tared 100-mLpolypropylene volumetric flask.2. Fill to the mark with water, weigh to the nearest 0.1 mg and mix by inverti

35、ng several times.Calculate the concentration of each fluoride working standard as follows:=QRFluoride, g/gS (3)where:Q = mass of primary or working standard diluted, gR = concentration of standard diluted, g/gS = mass of final solution, g6 of 8248-92Preparation of Sample for Analysis1. Weigh the sam

36、ple to the nearest 0.1 mg into a 100-mL polypropylene volumetric flask, weighed to thenearest 0.1 mg. Table 1 shows the appropriate sample mass to be used. Polypropylene pipets and volumetric flasks must be used.Table 1Approximate Sample and Aliquot Massfor Analysis at Various Fluoride Concentration

37、sEstimated FluorideContent of AlkalineSolutions, as KOH,Mass-%Sample Massfor Analysis,gAliquot,g310430 1 450 1 22. Dilute the sample with water to the mark, weigh to the nearest 0.1 mg, and thoroughly mix byinverting several times.3. Transfer an aliquot of the sample solution, weighed to the nearest

38、 0.1 mg, into a weighed 100-mLvolumetric flask with a plastic dropping pipet. Table 1 shows the approximate aliquot to be used.4. Dilute the aliquot solution with water to the mark, weigh to the nearest 0.1 mg, and thoroughly mix byinverting several times.Analysis of SolutionsStandards1. Drain the e

39、lectrode filling solution from the electrode each day, rinse twice with water and refill withfresh solution. The filling solution level should be at least 25 mm above the expected level of the sample in the beaker toensure a proper flow rate. If the filling solution is less than 25 mm above the samp

40、le level, the electrode potential may be erratic.2. Choose two standards, see Preparation of Standards, that bracket the fluoride concentration expectedin the sample solution. For example, if the sample reading is expected to be 30 ppm, choose the 10- and 100-g/g standards.3. Pipet 50 mL of the more

41、 dilute standard and 50 mL of TISAB into a 150-mL beaker and add a stirringbar. After the addition of the TISAB II, the sample must be analyzed within 10 min.4. Place the beaker on a magnetic stirrer and stir at a moderate rate. The measurement of all solutions must be made at the same temperature.

42、Magnetic stirrers may generate sufficient heat to change solution temperature. Therefore, place a piece ofinsulating material such as cork or cardboard between the stirrer and beaker for the standards andsamples.7 of 8248-925. Rinse the electrode with water, blot dry, and place it in the standard so

43、lution. Do not wipe or rub the sensing element.6. Wait for a stable reading, then adjust the meter to display the fluoride value of the standard. Instruction for this measurement accompany the electrode when purchased.7. Repeat Steps 3 through 5 using the more concentrated standard.8. Wait for a sta

44、ble reading, then adjust the meter to display the fluoride value of the second standard. The slope of the calibration as calculated by the meter should be in the range of -54 to -60 mV per decadewhen the solution temperature is 25C. If the value is not within this range remove the electrode from the

45、solution, polish it lightly with toothpaste and reanalyze the standards.Samples1. Add, by pipet, 50 mL of the sample solution and 50 mL of TISAB to a 150-mL beaker and add astirring bar. After the addition of the TISAB II, the sample must be analyzed within 10 min.2. Place the beaker on a magnetic s

46、tirrer and stir at a moderate rate. The measurement of all solutions must be made at the same temperature.3. Rinse the electrode with water, blot dry, and place it in the sample. The fluoride concentration isdisplayed on the meter.4. Store the electrode when not in use in 100-g/g fluoride standard.C

47、ALCULATIONSProcedure ACalculate the free alkali plus alkali carbonate to the nearest 0.01 mass-% as follows:(100)(56.1) A FAlkalinity, mass-% KOH 1000WM= (4)where:A = volume of hydrochloric acid required to titrate the sample, mLF = dilution factor, 12VVwhere:V1= mass of original sample dilution, gV

48、2= mass of diluted sample taken for analysis, gM = molarity of the hydrochloric acidW = mass of original sample, g56.1 = relative molecular mass of potassium hydroxide sample100 = required to convert to mass-%1000 = required to convert milliliters to liters8 of 8248-92Procedure BCalculate the fluori

49、de, expressed as percent alkali required for neutralization, to the nearest 0.1 mass-% asfollows:42.95 C D EFluoride, mass-% KOH 10 S= (5)where:C = fluoride concentration in final sample dilution, g/gD = mass of original sample dilution, gE = dilution factor, 43VVwhere:V3= aliquot taken for final sample dilution, gV4= mass to which V3was diluted, gS = mass of original sample, g2.95 = relative molecular mass of potassium hydroxide (56.1) divided by the relative molecularmass of fluoride (19.00)104= factor to convert to mass-%PRECISIONRepeatability