UOP 262-1999 PHENOLS AND THIOPHENOLS IN PETROLEUM PRODUCTS BY SPECTROPHOTOMETRY.pdf

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1、 COPYRIGHT 1959, 1991, 1999 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 atservi

2、ceastm.org, 610.832.9555 FAX, or 610.832.9585 PHONE.PHENOLS AND THIOPHENOLS IN PETROLEUMPRODUCTS BY SPECTROPHOTOMETRYUOP Method 262-99SCOPEThis method is for determining phenols and thiophenols in gasoline, refinery caustics and crude cresylicacids derived from refinery caustics. In this method, the

3、 term “phenols” refers to mixtures of phenol,cresols, xylenols and other phenolic compounds that are typically found in these samples. Similarly,“thiophenols” refers to the analogous sulfur compounds. The method can be applied to higher boilingpetroleum fractions such as kerosines and diesel oils, b

4、ut the results are biased low and thus results by thismethod for such fractions are considered semi-quantitative.The presence of high concentrations of thiophenols will interfere with the determination of phenols whilehigh concentrations of alkyl mercaptans will interfere with the determination of t

5、hiophenols. A specificdetermination for phenols can be made after removal of both thiophenols and mercaptans by extraction. Thequantitation range for phenols is 0.01 to 0.5 mass-% in gasoline, 0.01 to 40 mass-% in refinery caustic, and0.1 to 10 mass-% in crude cresylic acids. The lower quantitation

6、limit for thiophenols in gasoline is 0.002mass-%. Due to the possibility of oxidation of the sulfur-containing compounds, prompt analysis aftersampling is required to obtain correct results.OUTLINE OF METHODPhenols and thiophenols are extracted from the sample with 10% sodium hydroxide solution. The

7、extraction step is omitted for refinery caustics and crude cresylic acids. The ultraviolet absorption spectrumof the caustic solution is recorded and a baseline correction technique is used to compensate for backgroundabsorption of the sample. Average molar absorptivities are used to compute the mas

8、s-% phenols and mass-% thiophenols.High concentrations of thiophenols will interfere with the determination of phenols; however, an accuratevalue for phenols can be obtained by extraction of thiophenols and mercaptans, if present, using a coppersweetening solution.APPARATUSReferences to catalog numb

9、ers and suppliers are included as a convenience to the method user. Othersuppliers may be used.IT 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 FOLL

10、OWED 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 APPROPRI

11、ATE PERSONAL PROTECTIONEQUIPMENT (PPE).2 of 13262-99Absorption cells, quartz, 10-mm path length, PTFE cover, Fisher Scientific, Cat. No. 14-385-902C, tworequiredBalance, readability 0.1-mgBeaker, borosilicate glass, 400-mL, Fisher Scientific, Cat. No. 02-540LCylinder, graduated, Pyrex, Class A, 50-m

12、L, Fisher Scientific, Cat. No. 08-553AFlasks, volumetric, glass, Class A, 100-, 200-, 250-, 500- and 1000-mL, Fisher Scientific, Cat. Nos. 10-210-5C, D, E , F and G, respectivelyLead donuts, a PVC-coated stabilizer weight (one per separatory funnel needed, see Fig. 3), orange,inside diameter 5-cm, 6

13、50-g mass, I2R, Cat. No. LD-5CMagnetic stirrer, Fisher Scientific, Cat. No. 11-500-49SMagnetic stir bars, TFE Starburst stirring heads, 19-mm diameter (must fit inside separatory funnel) andoctagonal stir bar, Fisher Scientific, Cat. Nos. 14-511-96B and 14-511-63, respectivelyPipets, Class A, borosi

14、licate glass, 5-, 10-, 15-, 20-, 25-, 30- and 50-mL, Fisher Scientific, Cat. Nos. 13-650-2F, -2L, -2M, -2N, -2P, -2Q and -2S, respectivelyRegulator, nitrogen, two-stage, 0 to 345 kPa (0 to 50 psi), Matheson Gas Products, Model 3122-580Separatory funnels, 125-mL, Pyrex, with Teflon plug and polyethyl

15、ene stoppers, Fisher Scientific, Cat.No. 10-437-5BSupport stand with funnel support arm, Fisher Scientific, Cat. Nos. 14-670 and 14-740Ultraviolet spectrophotometer, capable of scanning and operation in the 360- to 220-nm region with aspectral slit width of 1 nm and capable of 0.5% precision in abso

16、rbance measurement at the 1.0 level atthis resolutionREAGENTS AND MATERIALSAll reagents shall conform to the specifications established by the Committee on Analytical Reagents ofthe American Chemical Society, when such specifications are available, unless otherwise specified.References to water mean

17、 distilled water.Bottle, round, clear glass, narrow mouth, Quorpack, 120-mL, with Poly-Seal lined closures, FisherScientific, Cat. No. 03-326-5CCupric sulfate, CuSO45 H2O, 98% purity, Fisher Scientific, Cat. No. C-493Copper sweetening solution, weigh 600.1 g of sodium chloride into a 400-mL beaker.

18、Add 200 mL ofwater and stir until the sodium chloride dissolves. Add 450.1 g of cupric sulfate and continue to stir.Add water as needed, without exceeding a volume of 225-mL. If necessary, warm the solution to 30 to35C to effect dissolution. Quantitatively transfer the solution to a 250-mL volumetri

19、c flask, dilute tovolume with water and mix. Do not refrigerate, store at room tempertaure. A small amount ofprecipitate is allowed. If salt does precipitate, use the solution above the precipitate, do not shake.Filters, Millipore, Millex-HV, 0.45-m, non-sterile, Millipore, Cat. No. SLHV025NSIsoocta

20、ne, 99% purity, Fisher Scientific, Cat. No. O-3003 of 13262-99Nitrogen, 99% minimum puritySodium chloride, 99% purity, Fisher Scientific, Cat. No. S-271Sodium hydroxide solution, 2.5-M (10%), aqueous, Fisher Scientific, Cat. No. SS414-1Sodium hydroxide, 0.4%. Dilute 20 mL of the 10% solution to 500

21、mL with water in a volumetric flask,stopper and mix. Prepare fresh prior to use.Syringes, plastic PP/PE, disposable, 50-mL, graduated, Aldrich Chemical, Cat. No. Z11,840-0Syringe needle, pipetting, PopperTM, stainless steel, 14-gauge x 6-inch (15.2-cm) length, Fisher Scientific,Cat. No. 14-825-16NST

22、ANDARDIZATIONRefer to Table 1 for the average absorptivities, which have been used to derive the equations inCALCULATIONS, for wavelengths 265 nm (thiophenol absorption maximum) and 290 nm (phenolabsorption maximum) (Fig. 1). Each absorptivity value is the average absorbance (-log transmittance) oft

23、ypical petroleum phenols and thiophenols as measured in a 10-mm cell at a concentration of 1 g/L inaqueous 0.4% sodium hydroxide. These absorptivities are applicable for the analysis of gasolines andrefinery caustics used in treating gasolines. For higher boiling petroleum fractions these absorptivi

24、ties giveresults that are lower than the actual values, but the results are consistent for a given fraction. Therefore, thetest can be used only for control purposes on samples of this type.Table 1Absorptivities (L/g-cm)Components 265 nm 290 nmPhenols 6.88 23.7Thiophenols 118.5 18.9PROCEDUREGasoline

25、sBecause thiophenols are rapidly lost from hydrocarbon solutions due to oxidation, particularly in thepresence of olefins, it is necessary that caustic extracts containing the phenols and thiophenols be preparedwithin one hour of the time of sampling the gasoline.1. Purge a 125-mL separatory funnel

26、with nitrogen for 2 minutes.2. Add a magnetic stir bar to the funnel.3. Pipet 50 mL of the gasoline sample into the separatory funnel, while purging with nitrogen.Determine the sample density by ASTM D 4052 or other suitable method for later use inCALCULATIONS. A separate 50-mL sample will also be r

27、equired if a high amount of mercaptans is suspected.4 of 13262-994. Add by pipet 20 mL of the 10 mass-% sodium hydroxide solution to the separatory funnel. Stopperand shake the funnel vigorously for 20 seconds. Vent the funnel by inverting and opening thestopcock.5. Place the separatory funnel on th

28、e magnetic stirrer as shown in Fig. 3. Secure the funnel with a leaddonut and stir, using the highest setting motor speed, for 15 minutes. The purpose is to create an organic-aqueous phase emulsion for maximum quantitative extraction.6. Vent the funnel at intervals by opening the stopcock.7. Remove

29、the lead donut from the funnel and mount the funnel in the funnel support arm. Allow thephases to separate for at least five minutes.8. Drain the lower aqueous caustic solution, quantitatively, into a nitrogen purged 500-mL volumetricflask. Dilute to the mark with water and mix. The resulting diluti

30、on has the required 0.4% sodium hydroxide concentration. If any organic phase is transferred to the volumetric flask, dilute the aqueous phase to the mark.9. Discard the upper hydrocarbon layer.10. Fill two 10-mm absorption cells with the 0.4% sodium hydroxide solution to be used as a reference.Perf

31、orm a background correction by scanning in the region of 360 to 220 nm. Sodium hydroxide solution should not be stored in the reference cell since it etches quartz.11. Remove the absorption cell in the sample beam from the spectrophotometer and discard the sodiumhydroxide.12. Rinse and fill the abso

32、rption cell from Step 11 with the diluted sample solution.13. Return the cell to the instrument and obtain a scan in the region of 360 to 220 nm, measuring theabsorbances at 350, 325, 290, 265 and 238 nm.14. Make successive dilutions with 0.4% sodium hydroxide, as required, if the absorbance is grea

33、ter than1.0 at 290 nm or 265 nm and repeat Step 13.15. Determine if there is a mercaptan interference by performing the calculations, Eqs. 1 through 8 inCALCULATIONS. If there is mercaptan interference (R is greater than 4) and a value is required for phenols, proceed toGasolines Containing Mercapta

34、ns. During the determination of the R factor, the absorbance at 238 nm should be within the operating rangefor the instrument. It may be necessary to confirm the absorbance at 238 nm by diluting the sample.Gasolines Containing MercaptansBecause thiophenols are rapidly lost from hydrocarbon solutions

35、 due to oxidation, particularly in thepresence of olefins, it is necessary that caustic extracts containing the phenols and thiophenols be preparedwithin one hour after sampling the gasoline.5 of 13262-991. Purge a 125-mL separatory funnel with nitrogen for two minutes.2. Add a magnetic stir bar to

36、the funnel.3. Pipet 50 mL of the gasoline sample into the separatory funnel while purging with nitrogen. Determinethe sample density by ASTM D 4052, or other suitable method, for later use in CALCULATIONS.4. Add 10 mL of copper sweetening solution to the separatory funnel and stopper.5. Place the se

37、paratory funnel on the magnetic stirrer as shown in Fig. 3. Secure the funnel with a leaddonut and stir, using the highest motor speed possible, for 15 minutes.6. Vent the separatory funnel at intervals by opening the stopcock.7. Remove the lead donut from the funnel and mount the funnel in the funn

38、el support arm. Allow thephases to separate for at least 15 minutes. The color of the lower aqueous phase should be green to greenish brown (see NOTE).8. Drain and discard, while purging with nitrogen, the lower aqueous copper solution ensuring completeremoval from the separatory funnel.9. Add, by p

39、ipet, 20 mL of the 10% sodium hydroxide, stopper and briefly hand shake the funnel for 15seconds. This is to desorb small droplets of copper solution adhering to the interior glass walls of the funnel. Thesecopper ions will form a deep-blue, soluble, copper complex in a strong alkaline medium.10. Pl

40、ace the separatory funnel on the magnetic stirrer as shown in Fig. 3. Secure the funnel with a leaddonut weight and stir, using the highest setting motor speed, for 15 minutes. The purpose is to create an organic-aqueous phase emulsion for maximum quantitative extraction.11. Vent the funnel at inter

41、vals by opening the stopcock.12. Remove the lead donut from the funnel and mount the funnel in the funnel support arm. Allow thephases to separate for at least five minutes.13. Drain, as completely as possible, the lower aqueous caustic solution, quantitatively, into a nitrogenpurged 500-mL volumetr

42、ic flask.14. Dilute to the mark with water, add a magnetic stir bar to the flask and stir vigorously for fifteenminutes. The resulting dilution has the required 0.4% sodium hydroxide concentration. The purpose of the stirring is to precipitate the copper ions from a deep blue soluble copper-complex

43、toform a light blue, insoluble copper hydroxide that will be filtered off prior to spectrophotometricmeasurements. A higher sodium hydroxide concentration (0.4%) will not allow a quantitative separation of the solublecopper ions since the copper complex will remain intact.15. Decant approximately 50

44、 mL of the caustic solution into a disposable syringe. Attach a Milliporefilter to the syringe and pressure filter, by hand, into a 120-mL nitrogen purged bottle, and thenstopper the bottle.6 of 13262-9916. Rinse and fill two 10-mm absorption cells with the 0.4% sodium hydroxide solution to be used

45、as areference. Perform a background correction by scanning in the region of 360 to 220 nm. Sodium hydroxide solution should not be stored in the reference cell since it etches the quartz.17. Remove the absorption cell in the sample beam from the spectrophotometer and discard the sodiumhydroxide.18.

46、Rinse and fill the absorption cell from Step 17 with the filtered sample solution.19. Obtain a scan in the region of 360 to 220 nm and measure the absorbances at 350-, 325- and 290-nm.20. Make successive dilutions with 0.4% sodium hydroxide, as required, if the absorbance is greater than1.0 at 290 n

47、m, and repeat Step 19.Refinery Caustics and Crude Cresylic Acids1. Weigh 80 to 120 mg, to the nearest 0.1-mg, of sample into a 200-mL volumetric flask.2. Dilute to the mark with 10% sodium hydroxide and mix.3. Dilute a portion of this solution with the 0.4% sodium hydroxide solution so as to bring t

48、heabsorbances at 265 and 290 nm into the 0.2 to 1.0 range for a 10-mm absorption cell.4. Fill two 10-mm absorption cells with the 0.4% sodium hydroxide solution to be used as a reference.Perform a background correction by scanning in the region of 360 to 220 nm. Sodium hydroxide solution should not

49、be stored in the reference cell since it will etch the quartz.5. Remove the absorption cell in the sample beam from the spectrophotometer and discard the sodiumhydroxide.6. Rinse and fill the absorption cell from Step 5 with the diluted sample solution.7. Obtain a scan in the region of 360 to 220 nm and measure the absorbances at 350, 325, 290, 265 and238 nm.CALCULATIONSSignificant FiguresWhen using the equations that follow, carry a minimum of three significant figures through allcalculations. When reporting final phenols (from either Eqs. 9 or 11), report a single