UOP 304-2008 Bromine Number and Bromine Index of Hydrocarbons by Potentiometric Titration.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 1959, 1990, 2008 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. Bromine Number and Bromine Index of Hydrocarbons by Potentiometric Titration UOP Method 304-08 Scope This method is for determining bromine number and bromine index, by potentiometric titration, in hydrocarbons that are stable at room temperature and have endpoints below 550C (10

5、22F) as determined by ASTM Method D 1160, “Distillation of Petroleum Products at Reduced Pressure,” or D 2887, “Boiling Range Distribution of Petroleum Fractions by Gas Chromatography.” The results denote those compounds that react with bromine under the analytical conditions prescribed in this meth

6、od, and, in general, are relatable to olefin content. However, certain non-olefinic compounds can constitute a positive interference, while some olefins will not react stoichiometrically (see ASTM D 1159, “Bromine Number of Petroleum Distillates and Commercial Aliphatic Olefins by Electrometric Titr

7、ation”). The olefin content can be estimated using the calculation in ASTM D 1159. References ASTM Method D 1159, “Bromine Number of Petroleum Distillates and Commercial Aliphatic Olefins by Electrometric Titration,” www.astm.org ASTM Method D 1160, “Distillation of Petroleum Products at Reduced Pre

8、ssure,” www.astm.org ASTM Method D 1492, “Bromine Index of Aromatic Hydrocarbons by Coulometric Titration,” www.astm.org ASTM Method D 2710, “Bromine Index of Petroleum Hydrocarbons by Electrometric Titration,” www.astm.org ASTM Method D 2887, “Boiling Range Distribution of Petroleum Fractions by Ga

9、s Chromatography,” www.astm.org ASTM Method D 5776, “Bromine Index of Aromatic Hydrocarbons by Electrometric Titration,” www.astm.org UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method The sample is dissolved in a titration solvent containing a catalyst that aids i

10、n the titration reaction. The solution is titrated potentiometrically at room temperature with either a 0.5-N (0.25-M) or 0.02-N 2 of 13 304-08 (0.01-M) bromide-bromate solution depending upon whether bromine number or bromine index, respectively, is being determined. The titration uses a combinatio

11、n platinum electrode in conjunction with a recording potentiometric titrator. Bromine number or index is calculated from the volume of titrant required to reach a stable endpoint. Definitions Bromine number, the number of grams of bromine consumed by 100 g of the sample when reacted under the condit

12、ions specified. Bromine index, the number of milligrams of bromine consumed by 100 g of the sample when reacted under the conditions specified. By definition the bromine index divided by 1000 is essentially equivalent to the bromine number. Other methods for the determination of bromine index or bro

13、mine number, that may be useful for reference purposes, include: ASTM Method D 1159, “Bromine Numbers of Petroleum Distillates and Commercial Aliphatic Olefins by Electrometric Titration,” ASTM Method D 1492, “Bromine Index of Aromatic Hydrocarbons by Coulometric Titration,” ASTM Method D 2710, “Bro

14、mine Index of Petroleum Hydrocarbons by Electrometric Titration,” and ASTM Method D 5776, “Bromine Index of Aromatic Hydrocarbons by Electrometric Titration.” Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Balance,

15、 readability, 0.1-mg Beaker, 250-mL, tall, without spout, borosilicate glass, Wilmad-LabGlass, Cat. No. G-9906-002 Cylinders, graduated, Class B, 25-, 50-, 100-, and 1000-mL, VWR, Cat. Nos. 89001-112, -114, -116, and -122, respectively Electrode, platinum ring, combination, Metrohm USA, Cat. No. 020

16、924357. See Note 1. Flasks, volumetric, Class A, 100- and 1000-mL, VWR, Cat. Nos. 89001-964 and -966, respectively Pipets, volumetric transfer, Class A, 20- and 100-mL, VWR, Cat. No. 89002-762 and -768, respectively Pipet filler, VWR, Cat. No. 53497-055 Refrigerator, hazardous location or flammable

17、storage, VWR, Cat. No. VF-6EAR Stir bar, Teflon coated, VWR, Cat. No. 58948-950 Stirrer, magnetic, VWR, Cat. No. 11301-010 Titrator, potentiometric, recording, 2000-mV range, 1-mV resolution, capable of following a maximum allowable drift throughout a titration and/or reducing the titration rate to

18、a minimum in the vicinity of the equivalence point, with dispenser having a volume readout of 0.001-99.999 mL with a 0.0001 of the buret volume resolution, Metrohm 835 Titrando system with optional 814 sample changer, and 1-, 5-, and 10-mL burets. Reagents References to catalog numbers and suppliers

19、 are included as a convenience to the method user. Other suppliers may be used. References to water mean double-deionized or triple-distilled water. 3 of 13 304-08 Acetic acid, glacial, 99.7% minimum purity, VWR, Cat. No. EM-AX0074-2 Cyclohexene, 99+% minimum purity, VWR, Cat. No. AA32673-K2 Cyclohe

20、xene-Bromine Number reference standard solution. Weigh, to the nearest 0.1 mg, 1.78 g of cyclohexene into a 100-mL volumetric flask, tared to the nearest 0.01 g. Dilute to the mark with toluene, mix well and reweigh. Calculate the theoretical bromine number (Equation 1). Store the solution in the re

21、frigerator when not in use. When refrigerated, the solution is stable for 6 months. Cyclohexene-Bromine Index reference standard solution. Weigh, to the nearest 0.1 mg, 4.33 g of cyclohexene Bromine Number reference standard solution into a 100-mL volumetric flask, tared to the nearest 0.01 g. Dilut

22、e to the mark with toluene, mix well and reweigh. Calculate the theoretical bromine index (Equation 2). Store the solution in the refrigerator when not in use. When refrigerated, the solution is stable for 6 months. Mercuric chloride, powder, 99.5% minimum purity, VWR, Cat. No. EM-MX0345-4 Mercuric

23、chloride methanolic solution. Weigh 10.00 0.01 g of mercuric chloride powder into a 100-mL volumetric flask. Dilute to the mark with methanol. Mix well. Methanol, 99.8% minimum purity, VWR, Cat. No. BJ230-1 Methylene chloride, 99.9% minimum purity, unstabilized, Fisher Scientific, Cat. No. D150SK-1

24、(see Note 2) Potassium bromide, crystal, 99.0% minimum purity, VWR, Cat. No. EM-PX1380-1 Potassium bromide, 30% solution. Dissolve 30 0.01 g of potassium bromide in 80 mL of water in a 100-mL volumetric flask. Dilute to the mark and mix well. Potassium bromide-bromate solution, certified, 0.5-N (0.2

25、5-M), as generated bromine (Br2), Lab Chem, Inc., Cat. No. LC11970-1. See the Appendix for an alternative procedure to prepare and standardize this solution in the laboratory. Potassium bromide-bromate solution, 0.02-N (0.01-M), as generated bromine (Br2). Pipette 40 mL of 0.5N bromide-bromate solut

26、ion into a 1000-mL volumetric flask. Dilute to the mark with water and mix well (see Standardization of Titrant). Sulfuric acid, approximately 6-N (3-M), VWR, Cat. No. VW3485-1 Stopper, silicone rubber, VWR, Cat. No. 59590-084 Syringes, disposable, all PP/PE, 5-, 20-, and 50-mL. VWR, Cat. Nos. 53548

27、-004, -008, and 010, respectively, with needle, VWR, Cat. No.BD305187. These syringes must not have rubber tips, nor contain silicone oil. Titration solvent-bromine index. Prepare one liter of titration solvent by mixing the following in a 1000-mL volumetric flask, in the order shown. The solution m

28、ust be mixed well after each addition: 704 mL of glacial acetic acid, 134 mL of methylene chloride, 98 mL of methanol, 18 mL of 3-M sulfuric acid, 36 mL of methanolic mercuric chloride and 10 mL of 30% potassium bromide solution (see Note 3). Allow to stand overnight before use. Titration solvent ca

29、nnot be stored longer than one week. Titration solvent-bromine number. Prepare one liter of titration solvent by mixing the following in a 1000-mL volumetric flask: 714 mL of glacial acetic acid, 134 mL of methylene chloride, 116 mL of methanol, 18 mL of 3-M sulfuric acid and 18 mL of methanolic mer

30、curic chloride. Allow to stand overnight before use. Titration solvent cannot be stored longer than one week. 4 of 13 304-08 Toluene, high purity, VWR, Cat. No. BJ347-4 Vials, glass, with polyseal cone lined caps, 15-mL, VWR, Cat. No. 16087-062 Water, double-deionized or triple-distilled Wiper, Kimw

31、ipes, VWR, Cat. No. 21905-026 Procedure The analyst is expected to be familiar with general laboratory practices, the technique of titration, and with the equipment being used. Electrode Preparation and Blank The electrode must be properly conditioned to obtain reproducible and noise-free titration

32、curves. Condition the electrode at the beginning of each day, or if 2 or more hours have elapsed between sample titrations, by titrating a minimum of 2 blank determinations. Use the procedure described under Determination of Bromine Index or Determination of Bromine Number except that no sample is a

33、dded. The results from the two blanks are compared and if they are within 0.02 mL, samples can be analyzed. If the two blanks do not agree within 0.02 mL, the blank titration must be repeated. If the blanks do not consistently repeat within 0.02 mL, reanalyze the blank after every sample. Use the av

34、erage of the blank titration results, before and after the sample titration, in the calculation. Standardization Calculate the theoretical bromine number to one decimal place for the dilute Cyclohexene-Bromine Number reference standard solution using Equation 1: Theoretical Bromine Number =XB556.194

35、 )1( where: B = mass of cyclohexene, g X = mass of cyclohexene plus toluene diluent, g 194.556 = factor for converting g of cyclohexene per g of cyclohexene plus toluene diluent to bromine number, equal to the product: 14.82)100)(808.159(1a) where: 82.14 = the molecular weight of cyclohexene, g/mole

36、 100 = conversion of g/g to g/100 g 159.808 = the molecular weight of bromine, g/mole Calculate the theoretical bromine index to the nearest unit for the dilute Cyclohexene-Bromine Index reference standard solution using Equation 2: Theoretical Bromine Index =ZY)1000(R )2( where: Y = mass of Cyclohe

37、xene-Bromine Number reference standard solution, g Z = mass of Cyclohexene-Bromine Number reference standard solution plus toluene diluent, g R = Theoretical bromine number for the dilute Cyclohexene-Bromine Number reference standard solution as calculated in Equation 1. 1000 = conversion of grams t

38、o milligrams, mg/g 5 of 13 304-08 Verify the concentration of the potassium bromide-bromate standard solution by titrating one gram of Cyclohexene-Bromine Number reference standard solution as described under Determination of Bromine Number, or one gram of Cyclohexene-Bromine Index reference standar

39、d solution as described under Determination of Bromine Index. If the determined bromine number or bromine index is not within 3% of the calculated theoretical value for the reference solution (Equations 1 and 2), standardize the titrant using the procedure described in the Appendix. Standardization

40、of Titrant The 0.5-N bromide-bromate solution is purchased as a certified standard. Alternatively, it may be prepared and standardized in the laboratory as described in the Appendix. Prepare the 0.02-N bromide-bromate solution as described in Reagents. Calculate the normality of the nominally 0.02-N

41、 bromide-bromate solution using Equation 3: Normality of the nominally 0.02-N bromide-bromate solution = 0.04U (3) where: U = certified or standardized normality of the nominally 0.5-N bromide-bromate solution 0.04 = dilution factor, 40 mL / 1000 mL Determination of Bromine Number Since potentiometr

42、ic recording titrators can vary, the exact settings are judgmental. Experience gained in the titration of Cyclohexene-Bromine Number reference standard solution (see Standardization) will provide guidance in the choice of settings that will produce an accurate value in a reasonable time. When the ap

43、proximate bromine number is determined, a more appropriate sample size can be selected and the sample reanalyzed to obtain a precise result. Samples with bromine numbers less than 0.8 are analyzed by the bromine index procedure, while samples with bromine numbers greater than 24 are diluted prior to

44、 analysis (see Table 1). Table 1 Sample Size for Expected Bromine Number Bromine Number Sample Size, g 0.8-3 4 3-6 2 6-12 1 12-24 0.5 24-120 Dilute 1 g in 10 g* 120-240 Dilute 0.25 g in 10 g* * Dilutions are prepared in a glass vial in toluene. Weigh 1 g of the diluted sample into a titration beaker

45、 and titrate. 1. Pipet 100 mL of the bromine number titration solvent into the 250-mL titration beaker (see Note 4). 2. Flush a disposable syringe with needle and draw an aliquot of sample for analysis. Quickly remove any liquid adhering to the outside of the needle with a wiper and stopper the tip

46、of the needle with a silicone rubber stopper. The sample size needed is dependent on the expected bromine number. Use Table 1 as a guide in determining the sample amount needed. 3. Weigh the stoppered syringe plus sample to the nearest 0.1 mg. 6 of 13 304-08 4. Remove the silicone rubber stopper and

47、 inject the sample aliquot into the bromine number titration solvent The needle tip is inserted directly above the level of the bromine index titration solvent to ensure that the entire sample dissolves in the solution and does not adhere to the cell walls. 5. Replace the stopper and reweigh the sto

48、ppered syringe to the nearest 0.1 mg. Calculate the mass of the sample injected by difference and record. If an expected bromine number is not known, add approximately 1 g of sample to the titration cell and titrate. After an approximate bromine index is determined, a more appropriate sample size is

49、 selected and the sample is reanalyzed to obtain a precise result. If, upon the addition of the sample to the titration solvent, or if, during the titration, the solution separates or becomes cloudy, then the sample size must be reduced by 50% and the titration repeated. Samples such as detergent alkylate are slow to react and must be analyzed accordingly. 6. Place a Teflon stir bar in the titration beaker and set it on the magnetic stirrer. 7. Insert the combination electrode and adjust the stirring speed to create a vortex in the solvent that does not develop bubb