UOP 565-2005 ACID NUMBER AND NAPHTHENIC ACIDS BY TITRATION.pdf

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1、 uop 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 PRES

2、CRIBED 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 1971, 1984, 1992, 2004, 2005 UOP L

3、LC. All rights reserved. Nonconfidential UOP Methods are available from ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. The UOP Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at serviceastm.or

4、g, 610.832.9555 FAX, or 610.832.9585 PHONE. ACID NUMBER AND NAPHTHENIC ACIDS BY TITRATION UOP Method 565-05 SCOPE This method is for determining the acid number of petroleum products, petroleum distillates, and similar materials by potentiometric titration. Inorganic acids, organic acids, mercaptans

5、 and thiophenols respond to this analysis, but their respective salts do not. For naphthenic acids, it is frequently desired to include the salts in the measurement. Therefore, a procedure is also included for the determination of sodium naphthenate salts. The typical range for acid number determina

6、tion is 0.002 to 5 mg KOH/g of sample, although higher concentrations can be accommodated. There are three procedures included in the method. The acid number of a sample can be determined on an as-received basis or on a mercaptan- and thiophenol-free basis. The method can also be used to determine n

7、aphthenic acids including sodium naphthenates (soaps) in caustic-washed hydrocarbons. For an estimated relative molecular mass of 130, the range of quantitation for naphthenic acids is 5 to 500 mass-ppm. The latter two procedures apply almost exclusively to light kerosines and gas oils where it is a

8、ssumed that the organic acids are entirely naphthenic. If no potentiometric titrator is available, and the sample is light in color, the titration may be performed colorimetrically; see the APPENDIX. REFERENCES ASTM Method D 86, “Distillation of Petroleum Products at Atmospheric Pressure,” www.astm.

9、org UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org OUTLINE OF METHOD PROCEDURE A, determination of acid number on an as-received basis: A weighed amount of sample is mixed with a titration solvent and titrated to a potentiometric endpoint with alcoholic KOH using a titrator equi

10、pped with a CO2guard tube. The titration is performed using a combination glass electrode. After a blank correction, the acid number is calculated as mg KOH/g of sample. PROCEDURE B, determination of acid number on a mercaptan- and thiophenol-free basis: Copyright by ASTM Intl (all rights reserved);

11、Reproduction authorized per License Agreement with Monique Tyree (IHS); Fri Aug 26 14:02:28 EDT 20052 of 13 565-05 The sample is shaken with a copper sulfate-sodium chloride solution in the presence of air in order to oxidize (sweeten) the mercaptan and thiophenols to disulfides. After filtration, t

12、he sample is titrated as described in PROCEDURE A. PROCEDURE C, determination of naphthenic acids including sodium naphthenates (soaps) in caustic-washed hydrocarbons: The sample is shaken with a copper sulfate-sodium chloride solution (sweetened) and filtered. The sample is then washed with dilute

13、sulfuric acid in order to convert the sodium naphthenates to naphthenic acids. The sample is then washed with water and filtered. The treated sample is then titrated as described in PROCEDURE A. The mid-boiling point distillation temperature of the sample is determined by ASTM Method D 86, “Distilla

14、tion of Petroleum Products at Atmospheric Pressure,” from which the molecular mass of the naphthenic acids is estimated. The naphthenic acid value is calculated in mass-ppm. APPARATUS References to catalog numbers are included as a convenience to the method user. Other suppliers may be used. Balance

15、, readability 0.01-g Balance, readability 0.1-mg Beaker, 250-mL, tall, without spout, borosilicate glass, Reliance Glass, Cat. No. G-9906-002 Bottles, wash, for 2-propanol and water, Fisher Scientific, Cat. Nos. 02-897-6 and -11, respectively Crucible, high form, 10-mL, porcelain, Fisher Scientific,

16、 Cat. No. 07-965C, with cover, Fisher Scientific, Cat. No. 07-970D Cylinders, graduated, 10-, 100-, 250-, and 1000-mL, borosilicate glass, Fisher Scientific, Cat. Nos. 08-549-5B, -5E, -5G, and -5J, respectively Desiccator, 160-mm ID, and porcelain plate, Fisher Scientific, Cat. Nos. 08-632 and 08-64

17、1A, respectively Electrode, combination glass, with sleeve diaphragm, double junction, Brinkmann Instruments, Cat. No. 20 91 050-0. Store in water when not in use. Flask, Erlenmeyer, 500-mL, borosilicate glass, iodine, with borosilicate glass stopper, Fisher Scientific, Cat. No. 10-094C, two require

18、d Flasks, volumetric, Class A, 100-, 1000-, and 2000-mL, borosilicate glass, Fisher Scientific, Cat. Nos. 10-210-5C, -5G, and -5H, respectively Funnel, filtering, general purpose, borosilicate glass, Fisher Scientific, Cat. No. 10-322E Funnel, separatory, 500-mL and 1-L, borosilicate glass, Fisher S

19、cientific, Cat. Nos. 10-437-5D and -5E, respectively Hot plate, Fisher Scientific, Cat. No. 11-600-49H, if needed to heat heavy or viscous samples Copyright by ASTM Intl (all rights reserved);Reproduction authorized per License Agreement with Monique Tyree (IHS); Fri Aug 26 14:02:28 EDT 20053 of 13

20、565-05 Magnetic stir bar, Fisher Scientific, Cat. No. 14-511-64, three required Mortar, porcelain, 130-mm OD, Fisher Scientific, Cat. No. 12-961-C, with pestle, porcelain, Fisher Scientific, Cat. No. 12-961-5C Oven, drying, capable of operation at 120C, Fisher Scientific, Cat. No. 13-246-506G Pipet,

21、 volumetric transfer, Class A, 100-mL, Fisher Scientific, Cat. No. 13-650-2U Regulator, nitrogen, two-stage, high purity, delivery pressure range 15-200 kPa (2-30psig), Matheson Gas Products, Model 3121-580 Shaker, wrist action, Fisher Scientific, Cat. No. 14-260 Spatula, micro, Fisher Scientific, C

22、at. No. 21-401-15 Stopper, size 7, rubber, Fisher Scientific, Cat. No. 14-130L Thermometer or thermocouple, if needed for heating heavy or viscous samples Titrator, potentiometric, recording, 2000-mV range, 1-mV resolution, capable of reducing the titration rate to a minimum in the vicinity of the e

23、ndpoint, with dispenser having a volume readout of 0.00 - 99.99 mL, 0.0001 of the buret volume resolution, Metrohm Model 836 Titrando system with optional sample changer, and 20-mL buret with a reservoir guard tube, Brinkmann Instruments Tongs, stainless steel, crucible, Fisher Scientific, Cat. No.

24、15-186 Tubing, thick walled, rubber, for vacuum use, Fisher Scientific, Cat. No. 14-173D Vacuum pump, Precision Model No. DD-20, Fisher Scientific, Cat. No. 01-182 REAGENTS AND MATERIALS References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may

25、 be used. References to water mean double deionized or distilled, unless otherwise specified. Absorbent, carbon dioxide, Ascarite II, 20 to 30-mesh, Fisher Scientific, Cat. No. A184-500 Chloroform, 99% minimum purity, Fisher Scientific, Cat. No. C606 Copper sulfate pentahydrate (cupric sulfate), 98%

26、 minimum purity, Fisher Scientific, Cat. No. C493-500 Desiccant, 8-mesh, indicating, Fisher Scientific, Cat. No. 07-578-3A Electrolyte, ethanol saturated with lithium chloride, for filling reference electrode, Brinkmann Instruments, Cat. No. 20 09 444-3 Filter paper, acid-free, non acid-washed, What

27、man No. 4, available from Fisher Scientific, Cat. No. 09-825A Methanol, 99.8% minimum purity, Fisher Scientific, Cat. No. A-412 Copyright by ASTM Intl (all rights reserved);Reproduction authorized per License Agreement with Monique Tyree (IHS); Fri Aug 26 14:02:28 EDT 20054 of 13 565-05 Nitrogen, 99

28、.999% minimum purity Phenolphthalein solution, 1% in 2-propanol, Fisher Scientific, Cat. No. LC18210-7 Potassium hydrogen phthalate, primary standard, Fisher Scientific, Cat. No. P243-100 Potassium hydroxide, 0.5-N (0.5-M), alcoholic (methanol), Fisher Scientific, Cat. No. SP222-1 Potassium hydroxid

29、e, 0.05-N (0.05-M), alcoholic (methanol). Pipet 100 mL of 0.5-N alcoholic (methanol) KOH into a 1-L volumetric flask, and dilute to the mark with methanol. Mix thoroughly by repeated inversions. 2-propanol, 99% minimum purity, Fisher Scientific, Cat. No. A451-4 Sodium chloride, Fisher Scientific, Ca

30、t. No. S671-500 Sulfuric acid, approximately 0.1-N (0.05-M), Fisher Scientific, Cat. No. SA220-1 Sweetening reagent. Dissolve 140 1 g of sodium chloride and 150 1 g of copper sulfate in one liter of water. Tape, electrical, Fisher Scientific, Cat. No. 09-356 Titration solvent 1. Add, by graduated cy

31、linder, 1000 mL of toluene, 990 mL of 2-propanol, and 10 mL of water to a 2000-mL volumetric flask. Mix thoroughly by repeated inversions. Titration solvent 2. Add, by graduated cylinder, 500 mL of toluene, 500 mL of chloroform and 500 mL of 2-propanol to a 2000-mL volumetric flask. Mix thoroughly b

32、y repeated inversions. Toluene, 99.8% minimum purity, Fisher Scientific, Cat. No. T290-4 STANDARDIZATION OF POTASSIUM HYDROXIDE The analyst is expected to be familiar with general laboratory practices, the technique of titration, and with the equipment being used. 1. Assemble and operate the titrato

33、r and electrodes according to the manufacturers instructions. 2. Fill the dispenser reservoir of the titrator with the 0.05-M potassium hydroxide solution. The solution must be protected from atmospheric carbon dioxide by attaching a guard tube containing an absorbent, such as Ascarite, to the dispe

34、nser reservoir. 3. Crush approximately 1 g of potassium hydrogen phthalate using a mortar and pestle. 4. Transfer the potassium hydrogen phthalate to a clean crucible, and dry at 120C for 2 hours in a drying oven. 5. Remove the crucible from the oven using tongs, place it in a desiccator, cover it,

35、and allow it to cool to ambient temperature. 6. Weigh approximately 0.1 g of dried potassium hydrogen phthalate, to the nearest 0.1 mg, into each of three 250-mL beakers, and record the masses in each beaker. The standardization is performed in triplicate. Copyright by ASTM Intl (all rights reserved

36、);Reproduction authorized per License Agreement with Monique Tyree (IHS); Fri Aug 26 14:02:28 EDT 20055 of 13 565-05 7. Add, by graduated cylinder, 100 mL of carbon dioxide free water and a stirring bar to each beaker. The water must be carbon dioxide free. Prepare immediately before use by boiling

37、for approximately 10 minutes to expel carbon dioxide and then cooling while purging with nitrogen, or by placing the water under vacuum for sufficient time to degas. For example, 500 mL of water requires approximately 90 minutes under vacuum to fully degas. 8. Place one of the beakers on the titrati

38、on stand, immerse the electrodes and buret tip, and stir. Adjust the stirring speed to create a vortex in the solvent such that bubbles do not develop at its center. Obtain a stable reading before proceeding to Step 9. 9. Adjust the titration parameters so that the initial titration rate in the plat

39、eau region is 0.3 mL/min and the titration rate in the region of the endpoint is reduced to 0.1 mL/min. Titrate the potassium hydrogen phthalate solution with the 0.05-M potassium hydroxide. Record the volume of titrant used to reach the endpoint of the titration. The endpoint is the midpoint of the

40、 inflection; the point at which the curve changes from concave to convex, see Figure 1. 10. Titrate the contents of the other two beakers in the same manner. 11. For each titration, calculate the molarity of the potassium hydroxide, to four significant figures, using Equation 1: B2.204A10M3= )1( whe

41、re: A = mass of potassium hydrogen phthalate weighed into beaker, g B = volume of potassium hydroxide solution used to reach the endpoint, mL M = molarity of the 0.05-M potassium hydroxide, moles/L 204.2 = molecular mass of potassium hydrogen phthalate, g/mole 103= factor to convert moles/mL to mole

42、s/L 12. Average the results of the three determinations to four significant figures. Results from each of the triplicate runs should not deviate by more than 0.001M. If greater deviations occur, make certain that there are no problems with the equipment or the procedure; then repeat the procedure un

43、til the required repeatability is obtained on three consecutive runs. The potassium hydroxide solution must be standardized at least weekly to detect changes in molarity. A reference quality assurance sample may be run daily to confirm the stability of the titrant between standardizations. PROCEDURE

44、 Part A: Acid Number, As-Received Basis 1. Select the appropriate titration solvent (see REAGENTS AND MATERIALS) and sample size for the sample being analyzed; use Table 1 as a guide. 2. Determine a blank by performing the following Steps 6 through 10, using only the titration solvent, omitting the

45、sample. Copyright by ASTM Intl (all rights reserved);Reproduction authorized per License Agreement with Monique Tyree (IHS); Fri Aug 26 14:02:28 EDT 20056 of 13 565-05 3. Heat heavy or viscous samples containing suspended materials to 60 5C until the sample is completely fluid. The heating may be ac

46、complished by using an oven, a heated bath, a hot plate, or other convenient means. Do not use the oven used to dry the potassium hydrogen phthalate to warm the samples. Subsequent batches of potassium hydrogen phthalate could be contaminated by sample residue. 4. Shake vigorously to obtain a repres

47、entative sample. Table 1 Titration Solvent and Sample Size Sample Type TitrationSolvent Approximate Sample Size, g Light petroleum distillates such as kerosines, diesel fuels, jet fuels, gas oils, both sweetened and unsweetened 1 100a Vacuum gas oil, resid, coal oil, shale oils and crude oils 2 50 a

48、 Do not exceed 120-mL sample volume. 5. Weigh the sample, to the nearest 0.01 g, into a 250-mL titration beaker. 6. Add, by graduated cylinder, 100 mL of the titration solvent selected in Step 1. 7. Add a stirring bar, position the beaker on the titration stand, start a slow flow of nitrogen to the

49、headspace of the beaker to expel air, and stir. Adjust the stirring speed to create a vortex in the solvent such that bubbles do not develop at its center. Continue applying a nitrogen blanket throughout the titration. 8. Immerse the electrodes into the solution and wait for a stable reading. 9. Titrate the solution with the 0.05-M potassium hydroxide using the following conditions. Adjust the titration parameters so that the initial titration rate in the plateau region is 0.3 mL/min, and the titration rate in the region of the endpoint is reduced to