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 1965, 1982, 2007, 2008 UOP LLC. All ri
3、ghts 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.org, 610.832
4、.9555 FAX, or 610.832.9585 PHONE. Diene Value by Maleic Anhydride Addition Reaction UOP Method 326-08 Scope This method is for determining maleic anhydride reactivity with a wide variety of oils, ranging from debutanized light hydrocarbon distillates to heavy drying oils, using titration. The method
5、 gives a measure of the conjugated diolefin content of the sample. The determination is somewhat empiricalsince some conjugated diolefins may not react completely, while certain compounds other than conjugated diolefins also may be reactive. For example, anthracene, along with many of its homologs a
6、nd corresponding alkylated compounds, as well as certain vinyl aromatics, react as dienes with maleic anhydride. Therefore, the results obtained by this method must be carefully interpreted in the light of these specified limitations. The range of quantitation for diene value is from 1.2 to over 100
7、. A modified procedure can be used to estimate diene values less than 1.2. If the average molecular weight of the conjugated diolefins is known or can be estimated, the mass-% concentration of conjugated diolefins can be calculated. References AOCS Official Method Th 1a-64, “Diene Value,” www.aocs.o
8、rg Ellis, B. A. and Jones, R. A., Analyst 61, 812 (1936) McKinney, R. S., Hallbrook, N. J., and Rose, W. G., Oil and Soap 19, 141-143 (1942) Norton, J. A., Chem. Rev. 31, 319 (1942) UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method Maleic anhydride is refluxed wit
9、h the sample in boiling toluene for 3 hours. The unreacted maleic anhydride is hydrolyzed to maleic acid, extracted from the reaction mixture, and titrated with sodium hydroxide. A blank is run using the same amount of maleic anhydride as charged to the reaction flask. The amount reported as having
10、reacted with the sample is the net volume obtained by potentiometric titration difference, and from this data the diene value and/or the percent dienes can be calculated. An alternative titration technique, using a manual (colorimetric) procedure, is described in the Appendix. Additional information
11、 regarding this technique is provided in References. 2 of 10 326-08 Definition Diene value, the number of grams of iodine equivalent to the amount of maleic anhydride that reacts with 100 g of sample (on the basis of 2 atoms of iodine per mole of maleic anhydride) under the specified reaction condit
12、ions. Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Balance, readability 0.01-g Beaker, 250-mL, tall, without spout, borosilicate glass, Reliance Glass, Cat. No. G-9906-002 or Brinkmann, Cat. No. 020212128, three
13、required Bottle, polyethylene, 1000-mL, Fisher Scientific Co., Cat. No. 03-313-5D Condenser, Liebig, with Ts 24/40 ground-glass joint, Fisher Scientific, Cat. No. 07-721C, at least two required Crucible, high form, 10-mL, porcelain, Fisher Scientific, Cat. No. 07-965C, with cover, Fisher Scientific,
14、 Cat. No. 07-970D Cylinders, graduated, 10- and 25-mL, Class B, Fisher Scientific, Cat. Nos. 08-549-5B and -5C, respectively Desiccator, 160-mm ID, and porcelain plate, Fisher Scientific, Cat. Nos. 08-632 and 08-641A, respectively Electrode, combination glass, with sleeve diaphragm, double junction,
15、 Brinkmann Instruments, Cat. No. 20 91 050-0. Store in water when not in use. Flask, Erlenmeyer, 250-mL, Fisher Scientific Co., Cat. No. 10-040F Flask, Erlenmeyer, 250-mL, with Ts 24/40 ground-glass joint, Fisher Scientific, Cat. No. 10-047C, at least two required Flask, Erlenmeyer, 500-mL, borosili
16、cate glass, heavy walled, with side arm, Fisher Scientific, Cat. No. 10-180K, optional, see Standardization of Sodium Hydroxide Flask, volumetric, 1000-mL, Class A, Fisher Scientific, Cat. No. 10-210-5G Funnel, filter, Fisher Scientific, Cat. No. 10-326-2C Funnel, separatory, 250-mL, Fisher Scientif
17、ic, Cat. No. 10-437-5C Hot plate, Thomas Scientific, Cat. No. 5983C06 Magnetic stir bar, Fisher Scientific, Cat. No. 14-511-64, three required Mortar, porcelain, 130-mm OD, with pestle, porcelain, Fisher Scientific, Cat. Nos. 12-961-C and 12-961-5C, respectively Oven, drying, capable of operation at
18、 120C, Fisher Scientific, Cat. No. 13-246-506G Pipet filler, Fisher Scientific, Cat. No. 13-681-102A Pipet, Mohr, 25-mL, Fisher Scientific, Cat. Nos. 13-665-100F Pipets, volumetric transfer, 2-, 3-, 5-, 10-, and 20-mL, Class A, Fisher Scientific, Cat. Nos. 13-650-2C, -2D, -2F, -2L, and -2N, respecti
19、vely 3 of 10 326-08 Regulator, nitrogen, two-stage, high purity, delivery pressure range 15-200 kPa (2-30psig), Matheson Gas Products, Model 3121-580 Ring stands and clamps, to hold apparatus Stirrer, magnetic, Fisher Scientific, Cat. No. 14-493-120S Stirring rod, glass, Fisher Scientific, Cat. No.
20、11-380D Titrator, potentiometric, recording, 2000-mV range, 1-mV resolution, capable of reducing the titration rate to a minimum in the vicinity of the endpoint, 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 o
21、ptional sample changer, and 20-mL buret with a reservoir guard tube, Brinkmann Instruments Tongs, stainless steel, crucible, Fisher Scientific, Cat. No. 15-186 Tubing, thick walled, rubber, for vacuum use, Fisher Scientific, Cat. No. 14-173D, optional, see Standardization of Sodium Hydroxide Vacuum
22、pump, Precision Model No. DD-20, Fisher Scientific, Cat. No. 01-182, optional, see Standardization of Sodium Hydroxide Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. References to water mean deionized
23、water. Absorbent, carbon dioxide, Ascarite II, 20 to 30-mesh, Fisher Scientific, Cat. No. A184-500 Boiling chips, silicon carbide, Thomas Scientific, Cat. No. 1590D33 Desiccant, 8-mesh, indicating, Fisher Scientific, Cat. No. 07-578-3A Electrolyte, 3 mol/L potassium chloride, Brinkmann, Cat. No. 20
24、09 610-1 Filter paper, qualitative, medium, acid-free, non acid-washed, Whatman No. 1, Fisher Scientific, Cat. No. 09-805F Maleic anhydride 108-31-6, 99%, mp 52-55C, Acros Organics, Cat. No. 36494, Fisher Scientific Maleic anhydride in toluene. Dissolve 60 g of maleic anhydride in warm toluene. Cool
25、, transfer to a one-liter volumetric flask, and dilute to the mark with toluene. Allow the solution to stand at least one day, and filter through a qualitative-grade filter paper before using. Methyl-tert-butyl ether 1634-04-4, (MTBE), or tert-butyl methyl ether, 3 degree boiling range, Fisher Scien
26、tific Co., Cat. No. E-128, or equivalent Nitrogen, 99.999% minimum purity Pencil, soft lead, local supply, source of graphite lubricant Phenolphthalein indicator solution, 1% w/v, Fisher Scientific, Cat. No. SP62-500 Potassium hydrogen phthalate, primary standard, Fisher Scientific, Cat. No. P243-10
27、0 Sodium hydroxide, 0.1-M, Certified, Fisher Scientific, Cat. No. SS276-1, for low diene value analysis only Sodium hydroxide, 1.0-M, Certified, Fisher Scientific, Cat. No. SS266-1 Toluene, 99.8%, HPLC grade, Fisher Scientific, Cat. No. T290-1 4 of 10 326-08 Water, carbon dioxide free, see Standardi
28、zation of Sodium Hydroxide Water, deionized Procedure The analyst is expected to be familiar with general laboratory practices, the technique of potentiometric titration, and with the equipment being used. Standardization of Sodium Hydroxide 1. Assemble and operate the titrator and electrodes accord
29、ing to the manufacturers instructions. 2. Fill the dispenser reservoir of the titrator with the 1.0-M sodium hydroxide solution. If a diene value less than 1.2 is to be determined, standardize the 0.1-M sodium hydroxide solution in the same manner. The solution must be protected from atmospheric car
30、bon dioxide by attaching a guard tube containing an absorbent, such as Ascarite, to the dispenser reservoir. 3. Crush approximately 3 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
31、oven. 5. Remove the crucible from the oven using tongs, place it in a desiccator, cover it, and allow it to cool to ambient temperature. 6. Place a stirring bar into each of three 250-mL beakers. The standardization is performed in triplicate. 7. Weigh approximately 0.5 g of dried potassium hydrogen
32、 phthalate, to the nearest 0.1 mg, into each of the three 250-mL beakers and record the masses in each beaker. If the 0.1-M sodium hydroxide solution is being standardized, weigh in approximately 0.1 g of the dried potassium hydrogen phthalate, to the nearest 0.1 mg. 8. Add, by graduated cylinder, 1
33、00 mL of carbon dioxide free water to each beaker. The water must be carbon dioxide free. Prepare immediately before use by boiling deionized water for approximately 10 minutes to expel carbon dioxide and then cooling while purging with nitrogen, or by placing the water under vacuum for sufficient t
34、ime to degas. For example, 500 mL of water requires approximately 90 minutes under vacuum to fully degas. 9. Place one of the beakers on the titration stand, immerse the electrodes and buret tip, start a slow flow of nitrogen to the headspace of the beaker to expel air, and stir. Adjust the stirring
35、 speed to create a vortex in the solvent such that bubbles do not develop at its center. Obtain a stable reading before proceeding to the next step. 10. 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
36、endpoint is reduced to 0.1 mL/min. Titrate the potassium hydrogen phthalate solution with the 1.0-M sodium hydroxide. Record, to the nearest 0.001 mL, the volume of titrant used to reach the endpoint of the titration. The endpoint is the midpoint of the inflection; the point at which the curve chang
37、es from concave to convex. 11. Titrate the contents of the other two beakers in the same manner. 12. For each titration, calculate the molarity of the sodium hydroxide to three decimal places, using Equation 1: 5 of 10 326-08 B2.204A10M3= )1( where: A = mass of potassium hydrogen phthalate weighed i
38、nto beaker, g B = volume of sodium hydroxide solution used to reach the endpoint, mL M = molarity of the 1.0-M sodium hydroxide, moles/L 204.2 = molecular mass of potassium hydrogen phthalate, g/mole 103= factor to convert moles/mL to moles/L 13. Average the results of the three determinations to th
39、ree decimal places. 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 until the required repeatability is obtained on three consecutive r
40、uns. The sodium 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. Sample Analysis 1. Weigh a sample of appropriate size, usually 5-20 g, into t
41、he dry 250-mL Erlenmeyer flask with a ground glass joint. If a diene value greater than 1 is expected, use 5-10 g; if a diene value less than 1 is expected use 20 g. 2. Using a volumetric pipet, add 20 mL of the filtered maleic anhydride-toluene solution and a few boiling chips to prevent bumping. I
42、f the measured diene value of the sample was previously determined to be less than 1.2, and an estimate of the value below 1.2 is desired, pipet only 2 mL of the filtered maleic anhydride-toluene solution into the flask containing 20 g of the sample. With a Mohr pipet (or individual volumetric pipet
43、s), add 18 mL of toluene and a few boiling chips to prevent bumping. 3. Pipet the same amount of filtered maleic anhydride-toluene solution used for the samples to an empty 250-mL Erlenmeyer flask with a ground glass joint. This will be the blank, and should be treated in the same manner as the samp
44、les. 4. Lubricate the joint on the condensers with a thin layer of graphite using a soft pencil. 5. Fit the Erlenmeyer flasks to the condensers and suspend the assemblies over a hot plate. Adjust the temperature of the hot plate to achieve a mild boiling condition. Reflux for three hours. 6. Allow t
45、o cool to ambient temperature. 7. Using a graduated cylinder, add 5 mL of water into the flask through the top of the condenser; then gently boil the contents for an additional 15 minutes. 8. Allow to cool to ambient temperature. 9. Using a graduated cylinder, add 5 mL of MTBE through the top of the
46、 condenser, followed by 20 mL of water. 10. Remove the condenser and carefully transfer the contents of the flask into a 250-mL separatory funnel. Wash the flask with 20 mL of MTBE in 3 portions, then with 25 mL of water, also added in 3 increments. In each case, add the washings to the separatory f
47、unnel. 6 of 10 326-08 In some cases an insoluble substance forms which makes the recovery of the maleic acid difficult. In the event this has occurred, break up the insoluble compound with a stirring rod and extract with hot water: a. Using a graduated cylinder, add 15 mL of water to the reflux flas
48、k, heat to boiling and continue boiling for several minutes. b. Cool and transfer the water extract to the separatory funnel. c. Repeat Steps a and b at least twice more, adding each extract to the separatory funnel. d. Continue to Step #11. 11. Shake the contents of the separatory funnel 4-5 minute
49、s with occasional venting. Allow the two phases to separate. 12. Place a stirring bar into a titration beaker. Draw off the aqueous layer into a titration beaker. Extract the residual liquid in the separatory funnel, as described in Step 11, three times with successive 25-, 10- and 10-mL portions of water, in each case adding the water extracts to the titration beaker containing the aqueous layer drawn off previously. 13. Position the beaker on the titration stand, start a slow flow of nitrogen to the headspace of the beaker to expel air, and stir.
