1、 COPYRIGHT 1978, 1981 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.WATER IN REGENERATOR BOTTOMSFROM HYDROGEN FLUORIDE ALKYLATIONUOP Method 382-81SCOPERegenerator bottoms from hydrogen fluoride (HF) alkylation are often 2-phase systems. The lower phaseis relatively rich in HF, containing about 30-40%; and the upper phase
3、 is essentially hydrocarbon containingsmall concentrations (about 0-5%) of HF. The water content of the HF-rich lower phase is usually less than10%, and that of the upper phase is usually less than 5%. This method is satisfactory for the determinationof water in both types of samples. The unsaturate
4、s present in the oil do not interfere in the titration forwater.OUTLINE OF METHODThe sample is weighed into a dried polypropylene bottle and the excess HF vaporized in the presence ofpentane or isooctane. Pyridine in excess is added to the oily residue. The resulting solution is titrated withdilute
5、Karl Fischer reagent, using a dead-stop indicator to detect the endpoint. The titration is based onreactions represented as follows:22 2 3H O+I +SO 2HI+SOKarl Fischer reagent is a mixture of iodine, pyridine, and sulfur dioxide. Iodine does not oxidize sulfurdioxide except in the presence of water.
6、As can be seen from the equation above, the consumption of iodineand sulfur dioxide is stoichiometrically related to the amount of water present.On reaction with water, the dark brown reagent (the brown color is caused by the presence of free iodine)becomes light yellow as the “free” iodine becomes
7、chemically combined. A small excess of the reagent willchange the color back to brown because “free” iodine again exists. This phenomenon is commonly taken asthe endpoint of the reaction when the visual endpoint technique is used.The dead-stop electrometric method for detection of the endpoint is a
8、special case of a two platinumelectrode system with a small dc voltage applied. Karl Fischer reagent is added to the titration cell. In thepresence of an excess of the Fischer reagent, the cathode is depolarized and current flows between theelectrodes. Water in excess of that required to react with
9、the Fischer reagent is added. The electrodesbecome polarized and current no longer flows between them. The excess water is then titrated with theIT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TODETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. E
10、FFECTIVE HEALTH ANDSAFETY PRACTICES ARE TO BE FOLLOWED 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 PROCEDUR
11、E SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTIONEQUIPMENT (PPE).2 of 8382-81dilute Fischer reagent. At the endpoint, when a slight excess of the dilute Fischer reagent is present, thecathode is again depolarized and current again flows between the electrodes. This current ch
12、ange isdetected by a galvanometer.APPARATUSBeaker, polypropylene, 500-mLBottles, polypropylene, narrow mouth, screw cap, 60-, 480-, and 960-mLKarl Fischer moisture determinator. See Fig. 1 for diagram and assembly of the various componentsrequired. If desired, a simpler apparatus or a commercial uni
13、t may be substituted, provided that resultsare comparable to those obtained by the described assembly.1. Titration cell. See Fig. 2 for details of fabrication. The cell is designed with 4 openings. The Ts 29/42male joint accommodates a Ts 29/42 female joint, through which the platinum electrodes are
14、 fused. ATs 19 stopper fits into another opening through which the sample is introduced into the cell. The thirdopening accommodates a buret tip to which is attached a spherical 12/5 female joint. Fit an exhausttube into the cell through a stopcock and a spherical 12/5 male joint to remove the spent
15、 liquid afterthe completion of an analysis.2. Platinum electrodes. Fuse 2 platinum electrodes, available from Leeds and Northrup, Cat. No. 117421complete with glass insulators, into a cylindrical head equipped with a Ts 29/42 female joint whichfits into the male joint of the titration cell. Equip th
16、e head with a glass tube fitted with a spherical 12/5female joint as a vent when the cell is drained of spent liquid.3. Dead-stop indicator. Construct according to Fig. 3 or use a commercial equivalent employing amicroammeter of 0-20 a range. Switch No. 1 must be in the “On” position during operatio
17、n.Switch No. 2 is used to set the instrument for maximum sensitivity prior to titrating. This setting ismade by adjusting the needle of the meter to full-scale deflection with the variable rheostat whenSwitch No. 2 is in the “Off” position. Switch No. 2 must be moved to the “On” position duringtitra
18、tion. The meter is connected to the platinum electrodes with alligator clips. A more permanentconnection may be made if desired.4. Buret, 2-way, 50-mL modified. Modify the delivery tip of the buret with a spherical 12/5 female jointand connect to the titration cell by means of a connecting tube equi
19、pped with spherical 12/5 joints.The refill tube is also equipped with a spherical 12/5 female joint.5. Karl Fischer reagent reservoir. A 2-liter brown bottle fitted with a Ts 29/42 male joint. The cap is aTs 29/42 female joint with a glass tube fused to it and extending down to within 1 mm of the bo
20、ttomof the bottle. A glass tube with a spherical 12/5 female joint is fused at a 90 angle into the headwhich serves as a pressuring system for refilling the buret. The reservoir is connected to the refill sideof the buret by a glass tube fitted with spherical 12/5 joints.6. Waste trap. A 500-mL filt
21、er flask equipped with a 1-hole rubber stopper and a glass tube. Connect theside arm of the flask to the exhaust tube of the titration cell. With the stopcock open and a fingerclosing off the vent on the constant N2pressure control scrubber, the waste will be pressured out fromthe cell into the trap
22、. Drying tubes filled with Drierite or equivalent are used to protect reagents andthe titration cell from the inclusion of atmospheric moisture. Closing of the vent from the constant N23 of 8382-81Figure 1Diagram of Karl Fischer Moisture Determinator4 of 8382-81Figure 2Karl Fischer Titration Cell5 o
23、f 8382-81Figure 3Dead-Stop Indicator For Determination Of Watercontrol scrubber is also used to apply pressure to the Karl Fischer reagent reservoir when refilling theburet. Fig. 1 is a schematic sketch of the equipment and is not drawn to scale. In making theseconnections, use discretion to make th
24、e whole assembly compact. However, be sure there is enoughspace around the stopcock of the buret so that it may be manipulated without hindrance from theelectrode system.7. Constant N2pressure control scrubber. A 250-mL gas washing bottle fitted with a bell bottomdispersion tip. Sufficient glycol is
25、 added to cover the dispersion tip 2-1/2 to 4 cm.Pipet, glass, 5-, 10-, 25- and 50-mL capacityPipet, polypropylene, 10-mLStirrer, magnetic, with Teflon-coated stirring barREAGENTS AND MATERIALSAll reagents shall conform to the specifications established by the Committee on Analytical Reagents ofthe
26、American Chemical Society, when such specifications exist, unless otherwise specified. References towater mean distilled or deionized water.Acetone, commercial gradeDilute Karl Fischer reagent. Mix 1 liter of Karl Fischer reagent, stabilized, Cat. No. So-K-3, and 1 literof Karl Fischer diluent, Cat.
27、 No. So-K-5, available from Fisher Scientific Co., and store in the 2-literreservoir provided. The titer of the dilute Fischer reagent is approximately 2.5 mg H2O/mL.Drierite, or equivalentGlycol, Dry6 of 8382-81Isooctane, commercial gradeNitrogen cylinder, high purity dry, fitted with a reducing va
28、lvePentane, commercial gradePyridine, Bakers Reagent Grade, or equivalentPROCEDUREStandardization of Dilute Karl Fischer ReagentAssemble the apparatus as shown in Fig. 1. Add 20 mL (measured to the nearest 0.05 mL) of the diluteFischer reagent by buret (see NOTES AND PRECAUTIONS) to the titration ve
29、ssel. Move Switch No. 1 ofthe dead-stop indicator to the “On” position and Switch No. 2 to the “Off” position. Current now flowsthrough the meter. Start the magnetic stirrer. Adjust the dead-stop indicator by means of the variable resistorto give full-scale deflection. Now move Switch No. 2 to the “
30、On” position. The needle will move to aposition to the far left of the scale as current flows between the platinum electrodes (see Fig. 3).Add 2 drops of water from a previously-weighed dropping bottle. Reweigh the dropping bottle to thenearest 0.1 mg to obtain the weight of water added. The needle
31、on the meter will now move to a position onthe far right. The dilute Fischer reagent will be a very light yellow color.Titrate the solution with the dilute Fischer reagent. The approach to the endpoint can be observed by agradual change of color of the solution from a light yellow to a light brown.
32、The endpoint occurs when,upon the addition of a small excess of the dilute Fischer reagent, there is a sharp deflection of the needle ofthe dead-stop indicator to the far left as current now flows between the platinum electrodes. The needleshould hold a constant deflection to the far left for at lea
33、st 30 seconds before moving to the right, tomaintain a correct and consistent endpoint. Record the volume of the dilute Fischer reagent used.Calculate the titer of the dilute Karl Fischer reagent as follows:121WReagent titer, T, mg H O/mLA=where:W1= weight of water added, mgA1= total volume of dilut
34、e Fischer reagent (initial 20 mL addition plus that used fortitration), mLSample AnalysisPut on full protective clothing when handling HF solutions, including rubber gloves and safety glasses ora face shield, because HF solutions can produce severe burns.Draw one-half to one liter of regenerator bot
35、toms into a polypropylene bottle, taking care to get ahomogeneous upper- or lower-phase sample as required.Dry a 60-mL polypropylene bottle and cap by washing with acetone and blowing it with dry air (dried bypassing through a tower of indicating “Drierite”) for 15 minutes. Weigh the dried bottle an
36、d cap to thenearest milligram. Dry the polypropylene pipet by washing with acetone and passing dry air through it.7 of 8382-81Draw a sample with the pipet from from about the center depth of the sample bottle, wipe the outside of thepipet with a disposable paper towel and deliver 10 mL of sample to
37、the 60-mL bottle. Cap and reweigh thebottle to the nearest milligram. Add 5 mL of pentane to the 60-mL bottle and swirl to mix.Open the 60-mL polypropylene bottle and place it in a 500-mL polypropylene beaker half filled withwarm tap water (40-60 C) and allow the HF and pentane to vaporize in a hood
38、. When there is no longer anyevidence of boiling pentane and HF, remove the polypropylene bottle from the warm water and immerse itin an ice bath. When the bottle and oily residue are cold, pipet 25 mL of pyridine into the bottle, adding thepyridine a few drops at a time so that any heat of neutrali
39、zation will be dissipated. Swirl the contents of thepolypropylene bottle and remove the bottle from the ice bath. Carefully wipe the cap and bottle with a dryabsorbent paper towel to remove any water that may be present.TitrationArrange the titration apparatus as illustrated in Fig. 1. Fill the bure
40、t with dilute Karl Fischer reagent.Transfer the cooled, neutralized HF sample to the titration cell by pouring it through one of the openings atthe top of the cell. Add an additional 25 mL of pyridine to the sample bottle and swirl it to wash the walls ofthe bottle. Add the pyridine washings to the
41、titration cell. Turn on the magnetic stirrer and slowly titratewith the dilute Fischer reagent, continuing until the meter needle deflects to the far left and remains so for atleast 30 seconds. Record the volume of reagent used.Without discarding the contents of the cell, add 50 mL of pyridine and r
42、un a reagent blank. Dispose of thespent contents of the cell.CALCULATIONS22(A E)TWater, wt-%10 W=where:A2= volume of Fischer reagent used in titration, mLE = reagent blank, volume of Fischer reagent, mLT = reagent titer, previously definedW2= weight of sample, gNOTES AND PRECAUTIONSInstant shower fa
43、cilities should be available near the area where a HF alkylation plant may be sampled aswell as the area in which the analysis is to be carried out.Wear protective clothing, face shield and rubber gloves at all times while handling the sample.Regenerator bottom samples occasionally run very high in
44、HF. Therefore, observe the same precautionsused when handling liquid HF when working with regenerator bottom samples.Use isooctane as diluent for the regenerator bottoms upper-phase samples in case they are very viscous.Since extremely small amounts of moisture cause interference, all glassware and
45、polypropylene waremust be dried before using. Protect reagents from atmospheric moisture by drying tubes charged with anindicating-type drying agent, such as Drierite. Keep the titration vessel stoppered except when the sample isintroduced.8 of 8382-81Samples which approach a constant-boiling compos
46、ition of HF in water content may be diluted withanhydrous methanol and a suitable aliquot taken.A convenient way to fill the delivery tube of the buret is from the titration cell. Fill the cell above thedelivery tip with the dilute Fischer reagent and close off the opening to the waste trap. Apply a
47、 smallamount of N2pressure to the cell by temporarily closing the N2vent on the constant pressure controlscrubber and open the stopcock on the buret. The liquid will be forced through the delivery tube and will fillit, excluding all air. When the level passes through the base of the stopcock, close
48、the stopcock and allowthe N2pressure to vent from the N2pressure control scrubber. Remove the excess dilute reagent from thecell to the waste trap by opening the stopcock on the titration cell side arm and applying N2pressure to thecell by temporarily closing the N2vent on the constant pressure cont
49、rol scrubber. Fill the buret from thereservoir using the N2pressure system and pass about one buret-full into the titration cell to flush out theburet. Remove the liquid from the cell as described above. The cell is now ready to use, either forstandardizing the dilute Fischer reagent or for analyzing sample.PRECISIONThe estimated standard deviation (esd) based on the indicated replicates is shown below. Duplicate resultsby the same operator should not be considered suspect unless they differ by more than the amounts shownin the “allowable difference” column (95% probability).Type ofSam
