1、TOTAL AMINE IN SOLUTIONSUOP Method 828-81SCOPEThis method is for determining total amine in amine solutions by the Kjeldahl technique. The molecularweight of the amine in the sample must be known or assumed to make the proper calculation. An amineconcentration of 1 to 50 wt-% is typically determined
2、.OUTLINE OF METHODThe amine sample is digested with concentrated sulfuric acid using specially purified reagents and precisetime and temperature control. Following digestion, the ammonia formed is distilled from a strongly alkalinesolution containing sodium thiosulfate. The liberated ammonia is abso
3、rbed in a saturated boric acid solutioncontaining methyl purple indicator and is determined by titration with 0.05 M and 0.0025 M sulfuric acid.APPARATUSKjeldahl digestion unit. If a commercial unit is used, the heater must be modified to provide a full rangeof heats. The following have been found s
4、atisfactory for heat control: “Type II” 750-W heater with avariable transformer, available from Precision Scientific Co.; or the “Labconco Infinite Heat Control”heater, Cat. No. S-63065, available from Sargent-Welch Scientific Co., or equivalent apparatus.Kjeldahl distillation unit. Any commercial o
5、r improvised setup may be used if it utilizes and 800-mLKjeldahl flask, condenser and a spray trap.Kjeldahl flask, 800-mL, with thermometer well (see Fig. 1)Spray trap. (see Fig. 2), available from UOP Inc.Thermometer, total-immersion, gas-filled, 500 C maximumThe following conventional equipment is
6、 also required:Balance, capable of weighing to 0.1 mgBeakers, 500- and 1000-mLBottle, polyethylene, 4-literIT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TODETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH ANDSAFETY PRACTICES AR
7、E 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 PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF
8、THE APPROPRIATE PERSONAL PROTECTIONEQUIPMENT (PPE). COPYRIGHT 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
9、 by contacting Customer Service atserviceastm.org, 610.832.9555 FAX, or 610.832.9585 PHONE.2 of 7828-81Figure 1Kjeldahl Flask 800-mL, With Thermometer WellCylinder, graduated, 250- and 500-mLFlask, Erlenmeyer, 500-mLFlask, volumetric, 100-mLHot platePipets, 5-, 10-, 25- and 100-mLREAGENTSAll reagent
10、s shall conform to the specifications established by the Committee on Analytical Reagents ofthe American Chemical Society, when such specifications are available, unless otherwise specified.Boiling chips, carborundum. Remove any nitrogenous matter by digesting a quantity of carborundumchips in boili
11、ng concentrated sulfuric acid for 30 minutes. Rinse with copious quantities of water anddry in an oven. Available from Arthur H. Thomas Co., Cat. No. 1590-D30, or equivalent.Boric acid, saturated. Dissolve approximately 40 g of boric acid crystals in one-liter of water.Mercuric oxideMethyl purple in
12、dicator, 0.1% aqueous solution. Store in dropping bottle.3 of 7828-81Figure 2Spray Temp4 of 7828-81Potassium sulfate. Purify by heating in an electric furnace for 12 hours at 500-600 C. It has been foundconvenient to use a porcelain dish large enough to hold a pound of crystals. Place the dish and c
13、ontentsin the furnace while the furnace is still cool to minimize spattering at higher temperatures. Store in aclean, dry bottle.Sodium hydroxide-thiosulfate solution, approximately 50% sodium hydroxide and 5% sodium thiosulfatepentahydrate (Na2S2O3 5H2O) when prepared. Fisher Scientific Co., suppli
14、es a carbonate-free 50%sodium hydroxide solution, Cat. No. So-S-254.Weigh 229 g of Na2S2O3 5H2O crystals into a 500-mL beaker, add 200 mL of water, 10g of 50%sodium hydroxide solution and few boiling chips. Boil until the solution turns yellow.When the thiosulfate solution has cooled, pour it into a
15、 4-liter polyethylene bottle. Add 4575 g of the50% sodium hydroxide solution to the polyethylene bottle containing the thiosulfate solution. Shake thebottle well to ensure proper mixing.Stopcock grease. Dow-Corning Silicone Stopcock Grease has been found to be free of nitrogenous matterand is safe t
16、o use without fear of contamination, available from Sargent-Welch Scientific Co., orequivalent.Sulfuric acid, 0.05 M and 0.0025 M. Standardize by any acceptable method. Titration withtris(hydroxymethyl) aminomethane is recommended.Sulfuric acid, concentrated. E. I. DuPont de Nemours and Company, sup
17、plies a low nitrogen contentsulfuric acid (less than 1 ppm nitrogen) and is the only known commercial source. Purification of thisacid is not necessary.Tris(hydroxymethyl)aminomethane, available as THAM from Fisher Scientific Co., or equivalentWater, distilled or deionized. It is necessary to use wa
18、ter which has a consistent and low nitrogen content.Double-deionized water obtained from a deionizer in good condition has been found satisfactory. Theterm “double-deionized” refers to water which has been processed in a central deionizer followed byprocessing in a small deionizer in the laboratory.
19、Zinc metal, 20-30 mesh, granulatedPROCEDUREDirect Sampling for High-Nitrogen SamplesWeigh one-gram to the nearest 0.1 mg of the sample into a 100-mL volumetric flask and dilute to themark with water. Mix the contents and pipet a 10-mL aliquot into the 800-mL Kjeldahl flask modified witha thermometer
20、 well, add 25 0.5 g of heat-treated potassium sulfate crystals, 1.1 0.2 g of mercuric oxide,a few carborundum boiling chips and 70 mL of concentrated sulfuric acid. Add the acid slowly while theflask is inclined and rotate it in order to wet the inner wall.DigestionPrior to starting the analysis, pu
21、t on protective clothing (see Notes 2, 3 and 4).Wrap the upper 2 to 5 cm of the neck of the Kjeldahl flask with glass wool to prevent condensed sulfuricacid from creeping around the lip of the flask and running down the neck toward the heating element. Placethe flask on the digestion rack. Apply a m
22、edium heat (50-60 V); continue heating until frothing and charringcease, then maintain this medium heat for 45 15 minutes.5 of 7828-81Starting the digestion with a medium rather than a low heat is practical because of the small amount ofhydrocarbon that is extracted by the concentrated sulfuric acid
23、. This permits the digestion time to beshortened from the usual 5 to 6 hours to as little as 2 to 2-1/2 hours from start to finish.When charring is completed and the contents of the flask are liquid, increase the heat over a 15-20 minuteperiod until high heat (100-110 V) is applied. If severe frothi
24、ng develops, lower the heat to medium (50-60V) and add a small quantity (10-15 mL) of concentrated sulfuric acid.Maintain the rate of boiling so that condensation of the acid vapor occurs 1/2 to 3/4 of the way up theneck of the flask. The reflux serves to wash back into the bulb of the flask any par
25、ticles of froth of char. Ifnecessary, add small amounts of acid to wash back any particles lodged high in the neck of the flask. Avoidthis use of additional acid, if possible, by exercising care during the initial charring.Continue heating at the high rate until the liquid in the flask becomes color
26、less and is approximately 20-30 mL in volume. The temperature of the boiling liquid should be between 360 and 380 C, determined bycarefully inserting a thermometer into the thermometer well of the Kjeldahl flask (see Notes 6 and 7). Thedigestion is timed when this temperature is reached and continue
27、d for one hour at the same reflux rate.Too large a volume of sulfuric acid in the digestion flask results in a low digestion temperature andincomplete nitrogen recovery. Too small an acid volume results in an excessive digestion temperature andloss of nitrogen. Do not allow the volume to decrease so
28、 that the temperature exceeds 380 C. Add additionallow-nitrogen sulfuric acid as required to keep the temperature at the maximum of 380 C. If the volumeexceeds 30-mL and the temperature is below 380 C, increase the reflux rate so that the excess acid isdistilled from the flask; accomplish this eithe
29、r by increasing the heat or by wrapping glass wool around theneck of the flask in order to insulate it. After a 20- to 30-mL level is attained and the temperature is between360 and 380 C, remove the glass wool (or decrease the heat) and continue digestion for one hour at the samereflux rate.When the
30、 digestion is completed, turn off the heat and allow the flask to cool to room temperature. Add400 mL of water in the following manner: Very cautiously and with continuous swirling, add about 50 mLof water. Continue adding by increments, followed by swirling, until the salt cake dissolves in the hot
31、solution. Then add the remaining volume of water with continuous swirling. Cool the flask in an ice bathuntil cold to the touch.DistillationWhile the flask is cooling, thoroughly rinse the distillation apparatus with distilled water (see Note 5).Place 25 mL of saturated boric acid solution in a 500-
32、mL Erlenmeyer flask. Place the flask on thedistillation rack so that the condenser tip is well beneath the surface of the liquid. In order to avoidobjectionable pressure build up, do not permit the condenser tip to press tightly against the bottom of theErlenmeyer flask.When the digestion flask is c
33、old, the receiver in place and the condenser is cold, add a pinch of granulatedzinc to the Kjeldahl flask. Then, inclining the flask, carefully add 100-110 mL of the caustic-thiosulfatesolution in such a manner as to maintain 2 discrete layers. Quickly place the flask on the distillation rack,connec
34、t the spray trap and carefully swirl the flask so that there is a gradual but thorough mixing of thelayers.When mixing is completed, apply full heat and start the distillation. Continue distillating until “bumping”commences (see Note 2). At this point, 150-200 ml of distillate will have been collect
35、ed, a sufficientamount to ensure that all the ammonia has been taken over. Care must be used not to allow any alkali to be6 of 7828-81carried over into the distillate during the distillation, since even a trace of caustic in the distillate willincrease the basicity and cause erroneously high results
36、. Use of the spray trap mentioned underAPPARATUS, Kjeldahl distillation unit, has been found to make it virtually impossible for any caustic to becarried over. In addition, distillation should not continue after bumping commences or a total of 200 mL isin the receiver (see Note 3). When either point
37、 is reached, turn off the heat, raise the Kjeldahl flask from theheating element and immediately lower the receiving flask so that the condenser tip is no longer submerged.TitrationAdd 4 drops of methyl purple indicator to the distillate and swirl to mix. Titrate the distillate withstandard 0.05 M s
38、ulfuric acid until the endpoint is being approached. Finish the titration with 0.0025 Msulfuric acid until a purple tint is exhibited.Reagent BlankA reagent blank must be run each time a new lot of reagents is prepared. Run the reagent blank in thesame manner as described for an unknown, using 0.002
39、5 M sulfuric acid for the titration.MERCURY REMOVAL FROM USED KJELDAHL SOLUTIONSIn order to minimize mercury residues going to the drain, solutions remaining in the Kjeldahl flasks afterdistillation are accumulated (settled) in containers overnight and filtered.An acceptable filtration setup would i
40、nclude a Buchner funnel, a vacuum filtration flask and a source ofvacuum. Using 15-cm filter paper and adequate vacuum, four liters of solution can be filtered in four hours.Overnight settling and filtration using Whatman 42 paper are required to reduce the mercuryconcentration to 20 to 40 wt-ppm in
41、 the filtrate. The filtrate may be discarded.Mercury collected on the filter paper should be treated as a solid toxic waste and stored until enough iscollected to be sent for commercial processing to recover the mercury.CALCULATIONSCalculate the wt-% amine in the sample where it is assumed that all
42、the free amine present corresponds toeither MEA, mol-wt 61, or DEA, mol-wt 105.+=11 a 10.2A(V V V )Amine, wt-%WMM Mwhere:A = molecular weight of the amineM = molarity of strong standard sulfuric acidM1= molarity of weak standard fulfuric acidV = volume of strong standard sulfuric acid used in titrat
43、ing the sample, mLV1= volume of weak standard sulfuric acid used in titrating the sample, mLVa= volume of weak standard sulfuric acid used in titrating the blank, mLW = weight of sample in 10-mL aliquot, gNOTES AND PRECAUTIONS1. This one point cannot be emphasized too strongly: To obtain accurate re
44、sults the analyst must use greatcare to avoid contamination by nitrogenous substances.7 of 7828-812. As soon as the contents of the Kjeldahl flask begins to “bump” during the distillation, turn off the heatimmediately, since the bumping can become violent. Use of a safety shield is recommended. Glas
45、s wool hasbeen helpful as a cushion to reduce flask breakage. Wind 2.5-cm width tape onto the ceramic plate in such amanner that the flask contacts the tape at 5 or 6 places.3. The walls of the Kjeldahl flasks become thinner with continued use because of attack by the alkaliadded in the distillation
46、 step. Flasks should be discarded after 40 or 50 analyses, or upon any visibleevidence of weakening.4. Distillation of sulfuric acid obviously presents some hazard. Have adequate personal protectivefacilities at hand; e.g., safety glasses, face shield, protective clothing, etc. Have sodium carbonate
47、 availableto neutralize spills.5. The last traces of ammonia must be removed from the distillation equipment to avoid possiblecontamination of subsequent samples after high nitrogen content samples have been distilled. Rinse thespray trap and condenser several times with water, then add 400 mL of wa
48、ter to the Kjeldahl flask anddistill until 200 mL are recovered overhead. Rinse the spray trap and condenser again with water.6. Since the volume of acid in the Kjeldahl flask is difficult to determine, the use of temperature control isa more accurate method of maintaining the critical 20 to 30-mL v
49、olume of sulfuric acid. The temperature ofthe boiling sulfuric acid solution can be determined by a thermometer well inserted into the Kjeldahl flaskso that the bottom of the well is beneath the liquid level of the sulfuric acid. A full-immersion, gas-filled,500 C maximum thermometer can be used to measure the temperature of the boiling solution.7. Do not insert any cotton or glass wool at the bottom of the thermometer well to act as a cushion for thethermometer. Such a cushion would raise the mercury bulb of the thermometer above the liquid level of thesulfuric acid in the Kjeldah
