Determination of Oil in Refinery Waste Waters A Benzene-Extraction Method -4. F . S. MLSAhTE, Sun Oil
Most pollution-abatement processes relating to petroleum production and refining require determination of the oil content of waste water samples, and the need for a rapid reliable method is evident. A wet extraction method has been devised in which the solvent is removed froni the extract by distillation, thereby avoiding losses incurred when the extracted oils are recovered in evaporating dishes on a steam bath. Average deviations of less than 59'0 from known values are obtained with oils boiling above 300" F. About 1 hour is required per determination and the method is readily adaptable to multiple sini ul taneous deterniinations.
M
ORE than 20 yeaib ago the pet~oleuniindustry recognized
Co.,Marcus Hook, P a .
A re-examination of the method using similar petroleum fractions and the intended quantity of benzene resulted in lower losses, but during the test the inability of several observers to agree on the point of complete solvent removal became evident. A survey was conducted to determine the uncertainty involved in the designation, by odor, of the point of complete solvent removal. With a number of evaporations proceeding at various stages of completion to provide a typical odor background, differences on the order of 10 minutes in the times designated by the observers were common and variations up to 30 minutes were noted. Although this uncertainty prevented an accurate evalua, tion of the losses of oil during the evaporation of solvent, it suggested another possible source of error-the loss resulting from prolonged heating after the solvent had gone. Experiments were run to determine the magnitude of evaporation losses which would result from prolonged heating of oile in open dishes in the absence of benzene.
the need for, and embarked on, a vigorous program of pollution abatement and prevention--a pi ogram which eventually led to adoption by the industry of the attitude that no Samples of five petroleum fractions ranging from kerosene to a li h t lubricating oil were heated in evaporating dishes on a steam refining process can be considered fully developed until methods bat! in a well ventilated hood for successive increments of time up have been provided for the disposal of aaste products iesulting to a total of 30 minutes. The quantities of sample used-100, therefrom. Because most abatement pi oceises peculiar to 250, and 500 mg.-were in the range generally encountered and petroleum production and refining are conccar ned with the control were equal to the oil from %liter samples of water containing of pollution of water by oil, evaluation of the effectiveness of such from 30 to 170 p.p.m. processes d l require the determination of the oil content of numerous waste water samples; the need for R rapid reliable As careful inspection throughout the experiment revealed no method is evident. A search for such a method to supplement the evidence of oil creeping over the edge of the dishes, the losses procedures of the American Petroleum Institute ( 1 ) was initiated tabulated in Table I must have resulted from evaporation only. by the Subcommittee on Sampling and Testing and this laboraThe data show that loss of components boilihg as high as 600" tory submitted a benzene-extraction procedure for consideration. F. could result from heating the oils for 10 minutes past the point A subsequent critical study of the method revealed several shortof complete solvent removal. Figure 1 is a plot of some of the comings and led to the develonnwnt of the improved qcmimivroloss data. The almost vertical curves ahich represent the procedure herein described. kerosene loss and the steep slopes showing the initial loss from the h comparative study of the niost commonly used methodb f o r d e t e r m i n a t i o n of oil Table I . Evaporation Losses from Open Dishes on Steam Bath sholi ed the wet extraction Kerosene Light Furnace Oil Fresh Gas Oil Transformer Light Lube Oil procedure to be the simplest -~ 4 P I Gravity and most direct and was the 42.5' 32.2' 31.2' 26" 2 3 r basis for its recommendation Weight of Samples, Mg. as a suitable short method. 100 256 524 101 248 540 107 244 491 104 248 495 100 252 507 Briefly summarized, the waste Heating. Per Cent Loss after Heating hIin. water sample was twice ex2 92 68 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . tracted with benzene in a 4 . . . 93 73 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 . . . . . . 71 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . separatory funnel, the extract 8 . . . . . 93 . . . . . . . . . . . . . . . . . . . . . 22 i 3 . : : : . . . . . . . . . 10 . . . . . . . . 75 58 40 41 29 21 . . . . . . . . . was filtered, and the solvent 15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 11 5 3 20 . . . . . . . . 96 76 59 63 42 32 40 24 13 . . . . . . . . . was evaporated from an open . . . . . . . . . . . 87 67 66 50 39 46 29 17 19 10 >i 30 dish on a steam bath. The Engler Distillation, F. apparatus and rcagents required were all readily avail53 1 564 Initial 320 352 462 5 557 590 364 404 506 able laboratory supplies. An 10 3741 434 528 572 599 586 611 20 384 458 552 ambiguity in the written pro395 470 566 596 622 30 cedure was responsible for the 582 604 633 413 484 40 50 422 496 5Y8 612 645 use of an excessive quantity of 614 622 658 60 432 508 solvent by some operators, who 444 520 636 633 673 70 reported extremely high losses 672 649 696 456 538 80 90 484 566 726 679 733 of oil in the gas oil boiling 95 490 588 748 707 766 range through the evaporation (98%) 530 (98%) 630 (98%) 758 (97%) 755 (98%) 786 E P. of large quantities of solvent. I
1374
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 furnace oil emphasize the unreliability of any quantitative analytical procedure which utilizes evaporation from open dishes on a steam bath. In view of the losses found, the procedure was altered t o avoid the use of open dishes and the solvent was removed from the extract by distillation. For this purpose a 250-ml. flask wak used, heated by a hot plate at :i temperature xl>ovc. 600" F.
1375 prevent cont'inuous contact with the flared top of the flask, thus minimizing accumulation of condensed benzene a t this point. The still heater consists of a 20-watt unit constructed from 5 feet of No. 30 B. & S.gage Chrome1 wire wound on a l/B-inch :trbor and partially embedded in a refract,ory support. The heater should provide contact between the walls of the flask sump and tmheexposed heating coils. The resulting "hot spots" supplement the action of the glass particles in the flask sump in promoting satisfactory boiling. The heater is operated from a variable voltage transformer at about 25 volts, and the voltage is finally adjusted to maintain a temperature between 550" and 575' F. in the sump. As this adjustment is critical, a voltmeter should he used when setting t.he voltage and t o check the constancy of the line voltage. The life of the unit is practically unlimited, because of the relatively low operating temperature, and for convenience is operated continuously. The cut point designation for the semimicro distillation waa determined empirically by a study of the overhead vapor temperature variations as the distillation of known benzene-oil .solutions approached completion. LYith thr solutions containing transformer oil? the temperature dropped from the boiling point of the solvent (177" F.) when the cut point was passed and the resulting residue invariably weighed more than the sample taken. Heating uftei, the indicated cut point effected no further deci.case in w i g h t and a blank correction had to be applied. In the case of the t w t solutions containing keroscne, the temperature rose above the boiling point of the solvent as the point of solvent tkplt~tionwas appioached and cut point was chosen (190" F.) which yielded the same increase in weight of the residue over the sample weight as with the heavy fraction. In this manner a constant blank correction was required for all samples. The cut point was finally designated as occurring 1 minute after the temperitture has dropped below 170" F. or \Then the temperature has reached 190" F.. whirhevrr occurs first. HIGH PEE0 S?7RRER GALLON SAMPLE BOTTLE BY S L E M flT7W THRU CORK sroppER
TIME IN MINUTES Figure 1.
Evaporation Loss from Open Dishes on Steam Bath
SHAFTEXTENDS ABOUT TWO INCHES INTO WATER LAYER
2 \\.hen tested by distillation of l)enzc.lie-fui~nuccoil solutions of known oil content, with the distillation carried to virtual di.yriess, the results were invariably high, as solvent contiensed from the benzeric vapor remaining in tho flask. Although fairly consistent results were obtained by reheating and tilting the flask to pour out the solvent vapor, as subsequently described by Kirschman and Pomeroy (Z), the manipulation a a s not readily reproducible and was superseded by the semimicro distillation procedure. In the latter procedure, after the solvent estrart has been concentrated by rapid distillation in the 250-in]. still, the distillation is concluded in a miniature 10-nil. still under reproducible conditions, with the point of solvent removal tletet~minedby vapor temperature measurement. By the use of aminiature flask in a suitable heater, the quantity of trapped solvent a t the end of the distillation is kept low and constant and is compensated for b y the blank correction. The miniature still (consisting of the flask and heater shown in Figure 4), is the only special equipment required t o determine oil by the semimicromethod. The IO-ml. flask contains t,he concentrated solvent' extract' resulting from the rapid preliminary tlistillat,ion, while the sump permits t,he oil residue to enter the hot zone of the heater, where it attains a temperature high enough to distill off the final portion of solvent. The sump extension makes easy and st'able positioning of the flask in the heater possible and no other support is required. Particles of glass fused on the inner walls of the sump promote bubble formation and are csnducive to smooth distillation. The thermocouple well fits loosely into the top of the miniature still and consists o f a thin-walled glass capillary tube just large enough t o permit the entry of a thermocouple constructed from KO.30 I3. & S.gage enamel-covered wires. Three small tips on the well
2
$ $ BENZOL LPMR
t
WASTE WATER SAMPLE
u
Figure 2.
Extraction Assembly
After suitable operating conditions had been established for the semimicro distillation step and before a thorough testing to dekrmine the over-all accuracy of the method was undertaken, all the steps in the procedure were examined for possible simplification and standardization of apparatus and operating technique. The most significant change was made in the extraction step. Although the relative solubility of oil in benzene and in water is favorable for extraction by this solvent, substantially complete extraction presupposes adequate contact, with the waste water sample. B s this is not always obtained through manual agitation in separatory funnels, a motor-driven stirrer was used (Figure 2). Normal motor speeds of 1725 and 3450 r.p.m. proved satisfactory and pi'oduced a finely dispersed milklike suspension of solvent throughout the sample within the first 2 seconds of opera-
1376
ANALYTICAL CHEMISTRY
tion when an impeller with adequate pitch was used. The impeller was made small enough to permit extraction in the sample collecting bottle, thereby eliminating possible loss of oil in transferring the sample to a separatory funnel.
INNER SEGnON 24/40 B J O f N 7
OIST/LLAVON SINGLE POINT CONmCTBETMEN FLASK AND HOT-PLATE
IOOINE FLASK 250ML WITH NO 22 5 STOFPER
Figure 3.
Preliminary Still Aeeemblj-
The preliminary still for the rapid removal of the major poition of solvent is shown in Figure 3. All the component parts are readily available laboratory supplies and, except for the column which is made by sealing an extension on the inner section of a standard-taper ground joint, requires only elementary skill foi assembly. The convenience of the loose coupling shomn between the column and condenser will become evident in use, as the still is frequently removed from the hot plate. For obvious reasons, the ground joint between flask and column is not lubricated. The remainder of the equipment required is standard laboiatory ware, such as 4-liter separatory funnels and 2-liter graduates Sitration grade benzene is satisfactory for this determination and each batch used should be tested as directed below. A potentiometer or millivoltmeter provided uith a therniocouple constructed of No. 30 B. & S. enamel-covered wire is needed for the cut point determination. ANALYTICAL PROCEDURE
Extraction. T o about 3000 ml. of waste water sample in a gallon bottle add 10 ml. (measured) of concentrated hydrochloric acid and then 150 ml. of nitration grade benzene. Insert the stirrer and adjust in the stopper support, so that the impeller dips 1 to 2 inches (2.5 to 5 cm.) into the aqueous layer. Tilt the sample bottle to about 30" off vertical to avoid vortex formation and stir the contents for 15 seconds. Transfer the entire contents of the bottle to a 4-liter separatory funnel, allow to settle 1 minute, and draw the aqueous layer into the same gallon bottle. Repeat the extraction operation using a second 150-ml. portion of benzene and again transfer the entire contents of the bottle to the separatory funnel containing the first extract. Settle 15 minutes, then carefully draw the aqueous layer into a graduated cylinder, measure, and discard. Transfer the benzene extract to a clean 500-ml. flask. Carefully rinse the sample bottle with a new 50-ml. portion of benzene solvent, then rinse the separatory funnel using the same 50 ml. of benzene, and combine the rinsings with the extract in the 500-ml. flask. If the benzene layer from the second extraction of a sample shows appreciable color or other evidence of high oil content repeat the extraction with a third portion of fresh solvent and combine the extracts for distillation.
The following variations in the standard extraction procedure are employed with samples knom-n to have exceptionally low or high oil contents.
Low OIL COXTEXT (belon 20 p.p.ni.). Extract several 3000nil. portions of sample as described above, carrying along both extracts separately for re-use in each successive 3000-ml. portion of sample. Unite the extracts and proceed with the rapid distillation as described in the section on solvent removal. HIGH OIL CONTEXT(above 300 p.p.m.). Extract a smaller sample in a container of suitable size, or place a small measured portion of sample in the gallon extraction bottle and bring the volume up to 3000 ml. with oil-free water before extraction. This is necessary in order to bring the liquid within reach of the impeller, which is mounted on a relatively short shaft to niinimize whippin a t high speeds. A final resifue of b e b e e n 0.1 and 1.0 gram in the miniature still is preferred. Solvent Removal. RAPID P R E L n n N m Y DISTILLATION.Set the hot plate at high heat and reduce the benzene extract to about 5 ml. by a rapid distillation (about 20 ml. per minute) of the solvent in the preliminary still described above. As upwards of 350 nil. of extract must be distilled from a 250-ml. still pot, carry out the distillation stepwise by successive reduction of 150-ml. portions of the extract to about 20 ml. The still may I)e recharged after a brief cooling of the flask and the distillation resumed. Near the end of this distillation, tilting the still assembly so that the flask is in contact with the,hot.plate at only one point (see the position of flask at the right In Figure 3) permits a better estimation of the volume of the residue and prevents superheating with resultant cracking of residual oil and consequent loss of light-end products. I t is not necessary to filter the benzene extract to remove a slight haze before this distillation, because the water. will distill over with the benzene. However, extracts containing troublesome emulsions which hold large amounts of water must be heated and filtered through a small portion of glass n-001, which is rinsed thoroughly with solvent. The resulting filtrate usually consists of two layers, from which the water may be readily separated before preliminary distillation of the solvent. Rleasuie the volume of separated water, then discard. I n an alternative procedure, when rapid determinations are required, the first extract is withdrawn from the separatory funnel and distilled during the &minute settling period required for the complete separation of the second extract. The second extract, with rinse benzene, is then added and the volume is reduced as directed. In the special cases where the benzeiie extract contains unusuallv large quantities of oil, the extract is concentrated by rapid distillation to a volume of about 10 to 15 ml. and then transferred to a glass-stoppered 25-ml. graduate. After the transfer is completed by rinsing, the volume is made up to 25 ml. with benzene and mixed. An aliquot portion is used in the miniature still f o ~ oil determination. SEMIUICRO DISTILLATION.Transfer the residue from the preliminary rapid distillation to the miniature still through a small funnel and rinse the container thoroughly with several milliliters of benzene. The miniature still, which should not be more than half full, may be placed in the hot still heater to start the distillation before the transfer of residue is completed. The liquid should start to boil briskly within 1 minute after insertion in the heater and the rate of distillation should be enough to raise the top level of the ascending vapors (as indicated by the wetting of the flask walls) above the top of the side arm tube. Add the remaining residue and rinse benzene during the distillation as space becomes available and without removing the still from the heater. If the residue is transferred in increments, take care to complete the transfer without permitting the still charge to become free of solvent. When the transfer of residue to the miniature flask is completed, insert the thermowell and adjust the couple to a position about midway between the still bulb and side arm (see Figure 4). As the distillation approaches the point of complete solvent removal, the temperature variations will follow either of two patterns, depending on the boiling range of the extracted oil. A drop in the vapor temperature below the boiling point of benzene (177" F.) generally indicates the absence of compounds boiling below 400' F., while a gradual increase denotes the presence of components boiling above benzene. The solvent may be conbidered completely removed 1 minute after the temperature has dropped below 170" F. or when the temperature has reached 190" F., n-hichever occurs first. Take the flask from the heater, remove the thermowell, and blow gently (Fithout approaching closer than about 3 inches) into the top of the warm flask to vaporize any solvent that may have condensed in the neck or side arm.
1317
V O L U M E 23, NO, 10, O C T O B E R 1 9 5 1 ( ' u o l and wipe thoroughly. Weigh the flask by placing it on the xnalytical balance pan on its side, using the side arm as a convenient handle. Determination of Blank Correction. In order to compensate for condensed solvent resulting from the vapor trapped in the flask a t the end of the distillation from the miniature still, and for posbible high boiling residue in the solvent, blank runs should be made on each new shipment of benzene. Weigh accurately 100 to 250 mg. of oil (transformer oil is satisfactory) into the iodine flask used for the rapid preliminary distillation step, then add 350 ml. of benzene and distill as directed under "Solvent Removal." At the conclusion of the semmicro distillation, allon the flask to cool in a vertical position and weigh within 10 minutes after removal from the heater. The average increase in weight noted in five such determinations is the blank coriection which must be subtracted from the residue in the final calculations. Calculations. The results are reported as parts per million by neight, assuming 1 ml. of water sample to weigh 1 gram. In cases where this assumption would cause appreciable error, the proper correction should be applied. Weight of oil equals weight of residue minus blank correction. Weight of sample is equivalent t o milliliters of water from s e p ai atory funnel plus milliliters of water from solvent-mater emu!>ion (if any) minus milliliters of acid added. Oil content (in p.p.m. by weight) =
weight of oil in grams X 106 volume of sample in milliliters
cleaning operation which niay dislodge the built-in "aritibuml)ing" glass particles. Geneially the tare weights of the flasks are close enough to 10 grams to warrant an adjustment in weight during fabrication to just above this value, so that weighings niay be made on a Chainomatic balance fitted with a 1-gram notched beam with the use of only the 10-gram balance weight. .1 simplification of procedure is possible if the waste sample is knoivn to contain no appreciable quantity of hydrocarbons boiling in the low 300" F. range. In this case if the quantity of residual oil is kept below about 250 mg. by the choice of a suitable quantity of sample, the semimicro distillation \vi11 terminate automatically when the solvent is gone and the temperature-indicating equipment may be eliminated. When the solvent condensate ceases to drip from the side arm, the level of the refluxing liquid in the flask neck will recede down into the flask and 1 minute after it descends below the mid-point between side arm and flask (the position the thermocouple junction normally occupies) the distillation may be considered c~miplete.
THEpMocowL 30 B a s GA wipE:
13
-___
~
THiN WALL GLASS CAPilLARI THERMOWELL
NOTES ON ANALYTICAL PROCEDURE
I n setting up the procedure, every attempt was made to provide an easily workable, rapid, routine method. The general procedure permits some flexibility with respect to choice of sample volume and adjustment of extract volume to produce convenient amounts of oil residue, but the manipulations required are rigidly specified and standardized, particularly the conditions for tcrminating the distillation in the semimicrostill. I n attempting to attain the greatest possible speed of operation, the distillation rat.es in both the preliminary and final distillations were set relatively high. Some operators have experienced superheating and irregular boiling during the semimicro distillation which was attributed to the high temperature maintained in the heater. This superheating and the resultant bumping can be completely avoided if solvent is not distilled from a flask in which the inner surface of the sump has become coated with solvent-free oil. K i t h a suitably constructed 20-watt heater maintained withiri the proper temperature range, smooth boiling, characterized by small bubbles, will result within the first minute of heating. If this condition is not attained in this period of time, bumping will invariably result on further heating, and to avoid loss of sample the contents should be transferred to a clean flask for the completion of the determination. As a shield has not been specified for the semimicrost~ill,care should be exercised to avoid drafts of cold air during this distillation, both in the blank and actual oil determinations. Any other factors which tend to cool the neck of the flask, such as removal from the heater to observe the volume of residue before the cut point has been reached, \!-ill increase the reflux and usually result in inconsistent results. Yo condenser is provided for the benzene distilled during the seinirnicro distillation, but more than half condenses in the flask side arm and is collected in a small graduate. The uncondensed portion? if objectionable, may be removed through a plastic tube connected to a laboratory aspirator Ivith the suction end supported near the tip of the side arm. The flasks are best cleaned by adding successively separate small quantities of benzene, acetone, and water, heating gently in each case. Tenaceous deposits remaining after this treatment are removed by adding enough fresh chromic acid cleaning solut,ion to fill the sump and heating to boiling. Flask weights remain constant through many determinations if no probes are used in the
TIPS ON THERMOWELL PROJIOE SPACING WHICH PREVENTS ACCJ MUL ATION OF CONOENSEO SOLVPJT
THERMOCOUPLEJUNCTION MiDWA/ BETWEEN FLASK AN0 SIDE-ARM
A-
MlNiATURE OISNLLING FLASK IOML CAPACITY- 1M.INSUMP HEATING UNIT -2OWATTS-25VOLrS5FT JOEBS GA CHROME1 WIRE COiiEC ON I/B"AREOR AN0 PARTIALLY EMBEDEG IN R€FRACTORY S(Pp0RT APPLiEO VOLTAGE ADJUSTED TO MAINTAIN TEMP IN n m m BEWEEN 550*-5n*F
Figure 4. Jfiniature Still isqetnbly In contrast to the high losses experienced when oils in open dishes were heated too long on the steam bath, prolonged heating in the miniature still, even though a 550' to 575" F. temperature is maintained in the heater, will produce relatively small losses. For eyample, a test using kerosene showed only 5% loss when a 150-mg. portion was heated in the still for 40 minutes, whereas the same quantity of sample in an open dish on a steam bath nould have evaporated almost completely within 2 to 4 minutes. During the heating, the low boiling portion of the kerosene was distilling from the sump into the bulb and refluxing liquid was noted on the flask walls nearly up to the neck. The temperature of the boiling liquid in the sump \Tas 42.5" F. The quantity of the oil that can be heated for piolonged periods in the still without qerious loss will vary with composition and is limited only to that quantity PI hich when brought to equilibrium in the still will not produce vapor in excess of the flask volume. LIMITATIONS AND ACCURACY
The limitation of the method, with respect to the loss of light ends in the distillation steps, was determined by distilling simulated benzene extracts prepared from known quantities of petroleum fractions with successively lower initial boiling points. Recovery began to decrease when samples containing appreciable quantities of hydrocarbons boiling below 300" F. were reached In this range, using a naphtha cut, recoveries became erratic anti
ANALYTICAL CHEMISTRY
1378 Table 11. Oil Content of Known Samples Emulsified Oil in Water Present, P.P.M. 10.8 10.8 18.8 20.5 22.3 34.5 45.5 53.3 69.4 75.5 75.5 85.6 113 140 140 190 199 246 288 316
Recovered, % 90.2 88.5 103 109.8 112.1 93.5
Found, P.P.M. 9.8 9.5 19.5 22.5 25.0 32.2 45.9 51.4 72.8 73.0 81.8 82.8 116.2 139.0 145.5 196.5 192 244.8 278 305
100.8
Av. hIean deviation from known Max. deviation from known
9c.5 100.0 96.8 108.0 97.8 102.9 99.3 103.3 103.7 96.5 99.3 96 3 96.8 99.9 5.1 12.1
Figure 6. Comparison of Oil Contents of Refinery Waste Water. Evaporation us. Semimicro Distillation of Solvent from Extract
Table 111. Oil Content of Known Samples Oil Dispersed in Water by Agitation Oil
Present, P.P.M. Sample 1, SAE 70 oil
Oil Found, P. P.AI. 9.5 8.5 13.2 9.8 18 14.2 15.6 14.5 14.7 1.5.9 23.4 42.5
Recovered.
%
104.4 12 0 36 0
AV.
Mean deviation from known Max. deviation from known 40 5 49 3 54 9 57 5 57.0 59.0 51.7 80 9
Sample 2, 2 / a SAE 70 oil 1 / 5 kerosene
0
50
75
OIL CONTENT PRESENT
100
RRM.(WT)
107 104 in3 110 105 in8 95 99 104
hv. Mean deviation from known Max. deviation from known
Figure 5. Determination of Oil in Known Samples b y Semimicromethod Sample 3a '/a SAE 70
56 3
011
59
5.5
10
43 43
76 72
values for the lower boiling point limit of recoverable oil varied kerosene 68 60 3 89 1 / t gasoline 71 7 62 86 from 260" to 305' F. The approximate value of 300" F., set 64 7 F, 84 8 early in the test program, seems t o be conservative in the light 78 109 84 114 95 83 of results obtained recently when a mixture of equal parts of 80 133 106 lubricating oil, kerosene, and gasoline was used as the test 139 108 78 AV. 79.9 mixture (Table 111). Based on a recovery of 80% of this mi.;ture, and assuming all the loss t o be light ends, recovery of corna Sample 3 contains 28% of components boiling below 300' F. and is ponents boiling above 275" F. was indicated. heyond the scope of the present semimicromethod. T h e d a t a from sample 3 are not plotted in Figure 5. The over-all accuracy of the seniimicromethod was determined by analysis of water samples containing known quantities of oil ranging from 10 to Table 1V. Oil Content of Refinery Waste Water Streams 300 p.p.m. Forty samples were used, twenty preOil Content, P.P.M. ,\Iet hod __ pared from an emulsifiable oil and the remainder from mivturesof oil and kerosene suspended in &IllimiCrO 10 11 13 14 16 18 19 19 23 25 26 27 28 water by shaking. The results are tabulated in Tables I1 and 111, where the averages for three classes of samples are shown to be 99.9, 104,and 104.4% of the actual values with an over-all average of 102.i%. These data are plotted in Figure 5.
Evaporation 3 3 3 4 Semimicro 29 32 45 55 Evaporation 2 16 17 34 113 Semimicro 104 109 Evaporation 67 72 84 Semimicro 146 150 170 Evaporation 95 123 97
3 3 3 a 12 11 3 7 3 56 6 4 72 75 83 88 96 97 25 15 34 36 44 47 67 61 39 119 127 129 134 115 115 56 79 103 90 72 102 171 175 184 186 189 200 85 140 133 89 83 137
134 105 240 200
136 98 245 156
143 97 466 334
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 In order to provide a basis for comparison between the oil content of refinery streams determined by the semimicromethod and those obtained by the evaporation procedure, a large number of samples were run by both methods; some of the results are tabulated in Table IV and plotted in Figure 6. The results by the evaporation method in the region from 100 to 200 p.p.m. are about 60 to 707, of the results by the semimicromethod. The relatively lower results for the evaporation method in the lower range (only 25% of the semimicromethod values in the 10 to 25 p.p.m. range) are to be expected in view of the proportionately higher losses shown for the smaller samples in Figure 1. The reduction to 1 hour in the elapsed time required pel d e t e r m i n a t i o n 4 5 minutes if the extraction and distillation steps are overlapped-was achieved principally by the substitution of the rapid distillation procedure for evaporation from dishes in the removal of solvent from the extract. Additional saving accrued from this substitution because it eliminated the need for dehydration of extract by filtration, as the water is carried over with the distilling solvent. The method is readily adaptable to
1379 multiple simultaneous determinations, in which case an average time per determination of less than a half hour is possible. Recent tests, in which the individual losses from the two distillation steps of the present method were determined separately, showed the semimicrostill (sapable of recovering components boiling above 225" F. This indicates that the present 300" F. limitation is determined by the performance of the preliminary still. A modification of the unpacked column now used which will provide reflux is under way and should extend recovery toward the 225" F. limit set by the present miniature still. Further recovery of light ends will require the use of a lower boiling solvent and this modification of the present procedure will also be investigated. LITERATURE CITED
( 1 ) American Petroleum Institute, "Manual on Disposal of Refinery Wastes," 3rd ed., Section I. Appendix 5, 1941. (2) Kirschman, H. D., and Pomeroy, R., ANAL. C H E i i . , 21, 793 (1949). RECEIVED April 20, 1951.
Determination of Total Alkyl Benzenes in Selected Crude Fractions A n Ultraviolet Method JOHN F. KINDER, Sinclair Research Laboratories, Inc., Harvey, 111.
Solvent properties of petroleum fractions, interest in petrochemicals, and expanded output of heavier fuels have demanded additional information as to the aromaticity of crude fractions boiling above 300' F. A n application of ultraviolet analytical methods for a rapid estimate of total aromatics in petroleum crude cuts which have a boiling range of 200' to 395' F. is described. The basis of the test is the use of an average aromatic absorptivity calculated at a wave length of 215 mp. Typical analyses,
T
HE classification of aromatic compounds contained in petro-
leum crudes is based commonly upon the type of nuclear structure. Within boiling ranges characterized by naphthas, gasoline, and distillate fuels, most identified aromatir compounds consist of alkyl derivatives of benzene, Tetralin, naphthalene, biphenyl, phenanthrene, and/or anthracene. Gasoline is the most important of the crude products. An ultraviolet spectrometric niethod has been devised for the detection and analysis of specific aromatics contained in such petroleum stocks ( 5 ) . Solvent properties of petroleum fractions, interest in petiochemicals, and expanded output of heavier fuels have demanded additional information as to the aromaticity of crude fractions boiling above 300' F. This knowledge, to a certain extent, may be made available by application of the ilSTM method ( 1 ) . Ultraviolet inspection of closely fractionated crude cuts which boil between 200" and 395' F. shows that aromatic content can be rapidly estimated. The results are not separated widely from those obtained by the ASThl method.
and comparisons with the ASTI11 D 875-46T acid absorption procedurc, are giben for fractions from three crudes. The ultraviolet procedure is not designed for crude fractions containing benzene and/or naphthalene; both of these compounds are removed readily by distillation. To date, the analytical data have been obtained from petroleum stocks which have low bromine numbers. For such materials, the ultraviolet method should be useful as an analysis to confirm o r supplement the ASTM test. ment of calibration data, and subsequent analysis of test samples. .4t a scanning speed of 0.4 mg per second, absorption curves were recorded directly in terms of absorbance. Iso-octane (2,2,4trimethylpentane), treated with silica gel for removal of aromatics, was employed as a solvent. Calibration data were obtained from aromatics supplied by the American Petroleum Institute. All had a purity higher than 99%, as tested and certified by the Sational Bureau of Standards. DEFINITIONS AND SYMBOLS
Absorption relationships in the ultraviolet region are defined by the Bouguer-Beer law ( 3 ) . log,,
whrre
A I c
O I = '1
=
alc
sample absorbance path length of light in absorbing medium sample concentration ZO = energy incident on sample Z = energy transmitted by sample a = absorptivity, A/lc JV-ave lengths are expressed in millimicrons. = = =
APPARATUS AND MATERIALS
THEORY AND DEVELOPMENT OF METHOD
The Cary ultraviolet automatic recording spectrophotometer was used for preliminary exploration of crude fractions, develop-
The strongest ultraviolet absorption band for each type of aromatic nuclei occurs at a wave length dependent upon the
