V O L U M E 2 1 , NO. 7, J U L Y 1 9 b 9 LITERATURE CITED
(1) Ani. SOC.Testing Materials, “A.S.T.M. Standards on Petroleum
Products and Lubricants,” Method D155-45T, November
1948. (2) Zhid., Method Dl56-38. ( 3 ) -in,. yoc, ~~~~i~~ Llarerials, ~ ~ ~ y m p o s i u non l Color,vslLlarch 1941. (4) Diller. I. M..Dean, J. C., DeGray, R. J., and Wilson. J. W., I X D . E X G . C H E Y . . . i S A L . ED.,15,367-73 (1943). ( 5 ) Diller. I. M.. DeGrq.. 11. J.. and Wilson, J. W,, Ibid., 14, 60i-14 (1942’.
793 (6) Gardner, H. A . , and Sward, G. G., “Physical and Chemical Examination of Paints, Varnishes, Lacquers, and Colors,” 10th ed., Washington, D. C., Institute of Paint and Varnish Re-
search, 1946. (7) Haren, Allen,Am. Chem. J . , 14, 300-10 (1892). (8) Osborn, R. H., and Kenyon, W.C., IND.ESG. CHEM.,;IN.~L.
ED., 18, 523-30 (1946), (9) Story, B. W., and Kalichevsky, V. rl., Ibid.,5 , 214-17 (1933). (10) U‘hyte, L. K., J . Am. Oil Chem. Soc.. 24, 137-40 (1947). RECEIVED A u g u s t 23, 1948.
Determination of Oli in Oil-Field Waste Waters H. DARWIN KIRSCHRI.4N, Lnicersity of California, Los Angeles, Calif.,
4hD
RICHARD POTIEROY,
.Montgomery and Pomeroy, Pasadena 1 , Calif. In anal5ses of oil-field waste waters “oil” is considered as the relativelj nonvolatile liquid component that contributes to the formation of oil films and deposits. The nonsaponifiable hexane-soluble fraction most closelg represents “oil content” in this sense. In anj analjtical procedure that uses a solvent, renioial of this so1,ent prior to weighing or iolumetric measurement must be accomplished in a manner to minimize evaporation of the oil. Drging the oil at room temperature after boiling off the solient has been found satisfactorj. In the wet-extraction method, samples of low oil content (below- 25 p.p.m.) jield about 9 5 q ~of the oil in two extractions and 999’~ in three; higher percentage recoiery is attained at higher oil contents. Naph-
T
HE determination of oil in oil-field waste waters is of considerable importance where pollution control agencies have set up standards of quality for wastes discharged into bodies of natural water, or where the efficiency of facilities for waste water treatment must he evaluated. In general, procedures previously recommended have not been investigated with enough thoroughness to provide an adequate basis for judging their accuracy and suitability: the results of such investigations, if any have been made, are not available in published form. This paper reports the results of an investigation undertaken to develop procedures that will yield valid results in terms of a reasonable understanding of the objectives of the “oil” determination. Two basic plans, the “wet extraction” procedure and the “flocculation” procedure, have been elaborated and compared. C O S S T I T U E N T S CONSIDERED A S OIL
Before evaluating analytical procedures for determination of the oil content of waste water, a decision should he made as to what materials are to be included in the category of oil. Oilfield waste waters contain all’the hydrocarbons of natural gas and oil from nietharie up, plus asphaltic and resinous materials, fatty acids, and other organic matter. The hydrocarbons having boiling points above normal atmospheric temperature-i.e., isopentane (2-methylbutane) and heavier-could he considered as constituting the oil component of the sample. \Then the oil is separated by solvent extraction, either with or without the aid of flocculation, there is no practical \yay of separating the solvent from the extracted oil without the loss of highly volatile fractions. In one published procedure for determination of oil in waste waters an attempt is made to overcome this difficulty by partially distilling the sample and separating the distilled oil from the water by gravity, with a subsequent volumetric measurement
thenic acids are extracted with the oil and must be separated by saponification. -4new procedure gives results differing by an average of less than 1 p.p.m. on duplicate samples. Ferric chloride is unsuitable as a flocculating agent, because it produces sulfur in the extract if the waste w-atercontains sulfide. Zinc salts are satisfactxy. Results by the flocculation method are reproducible with an average difference below 1 p.p.m. on duplicates, but the results are about 2 p.p.m. lower than those of the wet-extraction method, because of incomplete trapping of the oil by the floc and incomplete removal of the oil froni the floc. Because the wet-extraction method gives results of superior accuracy in less elapsed time, the authors consider it generally preferahle.
( 1 ) . But even in this procedure, a small amount of ethyl ether is used to collect all the oil in a capillary tube. Because of the necessity of evaporating this ether, all the pentanes and a t least part of the hexanes are lost. Some type of distillation procedure may he the only way to get accurate results as far as highly volatile components are concerned, hut any such procedure, if exact, is certain to he complicated and too lengthy to he of value for routine testing. The best way out of this difficulty is to ignore hydrocarbons that evaporate rapidly a t room temperature, and to consider that “oil content,’’ for practical purposes, means the oil that remains as such after moderate exposure to the air. This is a logical view, in so far as the pollutional character of the water is concerned, for the highly volatile oils do not contribute to oily films on the surface of polluted streams. The volatile hydrocarbons may contribute to explosive atmospheres in sewers, hut this condition may result from the presence of hydrocarbon gases as well as vaporizable oils. From an analytical standpoint this is a problem entirely separate from oil content. The final delimitation of the category designated as “oil” rvill depend in part upon the practicability of laboratory procedures. The objective chosen in this research Mas the separationof the components that are ielatively nonvolatile liquidsat room temperature and contribute to the formation of oil films and deposits. With this in mind a solvent should be chosen which will dissolve the oils effectively, hut ~villhave a minimum solvent action on nonliquid materials. In drying the separated oil prior to weighing, a procedure should he followed in which it will he possible t o evaporate the solvent used in the analysis, together with fractions of the oil similar to the solvent in volatility, hut without too great evaporation of heavier fractions. Solvent and drying technique must he chosen before comparisons of extraction procedures can be made.
.
794 .
~
Table I.
... ..
-
Solubilitj of JIontebello Crude Oil in Solvents (100 ml. of solvent
pliic
600 mq. of crude oil)
Insoluble Residue, 70of Sample 10.3 4.8 1.4 1.0 0.95
Solvent Neohexane Cyclopentane Carbon tetrachloridr Benzene Chloroform
- __ CHOICE OF S O L V E N l
Ariiung the aolveiits that may be considered in the aiialysi5 of oil-field waste waters, some-for example, benzene, the ethers, chloroform, and carbon tetrachloride-dissolve not only the liquid hydrocarbons but also materials of the asphaltene class. Alkane solvents, on the other hand, have very little solvent action on the asphaltenei. Saphthenic hydrocarbons, such as cyclopentane, are intermediate in action. The relative strengths of various solvents toward petroleum components are revealed by treating small bamples of crude oil a i t h the solvents and weighing the insoluble residue. A series of tests of this sort with Montehello crude is shown in Table I. When strong solvents are used in extiactions of oil-field waste waters, and the dried extract is treated with hexane, an insoluble residue remains, which generally amounts to about 10% of the total exti art. These hexane-insoluble residues from crude oil or from evtractions of oil-field waste waters are black, amorphous solids, typically asphaltenes. Samples of these residues from various sources have been examined many times, and have not 8hon.n an oily or tarry consistency, with the exception of a single anomalous case ( 3 ) . The decision as to the inclusion of asphaltenes as a part of “oil content” depends on the purpose of the analysis. Crude oils hold asphaltenes in solution to some extent; hence these components might be included as possibly rontributing to the total quantity of an oily phase separating from waste waters. I t does uot necesbarily follow, hon ever, that such materials would always be a part of the oily phase. Hecause they are not themselves oils, and the objective is to determine, as nearly as possible the “relatively nonvolatile liquids,” the decision in this research was to consider only the alkanr-boluble material as oil. ThcI solvent selected for this purpov is rssentially a mixtulr of isomeric hexanes, \old as “mivetl hpxanrs” anti hereinafter referreti to a i “hevarir.” In certain Y i e p of the procedures stronger solvent9 are usrd, hut the final vparatiori is made a i t h hexant, T h r standard procedure of thr Inieiiran Public Health .issociation for determining “grease” i l l +w:ige ( 2 ) tilw II+* a n alkane solvrrit (petroleum ether)
ANALYTICAL CHEMISTRY
T l i c ~oils used m r e lfontebello crude having an il.P.1. gravitl of 25 (specific gravity 0.902) and Yanta Maria crude with a n 4.P.I. gravity of 10 (specific gravity 1.00). Small samples of the crudes were weighed into 3OO-ml. conii.a) Hasks, spread adequately over the bottoms of the flasks. and ~lloivedto stand at room temperature, with subsequent weighing,. Rt appropriate intervals. In one case, 10 ml. of chloroform w r e added to the oil with subsequent evaporation of the chloroforni by a stream of air until it W A ~apparently all gone. Result- ? r e -honm in Table IT.
-4comparison of the t h o ~ a i n p l a sof Montebello crude >how. that the percentage loss of a eight is greater for the smaller sample as would be expected, yet the difference is relatively slight. The rhxperinient also shows relativdy little difference in behavior of the two crudes. Rather surprisingly, the heavy Santa Maria crude shows a slightly greater loss in n eight than the less dense Montehello crude. A greater range of behavior would n o d ( ~ u b t he found if a greater variety of crudes were tested. The fourth test shows that some of the added solvent raiiiained with the oil for an hour or more, but after 2 hours the figuret for percentage of loss are the same as for the sample to w h i v h rir rhloroform had been added. VOLATILITY LOSSES DURING DISTILLATION OF SOLYE17
The losses attending the proresr; of distillation of the soh-rnt were studied. In each test a sample of Montehello crude was weighed iiitu a 300-ml. conical flask, and a 200-ml. portion of solvent’was added, and then distilled off. I n the distillation process, a water bath was used for heating and the flask was connected to t,he condenser by corks and a glass angle tube 10 mm. in diameter. The solvent was dist’illed down to a volume of 3 to 5 ml. The flask was then disconnected and the last of the solvent removed by tilting to pour out the vapor, reheating, if necessary, by a momen.. tary immersion in the water bath and tilting again, until removat of the solvent appeared to be complete. The flask was theis placed upright near the balance and wrighed at interval. The results are .shown in Tahle 111.
l h e losses are substantially grritttlr than when the saiiipler \yere merely exposed to the air, aiid generally increase with increasing boiling point of the solvent used. Exceptions are noted in the case of benzrne u t 1 and 2 hours, but this WAS prole:ibly due to incomplete removal of the txnzene. The last line of Table I11 shows the results of re-use of a solvent previously used in a similar experiment. The accumulation in the solvent of volatile fractions of the crude oil evidently diminishek dmequeiit lossrs. This wis obsrrvrd also with other solvents in preliminary experiments. After this behavior became apparent, all solvents were redistilled before reuse, and roughly 20% To secure information about the loaves of oil due to evaporatioii reproducible values. and to develop a suitable technique for drying the extracted oil The foregoing experinlent?;led to the adoption of a procedure prior to weighing, a study was made of the evaporation losseq of ,*iihstantially :is outlined ahorr-distillation on a water bat’h. small samples of crude oil when expospd to thP air. with reinoval of the last of the solvent . . -. . . _____ ___ by gentle warmirig and tipping of t’he flask. Subsryuently the flask is supTable 11. Loss of Oil I h r to E\aporatinri ported in the balance room for 1 to 2 Original Weight of Time, tIours ......24~hours i n an inverted position. When the ’I’ypeof Crude Oil, 0.25 0.5 1 2 3 .. 4 6 Crude Oil RIg. Per Cent Change of Weight quantity of oil is too great to permit this. Montebello 530.1 -1.2 -1.9 -2.4 -2.9 -3.5 ... the flask is left on its side for approxiMontebello 48.4 -1.2 -1.6 -3.1 -3.5 -4.5 .. ... . , BantaMaria 544.3 -1.2 -2.2 -3.1 -3.6 -4.1 -4.8 -4.5 ... mately one day. The tare weight Santa Maria + the flask is determined after w-eighing chloroform 593.7 +28 +8 -1.8 -3.5 -4.1 -4.3 -4.5 -5.0 flask plus oil, hy rinsing out t h r nil --__ -. ~
~
I
,
V O L U M E 21, NO. 7, J U L Y 1 9 4 9 Tahle TIT.
Loss of Oil During Distillation of Solvent Boiling Original Point of Weight Solvent, of Oil, hIg.
c.
Solvent
Ethyl ether 35 40 Methylene chloride Chloroform 61 Benzene 80 Methylene chlorideu 40 " Sample re-used as ret-overed
Table 1V.
79s
Time, Hours 1 2 3 24 % Change from Original Weight of Oil
-
497.1 498.4 505.7
-
-7.0 -8.5 8,9.2 -7.5 -8.6 8. 9.8 -7.8 -1O.U -10.7 -9.6 :04. -3.4 -9.0 , . . . -11.00 ~ 2 8 . 8 -4.4 -4.7 ... , .. b y distillation from previous analysis
.
Effect of acidification upon Quantity of Hexane Extract Acidified Not Sample .Icidified Difference Parts p e r million of extract 261 141 123 12 15 27 19 6 13 3325 162 163
kirat extrnction Second extraction Third extraction Total ~
.
-. ....
. . ... -. . .
. . ..
with the solvent and allowing the flask to stand in the balance rnnm for 2 hours or more. UET-EXTRACTION PROCEDURE
The wet-extraction method has been shown to be suitable for the determination of grease in sewage and certain industrial wastes ( 3 ) . Detailed examination of its performance as applied to oil-field waste waters revealed two problems requiring special investigation: possible extraction of organic acids from the water arid attaining complete extraction of the oil. The magnitude of the first effect became apparent when successive extractions were made of two identical samples of Santa Fc Springs waste water, one of which had been acidified, while the othtar was left at its normal p H value of 7.6. R e s u h are shown in Table I\-. The increase of extracted material in the acidified sample aniounted to 163 p.p.m. in three extractions, which indicates that organic acids are potentially a source of large errors when thik pH is low enough to perinit their extraction. 111 another test, a sample of Wilmingtoii oil-field waste wat(Jr was extracted with hexane, using high speed stirring. The total extract recovered was dissolved in an ether-alcohol solution and titrated lvith sodium hydroxide. Subsequently hexane and water were added and the mixture was shaken, thus transferring the oil t o the hexane layer and leaving the saponified acids in the aquwus phase. Two additional extractions were also made of t'he original waste water sample using chloroform, with subsequent titration with base. For comparison purposes, the weights of extract obtained by :ihexane extraction at pH 11, by the flocculation method, and hy a hesane ext,raction of the saponified chloroform estract are inrluded i n t h e quantit:atire result,s summarized in Table \-. The result obtained by hexwile extraction at pH 11 led to the hope that this might afford a simple way t o prevent extraction of the acids. An attempt was made to analyze Saiita F'e Springy waste water by this means, but if wili impossible to prevent the extraction of fatt'y acids until the pH TWS raised to such a value that the voluminous precipitate of calcium carbonate and magnesium hydroxide prevented coniplete recovery of the oil. Corrections for extracted acids might be made on the basis of a titration of the extract, using an assumed equivalent weight for the acids. This equivalent n-eight is variahle, however, and if the acid con ten^ is high and the oil content is lowl as in the case of the Kilmingtori water (Table I-),uncertainty of the correction will he large relative to the true oil content. The most practical way to overcome this difficulty appears to be extraction under ronditions suitable for complete recovery of the oil, regardless of the a m o u n t of organic acids extracted. and
a subsequelit separation of these acids by saponification. The details are given in the elaboration of the procedure below. COMPLETENESS OF EXTRACTION OF OIL BY DIFFEREh'I TECHXQUES
.ittempts to extract oil from oil-field waste water by niaim ally shaking with hexane gave unsatisfactory results (Table VI). Complete extraction could not he a,ttained with a reasonnhle rxpenditure of time and energy. If the oil were present i n the waste waters entirely ill the foriii o f colloidal droplets, complete ext,raction should be readily attained. Much of the difficulty is no doubt due to the fact that R considerable amount of the oil is bound up with particle& of :Isphalt and other solid material, ,so that effective contact betweell wlvent and oil is not easily attained. With a solvent, such ar htinzene or chloroform, which will dissolve asphaltic materials. the extraction end point ~hould.be more rapidly approached. 'To determine the correc*triess of this concept, samples of oilt i ~ l dwaste water were subjected to successive extractions Lvitl: rhloroform, employing manual shakiiig (Table VII). Comparison of Tables VI and VI1 shows, as expected, that the eixtraction by manual shaking approaches an end point niore rapidly when using chloroform than when using hexane. .illthough the oil can be quantitativelj- recovered by manua! -haking with chloroform, this requires considerable expenditure of time and effort. ZIec-hilnicaI agitation was then tried as R I wqier method.
Aisewing-machine iiiutur wac equipped with a Monel stirrrr 35 mm. in diameter which could be loivered int'o a wide-mouthed 1-gallon bottle. Use of a rheostat controlled the speed of rotation to about 2000 to 1000 r.1i.m. Hot,h hexane and chloroforni were tried: 200 to 300-ml. portioiiu of solvent were used in each extraction with similar liut n o t idmtical water samples of 2 to 3 liters. I t is evident that mechauical agitation gives much better recovery in each extraction than manual shaking, and that there is little difference in this case hetween the two solvents. (However, longer periods of agitation employed with hexane may liavr winpensated for some difference in solvent action.) Eaclb extraction yielded 75 to 80% of the oil remaining in the sainple: thus substantially complete removal can be effected in four extractions and for approximate piirposes two or three extraction* would be satisfactory. Table V.
Quantity and Acidity of Extracts
Weight of Extract, M g . Firat extraction, hexane a t p H 7.2 16.8" Two additional extractions, with chloroform 30.3 Hexane extraction of identical sample at P H 11 12.4 Flocculation method, hexane extraction 13.0 Chloroform extraction with saponification a n d hexane extraction of unsaponified oil 12.5 Saponification left 11.8 mg. of oil.
Table VI, Extraction No. 1 2 3 4
Tahle VII.
oj
Aside 0.028 0.13 0.005
Hexane Extraction Using Manual Shaking Shaking Time .Win. 2 2 2 30
Oil Recovered P.p.m. "IC 15 28 13 25 9 17 15 28
Removal of Oil by Successive Extractions. Using Chloroform
Method of Agitation Alnnual shaking, 5 min. Second manual shaking, 5 min. Third manual shaking, 5 min. Additional motor stirrer extraction .5 min.
Total extract
Me.
Sample 1 P.p.m. % 28.8 70.5 6.7 16.3 3.2 7.8
Samplr. 2 P.p.m. LI 26.8 53.5 13.7 27.3 7.8 l5~.5
2.2 6.4 40.9 100.00
1.9 3.7 50.2 100.00
ANALYTICAL CHEMISTRY
796 Table YIII.
81 14 4 1
95.4 16.8 4.3 1.1
4 a
Hexane and Chloroform Extractions Using Mechanical Stirring
__
102.2 15.7 5.8 (1.3)a
.
82 13 4
__
la
Total 117.6 100 125.0 100 Assuming that a n additional 1% would be recovered in fourth extraction.
Table IX. Time, Minutes 1
5 15 30
Table X.
Water KO,
Extraction of Oil by High-speed Mixing with Hexane Oil in First Extraction. % of Total 70 83 81 90
Oil in Emulsion Layer, % of Total 2 7 7.3 12.7 2.0
Duplication First analssis
Total Extracted,
%
73 90 94 92
LABOR4TORY DIRECTIONS FOR WET-EXTRACTION PROCEDURE %,Remaining in 1% ater 27
10 6
8
of Results by Wet-Extraction Method Oil Content, Parts per Million Second analysis Ar.
With the usual oil-field waste waters of moderate oil content this sludge layer appears very light in color after the second extraction. The small fraction of the original oil content of the sample remaining in this layer may be neglected in most cases, but when more voluminous than usual and when maximum accuracy is desired, a third extraction may be indicated or this sludge layer may be separately extracted with a small portion of solvent. At the conclusion of an analysis, a small amount of emulsified chloroform remains in the water and settles to the bottom of the vessel after a few hours’ standing. The amount is generally so small that additional operations to recover its oil content are not worth while.
Difference
Ar. difference hetween 1st and 2nd analyses 0.86
I n contrast to sewage, in which the sample yields its grease content readily on moderate shaking with the solvent for short periods of time, the oil-field waters require vigorous agitation. During this agitation, a certain amount of viscous emulsion is produced which accumulates between the water and solvent layers when the mixture is allowed to settle. I n the experiments shown in Table VIII, this emulsion layer was left with the water to be subjected to subsequent extractions. It appeared likely that a substantial portion of the oil unrecovered after each successive extraction by high speed motor stirring might be present in this emulsion layer. .kccordingly, a series of tests was run n i t h four identical samples, in which the emulsion layers were in each case separately extracted. The time of stirring was also varied. Table I X presents the results. After agitation for 5 minutes or more the amount of the oil remaining in the water is 10% or less of the total oil content. Agitation for 1 minute gives poorer removal, but there is relatively little advantage in times longer than 5 minutes. When chloroform is used as the first extracting solvent, the problems of sludge or emulsion layers become somewhat different than when hexane is used. mhen chloroform and waste water are vigorously agitated, and allowed to settle for a few minutes, three principal layers separate: an aqueous phase on the top; a bottom layer which generally consists of droplets of chloroform separated by aqueous films; and, between the two, a “sludge” layer of water, solvent, air, and solid matter. I n the recommended procedure set forth below the water is poured from the top of the bottle used for agitation and the lower layers are transferred to a separatory funnel. Subsequently, the bottom layer in the funnel, consisting principally of chloroform, is run into a second separatory funnel. This operation usually causes the separation of clear chloroform, apparently by disrupting the films that separate the chloroform droplets. The sludge layer is returned to the water for a second extraction, whereby any oil that it contains is largely removed by dilution in successive extractions.
Transfer the sample of water (about 2.5 liters) to a 1-gallon bottle with a sufficiently wide mouth to admit a motor-driven stirrer but not wider than necessary, so that loss by spray during agitation may be kept down. Add a 30 to 50-ml. portion of chloroform to the original sample bottle, taking care to rinse off the stopper, and shake. Add this solvent to the water sample and repeat the process with fresh portions of chloroform until tile bottle is sufficiently cleaned for the accurary desired in the analysis. Add to the water enough more chloroform to make a total of about 200 ml. and then subject it to 5 minutes’ stirring with a motor-driven agitator a t sufficient velocity of rotation to keep the solvent and water well mixed. Decant most of the supernatant water back into the original sample bottle and pour the chloroform with the remaining tvater into a 500-ml. separatory funnel. Run the unclear solvent layer off into a second separatory funnel. I t mill usuitlly become clear with a small amount of viscous sludge at the solvent-water interface. If the solvent layer is not cleared by this procedure, allow the second funnel to stand for a fetv minutes and give it a single, sharp shake which will usually break the “emulsioii” and give a clear solvent layer. With care to keep the stem of the separatory funnel free from water, run the clear chloroform througn a filter paper into a 300-ml. conical flask. Add the water remaining in the first separatory funnel to the original sample bottle. \“ash the sludge in the second funnel out of the funnel top into the water and repeat the extraction process as previously outlined. While the second extraction is being made, connect a condenser to the flask containing the filtered cdoroform solution and distill the chloroform by partially surrounding the flask with hot water. When the volume is reduced to 10 to 20 ml., add the second extract to the same flask and distill in a similar fashion down to a volume of about 1 ml. Remove the last portion of solvent by pouring the vapor out of the flask. To the cooled flask, add 5 ml. of ethyl ether, followed bv 10 ml. of ethanol or 2-propanol, about 1 ml. of 1 S sodium hydroxide, and 2 drops of phenolphthalein indicator solution. S o w wash the contents of the flask with 200 ml. of hevane into a separatory funnel containing about 200 ml. of distilled water. Gently shake the mixture, then draw off the water layer. Repeat this washing with water until the water shows no color of the phenolphthalein. Draw off the last portion of wash water and filter the hexane layer into a 300-ml. conical flask. h 50-ml. pipet equipped with a rubber suction bulb IS convenient for the transfer of hexane to the filter. Wash the filter paper well with small portions of hexane. Distill off the hexane down to a volume of about 1 ml. Remove the flask from the water bath, and remove the vapor by tipping. Wipe o f f the outside of the flask with lintless cloth or paper and place it neck down through an iron ring on a stand near tile balance; weigh after 1 to 2 hours. (If the quantity of oil is so large that it may run out of the flask, lay the flask on its side and weigh the next day.) To obtain the tare weight of the flask, warn it out with several portions of hevane and again bring to equilibrium with the atmosphere. Inasmuch as the flask is now cool, a longer time is needed; 2 hours are adequate. Reproducibility of results attainable by this procedure is indicated by the series of analyses of duplicate samples shown in Table X. FLOCCULATION METHOD
The flocculation procedure as developed by the Committee on Waste Disposal of the American Petroleum Industry ( I ) recommends that the final measurement of the separated oil be made volumetrically in a special apparatus. This volumetric
V O L U M E 21, NO. 7, J U L Y 1 9 4 9
797
a d d i t i o n a l . From the remaining water, another 22% (Comparison of wet-extraction a n d flocculation methods. All figures in parts per million) was recovered by a single wet Samples e x t r a c t i o n . The total re4 5 1 2 3 6 7 8 9 Oil Recovered from Line covery averaged 110% of the 3.21 5.70 3.41 2.Y8 4.26 4.15 1.89 1 19,68 2 9 . 7 First extraction, first floc amount found by the proposed Second extraction, first 2 0.06 0.00 1.00 0.88 0.69 0.65 1.38 0.85 floc ... wet procedure, using two ex0.52 0.75 0.06 0.70 0.06 0.29 1.19 1.5 3 Extraction of second floc 0.05 6.46 3.47 21.68 31.2 5.59 4.14 2.80 4.27 6.10 4 Total by floc tractions. ; i third extraction Wet extraction of filtered 5 presumably would have yielded 3.6 L54 2.10 2.00 2.16 0.23 0.43 1.04 0.61 water 31.8 7.13 6.24 22.62 3.41 Total recovered 8.46 5,63 4.50 6.53 6 an additional 5%, leaving a By standard wet extrac7 4.60 7.10 4.05 6.22 3.92 6 . 6 2 22.20 3 5 , l 5.48 tion d i s c r e p a n c y of 5 % . This -2.95 -2.16 -0.52 -2.07 -0.94 -2.36 -2.52 -5.4 Difference, line 7 - line 1 - 1 . 3 9 8 difference p r o b a b l y is n o t Difference, line 6 - line 7 + 1 . 6 4 + 0 . 0 3 - 0 . 6 4 +2.24 +O.l5 +0.58 -0.09 +0.42 +0.30 9 significant, as it would average only 0.5 + 1.5 mg. of oil in the samples taken. This may measurement is only slightly faster than weighing and is decidedly be considered satisfactory agreement, in vie\\- of the fact that less accurate. In the present research it was desired to secure the two groups of analyses involve five operations and ten flask results of maximum accuracy, often using samples from which the weighings on each sample. yield of oil was only a few milligrams, and to obtain results suitWith samples of higher oil content, the discrepancy between the able for comparison with gravimetric results secured by the wettwo methods is relatively less, but nevertheless substantial. extraction method. Hence the extraction of the floc was folThus sample 8, containing 22.2 p.p.m. as determined by two wet lowed by the removal of solvent, drying, and weighing of oil extractions, yielded 89% of this amount by a single flocculation in the manner previously described for the wet-extraction proand extraction, and 106% by t x o flocculations, re-extraction, cedure. and wet.extraction of the water. Sample 9, showing 35.1 p.p.m. Tests of the flocculation method were first made with ferric by two wet extractions, yielded 85% of this amount by the simple chloride as the flocculating agent. I t was found that if the waste flocculation procedure, and 99% by double flocculation and wet water sample contained sulfide, the material extracted from the extraction of filtrate. dried ferric hydroxide floc included sulfur. Other flocculating REL4TIVE MERITS O F FLOCCULATIOY 4 Y D WET-EXTR4CTION agents were then tried. -4luminum hydroxide and zinc carMETHODS bonate appeared most suitable. Both trapped the oil just as The wet-extraction method, as previously shown, gives results well as iron hydroxide and neither yielded sulfur vrhen used with (Table X ) which, on samples with 3 to 125 p,p.m. of oil, are sulfide-containing aaters. Zinc carbonate is more compact duplicable within an average difference less than 1 p.p.m. On and filters much more easily than aluminum hydroxide and samples of oil content up to 35 p,p.m. a comparison of the results therefore was used in most of the flocculation experiments. of the wet-extraction procedure with those obtained by two sucA number of tests for acidity in the material extracted from the cessive flocculations followed by a wet extraction showed differfloc by hexane showed no evidence of the presence of organic ences averaging less than 1 p.p.m. (Table S I ) . These facts acids. indicate that the wet extraction method gives a reliable measure The procedure finally adopted for the flocculation method is as folloR s: of the oil content of the sample; “oil” is understood to mean the hexane-soluble, nonsaponifiable, relatively nonvolatile liquid T o a sample of 2 to 3 liters, add 5 millimoles each of zinc component of the n-aste water. acetate and sodium carbonate in solution. -4fter thorough mixing, allow the floc of zinc carbonate to settle and filter the The flocculation method gives results that are similarly reprosupernatant liquid through a qualitative paper. Toward the end ducible and consistent among themsevles, but in waters of low oil of the filtration, transfer the floc to the filter paper and allow the content are about 2 p.p.m. lower than the Ret-extraction method. paper to stand in the air until thoroughly dry. Wash out the As it has been demonstrated that this amount of additional oil oiiginal sample bottle with 50 to 100 ml. of hexane to remoye any oil on the walls and stopper. Separate the water with a separaactually can be recovered from the water by an additional tory funnel and transfer the hexane to a Soxhlet apparatus, taking wet-extraction operation, it may be concluded that the discare that no drops of water arc included. Place the dried filter crepancy is due to incomplete recovery hy the flocculation method. paper and floc in a Soxhlet thimble and extract for 2 to 3 hours K i t h adequate equipment, the working time per analysis is with hexane. At the end of the extraction period, reduce the volume of solvent in the receiving vessel to 2 to 3 ml. Disabout the same for the two methods. However, results can be connert the flask and remove this last portion of solvent as diobtained in considerably less elapsed time by the wet-extraction rected in the wet-extraction procedure. After removal of the method. Six hours of elapsed time are adequate for a wetsolvent, place the flask in an inverted position near the bslance for estraction analysis, but in the flocculation method the precipi1 to 2 hours; then weigh. Wash the oil out of the flask with several small portions of solvent and dry the flask as before to tated floc must be dried at least overnight, so that results cannot secure its tare weight. be secured in less than 2 1 hours. Early tests on duplicate samples by the two methods showed ACKYOWLEDGMEYT that results were generally somewhat lower by the flocculation The authors acknowledge the sponsorship of the Los .4ngeles method. This discrepancy was found to be due to incomplete County Sanitation Districts and the Santa Fe Springs Waste removal of the oil by the floc and incomplete extraction of the Water Disposal Company for research on this subject. oil from the floc by hexane. This is well demonstrated by the series of comparative experiments shown in Table S I , in which LITERATURE CITED repeated flocculations of the water, repeated extractions of the (1) .lm.Petroleum Inst., “Report on Disposal of Refining Wastes,” floc, and a wet extraction of the water after flocculation give a 3rd ed., Sec. I, ;ippendix 5, Sheets 1-5. April 1941. basis for comparison with the results secured by the wet-extrac(2) Am. Public Health Assoc., “Standard Methods for Examination tion method as previously described. of Water and Sewage,” 9th ed., p . 155, 1946. The first group of seven waters had oil contents below 10 p.p.m. (3) Pomeroy, Richard, and Wakeman, C. M.,ISD EX. CHEY., For these, on the average, a single flocculation and extraction ANAL.ED.,13, i95 (1941). yielded 6170 of the total oil recovered. A re-extraction of the first floc yielded another lo%, and second flocculation gave i % RECEIVED October 29, 1948
Table XI. Wet Extraction Versus Flocculation with Zinc Carbonate
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