Colorimetric Determination of Phenolic Materials in Refinery Waste Waters Removal
of Sulfides by Silver N i t r a t e
G. E. GORDON' I aboratory Division, Manufacturing Department, Sfandard Oil Co. of California, Richmond, Calif. Determination of phenol, b y the 4-aminoantipyrine method in water samples containing sulfides, has required distillation to separate the phenol from the sulfides. The usual procedure has been that suggested b y the American Petroleum Institute. Another procedure, using silver nitrate to remove sulfides, i s faster and believed to b e more accurate because it does not involve steps where phenol might be lost. It can b e easily adapted for field use to give approximate results b y the use of several standardized phenol solutions. The results show good agreement with the distillation method, but in general, are slightly higher. The method i s also applicable to water used in refinery processes.
HE usual colorimetric methods for T p l i e n o l i c material? in inciustrial \v:is;tes (I, NO) include a sulfide-removal s t c y in which the p H is adjusted t u 4 with phosphoric acid, and copper sulfate is added in excess t o precipitate the sulfide as copper sulfide. Tlic -ample is t'hen distilled until the volume of distillate is equal to the volume of the original sample. This step is time-con,xniing and requires considerable equipiiieiit, and, because some water remains in tlie flaek, complete recovery of plicnol is difficult if not impossible. -1niethod has h e n developed diicli eliminates the distillat'ion step by using silver nitrate to precipitate thc sulfide :ind then sodium chloride to prccipit,ate the ivxcess silver ion. Precipitation has been suggested as :I purific-ation procedure ( 3 ) , but silver was not used in the earlier work. Metals suggested are copper, cadmium, and lead. Copper m s eliminated berause of the color of its ions. Cadmium was not tried in this procedure. Lead gave results almost as satisfactory as silvrr. However, silver Tyas chosen 1)cc:iuse the very low solubilit'y of the 1 Present ad& css, Eastern Latmratorj-, hnierican Bitumuls arid Asphalt Co.. Baltimore. Md.
sulfide and the almost equally low solubility of the chloride made i t possible easily to remove essentially all the qilver ions, which is not the c a v v i t h lead or cadmium ions. This removal of the metallic ions is esqential to prohibit their precipitation n i t h ferricyanide ions. Some efRuent water samples contain both sulfides and chlorides and nhen silver nitrate is added both m-ill precipitate; liow-cver. because the solubility of sulfide is less than that of the chloridc, the sulfide Trill be removed from the solution. PRESERVATION OF SAMPLES
Becsusc many of the phenolic materials in petroleum refinery effluent waters are oxidized in acidic solutions, the samples should be stabilized by the addition of some caustic. It was deter-
m i n d that n pellet of sodium hydroxide, added to the 4-ounce bottles norinally used for sampling a t the refinery where this method was developed, stabilizes the plicmol content of the saniples for a t least a week: vithout the addition of caustic, the phenol content decreases nithin 6 hours. The pH of the solution in the 4-ounce bottles will vary somen h a t because of tlie differing p H of eEucnt waters; however, most refineries t r y to control the p H of the effluciit waters b e h e e n A and 8. Tliis nicans that the. pH of the sample n i t h the pellet adtltd nil1 normally be bctween 8 and 11. Khile some phenolic materials hill be olidized in a basic solution-i. e., hydroquinone and pyrogallol-the quantities in the effluent maters of a refinery prob'ibly are extremely small, if they esiqt a t all. PROCEDURE
PHENOLIC MATERIAL, MG.
Figure 1. Effect of phenolic materials on colorimetric determination o f phenol B & L Spectronic 20 Wave length 510 ml.r
Z\leasui,e 50 ml. of sample into a 250ml. beaker. Add 10 drops of niet'hyl red indicator and appi~oximately8Jf nitric, acid with stirring until the color is pink. Add approximately 0.5Asodium hydroxide dropn-ise to bring the color just liack to yellow. Pour the sample into a 4-ounce lmttle, add 3 nil. of 1 S silver nitrate solution, and shake thc bottle. If a white or grayish white precipitate appears, add 1 gi'ain of sodium chloride and dilute the sample t o 75 nil. If a Mack precipitate forms, a1101~-one drop of a 10% sodium chloride solution to run d o w i the side of the bot'tle. If a white cloud appea1.s: add 1 gram of sodium chloride and dilutr the sample to 7 5 ml. If there is no white cloud, add I S sill-er nitrate solution, 1 ml. a t a time, until a whitc cloud is producrtl upon testing with the drop of 10% sodium chloride solution. l'hcn add 1 gram of sodiuni chloride aiid dilute the sample to 7 5 nil. Shake the sample and either centrifugc at 1000 r.p.m. for 10 minutes to aettlc t8he precipitate 01' filter through No. 42 Whatman filtei, paper. Take a n auurouriate alinuot of tlie clear liquid (i;sua'lly 1 to 10 ml.) 133, pipet and place in a 50-ml. glass-stoppered graduatc. Akkl di~tillccl water to bring the volume to 50 ml. Then add 1.0-nil. of bora.: buffer, (38.1 grams of Sa21340i.10H20in 1 liter of watrr), VOL. 32, NO. 10, SEPTEMBER 1960
1325
1.0 ml. of 4y0 ammonium hydroxide, and 0.3 ml. of a 2% solution of 4-aminoantipyrine in the order named. Stopper the cylinder and mix thoroughly. Add 1 ml. of a 2% solution of potassium ferricyanide. Stopper the cylinder, and mix thoroughly. Allow the solution to stand 10 minutes for color development, and within the next 15 minutes determine the per cent transmittance or absorbance at 510 mp in a spectrophotometer, using a blank (all reagents except sample) as the reference liquid. If the color is too light or too intense to measure, take a more suitable sample size and place in the 50-ml. graduate for testing.
Prepare a standardization curve from either a pure phenol standard (1.000 gram per liter, kept under refrigeration or made fresh) or a phenolic material standard (phenolic material extracted from effluent waters, 1.000 gram per liter of solution). Dilute the standard solutions 10 to 100 vvith water to give a solution of 1 ml. equal to 0.1 mg. of phenol. Then add 1.0, 2.0, 3.0, 4.0, and 5.0 ml. of the dilute standard to 50-ml. glass-stoppered graduates and dilute to volume n-ith water. Add the reagents as listed under the sample determination and read the per cent transmittancr or absorliance.
Phenol, p.p.m. = mg. of phenol from curve x 1000 X total volume of prepared solution (75) ml. of sample X aliquot (if any) X volume of original sample (50) DISCUSSION
Table 1. Effect of Sulfides on 4Aminoantipyrine Reaction Product
( A 4-p.p.m. phenol sample xvith varying concentrations of sulfide was subjected to the 4-aminoantipyrine procedure witho u t sulfide removal)
Sodium Sulfide. P.P.M. 0 10 20
Phenol, P .P.M . 4.0
40
3.7 3.5 2.4
60 80
0 0
Table II. Effect of Sulfides on Phenolic Materials (80 p.p.m. of sodium sulfide were added
to 4-p.p.m. phenol samples. Sulfides were removed after 90 minutes by the silver nitrate procedure) Phenol Concn., after Sulfide Contact and Sulfide Removal, Phenolic Material P.P.M. Pure phenol 3.6 Extracted phenolic 1 4.0 Extracted phenolic 2 4.0 Extracted phenolic 3 3.7 Table 111. Distillation vs. Silver Nitrate Method on Plant Process Waters
Sample I I1 I11 IV
Phenol, P.P.M. Distillation AgN08 method method 17 19 14 15 25 26 30 29
Table IV. Chloroform Procedure on Samples with Less than 1 P.P.M.
Sample A
B C D
1326
Phenol, P.P.M. Without AgNOj purification purification 0.5 0.4 0
0.5 0.3
0
0.4 0.4
ANALYTICAL CHEMISTRY
The procedure was investigated to determine the effect of the reagents on the color development and phenol content of the samples and the response of the test to various phenolic substances which do or may occur in petroleum refinery waste waters. Silver nitrate, nitric acid, or chlorides had no effect on phenol content. Sulfides have a very definite effect on thc detection of phenol by the 4-aniinoantipyrine reagent (Table I); however, they do not appear to affect the phenol content of the sample, and when they arc rcmoved, the determination of phenol is still valid (Table 11). The 4-aminoantipyrinc method, like all other colorimetric methods for phenol, can be considered quantitative only when the sample is a solution of pure phenol or of pure homologs of phenol of known characteristics. The method is necessarily calibrated with a specific phenolic substance, and an error of variable magnitudr is introduced when another phenolic substance is measured using this calibration. Phenolic substances n-ith the ortho positions s u b s t i t u t d will give little or no responqe to the 4-aminoantipyrine reaction. The ideal situation seldom prevails with refinery effluent streams because the nature of the phenolic materials is neither known nor constant, and a variety of unknonn, nonphenolic interfering substances may be in solution or suspension in the water. Under these usual conditions the 4 aminoantipyrine test bwomes a t best empirical and approximate. The experimental work on the method was done with pure phenol and various extracted phenolic materials obtained from locations within the refinery. A standardization curve was set up for each substance and is shown in Figure 1 to illustrate the effect of different phenolic materials on the colorimetric determination of phenol. For
routine refinery control a composite standardization curve was prepared, based on phenolic materials extracted from all refinery effluent waters. Other samples of water used in plant processes containing phenol or phenolic materials may also be tested by this procedure. Table I11 compares results from the distillation and silver nitrate procedures for some typical effluent water samples obtained from the refinery. These samples were determined to h a w sonic‘ bulhde content and therefore a purification step Ras required. I n some cases within a refinery there will be effluent naters nhich contain no interfering materials; after this has been ascertained, purification is not required. Table IV shows results on samples c>ontaining less than 1 p.p.m. of phenol, wing the chloroform extraction procedure of the Americ-an Petrolcum Inititute. These samples were also obtained from various refinery effluent +ources and i t was determined that no interfering materials \?ere prrsvnt. Samples were trsted in accordance with the American Pctroleum Institute chloroform extraction procedure (column 2). Portions of the same samplw were treated b y t h r silver nitrate purifiration procedure and again tested by the American Petroleum Institute procedure (column 3). The small difference between results could be partly due to inaccuracies of the routine laboratory equipment uicd. I n niost rcfincries so small a difference in routine control samples would not be a matter for concern. The reproducibility of this method has been satisfactory on all samples tested, and while results are generally a little higher than by the distillation method, it is believed that this is due to incomplete recovery of the phenol in the distillation procedure. The testing time is also a n advantage of this method, being approximately one half that of the distillation procedure ACKNOWLEDGMENT
The author thanks Jim Lusk and other members of the Richmond Refinery Laboratory for the preparation of data for this report. LITERATURE CITED
(1) American Petroleum Institute, Phil-
adelphia, “Manual on Disposal of Refinery Waste,” Vol. IV, Method 716-57,. p. 2 . (2) rAmerican Public Health Association, hew York, “Standard Methods for the Examination of Water, Sewage, and Industrial Waste,” 10th ed., p. 336, 1955. (3) Ettinger, M. D., Kroner, R. C., Proc. 5th Industrial Waste Conference, Purdue University, 1949, p. 348. RECEIVED for review December 8, 1959 Accepted June 16, 1960.
