Determination of Furfural in Oil in Refinery Operations by UIt raviolet Spectrophotometry L. L. GENT, R. C. POMATTI, and HARRY LEVIN N. Y.
Beacon Laboratories, The Texas Co., Beacon,
0
APP4R4TL S A1D RE4GEVTS
S E of the steps in the production of many high grade
lubricating oils is solvent extraction refining and one of the most extensively used solvents for this purpose is furfural. It is unlikely that any finished product so refined would contain furfural, since finishing procedures which follow the furfural extraction eliminate all solvent. -4s furfural is recovered for reuse, analytical surveys and material balance studies are made to keep solvent losses to a practical minimum. The present paper describes a method primarily intended for determination of low concentrations of furfural in various petroleum fractions obtained in refining operations. Gravimetric and volumetric methods arc available for higher concentrations of furfural. Javes(3) determined 0.0001 to 1.001, of furfural in oil by sweeping it from the sample with a stream of air, which then passes over a strip of filter paper previously soaked in an acid solution of 2,4dinitrophenylhydrazine. The resulting red color is compared with standards prepared from oils blended to contain known amounts of furfural. Stillings and Browling ( 4 ) in studying the conditions for analysis in colorimetric work determined small amounts of furfural (0.05 to 0.46 mg,) using acetic acid, sodium chloride, and aniline as reagents to develop color. JT'oelfel et al. (6) determined furfural in lubriczting oil by extracting with sodium bisulfite, oxidizing the bisulfite with excess iodine, and reducing the excess iodine with sodium thiosulfate. Aniline in acetic acid is then added to produce a red color for photometric measurement. Dunstan and Gillam ( 1 ) detei mined pentoses by dehydration a i t h 85y0 phosphoric acid and conversion to furfural which was then steam distilled and determined spectrophotometrically a t 278.5 mp in a Beckman D L spectrophotometer. Wahhab ( 5 ) ,studying deterioration of dried fruits, determined small quantities of furfural-after rapid distillation without refluy-at 277 mp. Fuchs ( 2 ) determined 0.1 mg. of furfural obtained from distillation of pentoses and uronic acids with hydrochloric and hydrobromic acids, by ultraviolet absorption a t 277 nip. Those of the above methods which are applicable to low concentrations of furfural in oil involve relatively lengthy preliminary preparation or standardization. The method described is believed to be someLyhat simpler. I t involves extraction with sodium bisulfite solution and spectrophotometric measurement after alkali decomposition of the sodium bisulfite-furfural addition product. Sodium bisulfite react8 with furfural to form an addition product; HC-CH
I'
€IC
I1
+
C-CHO
'd
SaHSOL
F-C
HC-CH 11
I'
Beckman DU spectrophotometer fully equipped for ultraviolet measurements, or an equivalent instrument. Iso-octane, c.P., for diluting oil samples. Sodium bisulfite solution, 10% aqueous. Potassium hydroxide solution, 10% aqueous. Furfural, freshly distilled. Straight mineral oil for preparing Etandards. PREPAR4TIOY OF STANDARDS
Standards should be prepared covering any range of interest between 0.0002 and 1.0% of furfural. A standard blend of furfural in iso-octane is first prepared-for example, one containing 0.5 mg. of furfural per ml. of solution. This solution is diluted by a factor of 10 with iso-octane, giving a solution containing 0.05 mg. per ml. Csing different volumes of these solutions and different weights of base oil, standards can be prepared covering the range of concentration of furfural needed. I n any one range the same weight of base oil is used for standards and blank. These standards and the base oil used in preparing the analytical curve are analyzed as outlined below. Distilled water is used in the reference cell. The absorbance of the base oil blank is subtracted from the absorbance of the blends containing the furfural to obtain the net absorbance due to the furfural. An analytical curve is drawn on linear paper plotting net absorbance against milligrams of furfural. EXPERIMENTAL
Before developing the present procedure the following techniques were tried. The oil samples were diluted with iso-octane and shaken with sodium bisulfite solution, and sodium carbonate or sodium bicarbonate was added to decompose the addition product. It was found that the carbon dioxide liberated caused erratic absorbance readings. Hydrochloric acid was substituted as a decomposition reagent. The sulfur dioxide liberated interfered. Seither sulfur dioxide nor carbon diox+de could be satisfactorily removed by heating, shaking, or allowing to stand for prolonged periods. I n another experiment the furfural liberated after addition of sodium carbonate was extracted with carbon tetrachloride or iso-octane and the absorbance Kas measured a t 277 mp. The readings were extremely difficult to reproduce and this extraction procedure was eliminated. An attempt was made to measure abeorption of the addition product before decomposition. This was unsatisfactory because of interference by the excess bisulfite. Kater extraction of the oil was tried and the furfural was determined directly on the water extract by measuring absorbance at 277 mp. The results were not satisfactory because extraction was not complete. The following satisfactory procedure was developed.
H
/
'
HC C-C-OH O \/ SOsNa
PROCEDURE
Accurately weigh the oil sample into a 126-1113. separatory funnel. Dilute with 50 ml. of iso-octane. I n the range of 0.0002 to 1.0% a sample of 25 grams to 0.1 gram, respectively, is usually satisfactory. Add by pipet 20.0 ml. of 10% sodium bisulfite solution and shake vigorously for 5 minutes. Let stand for the water and iso-octane layers to separate. Draw off more than 10 ml. of the aqueous lager into a small beaker. Pipet 10 ml. of this solution into a 50-ml. volumetric flask, add from a graduate 15 ml. of 10% potassium hydroxide solution, and dilute to the mark with distilled water. Transfer a portion of this solution to a 1-cm. quartz cell and measure the absorbance a t 277 mp with a
The use of a large excess of bisulfite ensures substantial completeness of reaction. The furfural can be regenerated by adding an aqueous solution of a base. Furfural is readily extracted from oil samples with aqueous bisulfite solution if the viscosity of the sample is reduced with a solvent-iso-octane, for example. After the furfural is regenerated by addition of potassium hydroxide to the aqueous layer, absorption is measured a t 277 mp directly.
413
ANALYTICAL CHEMISTRY
414
Table I.
Analysis of Known Blends of Furfural in Oil
Blend No. 1
2
3 4 5 6 7
8 9
Furfural, % Added FounT
Difference, %
+-0.0001 0,00002
0.00020 0.0010 0.0010 0.0010 0.0010
0,00022 0.0009 0.0009 0.0010 0.0010
0.0030 0.0080 0.014 0.060 0.100 0.100 0.100 0.100 1.00 1.00
0.0033 0.0080 0.015 0.060
+0.0003 0 0000 +o 001 0.000
0.098 0.10 0.098 0.10 1.03 0.93
-0.002 0.00 -0.002 0.00 $0.03 -0.07
-0.0001 0,0000 0,0000
slit width of about 0.6 mm., using water in the reference cell. If the absorbance is above 0.8,this solution should be diluted. Determine the reagent blank, using only iso-octane and the reagents and carrying them through all the operations. Subtract the absorbance of the reagent blank from that found on treatment of the sample. From the net absorbance and the analytical curve determine the milligrams of furfural and calculate to percentage in the sample. DISCUSSION
To ensure greatest accuracy, all standards should be prepared either from freshly distilled furfural or from dilute solutions of furfural in iso-octane, as the latter appear to remain stable and, therefore, do not have to be freshly prepared for each determination.
I n decomposing the addition prodact, excess potassium hydroxide must be added because a t 277 mp sodium bisulfite interferes with the measurement of furfural. The most reliable results are obtained by testing the final alkaline solution within 0.5 hour after preparation. If emulsions are formed during the extraction procedure, they may be broken by being alloiyed to stand, by gently disturbing with a glass rod, or by filtering. The single extraction procedure is sufficient, as shown by the fact that the absorbance of a second extraction of the same standard was not significantly different from the absorbance of the reagent blank. RESULTS
Table I is typical of results obtained on blends of oil with known quantities of furfural. ACKNOWLEDGMENT
The authors are indebted to Henry Chaya, Emil Poti, Raymond D o h , and R. H. Gaddy for their assistance in the preliminary work on this method. LITERATURE CITED
(1) Dunstan, Sonia, and Gillam, A. E., J . Chem. Soc., 5, $140 (1949). (2) Fuchs, L., Monatsh., 81, 70-6 (1950). (3) Javes, A. R., Proc. A m . Petroleum Inst., I I I , 29M 39-41 (1949). (4)
Stillings, R. A., and Bron-ning, R. L., ISD. ENG.CHEM.,ANAL.
ED., 12, 499 (1940). ( 5 ) TVahhab, A,, J . Am. Chem. Soc., 70, 3580-2 (1948). (6) Woelfel, TV. C., Good, W. D., and Keilson, C. A,, Petroleum Eng., 24, S o . 7, C-42 (1952). RECEIVLD for review J u n e 22, 1953. Accepted September 2 5 , 19.53.
Refractive Indices of Some Morpholine Solutions CHARLES M. WHEELER, JR.,
and
CONRAD G . HOULE N. H.
University o f N e w Hampshire, Durham,
ORPHOLINE, being both an ether and an amine, isaversatile solvent and, consequently, enjoys many commercial uses both alone and in combination with other solvents. For this reason, a rapid method of determining the concentration of binary morpholine solutions would be useful. I n view of the limited data reported for binary systems containing morpholine, a number of important morpholine solutions mere investigated to determine the feasibility of using refractive index measurements for rapid analysis of the solutions. Wilson (6) and Greenberg ( 2 ) have reported liquid-vapor equilibrium data for the systems morpholine-water and morpholine-o-xylene, respectively. However, neither author indicated the method he used to determine concentrations of the morpholine solutions. In spite of the well-known solvent power of morpholine, there are no other reported data for binary morpholine systems. The present paper reports refractive index data which may be used for determining the compositions of binary solutions of morpholine-aniline, morpholine-benzene, morpholine-ethyl alcohol, and morpholine-water. These data might be used commercially for rapid accurate determinations of the concentrations of binary morpholine solutions. The authors have used these data in determining concentrations in liquidvapor equilibria studies of binary morpholine systems. Although refractive index values for the pure components of these binary solutions have been reported (1, 3-5, 7 ) no refractive index data for these binary systems are found in the literature. PURIFICATION O F MATERIALS
Morpholine waa fractionally distilled a t 128.1' C. and 758.7 m. (corrected), through a Fenske-packed column of 25 theo-
retical plates. I n order to prevent the contamination of morpholine with carbon dioxide, the distillation was carried out in a closed system and the distillate receivers were vented through Ascarite-filled drying tubes. The aniline and benzene used were fractionally distilled; corrected boiling points of the fractions used were 184.57' C.
Table I.
Refractive Indices of Pure Components
Aniline Morpholine
Experimental, n $o
Literature, n $o
1.5861 1,4547
1 58629 1 ,4545
n
Benzene Ethyl alcohol Water
Table
11.
L5
1.49807 1.35929 1 ,33250
Indices of Solutions
Experimental D a t a Aniline, Refractive index, weight % n D a t 25,00° C.
(6)
(1)
n k5
I
1.4979 1.3593 1.3327
Refractive
Reference
( 7)
(9)
(4)
Morpholine- Aniline
Smoothed Values Aniline, Refractive index, weight % n~ a t 25.00° C.
