Determination of Tetraethyllead in Aviation Gasoline Rapid Iodometric Method LESTER NEWMAN1, JOHN F. PHILIPz,
4hD
ADOLPH R. JENSEN
Aircraft Engine Research Laboratory, fi-ational Advisory C o m m i t t e e f o r Aeronautics, Cleveland, Ohio
excess iodine is titrated with sodium thiosulfate. The method requires about 15 minutes for two concurrent determinations on the same fuel. It is applicable to all aviation gasolines that are in current use and has a maximum deviation of +0.05 ml. of tetraethyllead per gallon when it is compared with A. S.T.31 results.
An iodometric method for the determination of tetraethyllead in aviation gasoline is presented. The fuel is shaken with an excess of alcoholic potassium triiodide solution which reacts with the tetraethyllead; interferences due to olefins and aromatic amines are minimized, if necessary, by previous e x traction with 70% (by volume) sulfuric acid. The
.
and 20 grams of potassium iodide, .4.C.S., t o 1 liter of absolute ethyl alcohol and mix thoroughly. All the iodine should dissolve b u t a n excess of potassium iodide may be expected. This does not interfere with the reagent. Standardize the iodine solution against sodium thiosulfate, following the same procedure used in a n actual determination, but use unleaded gasoline; the shaking may be eliminated. The iodine solution should be kept in a dark bottle and checked weekly. Sodium Thiosulfate, 0.05 N . Add 62.5 grams of sodium thiosulfate, A.C.S., and 0.25 gram of sodium carbonate, A.C.S., to 5 liters of freshly boiled water. Standardize the sodium thiosulfate by a n y accepted procedure and check every 2 weeks. Starch Solution, lY0. Add 5 grams of soluble starch and 10 mg. of mercuric iodide, A.C.S., to 500 ml. of boiling distilled water. Such a starch solution if poured into sterilized dark bottles equipped with droppers has been found to be usable for several months. Potassium Iodide, A.C.S. Sodium Sulfate, A.C.S., anhydrous. Apparatus. Two 10-ml. microburets. A 25-m1. pipet, calibrated for gasoline. A 250-ml. glass-stoppered iodine number flask. Separatory funnel. Shaking machine, simulated wrist motion, Burrell type. Dark cover for iodine number flask (black cloth).
T
HE commercial blending of fuels and the engine rating of leaded fuels require a method for the determination of tetraethyllead t h a t is accurate and not too demanding of time, technique, or special equipment. During the past 15 to 20 years, many methods for the determination of tetraethyllead have been proposed. Lykken, Treseder, Tuemmler, and Zahn (2)have given an excellent review of these existing methods and proposed an improved procedure. This laborat,ory has used the A.S.T.M. gravimetric chromate procedure ( 1 ) with a n additional 15-minute refluxing time in order to ensure the complete decomposition of the tetraethyllead. Although the time per sample for a number of samples is not escessive, the time elapsed between the entrance of the sample into the laboratory and the completed report in ma’iy cases unnecessarilv delays engine projects. The proposed method requires aboct 10 minutes per determination for most fuels and is accurate enough for some laboratory needs. Kidmaier (4)proposed a method based on a principle which differs from t h a t employed in most of the methods now in use. It has been customary to decompose, the tetraethyllead in gasoline with one or more reagents and then to determine the’extracted inorganic lead by either a gravimetric or volumetric procedure. Widmaier (4)suggested a procedure involving the direct reaction betireen a potassium triiodide solution axd tetraethyllend. The Shell LIarketing Company, Ltd., of London has also developed a method ( 3 ) based on the same reaction. This paper gives the esperience of this laboratory with Widmaier’s method modified so as t o make use of the sharper end point obtainable from the starch-iodine resction in aqucous solution. The reaction produces lead triethyliodide and ethyl iodide as expressed by the equation : P b (C:Hi)4
PROCEDURE
Two procedures are presented. The direct procedure may be used when interfering substances are absent and the indirect procedure may be used n.hen such substances are present. Interferences include olefins (above 1% by weight) and aromatic amines.
+ I?+P b ( C Z H ~I) +. ~ CzHJ
Direct Procedure. Transfer 25 ml. of fuel by pipet into a 250-ml. glass-stoppered iodine number flask. S o t e the temperature of the fuel a t the time of this transfer. iidd enough iodine solution from a buret to provide approximately 1 ml. in excess. For most fuels, the concentration of tetraethyllead is approximately knox-n. The amount of iodine solution to be added can 1 where I’ is the be determined bv the equation T.’ = 0.7 C milliliters of iodiik solution to he added and C is the approximate concentration of tetraethyllead in milliliters per gallon. When the tetraethyllead concentration is entirely unknown, the first determination should he made using about 6 ml. of iodine solution, which will he sufficient for a tetraethyllead concentration up t o 8 ml. per gallon. This determination can be used to decide on the correct amount of iodine to he added in subsequent determinations, hut should not be used in calculating the tetraetlyllead content of the fuel. Stopper the flask, cover with a dark cloth, and shake for 5 minutes a t the medium rate on the shaking machine. The akes the flask about 260 r minute Trith a motion; each shake COT. izontal distance . (0.75 inch) a t the base sk. rlfter shak-
+
.in excess of iodine is added to a measured volume of gasolirie and after complete reoction the uiireacted iodine is titrated with sodium thiosulfate t o a st:irch end point. Kidmaicr ( 4 ) has shown t h a t most baie stocks containing olefins d o not rcact with the iodine from potassium triiodide solution to an appreci:it)lc extent j hoTvever, catnlytically cracked stocks containiug large amounts of olefins may ab-orb iodine. ch as :ironiatic amines will also intei,fere by reaction r i t h iodine. In such crises, the interfering substances must either be removed or rendered nonreactive with iodine. Kidmaier (4) accomplished this by treatment with 70% sulfuric acid. REAGENTS A‘rD APPARATUS
Sulfuric Acid, 70y0 by volume. 1Iix 700 ml. of sulfuric acid’ (specific gravity 1.84) with 300 ml. of distilled n-ater. Iodine Solution, 0.1 N . Add 12.7 grams of iodine, A.C.S., 1
3
.
in the aqupoua layer disappears. Indirect Procedure. Add 40 ml. of 70% sulfuric acid to about
Present address, 19 West Nosholu Parkway S . , Bronx 67, S . Y On militaryleave v i t h the C . S . Army. ,
45 1
-
V O L U M E 19, NO. 7
452 Table I .
\'ariation of Shaking Time Shaking Time= 5 niln. 10 min. .\pparent TEL Content Mi./ g a l , 4.07 4,12 4.00 4.06 2.57 2.63 4.25 4.32
Furl 1
2 i 4 0
Llrdiuln rate used in a l l ca-er
Table 11.
Variation of Temperature .ipparent TEI, Content .ill . / g a l . 3.94 4.01 4.07
Teiuperature of Bath during Shak~iig
c.
20
25 30 -
.~
~~~
_.
~
.
150 ml. of fuel in a separatory funnel, shake for exactly 40 seconds, and remove the acid layer immediately. K a s h twice with amounts of lyater equal in volume to the fuel. Discard the acid and water washing. Pour the extracted fuel into a flask containing about 35 grams of anhydrous sodium sulfate, and shake well. Allow the sodium sulfate to settle. Using the dried, extracted fuel, continue with the direct procedure.
tiveen the ,1.S.T.lI. and the rapid iodometric method when the the acid is used on fuels. Occasionally, this laboratory has analyzed fuels containinp dyes'that are slightly soluble in water. I n such cases, the dye ma>interfere with the determination of the end point if the analyst is riot experienced lvith the method. The same condition might occur if the dye present in the gasoline is of an i'ntense blue color. In order to eliminate this difficulty, the modified procedure map he used because 70';; sulfuric acid will remove most' dyes from y:isoline. It was found that shaking time affected the results, a fact which had been previously observed by Widmaier (4) and by the Shel! hrarketing Company, Ltd., of London ( 3 ) . Table I compitres the results ohtained by shaking the same fuels for 5 and 10 minut,ei uring the rapid iodometric method. The rate of shaking n-ill influence the results. The 5-minute shaking period a t a medium rate was selected when such a combination of time and rate gave results that agreed with results obtained by the modified .i.S.T.II. gravimehic chromate method (1). Conditions in various laboratories may have to 1~ varied somewhat to eiisure good agreement. Escessively high or lou- room temperatures will producr higli :tiid Ion results, rrspwtively, \vith the rapid iodometric method. _ _
~ _ _ _
~~
CALCULATIONS
The tetraethyllead rontent of the sample is calculatrd by the equation:
Table 111. Comparison of Results Obtained b? Hapid Ioctometricand 4. S.T.11. Graiimetric Chromate JIethodk Tetraethyllead Rapid Iodouietric Method .\.S.T.lI. 1 2 hv. .I11 . / g a l . .If 1 ,/ g a l .
-~
Coniposition of Fuel
L = IT1 = N, = Fy2 = N2 = A =
tetraethyllead, milliliters per gallon iodine solution used, milliliters normalitv of iodine solution sodium thiosulfate solution used, milliliters normality of sodium thiosulfate solution percentage of constituents of original fuel that are soluble in 707, sulfuric acid (if acid is used)
The factor 14.84 is the theoretical factor based on the stoichiometric equation when a 25-ml. sample of gasoline is used and the density of tetraethyllead is taken as 1.65.
It is appareiit that nlien the direct pt,ocedure ik used the coni- T ' i S ? ) 14.84. plrx equation simplifies t o : I, = ( i7,AY, This equation will also he w l i d \vlieii the indirect p1,ocrdur.e ih followed if the acid treatment does not result, in a reduction in volume. For example, c:italytically cracked stocks contain olefins n.hich may i11tri.fei.ein the rapid iodometric method hy the addition of iodine to the unsat,urated linkages. Preliminary treatment with 7OCc,sulfmic acid rendered the olefins rionreactive to iodine, hut the ulkgl mlf:rte* presumably formed werr insoluble in the iicid and t h r \vater with ivhich the fuel \vas ivashed, resulting in no volume change. K h e n the original fuel contains ruhata~lcrrwhich react \\.itti iodine and \vhich are removed h>-70'{ sulfuric acid, the more complicated formula must be used. .is ati example, aromatic amiqes and aliphatic ethers, which have been huggested a? additives to aviation furls, are removed by 70'1 sulfuric acid follo\ved t)y a reduction in volume of t,he rample. I n both cases the correction of tetraethyllead content from t h r observed temperature to 1.5.5" C'. (60" F.) i; accomplished hy the .I.S.T.II. eqiiatioti ( I ) :
P = 0.1(2'-15,5) 5vhei.e P = percentage mrrectiori
and T
=
obsewed temperat,ure,
O
C.
1>Is(:1;ssIOo
Sulfuric acid (70L2 by volume) ha* not beeti f ( i i i r i d to t~eniov. H w d r y ( 5 : ; ole-
fin)
One-pass Houdry (15?%olefill) Y7Cz 18R, 3 < ; i aruinatic aillines
3 i6
:3.74 3 . 7 7
3.76
0.00
:i88
:i, 83
3 . 85
3 . 84
0.01
5 (13
6 . 9 9 5.97
5.98
0 05
JULY
'
453
1947
The vari:ition in room temperatures in most laboratories is not sufficiently high to require the use of a constant-temperature bath. Should the temperature be a hove 28' C. or below 23' C. it would he advisable to use a constant-temperature bath for shaking the fuel and iodine mixture or to modify the shaking time or rate. As an esample of the variation to be expected Tahle I1 gives the results ohtained n-ith the same fuel using different temperatures during shaking. The rapid iodometric method lins herri used successfully on many differelit types of fuel. Fuels containing paraffins, naphthenes, aromlitics, olefins, and vai,ious other additives have been m a lyzed, :is shown in Tahle 111. The table lists first the fuels that did not requiye acid estraction and then those which do. Since the experience of this lahoratory with unsaturated gasoline types i h limited, it may he well to restrict the method to the usual aviation fuels unless esperinientation sIioi~-sthat, the acid est,raction method will apply. -1comparison of the results ohtained by the .I.S.T.lI. (1) and the rapid iodomet1,ic methods indicates a masimuni deviation of ==0.0t5ml. of tetrarthyllrad per gallon for the rapid iodometric
method; duplicate determinations agree ivitliiii the 0.03 ml. of tetraethyllead per gallon limit specified in the A.S.T.M. procedure (1). It has been the experience of this laboratory that the approximate tetraethyllead concentration is kriown for most of the fuels analyzed. I n addition, very few fuels contain interfering substances, so that the direct procedure is the one most frequently used. Thus the time required for most rapid iodometric method determination? is ahout 10 minute$. By use of the shaking machine, txvo Concurrent determinations on the same fuel can be made in about 15 minutes. If the acid estraction is required, the time per determination is about 20 minutes, or two concurrent determinations on the same fuel can he done in 25 minutes. LITER.ATUKE CITED
(1) A I I I . Sor. Te6ting Materials, .\.S.T.M. Standards P a r t 111. p. 219,1944. (2) Lykken, L., Tiesedei, K.S..Tueiiiiiilei, F. D., and Zahn, V.!Isu Esc. CHEM.,A N ~ LED.. . 1 7 , 3 5 3 (1945). (3) Shell Marketiiig C h . , Ltd.. London, private conimunication. (4) Vidiiiaier, O . , L r i f f f u h r f - F o r i c h . .20,181 (1943).
Rapid Method for Determining Oil Content of Tung Kernels JOSEPH H43IlLTON
4ND
SEY3IOUR G. GILBERT
Hureau of P l r m t Itidustry, Soils, and Agricultural Engineering, .4grictcltural Reseurch 4dmini.stration, z'. S . Department of Agriculture, Gainescille, Fla. In a rapid method for determining oil in tung kernels, a flaked or ground sample is dispersed in a Waring Blendor t y p e of disintegrator w ith a commercial hexane soltent. The solution of oil that resultk is separated from the kernel residue by allowing the sedinieut to settle in a bolunietric flask. The oil in an aliquot of the supernatant liquid is w eighed after elaporation of the solbent, and the percentage of oil is calculated on the basis of the total >olume occupied bj sediment and solution. On the basis of precision, accuracj, and rapidity, the method appears to hale distinct adlantages oler the iisrial percolation procedures.
A
H0L-T 2000 oil determinations are made ari~iuall>-at this station in the evaluation of experiments 011 tung culture. is thus of importance and an effort has beni made to find a procedure of sufficient accuracy and precision that would require less time thart the percolation typt. of cxtraction, using the Goldfisch apparatus heretofore in regular use at this laboratory ( 7 ) . Methods involving o t h n principles liavtr htwi developed ( 2 , 6) but have not been found suitable. The use of the \Taring Blendor for the determination of carotene with prtroleum ether ( 3 ) suggested the possibility of using this apparatus for the determination of oil in tung kernels. Preliminary experiments in 1941 showed that use of the Blendor was feasible, and in 1945 detailed n t u d i s were varried out, the results of which are reported here. Routine use of the niethod during 1945 and 1946 has given very satisfactory results. Since initiation of this work others have publiehed results o n the use of the blender for detrrmining oil in plant (4) and animal (5) material. In both of these studies the lipides were first eniulsified with water in the blendw and then freed from the emulsion bj- a sequence of manipulations. The method developed in this lahoratory for samples of low nioi?;tuw content is simpler since 110 emulsions are required. DETAILS OF RIETHOU
-1representative sample of the kernels from air-dried fruits is flaked (7'1, or ground twice in a Vniversal S o . 73 food chopper using a 16-tooth cuttPr, Thrl flaked or ground krrnrl material is
r horoughly riiisecl, a 10-gram portion of the uaniple is transferred t o a Waring Blendor, 170 ml. of Skellysolve B are added, and thr
material i.- agitated for 5 minutes. The blender disintegrates thr Haked or ground krrnel, the oil being dissolved in the solvent. Thr resulting solution of oil, with its suspension of tung meal, is transferred through a funnel into a 250-ml. volumetric flask, prefclrably a flask that is calibrated from 245 to 255 ml. in 0.5-ml. diviiicnis. The entire contents of the blender jar are carefully rinsed into thta ,flask, enough solvent is added to adjust the total volunit' t o ahout 252 nil., the contents are thoroughly mixed, and the flask is set aside t o cool and settle a t room temperature. In determinations on kernels from air-dried fruits the solutions at'e usually sufficiently clear after settling for about an hour. Smiplt~.;ext rcsmely lo\\- in moisture content, appear to require a longer time t o settle. The solution comes from the blender at B rrlnperature of 40 to 50' C. and hence will shrink several niilliLiters on wioling to room temperat,ure. Following settling, the final voluinc of the contents is read from the calibratioiis of the Hask, and a 50-nil. portion is pipetted into a thoroughly cleaned, tared 250-nil. heakrr . For routine determinations of a number of samples, only one graduatcd flask is required for each group of samples. Ordinary 250-nil. volumetric. flasks are used for the rest of the group, all ht:ing made to volunie a t the same temperature in a water bath. Subsequent volume changes during settling are corrected for by reading the graduated flask. A 1-ml. Mohr pipet can be used in d i b r a t i i i g t h r flasks above and below the 250-nil. mark. Foi precise work, the temperature of the oil solution should be within 1 of rooni temperature a t the tinir of aliquoting. The solvent is evaporated OII a steam bath, the final traces being removed in a vacuum oven a t 70" C. and I-mm. pressuw. Hoa-evrr, a skilled operator can obtain essentially the same results Iiy distilling the solvcnt on a hot platt,, prt,ferahly unticxr a hootl,
