,ANALYTICALCHEMISTRY
526 Table I. Phosphate NasPsOio
NalPzOr
is used in preference to sodium chloride. Place a, watch glass over the beaker, and boil the sample to dryness. Take care to reduce the temperatures of the sample as the crystals begin to form; otherwise, the sample mill splatter. Next, dilute the sample t o 50 ml. and titrate the sample as orthophosphate, using the procedure recommended in the previous paper (3).
Titration of Pure Phosphates after Hydrolyzing Calculated Weak Acid to Be Titrated, Meq. Theory
Weak Acid p u n d , Meq.
Deviation from Theory, Part/lO(l
4.531 3.873 4.531 3.874 3.581
4.540 3.897 4.544 3.900 3.548
f0.2 +0.6 +0.3 4-0.6 -0.9
3.701 3.615
+0.6 +0.1
3.677 3.610
,
[KPOsln
4.395 4.356
4.383 4.401
+1.0
NarPiOli
4.402 4.377
4.386 4.337
-0.4 -0.9
NasPiOo
5.250 5.250
5.271 5.233
$0.4 -0.4
Absolute average
DISCUSSION OF RESULTS
Table I is a compilation of some typical results obtained by the rapid method. The results are as good as those obtained by the slower method, and less than one tenth of the time was required to obtain the results. Most soluble phosphate may be analyzed for percentage of phosphorus pentoxide by the above method, but the procedure is specifically designed for alkali metal phosphates. Any anionic substance exhibiting a weak acid titration will interfere with the above analysis, as will amphoteric cations such as aluminum. I n case of interference of this type, it is recommended that one of the molybdate methods be employed to analyze the samples after they have been hydrolyzed (1).
-0.3
-0.5
Determined with Precision-Dom automatic Titrometer.
EXPERIMENTAL
LITERATURE CITED
Use an analytical balance to weigh about 0.5 gram of the mix(1) Am. Soc. Testing hIaterials, Philadelphia, “ASThI Methods of ture of condensed phosphates to be analyzed. Transfer the Chemical Analysis of Metals,” p. 88, 1950. sample to a 250-ml. beaker, and add 50 ml. of mater. Next, add about 10 ml. of concentrated hydrochloric acid to the ~ 0 1 ~ - (2) Fiske, c. E., Subbarom, Y . ,J.B i d . Chem. 6 6 , 3 7 5 (1925). (3) Van Wazer, J. R.,Griffith, E. J., McCullough, J. F., AKAL.CHEM. tion of hosphates and then add ca. 1 gram of potassium chloride 2 6 , 1 7 5 5 (1954). (or s o & m chlohde). Potassium orthophosphates are more soluble than sodium orthophosphates, and less splattering is enRECEIVED for review November 4, 1955. Accepted December 9, 1955. countered as the sample goes to dryness when potassium chloride
Total Naphthenes in Gasoline by Refractivity Intercept Analysis of Six- to Eight-Carbon Saturates J. C. S. WOOD, ALBERT SANKINI,
and C.
Research and Development Department, Sun
C. MARTIN
Oil Co,, blorwood, Pa.
Refractivity intcrcept has been used for many years to determine naphthenes in gasoline. The method is applicable to mixtures of paraffins and monocyclic naphthencs; the presence of polycyclic naphthenes causes erroneous results. Improved graphs, one for the c6 to c g range and one for the cs range only, are prcsented and cvaluated. The graphs are based on the relative amounts of individual saturated hydrocarbons in crudes. When applied to the C6 to Cg rangc of straight-run gasoline, total naphthenes can be dctermined with an accuracy of 1270. Application to other gasolines is dependent upon the type of paraffins present.
16-18, 66). When the first refractivity intercept graph (2) was derived for naphthene determination, very little information mas available on the relative amounts of individual hydrocarbons in gasolines. Since then, American Petroleum Institute Project 6 ( 1 9 , 2 3 ) and the Bureau of Mines, Petroleum Experimental Station (24), have determined individual hydrocarbons in about 35 different crudes. A study of the hydrocarbon distribution in several crudes (9, 19, 23-25) led to the development of new refractivity intercept-density graphs. This paper presents improved graphs for the CSt o Cg range. The improvement has
r 1.045
T
HE yield of benzene, toluene, and xylenes produced by
catalytic reforming of straight-run naphtha depends t o a large extent on the amount of naphthenes (cycloparaffins) in the charge stock. A comparison of various methods for determining total and individual naphthenes was recently reported (20). I n one of those methods the total naphthenes in the paraffin-naphthene (saturated) fraction were determined from refractivity intercept-density correlations requiring only the experimental determination of density and refractive index. Refractivity intercept is the refractive index minus one half the density (n - d/2) (le). It has been known for a number of years that refractivity intercept could be used for naphthene determination ( 2 , f 1, I S , I
Present address, Socony Mobil Oil Co., Paulsboro, N. J.
’0 U
1040
z t
Pa 0.65
0.70
0.75
DENSITY AT LO’G
Figure 1. Total naphtlicnes
0.80
527
V O L U M E 28, NO. 4, A P R I L 1 9 5 6
Special graphs are necessary for accurate naphthene analysis of narrow-boiling fractions (IS). For example, Figure 2 was specially drawn for determining the c6 naphthenes, methylcyclopentane and cyclohexane. This graph may be used for any saturate fraction in the 60" to 86" C. (140" to 187" F.) range.
I
I
c -1.045
FOR NARROW-BOILING FRACTIONS
! i
IN THE 60*-86OC RANGE
0 W
8
c
z
1'0411
> 0
C, NAPHTHENES A
1.040
0 CYCLOPENTANES A -CYCLOHEXANES
a
Lw (r
1.037
,035
-
,
0.65
,
u
0 10 20 30 40 50 60 70 80 90 100 Boundary lines
c-
1 , 0 3 5 1 0.75
u 0.80
C7 NAPHTHENES
Six-carbon naphthenes
Table I. Data for Construction of Figure 1 Naphthenes, Volume %
-
0.80
0.75 OENSITY AT 2 0 ~ .
0.70
Figure 2.
I
d:'
0.650 0.660 0.671 0.680 0.690 0.700 0.710 0.720 0.730 0.740 0.745 0.650 0.710
1.04470 1 04380 1.04300 1.04210 1.04128 1.04040 1.03962 1.03884 1.038O6 1.03730 1.03620
0.710 0.715 0.726 0.730 0.740 0.750 0.755 0.765 0.770 0.780 0.790
n - d/2 1.04600 1.04528 1.04466 1.04390 1.04334 1.04280 1.04200 1.04142 1.04064 1.04008 1.03950
1.04470 1.04600
0.745 0.790
1 ,03620 1.03950
n
- d/2
d:'
I . I I I J I I I I I I e2 LO35 ( 0.70 0.75 0.80 C a NAPHTHENES
0.70
Figure 3.
0.75
0.80
MNSITY AT 20.C.
Placement of 100% naphthene line
Data for Zonstruction of Figure 2 ':d 0.652 0.663 0.671 0.683 0.691 0.700 0.711 0.722 0.731 0,740 0.748 Boundary lines
0.650
0.670
n
- d/2
1.04505 1.0441 1.0431 1.0422 1.0412 1.0402 1.0393 1.0384 1 ,0374 1.0364 1.0354 1.0452 1.0455
4' 0.675
0.685 0.690 0.704 0.715 0.726 0.734 0.745 0.757 0.765 0.776 0.750 0.780
- d/2 1.04515 1.0443 1.0434 1.0426 1.0418 1.0410 1.0401 1.0393 1.0385 1.0376 1.0368 1.0352 1.0368
n
been achieved by adjusting the paraffin and naphthene lines for t h e approximate distribution of the individual hydrocarbons in naturally occurring petroleum. Use of this refractivity intercept method for naphthenes is limited to samples in which polycyclic naphthenes are negligible. Polycyclic naphthenes have a relatively low refractivity intercept and a high density, which cause them t o have a n exaltation effect on the total naphthene content determined by this method. I n many crudes, this limits the application of the method to fractions boiling below 150" C. For this reason and because individual hydrocarbon data on crudes are not available in higher boiling ranges, the reliability of the method can only be stated in the C, t o Cs range, where it is accurate to &2%. NEW REFRACTIVITY INTERCEPT GRAPHS
The graph for the c6 to CS range, for wide-boiling saturated hydrocarbon fractions in the 60" to 135' C. (140" to 275" F.) range, is shown in Figure 1. On samples containing negligible amounts of polycyclic naphthenes, this graph may be used for higher-boiling ranges by extending t8helines to the right.
Tables I and I1 give data for construction of the two refractivity intercept-density graphs. The graphs should, be drawn on coordinate paper so they can be read to 0.0001 unit in refractivity intercept and 0.001 unit in density. PARAFFIN AND NAPIITHENE DISTRIBUTION
The new graphs are based on the distribution and amount of individual saturated hydrocarbono in the Cg to C8 range of crudes. The 100% naphthene lines are based on the relative amounts of individual naphthenes, and the 0% naphthene lines are based on the relative amounts of individual paraffins. Individual naphthene isomers are plotted in Figure 3 and compared with the position of the 100% naphthene line from the general purpose graph. Crudes differ considerably in the relative amounts of naphthenes of the cyclopentane and cyclohexane types. However, within thc two classes the relative amounts of the individual isomers remain fairly constant (19). Fortunately, differences in the ratio of cyclopentanes to cyclohexanes do not affect the placement of the 100% naphthene 6 to C8range. As shown in Figure 3, the cyclopenline in the c tanes fall a t the lower end of the line and the cyclohexanes a t the higher end. The new 100% naphthene line differs from that on the previous published graph ( 2 , 17) by an amount equivalent to only 1% naphthenes. This is a very minor change. The position of the Cg naphthenes with relation to the general purpose graph (top of Figure 3) shows why a special graph is needed for the c 6 range. The 100% naphthene line in the special graph, Figure 2, connects these two points. The relative amounts of paraffin isomers are much more important in deriving an accurate refractivity intercept chart. Individual isomers are plotted in Figure 4. The new 0% naphthene line differs considerably from the previously published
ANALYTICAL CHEMISTRY graph because of the predominance of normal and singly branched paraffins in petroleum fractions. As shown a t the bottom of Figure 4,the change amounts to about 4 to 7% in very low naphthene content samples. Literature data (19, 2S, 24) stress the predominance of normal and single methyl-branched paraffins in straight-run gasoline. Even in crudes that can be classified as high in isoparaffins, such as that from Winkler, Tex. (19, bS), the amount of paraffins containing more than a single methyl-branch is only about 10% of the total paraffin content in the c6 and C? range. Doubly branched paraffins are present in small amounts and triply branched paraffins are absent or barely detectable (9, 24, 25). n-
r
PARAFFINS h
9
I''9-k IUIO-
e-1.0431
t
1 I I 1 0.70 MONOMETHYL PARAFFINS
*
I
0 65
1
I
I
a75
"
POLYBRANCHEI~ PARAFFINS
r
0 DIMETHYL
PARAFFINS PARAFFINS
a: w
r
0.65 0.70 0.75 COMPARISON OF 0%NAPHTHENE LINES
l,,k / I
I
0.65
I
I
I
s
t
0.78
9
I
0.75
DENSITY AT 20 C.
Literature data on the products from thermal and catalytic cracking show a difference in the paraffin isomer distributions. Thermal gasolines (8, 10) contain very few highly branched paraffins; the normal paraffins and single methyl-branched paraffins are in about the same relative amounts as found ir virgin naphthas. Catalytic gasolines (8, 10, 12, 14, 21, 23'1 contain relatively low amounts (
