Distillation Micromethods for the Analysis of Petroleum A. R. JAVES, CHRISTIAN LIDDELL,
and
W. H. THOMAS
British Petroleum Co., Ltd., Research Station, Sunbury-on-Thames, Middlesex, England
hut a means of distilling the sample is essential for a more complete evaluation. This paper describes the stills that have been devised to satisfy this requirement and records the work carried out to evaluate their effectiveness. Apparatus and procedure have been developed whereby distillation data a t atmospheric pressure can be obtained on samples as small as 0.8 ml. Similar equipment for operation under vacuum and a miniature fractionating column and still for the removal of solvents from extracted crude, or for the separation of petroleum fractions for further examination, have also been devised. In addition t o assay work, the stills can be wed for miniature distillation tests on petroleum products.
During the assay- of miniature samples of crude petroleum or the analysis of small quantities of petroleum products, i t is frequently necessary to distill samples that are much too small for distillation by the usual methods. Tests with microstills developed in this laboratory on 0.8- or 1-ml. portions of oil gave results which are in agreement with those by the corresponding methods IP 24, IP 123, or ASTM D 86 a t atmospheric pressure or ASTAMD 1160 under vacuum, but they have about three times the experimental error. The properties of distillates and residues from S m l . portions of crude oil cut in a microstill having a packed column had properties that were in satisfactory agreement with those prepared from several liters of crude oil using a large 14-plate column. The atmospheric microstills and the vacuum microstill have been in frequent use since 1949 and 1952, respectively, and have given results of practical value.
APPARATUS
Microdistillation without Fractionation. The apparatus consists essentially of a flask, side arm condenser, and receiver all in one piece arranged as shown in Figure 1, with the condenser positioned vertically above the receiver. Most of the distillate condenses in the side arm and flows directly to the receiver. The receiver is calibrated with heptane or other suitable hydrocarbon in milliliters per millimeter length and the volume of distillate is read by means of a removable transparent double scale arranged to avoid errors due to parallax. Dimensions of the stills examined during this work are given in Figure 2.
A
PPARATUS suitable for use a t atmospheric pressure or under vacuum has been described by Sommer arid \Tear for carrying out distillation tests on IO-ml. samples of crude oil and 3-ml. portions of distillate oils without fractionation ( 3 ) . However, instances arise when analyses are required on even smaller quantities of oil. For example, it is frequently desirable to determine the type and quality of crude oil present in core samples immediately after they have been obtained from a bore hole. The crude oil can be extracted from the core by means of a solvent at the laboratory, and the solvent subsequently removed from the extract by distillation. The quantity of oil finally obtained is often too small to provide complete information regarding quality and type by conventional methods and even by the Sommer and \\-ear apparatus. Specific gravity, sulfur content, and asphaltene content can be determined on such samples using microprocedures,
B , OX
\ARROW
-
NECK
F - A S K TO TAKE MINIATURE THERMOMETER
Im/. W I D E DISTILLATION
NECK FLASK
THERMOMETER I P 4 W
THERMOMETER
3ml
DISTILLATION
FLASI(
7m* I
25mm
35 m m .
Figure 2.
U
d
Micro atmospheric distillation flasks
The flask is mounted in a draft screen provided with a lid (Figures 1 and 3), the source of heat being a gas microburner. The air temperature in the upper part of the draft screen is observed by means of a thermometer fitted through the lid of the screen and during distillation must be less than the still head temperature. Smooth boiling of the charge in the flask is assisted by a micro boiling stick (Figure 2). Institute of Petroleum (3) crude oil distillation thermometers (IP 4C) and microthermom-
Figure 1. Section through micro atmospheric distillation assembly
991
992
ANALYTICAL CHEMISTRY
eters were emdoved. The latter had the same scale range as Table I. Summarized Distillation Conditions the IP 4C and were selected to Micro Vacuum Distillation have a stem length suitable for Microdistillation (10 Mm. t o ISTILLAT SECEIVER
'28
1 /r
SCALE
5 W G.WIRE
Figure 4. Micro fractionating column
,RECEIVER
--/-v?
V4LVE
Figure 3.
DETACHABLE 'RECEIVER
and prevented the oil from being "bumped" too far from the heating zone. The nickel tape was more effective than the boiling stick for promoting smooth boiling, and, moreover, because of its pliable nature, it was easy to insert into the flask without risk of breakage. Copper would probably be corroded during the distillation. Later work has shown that small pieces of porous pot can be used in place of the above boiling aids.
Micro atmospheric distillation assembly WORK CARRIED OUT AND RESULTS OBTAINED
Micro Vacuum Distillation. The dimensions of the flask employed for microdistillation under vacuum are given in Figure 5. The neck of the flask is bent in order to prevent foam from the boiling oil touching the thermometer and causing false temperature readings. The flask is used with the draft screen, microburner, microthermometer, and distillate measuring scale described for microfractionations a t atmospheric pressure. The side arm from the flask is sealed into the junction between condenser and receiver and most of the distillate condenses in the side arm and flows directly into the receiver. The upper end of the condenser is connected in the normal manner to a manometer, a solid carbon dioxide or liquid nitrogen trap, and a vacuum pump. For the first distillations with the apparatus, smooth boiling was encouraged by means of a micro boiling stick placed in the flask, but for later tests the boiling stick was replaced by thin nickel tape twisted into a helix. The meshwork of metal formed in this way improved the distribution of heat through the oil
Microdistillation without Fractionation. A number of microdistillations were carried out on a sample of crude oil in order to determine the test conditions which would give results in closest agreement with those by the 100-ml. distillation method IP 24 ( 2 ) . These conditions are summarized in column 2 of Table I. The extent of this agreement for four different crude oils is shown graphically in Figure 6 and the experimental data for one of these oils are given in Table 11. The repeatability of the micromethod was then examined with three crude oils, and the results on one of them are given in Table I11 together with typical draft screen air temperatures. The reproducibility of microdistillation results in different I-ml. stills is shown by the results given in Table IV. The necks of the microstills had to be of sufficient diameter to accommodate an IP crude oil thermometer ( I P 4C) and also to
993
V O L U M E 27, NO. 6, J U N E 1 9 5 5 6 Omrn
-+
*8011% 13mm
CONDENSER
D
I
\
100mn
+I
U i
preliminary trials were made on 2 ml. of a 50 to 50 mixture of B solvent (ethyl ether) and a volatile paraffin hydrocarbon (nhexane). The results u-hen compared in Figure 7 with those of the standard 100-ml. distillation test IP 123 ( 8 ) show that the column provided a degree of solvent separation which could not be obtained by simple distillation without a column. The method IP 123 is very similar to ASTM D 86. Subsequent uses of the microfractionation equipment involved the preliminary step of removing the solvent from the crude oilsolvent mixtures fol!owed by fractionation of the crude oil remaining and the separation of fractions boiling up to 149' C. and between 149' and 232" C. In the case of 5.3 ml. of crude oil extracted from a rock core with benzene, the fraction boiling up to 149' C. u-as only sufficient in volume to permit the determination of specific gravity and sulfur content and accordingly, the cut point (81" C.) between solvent (benzene, and sample was taken as near as possible to the boiling point of benzene (80' C.). The benzene content of the fraction 81' to 149' C. was then determined and the necessary corrections applied t o the inspection data for the fraction. No intermediate cut was taken to ascertain how far the benzene extended into the "motor-fuel fraction" but the benzene content of the next cut (149' t o 232' C.)
C A P A C I T Y OF F L A S K T O L E V E L ' A ' I S A P P R O X I M A T E L Y 15mP T O L E R A N C E S : I N T E R N A L D I A M E T E R OF T U B I N G S H O U L D 0 E C O R R E C T 1 D +C,5mm. OTHER DIMENSIONS A R E PROBABLY N O T CRITICAL
Figure 5.
Micro vacuum distillation flask
Table 111. Repeatability of Typical Micro Crude Oil Distillations"
Table 11. Comparison of Typical Crude Oil Distillation Test Results by Institute of Petroleum and Micromethods IPO 24
Micromethodb
Initial boiling point, O C. 40 43 Distillate, 1-01. % T o 100' C. 8 2 T o 125' C. 12.5 9 T o 150' C. 16.5 13.5 T o 175' C. 21 20 T o 200' C. 25 25 To 225O C . 29.5 29.5 T o 250° C. 33.5 35 T o 275' C. 37.5 39.5 T o 300' C. 42.5 45.5 Institute of Petroleum (100-ml.) method IP 24. b Micromethod with 1-ml. wide-necked flask.
Difference between I P a n d hlicromethod
Difference between Test Results
Test Results Initial boiling point,
C.
43
42
Draft Screen Air Temp., OC.
I
3
G 3.5 3
1 0 0 1.5 2 3
a
hlicrodistillations in 1-ml. wide-necked flask.
Table IV.
Reproducibility of Microdistillations in Different 1-M1. Flasks" Flask
1
2
Difference between Flasks 1 a n d 2
42.5
43.5
0.5
Flask Initial boiling point,
C.
allow sufficient space around the stem to prevent the annulus Distillate, vol. % To 100' C. 3 2 1 being bridged or choked by a film of liquid. This resulted in an T o 125" C. 8 9 1 T o 150' C. 13.5 13.5 0 unnecessarily large vapor space in the still which caused the latter T o 175" C. 19 20 1 to go dry just after the "80% distilled" point u-as reached when T o 200' C. 24 25 1 T o 225' C . 29 29.5 0.5 distilling distillate oils. Special microthermometers were thereTo 250' C. 34.5 35 0.5 T o 275' C. 40 39.5 0.5 fore obtained and tried in the narrow-necked stills shown in T o 300' C. 45 45.5 0.5 Figure 2. This enabled kerosines to be distilled t o the 90% a Distillation of crude oil in wide-necked flasks with IP 4 C thermometer uoint in the 1-ml. still and the (9). 95% point in the 3-ml. still. The results of trial distillaTableV. Distillation of Crude Oil C in 1-RII. Stills tions on crude oils and kerosines Flask 100 1-M1. Wide1-MI. Wide1-M1. Narrow-Necked M1. Neckeda Neckeda in the narrow neck stills fitted Thermometer IP 4 C IP 4 c Microb with microthermometers are - Diff.Micro b Diff, Diff. Diff, given in Tables V, VI, and VII. from I P from I P from I P from IP Weighing the stills plus oil be43 c. 40 60 +20 .. ... 1 3 fore and after the distillations 1 -1 - 1 .. -1 .. -1 4 Trace -4 -4 -4 Tiace Ahowed that distillation losses .. .. -4 2 8 -6 2 - 6 4 -4 2 -6 from any of theabove stills were 12.5 9 -3.5 11 5 - 7.5 -1.5 10 -2.5 1 3 . 5 1 6 . 5 9 . 5 7 3 18 + 1 . 5 16 -0.5 negligible. 20 -1 14 - 7 21 25 -1 +4 20 25 M i c r of r a c t i ona ti on. RE0 20 - 5 25 +6.5 24 31.5 -1 0 26 - 3 . 5 35 29.5 29.5 30.5 +I MOVAL OF SOLVENTS. I n order +1.5 28 -- 35 .. 55 3 7 . 5 4-5.5 35 33.5 +4 37 f3.5 34 3 9 . 5 3 7 . 5 41.5 +2 +4 42 f4.5 to assess the efficacy of the mi45.5 42.5 37.6 -5 46 +3.5 47 $3 +4.5 crofractionation equipment for 0 Wide-necked flask 2 used for both tests. b Same microthermometer used for b o t h tests. the removal of solvents from crude oil extracted from cores,
ANALYTICAL CHEMISTRY
994 was found t o be negligible. Another sample dissolved in methylene chloride (boiling point 42" C.) for the removal of water and sediment was fractionated after these had been removed. The fractions were analyzed by the mass spectrometer for methylene chloride content, and, from the results obtained, 60" C. was chosen as the cut point for this solvent. OF
FRACTION.4TION
CRUDE
OIL. The crude oil microther-
Table VI.
I
1
1
I
I
I
IO
20
30
40 SO DIST'LLATE
Diff.
3-511. Still
1 2 Mean Initial boiling point, C , 52 56 54 Distillate, % To 7 5 ' C . 1.5 1 1 T o 100' C. 5 4 4.5 T o 125' C. 9 9 9 To 150" C. 15 14.5 15 To 175' C. 21 21 21 To 200' C. 28 27 27.5 T o 225' C. 34 33 33 5 To 250' C. 39 40 39 5 T o 275' C. 44 44 44 To 300' C. 51 49 50 Narrow-necked still, microthermometer.
mometers used with the microcolumn are of total immersion type and readings of true boiling point made therewith must be subjected t o emergent stem correction. The corrections can be calculated, but it is considered preferable t o determine them under actual conditions of use, employing pure materials of known boiling points. Corrections for use a t the conventional cut points (149" and 232' C.) are taken from a plot of the determined values which not only provide more reliable stem corrections but also allow for any calibration errors in the thermometer.
0
Distillation of Crude Oil E in 3-hIl. Stillo
I 10 VOL
I
I
I
20
30
40
Jo 50
from mean.
IP Repeatability,
=t% 2
+ %
..
0.5 0.5 0.0 0.5 0.0 0.5 0.5 0.5 0.5 1.0
1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
100-
M,l Stlll I
52
N e a n of 100- and 3-hI1. Results 53 2 6 11 16 5
2 5 8
13 18 23.5 29 34 5 39.5 45 50 5
22
28 34 39 5
44.5 50
Diff. IP from Reproducibility, Mean, =t% 1
A%
1.0 2.0 2.0 1.5 1.5 1.o 0.5 0.0 0.5 0.5
2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0
..
Table YII. Microdistillations of Kerosine Compared with Results by Institute of Petroleum Method Test Points,
C.
~p 1-M1. Narrow-Necked 3-M1. Narrow-Necked 123/53 Microstill Microstill Method Test Difference Test Difference B (X?) readings from IP 123 readings from IP 123
Initial boiling point
172
170
2
Temp., C. At 2 % distillate A t 5% At 10% A t 20% At 30% A t 40% A t 50% At 60% A t 70% At 80% A t 90% At 95%
179.5 182.5 188 192 197.5 203 209 214.5 221 229 239 246
182: 5 185.5 191 197 203 209 21R 223 231 241
0 0.5
, .
...
1 0.5 0 0 1.5 2 2 2
..
169
3
173.5 178 183 191.5 198.5 205 211.5 218 224 231.5 241.5 249.5
6 4.5 3 0.5 1 2 2.5 3.5 3 2.5 2.5 3.5
Two microfractionations were carried out on another crude oil using the column with removable receivers and the yields and properties of the fractions and residues were compared with data from a 14-plate column distillation carried out on a large sample. The results of this comparison are given in Table IX. Distillation losses were found t o be negligible. Micro Vacuum Distillation. Micro vacuum distillation tests were rarried out under the conditions given in Table I, column 4, on a typical wax distillate and the corresponding atmospheric residue. The results are given in Table X and are compared with values obtained by 100-ml. vacuum distillations by a British Petroleum Co. method similar to ASTbI D 1160. The micro and macro results are'compared graphically in Figure 8. Distillation losses were found to be negligible. The lowest distillation pressure employed was 0.75 mm. of mercury. The apparatus was easy to use and a distillation test could be carried out in about 2 hours. This estimate includes the time spent in calculating the test results from the experimental data.
Figure 6. Distillation of crude oil in 1-ml. still Charge.
-
0.8 ml. By IP 24/44 By microdistillation
- -.
-0-. --I-
The static hold-up in the column (usually about 0.1 gram) must be considered as part of the residue and should be recovered and blended back, or failing this, its amount must be assessed and allowed for. Using a column with a fixed receiver, eight microfractionations of crude oil C were carried out under the conditions given in Table I, column 3, in order to obtain various residues. The inspection data on these are given in Table VI11 and are compared with data for residues from multiplate column distillations. Weighing the stills plus oil before and after the distillations showed that distillation losses were negligible.
DISCUSSION
Microdistillation Without Fractionation. The results of the microdistillation tests on 0.8-ml. portions of crude oil in the widenecked flask shoiv that test results in different stills are reproducible and that the repeatability in the same still averages within the "tolerance" of i ~ l . 5 quoted 7~ for the IF' 24 method. The IP value, however, is not an average deviation but is slightly "w-eighted" to allow for a reasonable proportion of "strays." In this case, out of 61 individual microdistillation points, only 11 differed from the mean by more than 1.5%; of these, four differed by 2%, two by 2.5, one by 3, one by 3.5, and three by 4%. Statistically, the results gave a standard deviation of +1.72, which corresponds t o a n average deviation of about 11.270. The Institute of Petroleum has not yet determined the standard deviation of ite distillation tests on a statistical basis, but the authors'
V O L U M E 2 7 , NO. 6, J U N E 1 9 5 5
o
10
20
40 50 DlSTlLL4TE
30
60
'A
995
a0
70
90
100
iOL
Figure 7 . Distillation of 50 t o 50 m i x t u r e o f d i e t h ? I e t h e r and n-hexane
- 540 - 500 - 460
- 420
." w 3 L
- 380 $ LL
0 w
-340
2
- 300
---
A V L R A G E o r M I C R O VACUUM D I S T I L L A T I O N S -AVERAGE OF MACRO VACUUM D I S T I L L A T I O N S
I
I
I
I
0
10
20
30
I
I 40
50
DISTILLATE
F i g u r e 8.
I
I
I
60
70
80
- 260
probably about one third of that of a properly conducted IP test, assuming that "accuracy" is measured in the same terms for both methods. The comparison between 1-ml. wide-necked stills with IP and microthermometers and 1-ml. narrow-necked stills with a microthermometer (Table V ) shows that the best all-round agreement with the IP test for crude oil is obtained by the wide-necked still used with an IP 4C thermometer. In addition, the narrownecked still was not so easy to use. All the distillation points on a crude oil in a 3-nil. narrow-necked still (Table VI and Figure 7 ) agreed with the IP results within the IP tolerances. Microfractionations. The actual plate efficiency of the microcolumn has not been measured, but l/ls-inc.h Dixon rings in a column of that length would he expected to provide approximately eight theoretical plates under suitahle conditions of reflux and throughput. The results in Figure 7 confirm that a good degree of fractionation can he obtained. The utility of the microcolumn for the fractionation of crude is illustrated in Tables VI11 and IS, from which it can be seen that the residues and distillate fractions obtained compare well with those given by 14-plate column distillation equipment using several liters of crude oil. The residues from the fractionation of crude oil C (Table VIII) in the microcolumn have been rated as percentage residues on crude by calculation from known specific gravity and viscosity data. The percentages obtained by these means are in good agreement, the biggest difference being 1.9% and the average of the eight residues, 0.7%. Furthermore, the microtest? show differences between crudes that are similar to the differences shown with good fractionation on large samples.
12 2 0 90
VOL.
Distillation tests on wax distillate a n d a t m o s p h e r i c residue
T a b l e IX. Microfractionation of C r u d e Oil F Microfractionation
results indicate that the almve value of iz1.2 is about thrce times the probable repeatability error of I P tests. The comparison of average microdistillation values with the corresponding values hy thcx 100-ml. test IP 24 shows a standard deviation of 3.49y0 which corresponds to a n average deviation of approximately 2.40j0. The I P reproducibility "tolerance" is a difference of 4% and in most cases the micro and macro tests agree within this limit after 10% of distillate has been collected. The initial boiling points were in good agreement with the IP values, but no I P tolerance is quoted for this figure. A considerable portion of the differences between micro and IP tests is systematic. and some allowance can he made for it if the microresults are conipai rd (Figure 6 ) with results on a similar sample of known distillation characteristics. I n either case the results are sufficiently accurate t o give the type of information usually required of a microsample. Xs in the case of the lepeatability data, the general over-all accuracy of a microtest is
Fraction 15' t o 149' C. Yield, % ( W t . ) Specific gravity, 60°/600 F. Fraction, 149' t o 232' C. Yield, % ( n t . ) Specific gravity, 60°/600 F. Residue above 232' C. Yield % (wt.) Specific gravity, 6O0/6Oo F. Viscosity, cs. .4t 140' F. At 170' F. At 210' F. Sulfur, 70 (wt.)
14-Plate column Distillation
1
2
14 0.705
1$5 0.707
16.1 0,707
13 0.783
11.5 0.785
13.5 0.7855
67.5 0.923
69.5 0.923
68.5
27.10 15.64 8.69 2.77
26.32 15.32 8.67 2.77
26.02 14.89 8.41 2.74
0.917
The quantity of crude oil required for a microfractionation depends largely on the amount of data required on the distillates and residues. At the present date, approximately 2 t o 3 ml. of residue will suffice for most of the ordinary tests. The specific gravity, aniline point, and aromatic content of a distillate require a total of approximately T a b l e 1'111. 5Iicrofractionations of C r u d e Oil C 0.3 ml., hut sulfur content reResidue above quires at least 1 ml.unlessavery Residue above Residue a b o r e 232O C. without 149' C. without 232O C. Including approximate value will suffice. Holdup Holdup Holdup 1 2 3 1 2 3 1 2 Micro Vacuum Distillation. 0 945 0 945 Statistical examination of the Specific gravity CiOo/CrOo 1'. 0.925 0.925 0.92fi 0 949 0 949 0.949 Viscosity, cs. micro vacuum distillation re58.00 55.84 At 140' F. 23 .59 25.46 26.71 08.92 64 01 71.02 A t 170' F. 1-1 10 15.15 15.66 35 54 33.08 3fl.20 30.83 29.56 sults obtained on the wax dis15.50 15.15 At 210' F. 8.03 8 51 8.77 17 3 4 10 38 17 60 ..., .... tillate, given in Table X, shows Sulfur, % (mt.) 3 28 3.31 ... 3.72 3 03 . ... that the use of nickel tape in yo (1'01.) on Standard Crude 0 L i Ti0 3 73.0 A0 3 -4 from viscosity data 74 4 73 1 02 5 63.0 place of the micro boiling stick 62.7 62.7 60 0 00.0 73.0 (io 0 72 5 72.5 B from specific gravity data Difference between A and B 0.3 made no significant difference 0.2 0.3 0 5 1.5 I .9 0.6 0 0 to the accuracy of the results. ~
ANALYTICAL CHEMISTRY
996 ~~
Table X.
~
~~
~
~
Comparison of Riicro (1-Ml.) and Macro (100-Ml.) Vacuum Distillations” Wax Distillate
h e a n of 1Iacro Results Sone
Method Boiling aid
Initial boiling point, O C . 2% vol. distilled a t , ’ C. 570 vol. distilled a t , O C . 10% vol. distilled a t , O C. 20% vol. distilled a t , C. 30% voi distilled at 40% vol: distilled at: 50% vol. distilled a t , ’ C. 55% voi. distilled at, O C. 60% vol. distilled a t , O C. 70% vol. distilled a t , ‘ C. 80% vol. distilled a t , ’ C.
‘ g:
-~
Boiling aid
295.5 308,s 322 336 362 387 412.5 437 448.5 459.5 481 503
Boiling Stick Diff. from Results macro
....
3i o
+1.5
317 331 357 389 415 435 444
-- 52 -5
+2 +2.5
-2 -4.5
.. .. ..
h-one
....
Uicro Results ~-
Sickel Foil Diff. from Results macro 303 +7.5 311 +2.5 318 -4 320 -7 3311 -6 383 -2 412 -0.5 436 -1
....
4ii’l
fl.5 +3 +1
48-1
501
Nickel Foil
Nickel Foil Diff. from Results macro 279 -16.5 302 - 6.5 - 13 309 - 5 331 360 - 2 388 + 1 410 - 2.5 431 - 6
.4trnosplieric Residue _ K x e l Foil_
+
~
..
-
5.5 - 7 - 9
454 -171
494
Sickel Foil ~
+
+
-4.5 -1
-!.!
-a,> -4.5
+0.5 nil -3 ..., -2 -2 -4
457.5 479 499
232 265 +25 Initial boiling point, O C. 225 - 7 219 33 263,s 274 2% vol. distilled a t , C. +18.5 +10.5 263 - 0.5 273 286 303 5% vol. distilled a t , C . i17 296 + 8 297 10 312.5 325 1.5 f12.5 10% vol. distilled at, C. 323 +10.5 320 308 - 5.5 358.5 + 9 5 20% vol. distilled a t , C. 3R0 1.5 360 402 405 - 7 30% rol. distilled a t , O C. + 3 - 4 398 399 - 7 5 447.5 440 -20.5 40% 1-01, distilled a t , C. 437 -10.5 434 494 480 -11 - 14 50% voi. distilled at O C. 475 - 19 479 549 60% vol. distilled at: C. - 16 .... 530 - 19 531 a Temperature readings are boiling points a t atmospheric pressure which correspond to boiling points observed under vacuum.
’ ’
Difference between macro and micro results
Mean of micro results 29 1 307.5 314.5 330.5 357.5 387.5 412.5 434
+
~
~
~~
5 5 5 5 5 5
5
f 17 9.5 fll.5 + 8 + 2 - 2.8 - 13 -14.5 -17.5
+
__
The precision of the micro vacuum distillation results on the wax distillate and atmospheric residue (Table X and Figure 8) may be summarized as follows:
possible to compare the accuracy of initial boiling points obtained by the micromethod with published data because these are not given in standardized macro methods.
Precision of Micro Vacuum Distillation Results
Difference from mean (repeatability) Average Maximum (95% probability level) Difference from 100-ml. test Average Maximum (95% probability level)
Wax Distillate, i. c.
ACKNOWLEDGMENT
The authors are indebted to the chairman of the British Petroleum Co., Ltd., for permission to publish the results of their work.
Residue, Z t 0 C.
3 8
3.5 10
3.5 9.5
8 23
REFERENCES (1)
The micromethod has a repeatability equal to about one third of that of the macro test and it is to be noted that the precision of the microresults on the wax distillate is better than the corresponding value for the residue. This is to be expected because the steeper distillation curve given by the latter will accentuate errors in temperature and distillate readings. It has not been
Bm.SOC.Testing Materials, Philadelphia, Pa., “-4STM Standards
on Petroleum Products and Lubricants,” 1953. (2) Institute of Petroleum, London, England, “Standard Methods for Testing Petroleum and its Products,” 13th ed., 1953. (3) Sommer, J. V., and Wear, G. E. C., “Some Microphysical Apparatus and .Methods for Inspection of Petroleum Products,” American Petroleum Institute Symposium on Rapid Methods of Analysis, April 1949. R E C E I V Efor D review May 26, 19.54. Accepted February 1, 1955. Presented before the American Petroleum Institute, Houston, Tex., 1954.
Quantitative Determination of Certain Sulfenyl Halides NORMAN KHARASCH and MILTON M. WALD Department of Chemistry, University of Southern California, Los Angeles 7, Calif.
+
An iodometric method, involving the reaction 2ArSCl 21- + -4rSS.h ii 2C1-, has been adapted for the analysis of certain aromatic sulfenyl halides. Titrations accurate to =!=lo/,were easily obtained if water was excluded. In anhydrous acetic acid, the magnitude of the required blank was proportional to the oxygen tension. The titration may be applied t o following the rates of reactions involving sulfenyl halides.
+ +
I
S STUDIES of the kinetics of reactions of sulfenyl halides
T\ ith various substances, suitable methods for determining this key group of sulfur derivatives became necessary. This paper reports a general procedure for the quantitative estimations of 2,4-dinitrobenzenesulfenyl chloride (I), the corresponding sulfenyl bromide (11) and thiocyanate (111), and 2-nitrobenzenesulfenyl chloride (IV).
I n earlier work, Bohme and Schneider (1) carried out the successful iodometric analysis of benzenesulfenyl chloride (via Reaction 1, Ar = phenyl), by treating the sulfenyl chloride, dissolved in carbon tetrachloride, with aqueous potassium iodide. 2ArSC1
+ 2KI --+-ArS-SAr + 2KC1 + 12
(1)
More recently, Foss (2’) has reported the determination of certain sulfenamides and sulfenyl thiocyanates by reaction of these substances with thiosulfate ions and measurement of the unreacted thiosulfate. The method of Bohme and Schneider was attempted in the present work for the analysis of 2,4-dinitrobenzenesulfenyl chloride (I), but the release of iodine never exceeded 93% of the amount required by Equation 1 (Ar = 2,4dinitrophenyl). Elimination of other sources of error suggested that water was interfering; and this proved to be the case, as satisfactory titra-
