I N D UXTRIAL AND ENGINEERING CHEMISTRY
June, 1931
681
Composition and Crystal Form of the Petroleum Waxes' S. W. Ferris, H. C. Cowles, Jr., a n d L. M. Henderson THEL ~ T L A S T I CREFININGCOMPANP, PHILADELPHIA, PA.
Examination of t h e physical properties a n d crystal f o r m s of twenty highly purified paraffin wax fractions f r o m a m i d c o n t i n e n t p e t r o l e u m indicate that petroleum. wax consists of several hydrocarbon series which are homologous a t least w i t h respect to physical properties a n d crystal f o r m . T h r e e broad types of crystal f o r m m a y be distinguishednamely, plate, mal-crystalline, a n d needle; t h e plate type exhibiting, for a given boiling point, the highest m e l t i n g point, a n d t h e needle t h e lowest. T h e crystal form is a n i n h e r e n t property of t h e c o m p o u n d , a n d i s substantially
unaltered, except in detail, by factors s u c h as viscosity of t h e solvent. B o t h needle a n d mal-crystalline waxes have m a r k e d powers, u n d e r t h e proper conditions, of impressing t h e i r f o r m u p o n plate waxes, a n d indications a r e t h a t the m a l crystalline type is m o r e powerful in t h i s respect than t h e needle. These findings reconcile m a n y apparently contradictory observations which appear in t h e l i t e r a t u r e , a n d t h r o w considerable light u p o n certain wax-refining processes.
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N A previous paper (3) evidence was presented indicating that petroleum wax is by no means composed exclusively of normal paraffin hydrocarbons. The yield percentages obtained could not, however, be used to compute the relative concentrations of the several types of wax in the crude because, firstly, the starting stock was a mixture of various wax intermediates of indefinite history and, secondly, the information v a s secured for only one portion of the boiling range.
I
of the 10 per cent cuts were refractionated under the same conditions, resulting in fractions having the properties shown in Table I. Table I-Refrartionation FRACTION
POINT 0
0 to 0 . 2 5 0 . 2 5 to 0 . 7 5 0 . 7 5 to 2 . 2 5 2.25to 5.3 42.5to47.5 7 7 . 5 to 8 3 . 5
c.
23.1 30.8 32.1 34.6 49.4 57.2
of Oil-Free Wax
ASSAY
MELTING
I I
10%
oc~. 164 178 181.5 186.5 233 273
DISTILLATION AT 10 50%
c. 172 180 183 188.5 235.5 278.5
MM.
90%
c. 175 184 185 190.5 237 284
C and D-Each of the above distillate fractions was submitted to fractional crystallization from ethylene dichloride. Little or no separation into products of different melting point could be effected on the first four fractions (D). (See Figure 2.) Separation was easily obtained, however, on the 42.5 to 47.5 per cent cut, six fractions finally resulting which varied in melting point from 51' to 35.1" C. Similarly, ten fractions were secured from the 77.5 to 83.5 per cent cut. Physical Properties of Purified Fractions
Figure 1-Diagram
of Fractionation Process
The work has therefore been continued on a slack wax from a known crude source. After fractional distillation of the wax suitable close-cut fractions of widely different boiling points were selected and quantitatively resolved into highly purified products, whose physical and crystallographic properties were investigated.
The physical properties of the twenty final fractions are presented in Table 11. Fractions A to F are those reported in the previous art'cle ( 3 ) . They are included to demonstrate the close agreement in results in the two series, although they were recovered from an entirely separate stock. I
I HPI
M-
I
Preparation of Purified Fractions
The material selected for study was slack wax from a midcontinent crude. The processes of fractionation and purification are presented diagrammatically in Figures 1 and 2. Briefly, the procedure was as follows: A-The slack wax was freed of oil by four successive recrystallizations from ethylene dichloride a t -12" to -14' C. B-The oil-free wax was fractionally distilled, a t 1 to 3 mm. absolute pressure, through a &foot column packed with jackchain, taking 10 per cent cuts to 10 per cent residuum. Certain Received March 17, 1931. Presented before the Division of Petroleum Chemistry a t the 81st Meeting of the American Chemical Society, Indianapolis, Ind , hfarch 30 t o April 3, 1931. 1
Figure 2-Fractional
Distillation f r o m E t h y l e n e Dichloride
The degree of purity of the final fractions, particularly the extent to which one is contaminated by the other, may be judged from the cooling curves presented in Figures 3, 4, and 5.
ILVDUSTRIAL A N D ENGINEERIA;G CHEMISTRY
682
Crystalline Character of Final Fractions
Each fraction was crystallized from ethylene dichloride and nitrobenzene, respectively, a t room temperatures approximating 25” C., and the resulting crystals were photographed. Several of the fractions were crystallized from other solvents, and also photographed. A large number of the fractions formed plate type crystals; another group crystallized as unmistakable needles, but for several fractions no definite form could be recognized and, for lack of a better term, these forms were called “mal-crystalline.” Figures 6 to 9 present the photographs, separated into these three groups of crystal types. Properties of Purified Fractions
Table 11-Physical
50%
FRACTION
MELTING BOILING POINT
POINT
AT 0
4
F,A
5B
5c 5D
5E 5F 6A
6B
6C 6D BE 6F 6G 6H 61 6J A B C D E F
c.
2.5.1 30.8 32.1 34.6 51.0 49.9 47.3 44.9 40.2 35.1 6R.5 63.6 62.8 60.6 55.8 50.9 46.3 42.1 38 8 34.0
10 MM. 0
DENSITYMOLECULAR
AfizF& AT 800 C.
WEIGHT
c.
172 180 183 188.5 239 236 234 233.5 235.5 236 291 282.5 278.5 275 275 276 283 284 287 281.5
1.4161 1.4170 1.4175 1.4185 1,4252 1.4250 1.4255 1,4254 1.4258 1,4273 1,4310 1.4305 1.4301 1.4300 I . 4313 1.4332 1.4349 1.4359 1.4365 1.4375
0 7484 7450 7464 7475 7606 7606 0 7625 0 7612 0 7624 0 7692 0 7717 0 7711 0 7703 0 7706 0 7728 0 0 0 0 0
-
0 7819 0.7841 0.7856 0,7889 FRACTIONS PREVIOUSLY REPORTED (3) 269.5 1.4303 0.770 59.9 269.5 1.4308 0.773 55.2 272.0 1.4330 0.779 47.1 272.0 1.4350 0.7R3 40 5 272.0 1.4359 0.786 35,2 273.5 1.4380 0.792 29.4
263 261 274 276 34 1 341 333 336 334 344 420 5 409 407 400 402.5 409.5 407 401 410 402
EXPLANATION OF PHOTOMICROGRAPHS-The legends accompanying the photomicrographs can best be explained by an example: The first picture in Figure 8 is “5E in E . D. N420X.” This indicates wax 5E as crystallized from the solvent ethylene dichloride, photographed with normal illumination with a magnification‘of 420 diameters.
Additional notes on the four items just mention-d follow: Waxes-All waxes pictured are included in Table I 1 except three shown in Figure 16, which may be described as follows: Waxes T and W-Low-boiling fractions obtained by fractional dis tillation of oil-free commercial paraffin waxes and therefore (Figure 14) composed entirely of plate-type waxes.
COOLING CUti’Y‘S 4
Vol. 23, No. 6
at looo F. (100” oil), a vacuum distillate from a naphthenic crude, of 8000 seconds Saybolt viscosity at 100’ F . (8000” oil). Zllurninalion-Axial illumination, normal light ( N ) , crossed Nicols (P). hfagnificalion-The magnifications given are for the original photographs, which were approximately 6.2 X 8.2 cm., except those in Figure 15, which were 7.6 X 10.2 cm.
I n order to study the significance of these three crystal types, the physical properties of the fractions were plotted using the observed crystal form in lieu of the usual point (Figures 10, 11, and 12).
1
Figure 6-Plate
Wares In Ethylene Dichloride
INDUSTI2IAL A N D E\. GIhEb?RlND CHEMISTRY
Figure S-Mal-Crystal Wame in Various Soivenfs
Figure 9 -Needle Wercs in Y~lriuusSolvents
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