ELECTROSTATIC RESPONSES OF PIGMENTS IN RELATION TO FLOODING, DISPERSION, AND FLOCCULATION J. A. REISING St. Joseph Lead Company, Josephtown, Pa.
Data on the response of pigments in an electrostatic field were obtained by studying paint pigments suspended in different types of vehicles, as well as pigments in actual paint formulation. The suspensions were placed between aluminum foil electrodes mounted on a microscope slide. The electrostatic field was excited by means of a 450-volt direct-current potential drop between the electrodes. For observation the electrode slide was placed upon the stage of a microscope. The response of each pigment was dependent upon the type of vehicle in which it was suspended. Thus when
zinc oxide was suspended in raw linseed oil it migrated to the anode and to the cathode when suspended in a mixture of higher alcohols; it did not migrate to either electrode when suspended in neutral mineral oil but assumed a linesof-force arrangement between the electrodes. Dispersions in polar-nonpolar compounds and flocculation in nonpolar compounds were accompanied by a characteristic electrostatic response of the pigment particles. Flooding was not present when complete flocculation of the pigment existed ;flooding was present in good dispersions.
F
Apparatus
LOODING is a phenomenon which is responsible for considerable concern among paint manufacturers. Attempts have been made to determine its causes (1,2)" Several factors have been considered as being responsible for this condition; one is the relation of the electrostatic charge of the pigments to flooding ( 2 ) . I n paint formulation the particular charge on pigment particles appears to have some fundamental significance in flooding, flocculation, and dispersion. Previous workers (1, 2 ) showed that certain pigment particles exhibit an electrostatic charge when suspended in either an alkali-refined linseed oil or a spar varnish. In order t o obtain further information as to the response of other pigments in different types of vehicles with reference to flooding, thirteen pigments were studied in eleven different media. Several of these pigments and one vehicle are of the same types as were used by these previous workers. As the studies progressed, it became evident that dispersion, flocculation, and the particle size of the pigments were involved. Data are shown which indicate that in a dispersion of mixed pigments in paint the particles carry either a positive or a negative charge, with flooding present if a wide range in the particle sizes of pigments exists. I n a neutral medium such as mineral oil each particle carries both a positive and a negative charge simultaneously, and as a consequence flocculation will ensue and flooding will be absent, regardless of the differences in particle size range.
In general, the apparatus was so designed that migration of a pigment in suspension could be observed when placed in an electrostatic field. The apparatus consists of a microscope with a 16-mm. objective and a 1OX ocular, an illuminating apparatus for direct illumination, a special slide holder, a special electrode slide, a source of high voltage, and photographic equipment. The arrangement is shown in Figure 1. Since the wire electrostatic field apparatus used by previous workers (1, 9) did not give a flat area for observation of the electrostatic response, and because difficulty was involved in cleaning the wires, a special electrode slide and holder were designed. The efficiency of this arrangement was good. A sketch of the special slide holder is given in Figure 2. It is made with a piece of Bakelite 1/8 inch thick, 1 1 / 2 inches wide, and 4l/* inches long, with a recessed area to accommodate a microscope slide, and a hole 16/le inch in diameter drilled in the center. Binding posts for making electrical connections are attached to opposite corners on one side of the Bakelite holder. Under the binding posts and in contact with them, spring clamps of shim steel are mounted. These clamps serve a dual purpose; they hold the special slide firmly in the holder and make electrical contact with the aluminum foil on the special slide. The object of the hole in the center is to permit observation with transmitted light if desired. A sketch of the electrode slide is given in Figure 3. It consists of a regular microscope slide to which aluminum foil is attached by means of a paraffin of high melting point. The width of the gap was decreased from '/la inch, as used by previous investi ators (1, Z), to inch, so that a more intense electrostatic Eeld might be excited. These slides are satisfactory but must be replaced when any damage is done to the foil. As a source of high voltage, R direct current obtained from 565
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VOL. 29, NO. 5
in Tables I and 11. After examining the behavior of single pigments in different media, a further investigation was made of mixed pigments in various media. The mixing of the pigments was accomplished by rubbing together portions of the pigment suspensions on a glass plate with a spatula. Such mixtures were made both from freshly prepared pigment suspensions and also from pigment suspensions which had been aged for 3 weeks. Table I11 conS W R ~ E OF L~~~~ tains the data obtained from these tests. The numbers in Tables I, 11, 111, and V refer t o the types of response shown by the photomicrographs of Figures 4 to 11. These are typical responses and are referred to as examples of the types of response for given mixtures of pigment and vehicle. Seventeen paints, the compositions of which are given in Table IV, were formulated in order to investigate the electrostatic responses of pigments in paint formulations. Each of these paints was given a double grind on a tightly adjusted mill. These paints contain four different pigment combinations and four types of vehicle, with one additional vehicle for the Medium Chrome Yellow and Prussian Blue pigment combination. Immediately after grinding, 200 mg.
FIGURE 1. MICROSCOPE SET-UP
SLIDE
HOLDER
either a series of dry batteries or from a highly filtered rectified alternating current may be used with equally satisfactory results. The tests recorded in this paper were made with rectified alternating current of 450-volt potential difference across the electrodes. The photomicrographs were made with reflected light on Wratten M-plates in a vertical camera swung into place over the microscope. These photographs are 50-diameter reproductions of the area on the special electrode slide.
Procedure and Material In order to study the electrostatic response of pigments in different media, 500 mg. of the pigment were rubbed out in 5 ml. of the medium on a glass plate with a spatula until a uniform distribution of the pigment was obtained. A small amount of this mixture was spread out in a thin film upon the electrode slide (Figure 3) over the gap between the electrodes. The remainder of the mixture was placed in 8-ml. glass vials and saved for further investigations. The slide was then inserted in the special holder (Figure 2), placed upon the stage of the microscope, and examined by reflected light. After examining the mount, the electrostatic field was excited and the response of the pigment observed. Some of the pigments responded rapidly to the excitation by the current, others were sluggish. The time for completion of the response varied from 1 second to 10 minutes, depending upon the pigment and medium used. Ten pigments and three inerts were studied for their electrostatic response in eleven different media. A list of the pigments and vehicles used in these studies follows:
?\
BAKELITE
FIGURE 2,
SPECIAL
HOLDER
SLIDE
Pigments Zinc oxide (electrothermic) Basic carbonate white lead (H. T. S.) Lithopone Zinc sulfide Titanium dioxide Jozite (zinc-iron oxide pigment)
Medium Chrome. Yellow Prussian Blue Ultramarine Blue Lamp black Talc Silica Blanc fixe
Vehicles
Mixtures of eaters and organic acids
Hydrocarbons Organic acid Mixture of higher alcohols
-4cid No. Raw linseed oil 2.7 Alkali-refined linseed oil 0.57 Kettle-bodied linseed oil of Q body 9.S High-acid-No. refined linseed oil 14.2 Light-pressed Menhaden oil 4.7 Raw China wood oil 4 2 Olive oi! 1 2 Mineral oil SAE 30 0 Mineral spirits 0 Lauric acid 271.0 Lauryl 35% Myristyl 20-25% Cetyl and stearyl 40-45%
of each paint were diluted with 1ml. of additionalvehicle and observed for its response. After the pigments had settled out, 200 mg. of paste from each paint were diluted with 1ml. of the supernatant vehicle which was removed from the paint. This suspension was then observed for its response. Dilution was necessary in order to have sufficient liquid vehicle t o permit free movement of the pigment particles. Only in the nonpolar media was the electrostatic response of the pigment consistent. With polar-nonpolar media the type response was found in many cases to vary with dilution of the media and on aging. C L A S S MICROSCOPE
\ \
=&* FIGURE
Suspensions of these pigments and vehicles were examined for their electrostatic response immediately after preparation and also after aging 3 weeks. The observations are recorded
A L U M I W M FOIL
3.
t
ELECT ROD E SLIDE
3fl
I
T
MAY, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
567
RESPONSE OF FRESHLY PREPARED PIGMENT-VEHICLE MIXTURE TABLE I. ELECTROSTATIC Raw Linseed Pigment Zinc oxide
Oil 4
AlkaliRefined Linseed Oil 6 90
HighAcid-No. Refined Linseed Oil 6
LightPressed Menhaden Oil 6
Raw China Wood Oil 6
Olive Oil 8
Mineral Oil SAE 30 Neutral
Mineral Spirits
11
11
Lauric Acid
9
Lithopone
4
6
Zinc sulfide
4
4
Titanium dioxide
4
8
Jozite
4
5
99 o +
6
7 757 25% 5
6
4
8
Mixturea of Higher Alcohols
7
90
Bmic carbonate white lead
Medium Chrome Yellow
KettleBodied Linseed Oil, Q Body 6
6
+-
8
8
4
11
7
4
4
1%
11
7
-
+-
10
11
11
957 5% 5
11
11
4
5
11
11
5
5
5
5
5
75 25%+ 8
7
%2 10
6
%:g T
7
6
6
38:%+11
85
6 907
15gf 11
IO%+8
-
6
11
11
11
2800927
10
11
11 IO
.~
Prussian Blue Ultramarine Blue Lamp black Talc Silica Blanc fixe
4
6
g3& 4 9 9 5
9
9
11
6
9 9
9 9
11 11
11 11
4 5
4 10
9 9
6
9
9
9
11 11 11
11 11 11
10 9 10
9 9
9 7
9 9
9
R 8
9 11 5
9
6
5
9 11
11 11
9 9
11
a
10
11
E%2
TABLE 11. ELECTROSTATIC RESPONSE O F AGED PIGMENT-VEHICLEJ MIXTURE
Pigment Zinc oxide
Raw Linseed Oil 7
+
98 2% 4
Basic carbonate white lead
AlkaliRefined Linseed
Oil
KettleBodied Linsee? Oil Q Bohy
.
90
7 E% 7
011
LightPressed Menhaden Oil
Raw China Wood Oil
6
10%
T
90 10%
4
4
Zinc suifide
4
4
4
4
Titanium dioxide
4
7
+ 2% -
8
5
8
6
9
8
7
Medium Chrome Yellow
964
-
Mixture of Higher Alcohol8
11
11
+-
7
+ 1 0 2-
11
11
4
6
11
11
5
7 957 5 8 5
5
6
4
11
11
4
5
11
11
5
5
11
11
90
4
4
’
90 10%
T
98
+-
Lauric Aaid Reacted aolidified
7
7
6
90
Lithopone
7 98 2% 6
Mineral Oil SAE 30 Mineral Neutral Spirita
5
10%
4
Jozite
Olive Oil
Reacted solidified
4
6
HighAcld-No. Refined Linseed
Reacted solidified
7 9557 5% 7
+-
Reacted aolidified
Reacted solidified
+-
5
10
5
4
5%+
Prussian Blue
9
8
10
9
Ultramarine Blue
6
11
10
7 95 5%
9
11
9
g28% Lamp black
T 4
6
8
11
5
9
11
11
11
6
9
9
11
11
28% T
+-
E%7
Talc Silica
9 9
9 9
9 9
9 9
9 4
Blanc fixe
4
5
7
5
4
6
5
7
9
9 10
6
+ 5% -
95 9
9 9
11
11 11
11 11
11
11
e?
9
%:g 7
9057 10%
Columns 5 and 6 of Table V contain datd‘on the electrostatic responses of pigments in the paints formulated as shown in Table IV. In order to correlate dispersion of pigments in paints with effect of electrostatic response, each paint was subjected to the following test: Five grams of the paint were placed in a glass cylinder, diluted with 125 ml. of mineral spirits, and thoroughly agitated by shaking. The appearance of the
+-
7 95 5%
+-
5
10
F
mixture was,,then observed. I n some paints the pigment dispersed a n d ib others flocculated. If complete dispersions were obtained, the pigments remained in suspension for a considerable length of time withon? flocculation. When flocculation of the pigments occurred, the pigments settled out rapidly. The results of these tests are given in Table V, column 7. T o investigate the relation between flooding and electro-
INDUSTRIAL AND ENGINEEHING CHEMISTRY
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I
I
FIQWS
4 TO 11.
REPRESENTATIVE TYPE8
OF ELECTROSTATIC
RESPONSE ( X N )
VOL. 29, NO. 5
INDUSTRIAL AND ENGINEERING CHERIISTRY
MAY, 'I 937
569
TABLE 111. ELECTROSTATIC RESPONSEOF MIXEDPIQMENTS IN FRESHLY PREPARED AND AGEDSUSPENSIONS Freshly Prepared 90% raw
linseed
oil
Raw
Lightpressed
oil, 10%
neutrd 11
oil
oil
Q oil
4
4
4
6
4
907 10% 6
4
SO%+ 6
Miqeral
Mineral oil
kettle-
SAE 30 linseed Menhaden bodied
Pigment Zinc oxide and Ultramasine Blue Zinc oxide and lamp black
11
11
Jozite and baaic carbonate white lead
4 4
4
4
io
-
+
0 -
90
10% Chrome Yellow and Prussian Blue
11
4
4
Raw
SAE 30 linseed
6
9S%-
70
2%i-
6
30%7
4
neutral
oil
11
5
':@,
Aged 3 Weeks 90% raw linieed Lightoil, 10% pressed kettleMenhaden bodied oil Q oil 4 5
95 0 5%
6
11
5
4
6 997 1%+ 6
11
5
4
5
7
98% 11
72 %
Kettlebodied linseed oil Q bddy 6
6
4
98
'%7
2%;
2%4
+
-
kethrebpdied Q oil 2 8 7 mineraP spirits 4
+ 6
6
6
6
-
%& gi@T 6
6
965%
;%T
TABLEIV. PAINTCOMPOSITIONS so.1 Pigment : Zinc oxide Ultramarine Blue Vehicle : Raw linseed oil Mineral spirits Drier" No. 2 Pigment; Zinc oxide Lamp black Vehicle: Raw linseed oil Mineral spirits Driera NQ. 3 Pigment: Jozite Basic Carbonate white lead Vehicle: Raw linseed oil Mineral spirits Drier"
% by Weight 90 10
50
50
90
5 5
No. 5
Pigment: Zinc oxide Ultramarine Blue Vehicle: Raw linseed oil Kettle-bodied Q oil Mineral spirits Driera
0
90
50
10
80 10 5 5
50
No. 6
98 2
50
50
90
5
70 40
60 30 80 5 5
Pigment: Zinc oxide 9s Lamp blark 2 Vehicle: Raw linseed oil SO Kettle-bodied Q oil 10 Mineral spirits 5 Driera 5
No. i Pigment: Jozite 40 Basic carbonate white lead 60 Vehicle : Raw linseed oil 80 Kettle-bodied Q oil 10 Mineral spirits 5 Driera 5
50 50
70
30
No. 8
No. 4 Pigment: Medium Chrome Yellow Prussian Blue Vehicle: Raw linseed 011 Mineral spirits Driera
% by Weight
50
66'/3 33'/a 50
90 5 5
Pigment: Medium Chrome Yellow 662/s Prussian Blue 331/a Yehicle: Raw linseed oil 80 Kettle-bodied Q oil 10 ,Mineral spirits Driera
50
No. 9 Yo by Weight Pigment: 50 Zinc oxide 90 Ultramarine Blue 10 Vehicle: 50 Light-pressed Menhaden oil 90 Mineral spirits 5 Drier" 5
No. 13 Pigment: Zinc oxide Ultramarine Blue Vehicle Minerml : oil Mineral spirits
69 31
No. 10 Pigment: Zinc Lampoxide black Vehicle: Light-pressed Menhaden oil Mineral spirits Driera
No. 14 Pigment: Zinc oxide Lamp black T'ehicle: Mineral oil Mineral spirits
98 2
No. 11 Pigment: Jozite Basic carbonate white lead Vehicle: Light-pressed Menhaden oi! Mineral spirits Driera No. 12 Pigment: Medium Chrome Yell o w Prussian Blue
50
9: 50 90 5 5
io 40
60 30 90 5
Liquid naphthenete consisting of 4.2% lead and 0.8% manganese as metal.
static response, the seventeen paints were applied to clean sheet-metal panels. The flooding of the paint can be readily determined by disturbing the surface of the film with a spatula or by lightly rubbing the finger over the moist film. If flooding is present, the new surface is a different shade from that of the undisturbed surface. The flooding pigment tints the undisturbed surface; the other pigment tints the disturbed surface. The results of these tests are given in column 4,Table V. The estimated particle size range of the pigments used in making the paints is recorded in column 3, Table V. These data were obtained by examining amounts of the pigments at 1800 diameters.
Discussion The mixtures of esters and organic acids, the organic acid, and the mixture of higher alcohols are polar-nonpolar com-
36.8 90 10
63.2
36.8
03.2 69 31
50 40
60 69 31
50
5
50
662/~ 331/s
50
:
No. 15 Pigment: Jozite Basic carbonate white lead Vehicle : Mineral oil Mineral spirita
% by Weight
50
90
5 5
No. 16 Pigment: Medium Chrome Ye1,low Prussian Blue Vehicle: Mineral oil Mineral spirits
No. 17 Pigment: Medium Chrome Yel!ow Prussian Blue Vehicle: Kettle-bodied Q oil Gineral spirits
36.8 662/8
33vs , 03.2
69 31
28
pounds; the hydrocarbons are nonpolar. Tables I and I1 show that in nonpolar compounds all the pigments have a definite lines-of-force arrangement (Figure 11); with the polar-nonpolar compounds almost any type of response may be expected, depending upon the pigment used. For example, zinc oxide, when freshly rubbed out in raw linseed oil, migrates to the anode (Figure 4)and is negatively charged. Upon aging this paste, the zinc oxide migrates to the cathode (Figure 5) and is positive in charge. I n lauric acid and higher alcohols, zinc oxide migrates to the cathode (Figure 5 ) , and when in mineral oil or mineral spirits the particles do not migrate to either electrode but assume a lines-of-force arrangement. In general, with polar-nonpolar compounds the pigments tend to assume either a positive or a negative charge; pigments suspended in nonpolar compounds form a lines-of-force arrangement.
TABLE v. 2
1
7 ,
ELECTROSTATIC
Zinc oxide { Ultramarine Blue
Jozite Basic carbonate white lead
Estd. Particle Siee Range of Pigments, Microns
% ::!? }
IfR. 1 Lamp black
4
Same
No flooding
{$
~
~
~
n
95%-
~ { : ~ ~1w ~ Prussian ~ Blue , ” ~
12
16
No flooding
Yellow { Chrome Prussian Blue
98%-
~
Same Same
17
4
white lead Same
8
4 4 4
11
11 16 4
Pigment Flooding
5 6 Electrostatic Response Pigment paste Paint diluted diluted with with additional supernatant vehicle vehicle
zinc Oxide Same Same No flooding
0.1 to 2.1
O3toOS 0:05 to 45
1
Theoretical Considerations
RESPONSE O F PIGMENTS
4
3
Paint Formula Pigments Used in No. Paint
5 9 13
VOL. 29, NO. 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
570
Prussian Blue
6
6 11
2%+ 5 % f
4 4 6
9 8 % i l 2%+
6 95%-
5%+
The effects of the different pigments on one another in some of the various vehicles are shown in Table 111. I n the case of mixed pigments the electrostatic response of the combination seems to be different from that of the separate pigments. This may be shown by comparing the data in Tables I and I1 with data in Table 111. For instance, when Medium Chrome Yellow and Prussian Blue are suspended in kettle-bodied oil of Q body, each gives the type of response shown in Figure 11; but, when the two pigments are mixed in this vehicle, approximately two-thirds of the pigment combination is negative and one-third is positive. Upon dilution of this mixture with mineral spirits to paint consistency, approximately 95 per Eenb is negative and 5 per cent is positive. These data were also confirmed by the investigation recorded for paint 17, Table V. The data in Table V show that in paints 1, 5, and 9 the pigments in the paint vehicle are positive, the finer size zinc oxide floods out, and the paints, when diluted with mineral spirits, show a dispersion of the pigment. I n paints 2, 6, and 10 the pigments in the paint vehicle are positive, the finer size lamp black floods out, and, when the paints are diluted with mineral spirits, they show a dispersion of the pigment. In paints 3 , 7 , and 11 the pigments in the paint are approximately all positive. The finer size basic carbonate white lead floods out, and the paints, when diluted with mineral spirits, show a dispersion of the pigment. Zinc oxide is present in paints 1, 5, and 9, and 2, 6, and 10. I n the first group the zinc oxide is the smaller particle pigment and floods out; in the latter group the zinc oxide is the coarser pigment and does not flood. In paints 4, 8, 12, and 17 the pigments in the paint vehicle are approximately all negative. The finer size Prussian Blue floods out; and, when the paints are diluted with mineral spirits, they show a dispersion of the pigment. However, in paints 13,14,15, and 16, when the pigment in the vehicle is subjected to an electrostatic impulse, it responds with a lines-of-force arrangement. With these paints no flooding occurs. When the paints are diluted with mineral spirits, the pigment flocculates.
7
The photomicrographs of the various types of responses show three distinct types: (1) The majority of the particles are attracted to the anode; (2) 5 Dispersion the majority of the particles 5 Dispersion 4 Dispersion are attracted to the cathode; 11 Flocculation and (3) the particles align themselves between the elec5 Dismrsion trodes in a l i n e s - o f - f o r c e 5 Dispersion 4 Dispersion arrangement. Figure 4 illus11 Flocculation trates the first type, Figure 5 the second, and Figure 11 the 5 Dispersion third. The other types of re7 Dispersion sponses may be any combina98%+6 2%tion of these three. It is asDispersion 9 6 % r 1 5%sumed that the particles which Flocculation are a t t r a c t e d to the anode carry a negative charge, and 4 Dispersion that those which are attracted 4 Dispersion 6 Dispersion to the cathode carry a positive 9 8 % i l 2%+ Flocculation charge. To explain the linesof-force arrangement, it is as6 Dispersion sumed t h a t e a c h p a r t i c l e 96%5%+ carries both a positive and a negative charge, and, when they are under the influence of the electrostatic field, the particles arrange themselves in the same manner as iron filings under the influence of a magnet. Bodies carrying like charges repel each other. The relation existing between dispersion and electrostatic charge can be explained on this basis. If the pigment particles in a paint are either positively or negatively charged, they should repel one another with the result that each particle will be suspended in the medium apart from one another, resulting in what is termed a ‘(dispersion.” I n a dispersion, the finest particles flood out as shown in Table V, columns 3 and 4, probably because they are suspended as individual particles and are more susceptible to the convection currents set up within the film. These convection currents may be caused either by the settling of the coarser particles or by the evaporation of the volatile principle in the paint, or by a combination of both. Furthermore, oppositely charged particles attract one another. It is assumed that particles suspended in a nonpolar medium have both a negative and a positive charge. With this assumption we can visualize how oppositely charged ends of these particles may be attracted to one another to such an extent that large groups, known as flocculates, are formed. Since the fine and the coarse pigment particles carry both charges, all of the particles may go into the makeup of a flocculate, with a resultant lack of flooding (since there are no fine particles to flood out). Although flooding is not directly caused by the type of electrostatic charge carried by the pigment, it is a factor involved in this phenomenon. The type of electrostatic charge carried by the pigment particles in a paint seems to have a direct bearing on dispersion and on the flocculation of these pigment particles. Type qf Suspension in Mineral Spirits
Conclusions 1. When under the influence of an electrostatic field: Pigments exhibit an electrostatic charge, the nature of which is dependent upon the suspending medium. b. I n general, polar-nonpolar compounds cause pigments to assume either a positive or a negative charge. a.
MAY, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
c. The pigments which are suspended in nonpolar compounds exhibit a simultaneous positive and negative charge. d. Mixed pigments may exhibit a charge different from that exhibited by the individual pigments when suspended in a polar-nonpolar medium.
2. When mixed pigments exhibit either a positive or a negative charge in a polar-nonpolar medium, they will disperse when the mixture is diluted with mineral spirits. 3. Mixed pigments which exhibit a simultaneous positive and negative charge in a nonpolar medium, flocculate when the mixture is diluted with mineral spirits. 4. Flooding of the pigment of smaller particle size is present when the mixed pigments, while suspended in a polar-nonpolar medium, exhibit either a positive or a negative charge. 5. With pigments that disperse, flooding occurs with the pigment of the smaller particle size. 6. Mixed pigments which exhibit a simultaneous positive
571
and negative charge in a nonpolar medium, do not flood, regardless of the variation in the range of the particle sizes of the pigments. 7. Flooding is not present if the pigment is flocculated.
Acknowledgment The author takes pleasure in expressing his appreciation to J. J. Rankin and associates on the technical staff of the St. Joseph Lead Company for their helpful suggestions and criticisms during the preparation of this manuscript.
Literature Cited (1) Edelstein, Edwin, Am. Paint J . , 17, No. 53A, 11 et seq. (1933). (2) Ladd, E. V., Ibid., 15, No. 51E, 13-14 (1931).
RECEIVED September 14, 1936. Presented before the Division of Paint and Varnish Chemistry at the 92nd Meeting of the American Chemioal Society, Pittsburgh, Pa., September 7 to 11, 1936.
Fractional Distillation of Cracked and Polymer Gasolines A cracked and a polymer gasoline were fractionated in a hundred-plate column. Unlike the polymer gasoline, the cracked gasoline fractionates similarly to a Bradford straight-run gasoline as far as the general shape of the refractive index curve is concerned. The division of the cracked gasoline into molecular size approximates that of the straight-run gasoline. This is not true of the polymer gasoline. Blends of the polymer gasoline varied in octane number from 72 to 82 ; blends of the cracked gasoline varied from below 41 to 75.
T
HIS laboratory fractionated various straight-run gaso-
lines in efficient distillation columns and found marked differences in chemical composition (IO). At the same time certain fractions of particular value were obtained. Similar distillations of cracked and polymer gasolines should yield information regarding their composition and fractions with different properties and uses from those obtained from straight-run gasoline. Accordingly, a polymer and a cracked gasoline were fractionated. Ipatieff and co-workers hqd previously studied polymer gasoline (I, 4, 6). The polymer gasoline was obtained from the Universal Oil Products Company. This gasoline was produced commercially from a stabilizing unit for cracked gasoline, with a capacity of 3,000,000 cubic feet of cracked gas per day. The olefin content of the cracked gas was 25 per cent propene and butenes. The gas, under a pressure of 200 pounds per square inch and a temperature of about 232" C. (450" F.), was passed over solid phosphoric acid catalyst in a series of four
C. 0. TONGBERG, J. E. NICKELS, S. LAWROSKI, AND M. R. FENSKE The Pennsylvania State College, State College, Pa.
reaction chambers. The yield of polymer gasoline was 4.3 gallons per 1000 cubic feet of gas, which represents about 85 per cent of the propene-butenes present in the gas. The cracked gasoline was obtained from the Kendall Refining Company, Bradford, Pa. It was the product of a two-coil selective Dubbs cracking unit, where the feed was 20 per cent kerosene, 10 per cent foots oil and slack wax, and 70 per cent gas oil, all of Pennsylvania origin. The unit was processing about 1550 barrels per day, t o give a 74 per cent gasoline yield in a nonresidue or coking type operation. The No. 1 furnace coil operated a t 499OC. (930" F.) and 450 pounds per square inch pressure; the No. 2 furnace was run at 529" C . (985" F.) and 475 pounds per square inch pressure. The properties of these two gasolines are given below; for purposes of comparison a straight-run Bradford gasoline is included. A. 9. T. M. Engler Distn. Initial b. p. 30% 40% 50 % 60% %
;;
90% End point Gravity 'A. P. I. Octane hro. C. F.R. motor method
-Cracked-
' C.
-Polymer-
F. 86 129 164 201 236 268
30 54 73 94 113 131 152 306 171 339 189 372 208 406 219 426 58.3 66
-Straight-RunC. O F. 58 136 40 104 85 185 158 70 91 87 196 188 95 102 203 215 99 211 113 236 218 126 103 258 136 108 227 277 243 309 154 117 275 337 169 135 328 370 188 164 220 428 210 410 66.2 62.3
C.
81
O
F.
42
The distillations were run in a 0.95-inch i. d., 39-foot column with approximately one hundred theoretical plates when
