Depolymerization of Butylene Polvmers J
F. G. CIAPETTA, S. J. MACUGA, AND L. N. LEUM The Atlantic Rejining Company, Philadelphia, P a . Catalytic depolymerization of Cs homopolyrners of isobutylene and its copolymers with n-butylene has been studied with the object of making pure isobutylene. Attapulgus clay was found to be an excellent catalyst for this depolymerization, as it produced a Ca stream from homopolymers of better than 99o/c isobutylene. With various codimers as feeds, isobutylene concentrations of 90 to 9870 were obtained. Mass spectrometer analyses of both gaseous and liquid products on two experiments showed that carbon skeleton isomerization of the C8 olefins accompanied depolymerization. Evidence of the isomerization of 2,4,4-trimethyl-l- or -2-pentene into 2,3,4-trimethyl-l; or -2-pentene and 3,4,4-trimethyl-2pentene into 2,3,3-trimethyl-l-penteneYand changes of trimethylpentenes into dimethylhexenes was obtained. Explanations of depolymerizations and isomerizations by the carbonium-ion mechanism are given.
M
ETHODS of preparing pure isobutylene from C4 cracking gas streams have become important during recent years because of the need for this material in manufacture of synthetic rubber a n d plastics. The method in general use of selectively hydrating isobutylene to tert-butyl alcohol followed by dehydration to the olefin, although a means of preparing isobutylene of high purity, has certain disadvantages, chief among which is the highly corrosive nature of the dilute sulfuric acid used for the hydration. This work was undertaken to study the depolymerization of liquid polymers of isobutylene as an alternative method of preparing pure isobutylene. I n the course of the work both homopolymers of isobutylene and copolymers of the Cd olefins were investigated. The literature contains a number of references pertaining to the depolymerization of butylene polymers, but only a few of these indicate that high yields of pure isobutylene in the Cq fraction were obtained. Hurd and Eilers ( 7 ) as well as Moore and Shilyaeva (12) studied the thermal pyrolysis of diisobutylene. Although they obtained fairly highjields of isobutylene, the presence of other olefins, paraffins, hy rogen, and butadiene indicated that other pyrol tic reactions accompanied depolymerization. iebedev and Kobliansky (8) investigated the depolymerization of a number of isobutylene homopolymers over floridin catalysts at 175 to 200 C. They reported that the pentamer decomposes into dimer and trimer, the tetramer into two molecules of dimer, the trimer into the monomer and dimer, and the dimer into two molecules of isobutylene. Robertson (16) described the depolymerization of diisobutylene over catalysts wherein the olefin is diluted with an inert gas. He reported that 75% of the diisobutylene was converted er pass over a catalyst consisting of phosphoric acid on Attapufgus clay at 215' C. when the ratio of diluent to olefin was 20 to 1. Without the diluent and at comparable temperature and contact time conditions, 10% of the diisobut 1ene was converted to the monomer. Roetheli and Conn (17)ago described the depolymerization of isobutylene trimer over Florida earth or activated clay at temperatures of the order of 200" to 230' C. They claimed' the selective formation of isobutylene with practically no formation of carbon, methane, hydrogen, or hydrocarbon of fewer carbon atoms than isobutylene. I n a study of catalytic cracking of olefins, Greensfelder and Voge (4) found that diisobutylene and triisobutylene were exO
O
tensively converted to isobutylene at 400" and 350" C., respectively, over a synthetic silica-zirconia-alumina catalyst. Isomerization to n-butylene and hydrogen transfer to form butanes also took place. Approximately the same results were reported earlier by Egloff, Morrell, Thomas, and Bloch (2).
A large number of references are found in the literature on depolymerization and rearrangement of specific olefins accompanying dehydration of the corresponding alcohol with acidic reagents. I n this field the work of Whitmore and co-workers ( 2 1 4 4 ) has been especially productive. Pl'asarow (19, 14) also studied the depolymerization and isomerization of a series of C, to C ~ olefins, O employing 1-bromonaphthalene-4aulfonic acid. A consideration of the previous work on depolymerization suggested that the most logical attack for the development of a practical means of depolymerizing isobutylene polymers to obtain isobutylene of high purity was a vapor phase catalytic prqcess. Early work with several catalysts indicated a superiority of Attapulgus clay over the others tried for this operation, which led to a more extensive investigation of the action of this agent. (A considerable part of the data reported here was privately disseminated during the war to organizations concerned with the problem of manufacturing pure isobutylene.) EXPERIMENTAL PROCEDURE
APPARATUS AND PROCEDURE. A system of continuous flow experiments was used. The liquid polymer was pumped from a buret by means of a Tropsch-Mattox laboratory type bellows pump (19) through a capillary tube into a vertical catalyst tube suspended in a n aluminum bronze block furnace. This furnace with automatic temperature control has been described-e.g., (6). The hydrocarbon charge was passed downward through the catalyst bed. The product was conducted through a water-cooled condenser into a tared liquid receiver where the gas was separated. This gas was next led through a coiled tube cold trap immersed in ice water and then through a Sargent wet gas meter into a bottle where it was collected over brine. The catalyst tube, 28 mm. in inside diameter and 86 cm. in length, and the accessory equipment were constructed of Pyrex. A 7-mm. glass thermocouple well extended the length of the catalyst bed and a movable iron-constant thermocouple was used to measure the temperature at various positions in the bed by means of a Leeds & Northrup recording potentiometer. I n most of the experiments 30 ml. of catalyst were used in the tube extending over a length of 6.0 cm. Over the top of the catalyst bed some 20 or 25 cm. of glass wool were placed to act as a vaporizer and preheater. During the run a drop in temperature of 10 to 50 C. occurred in the bed, due largely to the endothermic nature of the depolymerization reaction. The temperatures reported in the data tables refer to the lowest temperature point in the catalyst bed. At the end of a run, the contents of the cold trap were transferred to the liquid receiver and the liquid product was debutanized through a ten-ball Snyder column equipped with an ice-water dephlegmator. The gaseous material from this distillation was combined with the gases collected during the depolymerization and, after cooling, the weight and gravity of the remaining liquid were determined. O
ANALYSES
GAS ANALYSIS. I n the early part of this work spectrometric equipment for gas analysis was not available. Because the main
2091
INDUSTRIAL AND ENGINEERING CHEMISTRY
2092
Freshly electrodialyzed attapulgite has a hydrogen ion dissociation considerably greater than the montmorillonites; this s u g gests that it is among the strongest clay colloidal acids. The clay used in this work had a surface area of 118 square meters per gram as measured by the Brunauer-Emmett-Teller method. I n general, this clay has a very low activity as a cracking catalyst, for gas oils.
object at the time was the preparation of a Ca stream of high isobutylene content, the method of gas analysis used consisted of 6rst removing the C4 fraction from the gas by distillation in a Podbielniak Heli-grid low temperature distillation column and then determining the isobutylene content of this fraction by the hydrogen chloride method of McMillan (9). Any material boiling higher than the C, hydrocarbon was combined with the debutaniaed liquid from the depolymerization run. Early attempts at determining isobutylene and n-butylenes in the Ccfraction by absorption in 64 and 87% sulfuric acid, respectively, were discontinued because of poor reproducibility. I n the last phases of this work, a Consolidated Engineering Company mass spectrometer was available for a more detailed investigation of the gas. The unusually high isobutylene content of the gases under consideration in this investigation required a slight modification of technique in order to determine small amounts of n-butylenes (If). The accuracy of isobutylene determination by this technique a t the concentration found in the work v a s of the order of * 0.370. LIQUID ANALYSIS. I n most of the experiments the liquid portion of the product was not analyzed, except for the inspections: gravity, bromine number, and an occasional distillation through a ten-ball Snyder column. I n a few selected ca3es (I), however, a complete analysis of the branched chain character of the hydrocarbons present was made by hydrogenating the liquid product, carefully fractionating the paraffiils produced, and analyzing the fractions by means of the mass spectrometer. CATALYSTS.The catalysts tried in this investigation included a synthetic silica-alumina cracking catalyst, a supported phosphoric acid polymerization catalyst, and Attapulgus clay.
HYDROCARBOXS. The polymers used in this work cover a variety of types of homopolymers of isobutylene and copolymer^ with n-butylene. The diisobutylene, triisobutylene, and "cold acid polymer" used may be considered homopolymers. The former was obtained from the Rohm and Haas Company and is the material commercially hydrogenated into pure 2,2,4trimethylpentane for use as a standard in determinations of octane number. The triisobutylene was made in the authors' laboratories as a fraction boiling from 172" to 175" C. distilled from a polymer made from Matheson isobutylene (95yo pure) absorbed in 67% sulfuric acid, followed by heating to form the polymer. The cold acid polymer is an industrial product, part of which was obtained from the Bayway laboratories of The Standard Oil Development Company and part from the Neches Butane Products Company, Port Neches, Tex. These two portions mav be considered similar. They are the product of the cold acid polymerization process where a Ca stream from cracking operations is passed through 60 to 6270 sulfuric acid in the cold t o absorb isobutylene, and the absorbate is heated to 115' C. t o form the polymer. This material is essentially a homopolymer of isobutylcne, but a small amount of n-butylene dissolves in the acid, so that 1 or 2y0 of copolymer is usually found in cold acid polymer. -4. variety of codimers were used in this work. They were all product,s of operations involving the polymerization of C, cracked gas st,reams over U.O.P.phosphoric acid-kieselguhr catalyst. Some were obtained from The Atlant,ic Refining Company's full scale commercial operation and others from pilot plant work being carried out a t the time this investigation wxs under way. These codimers vary in the amount of n-butylenc copolymerized with isobutylene-i.e., the ratio of n-butylene to isobutylene (n/i) consumed in forming the polymer has been varied by proper choice of the variables of temperature, pressure, and spacc vclocity. The polymer produced over phosphoric acid at n/i = 0, although substantially a homopolvmer of isobutylene, inasm.uch as no n-butylene was consumed, prbbably contains a greater number of Cs olefins than are found in cold acid polymer because of the greater isomerization tendency at, the conditions under which the former polymers n'ere made.
The first mentioned was the Universal Oil Products Company of '/*-inch pills. The phosphoric acid catalyst was a sample obtained from a commercial shipment of U.O.P. phosphoric acid on kieselguhr catalyst in the form of */ls-inch cylinders about 0.25 inch in length. The clay used in this work was Attapulgus Grade A material of irregular shape in 15- to 30-mesh granules calcined a t 900" F. prior to use. This clay is mined at Attapulgus, Ga., and is commonly used for decolorizing lubricating oils and for removing gumforming constituents of cracked gasolines. A typical analysis of Attapulgus clay or attapulgite, as it is also termed, free from volatile matter, is as follows:
B-5 10% alumina on silica catalyst in the form
Si02 AlzOr Fez01
MgO CaO
66.02 12.52 3.78
Table I shows the distillations of the charge stocks used in the work reported here. These distillations were carried out in a tenball Snyder column of about four or five theoretical plates. The data reported for stocks 1, 2, 8, and 9 were calculated from 1-liter distillations for preparation of charge stocks wherein any undesired lower or highcr boiling material was discarded. The data for the remaining stocks were from distillations of sniall quantities of the materials used in the experiments and show the normal column holdup as distillation residue.
10.19
3.41 4.08
Cndetermined
Vol. 40, No. 11
h'ot much is known about the structure of attapulgite, except that i t is a fuller's earth distinct from the montmorillonite type and closely related to the silicate, seprolite (10). I t has an ion exchange capacity much smaller than that obtained with montmorillonites and, as mined, it is essentially calcium-saturated.
EXPERIMESTAL RESULTS
TABLE I. No. Charge Ratio, CiHsn-CaHa/isoDensity, 20° C. Distillation, ' C.
INSPECTION D A T A ON CH.4RGE
1
2
Diisobutylene
Triisobutylene
*. 0.7168
..
6
7
8
9
3 4 6 Cold Pilot Pilot Pilot Pilot Acid Plant Plant Plant Plant Plant Plant Polymer Codimer Codimer Codimer Codimer Codimer Codimer
..
0.7599
0.7320
172.0 173.6 173.7 173.9 173.9 173.9 173.9 173.9 173.9 173.9 174.1 174.4 175.0
40.0 101.1 101.7 101.7 101,7 101.7 101.7
100.0 0.0
STOCKS
104.5
110.6 172.8 175.0 175.0 178.0
97.0 3.0
0
0.08
0.30
0.64
1.00
1.50
0.7309
0.7286
0.7339
0.7347
0.7351
0.7309
71.0
92.0 100.6 101.5 102.2
66.0 101.0 101.5 102.7 103.7 104.8 105.5 106.1 107.6 109.4
56.0 100.3
65.6
93.3
101.0 101.5 102.3 102.5 103.0 103.5 103.8
102,5
105.2 108.7 123.0
102.8 103.2 103.7 104.3 105,8 113.5
1ii:o
166.'0
6.4
5.2
93.6
94.8
148 0
176.0 177.0 96.6 3.4
102.8 104.6
105.4 106.2 107.0 107.7
108.8 111.1
119.5 175.8 176.0 96.6 4.4
loti: 1
... ...
... ... ... ... ...
...
.. .. .. ...
...
**.
iii:4
... ... 20i:i 100.0 0.0
...
lib: 5
100.0 0.0
-
PRELIMINARY IXVESTIGAAt the outset of this in-
TION.
vestigation, a number of materials were examined as possible catalysts for the vapor phase depolymerization of diisobutylene. These early experiments were limited to determination of gas yields, C d concentration in the gas, and isobutylene concentration in the C4 fractions. It was soon realized that Attapulgus clay was an excellent catalyst for this reiction and further study of other agents was abandoned in favor of a more extensive investigation of this clay. For
2098
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1948
ALY -- CLAY HsP04 - SiO2-Al
I
CA
O-DIISOBUTYLENE 0-DIISOBUTYLENE DIISOBUTYLENE
100
z 0
g OVER
CLAY
o ce.
'OLYYLR OVER >LAY
90
a a
D I ISOBUTYLENE
0
..
20
I
I
I
IIISOBUTYLENE 'R I ISOBUTYLEWL
0
a
8
-
DIISOBUTYLENE OVER H3PO4CATALYST
L
3 80
/
/
'// /
-
z OD I d
70
Y
'-?
3 60
k T M E O R E T I C A L EQUILIBRIUM / YIELDS OF ISOBUTYLENE / FROM DIISOBUTYLENE
i
0
'0
100
200
300
TEMPERATURE
400
500
C.
Figure 1. Catalytic Depolymerization Polymers
of
E
50 0
this reason most of the experiments reported here employ Attapulgus clay as a catalyst and only a few runs with two other catalysts, synthetic silica-alumina and phosphoric acid on kieselguhr, are shown for comparative purposes. Following the initial work with diisobutylene, other polymers of bobutylene were used as feed stocks, which included triisobutylme, cold acid polymer, and a number of codimers. Their source is described in the section on experimental procedure, and their distillation characteristics are given in Table I. Experimental results, shown in Table 11, were obtained at atmospheric pressures and covered a temperature range from 216 O to 428' C. Most of the runs were made a t space velocities of 2 ml. per ml. per hour; a few were conducted a t space velocities a8 low as 0.60 ml. per ml. per hour and as high as 3.22 ml. per
-
OL AY 1-01 ISOBUTYLENE -H3PO4 1-DIIBOBUTYLENE -8nOp-AI 203 I-COLD ACID POLYMER-CLAY
100
200
300
TEMPERATURE'
Butylene
Effect of temperature on C4 yield
)-DI ISOBUTY LLWE
Figure 2.
400 C.
500.
Catalytic Depolymerization of Isobutylene Homopolymers
Effect of temperature on i6obutylene concentration i n 0 fraction
ml. per hour. The experiments were less than 6 hours in duratiom except for three runs which were extended to 24 hours to obtain indications of catalyst life. The effect of temperature on the once-through yield of Cab for the three catalysts and various feed stocks employed is shown in Figure 1. Theoretical equilibrium yields of isobutylene from. the dimer, calculated from thermodynamic data reported by Thacker and co-workers (I??), are also shown in Figure 1. The calculated theoretical equilibrium yields of isobutylene and the experimental yields of C i s (essentially isobutylene) obtained from diisobutylene under the conditions investigated, appear t o be of the same order of magnitude. There is an indication that the trimer of isobutylene gives lower yields gf Ci's than the dimer but the difference. if actual. is small. Both A.ttaDulaus clav and. phosphoric acid on kieselguhr show similar activities for the depolymerization of diisobutylene. The activity of silica-alumina is somewhat obTABLE 11. EXPERIMENTAL DATAON CATALYTIC DEPOLYMERIZATION OF scured by the different space velocities that wereBUTYLENE POLYMERS employed with this catalyst and by the low Test Conditions Yields, Weight % of Feed ~~l~ over-all recoveries obtained in the runs which Hours Heavier 7 Isoindicate extensive coking of the catalyst and Run Feed Cata- Temp., Sp. vel., on than Over8 4 ~ 8 No. N0.a lystb a C. ml./ml./hr. teat C4's C4's Cs's all in Cd's probable loss in activity with time on stream, 24 1 A 216 1.10 3.0 73.7 26.4 0 . 0 100.1 97.0 Figure 1 also shows a number of scattered 25 1 A 260 1.08 3.5 43.2 57.0 0 . 0 100.2 94.3 32 1 A 319 2.09 6.0 20.6 79.7 0 . 0 100.3 100.0 points for the yield of Cd olefins obtained from 376 2.08 39 1 A 5.0 14.8 85.5 0 . 0 100.3 98.5 clay depolymerization of various codimers. The 428 2.08 40 1 A 5.0 11.6 85.0 0 . 0 96.6 100.0 yields are lower than that obtained from t h e 19 1 s 212 1.11 1.5 59.9 34.0 0.0 93.9 76.0 18 1 S 256 0.60 1.0 47.7 39.2 0 . 0 86.9 64.5 homopolymers of isobutylene, as might be ex12 1 S 360 3.22 0.5 17.4 69.2 0 . 0 86.6 85.0 pected. 16 1 P 217 1.03 2.0 68.7 30.6 0 . 0 99.3 91.3 26 1 P 263 1.01 23.0 55.4 42.5 0.0 97.9 91.2 The results listed in Table I1 show that under 41 1 P 318 2.05 4.0 11.6 85.0 0.0 96.6 87.0 the conditions employed, the gas produced in 2 A 76 263 1.95 2.0 50.5 50.7 0 . 0 101.2 98.0 the depolymerization of diisobutylene, triiso2 A 74 316 1.95 2.0 26.3 73.6 1.2 101.1 93.6 2 A 75 369 1.97 2.0 18.3 81.2 0.0 99.5 93.8 butylene, and cold acid polymer over the three 86 3 A 371 1.98 2.0 15.4 83.1 0 . 0 98.5 94.8 catalysts is composed entirely of Cd hydro84 3 A 374 2.03 2.0 16.6 87.2 0 . 0 103.8 98.0 carbons, with the possible exception of the prod320 2.06 2.0 44.5 54.3 0 . 0 98.8 100.0 uct from run 74. The isobutylene concentration 318 2.0 45.2 51.7 0 . 0 2.08 94.6 99.9 326 2.0 54.0 46.0 0.0 100.0 98.5 2.04 in the Cn fraction, however, is different for these 329 2.08 2.0 54.1 46.1 0.0 99.2 92.3 372 2.02 2.0 59.5 37.2 2.3 99.0 95.1 three catalysts; Attapulgus clay has a definite ad316 1.97 2.0 70.4 27.4 0 . 6 93.5 98.4 372 2.07 vantage. When diisobutylene was depolymerized, 2.0 59.5 37.9 2.3 99.7 92.8 428 1.95 2.0 51.8 41.1 4.6 97.5 90.2 Attapulgus clay showed isobutylene concentrations 0 See Table I. in the C4 fraction ranging'from 94 to 100% as 5 Catalyst A, Attapulgua clay. Catalyst 9,silica-alumina. Catalyst P,phosphoric acid on kieselguhr. compared to 87 to 91% for phosphoric acid on kieselguhr and 64 to 85% for synthetic silica-
. -
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
2094
Vol. 40, No. 11
- oo l
LL
0
8
60
I-
z
w 0 P
G
3 I
n
w a.
401
-I
w> rc Y
v
20
o Figure
-
I
1
5 3.
IO
15
HOURS ON TEST Catalytic Depolymerization Diisobutylene over Clay
CATALIST CLA7 SPACE VELOCITY - 2 NUMBERS REFER TO FEED
25
20
01 N o * " of
0
F i g u r e 4. alumina cracking catalyst. These results and those for other homopolymers are shown graphically in Figure 2. The other components of the C d fraction were not determined for the clay or phosphoric acid experiments but for one of the silica-alumina runs it mas found that 80% of the C4 fraction dissolved in 87% sulfuric acid; this indicated the presence of 20% paraffins. This evidence of hydrogen exchange is supported by the results of Greensfelder and Voge (A), who found 23% paraffins in the Cq fraction when 6370 of the diisobutylene charged was converted to gas over a silica-alumina-zirconia catalyst. As in the case of Ch yields, the concentrations of isobutylene in the Ca's for both triisobutylene and cold acid polymer are of the same order as those for diisobutylene. I n Figure 3 are shown two runs in which diisobutylene was passed over Attapulgus clay for periods of 24 hours as an indication of catalyst life. At the lower temperature of 262' C . there was a definite decrease in catalyst activity with time on stream. KOloss in activity was noted when operating at the higher temperature of 319 ' C . even though the conversion was significantly greater. Subsequent work on a pilot plant scale substantiated the laboratory indications of high catalyst life where throughputs as high as 1145 barrels per ton of clay were obtained a t temperatures around 350" C . with no indicated loss in activity. One run (run 26, Table 11) made at 262" C. with a phosphoric acid catalyst showed a decline in activity similar to that for clay ai the same temperature. As may be expected from the long catalyst life, Attapulgus clay after use in depolymerization does not show large deposits of carbon. It has a faint blue color as contrasted t o an original brown and analyses after considerable use show around 270 carbon, but this is probably due to residual polymer clinging to the surface of the catalyst. Figure 4 shows the yield of C , hydrocarbons and the concentration of isobutylene in the Ca fraction obtained in the depolymerization of a number of codimers over Attapulgus clay a t 320' C . as plotted against the n-butylene-isobutylene ratio of the codimers. The yields of C4 hydrocarbons decreased markedly and the isobutylene content of the Cq fraction decreased only slightly with increasing n-butylene-isobutylene ratio. These results might be interpreted as indicating a selective depolymerization of diisobutylene present in the codimer, but the actual yield of isobutylene obtained in many cases was higher than that which could be produced from the known or suspected diisobutylene content. The high isobutylene concentration in the Cq fraction from the codimer depolymerization could be attributed to an isomerization
TABLE
0.4
'
0.8
I t
1.2
I 1.6
I
2.0
CODIMER w/; R A T I O Catalytic Depolymerization of B u t y l e n e Codimers
EiTect of oodimer n-butylene-isobutylene ratio on Ci yield and isobutylene concentration in C1 fraction
of n-butylenes to isobutylene.on the surface of the catalyst follov ing depolymerization. This was shown to be unlikely, as 1-butene passed over clay under the conditions used for depolymerization showed no isomerization to isobutylene. The depolymerization of the dimer of n/i = 0, which should be essentially a homopolymer of isobutylene, produced 55% Cq hydrocarbons under conditions where diisobutyiene gives 80% of the same material. This is unquestionably due to a difference in Ca olefin composition of these two hamopolymers. Distillation of the liquid products of these depolymerization runs through a 4- or ;-theoretical plate column showed no marked change in composition over the feed when codimer was used as the charge. However, when homopolymers were charged a definite change in composition of the liquid product was detected. Figure 5 shows the distillation characteristics of the diisobutylene and triisobutylene used as the feed in run 32, and in runs 74 and 76, respectively, and the products from these runs. The iiquid product from run 32 boils appreciably higher than the diisobutylene feed, although it is still essentially in the Cg range. The two products from the triisobutylene runs are dissimilar, owing to different temperatures used in the depolymerization. At the lower temperature, and hence lower conversion, used in run 76, triisobutylene apparently decomposes into the monomer and a dimer composed largely of diisobutylene. At the higher temperature used in run 74 the liquid product is very similar to the liquid product obtained from diisobutylenr undpr the same depolymerizing conditions. From the results shown in Figure 5 i t was concluded that isomerization of the C S olefins accompanied depolymerization over clay, a t least at temperatures above 300 C. This was suspected t o be the reason why isobutylene in high concentration in the Cq fraction could be obtained by depolymerizing its copolymers v i t h n-butylene. T o learn the nature of these isomerizations, exhaustive analyses of the charge and both gaseous and liquid products of the depolymerization were required. Fortunately, a mass spectrometer became available for these analyses at the time this need developed. DETAILED ANALYSIS. I n order to study the depolymerization and isomerization reactions, two additional experiments were made wherein the hydrogenated feed and the products were analyzed by the mass spectrometer ( I ) . The reaction conditions, gas analyses, and yields for the cold acid polymer (run 118) O
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1948
are summarized in Table I, and for a plant codimer (run 119) with an n-butylene-isobutylene ratio of approximately 0.7 in Table V of the previous paper (1). I n order to fmd the effect of conversion on both the yield and the concentration of isobutylene in the Cd fraction, run 119 consisted of two passes wherein the product from the first pass was recycled. The results show that the gas produced in the depolymerization of cold-acid polymer is essentially isobutylene whose concentration in the Cq fraction is 99.3%. However, in the case of plant codimer the gas produced contains appreciable quantities of propylene, n-butylenes, and pentenes. The isobutylene concentration in the total gas decreased from 82.9% for the first pass t o 66.7% for the second pass. The over-all concentration of isobutylene in the gas was calculated to be 79.7% a t a total conversion of the feed of 59.3%. In the C4 fraction the over-all concentration of isobutylene was approximately 90%. The complete analysis of the hydrogenated cold-acid polymer feed and the liquid product as determined by means of the mass spectrometer ( I ) are summarized in Table 111. The calculations were made on the basis of 100 moles of octenes charged (in making this calculation the small amount of heptenes present in both the feed and product was eliminated from the liquid analysis). The last two columns show the number of moles of the individual hydrocarbons converted and formed during the reaction. The method of analysis of the liquid materials used in this work leaves the position of the double bond in the various hydrocarbons undetermined. To avoid confusion, the olefin names in the ensuing discussion in this section of the paper bear side chain numbers similar t o the numbers used in naming the corresponding paraffins formed by hydrogenation. The inability of the mass spectrometer to resolve the 2,2,4trimethylpentane and 2,2-dimethylhexane combination does not offer serious difficulty in interpreting the reactions occurring during depolymerization, because the small amounts of the other dimethylhexanes found in both thc feed and product indicate that the 2,2-dimethylhexane content is probably very low. The data of Table I11 substantiate the qualitative indication of isomerization previously obtained. It can be calculated from these data t h a t 72.2% of the 2,2,4-trimethylpentenes present in the original charge are converted into other products. Of this diisobutylene undergoing reaction 83.0y0 can be accounted for
1801
I
I
I
I
TRI ISOBUTY LENE W E D TO RUN8 7 4 AND 7 6
160
6
CLAY
0
3
c I4O
CATALYST
t
L i a u i o PRODUCT RUM 7 6
-RUN
74
I
80 0
I
I
I
I
20
40
60
80
PERCENT
DI ST I LLED
Figure 5. Catalytic Depolymerization of Diisobutylene and Triisobutylene Distillations of liquid products
I(
2095
T ~ I 111. X DEPOLYMERIZATION OF COLDACIDPOLYMER OVER CLAYCATALYST, RUN 118 Comoosition. Mblesa ' Based on 100'Moles of Octenea Charged I n feed I n product
nydrocarhon Found
r; RE
... ...
Propylene Propane Isobutylene Isobutane n-Butylene n-Butane Pentanes and pentenes Liquid (after hydrogenatiuu) 2-Methvlheotane
0.3 0.2
... ... ... ...
116.0
0.2
0.4
0.2
...
0.5
0.0 0.0 0.8 0.1 0.1 0.0
96.4
2,2-Dimethylhexane \ 2.2,3-Trimethylpentane 2,3.3-Trimethylpentane 3 3-Dimethylhexane 2:3,4-Trimethylpentane Summary Octenes Moles of octenes + 2 iso-
}
CAH.
MzGLbf octenes + isoC4H8 n-C4Hs Moles of ootenes + CSHE C6HlO Total moles of octenes formed and accounted for by above reactions Oc-tenes formed and accounted for (mole yo of octenes converted) Unaccounted for Propane Isobutane n-Butane Pentanes and pentenes
+
Composition Change, Moles Converted Formed
+
Trace Trace
...
0: 1
0.1
26.8
2.5 0.0 0.1
1.7
69.6 0.8
0.8 10.8
..
100.0
41.1
..
70.6
...
...
0.8 10.7 11.7 57.8
...
0.4
...
0.3
...
70.2
...
99.4
0.2 0.2 0.2 0.2
Both feed and products adjusted for C? oontent in feed.
by the formation of isobutylene and 15.4% in isomerization to olefins of the 2,3,4-trimethylpentene structure, making a total of 98.4% of the diisobutylene disappearing which can be attributed t o these twq reactions. It may also be inferred from these figures t h a t the rate of depolymerization under the experimental conditions used is five times as rapid as the rate of isomerization. The results in Table I11 also show that on the basis of 100moles of octenes charged, 0.8 mole of 2,2,3-trimethylpentenes disappeared while a like amount of a mixture of 2,3,3-trimethylpentenes and 3,3-dimethylhexenes, shown to be mainly the former ( I ) , was formed. It should not be inferred, however, that isomerization of 2,2,3- into 2,3,3-trimethylpentenes is the only r e action the former undergoes, as formation of n-butylene in small amount is probably due t o a depolymerization of this olefin. The results also indicate t h a t 0.2 mole of 2,3-dimethylhexenes disappeared while 2,s- and 3,bdimethylhexenes were formed (0.1 mole each). However, because of the small amounts of the dimethylhexanes present in the feed and product, and the accuracy of the analyses, these data should be considered as only an indication of the occurrence of this isomerization. If the reactions producing the small amount of propylene and n-butylene are assumed to involve CSolefins as listed in the table summary, a mole balance of octenes converted and accounted for amounts t o 99.4%, a figure that indicates good over-all accuracy but has no bearing on the individual changes. Table i V shows the composition and changes in composition accompanying the depolymerization of codimer over clay; 100 moles of octenes charged to the initial depolymerization were used as a basis for comparison. Elimination of heptanes and the material boiling higher than the octanes was believed justified, inasmuch as the detailed analyses showed that no depolymerization of these materials 'cook place. The inability of the mass spectrometer to resolve the 2,2,4trimethylpentane-2,2-dimethylhexane,and the 2,3,3-trimethyl-
INDUSTRIAL AND ENGINEERING CHEMISTRY
2096 TABLE
Iv.
DEPOLYMERIZATION O F CODIMER OVER CLAY CATALYST, RVN119 Composition, Moles Based on 100 Moles of Octenes Chargeda
In Hydrocarbon Found feed Gas Propylene Propane Isobutylene ... Isobutane n-Butylene n-Butane Pentenes Pentanes ... Liquid product after hydrogenation 2-Met hylheptane 0.1 3-Methylheptane 0.2 4-Net hylheptane 0.2 2 3-Dimethylhexane 5.0 2:4-Dimethylhexane 2.4 2,5-Dimethylhexane 1.3 3 4-Dimethylhexane 1.6 2'2-Dimethylhexane 2:2,4-Trimethylpentane 3,3-Dimethylhexane 2,3,3-Trimethylpentane 2,2,3-Trimethylpentane 16.0 2,3,4-Trimethylpentane 34.9 Summary Octenes 100.0 Mo_1eBsof octenes +2 iso-
... ... ... ... ..... .
C4H8
Moles of octenes + isoC4Hs n-ChHs Moles of octenes +.CzHa CSHIQ Total moles of octenes formed and accounted f o r bv above reaction Octenes formed and accounted for (mole 7% of octenes converted) Unaccounted for
+
+
Pronan~
Composition Change, Moles Feed-1st Pass 1st Pass-2nd Pass ,Feed-Znd Pass ConConConverted Fbrmed verted Formed verted Formed
pas4 product
product
1.9 0.3 70.4 0.4 6.4 0.6 4.7 0.6
3.5 0.8 26.2 0.4 3.8 0.2 3.9 0.2
0.5 0.7 0.3 7.8 5.0 3.0 2.2 3.4
1.0 2.0 0.3 8.8 6.3 3.4 2.9
.... *. ... .
1.0
29.0
4.6 7.1 22.4
2.6 2.7 6.5
1.3 8.9 12.5
pa-s
.. .. .. .. .. ..
1.9 0.3 70.4 0.4 6.4 0.6 4.7
.. .. ..
0.6
.* ..
0.4 0.5 0.1 2.8 2.6 1.7 0.6
.. .. .. .... .. ..
2.4
..
8.6
.. ..
.. *. ..
1.0
1.3 0.4 0.7 "
.. t .
31.4 3.3 13.3 28.4
0.9 1.8 0.1 3.8 3.9 2.1 1.3
.. ..
... .
57.0
37.5
51.7
24.7
5.2
76.4
13.9
..
..
..
32.0
..
11.2
..
43.2
.. ..
..
6.4
...
..
..
*.
1.9
...
..
..
..
49.0
...
.. ..
..
..
94.7
.. ..
..
..
0.3
..
...
.
I
..
,. ..
10.2
3.5 23.7
,.
72.7
96.0
,.
95.3
0.8
__ ..
3.8
0.2
6
i.1
0.8
0.5 1.3 0.0
I
5.4 96.6 0.8 10.2 0.8
...
...
8.7
2.0 4.4 15.9
*.
3.5 0.8 26.2 0.4 3.8 0.2 3.9 0.2
..
5.4
1.1 0.8 0.8
Adjusted for CT'Sand heavier than Cs contents.
pentane-3,3-dimethylhexane conlbinations creates some difBculty in interpreting the course of the reaction of the various olefins over clay, as at least some of the olefins giving these determined dimethylhexanes on hydrogenation are believed t o be present in the feed. Analyses of a number of commercial hydrocodimers by the American Petroleum Institute Research Project 6 a t the Kational Bureau of Standards (3) have shown that codimers produced over U. 0. P. phosphoric acid catalyst contain as much as 2.7 * 1.4% of 2,2-dimethylhexane but do not contain 3,3-dimethylhexane. Because of these results, the former has been considered in the following interpretation but the latter has been ignored. The data of Table I V reveal that of the octenes, the trimethylpentenes, with the possible exception of 2,2-dimethylhexenes, are practically the only components of the butylene codimer that undergo reaction in the presence of Attapulgus clay under the conditions studied. Except for the small conversion to CS, C4, and Cs paraffins, these trimethylpentenes were converted to olefins of lower molecular weight by depolymerization and to less highly branched octenes by isomerization. During the Erst pass, 77.9% of the trimethylpentencs converted was depolymerized to olefins of lower molecular weight and 16.8% mas isomerized to other octenes, mainly dimethylhexenes. I n the second pass, 74.9% of the trimethylpentenes was depolymerized and 21.1% isomerized. For the over-all reaction,77.0% of the trimethylpentenes was depolymerized to olefins of lower molecular weight and 18.2Yc was isomerized to less highly branched octenes. The octenes formed by isomerization from the trimethylpentenes appear to be mainly dimethylhexenes, although the formation of the methylheptenes cannot be entirely ignored.
Vol. 4'3, No. 11 Of the dimethylhexenes, thr 2,3- and the 2,4isomers werr the predominant compoundformed. The data of Table I V poiril out that the amount of t h r 2,2,4-trimethylpentenes disappearing is not sufficient to account for the number of moles of octenes depolymerized to isobutylene, I n the over-all reaction of 43.2 moles of the original 100 mole? of octenes charged were dcpolymerized to isobutylene and 31.4 moles of the origi. nal 32.4 moles of the 2,2,4-trimethylpentencs- 2,2 -dimethyl hexenes combination disappeared. In view of the observed isomerization of 2,2.4trimethylpentenes into 2,3,4trimethylpentenes in the cold acid polymer experiment, it is logical to assume that thc source of the excess isobutyl ene is the 2,3,4-trimethyl pentenes. I n other words, the isomerization of 2,2,4into 2,3,4-trimethylpentenc~i. is a reversible reaction and the formation of isobutylenr from the latter probably occur< in two steps:
It is interesting t o note the nearly constant molar ratio of 2,3,4 t o 2,2,4-trimethylpentenes in the first and second paw liquid products, 6.6 and 6.5, respectively, which indicates that under the conditions of depolymerization used, the equilibrium concentrations are obtained. The production of n-butylene is believed due to the depolv. merization of 2,2,3-trimethylpentenes (22): CHI CHI CH-&--&H-CR=CHI HI
CHI
I
--f
CHa-C=CH?
f CHz=CH-CRzCHi
or CHp-CH=CH-CHa
The number of' moles of octenes reacting t o form n-butylene mould account for 76.77c of the 2,2,3-trimethylpentenes disappearing. The propylene formed in the reaction is thought to be the result of depolymerization of one or more of the octenes into a pentene and propylene. The amount of propylene obtained in the first pass does not balance with that of the pentenes but there is fairly good agreement in the products of the second pass. It is possible that an error in experimental technique or analysis of either propylene or pentenes in the first pass product . is the cause of the discrepancy. A consideration of their structure indicates that the 2,3,4and the 2,3,3-trimethylpentenes could both be possible sourem for the formation of propylene. If the former were the source,
November 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
the data for the over-all reaction would indicate that 19 or 3oy0 of the 2,3,4-trimethylpentenes disappearing could be accounted for by this reaction, depending on whether calculations are based on the propylene or pentene figures. The amount of 2,3,4trimethylpmtenes converted into isobutylene through the 2,2,4isomer was about 41%, if the 2,2-dimethylhexenes are ignored, making a total of 60 or 71% of the 2,3,4-trimethylpentenes disappearing that have been accounted for. The 2,2-dimethylhexenes present in the feed would probably be isomerized into other dimethylhexenes and, as they were analyzed as a group with the 2,2,4-trimethylpentenes, their disappearance would be interpreted as too high a conversion of diisobutylene. This in turn would mean that a higher conversion of 2,3,Ptrimethyl pentenes into isobutylene took place through the 2,2,4-isomers than the 41% previously quoted. It is not likely, however, that there are sufficient 2,2-dimethylhexenes present in the feed to explain the entire disappearance of 2,3,4-trimethyIpentenes by the two depolymerization reactions postulated. Thus, if propylene is formed only from the 2,3,4-trimethylpentenes, some of the latter compound, part of the 2,2,3-trimethylpentenes, and all of the 2,3,3-trimethylpentenes disappearing would be isomerized into less highly branched octenes. On the other hand, if the propylene and pentenes were formed by the depolymerization of 2,3,3-trimethyIpentenes,the disappearance of the octenes of the latter structure and the remainder of the 2,2,3-trimethylpentenes not accounted for by the depolymerization into n-butylene and isobutylene could be explained by assuming that isomerization of 2,2,3-trimethylpentenes into the 2,3,3- compound took place prior to depolymerization. Some evidence of this isomerization was obtained in previous considerations of changes occurring in depolymerization of cold acid polymer. Table IV shows that 3.3 mole % of 2,3,3trimethylpentenes disappeared and that 3.1 mole yo of 2,2,3trimethylpentenes disappearing have not' been explained by depolymerization into n-butylene and isobutylene. This makes a total of 6.4 mole yowhich could be converted to propylene and pentenes, of which 5.4 and 8.6 mole yo,respectively, were found. Thus, if the 2,3,3-trimethylpentenes are the propylene source, only 2,3,4-triniethylpentenesmay be considered as isomerizing into less highly branched octenes.
carbonium ion which, depending on conditions, can either recombine with other unsaturated hydrocarbons or lose a proton and become another olefin as follows: CHa
CHs
CH~-&-CH?-&=CHZ
CHI
+
The experimental results reported in the previous section have shown a superiority of Attapulgus clay for depolymerization of butylene polymers over that obtained with synthetic silicaalumina cracking catalyst or solid phosphoric acid polymerization catalyst from the standpoint of selectivity of isobutylene production. An explanation of why this clay has such selective action is, presumably, connected with its surface character, of which little is known. Attapulgus clay, a t lower temperatures, will catalyze the polymerization of olefins, especially isobutylene (16). The character of the polymer produced from isobutylene over clay appears t o be similar to that formed in the presence of sulfuric acid. Therefore, it may be inferred that the mechanism of polymerization in the vapor phase over these solid catalysts is similar to mechanisms that have been proposed for liquid acid catalysts. Of these various mechanisms, the carbonium ion theory proposed by Whitmore ($0)probably has been most widely accepted as a means of accounting for the products formed. Whitmore and eo-workers ($%-!A$) have shown that olefins which form a carbonium ion containing the group R&-C-Cf, in the presence of acid catalysts, are susceptible to carbon-carbon cleavage a t the bond p to the carbon atom deficient in electrons. Such bond cleavage is brought about by the shifting of a bonding pair of electrons in order to satisfy the electronically deficient atom without carrying along the organic group t o which the dectrons were attached. This produces an olefin and another
CHa
Fi CHm-!%CH1-&CHI
1:
&Ha
HI
CHa
CHI
C&-&-CHZ-&CHX N
CHa
z 2 CHs=&-CHs
CHI
+ CHs-&+ +
&HI
&Ha CHm
+k
CHs=b-CHa
The high concentration of isobutylene in the gaseous producte obtained in this work indicates that these reactions predominate when butylene polymers are passed over clay. I n both the original feed and the products of the reaction, olefins with the same carbon skeleton structure but different double bond positions are undoubtedly present. However, in the reaction mechanisms shown, only one of these olefin isomers iF considered because isomerization involving the double bond probably occurs readily in the presence of the catalysts employed for the depolymerization reaction. The copolymers of isobutylene and n-butylene contain 3,4,42,3,3-, and 2,3,4trimethylpentenes in addition to diisobutylene. The n-butylene obtained in the reaction is believed due to depolymerization of the former (a$)according to the follonkg:
CHs CHa
I
I
CHa-C-CH-CH-CRB &Ha CHa CHa
CHa
e CHn-CH-CH-CHa
CHs&-bH-~H-CHa REACTION MECHANISMS
2097
+ CHs--b+ I
&HI
F!
CHI CHo
I
CHz=C--CHa
+k
As has been pointed out, the sourut: of propylene is thought t o be either the 2,3,4- or the 2,3,3-trimethylpentenes. If the former were the source the reaction would be C I h CHs CHa
CHa CHa CHa
4-
CHz=&--&H-&H-CHs
CHs CHs CHI
CH~-'$--~H-~H-CHI
CHs
F? CHa-&-CH-CHa
CHs-~-&H-(&H-CKa u
+ CHs-YH-CHs CHaCH=CHI
8
+6
which involves the splitting of an RZH-C-C-C
ion instead of + The rupture of these ions is probably connected #
R~-C-C-C.
*
with the electron release tendencies of alkyl groups and although at lower temperatures there may be some question as t o whether only two groups connected t o a carbon atom are sufficient to permit depolymerization, a t the temperatures used in this work, such rupture is not impossible. If 2,3,3-trimethyl-l-pent,ene is the source the following would be the mechanism:
2098
INDUSTRIAL AND ENGINEERING CHEMISTRY CHa CH3 CHa-C-C=CH-CHa I 1
QHa CHa
+ h F'
CH2=C-&-CHr-CHs
AH3
&Ha CHs CHI CH~-C-CH I I-CH~
+
-
H:
I
*
&Ha
CH3
+
i ?
*
Shift
I
CHa
CHa CH8
+ CHa=C-C-CHz-CHa I I
I
4-
I
C Ha
$I
CHa
&Ha CH3
CH3
1 + CHa-y-CHa-CHa
CHz=CH-CHa
In this case ai1 R3--C-C--C
t
G ~ C H ~ - A = C H ~ - C H ~4- I%
ion is involved in the depolymeri-
zation, but a shift of a proton and its bonding pair of electrons must be postulated in such a manner that a tertiary carbonium ion is converted into a primary ion. This is not a shift common to carbonium ions a t lovc.er temperatures but again may be possible under the high temperature condition used in this work. The analyses reported in the previous section show that isomerization of the octenes accompanies and, in some cases, probably precedes depolymerization. The substantial amount of 2,3,4-trimethylpentenes formed during the depolymerization of cold acid polymer can be considered only as coming from diisobutylene, which may be explained by the following carbonium ion changes: CHlr
+% +I
CHa-!2-CHa-&=CHa bH8
+
CHs-&-&--CH2--CHa
CHdH-&--CH%-CHa
CHa
CH3 CHI
Ha--C HaCHI: i? C Ha-C-0-CHz-CEi I I
CHI CH3
CHa CHs
+
H $
CHa CH? CEI&-&-C
CHI CH3 CH~~H-~-CIIICH~
Shift
CH8
T
Vol. 40, No. 1 1
CHa CHa CHa-C-CHy-b-CHa I
I
CHs CHs CHa
'
CHa-C= CH3 CHI H i :~ CH~-~-C+H-~H-CHI ? Shift
CHI
The only other isomeiizatioiis noted in this work are those of thc formation of less branched octcnes from the trimethylpentenes in the high temperature depolymerization of codimer. The origin of these compounds is obscured by the complex nature of the material charged to this depolymerization and by the uncertainty of the depolymerization reaction which gives rise to propylene. I n fact, some of these less branched octenes may not be formed by isomerization at all but by a combination of a secondary butyl carbonium ion with the n-butenes and with isobutylene. If such were the case, however, the amounts of these octenes found would require extensive isomerization of trimethylpentenes into the 3,4,4-trimethyl-2-pentene structure t o supply the required n-butylene. If the dimethylhexenes are formed from the trimethylpentenes by isomerization, a carbonium ion shift from a tertiary to a primary ion must again be postulated. Using 2,3,4trimethyl-2pentene as a likely source, the following reactions would explain the formation of the 2,3- and 2,4-dimethylhexenes: I
1
C-CH-CHa
+
bHs
CH3 CHa CHs H. C H Z - ~ H - ~ H - - ~ H - C H I Shift 4
CHa CHs CHa
CHa CH3 CH-!F--pH-kH--CHa
~Hr-&H-CH-hH--CHa I
CHs: F-?
CHs-C-CH-CH-CH3
l
F!
CHa CHa
I
CHs--CH=CH-LH-cH-cHI
CHa CHa CHs
CH3 CHs CHs
l
CHI CHa CIlr: ~2 CHi-CHe--i:H--dH-C!H-CHs Shift
Shift
&Ha
I
T
CH3 CHI CH3 CHs-~-CH--I:H-CHs I I
F;! CHa--d=
d--dH-CHa
4-
+ fi
fl
Hoog, Smittenberg, and Visser (6) also reported the isomerization of diisobutylene into 2,3,4-trimethylpentenes in the presence of supported phosphoric acid catalyst a t 140" C. The reversal of this reaction was indicated by the high yield of isobutylene obtained in the depolymerization of codimer in run 119. I n a study of the copolymerization of tert-butyl and secbutyl alcohol, Whitmore and eo-workers (21, 28) have suggested that the origin of the 2,3,4-trimethyl-2-pentene is 3,4,4-trimethyl2-pentene and that the former is obtained from the latter by a 1,3 shift of the methyl group and its bonding pair of electrons. The results reported here indicate that 2,3,4-trimethyl-2-pentene could, at least in part, be formed from 2,4,4-trimethyl-l-pentene in copolymerization, but not necessarily so, as the reaction conditions in the two investigations were greatiy different. The analysis of the liquid product of the depolymerization of cold acid polymer showed the presence of a small amount of the 2,3,3-trimethylpentane-3,3-dimethylhexane combination. As shown by infrared analysis ( I ) , this analytical combination is mainly 2,3,3-trimethylpentane. The formation of the corresponding olefin is probably due t o isomerization (see Table 111) of 3,4,4-trimethyl-2-pentene, suggested but unconfirmed by Whitmore (18):
More experimental evidence is needed to prove the origin of several of the products identified in this work. Depolymerization studies on relatively pure octenes such as 2,3,4trimethyl-2pentene, 3,4,4-trimethyl-a-pentene,and 2,3,3-trimethyl-l-pentene would be especially helpful. By extending such investigations to other less branched olefins and into a higher temperature range, it is possible that valuable information might be obtained leading to a general reaction mechanism of catalytic cracking of hydrocarbons. LITERATURE CITED
(1) Ciapetta, F. G., Macuga, S.J., and Leum, L. N., Anal. C h m . , 20, 699 (1948).
(2) Egloff, G., Morrell, J. C., Thomas, C. L., and Bloch, H. S., J.Am. Chem. Soc., 61, 3571 (193Q). (3) Glasgow, A. R., Jr., Streiff, A. S.,Willingham, C. B., and Rossini, F,-D., Petroleum Refiner, 25, No. 11, 527 (1946). (4) Greensfelder, B. S., and Voge, H. H., IND.ENQ.CHEM., 37,883 (1945).
November 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
(5) Grosse, A. V., Morrell, J. C., and Mattox, W. J., Ibid., 32, 530 (1940). (6) Hoop, H.,Smittenberg, J., and Visser, G. H., Cong. m o n d i a l petrole, $me Cong., Paris 1937, Vol. 11,p. 489. (7) Hurd, C. D., and Eilers, L. K., IND. ENG.CHEM.,26,776(1934). (8) Lebedev, S. V., and Kobliansky, G. G.,Ber., 63B,1932 (1930). (9) McMillan, W. A., IND.ENG.CHEM.,ANAL.ED., 9, 511 (1937). (10) Marshall, C. E., and Caldwell, 0. G., J . Phya. Colloid Chem., 51, 311 (1947). (11) iMelpolder,F.W., andBrown, R. A., Anal. C h m . , 20,139 (1948). (12) Moore, V. G., and Shilyaeva, L. V., J . Oen. Chem. (U.S.S.R.), 7 , 1779 (1937). (13) Nasarow, I. N., Ber., 69B,18 (1936). I (14)I b d , 69B,21 (1936). (16) Ramser, J., Atlantic Refining Co., unpublished data. (16) Robertson, A. E., U. S. Patent 2,196,363(April 9,1940).
2099
(17) Roetheli, B.E.,and Conn, M. E., U. S. Patent 2,314,457(Nov. 23, 1943). (18) Thacker, C. M.,Folkins, H. O., and Miller, E. L., IND.ENQ. CHEM.,33,584 (1941). (19) Tropsch, H., and Mattox, W. J., Zbid., 26,1338 (1934). (20) Whitmore, F.C., I b i d . , 26,94 (1934). (21) Whitmore, F. C.,Laughlin, K. C., Matusreski, J. T., and Surmatis, J. O., J. Am. Chem. Soc., 63, 756 (1941). (22) Whitmore, F.C., and Mosher, W. A.,Ibid., 68,281 (1946). (23) Whitmore, F.C..and Stahly, E. E., Ibid., 55,4153(1933). (24) Ibid., 67, 2168 (1945). RECEIVED June 4, 1947. Presented before the Division of Petroleum CHEMICAL SOCIETY, AtChemistry at the 111th Meeting of the AMERICAN lantic City, N. J.
Oil Composition in Alkaline Cleaning SAMUEL SPRING' AND LOUISE F. PEALE Frankford Arsenal, Philadelphia, Pa. Free fatty acid, present normally or as an additive in oil, facilitates the removal of oils from pickled steel surfaces. High free fatty acid content in the neighborhood of 10% reduces the ease of removal of sulfurized fatty or fatty oils from unpickled steel. Addition of oil-soluble sodium sulfonate soaps to mineral oils or lard oil results in improved cleaning, whereas its addition to sulfurized oils usually makes cleaning more difficult. The presence of considerable quantities of free fatty acid or oil-soluble sulfonate soap in oils, where effective in improving cleaning, reduces the differences normally found in cleaning pickled and unpiclrled steel or in the use of various alkaline cleaners. At nearly equivalent viscosities and free fatty acid content, the ease of removal of oils follows the series: mineral oil > sulfurized mineral oil > lard oil > sulfurized lard oil. In industrial processing, the addition of free fatty acid or oil-soluble soap to oils will facilitate cleaning provided these materials do not interfere with the functional application of the oils.
I
T HAS frequently been reported (2, S) that the type of soilin-
volved in a cleaning process determines the ease of its removal to a great extent. This paper presents data on this factor for a variety of oils in industrial use. I n addition, it concerns the process of addition of a component t o an oil before its application for the purpose of facilitating subsequent cleaning. This is in contrast with previous processes in which, prior to alkaline cleaning, parts are immersed in a solution of fatty acid in organic solvent (I) or in a solvent emulsion containing oil-soluble soap (4). This bears some relation t o the work of Speakman (6)who showed that the ease with which an oil can be removed may be modified by dissolving in it a few per cent of a polar substance. EXPERIMENTAL METHOD
The procedure used for evaluating the cleaners was similar to that reported previously (6). I n general, this consists of coating metal panels by immersion in the oil, followed b y drainage under standard conditions, particularly with regard to temperature. The panels are cleaned by a procedure in which time, concentra1 Present address, Whitemarsh Research Laboratories, Pennsylvania Salt Manufacturing Company, Wyndmoor, Pa.
tion, agitation, and temperature are controlled. After a prescribed rinsing operation, the panels are sprayed with water. This results in a uniform water film over the cleaned areas, whereas discrete droplets condense over the areas that have not been cleaned thoroughly. These delineated areas are sketched on graph paper having 100 squares, and the percentage of the panel area that has been cleaned is thus estimated. The cleaning index is the average value obtained for ten observations-that is, both sides of five panels. The reproducibility of the data has been indicated previously (6, 7 ) . I n the experimental work reported here, the tests were run at 60" C. for 5 minutes with agitation at 10 r.p.m. Except where otherwise stated, the cleaner was a solution of 1.5% sodium orthosilicate and 0.15% of an alkyl sulfonate type surface active agent. I n carrying out this investigation, care was taken to consider the factors found to be important in previous work. Thus, data were accumulated for cold-worked, oxide-covered surfaces both before and after pickling. The importance of the viscosity of the oil (Figure 1) required that comparisons be made at equivalent viscosities. I n addition, studies were made with mineral oils of different viscosity. RESULTS
EFFECT OF FREEFATTY ACIDCONTENT.The removal of lard oil from steel surfaces is dependent on the free fatty acid which is normally present in this oil. This i8 shown in Table I. Thus, removal of almost all of the free fatty acid from lard oil b y treatment with aqueous sodium hydroxide, fbllowed by thorough washing and drying, results in a considerable decrease in cleaning value. There is no difference between the effect of the naturally occurring free fatty acids and oleic acid since, after removal of the former, replacement with the latter gives similar cleaning performance. Increase of the free fatty acid content of prime lard oil b y addition of 1%oleic acid improves cleaning to a level of good performance but further increase t o 10% does not result in perfect cleaning. A lower grade of lard oil of normally higher free fatty acid content (4%) also gives this good level of cleaning. In addition to this, the presence of 3 or 4% free fatty acid lessens the difference between the results obtained with unpickled and pickled steel surfaces; this is normally large for lard oil containing 0.1 or 1.8% free fatty acid.
