Thermal Depolymerization of . Viscous 1soljut;lene Polymer
.
d
J
J. A. REID
AND
G . C. BAILEY'
Phillips Petroleum Company, Bartlesville, Okla. viscous isobutylene polymer was thermally depolymerized at pressures of 3-5 mm. of mercury, and at 10 and 1000 pounds'per square inch gage, under conditions which depolymerized from 26 to 94% of the charge. Increasing the pressure under which depolymerization occurred decreased the proportion of the gas and oil fractions in the product, and increased the proportion of intermediate liquid. Depolymerization at low pressure, under conditions where the product was continually removed from the reaction zone, gave the highest yield of products in the viscosity range of lube oils; also the viscosity indexes of these products were the highest obtained. Depolymerization under mild conditions produced mono-olefins, whereas under more drastic conditions the low boiling fractions of the products were more saturated than pure mono-olefins, and the high boiling fractions were less saturated.
of off-gas was measured by a meter, and samples of it were collected over mercury for analysis. The vacuum depolymerization was conducted in a 2-liter round-bottom flask heated on a sand bath. A water-cooled condenser, a receiver at ice temperature, a trap at dry-ice temperature, and a vacuum pump were assembled, in the order given. Pressure in the system was measured by a mercury manometer. A thermometer was so located in the flask that the liquid temperature during depolymerization could be determined. In each experiment the total liquid products were diitilled and fractionated in a vacuum fractionating assembly consisting easentially of a 3-liter glass kettle, an IS-inch fractionating column 2 inches in diameter packed with !/,-inch glass Raschig rings, and an air-cooled partially condensing still head. Distillation of a charge was started a t atmospheric pressure; to avoid further .depolyperization the pressure was reduced in steps to about 3 mm. of mercury. EXPERIMENTAL DATA AND DISCUSSION
T
HE production of oily polymers from low-molecular-weight
The charge for these experiments consisted of a composite of viscous products from the polymerization of isobutylene with zirconium tetrachloride catalyst under various conditions. These viscous products were residues from vacuum distillations conducted without noticeable depolymerization. The composite charge material had the following properties: light colored; clear;
mono-olefins has been studied by numerous investigators. Good summaries of work on this subject are given by Hall (8) and Sullivan (67and , some of the more recent developments are described in an article by Pritzker (6). In most cases polymerization of olefins with the objective of obtaining material in the viscosity range of lubricating oils produces polymers both more and less viscous than the desired product. Several investigators have suggested that the high molecular weight material can be partially depolymerized to give a further yield of oil (3,4 ) , but few data on this process have been reported. This paper describes some experimental work on the depolymerization of viscous isobutylene polymer at pressures of 10 and 1000 pounds per sqqare inch gage and 3-5 mm. of mercury.
TABLE I. THERMAL DEPOLYMERIZATION OF VISCOUS ISOBUTYLENB POLYMER
APPARATUS
Expt. No.
Pressure Lb./Sq. h. Gage"
Temp.,
C. 490-500 490-500 450-460 590-610 500-510 a
Charglng Rate
M!.]
Min.
%
Depolymerized
Wt. % Compn. of Depolymer Product Liquid, Liquid, b.p. < Gas 335O C. 450° C.
The pressure depolymerizations were conducted in a horizontal 1 8-10 50 26 44 37 2 8-10 50 34 43 37 steel tube with an internal diameter of 1 cm. This tube was 3 8-10 12 42 45 36 4 8-10 50 66 47 40 heated in a three-section electric furnace having a total length of 5 1000 25 94 31 59 90 cm. The temperatures along the tube were measured by ther6 3-5 mm. Hg 330 .. 84 46 30 mocouples a t the center of each section of the furnace and were a Last value is in millimeters of mercury. controlled by manual adjustment 6f variable-voltage transformers. A small positive-displacement v a r i a ble-s t r o k e EXPERIMENT No. 3 TABLX 11. DEPOLYMERIZATION pump was used t o force the charge through (Depolymerization conditions: temperature, 450' t o 46OO.C.; pressure, 8 to 10 Ib./sq.in. charging rate, 12 ml. per minute) the tube. The pressure on the system was Specific measured 'by a gage connected between Dispersion the pump and the cracking tube, and was VO1' Specific RefracnF - no Saybolt 7 Viscosity ~ i ~ ~ i l~ lg i 1~ - ~Gravity tive Index ' controlled manually by a needle valve at Fraction Range, C. late di: x 104 1000 F. 2100 F. the outlet end of the tube. The major 1.4190 120.8 0.7227 ... .. 19.6 450 .. .... .... ... ... ,. 1 Present
addrean, Parker Rust-Proof Company, Detroit, Mich.
a
Volume of residue, 1190 ml.: volume of distillate, 508 ml.
349
t3P19 20 19 13 10 24
gage;
2iL ..
.. .. .. .. 86 88 71
..
INDUSTRIAL AND ENGINEERING CHEMISTRY
350 XM,
.-
I
I
I
I
I
I
180
0
X
9"o
8 1
I
I
Vol. 40, No. 2 I
I
- CURVES OF GROSSE b WACKHER -A-EXPERIMENT -0-EXPERIMENT
-
i +EFiNS
5
9 4 % DEPOLYMERIZED
3
4 2 % DEPOLYMERIZED
CuNCoNJuG ATE>
.
-&--FA---
- --___ 0-.
O---,
I
60
I
IO0
I
I
180
140
L 220
I
260 BOILING POINT
Figure 1.
1 300
--@--
__c
I
I
340
380
I . 420
I
*c.
Composition of Liquid Products from Depoly-merization Experiments
contained substantially no niateiial boiling below about 450 O C. ; ferences shonm. In experiment, 4, in which 66'3 was dcpolymerspecific gravity dit, 0.883; refractive index n2$,1.493: Saybolt ized, the proportion of gas and light liquid increased at the expense viscosity a t 210" F., 225 seconds. (To avoid depolymerization of oil. The viscosity indices of the oil fractions from this expcriall distillations were conducted at ieduced pressures. The kettle ment, ranged from 87 for the lightest, to 58 for the heaviest, in temperatures were not allowed to exceed about 250" C. A11 dis-' contrast to the range of about 01 to 70 for the oils from each of tilling temperaturcs reported in this paper have been corrected to esperimrnts 1, 2 , and 3. In expcriincnt 5 the pressure mas increased to 1000 pounds per 760 mm. pressure.) square inch gage, and the charge wa.5 depolymerized to an extent Each distillation of total product n a s carried to about 450" C. (with one exception), and the percentage of material remaining of 947,. This resulted in a further decrease in the proportion of in the kettle was arbitrarily called the percentage not depolymeioil produced and also a pronounced decrease in the proportion of ized in the experiment. For purpose of comparison, the depolygas. Because of the small amount, of residue, all of the oil fracmerized products were calculated as gas, liquid boiling below tion could not be taken overhead; consequently it was necessary 335" C., and liquid boiling above 335' C., this latter fraction being t o estimate the proportion of oil and undepolymerized material in this experiment. Therefore, these figures are somewhat mnrc unin the viscosity range of crankcase lubricating oils. Samples of the normally gaseous product from each depolymerization experiment were analyzed by lo)? temperatuie TABLE 111. DEPOLYJIERIZATIOS EXPERIMENT To. 5 fractionation and sulfuric acid absorp(Depolymerization conditions: temperature, 500° to 510°, C.; pressure, 1000 l b . / w . in. gage; tion. Each of them contained about charging rate, 25 ml. per minute) 80% isobutylene, 3 4 % propylene and Specific n-butenes, and about 15% matelial Di-persion "" Specific RefracnF - n c \'iscos70 heavier than isobutylene; no significant Distilling ~ i ~ t i i -Gravity tive Index 7 ______ ity differences were observed in composition Fraction Range, C. late dig ny X 104 100' F. 210° F. Index 1 330 ., ,... 1,4920 ... 1737 95,9 53 made under the same conditions except that the exit end of the tube was slightly Volume of residue, 240 nil.; volume of distillate, 980 ml. higher than the inlet in experiment 1 and slightly lower in evperiment 2. When SO. 6 TABLE Iv. DEPOLYMERIZ.4TIOX EXPERIIIZXT slanting upwards there was less de(Depolymerization conditions: temperature, 330° C.: pressure, 3-5 mm. of Hg: vircous polymer polymerization; this indicated a shorter charged, 600 mi.; residue a f t e r depolymerization, 10 nil.; liauid recovered for fractionation, 360 ml.) contact time as the result of some differSpecific Refractire Saybolt VixosGravity Index Viscosity =istillkg 1tY ence in distribution and flow of gas and late dZ8 n ko looo F . 2 1 0 O F. Index Fraction Range, C. liquid in the tmo eupeliments. The 1 4239 ... ... 14.0 0.7313
