378
INDUSTRIAL AND ENGINEERING CHEMISTRY
predict,ing the relative viscosity-temperature nuinbcr of certain mixtures and of individual members of homologous series will be readily apparent. Since two viscositg-temperature points determine the relative viscosity-temperature number, tables similar t o those used for viscosity index may be compiled for convenience, if desired. However, the chart shown in Figure 5 provides an even simpler means of determining the relative viscosity-t,emperature number. Extension of a straight line connecting the viscosities at 100 and 210" F. on this chart will indicate directly the relative viscositytemperature number. The relative viscosity-temperature number should be useful as a means of describing, in a general way, the relative viscositytemperature propert,ies of a n oil. It' appears to be more fundamental and t,hereforc more reliable than the viscosity index. When it is necessary t o evaluate the ability of a lubricating oil to operate a t a certain temperature or over a wide temperature range, i t is the actual viscosities at the required temperature limits which are of most direct importance and must be determined, No single number method of describing viscosity-t,emperatmureproperties, such as the relative viscosity-temperature number or t h e viscosity index, can be used alone correctly as a criterion of the suit,ability of any oil for a specific application.
Vol. 41, No. 2
Bried. E. SI., Kidder, H. F., Murphy, C. hl., and Zisiniiii, K , .\.. ISD. ENG.CHEM., 39, 484-91 (1947). Davis, G. M . B., Lapeyrouse, M., and Dean, E. W.,Oil Gus J . , 30, NO. 46, 92-3 (1932). Dean, E. W.,Bauer, A. D., and Berglund, J. 13.. IND.Ex. CHFA., 32, 102-7 (1940). Dean, E. W., and Dnvis, G. H. B., Chern. & M e t . Eng., 36, 61819 (1929). Hardiman, E. W., and Nissan, A. H., J . I n s t . Petroleum, 31, 255TO (1945).
Ju, T. Y., Shen, C., and Wood, C . B., Ibid., 26, 514-31 (1940). Lausen, R. G., Thorpe, Et. R., and Armfield, F. A , IN]) ISxc;. CHCM.,34, 183-93 (1942). Larson, C.M., and Schwaderer, IT^ C., Oil Gas J . , 42, Xo. 10. 49-50, 53-4, 57-8, 61, 79 (1913). Mikeska, L. A , , I b i d . , 28, 970-84 (1936). Snndorson, R.T., I b i d . , 41, 368 (19493. Schiessler, K. IF7.,Clarke, D. G., Rowland, C. S., Sloatman. TI'. S., and Herr, C. H . , Proe. Am. Fetro2eum Zirst., 24 (IIT),49-74
(1943). Bchiessler, R. W., Coshy, J. K.,Clarke, D. G., Rowland, C. S., Sloatman. 1%S., '. and Herr, G. H., Petroleum Refiner, 21, 383.400 (1912). Schmidt, A. W., and Grosser, A., Ber., 73, 930-3 (1940). Schmidt, A. W., Ilopp, G., and Schoeller, V.. Ibid., 72, 1893-7 (1939). Schmidt A . W., Schoeller, V., and Eherlein, E., Ibid., 74, 131324 (1941).
Texas Company, unpublished n-ork. Vineali, G . J. C., Petroleum (London), 6, 41-3 (1943).
ACKNOWLEDGMENT
The cooperation of E. C. Rnowles and F. C, Toettcher in helpful discussions is appreciatively acknowledged.
RECEIVED October 2 4 , 1 9 4 9 .
f cis- to tr
onversio
e WM. F. SEYER AND C. W. YIP 7:niversity
os British Columbia, Vancouver, Cunudu
T h e velocity of the conversion of cis- to trans-decahydronaphthalene has been measured in the prcsence of aluminum chloride at Q", loo, 2 0 ° , 3 5 O , and 45" C. The results indicate an over-all reaction velocity of approximately the first order. At 25' C. the velocity of reaction increased with increased amounts of aluminum chloride until this reached a value of about 3QYo by weight of which addition of catalyst produced no increase in velocity.
c
OhIMERCIAL Decalin is largely a mixture of CIS- and transdecahgdronaphthalene. These two hydrocarbons can be separated from each other by fractional distillation at reduced pressures. Frequently, it is debirable to have a material Kith only one of these hydrocarbons present, so instead of setting u p a n apparatus for fractional distillation, it is customary merely t o add some aluminum chloridc to a commercial Decahn and t o allow the mixture to stand for about 24 hours a t room temperature. This treatment serves to convert almost all of the cis isomer present to that of the trans. Since neither the exact time of complete conversion nor the amount of by-product formed has been recorded, it appeared deslrable to study this reaction under normal laboratory conditions. REACTION MECIIANSM
T h e mechanism of the catalytic action of aluminum chloride or bromide in the isomerization of cyclic saturated hydrocarbons is far from being clearly understood. I n the case of saturated
hydrocarbons either cyclic or noncyclic isomerization is frequently accompanied by measurable amounts of by-product reactions. The extent of side reactions depends very much upon t,heactivity of the catalyst, the presence of unsaturated hydrocarbons, water or other oxygen-containing compounds, hydrogen halides, but most of all upon the temperature. Aluminum bromide is muah more active than aluminum chloride in this respcct, for Zclinslcy and TuroTra-Pollak (6) in their work with the former catalyst obtained almost 40% of by-products n-hen cis-Decalin was heated t o 100" C. for 12 hours. In contrast to this, Jones and Iinstead (1) in their x o r k found i t necessary when using aluminum chloride to raise the temperature t o 130" C. and t o use a heating time of 24 hours before getting an optimum yield of bg-product,s. Thc importance of small amounts of impurities in the isomerization of normal paraffins has recent,lybeen reported by Pines and Wacbher (3). I n a series of tests where no hydrogen chloride mas used with aluminum chloride they found that less than 1% of byproduct was formed even though t h e react,ion was carried out at 150' C. T h e first mentioned experimenters, %elinsky and Turova-Pollak, claim t o have obtained no indication of byproduct formation even with aluminum bromide if the reaction of cis- to tram-Decalin was carried out at room temperaturc and under conditions which did not exclude water vapor or air cntirely. Experience in general indicates t h a t the aluminum bromidc is very much more active than the chloridc, which may be due to the fact that the former is very soluble in most hydrocarbons
February 1949
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
uR
Figure 1. Apparatus Setup A , reaction bulb; R , stirrer. C, thermometer; D , insulated bath; E , bath stigrer; F, regulator; 6, heaterr H , relay
379
of a bond is sufficient. This is proably true a t low temperatures where isomerization is the reaction which predominates, while a t high temperatures (above 100" C.) bond rupture occurs. This investigator further makes the statement that "in saturated hydrocarbons the electrons are bound so fast to the carbon atoms that the formation of a stable molecular compound cannot be considered.]' Seyer and Yip's experiments lead them to doubt this because it was found that whenever freshly sublimed aluminum chloride came in contact with the pure cis hydrocarbon, a yellow compound was formed. This color gradually disappeared as the reaction progressed. No color change was observed when the freshly prepared aluminum chloride came in contact with the trans-Decalin. This observation corresponds to that of the aforementioned workers, Zelinslry and Turova-Pollalr ( 7 ) , who when studying the aluminum bromide complex found that this formed only with the cis compound hut not with the trans form. This cis-decahydronaphthalene complex was very insoluble because, if filtered off from the liquid, reaction ceased immediately and there was no sign of color in the filtrate. Further, no change in the refractive index of this filtrate could he detected even after 10 days' standing. This fact would also point to a very l o x solubility of the chloride catalyst. From our observations and those of others recorded in the literature, the cis- to trans-decahydronaphthalene transformation can be brought about by temperature alone if high enough. Under these conditions, a considerable amount of by-products are formed. In general, it would appear that a t temperatures below 50" C. either with aluminum bromide or chloride, even if traces of halogen acids, water, or air are present, only negligible amounts of side reactions occur'.
wiiile the latter is not. Hence one would expect the conversion rate for the chloride compound to be much less than that of the EXPERlMENTAL PROCEDURE bromide and also that there would be a smaller amount of byproduct material formed. The experimental arrangements are shown diagrammatically Preliminary tests showed that with aluminum chloride even in Figure 1. in the presence of small amounts of moisture or air, little or no The reaction bulb, A , was made of Pyrex tubing, 4 em. in by-products were formed if the reaction temperatures were kept diameter, 30 cm. long, and having a capacity of about 200 ml. below 50 C. at all times. No two layers or discolorations were At the top of bulb A were two openings, one for the stirrer and ever observed, nor did the permanganate test reveal any unone for the thermometer. A capillary tubing outlet was connected about 6 cm. from the bottom, so that samples of the saturation. The stability of the tmTo hydrocarbons was further Decalin could be taken out of the reaction bulb at any time tested by allowing samples of the two forms in the pure state to while the stirring was still in action. stand a t room temperature in contact with freshly distilled alumiThe reaction bulb, A , was immersed in a constant temperanum chloride for over a period of 20 days. The refractive index ture bath as shown in Figure 1. The bath consisted of a 150of all the samples corresponded to that of the trans-decahydrowatt knife blade heater, a n electrically driven stirrer, a liquidmercury thermal regulator, and a relay. For bath temperatures naphthalene. However, a simple fractional distillation of the 20' C., the bath was surrounded by rock-wool insulation above materials gave a small amount, about O.l%, of a clear liquid to prevent too great a heat transfer. For bath temperatures boiling from 15' t o 20" C. lower than that of trans-decahydrobetween 0 O and 20' C., ice replaced the rock wool in the insulation compartment. This ice, in conjunction with the heater nmhthalene. This would indicate ring - scission had taken place although no coloration or unsaturation was observed in any of the samples. However, 00 since this small amount of low boiling fraction was obtained whether the starting material was either the cis or trans hydrocarbon, 80 it is difficult to prove that any measurable amounts of by-products are formed during the conversion process at room temperatures. 60 The possibility of both isomerization and ring decomposition reaction would follow 40 from the spatial studies of Wightman ( 5 ) , who claims that the transformation of one form to another can take place only with PO a bond rupture. Thus i t would appear, if his assumptions are correct, that during the reaction for a short period of time one QO 40 60 80 100 IQO 140 160 180 PO0 220 of the rings opens up, introducing the possiTIME IN HOURS b i l i t y of b y - p r o d u c t f o r m a t i o n . Xenitzescu (9) is of the opinion that for Figure 2. Conversion Curves of Decahydronaphthalene in Presence of Aluminum Chloride isomerization to take place only a loosening
INDUSTRIAL AND ENGINEERING CHEMISTRY
380
Vol. 41, No. 2
with aluminum chloride for over 20 days. Even here the decrease in the refractive index was barely perccptiblc. Since this met,hod of nieasurement is o n l i accurate to 0.5% at best, the small ainouiil ol byproducts that might be produced would have negligible influence on the oiw-all results. For observing the eonversion rate a t the different temperatures 70 prams of thc: ais compound were used with 15 grains of resublimed alumiiiuni chloride of the ordinary C.P. laboratory grade. The procedure vas biiefly as folloim: The cis-decahgdrona~iEithalenewas allowed t o stand over metallic sodium for some Figure 3. Conversion of Decahydronaphthalene in Presence of Aluminum tinie before use. The charge of 70 grams Chloride n-as cooled to about 0' C. and thcn about one third of it TYRS poured into thc reaction vessel. This had been previously dried in an oven aiid, t o eliminate moisture a i much as possible, and regulator, enabled the bath to be kept at the desired temdry nitrogen was passed through the vessel while it was assemhlcd perature. in the temperature control bath. It n-aq fouritl iinpractical to The cis-decahydronaphthalene used was prepared froin comsuhlirne the nluminiim chloride dirrctlp int>othe reaction tribe mercial Decalin obtained from the Eastrnan Kodalr Company because of condensation in the upper parts; hence the catalvst in the manner previously described (4). It shoIved no signs n-as first sublimed into a rreighirig bottle and then the desi& of unsat,uration when treated wit,h an alkaline permanganate amount n-as poiired out into a fuiinel nnd washed down ivit,h solution. The freezing points of the material used lay between the remaining two thirds of the Decalin chargc. For a bricTE -43.2O to 43.3" C. Both pure and solutions cont,aining 2yc period of t,irne, contact, n-ith air and moisture coulci nor, bt: ol the trans iorin were used TTith no difference in the velocit?; avoided eo a small amount of liydrogeii chloriclo was ioriiietl results. This showed the nonexistence of an induction period. and drawn into the reaction vessel. This, howerer, a.a,s soon The conversion rate was measured at various temperatures carried out by the st,rearii of nitrogen gas that v a s passed through betwcen 0" and 45" C.: and also ivit,h various amounts of catat8heentire time of the reaction. iit a set lime a sample of ihc lyst a t 20" C. The course of conversion was folloved by obhydrocarbon was draxx-n off xith the aid of the extdrnal nitrogen serving the change in the rcfmct,ive index, given by the enigas pressure and the refractive index mcasurcd as quickly as pirical equation possible in a Pulfrich refractometer. This requircd about 0.5 ml. of the coriipourrd which was returned to tlre reaction vessel 1. = 12936 - 8734 n after each Iueauuremcnt. The per cent of the traiid iwnici, a t any t h e >is given in F i g u x 2. where 1' is the per cent t,rane isoilier and ~i is the refrartive index for the line D at 20" C. TlM,E IN HOURS
DISCUSSION O F RESULTS
The reiractive index n-as considered to be rlie most convenient method of measuring the rates, as it requircd very little oi the material. Previous experiments had aln-ays given the saiiie value for the refractive index of the trans product except in those case^ n-here samples of Decalin had heen standing in contact
TABLEI. COSvERSIoX O F C I S T O TRANS FORNO F D E C A H Y DROXAPIITIIALENE IS PRESEXCE or DIFFEREXT AMOLXTSOF A ~ u a r ~ x u CHLORIDE ar
Time. HOElF
A t Constant Temrxrature, 25" C . 'rime.
% Cis
Hours
% Cis
Aluminum Cnlotidc, 17.6% by Weight 0 1 7
3
4
1s 16
26
100 0 91 7 85 5 83 3 79 3 i3.3 50 3 43.2 31.3
.4luminum Chloride, 30.0% by Weiirht 0 100.0 4 36.8
8 10
13.9
s.,
31 36 43 48
55 62 66 70 80
26.0 21.5 15.4 12.2 0.7
e.7 i)
.4
3 ,d
n
Aluminum Chloride, 48.1% by JYeight
0 2
4
8
100.0 09.4 37.4 10.0
Plotting the rcsults in semilog grspliical forin, tlic acrios of curves in Figure 3 is obtained. Thcse curves suggcst immctliatcly that the over-all rate of reaction is of the first ordcr type. This becomes more evident ivhcn the log-per cent cis isomer is ploi tcd against time. Starting rr-ith a 100% cis hylrocarbon tho behavior is linear unt>ilabout 25Yc is 1' lied, \\-hen a slight clrviation sets in until about 50% conversion has taken place. Krom here on the first-order law is again consistently followed hut a marked change in slope appears a t about 85yo transformation. This is most cjbser\rablc along the 0" C. reaciion isotherm n - h w the change in slopc is at, a maximum. This change in slope i> just noticeable on the 45' C. isot,hcrrn. Apparently a t this point some other om of the conciirririi leactiolis begiris to beuonie of controlling irliporlance in 111' over-all rate. As ineutioned before, no evidence of a,n inthiclio period n-as obtained. It n-as found, hoivever, that thc amount ( catalyst present did materially affect the velocity, if 'diu amour !vas below a certain quantity. This is shown in Table I. I Table 11, the amount of catalyst in 70 grarns of hydrocarboii compared with the velocity con5tant k , where k is the nitinbvr grams of the cis isomer converted to the trans form in onc s c c i i ~ ~ It n-odd appear t
