PREPARATION OF CYCLOPENTANE From an Oklahoma Natural Gasoline J. W.TOOKE Phillips Petroleum Company, Bartlesville, Okla.
The application of precise fractionation to a pentane-hexane fraction of natural gasoline from the Burbank field has led to the isolation and testing of cyclopentane in high concentration. The best sample contained 95 per cent cyclopentane; a 44-gallon composite contained 91 per cent. The amount of cyclopentane in the original pentane-hexane stock is estimated to be 5.7 per cent, in the 12-pound Reid vapor pressure natural gasoline, 2.4 per cent.
ERTAIN hydrocarbon oils have long been known to contain small amounts of cyclopentane. Brown and Carr (1) in 1926 found an indication of cyclopentane in several gasolines. In 1938 Tongberg, Fenske, and Sweeney (5) cited the presence of cyclopentane in practically all of twenty naphthas investigated by them. They further mentioned the possibility of obtaining fractions (5 or more volume per cent of over-all naphtha) of 50 per cent of a particular hydrocarbon by applying efficient fractionation. Cyclopentane was listed as one of the definite possibilities from virgin naphthas. Rossini, Mair, Fordati, Glasgow, and Willingham (4) in 1942 showed the presence of cyclopentane in the paraffin-naphthene portion of an East Texas naphtha as a result of one distillation. Although these investigators and others have recognized the presence of cyclopentane in hydrocarbon oils, no one appears to have reported the actual isolation and testing of the material in high concentration. The purpose of this paper is to report a method for preparing cyclopentane from a natural gasoline. Appreciable quantities of cyclopentane in natural gasoline produced in the Burbank, Okla., field were h t suspected when kettle products from the fractionation of normal pentane from this source were observed to possess unusually low A. P. I. gravities. This was attributed to the presence of a cyclic hydrocarbon and, since it possessed a boiling point between normal n-pentane and n-hexane, was thought to be cyclopentane. A systematic effort waa made to obtain the cyclopentane by precise fractional distillation.
inches. Reflux was provided by an internal water-cooled coil so that the column operated under partial condensation. Product removal was from the head as a vapor and condensed in a separate water-cooled product condenser. The still had a 250-gallon kettle and was heated by steam. The second column (used for the h a 1 fractionation) was 6 inches in diameter and had an over-all height of 22 feet 9 inches. It was packed with '/pinch stoneware Raschig rings for a total depth of 18 feet 11 inches. The reflux arrangement and vapor takeoff assembly were the same as that for the first column. This kettle had a 100-gallon capacity and was also heated by steam. PROCEDURE. For the preliminary fractionation the still was operated a t an average pressure of 47 pounds per square inch gage, a vapor temperature of 181" F., and a kettle temperature of 205" F. The original stock was charged in six batches of approximately 225 gallons each for a total charge of 1350 gallons. For each batch the still was brought up to temperature and allowed to come to equilibrium under total reflux. When this had been accomplished, vapor was removed from the head of the column and condensed at the rate of about 6 pounds per hour and a reflux ratio of about 25 to 1 until nearly all of the n-pentane had been removed. At this point the vapor removal rate was reduced to 2 pounds per hour a t a reflux ratio of about 50 to 1. Fractionation was continued until all the material boiling between 110" and 130' F. had been taken overhead, The fractions of the distillate boiling below 110" and above 130' F. were discarded. From time to time during the fractionation, samples of the distillate were examined for A. P. I. gravity and boiling range. Boiling points and ranges were determined by a modified Cottrell boiling apparatus as developed by Quiggle, Tongberg, and Fenske (3). A typical boiling rangegravity curve showing concentration of the cyclopentane is given in Figure 1. All boiling points and ranges were obtained under controlled pressure of 760 mm. of mercury with a certified mercury thermometer. Stem corrections were also applied. From the six preliminary fractionations, 108 gallons of cyclopentane concentrate were accumulated. A sample of this had an initial boiling' point of 116" F., a dry point of 125.7' F., and an A. P. I. gravity of 65.8. This material was charged to the second still for final fractionation. The still was brought to temperature and refluxed until equilibrium waa established. During this final fractionation the still
C
FRACTIONATION OFUQINAL STOCIC. A pentane-hexane fraction from natural gasoline was used. The A. S. T. M. distillation and A. P. I. gravity follow: Initial b. p. 8 8 O F. 30
409' over 99'F.
ss$
%::
99
100 101 104
90% over 113OF. 95 135 Endpoint 210
OA.P.1.
89.8
EQUIPMENT. The fractionation equipment consisted of two steel batch-type packed columns. The first column or that used for the initial fractionation was 6 inches in diameter and had an over-all height of 20 feet 3 inches. I t was packed with l/rinch steel Lessing rings for a total depth of 17 feet 5 992
September, 1943
waa operated a t 40 p o u n d s p e r ’ q u a r e inch gage, with a vapor temperature of 201’ a n d a kettle temperature of 204’ F. Vapor r e m o v a l from the head of the column waa then started and continued at the rate of about 1.8 pounds per hour a t a reflux ratio of 115to 1. Cond e n s a t e waa collected in onegallon cuts, and for each cut the boiling range and A. P. I. gravity were determined. Results are plotted in Figure 2. RESULTS
Figure 2 shows t h a t a long plateau occurred between 19 and 69 per cent distilled with only slight f 1u c t u ations in gravity and boiling point. Twice during the distillation the column flooded a n d was s h u t down until equilibrium was again established. After 69 per cent distilled, the gravity curve showed a definite though slight rise which continued until the end of the distillation. Figure 2 shows that, although good fractionation was obtained, the gravity never reached the value for pure cyclopentane, 57.1’ A. P. I. (d:O 0.Z460). This is attributed to the presence of .a paraffin hydrocarbon which is thought to be neohexsne. Forty-four one-gallon cuts were selected from near the middle of the plateau and composited for further work. The characteristics of this composite are given in the following table, together with values for the “best sample” from the fractionation and those obtained from the literature for pure cyclopentane. -Thh Boiling point (760 mm. Hg), Bpsci60 grsvity, d i 0
Refraotivs index,
C.
Compdte 49,l
WorkBest utrrple 49.1
0.7891 0.7aa 1.m~ 1.40~)
Likmture U) 49 8
0.74~
i.lwa
Assuming the contaminant to be neohexsne only, the composite is estimated to contain 91 per cent cyclopentane and the best sample to contain about 96 per cent cyclopentane. Part of this composite mmple was used to obtain antiknock characteristics. The cyclopentane content of the original stock is estimated to be 5.7 liquid volume per cent, equivalent to 2.4 liquid volume per cent of a 12-pound Reid vapor pressure natural gasoline from a Burbank source. LITERATURE CITED (1) Brown and Cam, IND. ENQ.CEFJM., 18,718-22 (1926). (2) Egloff, “Physical Constants of Hydrocarbons”, Vol. (1940).
11, p. 64
(3) Quiggle. Tongberg, and Fenake, IND.ENG.C H ~ MANAL. ., ED., 6, 466 (1984). (4) Rowini. Mair, Forsiati. Glsegow, and Willingham, Oil Gas J., 41,
No. 27. 106-14(1942); Rejlner Natural h a l i n e Mfr., 21, No.11. 73-8 (1942); Proc. Am. Petroleum Inst.. 23, 111, 7-14
(1943). (6) Tongberg, Fenske, and Sweeney, IND.ENG.CHBIM., 30, 166-9 (1938).
