Neopentane in Refinery Butanes L. C. JONES, JR., R. A. FRIEDEL, AND G. P. HINDS, JR. Houston Refinery Research Laboratory, Shell
Oil
Company, Incorporated, Houston, Texas
Qualitative study of a straight-run refinery butane stream b y infrared spectrometry has established the presence OF a small amount of neopentane. A spectrophotometric method is described for the quantitative analysis of the system propane, n-butane, isobutane,
neopentane, and isopentane. Determinations by this method show that neopentane occurs in various Texas crudes to the extent of about 0.03% b y volume. The reFerence spectra necessary For this analysis are included.
T
for purposes of comparison, we1 e obtained wing :I recordirig infrared spectrometer of high resolution ( 2 ) . I n order to obtain more conclusive evidence, the neopentane of the n-butane sample mentioned above was concentrated by distillation. The sample was fractionated in a column of 30 theoretical plates a t a reflux ratio of 24 to 1. Calculations based on Smoker's equation ( 7 ) indicated that under these conditions less than 0.1% of neopentane (on a charge basis) wquld be lost in the overhead product, n-butane, when the liquid in the kettle consisted of SO% neopentane. Actually, operational difficulties prevented the attainment of this degree of enrichment.
HE occurrence of neopentane in natural gasoline has beeii reported ( 5 ) but no definite evidence of its presence in crude
oils has been published. The analysis of several crude oils by the National Bureau of Standards (6) has failed to indicate the presence of the hydrocarbon in the samples studied. Furthermore, low-temperature distillations of butane and pentane streams obtained in topping operations show no trace of neopentane. I t is generally believed, therefore, that the compound inot met in refinery operations. The study of refinery butaneby infrared spectrophotometry in this investigation has slio\vn, however, that this is not the case. QUALITATIVE DETERMINATION OF NEOPENTANE
I.
Operating Conditions for Spectrophotometric Analysis of Butanes Standard Pressure Principal Wave &lit. (10-Cm. Absorber Length Width Cell) Shutter Filter Mzcrons Mm. Jf m Propane 9 35 650 0 50 .\letal MgO Isobutane 8 46 0 45 200 .\letal LIgO 19 70 550 ,)-Butane 1 50 LIF None Xropentane i 96 0 30 100 Veta1 LIgO Isopentane 0 66 0 5rJ 420 3IetaI MgO
Table
An examination of a portion of the infrared spectrum ( A , Figure 1) of a sample from a n-butane stream revealed the preyence of a weak absorption band near 7.9 mu which could not be attributed to n-butane or to either of the known impurities, iaobutane and isopentane, but which corresponded closely to one of the strong absorption bands for neopentane, suggesting the presence of that hydrocarbon in low concentrations. The absorption spectra of the pure compounds, presented in Figure 1
.
B , Figure 1, s h o w the spectrum of the cwceutratc obtained by this procedure. The 7.40- and 7.96-mu bands of neopentane are both clearly present in the spectrum, as is also the highly characteristic neopentane band structure in the 3.5-mu region. -1s a matter of interest the complete spectrum of neopentane i; presented in Figure 2. httempts to purify t,he very small amount of neopentane on hand were unsuccessful, so the spectrum given is one previously obtained in this laboratory using a ,ample of about 90% purity. The agreement with an unpublished neopentane spectrum from another laboratory is satisfac-
I NEOPENTANE
my. QUANTITATIVE DETERMINATION OF NEOPENTANE
The method developed for the analysis of the system propane, ?;-butane, isobutane, neopentane, and isopentane is an application of the general method described by Brattain et al. (J). The routine infrared spectrophotometer used was designed by the Shell Development Company and is manufactured by Sational Technical Laboratories. Operating conditions for the :rnalyeis arc given in Table I. -111 the hydrocarbons other than neopentane used in the cdibration vere of 99.5+70 purity as determined by isothermal distillation (4). The best neopentane concentrate available was analyzed qualitatively on the recording spectrometer nient ioned above and found to contain only isobutane as a n impurity. An ijothermal distillation a t 0" C. Tvas performed and the mole per cent of isobutane calculated from a plot of m p o r pressure us. per cent sample evaporated, using the vapor pressure data of .\.ston and Nesserly ( I ) . The amount of isobutane thus determined was 11.5 mole %. Optical densities of the standards were corrected for the effects due to the impurities in all cascx The corrected working curves a t the 7.96-mu rieopentnntx :ibsorption band are shown in Figure 3.
Wave Length, Mlcronr
Figure I. Spectra of Refinery Butanesand Pure Hydrocarbons in 2.8 to 4.2 mu and 7.0 to 8.2 mu Regions All curves a! 200-mm. pressure In 30-cm. cell. A , unfractionated refinery butanes. E , concentrate from distillation
349
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
350 SO00 100
4000
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COMPOUND
NEOPENTANE 80
SOURCE AND PURITY
SHELL MVELOPMENT SY N THE TIC, 90t % 60
\ I
40
STATE
GAS
TEMPERATURE
CELL LEmGin
ROOM 30 CM
PRESSURE
200MM.
20
LABORATORY
SHELL OIL ca. INC. HOUSTON, T E X A S
0 9.0
9.5
10.0
105
110
11.5
120
125
Brattain's graphical method oi calculation (3) was employed with one modification: Since the deviations from ideal behavior are different for CSand C6 hydrocarbons, it Jvas necessary to recorrect the observed pressures on the basis of an approximate analysis obtained using the average deviations for the butanes. RESULTS
The results of the analyses of two typical synthetic blends are given in Table 11. The analysis of several such synthetics indicated that the neopentane could be determined to +=0.1% volume if present in low concentrations (up to 8 mole %). The development of this method made it possible to determine the source of the neopentane and the extent of its occurrence.
130
13.5
14.0
14.5
15.0
Thus, samples of both East and West Texas unstabihzed straightrun tops were collected and stabilized in the laboratory to 65' F. still-head temperature using a column of 20 to 30 theoretical plates. An analysis of the distillate from stabilization of the East Texas topa is given in Table 111. The concentration of neopentane indicated in this analysis corresponds to 0.03% of the crude by volume. Analyses of West Texas and Texas-Hobbs crudes shoived equal concentrations of neopentane. Other analyses shoiv that neopentane is found in
06-
05-
Table
II.
Component Propane Isobutane n-Butane Xeopentane Isopentane
Table
111.
Analyses
of Synthetic Blends
Blend I Blend I1 Known Found Known Found Mole Per Cent 3.6 0.0 0.0 3.5 14.8 15.7 6.9 6.6 59.8 69.8 85.3 85.6 8.2 3.9 4.0 8.3 13.7 3.9 3.8 12 7
04-
Analysis of Low-Boiling Friction from East Texas Crude Hydrocarbon Propane Isobutane n-Butane Neopentane Isopentane
Mole
7.3 13.1 67.8 0.6 11.2
1oo.o
M o l e Fraction
Figure 3.
Optical Densities
At 7.96 mu and 100-mm. pfessufe In
IO-mm. cell
ANALYTICAL EDITION
June, 1945
other straight-run Cq streams in the refinery to the extent of about 0.4 mole %. ACKNOWLEDGMENTS
The authors wish to express their gratitude to K. E. Train of this laboratory who performed the isothermal distillations of the reference standards, and to Edward Gelus for his advice and aid in the concentration by distillation of the neopentane samples and also in the interpretation of the isothermal distillation curves. The authors are-further indebted to the Shell Oil Company for granting permission to publish this work.
351 LITERATURE CITED
(1) hston, J . C.. and Messerly, G. H., J . A m . Chern. Soc., 58, 2355
(1936).
(2) Avery, W. H., J . Optical SOC.A m . , 31, 633 (1941). (3) Brattain, R. R., Rasmussen, R. S., and Cravath, .4. M.,J. A p p l i e d Phys., 14, 418 (1943). (4) Echols, L. s., and Gelus, E. (to be published). ( 5 ) Ellis. C. E., “Chemistry of Petroleum Products”, pp. 17, 32,
New York, Chemical Catalog Co., 1934.
(6) Rossini, F. D., Petroleum Engr., 14, No. 5, 41 (1943). (7) Smoker, E.H.. Trans. A m . Inst. Chem. Engrs., 34, 165 (1938).
PRESENTED before the Division of Petroleum Chemistry at t h e 108th XIeetIng of the A?IERXCASCHEUICAL S O C I E T Y , New York, N. Y
Determination of Aluminum Chloride and Hydrochloric A c i d in Hydrocarbon Streams W A L T E R G R E E N AND S. R. BAKER Wilrhire Oil Co., Inc., Norwalk, Calif.
THE
analytical method presented here does not depend on a new principle, since Craig (1) published a similar method in 1911 for the determination of free acid or aluminum oxide in alum and Scott modified this method to some extent ( 3 , 4). Martin published a method for the determination of aluminum in ore which makes use of the reaction between aluminum salts and potassium fluoride. Other methods of analysis are discussed by Willard and Diehl ( 6 ) . The method of Malaprade ( 8 ) probably could be adapted to the analysis of aluminum chloride and hydrogen chloride mixtures but requires the use of a potentiometer. The advantage would be that iron would not interfere. The author’s method is a new application of the use of potassium fluoride, inasmuch as hydrogen chloride or alumina is determined in addition to the aluminum chloride and iron chlorides. The method does not distinguish between the iron and aluminum cliloridcs. However, in the present application, iron chlorides are not present in sufficient quantities to cause serious errors in the result8. The method used in this 1aborat.ory is rapid and accurate and depends upon the fact that when a neutral solution of potassium fluoride is added to an aqueous solution containing aluminum chloride and hydrochloric acid, the aluminum chloride is decomposed into two stable compounds, neutral to phenolphthalein. The following reaction is believed to take place:
AlCla
+ 6KF + XHCl
= AlFJ.3KF
SAMPLING PROCEDURE
The following sampling procedure is designed for sampling butane streams containing aluminum chloride and hydrogen chloride. Construct a sampling arrangement similar to that shown in Figures 1 and 2, so that a sample may be taken from a circulating, steam-trace line. Do not attempt to warm up the sampling
LEAD FILL
+ 3KC1 + XHCl
The free hydrochloric acid may then be accurately titrated with potassium hydroxide. I n the absence of potassium fluoride, potassium hydroxide reacts with both the aluminum chloride and the hydrochloric acid. The aluminum chloride is found as the difference between the potassium hydroxide r e q u k d in a titration withnut and a titration with potassium fluoride. APPARATUS AND REAGENTS
Three gas-washing bottles. Wet test meter or dry ice trap, depending upon boiling range of hydrocarbon stream. Wide-mouthed DeRar flask. All reagents were of reagent grade. 0.5 X potassium hydroxide, 0.5 N hydrochloric acid, and 1% ’ phenolphthalein indicator solution. POTASSIUM FIXORIDE SOLUTIOS.Dissolve 200 grams oi potassium fluoride in 400 ml. of carbon dioxide-free distilled water, which has been neutralized with hydrochloric acid or potassium hydroxide, using phenolphthalein as indicator. This solution should be kept in a paraffin-coated bottle.
Figure 1. Detail of Sample Valve Assembly
