January 1.5, 1930
I S D r S T R I A L AiYD E S G I S E E R I N G CHEMISTRY
39
Problems in the Estimation of Unsaturated Hydrocarbons in Gases 11-Some Limitations in Separations by Sulfuric Acid1 Harold S. Davis2 and Dorothy Quiggle3 bfASSACHVSETTS ISSTITUTE
OF
.
TECHSOLOGY, CAMBRIDGE, hf ASS.
HERE is a mistaken belief running through most of
that isobutene actually is absorbed considerably faster than the literature of the past thirty years that all the butenes all three. Brooks (1) analyzed oil gas “by absorbing the are much more readily dissolved than propene by sul- higher olefins in 70 per cent sulfuric acid (Hempel pipet), furic acid and that, accordingly, this reagent in appropriate the propylene in concentrated sulfuric acid (sp. gr. 1.84) concentration can be used to separate them from propene at room temperature, and the ethykne in bromine water.” b y selective absorption. Sole-The reference ( 9 ) given b y Brooks appears t o have been misFritsche ( 7 ) who developed a method for estimating ethyl- interpreted. Nef absorbed t h e propene and butenes from their mixtures u i t h ethylene into concentrated sulfuric acid a t 0’ C a n d allowed t h e ree n e by absorption in concentrated sulfuric acid and measure- action product t o stand. ( H e stated t h a t t h e ethylene was unattacked ) ment of the ethyl alcohol which could be recovered, stated “By this treatment t h e butenes are changed completely into polrmers. t h a t the butenes could be first washed from the gas by f O while the propene remains as isopropyl sulfate, which according t o Berthelot, can be identified a s isopropyl per cent sulfuric acid, leavalcohol a f t e r diluting with water ing the ethylene and proa n d distilling.” S e i ’ s method pene unabsorbed. “Any appears t o have good possibilities, The main purpose of this paper is to point out the propene present appeared b u t i t must be standardized, for errors in certain methods which have been proposed, one of t h e authors has found t h a t as ethylene.” Michael and and are in some cases still being used, for the estimation propene also forms high-boiling Brunel (8) stated that exof the separate olefins i n gases by absorption in sulfuric oils when its absorption product periments carried out with in a n excess of sulfuric acid is acid. dry hydrochloric and hyallowed t o stand. See also Plant The rates of absorption of the propene and the normal and Sidgwick (ZZ) a n d Ormandy drobromic acids a t the butenes are too close to that of propene to permit their and Craven (10). same time and under exseparation from propene by selective absorption with actly the same conditions I t is evident that in this sulfuric acid. Gas analyses based on such a procedure showed “ t h a t ethylene method of analysis the norare misleading and the results should be rejected. unites less readily than mal butenes will be counted The saturation of 87 per cent sulfuric acid with silver propylene and this less as propene, and since both and nickel sulfates decreased its effectiveness for separeadily than n-butene, and, 1-butene and 2-butene have rating ethylene from propene in an Orsat pipet more in accordance with the been found in cracked prodthan one hundredfold. theory the difference in ucts (G), the figures given t h e velocities between the by Brooks for propene in first is considerablv less “oil gas” are much too than between the last-named hydrocarbons.” Without high. There has, perhaps, been a tendency to over,disputing the accuracy of the data, a warning must be estimate the amount of propene in commercial gases. ,given against extending their general conclusions to absorpHowever, concentrated sulfuric acid as used by Brooks, tions with dilute sulfuric acid. Davis and Schuler (unpub- when pure, gives a fair separation of ethylene from propene lished results) have s h o m that the rates of absorption of and the higher olefins, especially if correction is made for propene, 1-butene, and 2-butene into sulfuric acid are not the slow but appreciable absorption of the ethylene itself. very different. 2-Butene dissolves about twice as fast as Tropsch and Philippovich (IS) recommended 87 per cent sul1-butene and the 1-butene dissolves only slightly faster than furic acid for this purpose, but the results of Davis and propene in concentrated acids (87 and 95 per cent). How- Schuler throw doubt on the superiority of this particular conever, with dilute acids (70 and 80 per cent) the rates are so centration of acid for absorptions in Hempel pipets. Much close for 1-butene and propene that it is hard to tell which more misleading is the following procedure, recently recomis absorbed the faster. mended by the IT.S. Steel Corporation ( 2 ) :
T
~~
Sole-Dobrjanski ( 5 ) states t h a t 1-butene and 2-butene are absorbed at about t h e same r a t e as propene b y sulfuric acid. However no d a t a on t h e absorption rates of these t w o normal butenes are given in his paper.
These results show the futility of attempts t o separate propene from the two normal butenes by sulfuric acid. Perhaps part of the confusion on this subject is due to the fact ‘Received August 10, 1999. Joint contribution S o . 52 from t h e Research Laboratory of Organic Chemistry a n d S o . 244 from t h e Departm e n t of Chemical Engineering, Massachusetts Institute of Technology. T h i s paper contains, in p a r t , results obtained in a n investigation on “ T h e Relative R a t e s of Reaction of t h e Olefins” listed a s project No. 19 of Americ a n Petroleum Institute Re5earch. Financial assistance in this work has been received from a research f u n d of t h e -4merican Petroleum Institute donated b y John D . Rockefeller. This f u n d is being administered by t h e Institute with t h e cooperation of t h e Central Petroleum Committee of t h e National Research Council. Director a n d research associate, Fellowship No. 19, A. P. I. 3 Research assistant, Research Laboratory of Applied Chemistry, Massachusetts Institute of Technology.
For separating ethylene, propylene, and butylene in fractions containing no carbon monoxide, sulfuric acid of different strengths has been successfully employed a t the Bureau of Mines by adding silver and nickel sulfates as catalyzers. The solutions consist of sulfuric acid plus 10 per cent water, ordinary concentrated sulfuric acid (sp. gr. 1.84),and ordinary concentrated sulfuric acid containing 10 per cent fuming sulfuric acid (20 per cent excess SOs), all saturated with silver and nickel sulfates. The first is used to absorb butylene, the second propylene, and the third ethylene, in the order named. Sole-The references cited for t h e experiments a t t h e Bureau of Mines are Frey and B a n t , I N D .ENG.CHE)?., 19, 488,492 (1927). However, i t does not appear t h a t these investigators used sulfuric acid activated by t h e metallic salts f o r any other purpose t h a n t o determine t h e total unsaturated hydrocarbons in separate fractions of t h e gas which had previously been obtained b y fractional distillation.
The following experiments were carried out by one of the
ASALYTICAL EDITION
40
writers with a view to standardizing the U. S. Steel method. They show that, just as with pure sulfuric acid, there is little difference in the absorption rates of propene and the normal butenes. But they further show that the activated acid is very much less effective than pure sulfuric acid for separating propene from ethylene. Indeed, the errors in this procedure are so great that its standardization is hopeless.
20
80
16
5
60
,2
z
40
: k
r
$
0 0
Very striking, too, are the relative proportions of ethylene and propene removed in the first acid treatment. Bssuming, as a first approximation, that the rate of absorption of each olefin is proportionate at any time to the quantity undissolved, it can be readily calculated that the ethylene dissolved about one-fifth as fast as the propene from 20 per cent mixtures with air.
z
Propene removed
85 to 967,
Ethylene removed
32 to 37%
N-Butane removed
Sone
x
5
z
.\.
4 :
20
0 IO
20
30 40 % OF GLCF N
50 (OR
80
70
80
90
1
u:
y
Y
KO.
Table I-Absorption Procedures (U.S. Steel Corp.) a n d Their Characteristics a s Found b y Experimentation w i t h Individual Olefins Mixed w i t h Air FIRST SECOND THIRD ABSORPTION ABSORPTION ABSORPTION iiumber of passages of gas into pipet 3 2 2 Concn of HzSOc used, after saturation with silver and nickel su!fates 86 9% 9.5 6 % Fuming (30% excess SOs) Butenes removed 100%
24
100
1-01. 2,
AI1 residual from first absorption 45 to 78% of All residual from residual from second absorpfirst absorption tion None 3%
100
WTANE) A0SORBED
Figure 1-Results of A t t e m p t to Standardize t h e Three Absorpt i o n Steps of t h e U. S. Steel Corporation
It was decided to regulate the experimental procedure in the three recommended absorptions in such a way that the
Effect of Addition of Silver and Nickel Sulfates
This last conclusion was tested by experiments on the absorption rates of ethylene (99.5 per cent pure) and of propene (b. p. -47.5' A 0.3' C. a t 764 mm.) into 87 per
first step removed all the butenes, the second all the residual propene, and the third all the residual ethylene, and then to correct for the propene removed in the first absorption and for the ethylene removed in the first and second. This necessitated absorption tests on the individual olefins in various admixtures with air.
100 90 80
70 e0 50 40
30
Olefin Samples
20
The ethylene was a commercial sample in a steel cylinder. 0 IO 9 The propene was made by dehydrating isopropyl 5 8 7 alcohol over kaolin. It undoubtedly contained some 6 2 isobutene (4). 5 4 To prepare the butenes, pure secondary butyl alcohol was passed over kaolin a t 375-400' C. The 3 product consisted mainly of normal butenes, as Kas 2 shown by the fact that its absorption product in sulfuric acid yielded, with acetic acid, secondary butyl acetate. Accordingly, it could be used to find the I conditions necessary to absorb all the butenes, since o 8 10 It 14 18 20 NUMBER OF Pa55ES INTO PlPETTE isobutene is the most reactive of the three. Figure 2-Absorption of Ethylene a n d Propene (Orsat Pipet) i n t o Pure 87 The normal butene was separated from natural Per C e n t Sulfuric Acid a n d into t h e S a m e Acid Saturated w i t h Catalysts and Nicker gasoline by fractionation in a high-pressure column. 4
Method of Absorption
The gas sample was Over mercury, with a small quantity of water, in the absorption buret, It was intraduced and withdram from an Orsat absorption pipet blr raising and lowering the leveling bulb with a hydraulic lift ( I d ) set to move at a definite rate-15 seconds UP and 15 seconds down. Results
The results (Table I and Figure 1) show the absurdity of the supposition that the amounts of the gas absorbed by suecessive treatments with the three acids specified represent the quantities of butenes, propene, and ethylene present. They further show the hopelessness of applying correction factors to this method. For instance, the first treatment, when long enough to remove all the butenes, took out 85 to 95 per cent of the propene as well.
cent sulfuric acid and into the same acid after saturation a-ith silver and nickel sulfates. The results are summarized in Figure 2. The absorption curves plotted on semi-logarithmic Paper are nearly straight lines, confirming the assumption that the rate of absorption of an olefin in this pipet was always approximately proportional to the quantity undissblved. Accordingly, it is possible to calculate from the slopes of the curves that the relative rates of absorption of ethylene and propene were 1 to 1000 in the pure acid and only 1 to 8 in that activated by the metallic salts. From another point of view the salts increased the rate of ethylene absorption about 400 times but that of propene only 3.3 times. The effect of the addition of silver and nickel sulfates to sulfuric acid, as outlined in the U. S. Steel Corporation methods, is to decrease the effectiveness of the acid for separating propene from ethylene more than one hundredfold.
January 15, 1930
I S D C S T R I A L A S D ElYGIA-EERIlYG CHEJIISTRY Literature Cited
(1) Brooks, Chem. M e t . Eng., 22,630 (1920); “ T h e Son-Benzenoid Hydrocarbons,” p. 40 (1928). (2) Carnegie Steel Co., “Methods of Chemists of U. S. Steel Corporation f o r Sampling a n d Analysis of Gases,” 3rd ed., p. 36. (3) Davis, J . A m . Chem. Soc., SO, 2780 (1928). (4) Davis, IND. ENC.CHEII., Anal. Ed., 1, 64 (1929). ( 5 ) Dobrjanski, S e f l y a n o e Khozyaisivo, 9, 565 (1925).
41
(6) Frey and r a n t , ISD. ENG. C H E M , 19, 1358 (19271. 2. angezb. Chem., 9, 459 (1896). (8) Michael a n d Brunel, Am. Chem. J., 41, 127 (1909:l. lg4 (1901)‘ ()’ Nef’ Ann” ‘la’ (10) Ormandy a n d Craven, J . SOC.Chem. I n d . , 47, 317T (1928). (11) Plant a n d Sidgmick, I b i d . , 40, 14T (1921). (12) Tauch, IND.ENG.CHEN., 19, 1349 (1927). (13) Tropsch a n d Philippovich, Brennslof-Chem., 4, 147 (1923). ( i )Fritsche,
Construction of Platinum-Wire Chain for the Foulk Chain Hydrometer’ W. W. Koch and G. Frederick Smith U S I V E R S IOF ~ YILLINOIS,
D
ESIRABLE chain characteristics as indicated by
Foulk for use with his precision chain hydrometer are that each link be of the same shape and size, of exactly the same weight, and of low-density material. In addition, for use in strong acids or corrosive solutions the material of the chain should be non-reactive. Platinum-wire chains are particularly well suited in the last qualification, but not as to density; but this disadvantage may be offset by the use of Yo. 40 gage wire. Round links are desired to insure uniformity and links of equal weight are obtained by starting with equal lengths of wire for each link. Should such a chain be distorted by an appreciable overload, the original shape of each link is easily restored by means of a small tapered templet.
The platinum wire must be fused to bring about a smooth union. If platinum wire of very small gage is heated to the melting point in a blast flame, surface tension causes a minute ball of molten metal to “follow back” along the wire. The following method of forming the individual links solves this difficulty and at the same time governs their uniformity in weight. Construction of Links
A tungsten rod approximately 1.5 mm. in diameter is used as a templet. A 6 to 8 mm. length of the platinum wire is turned once around the end of the tungsten rod and the overlapping ends are twisted snuggly to the rod with small pliers and all but one and one-half turns of the twisted end cut off with sharp-pointed scissors. Since the wire can be twisted into practically perfect contact with the tungsten rod and since the point of the scissors will cut the twisted wire a t equal distances from the rod, equal lengths of wire for each link of the chain are obtained. A minute blast flame is then directed against the twist in the wire until the twisted portion is fused back to the point of contact with the tungsten rod. When two links are to be joined, there is a slight but inconsequential error due to the thickness of the wire of one link which is added to the diameter of the tungsten rod templet. The tungsten rod serves as a conductor for the heat which otherwise would follow back inside the twisted portion of Received August 20, 1929 T h e original paper should be consulted for details of design, discussion of t h e principle involved, factors influencing delicacy a n d precision, and specifications relative t o chain design. Foulk suggested t h e use of fine platinum wire as herein described 1
URBANA,
ILL.
the platinum wire and break the link. A rod of better conducting material would hinder fusion of the twisted platinum wire. A quartz rod is not suitable because of its poor heat conductance. A photographic enlargement of a portion of the chain described shows the nature of the fusion of thr. twisted portion of the wire. Small distortion of the original wire diameter is shown. (Some of the links were distorted slightly during the photographer’s manipulations.) Oblong links would result if the proper shaped templet were used. The advantage gained in increasing the chain length in this manner is offset by the increase in tendency to trap air bubbles during use. Weight of Links
The uniformity in weight of the individual links is shown by the fact that fourteen such links were found to weigh 0.56 =t 0.02 mg. each. The average weight of ten groups of seven links each m-as found to be 3.93 mg. and the average weight of each link in these groups was 0.56 * 0.01 mg. The weighings were made on a Troemner (No. 10) balance sensitive to a t least 0.02 mg. There were six links per centimeter, or a weight of 3.36 mg. per centimeter. Sensitivity as Illustrated by Foulk’s Formula
According to Foulk’s formula (1) relating the change in density of a liquid ( A d ) with change in position of a given float ( A b ) , Ad ( 2 D v = W A b ( D - d )
in which D and d represent the respective densities of the liquid and chain materials and V equals the volume of the float. Assuming the density of the liquid being measured to be unity (1.000), the volume of the float to be 5.0 cc., and the chain of the constant given above (3.36 mg. per cm.), the change in float position ( A b ) for a change of 0.001 in density is calculated to be 32.7 mm. For liquid of approximately 1.70 specific gravity, such as perchloric acid (HC104.2H20), an equal change in density would change the position of a 5-cc. float 32.4 mm. I t is interesting to calculate the value Ab using a 235-cc. float and the chain described for a change in density of one unit in the sixth place of decimals for a liquid of unit density. This volume of float in experiments of Lamb and Lee (2), in vhich the principle employing the chain in Foulk’s method n a s replaced by a magnetic pull exerted on a piece of iron sealed inside the float, gave a sensitivity of a few units in the serenth decimal place. The calculation for the corresponding Foulk chain hydrometer with the 236-cc. float and the small platinum chain shows a change in float position of 1.5 mm. per unit change in the sixth decimal place.
