B . R . S T A N E R S O N AND H A R R Y L E V IN , T h e T e x a s C o m p a n y , B c a c o n , N . Y .
A m e th o d is d escrib ed for d e te r m in in g o le fin c o n t e n t o f g a se o u s h y d ro ca r b o n s by d ir e c t t itr a t io n o f th e sa m p le d isso lv e d in co ld c h lo r o fo r m . B r o m in e in g la c ia l a c e tic a cid is u se d for t it r a t io n . T h e m e th o d h a s g iven sa tisfa c to r y r e s u lts o n s y n t h e t ic g a se o u s b le n d s c o m p r isin g t h e c o m p le te r a n g e o f u n s a t u r a tio n for C3 a n d C4 h y d r o ca rb o n s as w e ll as C5 o lefin s in s m a ll a m o u n ts . T h e h ig h e r g a se o u s o lefin s (C 3, C«, an d C6) ca n b e d e te r m in e d to th e e x c lu sio n o f e th y le n e i f n o t m o r e t h a n 1 0 per c e n t o f i t b e p r e se n t. T h e m e th o d is s u it a b le for r o u t in e p la n t c o n tr o l p u rp o ses b e c a u se o f it s s im p lic ity a n d r a p id ity .
H y d ro g en su lfid e , m e r c a p ta n s , a n d 1,3- b u ta d ie n e in te r fe r e a n d m u s t b e rem oved b efo re a n a ly sis.
T
H E im p o rtan ce of d e term in in g u n sa tu ra tio n in h y d ro carbon gases is e v id e n t from th e co m p arativ ely num erous p u b licatio n s on th e su b je c t in re c e n t years. Som e of these h av e d e a lt w ith im p ro v em en t of existing procedures (5, 7) an d o th ers w ith new m eth o d s of a tta c k (4
, 6). T h e p re se n t p ap er describes a m eth o d developed to sa tisfy th e need for one t h a t is ra p id a n d su itab le for ro u tin e p la n t control purposes.T h e m eth o d s com m only used for d eterm in in g u n sa tu ra tio n in gases involve a b so rp tio n in sulfuric acid solutions of various co n cen tratio n s, a b so rp tio n in brom ine solutions of v ario u s co n cen tratio n s, o r c a ta ly tic h y d rogenation. M eth o d s such as b ro m in atio n in th e v ap o r s ta te (6), fractio n al desorp
tio n (S), a n d d e so rp tio n -th e rm a l co n d u c tiv ity (2) are n o t su itab le for ro u tin e use.
M atuszak (5) extensively reviews and presents the principles and lim itations governing the selection of conditions for deter
mining gaseous olefins by absorption in sulfuric acid. By de
veloping an apparatus which requires very small portions (ap
proximately 1 ml.) of reagent, he minimizes such factors as re
versibility of absorption, solubility of gaseous paraffins, increase in solubility of hydrocarbons because of acid-soluble absorption products, solubility of hydrocarbons in precipitated polymeriza
tion products, and liberation of unabsorbable gas, M atuszak reports good results w ith olefins up to and including the C< hydro
carbons. T he tim e required for analysis m ay be slightly longer than th a t required for other absorption methods or catalytic hydrogenation.
B oth M cM illan et al. (4) and Savelli el al. (7) show th a t con
ventional bromine w ater methods for determ ining olefin give high results. T he la tte r had considerable success in using quarter-saturated bromine water, both w ith and w ithout excess potassium bromide. This solution is weaker th an usually em
ployed and its superiority over the more concentrated solutions is attrib u ted to its inactivity to butanes. Failure to obtain exact reproducibility was attrib u ted to absorption of small quantities of saturated hydrocarbons in th e liquid dibromidcs formed bv reaction of bromine w ith unsaturated constituents.
M cM illan ’s cataly tic h y d ro g en atio n m eth o d (4) fo r d e te rm in ing u n sa tu ra tio n of gases has been used successfully b y th is lab o ra to ry a n d o th ers; it is a cc u rate b u t h as certain d isa d v an tag es for ro u tin e use. M a n y p la n t gases c o n ta in im p u rities t h a t poison th e c a ta ly st, n ecessitatin g fre q u e n t reg en eratio n of it o r delaying hyd ro g en atio n . D ev iatio n s from p erfect gas law s a n d a d so rp tio n of sam ple on c a ta ly s t cause erroneous results unless p ro p e r corrections are applied.
T h e m eth o d of U hrig an d L evin (8) for determ ining bro
m ine a d d itio n n u m b er of liquid h y d ro carb o n s prom pted the in v estig atio n of a sim ilar pro ced u re for gaseous hydrocarbons.
T h e principle (b ro m in atio n b y a so lution of b ro m in e in glacial acetic acid, u n d er conditions of titra tio n ) rem ained th e same b u t m odifications were m ad e to a d a p t th e procedure to gases.
T h is w as easily done for gaseous h y d ro carb o n m ixtures con
tain in g C3, C 4) a n d C 5 olefins. T h e m eth o d w as also ex
ten d ed to d eterm in e th ese olefins to th e exclusion of ethylene if th e la tte r did n o t exceed 10 p er c e n t of th e sam ple.
Fi g u r e 1. Ap p a r a t u s
An adaptation of the method of Uhrig and Levin (S) has recently been published by Benson (/), who used it on a micro scale for determining olefins and obtained very good results, particularly when the end point of the direct bromine titration was illum inated w ith a blue-white lam p against a white back
ground.
M a ter ia ls U sed
T he butanes, propane, propone, ethylene, and m ethane used in the experimental work were all purchased as c . p. materials and tested 99.5 per cent pure or better. A commercial grade of propene, stated to be 95 per cent pure, was used in a few of the relim inary experiments on this compound. T he amylenes and utenes were prepared in this laboratory by conventional meth
ods and were 9 9 + per cent pure. T he ethane used was not purchased or prepared in the purified state b u t added in the form of certain plant gases.
R e a g e n ts a n d A p p a ra tu s
Bromine (1 per cent by volume) in c. p. glacial acetic acid, 0.1 N sodium thiosulfate, c. p. chloroform, 10 per cent potassium iodide solution, starch indicator solution, kerosene, and dry ice.
Standardize the brom ine solution by adding 5 ml. to 25 ml.
of 10 per cent potassium iodide solution and 5 ml. of chloroform in an iodine flask. T itra te this m ixture im m ediately w ith 0.1 A standardized sodium thiosulfate solution using starch indicator.
I t is advisable to standardize th e bromine solution daily until its stability is established under the conditions of use.
I n a d d i t i o n t o t h e a p p a r a t u s s h o w n d i a g r a m m a t i c a l l y i n F i g u r e 1 i t is d e s i r a b l e t o h a v e a 1 0 -m l. s e lf -fil lin g b u r e t f o r t h e b r o m i n e s o l u t i o n .
October 15, 1942 A N A L Y T I C A L E D I T I O N F, transfer the sample into the Erlenmeyer flask by mercu j placement to tube C. Agitate the flask to h a s t e n solution a condensation of the gas in the cold chloroform. T urn stop A, so th a t air will be drawn into the flask through th e hole end of the stopcock (Figure 2), thus displacing the sample
After the sample has condensed and dissolved in the chloroform, remove the flask and prom ptly titra te its contents w itn a per cent solution of bromine in glacial acetic acid. 1 he so is not cooled during titration. The end point is th a t a t w men a
used in all cases except on samples containing ethylene. The excess bromine reacts w ith some ethylene, b u t not quantitatively. U nder the condi
tions o iM ethod A ethylene does not react appre calculated to standard tem perature and pressure, is equivalent to 7.14 mg. of bromine on th e basis faint color of bromine persists for a t least 60 seconds, of very dilute bromine w ater (made by diluting
784 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 14, No. 10
Since ra p id ity of analysis was desired every effort w as m ade to develop such a m eth o d , even a t th e expense of ex trem e
Photometric Determination of Acetone-Insoluble
composition product of constituents of the oil rather than the con
stituents themselves.
Prior to th e introduction of the modified Gardner break test, the foots te st (2) was used to determine the quality of soybean oil.
The foots te s t measures the acetone-insoluble material in soybean oil by a volumetric procedure. This te s t was not entirely satis
factory because of th e difficulty of obtaining reproducible results and the time required.
G ravim etric m eth o d s of determ ining acetone-insoluble m aterial b y a c tu a l se p aratio n a n d weighing of th e m aterial are tim e-consum ing an d are com plicated b y in stab ility of the acetone-insoluble m aterial in oxygen and h e a t a fte r separation from th e oil phase. T h is m akes th e obtaining of reproducible results v ery difficult. I n th is investigation a photom etric procedure h as been developed for th e m easurem ent of acetone- insoluble m aterial in solvent-extracted soybean oil w ithout exposing th e m a te ria l to a ir or h e a t. T h e m ethod yields highly reproducible resu lts an d is sim ple an d rapid in opera
tion.
The p h o to m etric procedure is stan d ard ized against gravi- m etrically d eterm in ed values an d depends upon th e prepa
ration of stab le colloid sols of acetone-insoluble m aterial from solvent-extracted soybean oil in acetone. T hese sols rem ain acetone sol yielded a corrected extinction coefficient which was a m easu rem en t of th e tu rb id ity of th e acetone-insoluble