1093
V O L U M E 2 4 , NO, 7, J U L Y 1 9 5 2 Table I. Comparison of Results by Liquid Phase and Modified Gas Phase Acetylene Procedures Acetylenes, Weight Mod. Saiiiple
Liquid phase
gas phaee
1
0.07 0.06 0.07
0.07 0.05 0.08
llars iprctromrter
2
0.09
0.10
i
0.24
0.24
.. ...
4
0.74 0.73
0 67 0 68 2-1
2 4
>
..
equal volume of distilled water. Drain wash \sater into the flask containing the reacted silver nitrate. Add 3 drops of mixed indicator and titrate with standard 0.05 AV sodium hydroxide solution to a slight green color. To determine the acidity of water and silver nitrate solution drain 100 ml. of d v e r nitrate into the absorber, then drain into 500-ml. Erlenmeyer flask. Follow this with 100 ml. of water, add mixed indicator, and titrate with 0.05 .V sodium hydroxide to the same green rolor as ohtained in previous step. This titration is the blank.
Calculations. 1. Weight of wu1ple in grams = 1V
where PROCEDURE
Apparatus. An approximately 1200-ml. calibrated sample tube equipped with three-way stopcocks a t both ends. A long absorber tube having a fritted thimble a t the gas entrance, approximate volume 200 ml. (see Figure 1 for details). h supply of nitrogen. Reagents. A 5 7 , alcoholic silver nitrate solution. made very rlightl? acid with nitric acid. -1supply of distilled water. Mixed indicator solution, 0.1 gram of methyl red plus 0.05 gram of methylene blue in 100 ml. of 9 5 C c ethyl alcohol. Stored i n a brown bottle. An aqueous standard 0.05 S sodium hydroxide solution. Procedure. Flush the sample tube well with sample through the sample entrance and allow t'he sample tube to warm t o room temperature. Wash the absorber tube with distilled water. I3y gravity flow drain 100 ml. of alcoholic, silver nitrate into the absorber. Release excess pressure in the sample tube t o the :it mosphere. Turn stopcocks so that the sample can he forced through the fritted thimble with nitrogen. Adjust nitrogen flow through the ple tube so that the liquid level in the absorber tube gradualljto within 8 to 10 inches of the top. Displace sample from sample tube with nitrogen for 3 minutes, then ?top nitrogen flow, and drain silver nitrate from the absorber into :I 3OO-ni1. Erlenmeyer flask. Wash the nl)sorber with an
I'
=
P
= tiarometric pressure, nun. of mercury = room temperature, degrees centigrade = vapor density, grams per ml. a t 30"
t
D
voluriie of sample, nil.
C:. and 760
1~11.
pressure 2. Calculate the aretylene content as weight per cent of vinylacetylene. \Veight %
=
(S - B)(A\q5.2)
mr
where
S
volume of sodium hydroside solution needed to neutralize acid in sample run R = volume of sodium hydroxide solution needed to neutralize acid in blank -1- = exact norniality of sodium hydroside solution ft7 = neight of *:tniplr in grams =
LITER-ATURE CITED
(11 Office of Rubbe], Reserve, Reconstruction Finance Corp., S y u -
thetic Rubber Division, "Butadiene Laboratory 1Ianual." Method I,. 11.2.1.4.3 (1946).
RECEIVED for reriew 1 I a i c h 14,1952. Acrepted .June 7 , 1952
Routine Determination of C, Hydrocarbons in Furfural or Absorber Oil K. E. H I ZKK, Sinclair Rubber Inc., Houston 1 , Tex. In refinery or butadiene plant operations using an absorber or selective solvent system to segregate a Ca fraction, it is often necessary to determine traces of C4 hydrocarbons left in lean solvents or absorber oils after the dissolved (24's have been distilled out. This analysis can be made with Podbielnialr's low temperature Hyd-Robot, but because of the wide differences in boiling points between the C4's and the lowest boiling component in the absorber oil or the solvent it is a somewhat difficult and lengthy operation. -4 short vacuum-jacketed, Raschig ringpacked column equipped with a 500-ml. kettle was built, to which 250 ml. of sample plus 50 ml. of alcohol as a chaser can be charged. The C;'s driven overhead are condensed in a graduated pear-shaped centrifuge tube submerged in a dry ice-acetone bath. After volume corrections are applied, this procedure checks the results obtained on the Hyd-Robot verj closely and can be run in 15 minutes as compared to 1 to 2 hours by- Hyd-Robot distillation.
I
operationcr an absorber oil (usually 300" to 400" F. naphtha) is used for separating C, and C, hydrocarbons from lower boiling components by absorbing the Cd and Ca fraction in, and subsequently distilling them from, the higher boiling oil. This latter operation is knoTm as stripping. I n one of the processes used in the manufacture of butadiene, furfural is employed as the solvent in extractive distillation systems to separate desired components from a multicomponent Ca fraction Here, too, the dissolved material is removed from the solvent by stripping. I n order t'o adjust plant conditions properly, it is necessary to determine the trace quantities of (2,'s left in the solvent, or absorber oil after the stripping operation. Because there is a wide gap between the boiling ranges of the Cd's and absorber oil or furfural, this is a time-consuming and often a difficult determination using the conventional Podbielniak low temperature Hyd-Robot distillation apparatus. I n addition, furfural polymer present in small quantities in the furfural fouls the HeliGrid packing after two or three determinations. Because of the large number of such samples to he tested, a simple rapid procedure was needed for determining t,race quanti-
ANALYTICAL CHEMISTRY
1094
ties of light hydrocarbons in solvents. I t u w apparent that bccause of the wide difference in boiling range, very little fractionation would be required. Therefore, the short, glass, Raschig ring-packed column shown in Figure 1 was designed. APPARATUS
The W i n c h packed section is vacuum-jacketed to maintain as nearly adiabatic conditions as possible. The external and coldfinger condensers a t the top of the column are constructed so that the vapor space between them is kept to a minimum, and with sufficient cooling surface to condense the alcohol used as a chaser. The lines to the manometer and the overhead receiver are made from Hyd-Robot overhead lines, but could be made from any capillary (approximately 1 mm. in inside diameter) brass or copper tubing. Small-bore tubing is necessary in order to cut down on vapor space. A pear-shaped centrifuge tube calibrated in O:l-m1. divisions for the first 1.5 ml. is used for the overhead receiver. The manometer was added as a simple leak detector. The kettle is calibrated a t the 250-ml. and 300-ml. levels to indicate when the proper volumes of sample and alcohol have been added. PROCEDURE
The procedure is simple. Prior to charging of the sample, the system is evacuated through the vent line on the overhead receiver in order to check for leaks by observing the mercury level in the capillary tube. The sample (250 ml.) is admitted from a sample bomb through the stopcock on the pot, followed by 50 ml. of denatured ethyl alcohol to act as an intermediate boiling material between the Ca's and the absorber oil or furfural. The distillation is conducted a t atmospheric pressure. Heat is applied to the ot and slowly increased until reflux is observed dripping from %e water-cooled reflux condenser. Heating is continued for 1 minute. The overhead receiver is removed from the dry ice-acetone bath and the volume of the hydrocarbon is quickly read before the temperature rises appreciably. Calculations are as follows: loo X
ml. Of Overhead ml. of sample
"*
= liquid volume %hydrocarbon
((2,)
where 1.4 is average factor to correct observed volume to rooin temperature (78' F.).. A series of synthetic blends was made to check the procedure. These were prepared by adding n-butane to weighed samples of naphtha of 300" to 400" F. boiling point and then calculating the per cent added from the increase in weight. The weight per cent was converted to liquid volume per cent.
Blend Blend Blend Blend
1 2 3 4
Ca Hydrocarbon. Vol. R Synthetic Found 1.12 1.16 1.23 1.23 1.35 1,35 0.15 0 13
Figure 1. Column for Determining Cq in Furfural or Absorber Oil
This method has been in use for 4 years and has given very satisfactory results. A determination can be made in approximately 15 minutes. RECEIVED for review March 1 4 , 1952. Accepted June 7 , 1952.
[ End of Butadiene Symposium ]
