Water Determination in Chlorination Reaction Media by Gas Chromatography Henk van den Berg and Harry van Olst Chemical Engineering Laboratory, State University, Groningen, The Netherlands
I
In the laboratory, we investigate the influence on the reaction rate of the concentration of water in the substitutive chlorination of several organic substances. Since it appears that even very small amounts of water have a marked effect, it is necessary to find a method for determining these very small quantities of water in organic solvents in the presence of Cl2, HC1, and several types of catalysts. A review of water determination by techniques of gas chromatography is given by Neumann ( I ) . In the gas chromatographic method published by Hogan, Engel, and Stevenson (2), CH30H is used as an internal standard. Reaction of Cl2 with CH30H, however, makes the application of CH3OH as an internal standard impossible in the determination of water in chlorination processes.
EXPERIMENTAL Apparatus. A versatile gas chromatograph and an accurate electronic integrator were used. Details are given in Table I. Porapak Q is treated as prescribed by Hogan et al. (2). Super dry helium, containing less than 2 ppm wt HzO, proved to be necessary to obtain reproducible results. Calibration Procedure. Test samples were prepared in a conical flask closed with a rubber stopper (see Figure 1); both flask and stopper had been previously dried in an oven a t 110 "C. About 100 grams of benzene dried on molecular sieve 3-A, were first weighed into the flask. Then about 1000-3000 ppm wt dry internal standard CHzC12 was added by means of a syringe. Small amounts of water were added in the same way. The syringe was kept dry (after cleaning with acetone) by inserting it into a conical flask filled with Drierite and closed with a rubber stopper. Determination of Water in Chlorination Reaction Media. A 1-ml sample, drawn from the chlorination apparatus, is injected in a 2-ml Hewlett-Packard sample vial, which is then closed immediately. In order to destroy Clz, which interferes with the gas chromatographic water determination, the sample is irradiated with UV light, for about 20 minutes ( A = 360 mm). Then a given quantity of internal standard, CHzC12 in benzene, is added. The standard quantity is 70 pl. In order to eliminate HC1, 30 pl of pyridine dried on molecular sieve 4-A is added. After homogenization and centrifugation of the precipitate formed, a sample is injected into the gas chromatograph. After each operation, the syringe is cleaned and dried in a Hamilton syringe cleaner. The water content of the sample is calculated by the formula:
weight int. s t d (benzene
+
~
~
~~
~~
~~~~
~
~
~~~
Table I. Gas Chromatographic Water Determination, Operating Conditions Instruments : Gas chromatograph : Perkin-Elmer Model
900 lnfotronics Model CRS-104 Porapak Q, 50-80 mesh Length : 1.80 m Diameter : 0.003 m ('/8 in.) : Thermal conductivity Integrator
Column Detector Bridge current Carrier gas Syringe Sample charged Temperatures
:
: 225 mA : Helium, L'Air Liquide type B 56 (max. 2 ppm wt. H 2 0 , purity 99,9998%).Flow 0.3 X 10-6 m3/sec : Hamilton model 1710, gastight : 25 Injection port : 175°C Detector : 200 "C Manifold : 175 "C : 120 "C, after integration of Column
Relative retention time
-
CH2C12 peak program to 230 "C at 0.4 "C/sec : water 0.17 methylene 1.0 (-500
chloride
sec)
silicogel tube
CH2Clz) X
weight sample p p m w t CH2C12 in int. s t d
x
area HzO X
area CHzC12 correction factor
-
weight int. s t d X
weight sample p p m wt HzO in int. std -
weight pyridine X
weight sample p p m wt HzO in pyridine (1) G. M. Neurnann, Fresenius' 2. Anal. Chem., 244, 302 (1969). (2) J. M. Hogan, R. A. Engel, and H. F. Stevenson, Anal. Chem., 42, 249 (1970).
Karl Fischer titrat ion vessel
Figure 1. Set-up for calibration by Karl Fischer titration
ANALYTICAL CHEMISTRY, VOL. 45, NO. 11, SEPTEMBER 1973
1967
250r 200
Table II. Data of a Calibration Re1 area
-
Hz0
150 -
p
100-
I"
50-
pprn wt H20
CH2CI2
Exp. No.
:
1 2 3 4 5
3
o/
200
100
aroa H 0 area &t2.
-50-
400
300
pprn wt CHzCI2
58.4 131 280 285 478
No. of samples
...
Measured Added
2 5 1 5 9
2.7
... 3.1 3.2
0 39 120 123 226
byGC
30.7 70.4 150.7 153.4 257.1
ppm~CH2C12
Figure 2. Calibration
Table Ill. Data of a Karl Fischer Calibration Rel. area
Correction factor for H 2 0 = 0.535, residual H20:30 pprn wt
Hz0 CH2CIa
Re1 std dev
C6H6
\
Exp. No.
6 7 8 9 10 11 12
58 65 40 84 163 325 713
pprn wt H 2 0
X
CH2C12 ppm wt CHzClz
Re1 std No. of dev samples
...
1
8 12
8 5 3 3 7 4
... ... 7
...
-
by KF titrations
Measured by GC
23 28 29 39 71 145 298
24 27 17 35 68 146 298
Table I V . Results of Water Determination in the Chlorination of Cyclohexanone Exp. No. ppm wt H20
13
L I
0
I
I
1000
3000
2000
seconds Figure 3. Chromatogram of a water determination
C
3wt
.E200 LL:
Y
I
0
I
I
I
200
400
600
Figure 4. Calibration by Karl Fischer titration Correction factor = 0.41 7
1968
1 1 6.3 119.4 14 64.0 63.5 15 76.2 88.4 65.3 16 59.0 58.7 17 1 79.0a 111.0 111.0 18 90.2 90.8 19 54.9 56.8 20 406.3 390.1 21 398.7 416.8 22 230.0 213.0 23 119.2 132.2 24 119.9 105.5 25 94.0 83.8 26 114.5 117.7 27 99.3 1 1 5.2 28 140.8 144.9 29 272.8 233.4 202.2 Reliability interval duplicate f17 ppm wt; triplicate f14 ppm wt. a
Discarded.
ANALYTICAL CHEMISTRY, VOL. 45, NO. 1 1 , SEPTEMBER 1973
RESULTS AND DISCUSSION Direct Gas Chromatographic Method, Internal Standard CHZC12. The internal standard CHJOH used by Hogan and coworkers (2) is converted by the reaction mixture too soon. T o eliminate this effect, we use CH2C12 as an internal standard. A half-time for this standard of more than 24 hours is not a serious drawback in our determinations. The results of a calibration are shown in Figure 2. Figure 3 gives a representative chromatogram. Table I1 lists the data for Figure 2. The relative standard deviation a t each experiment proved to be 3%. Water concentrations varied from 70 to 260 ppm wt. In conformity with Hogan ( 2 ) and Hollis and Hayes ( 3 ) ,we measured a linear relation between relative area HZO/CHZC12 and H20 content. The additional HzO content caused by handling is 30 ppm wt, considerably less than the ca. 45 ppm wt found by Hollis and Hayes (3). The calculated correction factor is 0.535. The results of a second calibration procedure, executed by coupling the conical flask directly to the Karl Fischer apparatus, are given in Figure 4 and Table 111. Within experimental accuracy, the value found for residual water is zero, in contrast with Joseph ( 4 ) , who measures a peak height corresponding with about 55 ppm wt H20 content. A correction factor 0.417 is calculated. The difference between the correction factors measured is caused by the use of two different T C detectors. In accordance with Hollis and Hayes ( 3 ) , we find that the use of a back-flush valve reduces the accuracy and reliability of the determination. An example of water determination in chlorination reaction media is given in Table IV. The water content in this chlorination of cyclohexanone varies from 56 to 400 ppm wt. The confidence interval is *17 ppm wt for the duplicate and &14 ppm wt for the triplicate determinations. A second series of 24 samples taken from a continuous benzene chlorination process results in a mean value of 24 ppm wt HzO and a standard deviation of 27 ppm wt. A method for measuring the upper limit of the error caused by handling the sample is given below. The water added by the supply of internal standard solution and pyridine should be subtracted from the values measured gas chromatographically. To determine this correction, varying quantities of internal standard and pyridine are added to samples with a like amount of water (3) 0. L. Hollis and W. V. Hayes, J. Gas Chrornatogr., 4 , 235 (1966). (4) H. Joseph. IsraeiJ. Chem. 8, 575 (1970).
quantities of CH2CI2 and p y r . water analysis
Figure 5. S y s t e m a t i c e r r o r s in
a . H 2 0 added by CH2C12 and pyridine. b . H 2 0 added by handllng and residue in dry benzene
content, e . g . , benzene dried on molecular sieve. The value which is to be subtracted from the water content measured is indicated in Figure 5 by a . The value b on the ordinate is the sum of residual water in dry benzene and water introduced by handling the sample. Values for a and b of the order of magnitude of 20 ppm wt are normal. We showed that an accurate water determination is possible in the range of 50-440 ppm wt in chlorination reaction media, uiz., in the presence of chlorine, hydrogen chloride, and catalysts. In determining concentrations of 20 ppm wt, the accuracy decreases sharply ( D = 120%). Because a decrease in the accuracy in the 50-400 ppm wt range may occur accidentally, research is now concentrated on finding the factors affecting the reliability of the determination.
ACKNOWLEDGMENT Thanks are due to L. Balt for his helpful discussions. Received for review August 30, 1972. Accepted February 23, 1973.
Characterization of Pellicular Porosity by Gel Permeation Chromatography E. P. Otocka Bell Laboratories, Murray Hill, N.J. 07974
Pellicular ( i .e . , layered) chromatographic substrates have become a very important part of the resurgence of liquid chromatography (LC). These particles retain the advantage of large particle packings (low to medium pres-
sure drop across the column) while adding the advantage of small particle packings (greatly reduced plate heights). Since the porous surface layer on these beads represents such a small fraction of their total volume, characteriza-
ANALYTICAL CHEMISTRY, VOL. 45, NO. 11, SEPTEMBER 1973
1969
