I
MICHAEL HOMIAK and JOHN W. AXELSON Johns-Manville Corp., Manville, N. J.
Liquid Partition Chromatography
. . . . . for
Polyhydric Alcohols Refinement of analytical techniques shows promise of developing into a separation method for many industrial processes
CHROMATOGRAPHIC was carried out at room temperature. A weighed amount of adsorbent and a
techniques were investigated for the separation of polyhydric alcohols, as represented by ethylene glycol and glycerol, using columns of diatomaceous earth. I n previous work on the chromatographic separation of polyhydric and monohydric alcohols columns of silicic acid or silicic acidCelite mixtures (7), Celite-535 ( Z ) , or ion exchange resins (4,5) were used, but separations were carried out principally for analytical purposes and involved only microgram quantities of the component alcohols. Of the several earths investigated, Chromosorb was the most suitable for studying operating variables and establishing conditions that would permit a n effective separation of the alcohols. Experimental
Apparatus and Materials. Columns were of borosilicate glass of various diameters and lengths, each equipped with a valve, such as a stopcock, to regulate the flow rate. Most of the work was done with two identical columns having an inside diameter of 11.3 mm. and a height of 600 mm. Pipets of 3 and 5 ml. (Ace Glass Inc.), used to collect samples of equal volume, were developed by Rieman ( 3 ) . Fractions were collected automatically with a simple turntable activated by a balance. An Abbe-type refractometer with a sodium lamp was used to determine the index of refraction of the samples. Ethylene glycol and glycerol were chosen as representative of polyhydric alcohols. Methyl ethyl ketone was used as the column liquid and as the solvent for glycol. A mixture of 30:70 volume % of isopropyl alcohol in methyl ethyl ketone was used for glycerol. Various suitable diatomaceous earths were tested along with silica gel. One of the earths, Chromosorb, was used for the experimental work described. Procedure. All experimental work
measured volume of distilled water, used as the stationary phase, were stirred until the mixture was homogeneous. This normally required about 1 to 2 minutes after which time the adsorbent was a free-flowing powder with no free water present. This powder was then poured slowly into the chromatographic tube containing the solvent. The tube was tapped gently as the powder was added to eliminate voids and to ensure formation of a uniform column. From a suspended separatory funnel, used as a reservoir, the solutions were allowed to flow to the column at a rate controlled to maintain a constant head of liquid of 1 cm. In order to determine the optimum and limiting conditions in the use of Chromosorb to separate ethylene glycol and glycerol, a study was made of the capacity of the column for each of the alcohols, and of the effect of variables on capacity. The capacity is defined as the amount of solute retained by the column, expressed in ml. per gram of adsorbent.
Table I. Capacities of Various Diatomaceous Earths and Silica Gel for Glycol and Glycerol (Stationary phase-adsorbent ratio 0.66 ml./ gram) Capacity, M1 /G. for Adsorbent Glycol Glycerol Chromosorb, 35- to 80mesh" 0.454 0.339 Celite 535= 0.539 0.466 Catslyst Carrier Type IXQ 0.160 0.050 0.587 0.369 Celite 545" Chromosorb 35- to 80mesh acid washeda 0.413 0.296 0.288 0.161 Silica Gel Grade 922* Johns-Manville Corp.
* Davison Chemical Corp.
All capacities were determined by frontal analysis. A solution of definite composition was added continuously to the column. Equal volume fractions were collected, the composition of each being determined from its index of refraction. Samples were collected until the composition of the liquid leaving the column was the same as that of the feed to the column. From the data thus obtained, the total amount of solute retained by the column was calculated. A 20% solution of ethylene glycol in methyl ethyl ketone was used to determine the capacity of the column for this glycol. A 10% solution of glycerol in a mixture of 30:70 volume yo of isopropyl alcohol/methyl ethyl ketone was used to determine the capacity of the column for glycerol. The effects of flow rate, adsorbent particle size, and amount of stationary phase were determined for each of the alcohols. The actual separation of ethylene glycol and glycerol was carried out by elution partition chromatography. The effect of height to diameter ratio of the column on the separation was studied in this case. For a ratio of 50 to 1, the run was conducted as follows: The column was prepared as described previously using 18 grams of 35- to 80-mesh Chromosorb containing 15 ml. of distilled water. A mixture of 4 ml. of glycerol and 6 ml. of ethylene glycol was placed on the column. Ethylene glycol was eluted with methyl ethyl ketone and glycerol with the 30:7C mixture of isopropyl alcohol-methyl ethyl ketone, a flow rate of 0.5 ml. per minute being maintained in each case. Eighty milliliters of solvent were required to elute the glycol; 65 ml. were required for glycerol. Results. The adsorbents tested are listed in Table I. Chromosorb was selected for the study of variables and separation of the alcohols because its capacity was relatively high, it could be varied in particle size, and columns could be prepared and handled easily. VOL. 52, NO.
a
AUGUST 1960
689
0.420
0.400
I..
FLOW
GLYCOL
0
RATE IO
0.470
ML. PER MINUTE 20
3.0
~0.3901
5z
- - - - ADSORBENT
I-
r0 a
\
>,(3.330 0
0
02g01
0.280
I
0,210'
I
30 40 50 60 ADSORBENT ?ARTICLE SIZE - AVERAGE MESH SIZE
0
0 0.2 0.4 0.6 0.8 1.0 STATIONARY PHASE PER GRAM OF ADSORBENT, ML. Figure 1 . Capacity of Chromosorb for glycol and glycerol increased as the amount of stationary phase increased
The capacity of Chromosorb increased as the amount of stationary phase present increased (Figure 1). An upper limit of 1 ml. of water per gram of adsorbent was set, because a greater volume of stationary phase formed a slurry with the adsorbent. A decrease in adsorbent particle size resulted in an increase in the capacity of the column for each of the two alcohols (Figure 2). The finest particle size of Chromosorb used was material retained on an 80-mesh screen. That portion passing through an 8O-nlesh screen formed a heavy paste when a column was prepared, and reduced the flow rate to such a low value-14 ml. in 24 hoursthat the time required for the run was impractical. The use of air pressure did not help. A decrease in flow rate also increased the capacity of Chromosorb for both alcohols (Figure 2). The effect of varying the column height to diameter ratio on efficiency of separation is shown by data in Table 11. Discussion
Mixtures of glycerol and ethylene glycol were separated with recoveries of 90 to 96y0for glycerol and 96 to 102Yo for glycol. Separation became more ef-
690
I
0.2701
0.260
0.220
RATE
\
i-
0.300
PARTICLE SIZE
-FLOW
IO
Height to Diameter Ratio Added Found Glycerol
Recovery, %
50 to 1 35 to 1 18 to 1
3.8 3.8 3.8
3.651 3.525 3.454
96.1 92.8 90.9
50 to 1
Glycol 6.0 6.2 6.0 5.913 6.0 5.812
102 98.5 96.8
-
70
each of the alcohols in a direct ratio, and a decrease in particle size of adsorbent also resulted in the expected increase in capacity. Data from the elution study were used to calculate the number of theoretical plates-there were 103. Because the height of the column was known, the height of a theoretical plate was calculated to be approximately 0.175 cm. Acknowledgment
fective as the column height to diameter ratio increased. For both glycerol and glycol the effect on the capacity of the columns prepared from Chromosorb followed the expected pattern, increasing as the rate of flow of the mobile phase was decreased. The increase was approximately 20y0 when the flow rate was reduced from a maximum of 3.0 ml. per minute per square cm. of cross sectional area to a minimum of 0.25 ml. The amount of stationary phase adsorbed on the inert support was found to increase the capacity of the column for
INDUSTRIAL AND ENGINEERING CHEMISTRY
~
Figure 2. The adsorption of glycol and glycerol on Chromosorb increased with a decrease in the adsorbent particle size and fell off with an increase in flow rate
Table II. Effect of Height to Diameter Ratio of Column on Efficiency of Separation Column
35 to 1 18 to 1
20
The authors thank the Johns-Manville Corp. for supplying the major portion of the adsorbent used in this investigation. Literature Cited (1) Dal Nogare, S., Anal. Chen. 2 5 , 1874 (1953). (2) Neish, A. C., Can. J . Research 28 B, 535 (1950). (3) Reiman, W., Lindenbaum, S., Anal. Chem. 24, 1199 (1952). (4) Reiman, W., Sargent, R . , Anal. Chem. Acta 14,381 (1956). (5) Reiman, W., Sargent, R., J . Phys. Chem. 60,1370 (1956).
RECEIVED for review July 27, 1959 ACCEPTED APRIL4, 1960 Taken in part from the M.S. thesis of Michael Homiak, Newark College of Engineering, Newark, N. J., June 1958.
