Gas Chromatography On The Modifications
Gas chromatography on the modifications
of Y-type zeolite with binding clay
O.S. Banach, I.M. Zybak, V.I. Rohovyk, A.F. Mynka
Danylo Halytskyi State Medical University, Lviv, Ukraine
Industrially produced Y-type zeolites have spherical or cylindrical shape and contain binding additions increasing their mechanical strength. Such adsorbents are used for effective dehydratation of gases and liquids and also as fillers in gas chromatography. Exchanging initial ions in zeolite by other cations allows to change substantially their absorbing properties and to obtain cation modifications with desirable chromatographic properties.
The aim of our work was to modify the industrial zeolite by exchanging 1 – 10 % of its Na+-ions by the cations Ag+ or Cu2+ and to study the obtained sorbents by the method of gas chromatography. For this we used model gas mixtures containing alkanes and alkels C1 – C4, carbon and nitrogen oxides, and air. The formed zeolite NaY containing 15 % of binding clay was ground and the fraction 0,5 – 1,0 mm was taken. The granules of the fraction were treated by various amounts of the salts AgNO3 and CuSO4 to obtain different samples with 1 – 20 % of Na+ exchanged by the cations of Ag+ or Cu2+. These samples were filled into the columns of a gas chromatograph and were studied in the temperature range from 300 down to 60° C. Obtained retentions times of separation of components of the model mixtures were used for calculation of specific retention volumes Vg per a mass unit of dehydrated zeolite samples. Results of this calculation are presented in the table.
The table shows that the increase of the amount of the Ag+-cations in AgNaY samples results in the increase of the retention volumes Vg for all gases. But the alkanes and N2O show a slower growth comparing to the olefins and CO whose molecules longer retent in the zeolite because of specific interactions. Having a quadruple, non-polar molecules of CO2 by their chromatographic properties occupy an intermediate position between alkanes and olefins.
After exchanging 5 – 12 % of Na+-ions by Ag+ there is a temperature inversion (change of the sequence) of eluation of components at the
chromatographic separations of binary mixtures: CO2 – C3H8, CO2 – C4H10, C2H6 – CO, N2O – CO, C2H6 – CO, C3H8 – CO etc, whose first component eluates earlier at lower temperatures. After heating the zeolites in the chromatographic columns these gases become inseparable and then eluates again but in the reverse order.
Table. The influence of Ag+-cations in AgNaY on Vg (ml/g) of gases
Compo-nents
Tempera-ture, °C
Exchange degree of Na+ by Ag+, %
0
1,1
2,4
4,9
7,3
9,7
12,2
n-C4H10
220
16,9
17,0
17,3
17,6
18,1
18,6
18,9
i-C4H10
220
15,7
16,3
16,6
16,9
17,0
17,5
18,0
C3H8
160
10,8
10,9
11,1
11,4
11,8
12,5
13,4
C2H6
100
9,2
9,4
9,6
9,7
10,1
10,3
10,7
CH4
60
3,6
3,7
3,7
3,8
3,9
4,1
4,2
C3H6
280
6,2
16,6
43,2
-
-
-
-
C2H4
260
2,0
6,4
13,0
25,2
40,3
55,4
75,9
CO
120
1,3
2,0
2,9
4,4
6,8
9,8
16,5
CO2
120
27,0
27,8
29,2
32,0
36,4
40,9
49,0
N2O
120
12,3
12,5
12,7
13,1
13,5
14,0
14,5
By analogy with the AgNaY zeolites we prepared and studied Cu2+–modifications with up to 20 % of Na+-ions exchanges by Cu2+. The decrease of the general quantity of cations as adsorption centers in the zeolite grid results in the decrease of the specific volumes of chromatographic retention for all alkanes and oxides CO2 and N2O. In contrast, these characteristics increase rapidly for alkanes and carbon dioxide at a small ion-exchange degree from 2 up 20%.
On the zeolite 0,06 CuNaY there appeared an effect of low substitution, which was observed for the first time on synthetic zeolites without binding clay. At presence 15 % of clay this effect is less contrast.
We would recommend using the formed Y-type zeolies modified by Ag+- and Cu2+- cations for selective extraction of various pollutants from air and also as adsorbents at chromatographic analysis and separation of various gas mixtures.
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