Biomedical Engineering Reference
In-Depth Information
table 1.
(Continued)
Molecule
Kinetic diameter
[nm]
MIN-1
Smallest dimension of the
molecule [nm]
MIN-2
Intermediate dimension
perpendicular to MIN-1 [nm]
SF
6
0.55
0.49
0.53
CCl
4
0.59
0.57
0.58
C
6
H
6
0.59
0.33
0.66
Cyclohexane
0.60
0.50
0.66
CO
-
0.28
-
We performed several separation tests targeting on separation of gases (Table 2)
which should be incapable to specific molecular interactions like dipole orientation.
For better illustration of separation capability of the fabricated carbons, we have cho-
sen chemically inert gases of similar symmetry that is neon and krypton. Nitrogen was
picked-up regarding its inertia but also its specific geometry (longitudinal two-atom
molecule) differing from a spherical shape ascribed to Ne and Kr atoms.
Figure 3(a)
and 3(b) present chromatographic peaks attributed to particular gases resulting from
gas mixture separation (Kr/N
2
and Ne/N
2
respectively).
It is visible that Kr/N
2
mixture undergoes separation more effectively at both tem-
peratures (30°C and 70°C) while Ne/N
2
cannot be separated at 70°C (peaks overleap-
ing). The effect may be explained basing on atomic and molecular dimensions given
in the Table 1. Minimal dimensions (MIN-1) of Kr and N
2
differ considerably (0.36
nm and 0.30 nm respectively) while minimal dimensions of Ne and N
2
are very similar
(0.30 nm and 0.28 nm respectively). Thus, the unique pore structure of
Salix viminalis
originated carbons helped to separate effectively atoms/molecules whose shape and
size differed only by 0.06 nm size difference. The results also suggest that N
2
mol-
ecules penetrate into pores of investigated carbons based on their minimal dimension.
table 2.
Effectiveness of binary gas mixture separation over
Salix viminalis
originated carbon
molecular sieve.
Temp
[
0
C]
CH
4
/N
2
CO/N
2
Ne/N
2
Kr/N
2
CH
4
/CO
Ne/CO
Kr/CO
CH
4
/Kr
Ne/Kr
CH
4
/Ne
70
+
-
+
+
+
+
+
-
+
+
60
+
-
+
+
+
+
+
-
+
+
50
+
-
+
+
+
+
+
-
+
+
40
+
-
+
+
+
+
+
-
+
+
30
+
-
+
+
+
+
+
-
+
+
“+”--separation coefficient > 1
“-”--separation coefficient < 1
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