Sorption Of Silicon Tetrafluoride
SORPTION OF SILICON TETRAFLUORIDE
ONTO ANION EXCHANGE RESINS
E. K. Malinovskiy, V. P. Petrosyan, B. M. Kats
Physical Research Institute, University of Odessa,
27 Pastera St., Odessa, 65026, Ukraine
The equilibrium sorption of silicon tetrafluoride on to styrene divinylbenzene anionites with the functional groups such as -NH2, =NH, N, –(CH3)4N+, -NH(CH2)2NH2 and -NH(CH2)2NH(CH2)2NH2 type and with the macroporous and geleous polymer matrix type was studied. The experiments were made according to the methodic described earlier [1,2] under the temperature 298, 313 and 323 K in the pressure interval 10-2 – 800 mm Hg.
It is stated that the waterless weak base macroporous anionites sorption capacity on to silicon tetrafluoride increases according to the increase of anionite exchange capacity value and is substantially higher than that of the geleous structure anionites. Their sorption capacity is influenced not by the total number of functional groups, but mainly by their being available in dry state.
The molecular size increasing while transforming from silicon tetrafluoride to germanium tetrafluoride leads to the natural anionite sorption capacity decrease. It happens due to the sterical difficulties, appearing under the germanium tetrafluoride diffusion in the resin macropores.
Using silicon tetrafluoride as a sample substance we found out the phenomenon of ionites swelling under the gas sorption process. The macroporous anionites swelling coefficients under the silicon tetrafluoride sorption are 1,08-1,13 while the resins with the helium structure polymer matrix practically don’t swell at all in the silicon tetrafluoride sorption process.
The mechanism of non-reversed silicon tetrafluoride sorption with anionites of different types is suggested. The silicon tetrafluoride molecule connecting by the first and second waterless weak base resins amino groups takes place due to the formation of the compounds with the donor-acceptor link Si←:N. In the case of strong base anionites it is due to the adsorbed sorbate hydrolysis by the remaining water with the subsequent exchange of silicohexafluoride-ions with hydroxyl counter-ions of quadruple ammonium
groups. While studying kinetics of silicon tetrafluoride sorption by anionites of different types we stated that the macroporous anionite adsorb silicon tetrafluoride much quicker than the gel resins. The calculated coefficients of the silicon tetrafluoride inner diffusion in the macroporous anionites possess the value of about 10-8sm/… and averagely are two decimal digits higher than the gel ones.
The bioporous kinetic model (3) explains the peculiarities of the silicon tetrafluoride molecules diffusion mass transfer process in the macroporous anion exchange resins, which in the studied conditions can’t be described satisfactorily with the help of the known quasihomogenic model with one inner diffusion coefficient. The silicon tetrafluoride adsorption by macroporous anionites proceeds in two stages. Correlation between them changes substantially with the gas sorbate pressure increase, however the limiting stage in all cases is the inner diffusion.
It is stated that the values of the total and reversed silicon tetrafluoride water sorption as well as the process velocity grow sharply with the growth of the preadsorbed water contents. With the initial water increase the silicon tetrafluoride effective diffusion coefficients grow on two decimal digits for macroporous anionites and on three decimal digits for gel ones in comparison with the respective values of the dry samples.
Basing on the comparison of the adsorption capacity and operation characteristics for the number of industrial adsorbents and the weakbase macroporous anionites we suggest the anionite A-H-251-12/80 for air purification from silicon tetrafluoride with the further chemical or thermal resin regeneration.
References
1. Kats, B.M. and Malinovskiy, E.K. (1978) Zh. Phys. Khem. 52, 1816.
2. Kats, B.M. and Malinovskiy, E.K. (1980) Zh. Prykl. Khem. 53, 1242.
3. Ruckenstein, E., Vaidynathan, A.and Youngquist, G.( 1971) Chem. Eng. Sci. 26, 1305.
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