Studies on the Granulation of Adsorbents Based on Magnesium Oxide with Clay Binders
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This study examines the use of clay binders to granulate magnesium oxide based adsorbents, addressing problems associated with powdered sorbents such as low bed permeability, entrainment, and caking. Granules prepared from magnesium carbonate containing potassium hydroxide were formed on a laboratory granulator with bentonite and kaolinite clays, then evaluated for usable size fraction, mechanical strength, and carbon dioxide adsorption under dry and wet conditions. The results show that clay additives generally increased the yield of 1 to 3 mm granules, while their effects on strength and adsorption depended strongly on clay type and concentration. Crimean kil reduced adsorption, Oglanlinsk bentonite at higher loading improved wet carbon dioxide adsorption, and Glukhov and Voronov clays largely preserved adsorption properties, suggesting that suitable binders for magnesium oxide adsorbents may be broader than for zeolite granulation.
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STUDIES ON THE GRANULATION OF ADSORBENTS BASED ON MAGNESIUM OXIDE WITH CLAY BINDERS
I. N. Lantsman, P. D. Khalfina, V. M. Vityugin, N. F. Stas,
M. S. Lantsman, Z. A. Gafarova
(Presented by the scientific seminar of the Department of General Chemical Technology)
The practical use of powdered sorbents is difficult because of the low gas permeability of the bed, mechanical entrainment, caking, and the like. Therefore, when producing active oxide sorbents and catalysts, the need arises for a shaping process.
As previous studies have shown [1], the introduction of alkali-metal hydroxides promotes, on the one hand, activation of magnesium oxide and, on the other hand, makes it possible to obtain granules that are sufficiently strong under static conditions. To obtain granules stable under dynamic conditions in a multicycle operating regime, it is necessary to introduce plasticizing additives inert with respect to the adsorbate.
As such additives we used clays of various mineralogical composition: bentonites—Crimean kil and Oglanlinsk; and kaolinites—Glukhov and Voronov.
The principal requirements for binder materials in shaping are as follows: 1) the binder material must not screen or poison the active sorption centers; 2) at a minimal content, the material must impart to the granules sufficient mechanical strength, water resistance, and heat resistance under the conditions of a dynamic process.
An analysis of the literature data showed that the influence of clay binders on the granulation process of oxide sorbents has not been studied. Studies on the granulation of zeolite adsorbents [2, 3] showed that the clays used as binders can be divided into three types: 1) clays that ensure high mechanical strength and high adsorption activity of zeolite granules; 2) clays that give high strength to the granules but substantially reduce the adsorption activity of the zeolite; 3) clays that ensure good adsorption activity of the granules but with low mechanical strength.
It should be noted that, among the large number of clays studied, very few proved suitable for the granulation of zeolites, including Crimean kil and Glukhov clay. It has been observed that, in the granulation of zeolites, bentonite clays most often belong to the third type [4]. At the same time, the plasticizing properties of bentonites in the granulation process of iron-ore concentrates are known [5].
The present work sets forth the results of a study of the influence of clay binders on the granulation process of an adsorbent based on magnesium carbonate with the addition of 20% potassium hydroxide, prepared by the procedure of [1]. Granulation of the powders was carried out on a laboratory ta...
ribbed granulator; the adsorption properties of the granules were determined on a gravimetric static apparatus [6]. The results of the experiments are given in Table 1.
Table 1
Effect of clay binders on the properties of magnesium carbonate granules
| Binder | Additive, % | Yield of the 1–3 mm fraction, % | Strength, kg/gr | Adsorption, mg/g, CO₂ dry | Adsorption, mg/g, CO₂ wet |
|---|---|---|---|---|---|
| Without binder | 0 | 6,0 | 2,3 | 159 | 141 |
| Crimean kil | 2,5 | 51,0 | 0,31 | — | — |
| Crimean kil | 5,0 | 49,0 | 0,29 | — | — |
| Crimean kil | 10,0 | 65,0 | 1,30 | 72,0 | 120,0 |
| Crimean kil | 15,0 | 63,0 | 1,40 | 57,0 | 89,0 |
| Oglanlinsk bentonite | 5,0 | 40,3 | 0,63 | 65,0 | 193,0 |
| Oglanlinsk bentonite | 10,0 | 70,2 | 1,00 | 74,5 | 65,6 |
| Oglanlinsk bentonite | 15,0 | 72,3 | 1,16 | 53,7 | 161,0 |
| Oglanlinsk bentonite | 20,0 | 85,2 | 1,30 | 104,0 | 181,0 |
| Glukhov clay | 5,0 | 50,0 | 0,40 | — | — |
| Glukhov clay | 10,0 | 49,0 | 0,45 | — | — |
| Glukhov clay | 15,0 | 60,0 | 0,55 | 112,0 | 196,0 |
| Glukhov clay | 20,0 | 67,0 | 1,10 | 97,0 | 103,0 |
| Voronov clay | 5,0 | 33,6 | 3,87 | 93,0 | 136,0 |
| Voronov clay | 10,0 | 30,8 | 3,34 | 28,4 | 128,0 |
| Voronov clay | 15,0 | 14,0 | 2,90 | — | — |
As can be seen from the data in the table, the introduction of all clays in amounts up to 5% sharply reduces the strength of dry granules without heat treatment. A further increase in the amount of clay introduced leads to an increase in the strength of the granules to 1.0–1.4 kg/gr. Such strength of the initial granules under static conditions is sufficient.
It is interesting to note the effect of Voronov clay on the properties of magnesium carbonate granules. The introduction of 5% of this clay leads to a substantial strengthening of the granules (about 4 kg/granule). However, a further increase in the amount of additive leads to a decrease in the mechanical strength of the granules.
The introduction of all the clays studied leads to a sharp increase in the yield of the usable fraction of granules with a size of 1–3 mm. Adsorption studies showed that the introduction of Crimean kil leads to a decrease in the adsorption of both wet and dry carbon dioxide over the course of 2 hours. The addition of Oglanlinsk bentonite in an amount of 20% increases the adsorption of wet carbon dioxide. The presence of Glukhov and Voronov clays in the granule does not substantially impair the adsorption properties of magnesium oxide.
The results presented make it possible to conclude that the range of clay binders that can be selected for granulating adsorbents based on magnesium oxide is substantially wider than for granulating zeolites. Apparently, the nature of the interaction of the binder and its distribution in the pore space of the magnesium carbonate granule are somewhat different.
REFERENCES
-
Lantsman M. S., Khalfina P. D., Vityugin V. M., Stas N. F., Lantsman I. N., Gafarova Z. A. Izvestiya TPI, vol. 259, 1975.
-
Gribkova L. V. Vibration Method for Forming Zeolites. Author’s abstract, Institute of Physical Chemistry, Academy of Sciences of the USSR, Moscow, 1968.
-
Slepneva A. T. Study of the Process of Forming and the Properties of Synthetic Zeolites with Clay Binders, Moscow, 1969.
-
Slepneva A. T., Kruglitskii N. N. Kolloidnyi zhurnal, vol. 29, issue 2, Moscow, 1967.
-
Vityugin V. M., Lantsman I. N. Kolloidnyi zhurnal, vol. 36, issue 1, Moscow, 1974.