New Materials Monoliths

The protection against chemical warfare agents is based on sorption on activated carbon, both in gas mask canisters as well as in protective clothing. The carbon applied are granulates (mask) or small spheres (clothing). A new development in adsorption processes is the use of monoliths,3 either carbon monoliths or carbon-coated ceramic monoliths. Figure 4 shows a carbon monolith. Monoliths consist of many parallel channels separated by thin walls. The main advantages are low-pressure drop and short diffusion distances.

Carbon Monoliths
Figure 4. Carbon monolith and detail of the channels on the right.

Carbon and carbon-coated ceramic monoliths have been studied for the dynamic adsorption of low-concentration «-butane.4 Figure 5 shows breakthrough profiles of carbon coated ceramic monoliths and of Norit R1 carbon extrudates. The experiments with Norit carbon were performed with an equivalent amount of carbon as the corresponding monoliths, under similar conditions. Experimental conditions were as follows. The total flow rate was 1.5 L/min, which corresponds to a superficial gas velocity of 0.017 m/s, and the «-butane concentration was 7.2 g/m3 (3,100 ppm). Bed lengths of 5

and 10 cm monolith (made from individual pieces of 5 cm length) were applied at a cell density of 400 cells per square inch (cpsi). Figure 5 clearly shows that breakthrough profiles are much steeper for the coated monoliths compared to carbon extrudates, especially in the low concentration regime. This makes monoliths an attractive option for gas mask canister applications, which is even more so taking into account the low pressure drop (low breathing resistance).

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Figure 5. Breakthrough profiles of «-butane on carbon coated ceramic monolith and Norit R1 carbon.

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Figure 5. Breakthrough profiles of «-butane on carbon coated ceramic monolith and Norit R1 carbon.

Carbon Monoliths

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Figure 6. Breakthrough profiles of «-butane on carbon coated ceramic monoliths, total length 15 cm; the 5 cm pieces are stacked without empty space and with 0.5 and 2 cm empty space between the pieces.

Time (min)

Figure 6. Breakthrough profiles of «-butane on carbon coated ceramic monoliths, total length 15 cm; the 5 cm pieces are stacked without empty space and with 0.5 and 2 cm empty space between the pieces.

Another interesting feature is presented in Figure 6. Breakthrough profiles are shown of «-butane on carbon coated ceramic monoliths with a total length of 15 cm. The individual 5 cm pieces are stacked without empty space between the pieces and with 0.5 and 2 cm empty space between the pieces. Clearly, empty spaces between the monoliths result in a positive effect on the breakthrough profiles, which become steeper when the empty space is increased. This effect can be related to redistribution of flow between the monolith pieces.

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