Barry Finn and Mike Morris

University College Cork

NEW RESULTS ON SORBENTS FOR ACETIC ACID IN MUSEUM AIR

ABSTRACT

There are several mitigations options to create low levels of volatile organic compounds in enclosed environments.

An often suggested method is dilution by forced air flow. Yet more air movement will result in increased off-gassing and a shift in the equilibrium. For a 1m³ cube the air flow should be 25 m³/min to reduce the pollutant levels.

Another option under study is absorption. For example with active charcoal which has an absorption capacity of 0.8 ng/cm²s, or with La₂O₃ which has a much higher capacity of 0.2 g/cm²s. With its large absorption surface area it can absorb up to 3.5 times its weight. However, disadvantage of these sorbents is that acetic acid is quite 'sticky' but not all molecules stick that well to the sorbent material and they desorb just as easily, giving rise to increased off-gassing. The sorbent material saturates rather fast and because the supply or movement of gases to the sorbent is hasr to control the process is unpredictable. In practice, one needs as much as possible sorbent to 'clean the air' and the air quality needs to be determined regularly to avoid the drawbacks.

A more promising method seems to be combustion. With the use of the proper catalyst acetic acid can be oxidised to carbon dioxide and water:

2 O₂   +   CH₃-COOH   ->   2 CO₂   +   2 H₂O

With a noble metal supported catalyst combustion can be achieved at 100°C and complete combustion is possible at temperatures below 300°C. These temperatures are still impractical for museum application, but the idea may prove useful in future.

(editor's abstract)