Adsorption of Acetic Acid by Activated Carbons, Zeolites, and Other Adsorbent Materials Related with the Preventive Conservation of Lead Objects in Museum Showcases

Abstract

To test the suitability of adsorbents such as activated carbons, zeolites, and other materials to adsorb acetic acid vapors that are liberated inside museum showcases and may destroy lead objects, the adsorption capacities at the saturation pressure and the isotherms of adsorption at lower pressures were determined. The results obtained show that the NaX zeolite in pellet form and the RB4 activated carbon are the best adsorbents. Additionally, they show that materials with sodium content exhibit an exchange process that may be very important, particularly in the case of NaX zeolite. Some of the parameters determined (saturation capacity, Henry constant, kinetic parameter) seem to be related in a simple manner (although there are adsorbents that do not agree with the general trend). However, a simple relation was not found between the specific surface area previously determined with nitrogen at 77 K and the acetic acid saturation capacity at room temperature.

Comparison of adsorbent materials for acetic acid removal in showcases

“…Considering these facts and the data provided by the thermograms, we can estimate the value of maximum adsorption for the RB4 carbon, at the conditions employed, as 41%. This value is significantly inferior to the value of 54% obtained in a previous study, by another method, for an atmosphere of pure acetic acid at its saturation pressure [24]. Therefore, due to the moisture in the atmosphere or the lower concentration of the acetic acid vapors, the maximum capacity of adsorption of the activated carbon, as determined with an atmosphere of pure acetic acid, the present case is not completely available.…”

“…7 which shows that the removal of the adsorbed compounds it is much easier in the case of the activated carbon than in the case of the zeolite. So, the superior efficiency of the zeolite in the beginning of the experiments can be explained by the stronger interaction between the adsorbent and the adsorbate, although this polar factor did not seem to have great importance in the conditions employed in the previous studies [24]. The fact that, for any of the adsorbents, the adsorbed amount in percentage is greater when a smaller amount of adsorbent is used can be explained by the easier diffusion of the acetic acid in the goblet with a reduced amount of the adsorbent.…”

“…Adsorbents were characterized and selected in previous studies [24]. RB4 is an activated carbon in pellet form (from Norit, Holland) with a specific surface area of 1320 m 2 g À1 and a microporous volume of 0.54 cm 3 g À1 .…”

“…NaX is a zeolite X, also in pellet form, from BDH, with a specific surface area of 533 m 2 g À1 and a microporous volume of 0.22 cm 3 g À1 . In previous publications was labeled as NaX(P) or NaXP [23,24].…”

“…Above all, in spite of the works already published, there is the need for systematic studies, conducted specifically for museum atmospheres, on the relative efficiency of the available adsorbent materials. It was in this context that we have initiate a study with the objective of comparing the efficiency of several zeolites, activated carbons and other adsorbent materials, namely silica gel and a clay pillared with aluminum oxide pillars (PILC), for the removal, in a passive mode, of acetic acid vapors from the atmosphere [23,24]. In a first stage, nine adsorbents were studied and for each one the adsorption capacity at the saturation pressure of the acetic acid and the adsorption isotherm at low pressures were determined at room temperature.…”