1.12 Air Pollution Control Within Museum Display Cases by Active and Passive Sorbent Strategies
Daniel Grosjean and Associates
The Getty Conservation Institute
Antoinette Van Neste
George deW. Rogers
Period of Activity: 6/87 to 6/88
The objective of this study, which was deemed to be very important, was to provide the art conservation community with simple and cost-effective methods for reducing environmental damage to objects of art exhibited in display cases. To achieve this objective, a large matrix of experiments was carried out to test the effectiveness of selected sorbent materials for the removal of pollutant gases.
The pollutants examined were SO2, NO2, H2S, O3, and HCHO both in a passive mode, i.e., as a static flat bed, or in an active mode, i.e., pumped through a packed bed of sorbent.
Parmar, S. S., and D. Grosjean, "Sorbent Removal of Air Pollutants from Museum Display Cases," Final Report to the (Conservation at the Getty) Institute, June 1989. Also Environment International, Vol. 17, 1991, pp. 39-50.
ABSTRACT-Experiments have been carried out under controlled laboratory conditions to investigate the removal of air pollutants using sorbents.The pollutants tested, ozone, nitrogen dioxide, sulfur dioxide, formaldehyde, and hydrogen sulfide, are ubiquitous in museum air, and their adverse effects on a variety of materials relevant to museum collections have been documented. The sorbents tested included conventional adsorbents such as activated carbon and silica gel, polymeric materials such as Tenax and Chromosorb 102, and chemicals (coated on solid support) known to react selectively with one or more of the pollutants tested, e.g., DNPH for formaldehyde.
Tests were carried out in the active and passive modes. In the active mode, air containing a known, stable concentration of the pollutant tested flows at a constant air flow rate through a small cartridge packed with the sorbent tested. In the passive mode, a small amount of sorbent is placed in a 1 m3 display case containing polluted air, and the pollutant removal rate by the sorbent is determined.
Tests carried out in the active mode indicated that many sorbents meet our target performance target, i.e., are capable of removing 20 ppb of pollutant for one year of continuous use by flowing air at 0.1 L min-1 through 200 g of sorbent. Tests carried out in the passive mode showed that pollutant concentration vs. time plots all obey first-order kinetics. The corresponding passive removal rate constants and pollutant half-lives were determined. Removal rates ranged from 0.5 to 3 x 10-2 min-1 and for carbon were in the following order: O3> SO2 > H2S> NO2 > HCHO.
Parmar, S. S., and D. Grosjean, "Removal of Air Pollutants from Museum Display Cases," American Chemical Society, Division of Environmental Chemistry, Miami, Florida, September 10-15, 1989.
ABSTRACT-Solid sorbents have been evaluated experimentally for their ability to remove air pollutants in museum display cases display cases;. The air pollutants studied, each at levels of 10-100 ppb in purified air, included ozone (measured by ultraviolet photometry), NO2 (chemiluminescence ), SO2 (pulsed fluorescence), H2S (catalytic oxidation to SO2, pulsed fluorescence), and formaldehyde (collection on DNPH-coated cartridges, liquid chromatography a liquid chromatography analysis). The display case was 1 m3 Plexiglas cube lined inside with Teflon film.
Sorbent tests were carried out in the active mode (air flowing through the sorbent packed in a small cartridge) and in the passive mode (small amount of sorbent placed in a tray inside the display case ). In the active mode, pollutant concentrations were measured upstream and downstream of the sorbent cartridge until breakthrough was observed. In the passive mode, pollutant concentrations were measured upstream and downstream of the display case. Control experiments (no sorbent) were carried out to determine the loss rate of pollutants onto Teflon, Plexiglas, and the empty sorbent tray.
Active mode tests, summarized in Table 1, indicated that several of the sorbents tested could remove pollutants for at least one year of operation under typical museum conditions. Silica gel (often used in museums for humidity control) and other commonly recommended sorbents failed to remove ozone.
Of the sorbents which removed all five pollutants in the active mode, one of the least expensive and most readily available, activated carbon, was tested in detail in the passive mode. Pollutant concentration vs. time plots obey first order kinetics in all cases. Additional experiments were carried out to investigate the effect of amount of sorbent, sorbent granulometry, and sorbent surface available for passive diffusion of the pollutant. Other tests included pollutant removal under conditions of constant pollutant supply to the display case as well as studies of the competition between the display case walls, the art object displayed, and the sorbent bed for passive removal of the pollutant by diffusion.
Parmar, S. S., and D. Grosjean, "Sorbent Removal of Air Pollutants in Museum Display Cases," 1989 Pacific Conference on Chemistry and Spectroscopy, Division of Atmospheric Chemistry, Pasadena, California, October 18-21.
ABSTRACT-The possibility of removing air pollutants (NO2, SO2 ,HCHO, and H2S) from museum display cases using sorbents has been studied under laboratory conditions. Sorbents tested include common adsorbents such as activated carbon, silica gel, polymeric materials (e.g., Tenax and Chromosorb 102), and chemicals coated on solid support (C18). Tests were carried out in both active and passive modes. In the active mode, air containing a constant concentration of pollutant flowed through a cartridge packed with the sorbent tested. In the passive mode, the sorbent was placed in a 1 m3 display case and the pollutant removal by adsorption on the sorbent bed was determined. The active mode results indicate that many sorbents met our target performance target performance;, i.e., were capable of removing, for one year of continuous operation, 20 ppb of pollutant at a flow rate of 0.1 L min-1. In the passive mode, pollutant removal rates were found to obey first-order kinetics, with removal rate constants on carbon ranging from 0.5 to 3 x 10-2 min. These results are discussed with focus on protection of objects of art in museum display cases.
Grosjean, D., and S. S. Parmar, "Removal of Air Pollutant Mixtures from Museum Display Cases," Final Report to the (Conservation at the Getty) Institute, September 1990.
ABSTRACT-Laboratory studies have been carried out to investigate the feasibility of removing air pollutant mixtures using sorbents, with focus on two sorbents, activated carbon and Purafil (4% potassium permanganate on neutral activated alumina). Two pollutant mixtures have been studied, one being an atmospheric oxidant mixture (ozone peroxyacetyl nitrate, PAN) and the other a photochemical smog mixture prepared in situ and containing oxides of nitrogen, (NOx), ozone, peroxyacetyl nitrate (PAN), nitric acid, aldehydes (formaldehyde and acetaldehyde), and organic acids (formic acid and acetic acid). In addition, tests were also carried out with single pollutants, including PAN and the chlorinated hydrocarbons methylchloroform, trichloroethylene, and tetrachloroethylene.
Tests were carried out in the active mode (polluted air passing through the sorbent contained in a cartridge) and in the passive mode (pollutant removal by diffusion to the sorbent bed in the display case), with pollutant concentrations of 95-100 ppb (PAN in pure air), 59-250 ppb (PAN in smog mixture), 145-220 ppb (PAN in the O3-PAN mixture), 112-287 ppb (NOx in smog mixture), 100-360 ppb (aldehydes in smog mixture), 13-820 ppb (chlorinated hydrocarbons in pure air), and 96-220 ppb (O3 in the O3-PAN mixture). In the active mode, the pollutant removal capacity of a sorbent was determined by measuring the pollutant concentration upstream and downstream of a cartridge containing a small amount of sorbent. In the passive mode, a small tray containing a layer of sorbent was placed inside the display case containing polluted air, and the rate of pollutant removal resulting from diffusion to the sorbent (after correction for dilution, loss to the display case walls, and loss to the Teflon®-covered empty sorbent tray and its metal stand, which were measured in separate experiments) was determined by measuring the pollutant concentration at the display case exit port. In all passive mode experiments, the pollutants were continuously diluted at a known flow rate (1-2 L/min) using purified air. All active and passive mode tests were carried out at room temperature (18 -2 °C) and at constant humidity (55-5% RH).
Active mode tests with activated carbon, Purafil, molecular sieves 13X and silica gel using PAN (in pure air), PAN and NOx (in smog mixture), and chlorinated hydrocarbons (in pure air) indicated that activated carbon was the more efficient sorbent. Activated carbon met or exceeded our target performance, i.e., removed an amount of pollutant equivalent to 20 ppb of pollutant for one year of continuous use by passing air at 0.1 L/min through 200 g of sorbent. Purafil, which is often used in HVAC systems equipped with chemical filtration, was less efficient than carbon in all tests, removing 80-85% of PAN, 66% of NOx, and only 0-10% of the chlorinated hydrocarbons.
In the passive mode, pollutant removal by sorbents and walls of the display case all obey first-order kinetics. The corresponding passive removal rate constants and pollutant half-lives have been determined. Removal rate constants ranged from 0.002-2.66 x 10-2 min-1, and for activated carbon were in the sequence: PAN (in smog mixtures) => PAN (in ozone PAN mixture) => NOx (in smog mixture) => PAN (in pure air) > O3 (O3-PAN mixture) > aldehydes (in smog mixture) >> chlorinated hydrocarbons (in pure air). Pollutant loss to carbon was one order of magnitude faster than the corresponding loss to display case walls made of Teflon or Plexiglas®. For all but one of the pollutants tested (ozone in the ozone-PAN mixture), passive removal by Purafil proceeded at a slower rate than removal by activated carbon: 8-15 times slower for PAN, 6 times for NOx, 4 times for formaldehyde, 1.5 times for acetaldehyde, 16 times for methylchloroform, 28 times for trichloroethylene, and 80 times slower for tetrachloroethylene.
Several passive mode experiments were carried out to simulate possible "real world" museum conditions including limited access of the air pollutants to the sorbent bed, the effect of varying the size of displayed objects, and the effect of varying the display case surface-to-volume ratio (S/V). As part of these tests, a demonstration of sorbent effectiveness was carried out, using fugitive colorants as surrogate objects. This experiment showed that severe fading and/or color change induced by object exposure to polluted air can be suppressed or drastically reduced by simply adding a bed of activated carbon. The removal rate constant for O3 on activated carbon was found to decrease when increasing the display case S/V ratio from 6 m-1 to 11 m-1. A sorbent tray containing activated carbon was covered with Teflon film, through which we cut slits of different sizes. Increasing the slit area by a factor of two resulted in a fivefold increase in the removal rate constant for ozone.
Among various measures aimed at minimizing pollutant damage to museum collections, none appears to be more cost-effective or easier to implement than the use of sorbents. We recommend that display cases be equipped with passive sorbent systems. Under the conditions employed in our study, activated carbon, which is inexpensive and widely available, was found to be the most efficient sorbent for removal of all pollutants and pollutant mixtures tested.
Grosjean, D., and S. S. Parmar, "Removal of Air Pollutant Mixtures from Museum Display Cases," Studies in Conservation, Vol. 36, 1991, pp. 129-141.
ABSTRACT-See Final Report above.