Difference between revisions of "Scavenger"

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== Description ==
 
== Description ==
  
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Any substance that actively absorbs or consumes unwanted impurities and pollutants in a system. For example, [[vapor%20phase%20corrosion%20inhibitor|vapor phase inhibitors]] are used to scavenge hydrogen sulfide before it can tarnish silver. The test results show that both under active and passive conditions (with/without forced air exchange), pure and impregnated activated carbons have the best adsorption efficiency for the target substances which were selected within this study as volatile organics which are often detected in museum environments as emissions from construction and furnishing materials. The substances which have been found to be of greatest concern for the preservation of heritage collections, namely formaldehyde, formic acid and acetic acid, were well adsorbed by the majority of activated charcoals tested. Under active conditions, charcoal cloths and foams, zeolites and other products, which are specially designed for museum purposes, showed a low adsorption efficiency. In addition, a breakthrough was observed after only a short time, meaning that a saturation of the adsorbents was achieved quickly.  
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Any substance that actively absorbs or consumes unwanted impurities and pollutants in a system. For example, [[vapor%20phase%20corrosion%20inhibitor|vapor phase inhibitors]] are used to scavenge [[hydrogen sulfide]] before it can tarnish [[silver]].  
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Test results from Schieweck (2020) show that both under active and passive conditions (with/without forced air exchange), pure and impregnated activated carbons have the best adsorption efficiency for substances often detected in museum environments, such as emissions from construction and furnishing materials. However, even under under active conditions, charcoal cloths/foams and zeolites, often specially designed for museum purposes, showed a low adsorption efficiency and exhibit breakthrough after only a short time. Silica gels, often installed to buffer RH were not shown to be effective VOC sorbents.
  
 
See also [[hydrogen%20sulfide%20scavenger|hydrogen sulfide scavenger]], [[oxygen%20scavenger|oxygen scavenger]] and [[desiccant]].
 
See also [[hydrogen%20sulfide%20scavenger|hydrogen sulfide scavenger]], [[oxygen%20scavenger|oxygen scavenger]] and [[desiccant]].
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! Sorbent
 
! Sorbent
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! Form
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! Types
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! Form/Examples
 
! Uses
 
! Uses
 
! Drawbacks
 
! Drawbacks
 
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| [[Activated carbon]] (granulated activated carbon, GAC)
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| Pure  charcoal
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| Black pellets
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| * [[Activated carbon]], extra-fine  pores<br> * Activated carbon, high inner surface <br>* Granulated  activated carbon (GAC)
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| Most commonly used; a catchall sorbent that removes hydrocarbons, chlorine, nitrogen oxides, and VOCs. Also removes organic carbonyl pollutants. Used in HVAC systems to filter gaseous pollutants.
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| black powder, beads or pellets  
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| Difficult to determine when exhausted and hence when to regenerate (by baking in high-temperature oven) or replace.  In some countries, used carbon is classified as a hazardous waste material. In high humidity situations such as rain or fog, water vapor can replace organic   compounds adsorbed within the pores of the carbon. These low-risk VOCs are   released into the environment, which accounts for the odor frequently  associated with rain events in facilities with carbon gas filtration media.  Small molecules not as effectively adsorbed as large molecules. Hence, effectiveness increases with molecular  weight of pollutant.
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| A catchall sorbent that removes   small hydrocarbons, chlorine, nitrogen oxides, and VOCs (including organic   carbonyls); physically adsorbs on inner surface; used in HVAC systems to   filter gaseous pollutants; pore size determines sorption capacity
 +
| Difficult to determine when   exhausted; may be regenerated (by baking in high-temperature oven with vent)   or replaced; in some countries, used carbon is classified as a hazardous   waste material making disposal  costly;  when exposed to high humidity (rain), water or water vapor vapor can replace   organic compounds adsorbed within the pores of the carbon thus releasing VOCs  into the environment; small molecules not as effectively adsorped as large   molecules
 
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| Activated   carbon and [[activated alumina]] impregnated with [[potassium hydroxide]]
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| Impregnated   charcoal
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| Irregular pellets
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| * GAC mixed with a base (NAOH,  KOH) <br> * GAC mixed with oxidizer (FeOH, KI, KMnO4) <br>* GAC  mixed with activated alumina impregnated with KOH or KMn04
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| Used to remove hydrocarbons, VOCs, and NO2.
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| black or gray irregular pellets
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| Potassium permanganate is caustic. Can only be regenerated as activated carbon without impregnated chemical.
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| As above, removes hydrocarbons,   VOCs, and NO2 with additional removal of sulfur dioxide, hydrogen sulfide,  amines, and organic acids; permanganate is an indicator wthat is purple when  fresh and brown when spent.
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| Avoid direct contact with  impregnated materials; Can only be regenerated as activated carbon without   impregnated chemical(s)
 
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| Activated  charcoal cloth or carbon cloth (Zorflex®)
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| Charcoal  cloth
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| Cloth or paper impregnated with   activated carbon
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| * Activated carbon between two   layers of polyester non-woven cloth<br>* Composite carbon filter media  fabric<br>* Activated carbon felt, fiber structure<br>* Open-cell  polyurethane foam coated with activated carbon granules
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| Useful in microenvironments with  low-level emissions starting with low concentrations of pollutants; eliminates same gases as activated charcoal; Good mitigation treatment for   display cases and storage cabinets; Easy to use; Apply between base and   object, e.g., under fabric liner
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| soft fabric , pillow or shaped   filter ([ https://flexzorb.com/ Flexzorb])
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| Small reserve of carbon to adsorb pollutants; Cannot expect longevity; Should be replaced frequently; Cannot be regenerated; Fire risk
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| Useful in microenvironments with  low-level emissions; eliminates same gases as activated charcoal; good  mitigation treatment for display cases and storage cabinets; easy to use;  durable; does not shed carbon particles
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| Small reserve of carbon to   adsorb pollutants; short longevity, thus requires frequent replacement;   cannot be regenerated.
 
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| Activated   alumina impregnated with [[potassium permanganate]] ([[Purafil]], [[Carusorb]], etc)
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| [[Activated alumina]] with [[potassium permanganate]]
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| Pink/purple spherical pellets
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| * Available in different pore  sizes
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| Highly reactive, strong oxidant.  Removes nitrogen monoxide, aldehydes, sulfur oxides, and other odorous gases   such as hydrogen sulfide. Also targets amines, mercaptans, and organic acids.  Fresh material is purple; spent (exhausted) pellets are brown. This is a  useful indicator that the sorbent should be replaced.
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| purple pellets ([https://www.purafil.com/ Purafil]); filters
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| Potassium permanganate is caustic. Use precautions when handling and avoid contact with objects. Quickly exhausted. Must be replaced frequently. Water vapor will decrease reactivity. Cannot be regenerated; must dispose of as hazardous waste.
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| Spherical, porous pellets remove gaseous pollutants from the air through chemisorption; harmful gases from the air into harmless materials that are irereversibly trapped inside the pellet; targets the removal of hydrogen sulfide (H2S), sulfur dioxide (SO2), nitric oxide (NO), and formaldehyde (CH2O).
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|  
 
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| Silica spheres
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| [[Molecular sieve|Molecular  sieves]] and [[Zeolite|Zeolites]]
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| Porous silica spheres, size approximately 2 microns;
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| * Available in different pore  sizes
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| High affinity for polar carbonyls, aldehydes, and aromatic VOCs
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| white powder, sticks, granules
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| A combination of small pore and large pore size silica is needed to captures both VOC as well as sulfur and nitrogen compounds
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| Naturally adsorbs water and  small volatile compounds; high sorption capacity;  selection of compounds is directly related  to pore size volume; may be regenerated with heat; best used for aliphatic  and aromatic hydrocarbons
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| Does not work well for polar materials, such as acids or amines; tends to be more expensive and difficult to obtain; are not as efficient as activated carbon.
 
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| Zeolites
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| [[Silica  gel]]
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| Form
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| * Available with [[Lithium  chloride]] or [[Aluminum oxide|Al2O3]]
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| Uses
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| White powder or pellets, often in packages
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| Drawbacks
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| Adsorb small amounts of VOCs;  best for polar molecules, such as alcohols and amines
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| Water molecules can replace  absorbed organics; degraded by acid compounds
 
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| [[Zinc  oxide]] catalyst G 72-D
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| Foam or  fabric embedded with [[silver]] or [[copper]]
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| cylindrical white pellets
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| cotton or polyester felted  acrylic cloth impregnated with finely ground silver or copper
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| Removes reduced sulfur gases,   e.g., hydrogen sulfide. Higher affinity for hydrogen sulfide than either   activated carbon or alumina impregnated with potassium permanganate. Easy to   use. Place a few pellets in a Petri dish in a microenvironment. Used by the   British Museum to protect silver and other susceptible objects.
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| ([[Corrosion Intercept]], [[Pacific Silvercloth]])
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| Reduces contaminants that can  tarnish metals (SO2, H2S and acids); acts as a sacrificial surface to rapidly  remove reduced sulfides before they can reach silver objects; cloth can be glued to drawers or cabinet   walls or ordered as bags to hold silver objects.
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| Limited lifetime, although the  cloth can be effective for several decades, depending on the environment   where the silver is stored. Cannot be   regenerated.
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| Acid-free  cardboard embedded with zeolites
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|
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|
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| Acid-free, durable, absorbs and   neutralizes pollutants; best used for solvents and plasticizers
 
| Cannot be regenerated.
 
| Cannot be regenerated.
 
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| Modified   zinc oxide (Miracle Sac)
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| Oxides
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| solid granules in porous bags   similar to tea bags
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| * [[Zinc oxide]] catalyst <br>   * Charcoal impregnated with oxides
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| Removes hydrogen sulfide, carbonyl sulfide, and mercaptans, which cause tarnishing.
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|
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| Oxides irreversibly capture   pollutants via reactions or chemisorption; designed to targed inorganic gases  (HCN, H2S, ammonia, acids, amines, phosphine and arsine)
 
| Cannot be regenerated.
 
| Cannot be regenerated.
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| Treated  silver cloth – similar to bags sold commercially to protect silver ([[Pacific  Silvercloth]]®)
 
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| Cotton or polyester felted acrylic  cloth impregnated with finely ground silver
 
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| Acts as a sacrificial surface to  rapidly remove reduced sulfides before they can reach silver objects  Cloth can be glued to drawers or cabinet  walls or ordered as bags to hold silver objects.
 
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| Limited lifetime, although can be effective for several decades, depending on the environment where the silver is stored.  Cannot be  regenerated.
 
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| Activated  carbon impregnated with [[potassium iodide]]
 
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| Irregular pellets
 
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| Used to remove hydrogen sulfide  and prevent generation of sulfuric acid in microenvironments
 
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| Can only be regenerated as  activated carbon without impregnated chemical.
 
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| Activated  carbon impregnated with iron oxide
 
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| Irregular pellets
 
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| Used to trap and oxidize gaseous  pollutants such as hydrogen sulfide.
 
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| Elemental sulfur is a byproduct  and can react in air to form sulfuric acid, which is damaging. Can only be  regenerated as activated carbon without impregnated chemical.
 
 
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Note: Portions of this table were extracted from: Cecily Grzywacz, [https://www.getty.edu/publications/virtuallibrary/0892368519.html "Monitoring for Gaseous Pollutants in Museums"], Getty Publications, 2006.
 
  
 
== Synonyms and Related Terms ==
 
== Synonyms and Related Terms ==
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getter; pollutant absorber; vapor phase corrosion inhibitor; activated charcoal; activated carbon; charcoal cloth;  
 
getter; pollutant absorber; vapor phase corrosion inhibitor; activated charcoal; activated carbon; charcoal cloth;  
  
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Brand names: Purafilter; Pacific silvercloth; Ageless®; Scavengel [Art Preservation Services]
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Brand names: Purafil; Puracarb; Pacific silvercloth; Ageless®; Scavengel [Art Preservation Services]
  
 
==Resources and Citations==
 
==Resources and Citations==

Latest revision as of 09:49, 6 November 2023

Description

Any substance that actively absorbs or consumes unwanted impurities and pollutants in a system. For example, vapor phase inhibitors are used to scavenge Hydrogen sulfide before it can tarnish Silver.

Test results from Schieweck (2020) show that both under active and passive conditions (with/without forced air exchange), pure and impregnated activated carbons have the best adsorption efficiency for substances often detected in museum environments, such as emissions from construction and furnishing materials. However, even under under active conditions, charcoal cloths/foams and zeolites, often specially designed for museum purposes, showed a low adsorption efficiency and exhibit breakthrough after only a short time. Silica gels, often installed to buffer RH were not shown to be effective VOC sorbents.

See also Hydrogen sulfide scavenger, Oxygen scavenger and Desiccant.

Table for selected sorbents.

Sorbent Types Form/Examples Uses Drawbacks
Pure charcoal * Activated carbon, extra-fine pores
* Activated carbon, high inner surface
* Granulated activated carbon (GAC) 		black powder, beads or pellets A catchall sorbent that removes small hydrocarbons, chlorine, nitrogen oxides, and VOCs (including organic carbonyls); physically adsorbs on inner surface; used in HVAC systems to filter gaseous pollutants; pore size determines sorption capacity Difficult to determine when exhausted; may be regenerated (by baking in high-temperature oven with vent) or replaced; in some countries, used carbon is classified as a hazardous waste material making disposal costly; when exposed to high humidity (rain), water or water vapor vapor can replace organic compounds adsorbed within the pores of the carbon thus releasing VOCs into the environment; small molecules not as effectively adsorped as large molecules
Impregnated charcoal * GAC mixed with a base (NAOH, KOH)
* GAC mixed with oxidizer (FeOH, KI, KMnO4)
* GAC mixed with activated alumina impregnated with KOH or KMn04 		black or gray irregular pellets As above, removes hydrocarbons, VOCs, and NO2 with additional removal of sulfur dioxide, hydrogen sulfide, amines, and organic acids; permanganate is an indicator wthat is purple when fresh and brown when spent. Avoid direct contact with impregnated materials; Can only be regenerated as activated carbon without impregnated chemical(s)
Charcoal cloth * Activated carbon between two layers of polyester non-woven cloth
* Composite carbon filter media fabric
* Activated carbon felt, fiber structure
* Open-cell polyurethane foam coated with activated carbon granules 		soft fabric , pillow or shaped filter ([ https://flexzorb.com/ Flexzorb]) Useful in microenvironments with low-level emissions; eliminates same gases as activated charcoal; good mitigation treatment for display cases and storage cabinets; easy to use; durable; does not shed carbon particles Small reserve of carbon to adsorb pollutants; short longevity, thus requires frequent replacement; cannot be regenerated.
Activated alumina with Potassium permanganate * Available in different pore sizes purple pellets (Purafil); filters Spherical, porous pellets remove gaseous pollutants from the air through chemisorption; harmful gases from the air into harmless materials that are irereversibly trapped inside the pellet; targets the removal of hydrogen sulfide (H2S), sulfur dioxide (SO2), nitric oxide (NO), and formaldehyde (CH2O).
Molecular sieves and Zeolites * Available in different pore sizes white powder, sticks, granules Naturally adsorbs water and small volatile compounds; high sorption capacity; selection of compounds is directly related to pore size volume; may be regenerated with heat; best used for aliphatic and aromatic hydrocarbons Does not work well for polar materials, such as acids or amines; tends to be more expensive and difficult to obtain; are not as efficient as activated carbon.
Silica gel * Available with Lithium chloride or Al2O3 White powder or pellets, often in packages Adsorb small amounts of VOCs; best for polar molecules, such as alcohols and amines Water molecules can replace absorbed organics; degraded by acid compounds
Foam or fabric embedded with Silver or Copper cotton or polyester felted acrylic cloth impregnated with finely ground silver or copper (Corrosion Intercept, Pacific Silvercloth) Reduces contaminants that can tarnish metals (SO2, H2S and acids); acts as a sacrificial surface to rapidly remove reduced sulfides before they can reach silver objects; cloth can be glued to drawers or cabinet walls or ordered as bags to hold silver objects. Limited lifetime, although the cloth can be effective for several decades, depending on the environment where the silver is stored. Cannot be regenerated.
Acid-free cardboard embedded with zeolites Acid-free, durable, absorbs and neutralizes pollutants; best used for solvents and plasticizers Cannot be regenerated.
Oxides * Zinc oxide catalyst
* Charcoal impregnated with oxides 		Oxides irreversibly capture pollutants via reactions or chemisorption; designed to targed inorganic gases (HCN, H2S, ammonia, acids, amines, phosphine and arsine) Cannot be regenerated.

Synonyms and Related Terms

getter; pollutant absorber; vapor phase corrosion inhibitor; activated charcoal; activated carbon; charcoal cloth;

Brand names: Purafil; Puracarb; Pacific silvercloth; Ageless®; Scavengel [Art Preservation Services]

Resources and Citations

  • Schieweck, A. "Adsorbent media for the sustainable removal of organic air pollutants from museum display cases". Herit Sci 8, 12 (2020). Link
  • Cecily Grzywacz, "Monitoring for Gaseous Pollutants in Museums", Getty Publications, 2006.
  • AIC Conservation Wiki: Exhibit Technical Notes: Environmental Control
  • Exhibit Guidelines Technical Note: Using Pollutant Absorbers Inside an Exhibit Case
  • Delaney P, Healy RM, Hanrahan JP, Gibson LT, Wenger JC, Morris MA, Holmes JD. "Porous silica spheres as indoor air pollutant scavengers", J Environ Monit. 2010 Dec; 12(12):2244-51. Link
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998

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