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The '''electrochemical regeneration''' of [[activated carbon]] based [[adsorption|adsorbents]] involves the removal of molecules adsorbed onto the surface of the adsorbent with the use of an [[electric current]] in an [[electrochemical cell]] restoring the carbon’s adsorptive capacity. Electrochemical regeneration represents an alternative to [[activated carbon#Regeneration|thermal regeneration]] commonly used in [[waste water]] treatment applications. Common adsorbents include powdered activated carbon (PAC), granular activated carbon (GAC) and activated carbon fibre.
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==Regeneration for adsorbent re-use==
In waste water treatment, the most commonly used adsorbent is granular activated carbon (GAC), often used as to treat both liquid and gas phase [[volatile organic compounds]] and [[organic compound|organic]] pollutants.<ref>{{Cite journal
  | last = Moreno-Castilla
  | first = C
  | authorlink =
  | coauthors =
  | title = Adsorption of organic molecules from aqueous solutions on carbon materials
  | journal = Carbon
  | volume = 42
  | issue =
  | pages = 83–94
  | publisher =
  | location =
  | year = 2004
  | url =
  | doi = 10.1016/j.carbon.2003.09.022| id =  
  | accessdate = }}</ref><ref>{{Cite journal
  | last = Das
  | first = D
  | authorlink =
  | coauthors = Gaur, V., & Verma, N.
  | title = Removal of volatile organic compound by activated carbon fiber
  | journal = Carbon
  | volume = 42
  | issue = 14
  | pages = 2949–2962
  | publisher =
  | location =
  | year = 2004
  | url =
  | doi = 10.1016/j.carbon.2004.07.008| id =
  | accessdate = }}</ref> Activated carbon beds vary in lifetime depending on the concentration of the pollutant(s) being removed, their associated [[adsorption#Isotherms|adsorption isotherms]], inlet flow rates and required discharge consents. Life- times of these beds can range between hours and months. Activated carbon is often landfilled at the end of its useful life but sometimes it is possible to regenerate it restoring its adsorptive capacity allowing it to be re-used. Thermal regeneration is the most prolific regeneration technique but has drawbacks in terms of high energy and commercial costs and a significant carbon footprint.<ref name= narbaitz>{{Cite journal
  | last = Narbaitz
  | first = R. M
  | authorlink =
  | coauthors = Karimi-Jashni, A
  | title = Removal of volatile organic compound by activated carbon fiber
  | journal = Carbon
  | volume = 42
  | issue = 14
  | pages = 2949–2962
  | publisher =
  | location =
  | year = 1994
  | url =
  | doi = 10.1016/j.carbon.2004.07.008| id =
  | accessdate = }}</ref> These drawbacks have encouraged research into alternative regeneration techniques such as electrochemical regeneration.
 
==Electrochemically regenerating activated carbons==
Once the adsorptive capacity of the activated carbon bed has been exhausted by the adsorption of pollutant molecules, the carbon is transferred to an electrochemical cell (to either the [[anode]] or the [[cathode]]) in which electrochemical regeneration can occur.
 
===Principles===
There are several mechanisms by which passing a current through the electrochemical cell can encourage pollutant desorption. [[Ions]] generated at the electrodes can change local pH conditions in the divided cell which affect the adsorption equilibrium and have been shown to promote desorption of organic pollutants such as phenols from the carbon surface.<ref name = narbaitz/><ref>{{Cite journal
  | last = Mehta
  | first = M. P
  | authorlink =
  | coauthors = Flora, J. R. V
  | title = Effects of electrochemical treatment of granular activated carbon on surface acid groups and the adsorptive capacity for phenol
  | journal = Water Research
  | volume = 31
  | issue = 9
  | pages = 2171–2176
  | publisher =
  | location =
  | year = 1997
  | url =
  | doi = 10.1016/S0043-1354(97)00057-2| id =
  | accessdate = }}</ref> Other mechanisms include reactions between the ions generated and the adsorbed pollutants resulting in the formation of a species with a lower adsorptive affinity for activated carbon that subsequently desorb, or the oxidative destruction of the organics on the carbon surface.<ref>{{Cite journal
  | last = Choi
  | first = J. J
  | authorlink =
  | coauthors =
  | title = Oxidative removal of malodorous volatile sulfur compounds by air over an activated carbon fiber
  | journal = Journal of Industrial and Engineering Chemistry
  | volume = 3
  | issue = 1
  | pages = 56–62
  | publisher =
  | location =
  | year = 1997
  | url =
  | doi =
  | id =
  | accessdate = }}</ref> It is agreed that the main mechanisms are based on desorption induced regeneration as electrochemical effects are confined to the surface of the porous carbons so cannot be responsible for bulk regeneration.<ref name = narbaitz/><ref name = zhang >{{Cite journal
  | last = Zhang
  | first = H
  | authorlink =
  | coauthors = Ye, L., & Zhong, H
  | title = Regeneration of phenol-saturated activated car- bon in an electrochemical reactor
  | journal = Journal of Chemical Technology and Biochemical Technology
  | volume = 77
  | issue =
  | pages = 1246–1250
  | publisher =
  | location =
  | year = 2002
  | url =
  | doi =
  | id =
  | accessdate = }}</ref>
The performance of different regeneration methods can be directly compared using the regeneration efficiency. This is defined as:
 
<math>\frac{adsorptive\;capacity\;before\;adsorption}{adsorptive\;capacity\;after\;adsorption\;and\;electrochemical\;regeneration} \times 100</math>
 
===Cathodic regeneration===
The cathode is the [[redox|reducing]] electrode and generates OH<sup>-</sup> ions which increases local pH conditions. An increase in pH can have the effect of promoting the desorption of pollutants into solution where they can migrate to the anode and undergo oxidation hence destruction. Studies on cathodic regeneration have shown regeneration efficiencies for adsorbed organic pollutants such as phenols of the order of 85% based on regeneration times of 4 hours with applied currents between 10-100 mA.<ref name = narbaitz/> However, due to [[mass transfer]] limitations between the cathode and anode, there is often residual pollutant left in the cathode unless large currents or long regeneration times are employed.
 
===Anodic regeneration===
The anode is the [[redox|oxidising]] electrode and as a result has a lower localised pH during electrolysis which also promotes desorption of some organic pollutants. Regeneration efficiencies of activated carbon in the anodic compartment are lower than that achievable in the cathodic compartment by between 5-20% for the same regeneration times and currents,<ref name = narbaitz/><ref name = zhang/> however there is no observed residual organic due to the strong oxidising nature of the anode.<ref name = zhang/>
 
===Repeated adsorption-regeneration===
For the bulk of carbonaceous adsorbents regeneration efficiency decreases over subsequent cycles as a result of pore blockages and damage to adsorption sites by the applied current. Decreases in regeneration efficiency are typically a further 2% per cycle.<ref name = narbaitz/> Current leading edge research focuses on developing adsorbents able to regenerate 100% of their adsorptive capacity through electrochemical regeneration.<ref>{{Cite journal
  | last = Brown
  | first = N
  | authorlink =
  | coauthors = Roberts, E. P. L
  | title = Electrochemical pre-treatment of effluents contain- ing chlorinated compounds using an adsorbent
  | journal = Journal of Applied Electrochemistry
  | volume = 37
  | issue = 11
  | pages = 1329–1335
  | publisher =
  | location =
  | year = 2007
  | url =
  | doi = 10.1007/s10800-007-9376-3| id =
  | accessdate = }}</ref><ref>{{Cite journal
  | last = Brown
  | first = N
  | authorlink =
  | coauthors =Roberts, E. P. L., Chasiotis, A., Cherdron, T., & Sanghrajka, N
  | title = Atrazine removal using adsorption and electrochemical regeneration
  | journal = Water Research
  | volume = 38
  | issue = 13| pages = 3067–3074
  | publisher =
  | location =
  | year = 2004
  | url =
 
  | pmid = 15261545| doi = 10.1016/j.watres.2004.04.043| id =
  | accessdate = }}</ref><ref>{{Cite journal
  | last = Brown
  | first = N
  | authorlink =
  | coauthors =  Roberts, E. P. L., Garforth, A. A., & Dryfe, R. A. W
  | title = Elecrochemical regeneration of a carbon based adsorbent loaded with cystal violet dye
  | journal = Electrochimica Acta
  | volume = 49
  | issue = 20
  | pages = 3269–3281
  | publisher =
  | location =
  | year = 2004
  | url =
  | doi = 10.1016/j.electacta.2004.02.040| id =
  | accessdate = }}</ref>
 
==Commercial systems==
Currently there are a very limited number of commercially available carbon based adsorption- electrochemical regeneration systems. One system that does exist uses a carbon adsorbent called Nyex in a [[Continuous Adsorption-Regeneration|continuous adsorption-regeneration]] system that uses electrochemical regeneration to adsorb and destroy organic pollutants.<ref>http://news.bbc.co.uk/1/hi/england/manchester/6176729.stm BBC coverage of an innovative electrochemical regeneration wastewater treatment technique</ref>
 
==References==
{{reflist}}
 
[[Category:Analytical chemistry]]
[[Category:Electrochemistry]]

Latest revision as of 10:25, 26 September 2014



For the duration of the 18th century cutlerers utilised springs to protected the blade in the two the open and shut place. This produced knives safer and firmer. In the 1800's the Swiss Military Knife turned common. It is a foldingthat serves as a miniature toolbox in your pocket. There are assorted utensils as nicely as slicing blades hooked up. Espada Big. This sort of cold steel folding knife was designed by Andrew Demko and the president of Cold Metal, Lynn Thompson. It has three sizes that you can choose from. If you have any type of concerns relating to where and how to use Best hunting Knives 2014, you could call us at our internet site. It is a blend the conventional and present day resources and mechanics and is created to produce a new breed of folding knives
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