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5664Re: Activated Carbon

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  • wromgbutton
    Aug 6, 2002
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      --- In Distillers@y..., "Mike Nixon" <mike@s...> wrote:
      > Grant Dunn wrote:
      > Subject: Re: [Distillers] Activated Carbon
      >
      > Hi Mike,
      >
      > Its nice to meet somewhere who does some research and doesn't just
      follow the pack.
      >
      > We don't entirely disagree. From what I have read, activated carbon
      acts in three ways:
      >
      > Adsorption - relying on electrostatic Van der Walls forces. This
      attractive "force" forms relatively weak bonds between the carbon and
      adsorbate. In theory activated carbon could release or desorb what it
      removed at some point, but from practical experience desorption rarely
      occurs.
      >
      > Absorption - refers to the diffusion of a gas or compound into the
      porous network where a chemical reaction or physical entrapment take
      place. Ozone for example is absorbed into activated carbon where it
      oxidizes a portion of the carbon's surface. Ozone (O3) is reduced to
      oxygen (O2) thus "detoxified". Ozone does not accumulate or build-up
      in the carbon structure.
      >
      > Chemisorption - an irreversible chemical bond between the carbon
      surface and the adsorbate. Pollutants are tightly bound to the
      sorbent.
      >
      > Chemisorption is associated with the removal of inorganic chemicals
      and the carbon used to remove these compounds is generally not
      regenerated. The filtering of alcohol primarily involves the removal
      of organics via adsorption. After the activated carbon has reached
      exhaustion and all the adsorptive sites are filled, it can be
      regenerated.
      >
      > Where we differ is on what is required to regenerate it. While I
      don't have the equipment to prove it either way, everything I have
      read suggests that this requires temperatures above 800 degrees. I
      would be very interested to see any documented reports that indicate
      otherwise.
      >
      > The surface area of activated carbon is calculated from measuring
      its adsorption of nitrogen gas. This clearly demonstrates the need to
      keep activated carbon in an airtight container. How then does rinsing
      it in water affect its reactivity? What are the impurities you are
      trying to remove? Do you know that rinsing removes them? Activated
      carbon is available in food grade so why don't you just use that?
      >
      > Regards,
      >
      > Grant
      > ---------------------------------------------
      > Hi Grant,
      > I really didn't want to confuse matters on the List by rabbiting on
      about the difference between 'physiosorption' and 'chemisorption', as
      the only activity we are really interested in getting clean booze.
      Specifically, we are interested in removing compounds that have taste
      or odor and which, like those that contribute color, tend to bind
      strongly. With these, the only bonding is by weak Van der Waals
      forces. There is no significant redistribution of electron density in
      either the molecule or at the substrate surface, and subsequent
      release of the molecules by heating is easy. Heating in an oven to 160
      deg C is quite sufficient to clean used carbon to the extent that it
      can be used again, particularly when the carbon is first soaked in
      water to provide active flushing with steam as it boils. Of course,
      this will not release all the adsorbed molecules . heating to a much
      higher temperature in an inert atmosphere is needed to do that
      thoroughly . but 90+% efficiency is good enough for all practical
      purposes, and has been used as a cost-effective recovery process by
      sugar refineries ever since 'white' sugar was processed.
      >
      > Wet activated carbon primarily removes oxygen from air, not
      nitrogen. Thus, an asphyxiation hazard exists inside enclosed spaces
      containing wet activated carbon. Dry activated carbon requires no
      special precautions. Rinsing activated carbon before first use is a
      sensible procedure as many carbons, particularly the 'stone' carbons,
      are produced using chemical etchants which may still linger in the
      final product (eg. zinc chloride and phosphoric acid). Those are the
      impurities you want to remove before letting newly procured carbon
      anywhere near liquids that you are later going to drink.
      >
      > As an aside, not that it matters much, knowledge of all this was
      gained during my time at Farnborough where I was engaged in work
      relating to purification of liquid coolants. Bottom line however, for
      anyone wanting to check on all this, is to leave aside all 'theory'
      and the boring ravings of idjits like me, and to simply go ahead and
      try it. If it works for you, then wear a happy smile. If it doesn't,
      then just blame me and still wear a happy smile!!
      >
      > All the best,
      >
      > Mike

      I regenerate my charcoal using steam from my boiler. Have done it 5
      or 6 times now with no appreciable change to the effectiveness of the
      charcoal. I get a huge pong for about 3 hours then no smell. If the
      smell is anything to go by, I have no problem reactivating. The smell
      coming off,is just the like shit you are trying to remove from your
      distillate only concentrated...green apples spring to mind.
      No science here but if it works.....
      Edward
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