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NOTE:
After further investigation into the producer I found out that granules are made of 100% coconut shell whereas pellets of 100% hard coal.
This renders this question meaningless.
Apologies for the inconvenience and thank you for the knowledgeable and enriching answers.

I'm looking for activated charcoal for my water distiller and I found a producer offering both granules and pellets made of steam activated carbon from hard coal and coconut shells.
Considering the similar grain size / diameter, I'm surprised to find out that the two have opposite properties.
The following is a table provided by the retailer:

                                  Granules   Pellets
Wastewater - water purification   ✓          ✓
Inorganic chemicals                          ✓
aquarium water                    ✓          ✓
chlorine / ozone                  ✓
Discoloration / Toxins            ✓
Electroplating                               ✓
Organic Chemicals                            ✓
Drinking water treatment          ✓          ✓

Summary, as I understand it:

Granules  let go  inorganic and organic chemicals  stop    chlorine and ozone
Pellets   stop    inorganic and organic chemicals  let go  chlorine and ozone

This is a trade off that I'm obviously not willing to settle with, I just would like to drink CLEAN water.
I'm considering mixing granules and pellets in order to avail of both properties, if that could possibly work.
I would like to know why granules and pellets made of the same material have such differences.
I'd also be glad to have an advice on which one may be best for water distiller.

Here are the specifications of both products:

                              Granules          Pellets
Grain size / diameter         0,6 - 2,36mm      Ø1,5mm
Bulk density                  500 +/- 30kg/m³   530 +/- 30kg/m³
Water content at packing      <5%               <5%
Iodine value                  >1050 mg/g        >900 mg/g
CCI4 - Adsorption             n.V.              >60%
Specific surface area (BET)   ca. 1100m²/g      ca. 1050m²/g
Ash content                   <5%               n.V.
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    $\begingroup$ Unless you ask the vendor or producer what is the difference and why, all would be just speculation. // The data the vendor provided are rather irrelevant for the difference. The statement claiming capturing organic and inorganic chemicals is a misleading statement of century. And even if it were true, what are chlorine and ozone if not inorganic chemicals? // What purity is guaranted for saltys added to distilled water? Are they certified for food industry usage? // Using distillation for producing drinkable water is rather foolish, unless there is no other way. $\endgroup$
    – Poutnik
    Commented Jan 30 at 9:06

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Pellets are obtained by pyrolizing vegetal material which is of course made of living cells. When heating this material to high temperature, water is eliminated, the inner parts of the cells are destroyed and mainly evaporated; the cells explode, then the membranes are pyrolized and transformed into impure charcoal, which usually stays unmodified in place. The obtained material has lost water and a large proportion of its mass. It is rather light.

Under the microscope, it looks like of a huge amount of broken and empty more or less spheric bubbles. Organic substances may enter the rest of these spheres where they are adsorbed, but they have more difficulty to get out. That is why this pyrolized substance can stop big chemicals present in air around. But this material cannot fix small molecules like chlorine or ozone. To adsorb these small molecules, granules having much smaller cages are needed, which are produced by much smaller living cells, after pyrolysis. And probably another surface adsorption mechanism is needed to explain this effect.

You can use a mixture of both charcoals to purify drinkable water.

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  • $\begingroup$ Both granules and pellets are made of the same activated charcoal. Why only granules are advertised as chlorine and ozone adsorbent? Why only pellets are advertised as inorganic and organic chemicals adsorbent? $\endgroup$
    – Claudio
    Commented Jan 30 at 8:33
  • $\begingroup$ @Claudio. Granules and pellets are not obtained form the same sort of living cells. They are not made of the same activated charcoal. $\endgroup$
    – Maurice
    Commented Jan 30 at 8:54
  • $\begingroup$ from the producer:"We obtain our activated carbon from hard coal and coconut shells. The production process is technically complex. We use the following method: Steam activation". from Wikipedia:"Extruded activated carbon (EAC) combines powdered activated carbon with a binder, which are fused together and extruded into a cylindrical shaped activated carbon block" @Maurice are you saying that in order to use a binder a different base material must be used? Is the producer false advertising? $\endgroup$
    – Claudio
    Commented Jan 30 at 9:35
  • $\begingroup$ @Claudio. The producer must be right, because my knowledge of this process is from many years ago. Apparently there has been changes in the process used during recent times. I did not know that activated carbon and a binder can be fused together and extruded into cylindrical carbon black. $\endgroup$
    – Maurice
    Commented Jan 30 at 16:38

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