Sciencemadness Discussion Board - Activated Carbon and Charcoal (AC)

Activated Carbon and Charcoal (AC)

aga - 31-7-2015 at 09:28

The 'Activated' word was intriguing, which is why any research was done at all.

What does it Mean ? Why is Activated Carbon (AC) different to plain Carbon ?

There are many references to AC yet very few regarding what the 'Activation' process actually is.

Essentially it means some form of Carbon (usually Charcoal) that has been altered by a process that vastly increases the surface area of the material.

AC can have a surface area of an incredible 1500m<sup>2</sup> per gramme !
https://en.wikipedia.org/wiki/Activated_carbon

Common methods of Activation are a steam process, and more easily achieveable in a home lab, treatment with a CaCl₂ solution.

Following the activation process, the AC carbon can be treated with other chemicals to coat this huge surface area with reagents that will specifically absorb, adsorb or react with the thing you wish the carbon to be 'active' with.

For example, AC can be impregnated with Sulphur to make it an effective filter for Mercury Vapour :-
www.temple.edu/borguet/Publication/Documents/pdf_files/2006-...

For all Activated Carbons, the standard measure is called the Iodine Number (IN).

The Iodine Number can be titrated using the following procedure :-

http://www.mazraehgroup.webs.com/Downloads/ASTM%20D4607-94%2...
(thanks to deltaH for finding that)

Currently i've managed to Buy the reagents, and make the sodium thiosulphate and iodine solutions.

The ASTM source says to wait four days before standardising the thiosulphate solution and this is day 1.

The test subjects are 4 samples that prepared from hardwood charcoal, and a Chinese filter material that was bought as 'Activated Carbon Filter'.

If anyone has the reagents and could perhaps perform the ASTM procedure to dermine the IN of any activated carbon or charcoal they have handy, that'd be great.

In 4 days, these home made samples will get tested and results posted.

deltaH - 31-7-2015 at 11:13

I'm really looking forward to your results aga, you are certainly being very thorough!

gatosgr - 31-7-2015 at 11:23

What method did you use for making the activated carbon foam?

aga - 31-7-2015 at 11:30

What foam ?

I've made activated carbon/charcoal from hardwood charcoal in 3 different ways.

The material is a powder, not a foam.

One sample will be the untreated carbon/charcoal, a 5th sample is some AC filter material off ebay.

If the testing procedure works out OK, i'll try other 'activation' processes and test the results of those too.

Edit :

The samples that i made were produced by treating different grain sizes with CaCl₂ as that seemed easiest.

Without a proven testing protocol it seemed silly to try other processes, such as steam, heat treatment, aerofoams etc.

[Edited on 31-7-2015 by aga]

Pumukli - 31-7-2015 at 12:06

I'm curious about the results!

When I was a child I read in a biology textbook how to make activated charcoal. The process was intriguing but never tried since then. Maybe now, that I know how to compare results I'll give it a go in the winter.

Why winter?
Besides that I'm fairly busy these days the process calls for dry, crushed (few mm particles) walnut husks. These should be impregnated (boiled in) with ZnCl₂, then dried, then heated (dry distilled), then thoroughly washed to remove the ZnCl₂ remains.

aga - 31-7-2015 at 14:19

ZnCl₂ is cited as an 'activation' agent for carbon, so that probably works.

The biggest thing was to find a way to properly Test the AC.

Thanks again to deltaH for finding a freeeeeee version of the ASTM test protocol.

This video is one of the few that 'just' makes activated charcoal.
https://www.youtube.com/watch?v=lN0fT1Uvcsw
Endure the garbage parts, if you can ...

[Edited on 31-7-2015 by aga]

[Edited on 31-7-2015 by aga]

deltaH - 31-7-2015 at 23:18

I'm a bit confused about when/how activation is taking place in that clip. Does it occur in his final oven baking step in 30min? Surely not the 24h room temperature soak

If so, I am confused why he washes the CaCl2 out before baking it, if it's not activated by then, then most of it will wash out. Maybe the residual is enough to activate, maybe not. Eitherway, since there's no reference provided by the demonstrator there, nor test of the resultant carbon, I am not reassured that this would work.

TGT - 3-8-2015 at 01:08

I have a huge carbon scrubber that I used for about a year and was wondering if the activated carbon in it could be useful. The scrubber was not used to filter water. It was used to reduce smell, so could it still be a good source, or being used to filter air could have decreased its uses? Thanks, I just hate to throw out twenty pounds of activated carbon if it can be used as is or cleaned some how.

AJKOER - 3-8-2015 at 03:28

Take a sample and subject it to a jet of steam and then oven dry.

I would then test it for its intended purpose.

[Edited on 3-8-2015 by AJKOER]

Some Experimentation

aga - 9-8-2015 at 07:46

The principle is that the adsorbtion properties of a sample of Activated Charcoal can be determined by measuring how many mg of iodine it can adsorb per 1g.

This is called the Iodine Number (I.N.), or Iodine Value commonly quoted by sellers. e.g. http://www.suneetacarbons.com/products

In the following experiment parts of the ASTM D4607-94 protocol are used to quantify the I.N. for 5 samples of charcoal subjected to different processes.

30g of shop-bought hardwood charcoal was ground to a rough powder as the feedstock

2g of the feedstock was added to pots A and B.
The feedstock was further ground down and 2g of this material was added to pot C.
This finer material was sieved though a 90um filter and 2g of this very fine material was added to pot D

A solution was made with 2.52g of CaCl₂ and the weight brought up to 10.5g with distilled water.

This solution was distributed between pots B, C and D, then mixed with a glass rod to make a paste.
Each pot was then sealed, then left to stand for 24hrs.

Each sample was filtered and washed 3 times with 30ml of water in a vacuum filtration setup, then left to dry on the filter paper.

A commercial AC filter pad was obtained for comparison.
It was impossible to extract the AC from the pad fibres, so ~2g of pad was cut into small pieces to create sample E.

All were then transferred to individual aluminium containers and weighed before being put into an oven set to 150 C for 3 hours along with a container of CaCl₂ to act as a drying agent.

All samples were also weighed on exiting the oven to determine water content. This failed as there was some spillage, and the range of differences was only 0.05g which would easily be operator error.

Previously 5 solutions were made according to the ASTM document :-
HCl solution 5 w%

Sodium Thiosulphate 0.1 N
(24.82g sodium thiosulphate + 0.10g sodium carbonate)

Standard Iodine Solution 0.1 N
(12.70g iodine+ 19.10g potassium iodide in 1 litre)

Potassium Iodate Solution 0.1 N
(1.78g potassium iodate in 500ml)

Starch Indicator Solution

The Sodium Thiosulphate solution was standardised by adding 25.0ml of the Potassium Iodate solution to a flask with 2.00g KI and 5.0ml of conc HCl, then titrating with the Sodium Thiosulphate with the Starch as indicator.

The average of 3 titrations was 0.1018 N (N1)

The Iodine Solution was standardised by titrating 25.0ml with the thiosulphate.

The average of 3 titrations gave 0.0969 N (N2)

According the the ASTM protocol these values are too far out for those solutions to be used, however they are close enough for this amateur experiment.

Next all samples were tested in the following way :-

Tare a conical flask or beaker.
Add the sample, record the Weight (M)
Add 10ml (H) of 5% HCl. Swirl to wet the sample.
Boil for 30 seconds. Allow to cool.
Add 75ml (I) of Iodine solution. Shake for 30 seconds.
Immediately gravity filter.
Rinse a 25ml pipette with some filtrate, discard rinsings.
Transfer 25.0ml (F) of filtrate to a fresh flask.
Titrate with the Sodium Thiosulphate solution & Starch.
Record burette reading (S)

The Iodine Number (or mg I/g) is given by :

[(12693 N2)-(DF)(126.93 N1)(S)]/M

where DF is (I + H)/F

The results were :-

A 263 (rough, raw)
B 226 (rough, treated)
C 357 (ground, treated)
D 451 (< 90um grain size, treated)
E 341 (commercial filter pad material)

The results indicate that the grain size is a major factor in the activity of charcoal, and that 'activation' by CaCl₂ at RT is likely to be an entirely bogus claim.

Given that the majority of the commercial filter material's weigh was the support fibres, it is likely that the AC used would give a significantly higher I.N. if just the carbon were tested.

[Edited on 9-8-2015 by aga]

blogfast25 - 9-8-2015 at 08:04

Quote:

According the the ASTM protocol these values are too far out for those solutions to be used, however they are close enough for this amateur experiment.

Are you sure it says that? Does it mention tolerances for the 0.1 N normalities? 0.1018 N and 0.0969 N are close enough to 01 N for almost any purpose, IMO. The point of standardisation is to account for discrepancies between nominal and actual normalities anyway.

Interesting you found no effect of the CaCl2 treatment: I can't really see how that is supposed to affect the IN to begin with...

aga - 9-8-2015 at 09:05

The document actually says that the Iodine solution must be 0.100 N +/- 0.001, not that the thiosulphate must be too.

I guess it can be done to that accuracy if you have an analytical balance down to 1mg, which i don't.

Amazing that some AC must be just finely ground charcoal with an IN of 500 - merely 2x the rating for plain carbon.

Now that the bulls**t CaCl₂ yootoob thing is disproven, i'll have a go at baking and steaming to see what they do to the carbon - hopefully
bash it all the way up to 1000 and beyond.

[Edited on 9-8-2015 by aga]

S.C. Wack - 9-8-2015 at 09:29

Quote: Originally posted by aga

ZnCl₂ is cited as an 'activation' agent for carbon, so that probably works.

It does. All kinds of waste materials have been used. I still have a years old jar of pistachio shells black from ZnCl2/HCl awaiting heating. I don't remember the right temperature but it's not low, and an inert atmosphere is needed, and there are of course fumes. Heating in sand was tried with mixed results. If you ever want pink sand, this is the way to go.

aga - 9-8-2015 at 10:04

Quote: Originally posted by S.C. Wack

I still have a years old jar of pistachio shells black from ZnCl2/HCl awaiting heating.

Would you care to elaborate ?

blogfast25 - 9-8-2015 at 13:10

aga:

You could also compare to Norit, very OTC:

http://www.drugs.com/uk/norit-200mg-leaflet.html

aga - 9-8-2015 at 13:21

Cheers Bloggers.

I think they sell those here as well.

Next step is to actually Activate some Carbon.

Buckyballs and electrozapping or High Heat and Steam or Acid ?

Decisions Decisions ...

S.C. Wack - 9-8-2015 at 15:36

Quote: Originally posted by aga

Would you care to elaborate ?

After an ammonia soak next, this is the next lutefisk. This hitherto untapped resource has the potential to feed nearly a quarter of those who are starving due to resources being diverted to pistachio plantations.

Or, I'm waiting until I get a vacuum retort before drilling a hole in my box furnace for it. I can't do strange things in the back yard, I can't even be outside more than 15 seconds anymore before someone is staring at me like I'm TV for as long as I'm outside. If zinc is dissolved in HCl and pistachio shells are added, they soon turn black and rubbery. The impregnation could be half the activation. The jar has been drained a few times and it's hard to say if that was chemical or absorbed water.

Oscilllator - 9-8-2015 at 17:10

Excellent work aga!
It is not a surprise to me that the CaCl2 failed to activate the carbon, since I don't imagine changing the surface area of something like carbon would be easy to do at room temperature.
Perhaps you could try adding some CaCl2 to a sample of carbon and popping it in the oven along with the other samples? It's possible that the CaCl2 claim is not entirely bogus, just a little mistranslated.

blogfast25 - 9-8-2015 at 17:22

Quote: Originally posted by Oscilllator

Perhaps you could try adding some CaCl2 to a sample of carbon and popping it in the oven along with the other samples? It's possible that the CaCl2 claim is not entirely bogus, just a little mistranslated.

And your very vaguely described experiment will clarify this assumed mistranslation, how, pray tell?

Oscilllator - 9-8-2015 at 19:27

Quote: Originally posted by blogfast25

And your very vaguely described experiment will clarify this assumed mistranslation, how, pray tell?

It was only an idea. Perhaps the CaCl2 does have an effect on the charcoal but only at high temperatures. If so, then it can be assumed that the original source got it wrong. Perhaps "mistranslation" was the wrong word to use, but I can't think of a better one.

aga - 10-8-2015 at 00:11

As far as i understand it, what's required First is an increase in surface area.

Grinding does that by reducing the particle size.

High temperature steam appears to crack the carbon structure, and also react, randomly removing some of the surface to create a more uneven texture.

Phosphoric acid appears to react with the carbon at elevated temperatures causing the same effect.

CaCl₂ is more likely to be simply adsorbed to some extent at RT, and would be unlikely to be removed completely by washing with water.

The traces of CaCl₂ would account for some possibility of 'activation' by that method, although the carbon would remain entirely unchanged.

[Edited on 10-8-2015 by aga]

aga - 1-10-2016 at 10:55

Finally, a year later, having bought more lead for my ball-mill, a pile of charcoal got ground up today, yielding rather a lot of black powder that makes a huge mess if you spill any.

For further 'normal activation', a.k.a. increase surface area, how about simply mixing it with water, stir a lot to form a paste, then freeze it, hopefully causing microfractures in those tiny grains of dust ?

A quick google for 'microfracture' brought this up (about rocks) :-
http://www.sciencedirect.com/science/article/pii/S0191814114...

Hence there's a small pot of black mush in the freezer overnight.

For more Sunday diversion, three lots of 5g each of the ground-up charcoal have been boiled up with 2g of NaOH, CaCl₂ and MgSO₄ respectively, then filtered & washed & dried.

I'm wondering if AC-treated CaCl₂ will perform the same, worse or better than straight CaCl₂ in absorbing water from a stream of air.

If nothing goes amiss, tomorrow there'll be some actual scientific data !

Sulaiman - 1-10-2016 at 11:44

I suspect that the CaCl₂ activation did not have a significant effect because the Wikipedia article states;
"Prior to carbonization, the raw material is impregnated with certain chemicals"
i.e. not after carbonisation

aga - 1-10-2016 at 12:09

Hmm. Makes some kind of sense, kind of.

Impregnate the wood with something, then the organic break-down can't go via a straight gas route to just carbon : basically there's bits in the way, causing it to end up all fractured.

A bit like mixing wood shavings with gravel, then setting fire to it - the gravel particles get in the way, so it does not end up as a fine dust.

Well spotted Sulaiman, i'll try it.

Perhaps this is what S.C Wack was alluding to with his pistachio nut shells in a bottle of zinc chloride.

[Edited on 1-10-2016 by aga]

aga - 1-11-2016 at 09:54

The existing sodium thiosulphate and iodinde solutions were re-standardised and came out +0.0005 N and -0.0008 N, so they were pretty much the same as earlier.

Some more materials were tested to see if they can up the Iodine Number (I.N.) of home-made activated carbon.

bread.png - 2kB

Pyrolysed shop-bought white bread is pretty close to the I.N. of 500 found in the lower-end commercial products, and is the best result yet, despite it being ground by hand in a pestle and mortar instead of in a ball mill.

Amazing that simply freezing milled charcoal also increases the surface area dramatically.

All-in-all, adding chemicals to milled charcoal seems pointless, unless they are targetted at something specific.

Used up the last if the iodine and sodium thiosulphate solutions doing that and there appears to be no iodine left

Gratuitous lab shot :-

NEMO-Chemistry - 5-11-2017 at 15:33

Sorry to jump in, I am looking at AC for different reason, what I did find out was normally AC is done at 850C-1200C.
Then steam/water is injected or Co2 or Steam and Co2.

I also got info on Calcium Chloride, but will get to that later.

The activation is done at the same time as making the charcoal, industrially this is apparently done is huge rotating drums, common amounts are to end up with 1/3rd material you start with.

From what I could make out (will locate and place links at end), the material (coconut favored,or HARD wood) is heated fairly rapidly, the atmosphere is inert or close to it, the material is still at the stage it is gassifying or giving material off.

Steam and CO2 are then injected into the vessel, this is supposed to react with the material and make the pores inside the material larger, it is also supposed to remove all tars/gums and resins.
This bit makes sense to me, even if you carbonize something, some of the chemical content will also be carbonized? and therefore become part of the matrix in the carbon.

injection of steam and CO2 clears all this out, there was a warning of increase of out gas during this. The material produced (AC) apparently will bubble when placed in water, the internal cavities are the highest in number of the processes.

Next we have low temp activation. Before going into this I will point out the following, the temperature matters and the point of injection seems to matter, the method used seems to dictate the internal structure pore size.

Cold temp process

I found 2 versions of this with calcium chloride, first one is pretty much as aga did. the second one however injected calcium chloride once the material or vessel with the material in, reached 250C.

It was said several times that it cant be done in a home oven, the 'home' options all used cans with tiny hole in tin can top (1-2 mm). This bit didnt make sense so i will explain the info.

One was a video and one was from a commercial manufacture description, they didnt match up in all details.
First of all at no point does the tin seem to be opened, so how would anything be injected? I assume in this case the home making guide had actually soaked the material, the professional guide mentions however injecting the calcium chloride once gassing commences.

I also found phosphoric acid etc mentioned, but again in all cases these were used before the material had been turned into charcoal. The other thing I found was constant reference to packing as much material in as possible, activation or completion is assumed once no further gas emits from the tiny hole.

I am looking into magnetic charcoal, this is to do with my bio fuel obsession. Anyway I will post what i find on the charcoal process here, any full papers i will put in the normal place.

I hope this helps someone else, thx to aga for linking me back to this thread and the initial experiment. I am after a way of removing ultra fine carbon with magnetic carbon, my application is purely about getting rid of discoloration.

I will post and come back in a few mins with the links.

I got bored watching this, but around 15.50 onwards, the guy explains a couple of things. This is a manufacturer of carbon products.

EDIT
At 24.45 he starts talking about activating carbon after its been made into carbon. While this goes against alot of reading, the process he mentions does fit with what I had read.

So in this instance i think he is talking about the cold (250C) process, where the carbon is placed in an air excluded drum and rotated, this is heated to 250C and water/steam is injected.

Hw talks about this 'carving' out the internal structure, to me this fits with the papers that talk about removing the volatiles that have carbonized. [this is edit 3, hence why it slightly contradicts what i say bellow]

https://www.youtube.com/watch?v=1UPxYVemno8

Also i didnt find ANY mention of softwoods being used, hard and dense seemed to crop up most, i will edit with more links as I refind them. Sorry I didnt keep all the links and papers as I was specifically looking for something else, then came back full circle.

[Edited on 5-11-2017 by NEMO-Chemistry]

This next video is from the same guy, i found this one contrary to alot of what I had read. In the first video i think its pretty clear he makes things on a pro level, this video he is in his back yard making charcoal, also he mentions activating the carbon after it has been made. Now I unsure here what to think, most the professional stuff I had read, indicated that activation was done at the time charcoal was made.

I also came across alot of information stating the charcoal is washed with extremely pure water to remove ash etc.

https://www.youtube.com/watch?v=3ii6S70bVY0&index=2&...

Sorry for constant edits, i am having to back track my browser history

.

I have a book listed in mendeley i havnt read yet, its too big to post but i got it from normal sources.

Mash, H. and Rodríguez-Reinoso, F. (2006) Activated Carbon. doi: http://dx.doi.org/10.1016/B978-008044463-5/50022-4.

sorry this post has gone a bit all over the place! I had intended just to add some snipits I had found out, but on trying to locate them again, i have come ac cross further information.

Sorry if some of what i said above is about to be contradicted!! I hadnt seen this further information at the time.

I have posted some screen shots from the book, these give further references related to activated carbon, i think aga was onto something, however i think at the time the information he was working from was slightly off.

I have no idea if he intends to revisit this topic, but if not, maybe this extra info will help others. The book link dosnt work, but the intention is merely to provide the name etc not a direct link to it.

One question that springs to mind, i am aware its likely the only way i will answer it though, is to do the experiment.
Alot of the activation is down to clearing out cells and gunk from the carbon, particularly in wood.

A thought occurred to me, while many of the processes inject steam etc to remove or etch the pore sizes, what about starting from drift wood?

I am sure everyone has seen the very old and grey driftwood, very very dry and hard, yet when broken in half it is mainly full of spaces, the contents of cells etc long long gone.

Maybe driftwood could produce activated carbon without the need to activate it? after all the VO's etc have already been removed via osmosis. Just a thought but its likely I will try and find out.. might be useful and quick for my purpose.

The only material I have found relating to this so far however, is papers regarding the high sodium and earth alkali metal content of driftwood. Maybe beat up Carbon is not as simple as beaten up carbon after all.

Attached a paper on tests

Added a review paper on activated carbon methods

Added paper by Laine in refs EFFECT OF THE PREPARATION METHOD ON THE PORE SIZE DISTRIBUTION OF ACTIVATED CARBON
[Edited on 6-11-2017 by NEMO-Chemistry]

[Edited on 6-11-2017 by NEMO-Chemistry]

[Edited on 6-11-2017 by NEMO-Chemistry]

Attachment: Additive-006.pdf (133kB)
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[Edited on 6-11-2017 by NEMO-Chemistry]

Attachment: review.pdf (229kB)
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[Edited on 6-11-2017 by NEMO-Chemistry]

[Edited on 6-11-2017 by NEMO-Chemistry]