Activated carbon

Sepulchritude Forum: The Absinthe Forum Archives Thru July 2001: Activated carbon
By Don_Walsh on Thursday, May 24, 2001 - 03:51 am: Edit

Vodka by definition is neutral spirits and water. Now neutral spirits are not all created equal, any more than all water is of the same quality. While Stoli is a premium vodka for export, many Russian vodkas are swill. And a survey of Russian and Eastern European potable-alcohol standards will show that in general these standards are very sloppy. A lot of congeners are allowed to be present.

GRAPE spirits, per the EU, are required to have a total of 200 mg/L congeners so that the organoleptic qualities associated with grape alcohol are present.

Grape NEUTRAL spirits, on the other hand, especially the best grades, have much lower congener levels, but are still softer feeling than grain neutral spirits, say. Poorer grades of grape neutral spirits are used to make wine vinegar. The best grades are used in pharmaceuticals (sometimes dehydrated to remove the last 4-5% of water).

The cost difference (on an industrial basis) of buying the best grades versus the cheapest grades is altogether trivial. Like 10 cents a liter difference. So there really is no excuse for using anything but the very very best.

By Pantrax on Wednesday, May 23, 2001 - 05:41 pm: Edit

I used to think that vodka was vodka and it was all the same. Then I did a side by side tasting of several vodkas. In order of price these were: Wolfschmidt (cheapest stuff), Smirnoff, Absolut, Ketel One, and Grey Goose. The differences were obvious. The first two smelled and tasted very strong, and drinking a shot of either was an unpleasant experience. Absolut was better, but still had a strong and heavy smell of alcohol. The last two were much lighter and cleaner tasting. Drinking them straight was not a painful experience. In addition, Grey Goose had an extra flavor to it that I couldn't quite identify. Nothing unpleasant, but something distinctly different from the Ketel One.

The one time I have had Russian vodka (that is, a bottle that someone brought directly from Russia, with a label I couldn't read) it had the same light and clean taste I found in Ketel One and Grey Goose. However, I have no idea if the Russian vodka I had was an upscale brand or something from a kiosk, so this data point may be meaningless.

By Zack on Tuesday, May 22, 2001 - 12:19 pm: Edit

There is a lot of vodka sold in Russia that is very bad. There are people that set up kiosks around city centers and sell "vodka" really cheaply, these people have been known to be selling things such as watered down jet fuel. I'm sure these kiosks are still around, it wasnt that long ago that I heard about this. You might read it in a Russian travel guide. This could have something to do with bad life expectancy.

Moskovskaya Osobaya (maybe this is what you are talking about) is a fairly popular brand of vodka. It used to be as well known as Stolichnaya is. However, it is only 40%. There is one Russian brand I have seen that has over 50%, called Krepkaya (strong), but I think it is 55%

By Dr_Ordinaire on Tuesday, May 22, 2001 - 12:14 am: Edit

Russia is also one of the few countries where life expectancy is actually declining, which is not surprising if they drink four or five soda size glasses of 50% vodka every day...

They should drink absinthe. It would go perfectly with the "slavic soul", wolves howling at the moon in a snow-covered landscape...and all that..

By Heiko on Monday, May 21, 2001 - 10:48 pm: Edit


Absolut is also sold in Germany - here it is spelled perfectly right ;-)

I once had Russian vodka (I can't remember its name, a friend brought it with him from a student exchange program. It was what the moscovian family was drinking). You could drink it like water. You did not taste any alcohol, it just tasted like smooth, clear water - yet it had 50% alcohol.
I have never bought any vodka in Germany that tasted like this, they all taste like pure alcohol.

According to what my friend told me, they drank incredible amounts of vodka there. He is someone who can drink more than most other people I know, but he told me it almost got too much for him. When he arrived, they had one bottle for three people before supper, one with supper and one after. At least he was able to drink as much as was offered to him. Others were forced to drink more because the people there considered it impolite if they offered more vodka and somebody said no... they just didn't believe that somebody already had too much after four or five soda-glasses of their good 50% vodka ;-)

By Zack on Monday, May 21, 2001 - 02:24 pm: Edit


I haven't noticed that problem with Stolichnaya before, but vodkas of the Russian and Polish styles contain more cogeners and other "impurities" than those of the Western style. (So, I guess that would make them more likely to freeze.)

By Lordhobgoblin on Monday, May 21, 2001 - 11:21 am: Edit

Yes Stolichnaya does taste good. The only problem with it (at least the Stolichnaya sold in the UK) is that if you keep it in the freezer it partly freezes, whereas other vodkas which are less tasty but stronger can be served straight from the freezer.

By Head_Prosthesis on Sunday, May 20, 2001 - 10:53 pm: Edit

Please dont be France.

By Dr_Ordinaire on Sunday, May 20, 2001 - 09:30 pm: Edit

Zack, I have decided that my part on this forum is going to be to present information, and not argue about how people interpret it.

So if you think that from:

"It is defined by government regulations as a spirit without any distinctive character, aroma, taste or color."

I cannot deduce that:

" One funny thing about vodka is that according to U.S. law it has to be tasteless.

Yep, vodka cannot claim to have ANY taste."

Well, buddy, it's fine with me...

By Zack on Sunday, May 20, 2001 - 08:07 pm: Edit

Oh, and "Absolut" is a deliberate misspelling of "absolute." They had to do that for advertising regulations here in the US. (not anything to do with the alcohol purity standards)

By Zack on Sunday, May 20, 2001 - 08:02 pm: Edit

"It is defined by government regulations as a spirit without any distinctive character, aroma, taste or color."

That in no way allows you to make the statements: " One funny thing about vodka is that according to U.S. law it has to be tasteless.

Yep, vodka cannot claim to have ANY taste."

Sure, something that tastes like Mandarin oranges isnt gonna be called simply "Vodka." There is not any law that prevents a "Mandarin flavored Vodka" though.

Hey, is chocolate-flavored milk illegal too?

By Dr_Ordinaire on Sunday, May 20, 2001 - 07:55 pm: Edit

Sorry, I get this "Server error" message. That's why I posted twice. Which, BTW, in this case allowed me to correct MY error. :-)

By Dr_Ordinaire on Sunday, May 20, 2001 - 07:53 pm: Edit


"Vodka is far and away the most popular spirit category in America, accounting for more than 20% of all distilled spirits consumption. It is defined by government regulations as a spirit without any distinctive character, aroma, taste or color. Vodka is essentially an non-aged neutral spirit that can be distilled from just about anything fermentable. Although the legendary potato is used in the production of some vodkas, most brands today, including the imported ones, are made from grain...any grain, including rye, wheat and barley, but principally corn."

Absolut (which may or may not be misspelled, depending on the language) may get away with it, for as long as the government ignores their ads. But have you noticed that they misspell flavours in the name, not in the ad? If the feds cry foul, they change the ad, which is far cheaper than changing a name.

By Dr_Ordinaire on Sunday, May 20, 2001 - 07:52 pm: Edit


"Vodka is far and away the most popular spirit category in America, accounting for more than 20% of all distilled spirits consumption. It is defined by government regulations as a spirit without any distinctive character, aroma, taste or color. Vodka is essentially an non-aged neutral spirit that can be distilled from just about anything fermentable. Although the legendary potato is used in the production of some vodkas, most brands today, including the imported ones, are made from grain...any grain, including rye, wheat and barley, but principally corn."

Absolut (which may or may not be misspelled, depending on the language) may get away with it, for as long as the government ignores their ads. But have you noticed that they misspell flavours in the ads' copy, not on the drink's name?

By Zack on Sunday, May 20, 2001 - 07:27 pm: Edit

"One funny thing about vodka is that according to U.S. law it has to be tasteless."

I'm sure there is something you are leaving out or misunderstanding about that.

" Yep, vodka cannot claim to have ANY taste.

Have you noticed that Absolut vodka's ads misspell the taste. As in: Mandrin?"

Have you ever read the stuff on the Absolut bottles under the name? This is what it says directly under the "Absolut Kurant" label: "This superb vodka bears the distinctive flavor of natural Black Currants..."
Thats what I would call "claiming to have a taste."

A more likely explaination for the "misspellings" of the flavors: Did you ever notice that its "Absolut" which is absolute misspelled?

By Dr_Ordinaire on Sunday, May 20, 2001 - 06:44 pm: Edit

One funny thing about vodka is that according to U.S. law it has to be tasteless.

Yep, vodka cannot claim to have ANY taste.

Have you noticed that Absolut vodka's ads misspell the taste. As in: Mandrin?

By Don_Walsh on Sunday, May 20, 2001 - 12:39 am: Edit

Well, there's always that adamantine lingual weapon.

Blue pills are an option, but I stand with mark Twain who believed that erections ought to be gotten naturally or not at all.

By Marc on Saturday, May 19, 2001 - 10:22 pm: Edit

What was once a diamond has now turned to ash.

By Don_Walsh on Saturday, May 19, 2001 - 10:14 pm: Edit

I reckon your carbon is if anything, already overactivated.

By Marc on Saturday, May 19, 2001 - 09:58 pm: Edit

Please, somebody activate my carbon!

By Head_Prosthesis on Saturday, May 19, 2001 - 09:01 pm: Edit

I heard it was real good. Hmmm? We got a good ole' Siskel and Ebert review going. Italy huh? I might have to make a call. Uncle Vito owes me a favor.

By Zack on Saturday, May 19, 2001 - 08:18 pm: Edit

Yes, it's from Italy. Ive never tried it, but I heard it was nasty.

By Head_Prosthesis on Saturday, May 19, 2001 - 08:08 pm: Edit

Have you ever heard of a vodka called Mezza Luna or something close?

By Zack on Saturday, May 19, 2001 - 08:01 pm: Edit

Nothing is for sure about the origins of vodka, but it was most likely first made from grains. It is also believed to be a Russian invention, but the Polish do dispute that. The potatoes didn't come into it untill the 1800s most likely, and this was because they were cheaper.

Chopin is made from potatos and rye as well. The Polish brand Luksusowa is all potato I believe. My favorite Polish vodka is probably Zubrowka (Bison Brand). It has a "different" flavor, almost like vanilla.

By Netsurfer on Saturday, May 19, 2001 - 07:35 pm: Edit

There is a polish potato vodka I believe named Chopan that is quite excellent as well.

I was told once that the original vodkas were made from potato - is that correct?

By Zack on Saturday, May 19, 2001 - 04:21 pm: Edit

I have read before that Stolichnaya is "filtered three times through quarts and activated silver-birch charcoal."

By Wolfgang on Saturday, May 19, 2001 - 12:51 pm: Edit

I sent them an email asking for some explanations ... I also tasted Stolichnaya Vodka for the first time yesterday and up to now, it`s the only vodka I can drink without mixing. It`s really a good product that make me understand why Russians can drink so much of it ;-).

By Don_Walsh on Saturday, May 19, 2001 - 01:04 am: Edit

Quartz makes no sense to me either. I don't believe it has any adsorbant qualities at all. Could this be a mistake or mistranslation?

By Wolfgang on Friday, May 18, 2001 - 10:26 am: Edit

Question for you Don,
I was searching information about the Stolichnaya vodka and found a site where they describe the filtering process. Apparently they use quartz filtering... What does that mean and why do they use quartz ? I don't see how they can filter alcohol using quartz...


Last Stoli is carefully filtered through both quartz and activated charcoal, then through quartz again.


By Marc on Thursday, May 17, 2001 - 10:43 pm: Edit

bon nuit, mon ami.

By Mr_Rabbit on Thursday, May 17, 2001 - 09:46 pm: Edit

Don, I'm in my cups so I hope this don't come out wrong, but here goes:

Thanks, man! When you strip all but the essentials away, what are you left with? For me, experiences. Beauty.

And I think you and Ted are working on making something cool, something right, something pure. You need to make a certain amount of money. Process must have fuel. But you aren't making Budweiser Absinthe. You are making the real deal. Something that makes the world more interesting.

Thank you Don, and Ted, for not going the mass production route. You could make an assload of money off of this all, you know. Market it right, and holy shit, you are rich. Hills proved it. Green piss can make money.

And money is worth as much as... dust. As much as being today's headline, president of the United States of Whatever, Miss Nowhere 2001. Take one leeetle step backwards. It's 1000 years ago, 1000 years from today. What is your money? Where are your accolades? Look on my works, ye mighty, and... what was I saying?

Anyhow, I can't help think, in my secondary-effects-have-worn-off-and-I'm-kinda-tipsy state, that some artist, some future Picasso, will see the work of Picasso, and buy some absinthe. Not Hills, not Strapowhatnot, not PissOTheWeek, but Jade, and dig it. And make good art. Like 'the absinthe drinker' by name your artiste.

And that will be because Ted and Don gave a damn. Both of you could have made more money than you will- you know that. And that's why I am writing this. In case you ever have doubts- know that what you do is Worth A Damn, rather than worth a buck. Thanks.

Having read what I just wrote, I have to say someting hostile to balance it out, or it won't be a Sepulchritude post. Hmm...

Don- You are mister poopy head! HA!

Ted- You are mister... um... Chemist... no... um... TETSUO!!! wait, that's from Akira.... mister Val Kilmer Like Guy.

I'm trying to say Fuck Off, You Wonderful Bunch Of Bastards. And thanks. For all the fish, pussy eating stories, fuckheaded arguments over nothing, and...

Drunk am I. Sleep. Yes. Deserve it I do!

By Marc on Thursday, May 17, 2001 - 09:27 pm: Edit


you're working too hard, brother. Time to take a break. Tell us about your sex life. If its as interesting as the rest of your life, you've got my attention.

By Don_Walsh on Thursday, May 17, 2001 - 09:07 pm: Edit

Dear Wolfgang

I was talking about the conventional wisdom, which is now shown to be wrong, that alcohol needs to sit over powdered Activated Carbon for weeks or months.

The truth is that PAC works by equilibrium. Maybe I need to elaborate on the meaning of that term as applied here? It means that at same time that the PAC is adsorbing the fusel oils, the alcohol is also desorbing them back into solution. Now, in this equilibrium, the adsorption is favored, about 4 to 1, so the PAC works reasonably well in about 24 hours, and after that (equilibrium being achieved) nothing changes any more. You can filter off the PAC and add more if you want to, and let is sit for another 24 hrs (with occasional shaking or stirring -- AC is not like a James Bond vodka martini, it doesn't care which.) But because 80% of the volatiles (fusel oils) have already been taken out, the virgin PAC isn't as efficient this time.

So rather than a second PAC treatment, it is better to switch to a granular AC column ('fixed bed') where the adsorption is driven by kinetics rather than equilibrium. Now one is using a massive amount of carbon with with a shorten contact time on the alcohol. If the GAC has been prepared properly, and chosen properly, and the bed packed properly, etc., this process is much more efficient than PAC, as well as faster. In fact the PAC pre-treatment is just to reduce the concentration of fusel oils prior to the GAC treatment so as to extend the life of the GAC porior to regeneration -- which anyway is cheap and easy and can be done in situ (in place, without having to repack the bed.)

And you can use as few as 1 bed or as many as you like in series, to achieve the desired purity level, or in parallel, to achieve the required throughput, or you can scale up the bed volume by increasing the diameter of the column, or both.

The important parameter is the rate of throughput which ought to be no faster than 1/4 the bed volume per hour, you control this with a valve at the bottom (basically a faucet.) Other than that you want to choose a GAC particle size that optimizes surface area while precluding clogging. Too small a mesh size, or too much dust left in, and the bed will clog. Zero flow, no filtration. 20x40 is perfect, 12x40 is OK. 20x50 is maybe too small on the low side.

There are a bewildering variety of AC grades, many are specialized. What you want for a GAC is:

-- Food grade
-- Steam activated NOT chemical activated
-- Acid washed (means less mineral deposits left in)
-- Lignite coal - high hardness and easy to steam reactivate

Norit GAC 20x40 and Norit DARCO 20x40 are both to all these specifications, are made in North America, and are also made in Holland if you are in Europe. A peat based GAC such as Norit PK 0.25-1 is also good, but not so suitable for regeneration, and softer. This is the Norit grade sold by Gert.

Avoid like the plague: coconut based carbons because they have unsuitable pore structure and a lot of mineral content; chemically activated carbons because they are chock full of phosphoric acid; non-FOOD GRADE carbons; and carbons which do not specifically state what material they are produced from, how they are activated, etc.

The Norit D10 powdered AC for pretreatment is a European grade and doesn't show up in Norit USA catalogs. However Norit has other suitable FOOD GRADE PACs made in USA. Steam activated and acid washed is still best. However, peat based PAC is just fine as PAC isn't reactivated anyway. Just throw it away after use.

At 0.15-0.25 cents per gram, PAC costs less than 1 US cent per liter of 40% alcohol treated, so who cares about reactivating it? Throw it away.

With GAC, it's up to you. To process 24-32 liters of 40%, if you use the GAC once you would be throwing away about $2.25, roughly 10 cents per liter. But if you have or can buy a steam source you can re-use this hundreds of times, and avoid having to re-pack the bed, wash more carbon etc. So reactivation by steam in situ is highly attractive if you are processing a lot of alcohol (like me.) If not, well, throwing away $2 and change isn't going to break you I hope, and packing a fresh bed the next time isn't too onerous. Not compared to a long tedious and somewhat hazardous fractional distillation.

For a fractional distillation to be effective you need a good (slow) column and a high (slow) reflux ratio like 10:1. By definition a 10:1 reflux means the distillation will take 11 times longer than a simple distillation (100% takeoff) -- not including the time to boil up and equilibrate the column. Ugh!

Since I have to (theoretically) prepare 100 liters a day of 95% I am faced with fermenting 800 liters a day to 14% mash, and distilling that to 40%, polishing it, and then concentrating it to the degree where we use it to make absinthe.

In practice this is a production process where 800 liters of mash enters the process daily, and 100 liters of highly purified high-proof potable ethanol comes out every day -- after about a 1 week journey in between.

Fermentation 3 days
Concentration (simple distill) 1 day
Rough polishing PAC 1 day
Fixed bed polishing 1-2 days
Fractionation to high proof 1 day
And monitored by GC at every step for QC/QA

Sorry I can't comment on how long it takes from that point to absinthe.

(I wonder what those who sit in the armchairs and talk economy of scale have to say about this? See what I mean about MY LABOR?)

By Wolfgang on Thursday, May 17, 2001 - 01:13 pm: Edit

In the "120 days of sodom" thread you said :

There are two main processes for cleaning up or 'polishing' typically dirty neutral spirits. One is fractional distillation and the other is activated carbon (activated charcoal). The first is fact and expensive, the second is cheap but painfully slow. Ask a vodka maker. A week over charcoal is better than nothing. A few weeks is better than a week. A few months, good. Six months, great.

Were you talking about the same process as you describe here with a column and everything ?

120 days of sodom

By Don_Walsh on Thursday, May 17, 2001 - 10:39 am: Edit

No problem, Malhomme.

1. Correction. I say "for 3.3 liters this is 32 grams (of PAC)." This is a typo. Should be 8 liters not 3.3.

2. I do not mean to impugn the generosity of 'Gert Strand' who went to a lot of trouble to translate their Swedish monograph on improved AC pirification of alcohol, into English. However it is true that GS has a vested interest in selling repacked ACs so he isn't very helpful in identifying grades of AC in a fashion that help one navigate a Calgon/Chemviron or Norit catalog. He states GAC particle sizes in mm rather than US Mesh sieve sizes as is standard worldwide. Thus, his 0.8 to 0.42 mm GAC for example is a standard 20x40 (mesh) product.

Carbon is cheap enough that it is not a burden to buy a 12.5 Kg bag or a 40 lb bag. Unless Norit has two tier pricing, the US made Norit grades ought to be cheaper at source than in Thailand and here they are like $2.25 a Kg. So a 12.5 Kg bag of Norit PK 0.25-1 peat GAC food grade ought to be $30 or less. A 40 lb bag of a PAC ought to be $50-$60 or less and will be enough to pretreat 4500 liters of 95% = 13,500 L of 40%. A 40 lb bag of GAC will be enough to load nine 38mm ID x 1.5 meter columns. Or a smaller number of larger diameter beds, which obvious can handle the alcohol faster. At 425 ml/hr a 38mm ID bed will take 20 hours to filter 8 liters of 40%. The volume goes up as the square of the radius so, a smallish increase in diameter will mean a largish increase in bed volume and therefore throughout which is 0.25 x bed volume. Note that bed volume is calculated without taking the carbon into account.

And the GAC (unlike PAC) can be easily regenerated with low pressure steam.

By Malhomme on Thursday, May 17, 2001 - 09:12 am: Edit

Thanks Don, this makes for very interesting reading indeed!!!

By Don_Walsh on Thursday, May 17, 2001 - 04:15 am: Edit

And here's my modest proposal regarding overall alcohol purification scheme, utilizing a minimum of distillation and a maximum of activated carbon treatment. So don't say I never gave you guys anything! As this has nothing directly to do with making absinthe, I don't think Ted will mind, and anyway I put this together by myself.

BACKGROUND: the usual Net manuals/handbooks/websites recommend distilling mash fractionally down to 95% in one or more passes. This is slow, tedious, and energy intensive, especially on anything but a bench scale. The, and only then, treating with carbon, whether PAC, GAC, or both.

I propose the following:

1. Simple-distill to 40% or so, this is possible in a single pass. Discard first 100 ml and last 100 ml (on a 25 L mash scale) and collect the main part, which if you ferment to 14% ought to leave you with 8 liters of c.40%. Check proof with a hydrometer. If your product is higher than 40%, you will collect less, and if lower than 40% you will collect more. As long as it is not higher than 50% you don't need to cut it back with water to carbon-treat it.

2. Add 4 grams per liter on 40% basis, of suitable FOOD GRADE powdered activated carbon such as NORIT D10 (-325 mesh). For 3.3 liters that is about 32 grams. Stir. Let sit for 24 hours and stir again every 6 hrs during that time. Now filter off the carbon and throw the PAC away.

3. Now filter the alcohol through a fixed bed (column) using FOOD GRADE granular activated carbon following the instructions for preparing carbon, packing column, and using the column that can be obtained from or other sources. One column is good, two columns in sequence is better. You want a flow rate of about 425 ml per hour through the column(s).

At this point you should have potable high purity ethanol with almost no 'tails' left. The first quick & dirty distillation will have removed some heads (low boiling fractions) and some tails (fusel oils etc, high boiling fractions) while the PAC and GAC will have removed almost all the remaining tails. I am less sure about the performance of carbon against heads. So the final step is to fractionate the 8 liters of 40% to 95%, using the best column and reflux control head you can get, and a reflux rate of 10 to 1. You will want a slow boil up, and you will start the still at 100% reflux until the column is fully equilibrated (temperature at still head, measured by a good thermometer, has dropped all it will drop, ought to be a little below 78 C.)

Now adjust to 10 to 1 reflux rate (one drop collected for every 10 drops returned to column). Discard anything collected at under 78 C and also discard first 100 ml collected at 78 C or above.

Stop collecting if temp at still head rises above 80 C.

The main fraction will be VERY VERY clean 95% potable ethanol. Much cleaner than Everclear. Much cleaner than USP grade. And much cleaener than usual food and beverage grades commercially sold and used in the liquor industry.

Save what is in the still pot and you can combine it with the next batch if you like.

The advantage of this procedure is that we have avoided fractional distillation until we have the minimum (8 liters instead of 25 liters) and already highly purified ethanol.



Therefore it stands to reason that the activated carbon should be allowed to do as much of the purification of the alcohol as possible. This is true for home distillers, and it is true for commercial distillers. In fact if you want to use your ethanol at 40% (i.e., vodka) you can skip the final fractionation.

If so I would recommend that you verify that the methanol in the product (which carbon does not remove) passes the simple analytical test from the USP standard. For this you don't need a GC, you just need a few pieces of glassware, a few common chemicals and one special one - chromotropic acid. All in small quantities.

Next time I will give you the USP test procedure for detection of methanol in potable ethanol.



By Don_Walsh on Wednesday, May 16, 2001 - 06:17 pm: Edit

I've recently completed a lot of study relating to purification of potable alcohol with acticated carbon. The information available on the Net is mostly from people reselling/repackaging such carbons for the home distiller market. Those resellers are not interested in educating their consumers more than necessary, as they are charging 3 times the actual cost of the carbons they sell, for rebagging the stuff for you.

Well, I'm here to tell you that food grade activated carbons of peat or lignite-coal origins, steam activated, and acid-washed, dust free, from Norit, sell for c.$2.25 a kilogram in either powdered (PAC) or gransular (GAC) forms. That is enduser price, including shipping, for a bag of 12 to 18 Kg, which is how they are packaged, usually.

Powdered carbons are used by dumping a measured amount into 40% ethanol/water, stirring, and letting the mixture equilibrate for 24 hrs or so. PAC works on an equilibrium basis, so it is never completely efficient, but with proper dose -- 4 grams per liter of 40% is a good place to start -- it is a good rough treatment, or a pretreatment before putting the alcohol through a GAC fixed bed. PAC is filtered off and thrown away after use.

Granular carbons are used in columns of 40mm ID or larger and usually 1.5 to 2.5 meters long. If necessary, such columns can be used serially. Contact time is the most important factor, and you want a throughput of 1/4 the volume of the empty bed. We use a 10" ID column of about 75 liters volume and run it at about 20 liters an hour, so we can process 100 liters of 95% alcohol a day (250 liters of 40%, stripped back to ethanol, is 100 liters.)

GAC can be regenerated (once it is saturated with fusel oils etc.) with steam, and reused. Peat based carbons are not suitable for this. They are too soft and their pores close down. Lignite based GACs are superior for regeneration.

A GAC bed has to be loaded properly, with well washed, water saturated carbon free of air bubbles.

Grades of Norit GACs that meet all requirements for purifying potable ethanol include PK 0.25-1 peat carbon; and DARCO 20x40 lignite coal carbon. Recommended Norit PAC for rough or pre-treatment is D10.

FORGET all the stuff on the Net about needing to polish alcohol over PACs for weeks or months. Equilibrium is reached in a day. After that nothing changes. Of course you can repeat the process with virgin PAC as many times as you like, but soon the equilibrium will turn unfavorable as the % of fusel oils drops.

A GAC column does not work by equilibrium, it works by kinetics, and that's why it is both faster and more efficient. Instead of 4 grams per liter like PAC, GAC beds are about 1 Kg carbon to 6 liters 40% EtOH -- and move 1 bed volume of product through in 4 hours.

You track the performance of both type of carbons by GC of course. Or by mouth. And that's the same way you know when the steam-cleaning of the saturated bed is complete. No more old socks taste of fusel oils. Or no more peak on the GC.

(GAC bed design can be a lot more complex, on an industrial scale, but it doesn't need to be. That's just process engineers showing off. At its simplest, it's a tube, carbon, 40% alcohol, and gravity.)

FORGET putting activated carbons in a kitchen oven to regenerate them. Fusel oils are FLAMMABLE. and they STINK. Don't bother trying to regenerate powdered carbons. And regenerate GAC's with steam. Doesn't have to be high pressure steam. Boiling water will do it, it will just take a longer time and you will get bored percolating boiling water through the column.

A public service message from Jade Liqueurs.

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