Ethyl Carbamate and copper reaction

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Lowerarchy
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Ethyl Carbamate and copper reaction

Post by Lowerarchy » Tue Feb 03, 2009 7:42 pm

Here's additional proof from our cousins in the craft that more copper is better (not that anyone ever doubted it) from the American Distilling Institute forums.

Interesting discussion about copper reactions and the toxin ethyl carbamate in whisky and stone fruit brandies. Basically, put the most copper early in the vapour path. This might be a consideration for those of us with copper mesh mixed with stainless packing. Post 11 in the above link sez "Our Holstein still which is all copper (and maybe the Christian Carl's too?) has a "catalytic convertor" right before the condensor that is I believe a group of tightly spaced copper plates to give additional copper surface area for contact with the vapor before it is recondensed." Easily implemented for folks with a liebig. Bokakob users may want to invest in copper packing if they make these kinds of distillate.

There's more info on ethyl carbamate available from the UK Food Standards agency.

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Re: Ethyl Carbamate and copper reaction

Post by HookLine » Tue Feb 03, 2009 8:33 pm

From that first link.

"As it was explained to me, copper contact has many salutary effects. Copper reacts with sulfides and keeps them in the still. The reaction creates a black film that has to be cleaned off every few days to keep the copper surfaces active."

So do we need to clean of the black stuff, but leave the patina?
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Re: Ethyl Carbamate and copper reaction

Post by Dnderhead » Tue Feb 03, 2009 8:58 pm

From my research, clean copper is good in the boiler and the column but not in lyne arm, condenser etc. (just where it can fall back to the boiler)
as a mater of fact condenser and connecting tubes is better off made of stainless.

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Re: Ethyl Carbamate and copper reaction

Post by BW Redneck » Thu Feb 05, 2009 1:11 pm

I've had the black film before. It can easily be wiped off with a wet rag, and it doesn't harm the patina underneath.

I seriously don't worry about it. Flush the column with water after the run and that'll do all the cleaning it needs.
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Re: Ethyl Carbamate and copper reaction

Post by schnell » Wed Apr 01, 2009 10:52 am

you have to regenerate your catalyst to keep it working. this means you need to remove the patina. Inside, not outside.
a rinse with a weak acid, such as citric, will brighten the metal and allow the catalyst to function properly.

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Re: Ethyl Carbamate and copper reaction

Post by punkin » Thu Apr 02, 2009 12:05 am

schnell wrote:you have to regenerate your catalyst to keep it working. this means you need to remove the patina. Inside, not outside.
a rinse with a weak acid, such as citric, will brighten the metal and allow the catalyst to function properly.


Do ya reckon a weak acid like boiled wash would suffice??



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Re: Ethyl Carbamate and copper reaction

Post by Hack » Thu Apr 02, 2009 7:58 am

Has anyone ever actually tested the pH of the boiled wash after a run? Now I'm curious. We know it likes to be around four or five before fermenting, but if using too much backset makes a wash too acidic I'm guessing that it might be more acidic than a pH of 3 or 4. Then again that just might be more acidic enough.

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Re: Ethyl Carbamate and copper reaction

Post by punkin » Thu Apr 02, 2009 11:08 am

Hack wrote:Has anyone ever actually tested the pH of the boiled wash after a run? Now I'm curious. We know it likes to be around four or five before fermenting, but if using too much backset makes a wash too acidic I'm guessing that it might be more acidic than a pH of 3 or 4. Then again that just might be more acidic enough.


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Re: Ethyl Carbamate and copper reaction

Post by muckanic » Thu Apr 02, 2009 5:45 pm

punkin wrote:Do ya reckon a weak acid like boiled wash would suffice??
The copper manifolds in my mash tun and beer boiler come out shiny at a pH of about 5, but that of course is with heat and a couple of hours' contact. Backset must be more acidic than that. Note that removing the patina could interrupt the sulphide trap effect, and that shiny copper seems to be desired early but not late in the path.

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Re: Ethyl Carbamate and copper reaction

Post by schnell » Fri Apr 03, 2009 4:33 pm

Of course spent wash has a suitable pH. But you'd need to wash the surfaces along the Vapor Path...

And regenerating the copper surface improves the catalytic effect on the sulphides as well.

As an example, Bavarian-Holstein brags about their catalytic unit and charges extra $ for it. It is attached to the top of the column and regenerated after runs by using a citric acid rinse through a CIP system. Of course the bulk of the still is copper and gets this wash down as well, but the catalytic unit has a very large surface area for vapor contact.

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Re: Ethyl Carbamate and copper reaction

Post by Lowerarchy » Sat Apr 04, 2009 7:16 am

You've examined one of these Holstein rigs, schnell?

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Re: Ethyl Carbamate and copper reaction

Post by muckanic » Mon Apr 06, 2009 7:18 pm

schnell wrote: And regenerating the copper surface improves the catalytic effect on the sulphides as well.
So what is the reaction that is being catalysed? All I can think of is oxidation of gaseous sulphides to sulphur/sulphites/etc. I have always assumed copper to be a reactant, not just a catalyst.

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Re: Ethyl Carbamate and copper reaction

Post by schnell » Sat Apr 25, 2009 9:18 am

You've examined one of these Holstein rigs, schnell?
Yes. They show them off when they try to sell you one...
So what is the reaction that is being catalysed? All I can think of is oxidation of gaseous sulphides to sulphur/sulphites/etc. I have always assumed copper to be a reactant, not just a catalyst.
I believe that the conversion of sulphides (volatile) to sulphates (not volatile) by way of an oxidation is the reaction we're primarily interested in. Atmospheric oxygen would be a reactant. This removes the rotten egg smell/flavor.

Copper should be catalytic, not consumed. However we know the stills wear out, degrade, and ablate (ie lose copper). This may be losses due primarily due to the acidity of several of the components present, including organic acids formed from ester hydrolysis. Some reactions are catalytic while some involve copper as a reactant. (Note: I would reasonably assume a typical spirit run would contain hundreds of discreetly identifiable components.) So really there's alot more chemistry going on than just one or two reactions.

I don't have access to the University library without a drive to town or I'd have posted some references. When I get some time on my hands I'll see what I can pull up and add to this thread.

Also the decomposition of ethyl carbamate by the special catalyzer unit is bragged about by Holstein. I think they even patented the application in Europe. They place it at the top of the column where the liquid phase is descending. Folks using a copper mesh packing will be approximating this approach.

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Re: Ethyl Carbamate and copper reaction

Post by eternalfrost » Sat Apr 25, 2009 9:32 am

schnell wrote: Atmospheric oxygen would be a reactant.
theres no oxygen inside a running still...

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Re: Ethyl Carbamate and copper reaction

Post by schnell » Sun Apr 26, 2009 7:57 am

Maybe not as much as ambient air, but there is some there. In laboratories you can use an inert gas manifold and special apparatus to get rid of any oxygen (and/or moisture) in the system for sensitive distillations. For booze I've never seen or heard of any such practices.

Some oxygen also comes out of solution from simply being dissolved in the mash as well. Another source of oxygen as a reactant is from the organic materials in the wash.

I'm not saying a still is some wonderful oxidizing apparatus with heaping hordes of oxygen compared to other components in the system. I am saying there's some there and it does have have a measurable effect on the chemistry of the system. Oxidation of sulphides is one such reaction.

This is one of the biggest subtle difference between spirit runs and beer runs. In a spirit run we are practicing a straight up application of seperation science. In a beer run there's still some really fancy chemistry happening.

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Re: Ethyl Carbamate and copper reaction

Post by cemik1 » Wed Apr 29, 2009 11:43 pm

There are some pictures of my column after ~300l triple rectification (sugar,tomatoe concentrate, dates, raisines mash). This took me about 3 weeks, without cleaning between processes.
Image Image Image
It now can not be removed by simple water flush. Should I treat it by an acid (eg. citron + H2O2) and clean the surface to raw copper? I am affraid about mesh, because several such a cleaning could destroy it.

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Re: Ethyl Carbamate and copper reaction

Post by HookLine » Thu Apr 30, 2009 12:11 am

Welcome cemik1

A simple soak in plain white vinegar or citric acid solution, maybe also with a bit of brushing, should clean all that off pretty easy.

As long as you do not leave the mesh in the solution all the time, it should not decay.
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Re: Ethyl Carbamate and copper reaction

Post by eternalfrost » Thu Apr 30, 2009 1:18 pm

i just finished soldering up a new column. to clean it out some before the final vinegar distillation cleaning i sealed the bottom and filled it with some diluted vinegar, lemon juice, and table salt let it sit a few days and its nice and shiny. you can see a sharp line where the water level was just under the lip seperating black solder/flux/oxidation crud and bright copper.

not sure why it works but a weak acid and salt solution cleans copper right up just by sitting in it

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Re: Ethyl Carbamate and copper reaction

Post by eternalfrost » Thu Apr 30, 2009 4:27 pm

after thinking some more, i still stand by my statement that there is zero to negligible oxygen inside a running still.

there will be no dissolved oxygen in the wash as the yeast will have eaten it all up (dissolved co2 theres loads of) and in a spirit run it will all have been driven out of the low wines from boiling.

now as for the breakdown of other things in the wash releasing o2, im not an expert in chemistry but know the basics. and organic things, what youll find in a wash, tend to like to attach to free oxygen i.e. burn. things that tend to release oxygen in reactions are inorganic things like rocket-fuel oxidesers and such like potassium cholorates

so yeah, im 99% sure that there shouldnt be any 'natural' o2 in there and maby 50% sure there shouldnt be any "created" inside it chemically.

...clarification from the chemists?

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Re: Ethyl Carbamate and copper reaction

Post by muckanic » Thu Apr 30, 2009 6:43 pm

schnell wrote:I believe that the conversion of sulphides (volatile) to sulphates (not volatile) by way of an oxidation is the reaction we're primarily interested in. Atmospheric oxygen would be a reactant. This removes the rotten egg smell/flavor.

Copper should be catalytic, not consumed. However we know the stills wear out, degrade, and ablate (ie lose copper). This may be losses due primarily due to the acidity of several of the components present, including organic acids formed from ester hydrolysis. Some reactions are catalytic while some involve copper as a reactant. (Note: I would reasonably assume a typical spirit run would contain hundreds of discreetly identifiable components.) So really there's alot more chemistry going on than just one or two reactions.
If sulphate is a product, then it is likely copper is the cation (assuming the product is neither sulphuric acid nor organic). For no net copper loss, that would require that the copper carbonate patina exchanges for copper sulphate (whether Cu+ or ++). That in turn would require that the carbonate either partners with some organic species or, more likely, heads off to the heavens as CO2 under the influence of acidity.

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Re: Ethyl Carbamate and copper reaction

Post by muckanic » Thu Apr 30, 2009 6:54 pm

eternalfrost wrote:so yeah, im 99% sure that there shouldnt be any 'natural' o2 in there and maby 50% sure there shouldnt be any "created" inside it chemically.
See Daltons Law of partial pressures. A still should be open to the atmosphere, otherwise it is a pressure cooker. If there is a higher concentration of O2 in the air than inside, then there should be a flow down the gradient. The fact that the still may be full of alcohol vapour doesn't mean that there is no room for the air. Having said that, lots of folks observe cold gaseous "stuff" getting pushed out of the still as it warms up, probably water vapour.

Similar discussions have cropped up before in the context of open fermentation, whereby some folks think the CO2 evolution stops O2 flowing in. The evolution probably does however stop dust particles dropping in.

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Re: Ethyl Carbamate and copper reaction

Post by eternalfrost » Thu Apr 30, 2009 7:17 pm

muckanic wrote:
See Daltons Law of partial pressures. A still should be open to the atmosphere, otherwise it is a pressure cooker. If there is a higher concentration of O2 in the air than inside, then there should be a flow down the gradient. The fact that the still may be full of alcohol vapour doesn't mean that there is no room for the air. Having said that, lots of folks observe cold gaseous "stuff" getting pushed out of the still as it warms up, probably water vapour.

Similar discussions have cropped up before in the context of open fermentation, whereby some folks think the CO2 evolution stops O2 flowing in. The evolution probably does however stop dust particles dropping in.

i agree that there would be o2 diffusing into the still as soon as you shut it off but while its running you have a pretty serious vapor flow rates on the order of inches or feet per second pushing everything out. same effect as a flow hood in clean rooms.

imagine having a nitrogen tank or similar hooked up to a pipe with a similar flow rate. the pipe will be totally purged. even if you really want to argue we are only talking the first few inches are the only place with even a remote chance.

there for sure is o2 present condensers because they are open to air with no appreciable vapor flow at the end, but thats a moot point because any copper interaction there wont serve to scrub out impurities as the liquid will fall into the product output rather then back into the condenser


now in a fermenter its a whole other story. there is much less volume of gs being produced per unit time and a much much much greater cross-sectional area it is traveling trough. for a fully open fermenter your talking say 24 inches across and a still is say 2 inches across giving a difference of a whopping 572 times more area for the fermenter! so the flow rate is essentially zero on the fermenter and quite fast in the still.

forget to turn your condenser on and the vapor shoots out a good three feet. put your hand over an open fermenter, do you feel any wind coming off it? no...

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Re: Ethyl Carbamate and copper reaction

Post by muckanic » Thu Apr 30, 2009 11:17 pm

eternalfrost wrote:i agree that there would be o2 diffusing into the still as soon as you shut it off but while its running you have a pretty serious vapor flow rates on the order of inches or feet per second pushing everything out. same effect as a flow hood in clean rooms.
My understanding of flow-hoods is that they provide positive pressure in order to stop dust particles getting in. That doesn't necessarily stop gas exchange. Gasses can be conceived of as invisible particles, but they behave slightly differently when it comes to diffusion.
there for sure is o2 present condensers because they are open to air with no appreciable vapor flow at the end, but thats a moot point because any copper interaction there wont serve to scrub out impurities as the liquid will fall into the product output rather then back into the condenser
Possibly so with a pot still, but there is an interesting question of what happens with a reflux still. If anything, the collapse of vapour in the condenser would tend to create suction through the column cap.

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Re: Ethyl Carbamate and copper reaction

Post by HookLine » Fri May 01, 2009 12:31 am

muckanic wrote:
eternalfrost wrote:
there for sure is o2 present condensers because they are open to air with no appreciable vapor flow at the end, but thats a moot point because any copper interaction there wont serve to scrub out impurities as the liquid will fall into the product output rather then back into the condenser
Possibly so with a pot still, but there is an interesting question of what happens with a reflux still. If anything, the collapse of vapour in the condenser would tend to create suction through the column cap.
I thought it would be more or less in balance. Where would the extra volume of gas sucked in through the cap go? The gas pressure underneath the condenser, coming up the column, would be much greater than the atmospheric pressure.
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Re: Ethyl Carbamate and copper reaction

Post by eternalfrost » Fri May 01, 2009 6:10 am

muckanic wrote:My understanding of flow-hoods is that they provide positive pressure in order to stop dust particles getting in. That doesn't necessarily stop gas exchange. Gasses can be conceived of as invisible particles, but they behave slightly differently when it comes to diffusion.
yes flow hoods are designed to keep out particulate matter like dust, spores etc. but it was just as an analogy.

heres a quote from wikipedia on diffusion: "Another, simpler experiment to show diffusion is to drip a drop or two of food colouring into a glass of water. At first the food colouring will be very dark and concentrated at the spot where it hit the water, but after a while it will drift apart and fill the whole glass with a lighter shade of its colour. This is the dye diffusing in the water."

this is a better example as it uses molecular scales. now imagine doing this experiment in a glass tube filled with water and connected to a faucet on the bottom end (like a reflux column). drop some dye in the top when there is no flow and yes eventually the entire column becomes evenly colored. but if there is even the slightest flow through the column(especially columns with small enough diameters to not get appreciable mixing) the dye will simply stay at the top and get pushed out and the majority if not all will remain clear.

and yes again condenser of any kind will have normal air in them. but anywhere else there is vapor and copper in contact will be purged of o2 by this effect.

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Re: Ethyl Carbamate and copper reaction

Post by schnell » Mon May 04, 2009 12:55 pm

Heck. I could be wrong.

back to the thread topic => ethyl carbamate and copper reaction

carbamates are formed by addition of alcohols to isocyanates
example: isocyanic acid and ethanol react to form ethyl carbamate

isocyanates can be hydrolysed by acid or base catalysis
example: isocyanic acid reacts with water in presence of catalyst to form ammonia and carbonic acid

i think this second reaction is the focus of the ability to remove ethyl carbamate using a copper catalyst. It removes the principle reactant from the distillate.

You can certainly check my chemistry. see Jerry March, Advanced Organic Chemistry, 4th ed, 1992, p886 and p891.

Take a look at holstein's site: http://www.a-holstein.de/index.php?id=183" onclick="window.open(this.href);return false;" rel="nofollow

Or take a look at their european patent ( EP19910108405): http://www.freepatentsonline.com/EP0459310.html" onclick="window.open(this.href);return false;" rel="nofollow

They talk about fruit distilling, because it's the stone fruit that specifically present this problem, due to the natural content of cyano compounds.

Sorry if my previous comments detoured the thread.

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Re: Ethyl Carbamate and copper reaction

Post by muckanic » Mon May 04, 2009 5:06 pm

schnell wrote:i think this second reaction is the focus of the ability to remove ethyl carbamate using a copper catalyst. It removes the principle reactant from the distillate.
One of the posts at the adiforums (the original link which kicked this whole discussion off), inspired by the UK food standards, suggests not. Note that the carbamate isn't especially volatile; nor for that matter are cyanates or urea. The column length could be just as significant as the column construction.
Charles@AEppelTreow wrote:On the wine side of things, ethyl carbamate tends to form from left over urea - which usually comes from the metabolism of certain amino acids. Copper doesn't seem to play much of a role in that pathway.

But for distillers, copper catalysizes reactions with cyanates to make ethyl carbamate. An important consideration for stone fruit distillates.

I think it's interesting that the cure is to apply more of the 'problem'. More copper, drive the reaction to completion and the carbamate stays in the pot, rather than forming from precursors later on.

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Re: Ethyl Carbamate and copper reaction

Post by fredniger » Mon May 04, 2009 10:22 pm

ethyl carbomate(beer stone) will form if you have a lot of grain over many years. Most here running sugar wash are in no danger of forming anything other than co2 and then etoh in the open area above the wash. If you have o2 coming back in you are not running hard enough sucka. deal with it.

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Re: Ethyl Carbamate and copper reaction

Post by Rude Boy » Tue May 05, 2009 2:32 am

cemik1 wrote: It now can not be removed by simple water flush. Should I treat it by an acid (eg. citron + H2O2) and clean the surface to raw copper? I am affraid about mesh, because several such a cleaning could destroy it.
I note that some guys on this site clean their copper with salt dissolved in vinegar. After trying this for myself I noticed it strips the oxide off copper much much more than vinegar alone.
I've started flushing my column with a little salt'n'vinegar then thoroughly flushing with water between most runs. The smell of fusels when the solution reaches the bottom of the column is really strong too.
NZ stillers be sure to use un-iodised salt in case any residual salt in the column can lead to chemical reactions which you want to avoid.
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Re: Ethyl Carbamate and copper reaction

Post by eternalfrost » Tue May 05, 2009 6:52 am

Rude Boy wrote:
cemik1 wrote: It now can not be removed by simple water flush. Should I treat it by an acid (eg. citron + H2O2) and clean the surface to raw copper? I am affraid about mesh, because several such a cleaning could destroy it.
I note that some guys on this site clean their copper with salt dissolved in vinegar. After trying this for myself I noticed it strips the oxide off copper much much more than vinegar alone.
I've started flushing my column with a little salt'n'vinegar then thoroughly flushing with water between most runs. The smell of fusels when the solution reaches the bottom of the column is really strong too.
NZ stillers be sure to use un-iodised salt in case any residual salt in the column can lead to chemical reactions which you want to avoid.
you dont want to fully bleach the copper like this after every run. the golden color is called a patina and is beneficial. having shiny copper will give off metallic tastes. after each run just pour some of the hot backset left in the still through the copper then rinse with water. it is hot and acidic and will do the job without stripping the patina.

take a look at classic copper scotch whisky alembics. thats the sort of color you want.

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