Jump to content
ADI Forums
Spitfire

Finding the right alcohol-proof rubber

Recommended Posts

Spitfire    1

Hello,

When working with GNS, we found that some "rubber" material used for seals are not alcohol-proof even though the manufacturer say they are "fit" for alcohol use.  There is chemically-speaking a huge difference between a 10% abv mash and 95% GNS.  Based on our experience, material like nitrile, viton and teflon tape are not suitable when used with 95% alcohol for a prolonged period of time.  We did a simple test by putting a small seal in a jar with a 50 ml of 95% alcohol for a week, then rectified the alcohol to 40% by using RO water.  Attached is the result for nitrile, viton and teflon tape.  Nitrile creates the most opaque solution.

What rubber material should we go for to prevent this?  We are about to do the same test with a silicon seal.

Chris

 

 

IMG_6853.jpg

  • reaction_title_1 1

Share this post


Link to post
Share on other sites

What manufacturer said that nitrile and viton are good for ethanol?  No testing is needed. All that you have to do is look at a chemical resistance chart. http://www.mossrubber.com/pdfs/Chem_Res.pdf  Sanitary EPDM tri clamp gaskets are rated excellent with ethanol, so they are impervious to ethanol. Here are some other materials that are rated excellent with ethanol:  Neoprene, Kalrez, Butyl, Hypolon, Viton Extreme, flourosilicone.  Here is another chart:  http://www.mossrubber.com/pdfs/Chem_Res.pdf

Share this post


Link to post
Share on other sites
Spitfire    1

SouthernHighlander,

Thank you for the reference, the chart says that nitrile, viton and teflon are rated "conditional" for grain alcohol ethanol which leads me to conclude that they don't work with pure alcohol.  I will look for seals made from other material rated "excellent".

Chris

Share this post


Link to post
Share on other sites
Skaalvenn    24

One thing I've noted is that it seems no two websites give the same data for all the materials and I'm not sure why.  Are they rating it at room temperature 95% ethanol?  High temperature? High temperature for very long periods of time?

One website will say Viton is excellent, the next will say moderate.  Same goes for silicone and the other common gasket materials.

Share this post


Link to post
Share on other sites
Skaalvenn    24
1 hour ago, Southernhighlander said:

Skaalven,

I haven't seen any charts that disagree with each other.  Please give some examples.

 

A.  https://www.coleparmer.com/Chemical-Resistance

B.  http://www.mossrubber.com/pdfs/Chem_Res.pdf

C.  http://mykin.com/rubber-chemical-resistance-chart-3

D. https://www.calpaclab.com/viton-chemical-compatibility-chart/

For Viton, A. D and C are conflicting between "Excellent" and "doubtful"
For Teflon/PTFE, A and B are conflicting between "Excellent" and "Conditional".

I noticed this long ago when I was researching materials. There's a lot more examples out there, I just don't have the time to find more.

Share this post


Link to post
Share on other sites
RobertS    10

I encountered this with tygon, and in its case the difference was caused by there being multiple formulations. Several sites only listed it as 'tygon' without formulas, and then disagreed on resistances. Pure PTFE is certainly excellent for alcohol - a PTFE rubber is claiming otherwise may have unspecified additives that are not.

Share this post


Link to post
Share on other sites
Spitfire    1

My take on this is that everything has to be tested first, never trust blindly what the manufacturer says.  Thanks to everyone.

Share this post


Link to post
Share on other sites
PeteB    45

So what happened to the pieces of "rubber" you put in the alcohol?

Were they dissolved, fell to pieces, or as I suspect, still look the same.

If they still look the same then the high proof alcohol has probably dissolved some oily substance off the surface. That "oil" or whatever causes the louching = cloudiness.

To progress this experiment further I suggest you put the same pieces of rubber in another test tube of clean alcohol and see if the same cloudiness forms.

If there is no cloudiness and if the rubber is still structurally sound then your experiment demonstrates that it would be a good idea to thoroughly wash gaskets in high proof alcohol before they are installed.

  • reaction_title_1 1

Share this post


Link to post
Share on other sites
Spitfire    1

PeteB,

The gasket looked exactly the same after a week marinating in alcohol, no change of colour or appearance.  Your suggestion is an excellent one, I haven't thought of that.  I will re-do the experiment after washing thoroughly each gasket and let everyone knows the outcome.  

Chris

Share this post


Link to post
Share on other sites

Consider the total surface area exposed by a typical sanitary gasket as well, you are talking about a minuscule amount of liquid exposed to gasketing surfaces. Considering thread seal on a threaded fitting, likely even less.

Teflon or other very high molecular weight thermoplastics are typically rated excellent.  I prefer Teflon personally.  Teflon tape in a test tube is not a reasonable proxy for a good quality seal.  There are better rated plastics (PFA for example), but they are very expensive and esoteric, and tend to use specialized fittings (this is more common in biopharm).  Question your source, unfortunately I would be very skeptical of cheap gaskets claiming to be something.

You mentioned silicone - the only reasonably acceptable silicones will be platinum cured, I would be very doubtful of any platinum cured silicone that isn't coming from a very reputable manufacturing source.

This all applies to valve seats as well, especially butterfly valves with significant surface areas, and the seals/valves in pumps, tubing inside bottling machines, the support housings for filter cartridges.

Share this post


Link to post
Share on other sites
Skaalvenn    24

This reminds me, I put a couple gaskets (viton I think?) in a jar of pure heads a year or more ago. It's still sitting in the back of my storage cabinet.  I'll post the results.

Also, there's a lot more to the science of what happens to X material when it's in contact with X chemical.  Is the chemical capable of permeating and softening the gasket?  Does that chemical dissolve or leach chemicals out of the gasket?

A very simple example: A latex balloon is not an acceptable storage device for helium because helium molecules will pass through the latex wall of the balloon. The latex does not contaminate the helium.  Now, would latex receive an "Excellent" score because it doesn't contaminate the helium? Or would it receive a "poor" score because it's not a good container for storing helium?


@Silk City.  I'd be cautious with the "it's a small surface area" argument. While 100% true, we as craft distillers should be trying to make the best, and safest product we possibly can.  You are exactly right about platinum cured and reputable sellers, it's like trusting your eyes to a pair of $1 sunglasses that say "100% UV blocking".  Platinum cured costs an arm and a leg, but it's worth using.

 

Share this post


Link to post
Share on other sites
Spitfire    1

A quick update on this topic, I finished another test this time with a silicon gasket and got same result although less cloudy than the other tests (see photo)  

I started another round of tests by washing all previously tested gaskets (nitrile, viton) and adding some fresh GNS in a small jar for a week, we'll see how it goes.  Also, a new test this time with a neoprene gasket.

 

IMG_6895.jpg

Share this post


Link to post
Share on other sites
Natrat    3

In many cases, it is the "plasticizer," and not the sealing compound, that is leaching into your NGS. Unless you are using a platinum-cured silicone, I suspect you will see clouding again. 

As mentioned before, gaskets with a higher durometer, such as PTFE (Teflon) or HDPE are the best for high proof ethanol storage. They don't have added plasticizers to make the material softer or less brittle. Best of all is to use a one-use copper crush gasket, preferably without added graphite. 

The question is, other than a bottle of calibration fluid, why are you storing high proof ethanol for long periods of time?

 

Dan

Share this post


Link to post
Share on other sites
Spitfire    1

The goal is to design a cam lock adapter to extract small amount of alcohol, as our tote tank is on a shelf and the top opening is not easily accessible. The adapter has a second valve at the end, controlling flow to a 1/4 vinyl tubing.  So when we need for instance to extract 1 liter of GNS for R&D, we open the tote tank valve, then the adapter valve, and there is a small flow of alcohol that we can put inside a beaker.  

What is happening is that a small amount of alcohol is alway trapped inside the adapter between the tote tank valve and the adapter valve, and after a week or this alcohol reacts with the gaskets/seals inside this adapter.  

Share this post


Link to post
Share on other sites

Alcohol in a tote?  You are going to have at least 3, if not maybe 4 plastics involved.

HDPE - Tote Bottle

Polypropylene - Valves, Cap

Viton/PTFE/EPDM - for the cap gasket and in the valve seals

 

Share this post


Link to post
Share on other sites
On 5/31/2017 at 10:50 AM, Skaalvenn said:

@Silk City.  I'd be cautious with the "it's a small surface area" argument. While 100% true, we as craft distillers should be trying to make the best, and safest product we possibly can.  You are exactly right about platinum cured and reputable sellers, it's like trusting your eyes to a pair of $1 sunglasses that say "100% UV blocking".  Platinum cured costs an arm and a leg, but it's worth using.

 

Just to be clear, in my opinion, PTFE/Teflon is superior to platinum cured silicone. If the goal is cost-no-object dedication to purity, fluoropolymers like PTFE, FEP, and PFA are the plastics of choice.

You see this when looking at the pumps used in high purity operations, for example, something like the Yamada High Purity pumps (DP-20F) - which has all wetted surfaces, gaskets, and check valve balls manufactured out of PTFE.   Same for the others like St. Gobain, White Knight, etc etc, very common in the biomedical, pharma, semiconductor, etc. etc.  Generally in these kinds of ultra high purity processes, even metals like stainless begin to be questioned.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×