Pro buchner vacuum filtration tips?

[artificer]

The A/B extraction via Vovin's Tek has given me excellent final results so far, and I will experiment with other methods in the future, but before I do, I want to work on better technique for filtration. This really applies to much more than just A/B forum, and if I should put this somewhere else please advise...

The general issue is boiling, bubbles, vapor when using buchner funnel. I acquired buchner glassware that is good for 15psi vacuum, which is adequate for absolute vacuum (1 atmosphere pressure at sea level=14.7psi) and I have a 20 micron HVAC vacuum that get close to this so all good there, but here's the problem:

Warm/hot acidic water with MHRB placed into buchner funnel isn't far from boiling temp at 1 atm. When the liquid gets pulled through the filter and is under vacuum, of course it starts boiling and soapy bubbles quickly work their way up to the vacuum line :x

SO.... to the experienced hand, I am asking for some pointers. Details of my situation:

-I have a trap between buchner and vacuum, but it doesn't take much for liquid and bubbles to form in trap and work their way toward vacuum anyway.

-I don't mind investing time/money in more elaborate setup to create more enjoyable-to-use tool for the job. It could be used for many many things in the future.

-Welding and machining components are non-issue for me

-Right now all my buchner gear involves porous funnel in conjunction with qualitative papers. Generally I like this setup as it thoroughly pulls the liquid out of MHRB each time.

-After the 45-60 minutes of heat soak with MHRB, would there be any downside (besides time) to cooling the liquid to room temp or even lower, and then doing the vacuum filtration? This would mean having to heat it back up and cool down for each pull, but I have the means to do it fairly quickly

-Is there anything that can be added to mix that reduces large bubbles?

-Is there a common moisture trap (desiccant?) designed for this sort of process under vacuum etc?

 

[downwardsfromzero]

There are several options. You might want to try adding a second trap on the vacuum line, and include a reasonable length of vertical tube between the two traps. Having the traps immersed in some sort of cryogenic bath stops the liquids getting through to the pump as well.

Or simply strain the MHRB tea with a sieve before letting it cool down. Some tannins may precipitate which will of course make filtration difficult. These will settle out in the fridge overnight and are worth keeping as they may trap some actives. Of course, this entirely defeats the point of having a suction filtration set up in terms of quickness.

The bark could be sewn into a giant tea bag made from a pillowcase or a tea towel. Adhering liquid could then be recovered using some sort of press - and this gives rise to the question as to whether a Buchner funnel is really the right tool for the job.

One more possibility is the use of silicone anti-foaming agent. You'd have to decide whether you want traces of silicone in your DMT before adding it to the bark soup, but a thin coating of silicone oil in the above-mentioned vertical tube might help to disperse any foam that made its way that far.

 

[artificer]

That's all good info.

You're right that Buchner funnel might not be right tool for the job, but I'm drawn to it, partly because it's got a "cool" factor to me, but also because it seems like I'd make more of a mess with other methods.

Side note: my least favorite part of Harmala extract from syrian rue is also in the filtration step.

I'm not sure when I'll have time to do another extraction, but out of curiosity I'm going to try A/B as follows:

-powdered bark and acidic water stirred for 60 minutes (borosilicate flask with magnetic stir bar submerged in heated oil kept at 80°C)

-place flask in cold water bath with ice until 15°C

-filter this with buchner

-repeat with fresh acidic water

Perhaps I'll be disappointed in results but I feel like I won't be satisfied until I try it. Fingers crossed that borosilicate is up for the temperature swings....

 

[downwardsfromzero]

MHRB tannins that precipitate on cooling make a dense plug that is extremely difficult to filter, hence the suggestion to settle and decant. Some good things simply take time, [swiss_tony_voice]like a fine wine or an artisan cheese, or making love to a beautiful woman[/swiss_tony_voice]

 

[artificer]

[swiss_tony_voice]like a fine wine or an artisan cheese, or making love to a beautiful woman[/swiss_tony_voice]

hah! so true. :d

On my my last batch, after initial Buchner filtration, I reduced 1400mL of acid/bark solution down to 800mL and then placed in fridge to decant, BUT after siphoning clear liquid on top, I also ran the remaining cloudy liquid and all solids from decant through Buchner filter again, to extract every bit of spice that I could. I felt this secondary Buchner filtration step went more smoothly here.

Did this make a difference in the end? I can't really say since I used different bark powder specimen than previous extract, but this yield was >1.3% vs. <1% on my last batch.

In the name of R&D for myself and this community, I'll skip the hot Buchner filtration next time and on each of the three acid pulls, I'll do a rapid cooling, decant what I can after an hour or two, Buchner filter the cold solution, and repeat. If it clogs up too badly here, I guess I've learned my lesson the hard way and DFZ you can tell me "I told you so" lol. Collection of these pulls will still go in fridge overnight and will likely get another decant/Buchner filtration step.

Not sure when I'll get to this, but I'll report back.

 

[Hailstorm]

Some vacuum pumps will let you regulate vacuum pressure so you can avoid boiling the water. You do not really need maximum vacuum for simple filtration.

A pump with a PTFE diaphragm, like the Chemker series, is especially suited for filtration - there is no oil to contaminate, so the water can boil all it wants.

 

[downwardsfromzero]

Some vacuum pumps will let you regulate vacuum pressure so you can avoid boiling the water. You do not really need maximum vacuum for simple filtration.

Good point. A simple bleed valve of some kind between the pump and the filter will allow this. And excessively hard vacuum can exacerbate clogging when filtering, of course. I'll refer back to the point that MHRB tannins precipitate readily on cooling. They instantly clogged an aeropress filter, for example.

A pump with a PTFE diaphragm, like the Chemker series, is especially suited for filtration - there is no oil to contaminate, so the water can boil all it wants.

That does sound like a case of having the right tool for the job.

 

[artificer]

Hailstorm, good to know about those Chemker series pumps.

I have had tannin precipitate build up on qualitative filters and certainly slow things down, but never come to a complete halt. I'm always able to keep pumping and extracting liquid til the solids get dry and cracks form in the "mud" from drying it out.

These operations may be classified as "simple filtration", but in my limited experience, 700+mm Hg of vacuum will continue to extract liquid from a cake of MHRB solids (albeit slowly) whereas it might seem fully clogged if only using half that vacuum.

 

[IridiumAndLace]

Looks like my first thoughts have already been covered in this thread: settle and decant prior to filtration, and use only as much vacuum as you need to keep the liquid moving.

Out of curiosity, are you using a perforated Büchner funnel, or are you using a fritted funnel? My first extraction taught me a cold hatred for fritted funnels, and my second extraction prompted me to throw the fritted funnel in the recycling and order a real 500ml glass Büchner funnel instead. Now I filter through a good filter paper and a Celite pad, and together they are a darn pleasure to use.

Granted, I'm using a hand vacuum pump, but foaming was one of several serious problems I had with that stupid fritted funnel. Even with a better hand pump than I was using before, I hardly get any foaming now.

 

[Dirty T]

The solution that worked for me is this. I drilled a hole in the polycarbonate lid of a vacuum chamber and epoxied an automotive vacuum T in place. The input to this T leads to your source chamber, the output (bottom side) leads to a tube in a jar with a lid and a hole drilled through it with a small amount of water in it. The end is submerged in liquid. The default vacuum lead goes to the pump. This chamber is placed in an ice bath. As the vapors are pulled through the water will then immediately condense and collect, bubbles form in the jar hence the need for the lid and the ice bath prevents further boiling of the water once it reaches the trap chamber. My trap chamber cost me 40 bucks including the stepped drill bits, epoxy, vacuum T and tubing.

I use a harbor freight vacuum pump and gauge set, Locktite epoxy, Bacoeng vacuum chambers and Ace Hardware tubing. This setup is good to 20 microns (2 atmospheres of vacuum). I have run the pump up to 12 hours straight without issue.

 

[artificer]

Out of curiosity, are you using a perforated Büchner funnel, or are you using a fritted funnel?

I'm only using perforated funnels with paper filters. I didn't see the fritted filter mentioned in any teks and it looked like a nightmare to clean those things so I haven't even tried one yet.

There's a couple different styles for the Büchner setup though, one is with thick-walled erlenmeyer like glass flask with the vacuum hookup and a perforated porcelain funnel seated on top of this flask with size approriete rubber stopper to seal it - this is what I've used so far. However..

The other style looks better - I recently acquired one but haven't tried it yet - it is all glass, no rubber or porcelain, and the vacuum hookup is a part of the funnel itself (see picture). My gut says this will do better to prevent foam/liquid from getting to the vacuum line compared to porcelain funnel setup.

Now I filter through a good filter paper and a Celite pad, and together they are a darn pleasure to use. .....I hardly get any foaming now.

This is interesting. I'm only using paper filters (20 microns of vacuum will easily punch holes through a single paper filter disc at the perforation hole sites, but I found that two filters holds up to the vacuum fine). I may have to try making Celite pad....

DirtyT, I like the ingenuity with the cold water vacuum trap setup, makes sense. Heck of a lot cheaper than one of those Chemker pumps.

This setup is good to 20 microns (2 atmospheres of vacuum)

In the spirit of education, gotta clarify the vacuum units of measurement:

at standard temp (0°C) at sea level, the atmospheric pressure is 1 atm (atmosphere)

1 atm = 760mmHg = 760,000 microns

perfect vacuum would be 0 atm, 0 mmHg, 0 microns

20 microns ≈ 0.000026 atm

 

[IridiumAndLace]

I'm only using perforated funnels with paper filters. I didn't see the fritted filter mentioned in any teks and it looked like a nightmare to clean those things so I haven't even tried one yet.

Speaking from experience, misery is having to pull concentrated sulfuric acid through your fritted funnel in an attempt to clear sludge from the frit. Total waste of time and money, don't bother.

This is interesting. I'm only using paper filters (20 microns of vacuum will easily punch holes through a single paper filter disc at the perforation hole sites, but I found that two filters holds up to the vacuum fine). I may have to try making Celite pad....

It's worth pointing out, that's an absurdly high vacuum to be using for filtration. In fact, it could be working against you; the vacuum is boiling the tea before it even gets all the way through the filter paper. That causes salts, tannins, and other gunk to precipitate in the filter itself, clogging it further. Even in a laboratory setting you'd either filter stepwise or switch to centrifuging long before you try to filter using that much vacuum.

For what it's worth, my hand pump pulls 500mm of vacuum and draws the tea through just fine. Comes through the color (and clarity) of Cherry Coke with no boiling, even at 60°C.

If you don't have one already, I'd suggest installing a valve between your flask and your vacuum pump to allow some air into the system and keep the vacuum below the vapor pressure of the tea you're working with. Then switch to a more efficient filter substrate (1x filter paper and 5-10mm of celite), let the tea settle before filtering, and just take your time.

 

[artificer]

I apologize for bumping a rather old thread, but I'm back after taking a break doing life things, and I wanted to say thanks to IridiumAndLace for the good information noted, I would be lost without a little external perspective.

I look forward to trying this, although I've got some time before exhausting extant extractions, extra excessive words that start with ex not withstanding.