So here's a look at the main plumbing at the bottom.

Notice that i added a traditional appleseed methoxide port with a check valve. That should make things easier and since i already have the plumbing parts, why not?

Also notice the vertical tube parallel to the main circulation tube. This 1/2" clear vinyl tubing so that i can squeeze it to see a color change after adding HCL. this could just as easily be routed to the suction side where the methoxide comes in. If you did this, it would still work and would use less clear tubing.

Notice also that i added a relief valve at the top... i just felt that it was a good safety measure since i have added enough shutoffs to build pressure if they are not in the right configuration. Safety first.

I also combined the glycerine drain and the site tube to kill two birds with one stone and not weld so much.

More pics:

Hello all. This thread made me go looking for a pressure vessel to give this a try. I found a 490ish liter/130 gallon domed on both ends air compressor tank. I am starting to tear into the tank now. What is the optimal headspace for the push pull> Same as GL1 day 70%? I am guessing I can go 75% as no pre-wash is needed. Woo hoo close to 100 gallon batches. I can fill up the truck, sawmill and loader off one batch.

quote:

My Muriatic Acid is storing just fine in the plastic gallon jug that it came in...

Well, my main point is not about storage (even when having a more forgiving option would be nice), but about transferring it to the reactor. The idea of a capillary method and a needle valve would be perfect, but there's no materials you can use for them. Plastics (that'd be a great option for HCL) can't be used because of the temperature, and metals cant be used because of the HCL, so unless you use hastelloy (and I don't even want to think about its price), your only other option is glass!

quote:

I'm sure you're right - other acids could be used. You'd want something which creates friendly by-products,

Well, I'm not a chemist, so if I'm right is pure coincidence...
I'm just asking questions because precisely I'd like to find an option that wouldn't, as you said, contaminate the biodiesel or the glycerol, and at the same time wouldn't wreck the equipment.
That's why I asked about using nitric acid, because even in concentrated form, it's still fully compatible with 304 and 316 SS, and bronze, and the way I saw it (remember I'm not a chemist), the only byproduct would be nitrogen.

As far as injecting the HCL is concerned, I have been thinking about putting a tee into the suction side of the main circulation loop with a shutoff on the tee end. Then cramming into the open end one of those chem supply rubber stoppers with the hole in it to allow things like thermometers and glass piping to be inserted and maintain an air tight seal. That should allow me to use a 500ml syringe such as those used for cattle antibiotics. Using one of those should allow for dosing small amounts at a time, but at the same time allow for the volume of HCL that i'll need.

Maybe they make those rubber stoppers in viton so that it won't get eaten!

Hmmm, that may be an option, but how are you going to deal with the vacuum when demething?
Are you planning to build some kind of bypass for the tee with the stopper?

Hi bernyjb

Another risk with nitric acid is that it can act as a strong oxidiser, so can be a combustion risk, especially with organic compounds such as oils and glycerol.

Plus, oxidising the oil / biodiesel could reduce its stability.

Too bad. Well, I guess I'm gonna have to find a hastelloy supplier, after all.
Thank you Graham.

PTFE capillary tubing may be another possibility.

http://www.zeusinc.com/ptfe_tubing.asp

quote:

Originally posted by bernyjb:
Hmmm, that may be an option, but how are you going to deal with the vacuum when demething?
Are you planning to build some kind of bypass for the tee with the stopper?

I mentioned having a shutoff after the tee end. I would just shut it off after injecting the HCL.

quote:

Originally posted by Graham Laming:
PTFE capillary tubing may be another possibility.

I'm currently checking out the site that Graham linked as that has always seemed like a better idea, but i've never dealt with those kind of materials/suppliers. Do you know how that material can be connected to standard pipe thread? Do they even make such an adaptive fitting?

quote:

Originally posted by GrahamLaming:
Hi bernyjb

Another risk with nitric acid is that it can act as a strong oxidiser, so can be a combustion risk, especially with organic compounds such as oils and glycerol.

Plus, oxidising the oil / biodiesel could reduce its stability.

Hmm well just taking a stab at this I know that they use citric acid to help perserve the vegetable oil of you could find a high enough purity if the stuff would that work?

This message has been edited. Last edited by: paulb3,

What about acetic acid?

quote:

PTFE capillary tubing may be another possibility.

It's not the capillary tubing that worries me (well, maybe a little): it's the needle valve. The capillary tubing can ultimately be made of glass, viton, hdpe, etc.

quote:

I mentioned having a shutoff after the tee end.

Sorry. I should've read your post more carefully.

Graham,

I'd really like to know more about capillary tubing and it's fittings. I've not yet been able to see how flexible capillary tubing can be connected to reactor plumbing, and as i don't know that much about lab supplies, i could use a little help.

I've been able to find some tubing on ebay, but without a way to plumb it into my reactor, i'm stuck.

I suppose they don't make a barb that small, do they?

On a slightly tangental subject;

Has anyone who is operating with the venturi vacuum design experienced a problem with the vacuum over powering the circulation pump?

We draw the vacuum on the condensed methanol receiving tank and as we approach 8-10 inches of vacuum the recirc pump on the demethylation tank locks up or fails to be capable of moving the tanks volume sufficiently...

Rick da tech, did a quick calculation and it seems that with 4-5 feet of head on the B100 Supply pump, a vacuum will quickly overcome its ability to move fluid.

GCG

Hi GCG

This sounds like cavitation in the recirc pump.

Are you using an external heater tube or a heater in the tank itself?

The heater tube should be immediately after the pump, in its outlet flow, because you want the boiling to occur in the pump's outlet stream only, not in its inlet.

You can reduce the effect by ensuring that all valves to the pump's inlet are wide open, and then add some restriction in the pump's outlet (partially close an output valve).

This should restore the pump's operation, but you may have to switch the pump off then on again, to allow it to reprime.

After stalling by cavitation, it may struggle to re-prime if the impeller is still moving.

This effect can also be reduced or eliminated by controlling the rate of heat input - if you use a PID controller with a % Power limit adjustment (most have), try reducing the % power limit and you will reach a point where this stalling never happens. Or, reduce the rate of the vacuum pump.

Effectively, there is mass boiling taking place in your system, and you want to limit the boiling zone. Boiling should only occur after the pump and within the tank. The slightly cooled, partly de-meth'd fluid returning to the pump inlet should have less ability to boil.

Hope that helps.

The pump takes its suction from the bottom of a 250 liter cone bottom tank and its output goes to an external 8000 watt instantaneous fluid heater.

The vacuum is drawn on the upper volume of the tank...

The discharge from the pump does however travel up and over the tank to a top inlet on the heater could this lift over my tanks head space some how be causing the problem?

GCG

Project Purity,

For injecting acid into the reaction volume - I would set up a T-fitting and a ball valve. Then on the ball valve a small 3/4" close nipple and a septa (or septum fitting)Website. And a better website: http://www.vici.com/vfit/sepnut.php


They are used in chemistry and medicine when using a needle to inject small amounts of fluid into a flask or sample.

By the way what's wrong with phosphoric acid...

GCG

GCG: there's a little problem with that setup: HCL corrodes the syringes' needles.
I don't know if there's something wrong with phosphoric acid. I wish a chemist saw this thread and shed some light into this issue. I also don't know if using sulfuric acid would really increase the sulfur content of the BD enough to create a problem with emissions, given the little amount of acid needed.

Would you believe its a plastic syringe

You probably could do a quick injection and then flush with acetone or the like...

GCG

I've read this thread through a couple times, and read Graham's page on the Push-Pull processor, but still don't fully understand the benefit of using the HCL. What does it do for you during the process? Does it help get the glycerine to drop out faster?

As for the note on the needles, if the HCL corrodes the needles, you can either purchase a quantity of needles and just get a new needle per batch (insignificant increase per gallon) or I believe there are steel needles/stainless steel needles on ebay from russia circa 1950's and 60s.

Thanks,
-Scott