What problems can you run into pumping methanol vapors through a "dry" vacuum pump. Seems easier to place a condenser after the pump.

Anyone actual running the condenser after the vacuum pump?

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What problems can you run into pumping methanol vapors through a "dry" vacuum pump.

Heat caused by friction due to the lack of lube will likely cook the seals and could possibly ignite the fumes?
They make a couple of different pumps made to pump fumes/liquid, look for "liquid ring" or "positive displacement" (piston) vacuum pumps, there may be others as well but these 2 stick out in my memory from the research I did last year...

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Anyone actual running the condenser after the vacuum pump?

Thats how GL uses the venturi in his push/pull setup. The venturi has a separate pump and canola oil bath with a heater. He heats the oil so the methanol fumes just evaporate out and pass through the condenser at atmosphere.
See HERE.
Jon

By "dry" I mean oilless rotary vane vacuum pump. The pumps are not lubricated.

In way to far to back up and go the GL route.

OH, I have not seen one of those.
GL's vacuum pump could be used for any application, no need to have a GL reactor to utilize his vac pump design.
I thought about installing a heater in the large oil sump of my pump to get the methanol to evaporate out like in GL's design and then have the condenser on the output but it worked too well as is...
The base with the cooling fins is the oil sump I was going to install a cartridge heater in. The vanes in the pump are aluminum and after running for several hours it gets only luke warm to the touch so I am not worried about it igniting any fumes.

Jon

I am thinking of using a pump like this.

https://www.surpluscenter.com/...m=4-1669&catname=air

I dont know what to tell ya!
It only draws a vacuum up to 20Hg, thats not that great. I find between 22 and 28Hg is were you need to be to get the last bit out.
If you do try that pump keep the motor in a well ventilated area as it has a sparking start switch and overload that will also spark.
You sure cant beat the price, just the motor would be worth more than that.
Let us know what you come up with.
Jon

I decided against using pumps like this b/c the internals are all steel - the vanes are spring tensioned against the housing and spin at high rpm with full time tip area contact. They get pretty hot. I don't have any knowledge of them sparking, but didn't feel like risking it. Used them on the super sucker with success tho.

The pump I took apart had nonmetal vanes and no springs. Just centrifugal force holds the vanes out against the housing. I guess the trade off is the pumps do not pull as much vacuum. I am hoping 20 inches and heat will get the job done.

FF, my vac pump is a larger version gast than the one in your link, centrifugal vanes, it is down stream of the condenser and drop out vessel, it does still see some methanol vapors and I have never had any problems, the vanes are pure carbon and will not spark, mine pulls 27" with no problem.

the only problem you might have with this pump is oil/glycerin vapor getting to the vanes..and all that does is gum them up so they don't move out the ring for sealing.

I have a 1023 and 0523 pump..I tried using them for vacuum dewatering..now I need to clean them.

-dkenny