Warm cooling water in nixon still

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defcon4
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Warm cooling water in nixon still

Post by defcon4 » Wed Jan 02, 2008 11:30 am

I built a nixon stone still recently and now that I've used it a few times, I have some questions. Being a cheap SOB, I put an old liebig or jacketed condenser on top of the stream splitter section instead of using a helix coiled condenser. I know that during the first part of a run with these stills you're supposed to slow down the water flow till it's very warm to the touch so that the methanol will concentrate at the top of the column right? Well even with my cooling water flowing as slow as it can go, the water coming out of the condenser is at best room temperature.

Does this mean that the methanol and heads cuts will not concentrate at the top of the column while running under total reflux?
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frikz
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Post by frikz » Wed Jan 02, 2008 12:33 pm

If I'm correct a nixon stone still is an offset head still (or at least equal in construction/operation principle)? If so, you should use a valve to control the reflux ratio and thus the temperature in the head of the column rather than the coolant flow ratio. The condenser should just knock down all vapour.
When heating up, just run it at full reflux and when the wash is heated up, decrease the reflux ratio until the distillate starts dripping out very slowly. The stuff that comes out first will be rich in the low boiling components as methanol and ethyl acetate.

Note: even if you use a very high reflux ratio, the temperature at top at the column will probably rise quickly to approximately 78 deg C (ethanol boiling point) because most washes just contain relatively small amounts of lower boiling congeners.

wineo
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Post by wineo » Wed Jan 02, 2008 12:50 pm

As long as you run it with the takeoff valve closed for the first 20-30 minutes,then open the valve a little,and get rid of whats in the top of the column,it shouldnt matter too much.I usually open and close the valve a few times,letting the bad stuff build up every time till its gone.Once its gone,I usually set mine to a slow steady stream,and leave it that way until the temp starts climbing.Then I increse the reflux some to stablize the temp until quitting time.

stoker
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Post by stoker » Wed Jan 02, 2008 2:08 pm

I've never heard of that output-water temperatur thing. and I don't believe it's a general rule. if I have an inefficient coil with water flowing at a high rate, the water will be much colder then an efficient one with flow rate.
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tracker0945
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Post by tracker0945 » Wed Jan 02, 2008 5:06 pm

stoker wrote:I've never heard of that output-water temperatur thing. and I don't believe it's a general rule. if I have an inefficient coil with water flowing at a high rate, the water will be much colder then an efficient one with flow rate.
Probably following what I have frequently advised.
The warm condenser water output advice is specific to the Bok mini-still because the condenser is located within the still column, directly above the packing and the thermometer location is within the packing directly under the product return point and cold product return plays havoc with thermometer readings.
I have tried to make it plain that this is not general advice for all configurations.
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Post by HookLine » Wed Jan 02, 2008 8:26 pm

tracker0945 wrote:Probably following what I have frequently advised.
The warm condenser water output advice is specific to the Bok mini-still because the condenser is located within the still column, directly above the packing and the thermometer location is within the packing directly under the product return point and cold product return plays havoc with thermometer readings.
I have tried to make it plain that this is not general advice for all configurations.
There is second reason for running the coolant output as warm as possible in a non-recirculating coolant system, and that is to minimise water use.
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defcon4
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Post by defcon4 » Wed Jan 02, 2008 8:36 pm

ok, thanks guys. I just wanted to make sure I was removing the heads right. Learning to drive this reflux still is a lot harder than it was learning how to use my pot still in my opinion.
Towering in gallant fame,
Scotland my mountain hame,
High may your proud
standard gloriously wave,
Land of my high endeavour,
Land of the shining rivers,
Land of my heart for ever,
Scotland the brave!

tracker0945
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Post by tracker0945 » Thu Jan 03, 2008 2:19 am

HookLine wrote:
There is second reason for running the coolant output as warm as possible in a non-recirculating coolant system, and that is to minimise water use.
Yes, failed to mention that point. AND all of us in drought mode.
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Pot still with Leibig on 45 litre boiler

HookLine
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Post by HookLine » Thu Jan 03, 2008 3:07 am

tracker0945 wrote:
HookLine wrote:
There is second reason for running the coolant output as warm as possible in a non-recirculating coolant system, and that is to minimise water use.
Yes, failed to mention that point. AND all of us in drought mode.
Well, some of us. :wink: We've had well over 300 mm in the last week here, and it is currently bucketing down monsoon style as I type. Even so, I don't like using any more town water than necessary.

But you're basically right. Most of Australia is in the grip of its most serious drought ever, which is saying something for the driest inhabited continent.
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