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Author: Subject: Synthesis of Diethyl Ether
Fyndium
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[*] posted on 15-2-2021 at 00:05


Why alumina catalyzed dehydration is not discussed anymore in here? It sounds like a perfect solution for ether generation.

I have some alumina powder purchased from a pottery store. Could it possibly have catalytic properties as is? It's not grit, it's just a very fine white powder as-is.

https://doi.org/10.1007/s10934-018-0663-7

This paper describes that an alumina catalyst at 200-300C will produce mostly ether, with some ethylene formed. The yields vary between 20 to 50 percent, lower being for zero ethylene, and upper being for 10%. So, for every liter of input ethanol, 200-500mL of ether should be obtained, and 0 to 100 grams of ethylene gas. These are very crude numbers, for the record.

I suppose a tabletop generator could be manufactured by submersing a 500mL rbf into a metal shot bath filled halfway with alumina, and a gas washer where ethanol vapor would be led in, and the exhaust gas would be led through a graham condenser into a collection flask, and exhaust tube with another condenser would be vented away for ethylene gas.

Graham should be cooled with cold water, as it will condense everything at first and a lot of energy will be transferred into it, so the water needs to be replaced often or recharged with ice, I noted this just as I stripped a batch of ethanol clean and the coolant water heated up very quickly.

The collecting flask and the exhaust condenser should be cooled with salt-ice water separately, as their purpose is to keep the condensate cold and prevent vapors escaping. If one's got the glassware and interest, one could actually make a double trap to condense the ethanol first at 40C and cool the second receiver to concentrate the formed ether, requiring less work afterwards. Continuously operating plant would warrant using dropper funnels to drain the receivers for reuse without stopping and dismantling the whole apparatus, and might be worth considering given the setup is arduous enough to get up so making only few hundred mL of ether would be extremely un-rewarding. Given the droppers are more expensive and difficult to cool with a bath because of their structure, simply draining the flasks with silicon stoppers in one of the joints and glass tubes and a primer pump could be an option.

For 200C silicone oil would work, but for 250C we're getting too high and it likely smokes like a BBQ, so a metal shot bath would probably be a better choice. Metal also conducts heat so well that it would work, as sand or salt are much better at insulating than transferring heat. Metal shots could be replaced with smallest nuts (M4, M5 otc) as they're sold 5€ a kg in bulk and are generally available everywhere. They are zinc coated, so it might be worth considering either pickling them first or heating them to high heat to burn it off. Prior flushing with any inert gas (CO2, argon, N2) would render it safe for DEE autoignition temp of 160C. The large thermal mass also makes temp control easy and fluctuations smaller to both directions.

[Edited on 15-2-2021 by Fyndium]
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macckone
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[*] posted on 16-2-2021 at 14:56


The high temperature catalytic route is usually not discussed because it is harder for the average person to do.
sulfuric acid or sodium bisulfate are easier for most people to get prior to the sulfuric acid crackdown in the EU.
I am guessing sodium bisulfate is still unregulated and does a good job.
In my opinion it is better than sulfuric acid. Sulfuric acid is formed in situ and reacts with the ethanol.
Less ethylene is formed to polymerize.

The usual method of doing a gas phase reaction is a silica or alumina tube, with the center heated with direct flame or nichrome wire.
With the tube method you can feed the ethanol in one end and extract the ether at the other.

However you need to periodically purge the system of water.
This is true regardless of the method used as the reaction is reversible at high temperatures.
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Fyndium
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[*] posted on 16-2-2021 at 21:41


Apparently sodium bisulfate would be the most otc straightforward method for ether if it works as depicted. It will produce ethyl sulfate at lower temperatures, and question is if the generation is equimolar or catalytic, as if it was molar conversion, it would require hefty amounts of bisulfate to produce ether.

Doesn't water come over with ethanol/ether/ethylene as vapor and condense to the receiver flask?

The tube method is apparently the classic, but my concern is that too high temp will produce more other products than desired, as the research paper indicates that much above 300C the main product by far will be ethylene. Hence my idea was to use metal/sand bath immersed flask trap with the catalyst to control the temperature. Flame heated tube temperature range can be anywhere between 200C and 900C, and temp control is difficult, along with hotspots.

Gotta test it out, as they say.
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