[SNorman]

Hi, I was just wondering how liquid/liquid extractions and separations are done in industry. As you know, in the lab we easily use a separatory funnel to extract products from various solvents (i.e. water vs ethyl ether) and then use the conical feature of the funnel to divide the two immiscible solvents - how do they do that in industry when they have for example 200L of solvents? What is the equipment called? How does it work? Links to actual equipment would be appreciated. Thanks!

[Pradeep]

They use larger extraction vessels and they use counter current flows.

[SNorman]

They use larger extraction vessels and they use counter current flows.

I'm assuming these larger extraction vessels are made of stainless steel or some metal of some sort, but are they conical in shape as well like a separatory funnel and how do they see the liquid/liquid interface (i.e. sensors, little window, etc.)? What is the device called that uses counter current flow? Thanks.

[skbuncks]

For a batch wise process a reactor vessel, basically shaped like a cylinder with either a conical or flat base is employed (conical is better for obviuos reasons but you don't always have the choice). The reactor is fitted with an agitator to stir the batch and possibly a heating/cooling jacket to control the temperature. To avoid the build up of a flammable atmosphere and static discharges the vessel should be kept under a positive nitrogen flow.
After first allowing the layers to separate after agitation (if the reactor has a sample loop then a sample of the agitated batch can be taken in order to gauge the separation time) the lower layer is discharged through a bottom run off valve (BRO) (depending to where it is being routed a positive pressure of nitrogen on the vessel may be required).
There are different ways to to spot the interface between layers, namely:
1) A sight class to visually watch for the interface.
2) Pack off to a known weight.
2) Measure the conductivity of the phase as it passes through the BRO (a change in conductivity indicates the change in phase).

skb

[Pradeep]

when they do those extractions batch wise they use Stainless steal vessels. some time they use contious extraction by counter current flows.

[Siddarth]

On a industrial scale, stage wise counter current or differential contact equipment at used for extraction. The most simple countercurrent stage wise extraction equipment is the extraction battery. Other common extraction equipment used in industries are mixer settlers, extraction towers, pulse columns and centrifugal extractors. For greater details just refer to McCabe, Smith and Harriot "Unit operations in Chemical Engineering), McGraw Hill. That would be very useful for you if you wish to get more knowledge on the  various operations carried out in a chemical engineering unit.