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ACR Liquid-liquid extraction

Aim

The purpose of this experiment is to perform liquid-liquid extraction within a Coflore ACR. This is to be achieved with cells performing as distinct mixing and settling zones within the Coflore ACR.

Theory

The Coflore counter-current system is currently available at the lab and pilot plant scale. They are based on the principle of mixers/settlers in series. Just like the Coflore reactors, the mixing is provided by an agitator free to move within the cell or tube. The system is sealed and mounted on a shaking platform which moves the block laterally at various speeds. The agitator inside the cells provides random mixing independent of fluid velocity, without the need of baffles, mechanical seals and rotating shafts. The frequency can be adjusted to achieve high interfacial area for the extraction to occur whilst avoiding forming stable emulsions which would hinder separation and limit throughput.

The Coflore ACX block fits into the same flanges and shaking platform as the Coflore ACR reactor and it can be heated to drive the separation. It comprises of up to 8 mixing cells and separate channels for the light and heavy phases. The fluid with higher density is injected at the second top cell of the block through the side port while the lighter phase is injected via the side port at the second cell from the bottom. The raffinate and the extracts come out from the bottom and top outlets respectively. The extractor performance is dependent on efficient mixing of immiscible fluids and good phase disengagement. A study with 1 molar sodium hydroxide and 2-ethylhexylformate on a single Coflore cell gave comparable mixing efficiency to a ½ litre stirred vessel with agitator speeds of 350-410 RPM. The separation speed depends on the physical properties of the system such as density and viscosity ratio. The agitators can be removed in alternate cells to create a series of mixer/settler cells to enhance separation.

Figure02-LLE_in_Coflore_ACR

Process Description

Figure03-LLE_in_Coflore_ACRPlease find photographs of the experimental set up on the right and a P&ID (below) for reference.

1.     Light phase feed is pumped using a peristaltic pump from a vessel to Cell 2 of the Coflore ACR.

2.     Heavy phase feed is pumped using a peristaltic pump from a vessel to Cell 9 of the Coflore ACR.

3.     Eight mixing zones between Cell 2 and Cell 9 promote mass transfer allowing for efficient liquid-liquid extraction to take place.

4.     Cell 1 and 10 perform as a heavy and light phase settling regions respectively.

Light and heavy phase product exits the ACR from the settling regions, travels to a height above the ACR and is collected into measuring cylinders.

Coflore ACR setup for Liquid-liquid extraction

Coflore ACR setup for Liquid-liquid extraction (click to enlarge)

Equipment List

The following equipment items are recommended to perform the liquid-liquid extraction experiments using

the ACR:

4 x Measuring cylinders

1 x Peristaltic pump

2 x Masterflex Easy-Load II Pump head

1 x L/S 14 Masterflex tubing

1 x L/S 16 Masterflex tubing

2 x ‘T’ pieces

1 x Coflore ACR-100 fitted with an ACX reactor cell block

10 x 50% agitators

1 x Clamp Stand

Methodology

In order to perform the liquid-liquid extraction experiments upon the ACR, the following experimental procedure is recommended:

1.     Fill the ACR with light phase. Ensure the heavy phase inlet (stream 1) and heavy phase outlet (stream 4) are positioned above the ACR cabinet. This will prevent light phase leaving the system as the ACR fills.

2.     Begin feed of the heavy phase. Equal flow rates of 5 ml/min of heavy and light phase have been tried and tested.

3.     Start ACR agitation once heavy phase feed is observed in Cell 9.

4.     Once steady state has been achieved, check the phase ratio in each cell by briefly stopping the agitation.

5.     Adjust phase ratio by adjusting heights of heavy phase outlet (stream 4) and light phase outlet (stream 3).

a.     To remove more heavy phase, lower the heavy phase outlet (stream 4) position down

b.     To remove more light phase, lower the light phase outlet (stream 3) position down

6.     Restart agitation and repeat steps 4 – 6.

Recommended Reading

Examples of successful counter current extractions taking place in a Coflore ACR can be found in the following technical notes:

AM Technology “Coflore ACX – Design and Result Summary”

AM Technology  Technical Note “Coflore – Counter Current Liquid-Liquid Extraction”

AM Technology “Continuous Extraction: Coflore ACR-X”

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