Types of liquid liquid extraction equipment

1.Mixer-settler

1.1 Brief introduction of mixer-settlerMixer settler is also called extraction tank, it is the earliest extraction equipment used in industry, which is still widely used at the present. A mixer settler consists of a first stage(mixing chamber) that mixes the phases together and a settling stage(settling chamber) that separate the light and heavy phases by gravity naturally.

1.2 Features of our mixer settler
Compact structure, easy and flexible operation,can fully observe the phenomena during the extraction process.
Low speed stirring, gravity clarification, and long material retention time.
The stable operation of the mixer settler can be ensured by adjusting the depth of the heavy phase adjustment pipe inserted into the liquid.
To change the efficiency of mixed mass transfer, the speed of the turbine can be adjusted
Flexible determination of stages.
easy to get sample in each stage, the distribution ratio of two phases' concentration can be obtained after chemical analysis.

1.3  Working principle of mixer settler
The work of mixer settler includes two processes, namely the mixing mass transfer process and the two-phase separation process. The mixing is completed by the rotation of the agitator, and the separation is completed by gravity. Two liquids with different densities enter the mixing chamber from the feed inlet, and the mixing and mass transfer process is completed through the agitating of the agitator. The suction force of the impeller drives the liquid of the mixed phase to rise, and it overflows into the clarification chamber through the overflow baffle of the mixing chamber. The two mixed phases are separated by gravity in the clarification chamber. In the clarification chamber, the height of the two-phase liquid level is controlled by adjusting the height of the heavy phase adjustment tube (with holes on top of the heavy phase adjustment tube), so that the heavy phase flows out of the heavy phase discharge tube, and the light phase flows into the light phase collection chamber from the light phase weir, and then discharged from each outlet. Please see the flow chart as following:

1.4  Material selection of mixer settler

2.Centrifugal extractor

Mixing and Mass transfer process

The light and heavy phase solutions entering into the internal mixing zone of the shell from the two feed inlets respectively, according to a certain ratio, so that let the two phases are rapidly mixed and dispersed, to complete the mixed and mass transfer process.

Factors affecting mass transfer effect:
Mixing intensity: Within a certain range, the larger mixing intensity, the smaller the two-phase dispersed particles, and the larger the contact area, the more favorable it is for mass transfer. However, the droplet is too small to separate. It could increase mixing intensity by increasing the rotating speed or replacing blades with stronger shear force.
Contact time: It is beneficial to mass transfer to increase the two-phase contact time. When mass transfer process reaches equilibrium, the increase of contact time will not improve mass transfer effect. Usually, a longer contact time can be obtained by reducing the flux.
Temperature: Temperature affect the mass transfer effect, some are increase with the increase of temperature, while some are just the opposite.
Material concentration difference: The larger the concentration difference, the better the mass transfer.

Separation process
Under the action of the feeder or turbine disc, the mixed liquor enter in bowl, in the cavity zone, it soon rotated with bowl , under the condition of centrifugal force, during the upward flow process, the heavier liquid is away from bowl center and towards to the bowl wall, while the lighter liquid is away from bowl wall and towards to the center, clarified liquids enter in collecting chamber through their respective weirs and discharged from light and heavy phase outlets, to complete the separation process.

Factors affecting separation effect:
Surface tension: The larger surface tension is beneficial to separate, which is related to the temperature and the property of interfacial two-phase material.
Viscosity: Low viscosity is beneficial to separate. Usually, increasing temperature could reduce the viscosity.
Viscosity difference: The larger viscosity difference of two liquids, the easier separation.
Separation time: Rising separation time could increase separation effect. Usually, reducing flux could increase separation time.
Centrifugal force: Increasing centrifugal force could improve separation effect, it could increase centrifugal force by increasing rotation speed or increasing bowl diameter under the condition of the same rotation speed.
Interfacial position: In some ways, the change of interface position could affect separation effect, heavy phase weir could adjust the two-phase interfacial position.

2.3Features of centrifugal extractor
Simple and stable structure --- top suspension structure, no bearing and mechanical seal at the bottom of equipment, no leakage risk, easy for maintenance and save maintenance cost, long service life.
Energy-saving --- large capacity, more energy saving( comparing if under same capacity condition, the power consumption is 1/3~1/10 to transitional annular type extractor)
Corrosion resistance --- Machine can be produced by PVDF, resistant with corrosion of strong acid(hydrochloric acid, mixed acid etc.)
Convenient cleaning --- optional online cleaning system(CIP cleaning system)
Good effect of mixing and separation --- variable structure could be chosen, good separation effect, adapt to easily emulsified system.
High grade of automation --- The operation is unmanned and the centrifugal extractor is fully capable of adapting to intermittent and continuous operation. It is also equipped with speed sensors, vibration sensors, and temperature sensors, which can constantly monitor the operation status of the equipment and prevent faults in advance.
Good operation environment --- By optimizing the design of the inlet and outlet channels, the extraction system composed of this model of centrifugal extractor does not need to be equipped with separate gas recovery or discharge devices. It can achieve closed operation of the system, with no odor escaping from the extraction line, reducing the volatilization of the extraction agent, and improving the on-site operating environment.
Easy to run and stop --- The centrifuge is fully capable of adapting to intermittent and continuous operation.  
Easy to change the heavy phase weir --- when changing the liquid system, heavy phase weir could be quickly replaced, simple and easy operation.

2.5 Material selection of centrifugal extractor