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When separation can be achieved by distillation, extraction is generally not considered as a viable option.  There are instances, however, when distillation is not feasible, and extraction becomes the most practical process solution.   

Extraction is the dissolving process of a chemical component with a liquid out of a second non-gaseous phase.  Depending on the kind of second phase, this process is called either solid/liquid extraction or liquid/liquid extraction.


Liquid/Liquid Extraction Solutions:

  • Batch operated Mixing/Settling Units
  • Continuously operated Mixer-Settlers
  • Continuously operated Extraction columns

Solid/Liquid Extraction Solutions:

  • Soxhlet Extraction Units
  • Trickle Bed Extraction Unit
  • Over Flow Extraction Units

De Dietrich Process Systems provides the extraction equipment and the process solution for recovering high boiling organic components out of industrial effluent water to accomplish solvent regeneration for industrial applications such as phenol recovery and acetic acid recovery. 


De Dietrich Process Systems has a long history in designing and manufacturing these extraction processes and system. Our extraction plants are built from corrosion resistant De Dietrich glass-lined and QVF borosilicate glass components, providing process optimization through these unmatched materials of construction.  

In addition to theoretical calculations and decades of extraction experience, DDPS can also perform trials in our experimental hall to develop the optimum process and to select the most suitable extraction equipment for your application.



Solid/Liquid Extraction


Solid/Liquid extraction process is a very common process in the pharmaceutical, cosmetic and food industries to obtain natural ingredients as flavors and fragrances from natural raw material.

The extraction can be carried out with hot or cold solvents.

The solid raw material is packed in a container with a retainer on the bottom (extractor B2 - see diagram below) and extracted batch wise.

The solvent is guided through the extractor in different ways

  • Continuous trickle bed extraction
  • Continuous overflow extraction
  • Soxhlet extraction (periodically filled and drained container)

Using solvents with a lower density than the raw material avoids floating of the raw material and eases the process.

Very often the solvent is evaporated in B1 from the extract directly after leaving the extractor, then condensed in W2 and guided back into the extractor B2.

A typical flow chart of a solid/liquid extraction process.Solid-Liquid_extraction_diagram.png

Once the ingredients are extracted from the raw material, the solvent is carefully evaporated to avoid degradation of the desired ingredient.

Liquid/Liquid Extraction

Distillation is based on liquid/vapor interaction;  Extraction is based on liquid/liquid interaction.


Requirements for the Solvent

The solvent will have to be checked for the following characteristics:

  • Maximum solubility of the product in the solvent
  • Minimum solubility of the solvent in the raffinate
  • Minimum solubility of the feed liquid in the solvent
  • Fast phase separation of the extract from the raffinate
  • Easy separation of the product from the extract/solvent

With the right solvent there are numerous applications which can utilized the extraction process.


When to Use the Extraction Process

The liquid/liquid extraction process is favorable for separations as for:

  • products having similar volatilities
  • products forming azeotropes
  • products which would require high energy input in distillation
  • products being temperature sensitive
  • non-volatile products as e.g. metal salts

Equipment to carry out extraction processes

Extractions can be carried out by batch (using mixers) or in continuous mode (using mixer-settlers or columns).  In addition to theoretical calculations and extraction expertise, DDPS can also perform trials in our experimental hall to develop the optimum process and select the most suitable extraction equipment for you. Borosilicate glass 3.3 is an ideal material for extraction equipment as the process can be optimized while visually observing the process.

Batch mode - Mixers/Reactors

Using a mixer in batch mode offers a huge flexibility to optimize the mass transfer by varying multiple aspects of the process, including ratio of the liquid phases, the type of stirrer, stirrer speed, and mixing time. The settling period can also be easily influenced by varying the time.

Extraction funnel                                                                 mixing and settling in reactor
Mixing and subsequent settling in a separation funnel                              Mixing and subsequent settling in a reactor


Continuous mode - Mixer-Settlers and Columns

Operating in continuous mode is less labor sensitive and the equipment is smaller, but the equipment has to be fitted more exactly to the mixing and settling processes.  For example, the “time” parameter can only be adjusted only by adjusting the throughput. Therefore various types of mixer-settlers and extraction columns are available to suit the many different extraction applications.


Stainless Steel Extraction Column
Stainless Steel Mixer-Settler

How to Find the Best Solution?

The phase distribution equilibrium coefficients are the basis for the selection of an extraction process and the calculation of the minimum number of theoretical extraction stages. The type and size of the real extraction stages are determined by the mass transfer and phase separation processes. Mass transfer and phase separation are strongly dependent on the characteristics of the interface between the 2 liquid phases. Any surfactants present, even small amounts, can have an important impact on the extraction process, making results from extraction trials with your real feed liquors important for a reliable process design. Testing at our experimental hall will help to optimize your process.  The information obtained from these trials, combined with theoretical calculations, are the foundation for selecting the most suitable extraction system.

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