What Is a Separation Process?

In order to meet the requirements of storage, transportation, processing and use, it is often necessary to separate these mixtures into relatively pure or almost pure substances or components.

The separation process is divided into two categories: equilibrium separation process and rate control separation process, and equilibrium separation process is divided into energy-added type and material-added type. ^[1]

There are many ways to classify the separation methods, but some classification methods are not very strict. This is because some separation methods involve more than two mechanisms; each separation method is nothing more than the following three processes performed separately, simultaneously, or sequentially. Process: chemical transformation; distribution in two phases; physical separation of phases. Studying the separation according to the relationship between distribution and phase separation produces multiple separation modes.

1. Batch separation This is the simplest separation mode. It only involves a single distribution equilibrium process between two phases. This mode is suitable for concentrating the separated materials in one phase. For example, the preconcentration separation method is due to the difference in equilibrium constants. Examples of complete transfer to one-phase batch separation with a small volume are single solvent extraction, co-precipitation, precipitation, and electrodeposition. The efficiency of their separation is mainly determined by preliminary chemical conversion to produce derivatives with the necessary separation.

2. Multi-stage batch separation When simple batch separation cannot achieve quantitative transfer, multi-stage batch separation can be used. Multi-stage batch separation, that is, distribution phase separation distribution phase separation. For example, a certain component in the aqueous phase is repeatedly extracted with fresh solvent until it is complete. For components with similar solubility, a more complex so-called "discontinuous countercurrent extraction method" should be adopted, but special equipment must be used, and this separation can reach more than 250 batches.

3. Continuous separation This is an extremely important separation technique, which includes all chromatographic techniques. Fractionation is also a continuous separation technique. Chromatography is a powerful means of separating substances with very similar properties. For most chromatography techniques, separation and detection are performed online.

4. Trapping technology This technology is very similar to the color resonance technology, except that the separated material is initially captured in the stationary phase. For this reason, the sample itself is often the mobile phase. For components that have a greater affinity for the stationary phase, it will be concentrated from the larger mobile phase to the smaller volume stationary phase. Then, the conditions were changed so that the concentrated components were quickly released from the stationary phase into the small volume mobile phase. This is actually a pre-concentration process with a trace energy of about 1 minute, for example, the concentration of water and organic compounds in the atmosphere with an adsorbent, and the concentration of ions in water with an ion exchanger.