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Chemical separation technology is an important branch of chemical engineering. It is essential for various applications such as petroleum refining, plastics and fibers production, hydrometallurgy, isotope separation, the purification of biological products, the preparation of nanomaterials, the desulfurization of flue gases, and the production of fertilizers and pesticides. In chemical production, the raw materials and products are mostly mixtures, and it is necessary to separate and purify these mixtures by taking advantage of the differences in the physical properties of their components or by using separation agents. It is often a key step in obtaining qualified products, making full use of resources, and controlling environmental pollution. With the rapid development of the chemical industry, separation technology has also seen swift progress. On the one hand, research and application of traditional separation technologies are continuously advancing, resulting in improved separation efficiency and greater processing capacity; the issues associated with scaling up these technologies are gradually being resolved, and new types of separation devices are constantly emerging ； On the other hand, new separation requirements have emerged to keep up with technological advancements, and the development, research, and application of existing separation techniques such as membrane separation technology, supercritical extraction technology, and adsorption technology have become key areas of focus in separation engineering research. A chemical separation process is an operation that separates a mixture into two (or several) different products. A standard chemical production facility mainly consists of a reactor along with several separation units for purifying raw materials, intermediate products, and final products ； First, the separation process provides high-quality raw materials for chemical reactions, removes harmful substances, and increases the yield ； Furthermore, it ensures that the reactants yield qualified products during separation and purification, while allowing the unreacted materials to be reused ； Furthermore, the separation process plays a vital role in making full use of resources and protecting the environment; therefore, its importance in chemical industry production is quite significant. The separation processes commonly used in chemical production can be divided into two main categories: mechanical separation and mass transfer separation. The object of separation in the mechanical separation process is a mixture composed of two or more phases. Its purpose is simply to add the various phases together in order to separate them; the two phases can be separated using simple mechanical methods, with no transfer of matter occurring between them ； For example, filtration, sedimentation, centrifugal separation, cyclone separation, and electrostatic dust removal. The mass transfer separation process is used for the separation of various homogeneous mixtures, and it is characterized by the occurrence of mass transfer. Depending on the physicochemical principles underlying it, the mass transfer separation processes commonly used in industry can be divided into equilibrium separation processes and rate separation processes, which are processes involving the separation of energy from matter. >>>> Equilibrium separation process: This process involves using a separating medium to transform a homogeneous mixture system into a two-phase system, and separation is then achieved based on the unequal distribution of the various components in the mixture between the two phases in phase equilibrium. For example: evaporation, distillation, absorption, adsorption, extraction, leaching, drying, crystallization, ion exchange, etc. For example, in the process of traditional extraction, energy is transferred to the extractant in a random manner; subsequently, the extractant diffuses into the matrix material, and finally, various components are dissolved out of or carried away by the matrix. Microwave extraction is a new technique designed to improve the efficiency of extraction using microwave energy. Due to the presence of substances with different dielectric constants, the degree of absorption of microwave energy varies, which in turn results in differences in the heat generated as well as the heat transferred to the surrounding environment. In a microwave field, the degree of absorption determines that certain areas of the matrix material are selectively heated, thereby allowing the substance to be extracted to be separated from the matrix and enter an extractant with lower microwave absorption capacity and a relatively smaller dielectric constant. >>>> Process flow of microwave extraction The process flow of microwave extraction is roughly as follows: raw material pretreatment (washing, crushing, or slicing) → mixing of the material with solvent → microwave extraction → filtration → concentration → separation. The process of separating the extracted components has been in use for a long time; with the advancement of science and technology and the rise of high-tech industries, it has continued to improve and evolve, giving rise to various new separation techniques with distinct characteristics. In traditional separation processes, distillation remains the most important method for separating substances in the petroleum and chemical industries; therefore, methods to enhance its efficiency are constantly being researched and developed. >>>>Rate separation process: The rate separation process is a method that, under the influence of some driving force (such as concentration difference, pressure difference, temperature difference, potential difference, etc.), and sometimes with the assistance of a selectively permeable membrane, utilizes the differences in the diffusion rates of various components to achieve their separation. The raw materials and products processed in such processes usually belong to the same phase state, with only differences in composition. The principle of membrane separation technology is a unit operation that achieves component separation by taking advantage of the differences in the permeation rates of various components through the membrane. The membrane can be solid or liquid, the fluid being processed can be a liquid or a gas, and the driving force for the process can be a pressure difference, a concentration difference, or a potential difference. Microfiltration, ultrafiltration, reverse osmosis, dialysis, and electrodialysis are well-established membrane separation technologies that have been widely used in industry and on the market. Among them, the common feature of the first four is that they are used to separate liquids containing dissolved solutes or suspended particles; the solvent or small-molecule solutes pass through the membrane, while the solutes or large-molecule solutes are retained by the membrane, with different membrane processes retaining solute particles of varying sizes. Electrodialysis uses charged membranes to remove or concentrate electrolytes from an aqueous solution under the force of an electric field. Gas separation and pervaporation are two membrane technologies that are under development for practical application. Gas separation is more mature; industrial applications include the separation of oxygen and nitrogen from air, the separation of hydrogen from mixed gases in ammonia synthesis plants, and the separation of carbon dioxide from methane in natural gas. Osmotic evaporation is a membrane separation process involving phase change, which utilizes the differences in the solubility and diffusion properties of various components in a mixed liquid within the membrane to achieve separation. Due to its ability to remove trace amounts of water from organic substances, trace amounts of organic substances from water, and to separate organic substances from one another, it has broad application prospects. Emulsion membrane is a branch of liquid membrane separation technology; it is a membrane separation process that uses a liquid membrane as the separation medium and relies on concentration differences as the driving force. Liquid membrane separation involves three phases: the feed phase containing the components to be separated, the product phase that receives those components, and the membrane phase located between the two aforementioned phases. Liquid membrane separation is mainly applied to the separation of hydrocarbons, wastewater treatment, and the extraction and recovery of metal ions. Unit operations with a long history, such as distillation, absorption, and extraction, which are used in the mass transfer separation process, have been widely applied. New separation technologies like membrane separation and field separation have demonstrated their advantages in product separation, energy conservation, and environmental protection. There are various types of methods for separating materials, and this is because there are many different chemicals used in industrial production. When choosing a separation method, the decision is usually made based on the distinct chemical and physical properties of the various components that need to be separated ； Based on their chemical and physical properties, there are five common types of separation methods: ① separation methods for solid mixtures, ② separation methods for gas-solid mixtures, ③ separation methods for liquid mixtures, ④ separation methods for liquid-solid mixtures, ⑤ separation methods for gas mixtures. >>>> Principles for selecting separation methods When choosing a separation method, it is necessary to take into account the level of refinement required for the product as well as the value generated by its production. For products that require a high degree of refinement and generate high values, the separation costs can be ignored, and more efficient separation methods can be used. For products with relatively low values but high volumes of production, however, the separation costs must be considered, and separation methods that involve fewer steps or are simpler in nature can be chosen. Try to avoid the presence of solids in the fluid streams during the production process; the solids should be removed as early as possible, as they result in relatively high energy consumption during transportation, and fluid streams containing liquids or gases can easily cause pipeline blockages. When separating mixtures containing various substances, the principles that should be taken into account regarding the order of separation are as follows: to prevent disruptions in the processing process, it is advisable to separate first those substances that are likely to cause extremely harmful side reactions. At the same time, for substances that can only be separated under high pressure, it is also necessary to consider separating them first ； Furthermore, the components that are easiest to separate are the first to be isolated, while those that are hardest to separate remain until the end. The main principles for selecting a separation method are still to consider economic rationality and technical reliability. For example, both distillation and extraction are methods for separating liquid mixtures. In terms of technical maturity, distillation is superior to extraction. If it is possible to use distillation for separation, extraction should be avoided whenever possible. When there is a significant difference in the boiling points of the components in a mixture, distillation can be used for simple separation, eliminating the need for distillation; this results in lower operational costs and investment requirements. The selection of a separation method must be done in a targeted manner, as it is a highly technical task. Only by having a clear understanding of the chemical and physical properties of the materials to be separated, as well as the requirements for separation, can the best choice be made.