Membrane separation technology

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1. Common separation methods used in bioprocesses such as distillation, extraction, filtration, crystallization, adsorption, and drying belong to traditional unit operations, while others are newly developed separation techniques, such as cell membrane disruption methods (including ball milling and chemical disruption), membrane separation, and chromatographic separation. The author focuses on membrane separation technology here. 2 Overview of Membrane Separation Technology Membrane separation technology is regarded as one of the high-tech fields with the greatest potential for development from the late 20th century to the middle of the 21st century, and it even has the potential to trigger an industrial revolution; it has thus become a focus of research around the world. As a newly developed advanced separation technology, membrane separation is seeing an expanding range of applications; it is widely used in fields such as chemical engineering, food processing, water treatment, pharmaceuticals, environmental protection, biotechnology, and energy engineering, where it plays a significant role. ]。 Research on membrane separation technology in our country began in the 1960s with studies on ion exchange membranes. From reverse osmosis technology in the 1960s to pervaporation technology in the 1990s, membrane separation technology in China has seen rapid development. Through decades of effort, China has now successfully developed a number of practical membrane separation technologies in research and development, which are at or close to the international advanced level, such as inorganic membrane reaction separation technology. 3 Principles and Advantages of Membrane Separation Technology Membrane separation refers to the use of a semipermeable membrane as a barrier layer, and by leveraging the selective permeability of this membrane, the different components in a mixture are separated and purified under the influence of energy, concentration, or chemical potential differences. Due to the varying pore sizes of the filter membrane in semipermeable membranes, certain components can pass through the membrane layer while other components remain in the mixture, thereby achieving a certain level of separation. Using membrane separation technology for separation has the following advantages: the membrane separation process involves relatively simple equipment, is easy to operate, has a compact design, requires low maintenance costs and is easy to automate ； Membrane separation processes generally do not involve phase changes, cause no secondary pollution, and have low energy consumption ； The membrane separation process can be operated at room temperature or low temperatures, making it suitable for the concentration and separation of heat-sensitive substances (enzymes, drugs) ； The membrane separation process possesses considerable selectivity and a wide range of applications; it can separate particles visible to the naked eye, as well as ions and gases ； This process can be operated continuously at room temperature; the equipment is easy to scale up, and it is possible to use membranes specifically selected to achieve a high recovery rate ； The membrane separation treatment system can operate in a closed cycle, thereby preventing external contamination ； No external chemicals need to be added during the process, and the filtrate can be reused, thereby reducing costs and minimizing environmental pollution. It is precisely because membrane separation technology possesses the aforementioned advantages, making it an efficient separation method among modern bioprocess separation techniques that it can completely replace traditional separation methods such as filtration, adsorption, evaporation, and condensation; therefore, membrane separation technology plays a significant role in bioprocess separation engineering. 4 Several major membrane separation techniques. The membrane separation techniques commonly used in biochemical processes include microfiltration (MF), ultrafiltration (UF), reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and liquid membrane (LM), among others. 4.1 Microfiltration: Microfiltration is a membrane filtration process that uses a porous, fine membrane as the filtering medium, operating on the principle of screening. Driven by pressure, solvents, water, salts, and macromolecular substances can pass through the membrane, while substances with particle diameters larger than the membrane pores, such as fine particles and supermacromolecules, are retained, thereby achieving separation and further purifying the solution. Microfiltration is the most widely used and economically valuable membrane separation technique at present, and it is primarily applied in the pharmaceutical industry within biotechnology. 4.2 Ultrafiltration Ultrafiltration is a process that separates the solvent from a solution based on the principle of screening, using a certain pressure difference as the driving force. Compared to the microfiltration process, the ultrafiltration process is more influenced by the chemical properties of the pores on the membrane surface. Under a certain pressure difference, solvents or substances with low molecular weights can pass through these membrane pores, while larger molecules and fine particles are retained, thereby achieving the purpose of separation. Ultrafiltration membranes are usually asymmetric membranes, where the size of the membrane pores and the properties of the membrane surface play distinct roles in retention. Ultrafiltration is mainly used for the purification and concentration of macromolecular solutions. It is most widely applied in biochemical processes. 4.3 Reverse Osmosis