Original title: Where is the way for membrane distillation technology? This is the 10th original article of the Sixth Master! Membrane Distillation (MD). To be honest, MD is also a once forgotten membrane technology, and at present, whether in academic or practical market applications, we can actually hear a lot of voices about it. Membrane distillation concentration technology is listed as a new separation technology focused on and developed in the 21st century in "Beyond Molecular Frontiers-Challenges Facing Chemistry and Chemical Processes" compiled by the United States. Know it, know how to use it. Distillation, as anyone who has studied chemistry must know, is a thermodynamic separation process. Expand the full text Distillation is a unit operation process that uses the different boiling points of each component in the mixed liquid or liquid-solid system to evaporate the low-boiling point component and then condense it to separate the whole component. It is a combination of evaporation and condensation. Membrane distillation system can be regarded as an effective combination of membrane technology and traditional distillation process. As far as the essence of the process is concerned, it is still an evaporation and condensation process. As far as MD technology is concerned, its driving force comes from the vapor pressure difference between the two sides of the membrane. The global membrane distillation technology really rose in the 1980s, while in China, in fact, since 2003, the number of domestic personnel engaged in related research and development work has increased year by year. It is not difficult to find that, in fact, in recent years, many membrane technologies have developed very fast in China, which of course also benefits from the promotion of market demand. There are many research and development teams of membrane distillation technology in China, but they mainly focus on scientific research, such as Tianjin Polytechnic University, Dalian University of Technology, Hebei University of Technology, Tongji University and Tsinghua University. In the membrane distillation system,wiped film distillation, the core is the membrane material. Membrane hydrophobicity and microporosity are the key factors for membrane material selection in membrane distillation, and mechanical strength, thermal conductivity and thermal stability are also the basic factors. At present, the main membrane materials used in membrane distillation are microporous polypropylene (PP), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), which have their own advantages and disadvantages. At present, there are few industrial application cases of membrane distillation in China, in which PTFE material is the main material,decarboxylation after extraction, and the equipment forms are mainly tubular, plate and hollow fiber. Among them, the tube type is used earlier in China, while the plate type should be used most at present. In the MD system, according to the different condensation modes on the downstream side of the membrane, the main types of membrane distillation processes are as follows: (1) direct contact membrane distillation (DCMD); (2) air gap membrane distillation (AGMD); (3) vacuum membrane distillation (also known as vacuum membrane distillation, VMD); and (4) swept membrane distillation. In the form of membrane distillation, the application of AGMD and VMD is relatively dominant, followed by DCMD, while the study of SGMD is less. MD System Strengths & Weaknesses Every membrane technology that exists certainly has its market position, and membrane distillation is no exception. According to the MD principle, in the salt concentration system, for example, from 1% to 10-20%, compared with other mature membrane processes such as ED and DTRO, membrane distillation does not have much advantage in terms of investment and operation cost, thin film distillation ,jacketed glass reactor, even if there is waste heat available in the plant area. For salt concentration of more than 20%, in fact, compared with evaporation, the investment cost per ton of water is 1 million. In addition, both of them are evaporating water in principle, but in fact, the evaporation system is relatively mature, the heat exchange and heat transfer effect is better, and its operation energy consumption is actually lower. Is MD technology really so weak? You can understand its characteristics first. MD is more specific to specific systems, such as: 1. Concentration system with special requirements for material , such as concentration of waste acid and waste alkali; 2. Concentration of certain organic products ；3. Some systems that cannot be directly concentrated by membrane ；4. Systems with specific requirements for concentration ；5. There is a lot of residual heat A system in which a low-grade heat source can be utilized. In many organic membrane systems, inorganic fouling, crystal precipitation, organic fouling and surfactant are important factors affecting the stable operation of the system, and these problems still exist in the membrane distillation system.
MD Technology-Domestic Application Although there are many research and development teams engaged in membrane distillation, there are very few enterprises engaged in membrane distillation industrialization in China. The successful application cases of membrane distillation are very limited, and the project system is generally relatively small, and the system above 100m3/d is basically a super-large system. On the basis of high process feasibility, investment cost and operation cost are often important factors affecting the landing of a project. In this respect, membrane distillation actually has disadvantages. Like tubular membrane distillation, the material is basically PTFE, the typical representative enterprise is Zhejiang Sennuo, and AGMD is generally used. They are more powerful in material research and development, but the application is actually less. In the past two years, their membrane distillation business has basically contracted. Like plate-type membrane distillation, the material is basically PTFE, the typical representative enterprise is Zhongke Ruisheng, and AGMD is generally used to reduce pressure and multi-effect. At present, it mainly relies on the MD technology of Memsys Group in Germany. In fact, they have done a good job in this area, and the promotion efforts are also strong. Like hollow fiber membrane distillation, the typical representative enterprise is middle ring membrane, but there is basically no industrial application at present. Where is the way for MD system? At present, it is not difficult to find in many industry conferences and seminars that, to some extent, membrane distillation technology has become a new hot spot in the fields of seawater desalination, concentration and separation, industrial wastewater treatment, crystallization and zero discharge. Despite this, membrane distillation does not seem to be favored by most people or the market. First, the cost of membrane materials is high, and the system investment is high. At present, it can only be applied to some specific demand systems. Second, the operating cost of the system is on the high side. Although waste heat, solar energy, geothermal energy and so on can be used, and the process can also be made into four-effect and five-effect, the operating cost is still a disadvantage. Thirdly, the inorganic fouling and organic pollution of the system still restrict the promotion of membrane distillation technology. In fact, many membrane technologies survive in the cracks. Although the application of membrane distillation technology is limited and there are some problems,wiped film distillation, driven by the large market demand, it still has a place in the membrane industry in the domestic environment. May you enjoy your life and be sincere and kind! / ———— Previous articles: 1. [Dry Goods] Electrodialysis (ED) Ionic Membrane Manufacturer Encyclopedia! 2. [Dry Goods] Bipolar Membrane Electrodialysis, Come and Learn! 3. [Dry Goods] Rare Earth Industry-Application of Membrane Treatment Technology! 4. [Dry Goods] New Energy Industry-Wastewater Treatment! 5. [Dry goods] Zero discharge of desulfurization wastewater-how to choose the process? 6. [Dry Goods] Landfill Leachate Industry-Secrets in DTRO Circle! 7. [Dry Goods] Bipolar Membrane Electrodialysis Technology Is Really Hot! 8. [Dry goods] The coolest electrodialysis equipment/project in the world! Return to Sohu to see more Responsible Editor:. toptiontech.com