What are the advantages and disadvantages of membrane separation technology?

Membrane is a kind of material with selective separation function. Membrane selective separation refers to the process of separation, purification and concentration of different components in feed liquid. Different from traditional filtration, the membrane can be separated in the molecular range, which is a physical process without phase change and additives.

The pore size of the membrane is usually micron. According to the different pore size (or molecular weight cut-off), membranes can be divided into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane. According to different materials, it can be divided into inorganic membrane and organic membrane. Inorganic membranes are mainly ceramic membranes and metal membranes, which have low filtration accuracy and low selectivity. The organic membrane is made of polymer materials, such as cellulose acetate, aromatic polyamide, polyethersulfone, fluoropolymer, etc.

Microfiltration (MF), also known as microporous filtration, belongs to precision filtration, and its basic principle is screen separation process. The materials of microfiltration membrane can be divided into two categories: organic and inorganic. Organic polymers include cellulose acetate, polypropylene, polycarbonate, polysulfone, polyamide, etc. Inorganic membrane materials include ceramics and metals. In view of the separation characteristics of microporous membrane, the application scope of microporous membrane is mainly to intercept particles, bacteria and other pollutants from gas phase and liquid phase in order to achieve the purpose of purification, separation and concentration.

For microfiltration, the retention characteristics of the membrane are characterized by the pore size of the membrane, which is usually between 0. 1 ~ 1 micron, so the microfiltration membrane can separate large-diameter bacteria and suspended solids. It can be used for clarification, safe filtration and air sterilization of general feed liquid.

ultrafiltration

It is a membrane process between microfiltration and nanofiltration, and the pore size of the membrane is between 0.05um- 1nm. Ultrafiltration is a membrane separation technology, which can purify, separate and concentrate the solution. Ultrafiltration process can generally be understood as a screening process related to membrane pore size. With the pressure difference between the two sides of the membrane as the driving force and the ultrafiltration membrane as the filtering medium, under a certain pressure, when water flows over the membrane surface, only water and small molecular substances smaller than the pore size of the membrane are allowed to pass through, thus achieving the purpose of purifying, separating and concentrating the solution.

For ultrafiltration, the retention characteristics of membrane are characterized by the retention molecular weight of standard organic matter, which is generally between 1000 ~ 300000. Therefore, ultrafiltration membrane can separate macromolecular organics (such as protein, bacteria), colloids, suspended solids and so on. Widely used in the clarification of feed liquid, separation and purification of macromolecular organic matter and heat removal.

Nanofiltration

It is a membrane separation technology between ultrafiltration and reverse osmosis. Its cut-off molecular weight is in the range of 80 ~ 1000, and its pore size is several nanometers, so it is called nanofiltration. Based on the superior characteristics of nanofiltration separation technology, it shows broad application prospects in pharmaceutical, biochemical, food industry and many other fields.

For nanofiltration, the rejection rate of the membrane is 60% ~ 90% for standard NaCl, MgSO4 _ 4 and CaCl2 _ 2 solutions, and the corresponding molecular weight is 100 ~ 1000. Therefore, nanofiltration membrane can separate small molecular organic matter from water and inorganic salts, and realize desalination and concentration at the same time.

antiosmosis

It is a membrane process in which the reverse osmosis membrane can only penetrate the solvent (usually water) and intercept the selective permeability of ionic substances or small molecular substances, and the static pressure on both sides of the membrane is the driving force to separate the liquid mixture. Reverse osmosis is an important part of membrane separation technology, which has many advantages such as high water quality, low operating cost, no pollution, convenient operation and reliable operation. It has become the most energy-saving and simple technology for desalination of seawater and brackish water and preparation of pure water. It has been widely used in medicine, electronics, chemical industry, food, seawater desalination and many other industries. Reverse osmosis technology has become the first choice of modern industrial water treatment technology.

The interception target of reverse osmosis is all ions, and only water is allowed to pass through the membrane. The rejection rate of NaCl is above 98%, and the effluent is deionized water. Reverse osmosis can remove soluble metal salts, organic matter, bacteria, colloidal particles and exothermic substances, that is, it can intercept all ions. Reverse osmosis membrane has been widely used in the production of pure water, softened water and deionized water, product concentration and wastewater treatment, such as landfill leachate treatment.

The advantages of membrane separation technology can be summarized as follows:

(1) at room temperature.

Less loss of effective components, especially suitable for the separation and concentration of heat-sensitive substances, such as antibiotics and other drugs, fruit juice, enzymes, protein and so on.

(2) No phase change

The original flavor is maintained, the energy consumption is extremely low, and the cost is about 1/3- 1/8 of evaporation concentration or freeze concentration.

(3) there is no chemical change

In the typical physical separation process, chemical reagents and additives are not used, and the products are not polluted.

(4) Good selectivity

It can separate substances at the molecular level, and has excellent performance that ordinary filter materials can't replace.

(5) strong adaptability

The treatment scale can be large or small, can be carried out continuously or intermittently, and has the advantages of simple process, convenient operation and easy automation.

(6) Low energy consumption

Only need electric energy to drive, the energy consumption is extremely low, and its cost is about 1/3- 1/8 of evaporation concentration or freezing concentration.

Disadvantages:

All technologies are not omnipotent, and membrane technology is not suitable for any occasion, nor can a single membrane technology solve all problems. For example, although the membrane technology has low concentration cost, it can't concentrate the product into dry matter; Another example is that although membrane technology has selective filtration, isomers cannot be separated. Therefore, in the process of designing production technology, it is necessary to combine the actual situation with the traditional technology, and the appropriate technology is in the right place to make the production technology smoother. The ultimate goal is smooth process flow, lowest energy consumption, least labor, least land occupation and best economy.