Application of membrane materials and microfiltration technology

If the microfiltration membrane was produced from Bechhold's serial porous porous cotton membrane in 1907, it has a history of nearly 100 years. Microfiltration is a precision filtration technology. Microfiltration membrane separation technology began in the 19th century with the application of filter membrane materials and microfiltration technology.

1 Background: In recent years, with the development of biomaterials, microporous membranes have gradually replaced or upgraded many traditional filtration processes in its application process, becoming a modern industry, especially high-tech, sophisticated and cutting-edge technology industries. Such as electronics, bio-pharmaceuticals, scientific research and quality testing are one of the indispensable important means to ensure product quality. The challenges of modern biotechnology and the development of the pharmaceutical industry have accelerated the progress of membrane technology.

Objective: To summarize the separation principle, characteristics and types of microfiltration technology, introduce the research progress of membrane materials at home and abroad and their application in various fields.

Method: Retrieved by the first author in 2011-03. Retrieve Chinese Full-text Periodical Database (http://www.cnki.net/index.htm) and Pubmed Database (http://www.ncbi.nlm.nih.gov/sites/entrez/) 1994-01 / 2010-12 For articles on microfiltration technology and microfiltration materials, the search term is "microfiltration technology, microfiltration membrane, microporous filtration membrane", and the article language types are Chinese and English, excluding repetitive research. 60 articles were obtained during the initial computer inspection. The titles were read and screened, and 20 of them were summarized, including 19 in Chinese and 1 in English.

Results and conclusions: Microfiltration, also known as microporous filtration, is a kind of precision filtration, which can filter micrometer or nanometer particles and bacteria. The basic principle is the sieving process, which can be divided into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane according to the difference of membrane pore size (or trapped molecular mass). At present, the application research of membrane separation technology in various aspects is very active, but the membrane is fouled and blocked, and the viscosity of the raw material liquid is high, which attenuates the membrane flux seriously and cannot continue the separation, which affects the rapid application and development of membrane separation in actual operation.

To achieve the large-scale application of purification of biological products, it also depends on the development of related aspects, such as the study of membrane fouling mechanism, the study of excellent performance, anti-fouling membrane materials.

In the future, various types of membrane separation technologies will develop in synergy in the application of biochemical products, taking advantage of each other's weaknesses, combining ultrafiltration, nanofiltration, and microfiltration technologies, and implementing multi-stage separation is its development trend.

Xu Yafu, Zou Dajiang, Xiong Jun. Application of membrane materials and microfiltration technology. China Tissue Engineering Research and Clinical Rehabilitation, 2011, 15 (16): 2949-2952. In the middle of the period, using the static pressure difference as the driving force, the "meshing" of the mesh filter media membrane was used to separate the membrane process. Its main function is to remove (retain) femurs, bacteria and solid materials from gas or liquid substances to achieve purification, separation and concentration.

Gannan Medical College, Asset Management Department, School of Information Engineering, Ganzhou, Jiangxi Province, Xu Yafu, male, born in 1958, born in Shantou, Guangdong Province, graduated from Jiangxi Radio and TV University in 2007, experimenter, mainly engaged in biological materials, experimental materials, instruments and equipment Research on maintenance and other aspects.

The membrane that performs microfiltration is called a microfiltration membrane. The microfiltration membrane is a uniform porous membrane with a thickness of 90150pm, a filtration particle size of 0.025 10) m, and an operating pressure of 0.010.2MPa. The main technical advantages of the microfiltration membrane are: uniform membrane pore size, high filtration accuracy, fast filtration speed, The adsorption amount is small, and there is no medium falling off. It is mainly used in food and beverage, medicine and health, electronics, chemical industry, environmental monitoring and other fields, such as the detection and analysis of water and air by scientific research and environmental protection departments, air and pure water purification in the electronics industry, manufacturing of edible pure water in the food industry, medicine and Sterilization and particle removal of water for the pharmaceutical industry. This article mainly summarizes the separation principle, characteristics and types of microfiltration technology, introduces the research progress of membrane materials at home and abroad and its application in various fields. 1 Data and method Source: Retrieved by the first author in 2011-03. The language of the retrieved articles is Chinese and English.

Inclusion criteria: articles related to microfiltration technology and microfiltration materials.

Exclusion criteria: exclude repetitive studies.

Data extraction: 60 articles were obtained from the initial computer inspection. The title was read and the initial screening was conducted to eliminate repetitive research. 20 of them were summarized, including 19 in Chinese and 1 in English.

2 results

2.1 Separation mechanism of microfiltration technology Membrane separation technology is a separation method that uses a membrane with selective permeability as the separation medium and uses a semi-permeable membrane. At normal temperature, there is a certain driving force on both sides of the membrane (such as pressure difference, Concentration difference, potential difference, etc.) Separation, concentration and purification of solute and solvent. Membrane separation technology mainly uses natural or synthetic polymer membranes. The materials are passed or trapped according to the size of the filter pore size. The external energy or chemical potential difference is used as the driving force for the two-component or multi-component fluids and solvents. Separation, classification, purification and enrichment operations. Reverse osmosis, nanofiltration, ultrafiltration, microporous filtration, dialysis electrodialysis, gas separation, pervaporation, controlled release, liquid membrane, membrane distillation membrane reactor and other technologies have been applied.

There are three types of microfiltration filtration principles: sieving, filter cake layer filtration, and deep filtration. The separation mechanism of the microfiltration membrane is very complicated, and there are many influencing factors. Based on the research that has been carried out, the separation mechanism of the microfiltration membrane is the sieve separation process, and the physical structure of the membrane plays a decisive role in the separation. In addition, factors such as adsorption, chemical properties and electrical properties of the membrane surface also have an effect on the separation.

2.2 Separation characteristics of microfiltration technology Membrane separation technology has the following characteristics: ① No phase change occurs in the membrane separation process, so membrane separation technology is an energy-saving technology. ②The membrane separation process is driven by pressure and separated at room temperature. It is especially suitable for the separation, concentration and purification of heat-sensitive substances such as enzymes, juices and certain drugs. ③ The membrane separation technology is suitable for a wide range of separation, from micro-particle level to microbial cells, even ion level has its place. The key is to choose different membrane types. ④The membrane separation technology uses the pressure difference as the driving force, so the device is simple and easy to operate.

2.3 Types of membrane materials and research progress Membranes can be divided into symmetric membranes and asymmetric membranes in terms of structure; according to different materials, they can be divided into inorganic membranes and organic membranes; depending on the membrane pore size (or molecular mass retained), Can be divided into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane, reverse osmosis membrane. Microfiltration membranes are mainly used to retain suspended solids and bacteria, ultrafiltration membranes are mainly used to retain macromolecular organics, proteins, peptides, etc. Nanofiltration membranes are mainly used to retain small molecule organics, dyes, heavy metal ions, etc. Reverse osmosis membranes are mainly used To retain inorganic salts such as sodium chloride. At present, the membrane separation technologies that have been developed in the pharmaceutical industry mainly include microfiltration, ultrafiltration, nanofiltration and reverse osmosis.

Microfiltration, ultrafiltration, nanofiltration and reverse osmosis membranes have basically the same permeation mechanism. They are all driven by the pressure difference. When there is a certain pressure difference on both sides of the membrane, a part of the solvent and less than the membrane can be used. The components of the pore size pass through the membrane, while particles, macromolecules, salts, etc. are trapped by the membrane to achieve the purpose of separation.

The difference lies mainly in the size of the particles or molecules of the separated material and the structure and performance of the membrane used. Microfiltration, ultrafiltration, nanofiltration, and reverse osmosis have their own characteristics, so each has its own specific occasion. Microfiltration can be used alone for sterilization, particle removal, or as a pretreatment for other membrane processes; ultrafiltration is mainly used to trap and concentrate large molecules including viruses, pyrogens, proteins, gelatin, etc. Microfiltration is used for pretreatment; nanofiltration and reverse osmosis are mainly used to treat molecular-level substances, but microfiltration is also required for pretreatment before the reverse osmosis process to ensure the life of the membrane. In the modern research of traditional Chinese medicine, microfiltration and ultrafiltration technology are applied more, especially ultrafiltration technology, and in recent years, the combined use of ultrafiltration technology and other separation technologies (such as macroporous adsorption resin) has become more and more extensive. be utilized.

2.3.1 Application of microfiltration membrane Microfiltration membrane is an important part of membrane separation technology, mainly based on the principle of screening. Microfiltration is between conventional filtration and ultrafiltration. It usually traps particles with a particle size greater than 0.05pm. Symmetric microporous membranes are mostly used. The pore size of the membrane is 0.15pm. It is mainly used for the clarification of chemical solutions to achieve solid particles and strands. Separation of body particles and water-soluble components, often used for pretreatment of ultrafiltration. There are two types of microfiltration membrane materials: organic materials and inorganic materials. Organic materials include cellulose esters, polyaluminum, polypropylene, etc. Inorganic materials include metals, ceramics, metal oxides, glass, zeolite, etc. Compared with organic membranes, inorganic membranes have the advantages of stable chemical properties, high temperature resistance, strong pollution resistance, easy cleaning, and high mechanical strength. They have developed rapidly in recent years.

2.3.2 Application of ultrafiltration membranes Ultrafiltration membranes are asymmetric porous membranes with a pore size of 250nm. Polymer membranes are used to select permeability. At room temperature, a certain pressure difference and flow rate are used to allow low molecular weight substances smaller than the membrane pore size to penetrate The polymer material is trapped by the membrane. Has developed various ultrafiltration membranes with different molecular interception (M "101.0 million"), which can select the membrane pore size according to the size of the molecule, and the fermentation broth can intercept the macromolecular substances such as viruses, proteins, enzymes, polysaccharides, etc. to purify the target product Compared with the traditional method, no phase change occurs in the ultrafiltration process, and the mild operating conditions are conducive to maintaining the physiological activity of the biologically active components, reducing environmental pollution, shortening the production cycle, and improving the separation efficiency.

2.3.3 Application of Nanofiltration Membrane Nanofiltration membrane is a new type of liquid separation membrane that came out in the late 1980s. The average pore diameter is about 2nm. It has two significant characteristics: ① Its relative molecular mass is between the reverse osmosis membrane and the ultrafiltration membrane. Between the filter membranes, it is 2002000. ② The nanofiltration membrane has a certain rejection rate for inorganic salts because its surface separation layer is composed of polyelectrolyte. According to the first feature, it is speculated that the nanofiltration membrane may have a microporous structure with a pore size of about 1 nm, so it is called "nanofiltration". The nanofiltration membrane concentrates the target product because the molecular weight cutoff is between ultrafiltration and reverse osmosis. Function, due to its low operating pressure, different selectivity for mono- and divalent ions, and high retention of small molecular organics, plus the negative surface of the membrane, anti-scale pollution, rapid development; and has no The characteristics that affect the biological activity of the separated substances, energy saving, and pollution-free are more and more widely used in various separation, purification, and concentration processes in the pharmaceutical industry.

2.3.4 Application of reverse osmosis membrane The basic principle of reverse osmosis separation is the dissolution-diffusion theory, which is mainly used in the concentration of small molecule organic matter, only allowing solvent molecules to pass through, and small molecules such as salts and amino acids are retained. Reverse osmosis uses the semi-permeable membrane to trap the solute in the solution. Under the driving force of the pressure difference higher than the osmotic pressure of the solution, the solvent permeates the semi-permeable membrane to achieve the purpose of desalting the solution. The surface layer of the reverse osmosis membrane has a very thin dense layer (0.11.0pm), that is, a desalination layer or active layer. At the bottom of the surface layer is a porous support layer with a thickness of 100 ~ 200pm. The active layer basically determines the separation performance and support of the membrane. The layer only acts as a carrier for the active layer and does not substantially affect the separation performance of the membrane. Reverse osmosis membranes are mainly used for the concentration of drug solutions in terms of drug separation. Zhang Zhiguo et al. Used the NFB38-2 reverse osmosis device to concentrate streptomycin in the production process of streptomycin in Jining Antibiotic Factory. Compared with the concentration of the rising membrane decompression evaporator, the quality and yield of streptomycin have improved. And save a lot of energy consumption. The traditional extraction method of ephedrine is derived from the traditional Chinese medicine ephedra with benzene. The process is complicated and causes benzene pollution. Zhai Jianwen et al. Conducted a systematic study on the reverse osmosis separation characteristics of ephedrine, and proposed the principle and basic data of the introduction of reverse osmosis concentration process in production.

2.3.5 Integrated and combined technology Membrane technology and other technologies are integrated and used to give full play to their respective advantages. This will be an important direction for the research and development of new technologies in the 21st century. Gao Hongning et al. Studied the combined use of microfiltration and macroporous adsorption resin in the combined extraction of total flavonoids in the aqueous extract of Sophora flavescens, and compared it with the results of the combination of alcohol precipitation and macroporous adsorption resin. The results show that the adsorption rate and removal effect of total flavonoids in the aqueous extract of Sophora flavescens treated with microfiltration macroporous adsorption resin method is better than that of alcohol precipitation macroporous adsorption resin method, and the process is simple and the production cycle is short, which can be effective Remove impurities from the ground and retain the active ingredients.

2.3.6 Application of molecularly imprinted composite membranes Molecularly imprinted membranes have the characteristics of both molecular imprinting and membrane technology. The principle is to add imprinted molecules to the polymerization medium. After the film is formed, the imprinted molecules are removed and will remain in the polymer network structure. The functional size of the lower imprinted molecules and the interaction between the polymer and the imprinted molecules. When the separation membrane is used to separate the mixture of imprinted molecules and other substances, the separation membrane can recognize the imprinted molecules, thereby effectively The mixture is separated. Molecularly imprinted composite membranes are coated with molecularly imprinted polymers on the surface of porous support membranes, with ultrafiltration or microfiltration support layers, which can obtain large flux and high selectivity, which is the focus of research and attention in recent years.

2.3.7 Membrane distillation technology Membrane distillation is a membrane separation process that uses a hydrophobic microporous membrane with the vapor pressure difference between the two sides of the membrane as the driving force for mass transfer. For example, when aqueous solutions at different temperatures are separated by a hydrophobic microporous membrane, due to The hydrophobicity of the membrane, the aqueous solution on both sides can not penetrate the membrane pores into the other side, but because the water vapor pressure at the interface between the warm side aqueous solution and the membrane is higher than the cold side, the water vapor will enter the cold from the warm side through the membrane pores Condensation on the side, which is very similar to the evaporation, mass transfer and condensation processes in conventional distillation, so it is called the membrane distillation process.

2.4 Application status of microfiltration technology 2.4.1 Preparation of biochemical products Domestic vitamins and enzyme preparations have achieved industrial production. The relative molecular mass of the protein in vitamins and fermentation broth is generally 10000100000, and an ultrafiltration membrane that retains the relative molecular mass can be selected to remove large molecular impurities such as protein. Li Chunyan and others chose the ultrafiltration membrane system and the membrane with a relative molecular weight of 30,000 to process the original fermentation broth of vitamins. The filtrate has good quality and high throughput, and simplifies the process and improves the yield. The relative molecular weight of the enzyme preparation is 10000100000, which is a special protein with high catalytic activity, which falls within the cutting range of ultrafiltration.

Ding Fengping uses ultrafiltration flat membrane modules with a relative molecular weight of 5000 and 10000 to concentrate and recover directly from the fermentation broth with the bacterial cells removed. The concentration rate is less than 20 times and a high recovery rate of 98.3% is obtained, which has application value. Ultrafiltration is also used in the separation, concentration, dealcoholization and endotoxin removal of plasma proteins. Liu Ting et al. Conducted animal experiments with polyethersulfone hollow fiber ultrafiltration membrane plasma apparatus for plasma separation. The results show that the membrane plasma separator has wide application area, simple device, low energy consumption, and can be separated at room temperature. At present, the biocompatibility of the existing membrane materials can not meet the clinical requirements. If it is to be applied in medicine, it is necessary to develop membrane materials with good separation and excellent compatibility.

In the field of biochemistry, microfiltration is mainly used as a pretreatment method and is used in conjunction with other technologies. Some scholars have combined the use of microfiltration, flocculation and centrifugation technology to recover the biologically active substances in soybean whey. When the protein loss rate is only 10%, all suspended solids can be removed, and the fat removal rate reaches 90%. 2.4.2 With the continuous development of genetic engineering technology, the separation and purification of microbial drugs produced by fermentation are facing a series of new problems, such as low content, high activity, easy inactivation, and low extraction yield.

As a new type of separation technology, membrane separation technology.