There are many types of activated alumina catalysts in exhaust gas treatment, and the classification methods are also different. According to the big aspects, it can be divided into acid-base catalysts, metal catalysts, semiconductor catalysts and molecular sieve catalysts. Their common feature is that they can produce different degrees of chemical adsorption on reactants. Therefore, catalysis is inseparable from adsorption, and the general catalytic process starts with adsorption. 1. Acid-base catalysts referred to here are acids and bases in a broad sense, that is, Lewis acids and Lewis bases. Both of them can provide acid-base active adsorption centers for chemisorption of reactants, thereby promoting chemical reactions. Such as activated clay, aluminum silicate, aluminum oxide and oxides of some metals, especially oxides of transition metals or their salts. 2. Metal catalyst Metal adsorption capacity depends on the molecular structure and adsorption conditions of the metal and gas. It was found through experiments that metal elements with d-electron empty orbits have different chemical adsorption capacities for some representative gases. Except for Ca, Sr, and Ba, most of these metals are transition metals. They rely on electrons or unbound electrons that do not participate in the hybrid orbitals of the metal bond to form adsorption bonds with the adsorbent molecules, which catalyzes the interaction between them Reaction. 3. Semiconductor catalysts are mainly some semiconductor-type transition metal oxides. They are divided into n-type semiconductors and p-type semiconductors in order to provide quasi-free electrons or quasi-free holes. The n-type semiconductor catalyst relies on its quasi-free electrons to form adsorption bonds with the reactants; the p-type semiconductor catalyst relies on its quasi-free holes to form adsorption bonds with the reactants. Due to the formation of adsorption bonds, the conductivity of the semiconductor is changed, which is one of the main factors affecting the activity of the catalyst. In fact, the formation of adsorption bonds between gas molecules and semiconductor catalysts is a very complicated process. In the study of the catalytic mechanism of semiconductors, it was also found that the energy bands due to electronic transitions play an important role in the formation of adsorption bonds. effect. Therefore, it cannot be simply assumed that a reactant molecule capable of donating an electron can only form an adsorption bond with a p-type semiconductor catalyst. 4. Zeolite molecular sieve catalyst is widely used as an adsorbent in drying, purification, separation and other processes. It began to make its appearance in the application of catalysts and catalyst carriers in the 1960s. Zeolite refers to the natural crystalline aluminosilicate, which has the same diameter micropores, so it is also called molecular sieve. At present, there are more than hundreds of species, and many important industrial catalytic reactions are inseparable from molecular sieve catalysts. The catalysis of molecular sieve also relies on acidic centers on its surface to form adsorption bonds. However, it is more selective than acid-base catalysts because it can reject molecules with a larger pore size from entering the inner surface. At the same time, the acidity and alkalinity on the surface of the molecular sieve can also be adjusted artificially by means of ion exchange, which has better performance than ordinary acid-base catalysts. In recent years, a kind of non-silicon-aluminum-based synthetic molecular sieve has been developed and has been widely used in the field of catalysis. It can be seen that molecular sieve has its special status and role in the field of catalysis.
Carbon molecular sieve is a new type of adsorbent developed in the 1970s. It is an excellent non-polar carbon material. It is mainly used to separate nitrogen from the air and enrich it with nitrogen. It is currently the first choice of PSA nitrogen generator in the engineering industry. This nitrogen is used in chemical industry, oil and gas industry, electronics industry, food industry, coal industry, pharmaceutical industry, cable industry, metal heat treatment, transportation and storage Widely used. Carbon molecular sieve uses the characteristics of sieving to achieve the purpose of separating oxygen and nitrogen. When the molecular sieve adsorbs impurity gases, the macropores and mesopores only serve as channels, and the adsorbed molecules are transported to the micropores and submicropores. The micropores and submicropores are the volumes that really play the role of adsorption. Due to differences in the relative diffusion rates of gas molecules of different sizes, the components of the gas mixture can be effectively separated. Therefore, when manufacturing a carbon molecular sieve, the micropore distribution inside the carbon molecular sieve should be 0.28 to 0.38 nm according to the size of the molecule. Within this micropore size range, oxygen can quickly diffuse into the pores through the micropore pores, but nitrogen can hardly pass through the micropore pores, thereby achieving oxygen and nitrogen separation. German BF molecular sieve, Japanese Takeda carbon molecular sieve, Japanese Iwatani molecular sieve, activated carbon for nitrogen generator, 13X molecular sieve, 5A molecular sieve, mainly used in pressure swing adsorption nitrogen production equipment. Molecular sieve is a new type of non-polar adsorbent, which has the property of adsorbing oxygen molecules in the air at normal temperature and pressure, so it can obtain nitrogen-rich gas. Maintenance method of nitrogen generator 1. The air outlet of the air storage tank is equipped with a timed drain to reduce the load pressure of the process. 2. The normal use of the equipment should pay attention to check whether each timing drain is draining normally, whether the air pressure meets above 0.6Mpa, and comparing the inlet and outlet of the cold and dry machine, whether there is a cooling effect. 3. The air filter must be changed at a frequency of 4,000 hours. 4. Activated carbon filter can effectively filter oil stains and prolong the service life of high-quality carbon molecular sieve. Activated carbon needs to be replaced every 3000 hours or 4 months. 5. Nitrogen generator pneumatic valve, solenoid valve is recommended for each model of the action components to prevent future problems. Activated carbon and carbon molecular sieve replacement steps: simply clean the site, cut off gas and power, two people remove the head of the adsorption tower, two people remove all the pipes of the nitrogen generator, remove the waste in the adsorption tower, you need to clean it, check the top of the adsorption tower And the bottom part of the flow plate is damaged, and the damage is repaired in time. All pipelines should be cleaned with compressed air, the pneumatic valve should be inspected for damage to the seal ring, and the pneumatic valve needs to be replaced seriously.
Air is the "life gas" that we breathe every day. Its main components are nitrogen and oxygen. Calculated by volume fraction, nitrogen is about 78% and oxygen is about 21%. The other 1% air composition includes rare gases such as helium, neon, argon, krypton, xenon, krypton, etc., with a volume fraction of about 0.934%, about 0.034% of carbon dioxide, about 0.002% of water vapor, impurities and other substances. Although these gases are transparent, colorless and odorless and cannot be easily noticed, they have an important impact on the survival and production of us humans. For example: Oxygen is a breathing organism that supports humans and all animals on the planet. People's industrial production: iron and steel making, ammonia synthesis, rocket combustion, etc. require a large amount of oxygen, but they are directly extracted from the air during production. ; The respiration of green plants also requires oxygen. Although nitrogen contains more than oxygen in the atmosphere, but because it is an inert gas, its nature is not active, and it is often used as a protective gas, such as: fruit, food, bulb filling gas. In order to prevent certain objects from being oxidized by oxygen when exposed to air, filling grain silos with nitrogen can keep the grains from mildew and germination, and keep them for a long time. With the rapid development of industry, nitrogen has been widely used in chemical, electronics, metallurgy, food, machinery and other fields. The demand for nitrogen in China has increased at a rate of more than 8% each year. The chemical nature of nitrogen is inactive, and it is very inert under ordinary conditions, and it is not easy to chemically react with other substances. Therefore, nitrogen is widely used as a protective gas and a sealing gas in the metallurgical industry, the electronics industry, and the chemical industry. Generally, the purity of the protective gas is 99.99%, and some require high-purity nitrogen above 99.998%. However, pure nitrogen cannot be directly extracted from the natural world. Therefore, in order to improve the utilization rate of nitrogen in industrial production, the company mainly uses air separation. The air separation method includes a cryogenic method, a pressure swing adsorption method, and a membrane separation method. The following is a brief introduction to the relevant application of the oxygen analyzer in the PSA nitrogen generator. Principle of PSA nitrogen generator PSA is a new gas separation technology. Its principle is to use the difference in the "adsorption" performance of molecular sieves to different gas molecules to separate gas mixtures. It uses air as the raw material and carbon molecular sieve as the adsorbent. The method of separating nitrogen and oxygen by the selective adsorption of oxygen and nitrogen by a carbon molecular sieve is commonly referred to as PSA nitrogen production. This technology has been rapidly developed abroad since the late 1960s and early 1970s. Features of PSA nitrogen generator 1. Low cost: The PSA process is a simple nitrogen production method. Nitrogen is produced within a few minutes after startup, and the energy consumption is low. The cost of nitrogen is much lower than the cryogenic air separation nitrogen production and liquid nitrogen on the market. 2. Reliable performance: imported microcomputer control, fully automatic operation, no operator who needs special training, just press the start switch, it can run automatically to achieve continuous gas supply. 3. High nitrogen purity: The instrument detects trace oxygen and trace water to ensure the required nitrogen purity, and the purity can reach 9999%. 4. Select high-quality imported molecular sieve: it has the characteristics of large adsorption capacity, strong pressure resistance and long service life. 5. High-quality control valves: High-quality imported special pneumatic valves can ensure the reliable operation of nitrogen-making equipment. Work flow of nitrogen generator. The work flow of the nitrogen generator is controlled by a programmable controller that controls three first conductive magnetic valves, and then the solenoid valves control the opening and closing of eight pneumatic pipeline valves. Three pre-conducting solenoid valves control the left suction, pressure equalization, and right row states, respectively. The time flow of left suction, equal pressure and right row has been stored in the programmable controller. When the process is in the left suction state, the solenoid valve that controls the left suction is energized, and the pilot air is connected to the left suction intake valve and the left suction gas valve. The right exhaust valve makes these three valves open to complete the left suction process, while the right suction tank desorbs. When the process is in the pressure equalization state, the solenoid valve that controls the pressure equalization is energized and the other valves are closed; the pilot air is connected to the upper pressure equalizing valve and the lower pressure equalizing valve, so that these two valves are opened to complete the pressure equalization process. From the principle of the PSA nitrogen generator above, we know that the adsorption tank of the PSA nitrogen generator, when the pressure is high, the carbon molecular sieve adsorbs oxygen in the air, and the nitrogen that is not easily adsorbed becomes the product; when the pressure is low, the oxygen Desorbed from the carbon molecular sieve. With the change in pressure, the required nitrogen can be effectively separated from the air. Among them, when testing the oxygen concentration in nitrogen, because most of them are trace levels, Industrial Mining Networks recommends a Southland oxygen analyzer-OMD-640. The OMD-640 oxygen analyzer combines a rugged and portable design, making the user interface easy to understand. At the same time, the design also makes the instrument more cost-effective and reduces maintenance costs. This is mainly reflected in the analyzer carrying an 8G removable USB A flash drive records data in a .csv (Excel) file format, and users have been using the instrument for approximately 50 years before running out of storage. OMD-640 oxygen analyzer has a full scale low range of 0-1ppm, lower measurement range and higher accuracy. The analyzer can see the screen clearly under direct sunlight without obstruction or other methods. On the other hand, the oxygen sensor used in OMD-640 is based on the principle of electrochemical fuel cells. All oxygen sensors are manufactured under strict quality inspection procedures. The standard sensor TO2-133 can work smoothly in inert gas, and can also choose the acid resistance TO2-233 sensor. In addition, the sensors are independent and require very little maintenance. There is no need to clean the electrodes or add electrolyte.
A psa nitrogen generator is a device that uses air as a raw material to separate nitrogen and oxygen from it to obtain nitrogen. According to different classification methods, namely cryogenic air separation method, molecular sieve air separation method and membrane air separation method, nitrogen generators applied in industry can be divided into three types. Nitrogen generator is a nitrogen equipment designed and manufactured according to pressure swing adsorption technology. The nitrogen generator uses high-quality imported carbon molecular sieve as the adsorbent, and uses the principle of pressure swing adsorption at normal temperature to separate the air to obtain high-purity nitrogen. Generally, two adsorption towers are used in parallel, and the imported PLC controls the imported pneumatic valve to automatically run, alternately pressurize adsorption and decompression regeneration, complete nitrogen and oxygen separation, and obtain the required high purity nitrogen. Cryogenic Separation of Nitrogen Cryogenic nitrogen separation is a traditional method of nitrogen production, which has been used for decades. It uses air as a raw material, which is compressed and purified, and then the heat is exchanged to liquefy the air into a liquid air. Liquid air is mainly a mixture of liquid oxygen and liquid nitrogen. The difference between the boiling points of liquid oxygen and liquid nitrogen is used to obtain nitrogen by rectification of liquid air to separate them. Cryogenic air separation nitrogen production equipment is complex, covers a large area, has high capital construction costs, a large one-time investment in equipment, high operating costs, slow gas production, high installation requirements and long cycles. Comprehensive equipment, installation and infrastructure factors. For equipment below 3500Nm3 / h, the investment scale of PSA units of the same specifications is 20% -50% lower than that of cryogenic air separation units. Nitrogen generator molecular sieve Air is used as the raw material, carbon molecular sieve is used as the adsorbent, and the method of pressure swing adsorption is used to separate nitrogen and oxygen by the selective adsorption of oxygen and nitrogen by carbon molecular sieve. This method is a new nitrogen production technology developed rapidly in the 1970s. Compared with the traditional nitrogen production method, molecular sieve air separation nitrogen production of nitrogen generator has simple process, high degree of automation, fast gas production, and low energy consumption. The purity of the product can be adjusted within a wide range according to user needs, and is easy to operate and maintain. Low operating cost and strong adaptability. Therefore, in the nitrogen production equipment below 1000Nm3 / h, it is quite competitive, and it is more and more popular with small and medium nitrogen users. PSA nitrogen production has become the preferred method for small and medium nitrogen users.