What Is Activated Alumina?
Activated alumina, also known as activated alumina, the English name is Activated alumina. The use of alumina in catalysts is commonly referred to as "active alumina". It is a porous, highly dispersed solid material with a large surface area. Its microporous surface has the characteristics required for catalytic action, such as Adsorption performance, surface activity, excellent thermal stability, etc., are widely used as catalysts and catalyst supports for chemical reactions. Spherical activated alumina pressure swing oil adsorbent is white spherical porous particles. The size of activated alumina is uniform, the surface is smooth, the mechanical strength is strong, and the hygroscopicity is strong. It does not swell or crack after water absorption, and remains intact, non-toxic, odorless, and insoluble. Water, ethanol. Activated alumina is a highly efficient desiccant for deep drying of trace amounts of water. It is suitable for non-thermal regeneration devices.
- Alumina, commonly known as
- Activated alumina belongs to the category of chemical alumina, which is mainly used in adsorbents, water purification agents, catalysts and catalyst supports. Activated alumina has the ability to selectively adsorb moisture from gases, water vapor and certain liquids. After adsorption saturation, it can be revived by heating to remove water at about 175-315 ° C. Adsorption and resuscitation can be performed multiple times. In addition to being used as a desiccant, it can also absorb the vapor of lubricating oil from polluted oxygen, hydrogen, carbon dioxide, natural gas, etc. And can be used as a catalyst and catalyst carrier and chromatography analysis carrier. Can be used as defluorinating agent for high-fluorine drinking water (large defluorination capacity), defluorinating agent for circulating alkanes in alkylbenzene production, deacidifying regeneration agent for transformer oil, used as gas drying in oxygen industry, textile industry, electronics industry Automatic instrument air drying and desiccant and purifying agent (dew point up to -40 ) in chemical fertilizer, petrochemical drying and other industries, and pressure swing adsorption dew point in air separation industry can reach -55 . It is a highly effective desiccant for deep drying of trace amounts of water. Ideal for non-thermal regeneration installations. [1]
- There are two kinds of raw materials for the production of activated alumina, one is "quick powder" produced by gibbsite or bayerite, and the other is pseudo-boehmite produced by aluminate or aluminum salt or both. .
- Standard of the Ministry of Chemical Industry of the People's Republic of China: HG / T 3927-2007
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- (1) Particle size: The smaller the particle size, the higher the adsorption capacity, but the smaller the particle size, the lower the particle strength, which affects its service life.
- (2) pH value of raw water: When the pH value is greater than 5, the lower the pH value, the higher the adsorption capacity of the activated alumina.
- (3) Initial fluorine concentration in raw water: The higher the initial fluorine concentration, the larger the adsorption capacity.
- (4) Raw water alkalinity: The concentration of bicarbonate in raw water is high, and the adsorption capacity will decrease.
- (5) chloride and sulfate ions.
- (6) Effect of arsenic: Activated alumina has an adsorption effect on arsenic in water. The accumulation of arsenic on activated alumina causes a decrease in the adsorption capacity of fluoride ions, and makes it difficult to elute arsenic ions during regeneration. [3]
- Activated alumina (molecular formula Al 2 O 3-x (OH) 2x , 0 <x <0.8) is currently used in large quantities in the world
Application of activated alumina in the field of adsorption and catalysis
- Activated alumina has a large specific surface area, various pore structures and pore size distributions, and rich surface properties. Therefore, it has a wide range of uses in adsorbents, catalysts, and catalyst supports.
- Alumina for adsorbent and catalyst carrier is a fine chemical and a special chemical. Different applications have different requirements for the physical structure, which is why it is highly specialized and has many varieties and brands. According to statistics, the amount of alumina used as a catalyst and a support is more than the total amount of catalysts of molecular sieve, silica gel, activated carbon, diatomaceous earth, and silica-alumina gel. This shows that alumina plays an important role in the catalyst and support. Among them, -Al 2 O 3 and -Al 2 O 3 are the most important catalysts and supports. They are both spinel structures with defects. The difference between the two is that the crystal structure of the tetrahedron is different (> ), The stacking regularity of the hexagonal layer is different (> ) and the AlO bond distance is different (> , the difference is 0.05-0.1nm).
Application of activated alumina as adsorbent
- The main industrial applications of activated alumina as adsorbents include gas drying, liquid drying, water purification, selective adsorption in the petroleum industry, and chromatographic separation processes.
- Because activated alumina has a strong affinity for water, it has been widely used in gas drying. The gases that can be dried with activated alumina are: acetylene, cracked gas, coke oven gas, hydrogen, oxygen, air, ethane, hydrogen chloride, propane, ammonia, ethylene, hydrogen sulfide, propylene, argon, methane, sulfur dioxide, Carbon dioxide, natural gas, helium, nitrogen, chlorine, etc. Because activated alumina emits a large amount of heat when it adsorbs water, it should be designed in a comprehensive manner in terms of drying capacity, drying speed, heat exchange and regeneration methods.
- The liquids that can be dried by activated alumina are mainly aromatic hydrocarbons, high molecular olefins, gasoline, kerosene, cyclohexane, propylene, butene, and many halogenated hydrocarbons. When these liquids are in contact with alumina, the two do not react or polymerize. At the same time, the dried liquid does not contain components that are easily adsorbed on the alumina surface and are not easily removed during regeneration.
- In terms of water purification, in addition to mainly removing fluoride in drinking water, activated alumina is also effective in eliminating the color and odor of industrial wastewater. In addition, activated alumina is also widely used in the recovery of carbohydrates and selective adsorption and the maintenance of power system oils.
Application of activated alumina as catalyst and support
- The alumina used as a catalyst support can be summarized into the following types according to its physical and chemical properties and the role played by alumina:
- (1) High temperature alumina carrier. This type of alumina has a small specific surface area, high temperature resistance, chemical resistance, and high mechanical strength, so it can withstand harsh operating conditions. Due to the inertness of alumina, the high-temperature alumina support will not become a potential source of activity causing side reactions and selectivity degradation, nor will it become a potential source of poison for the catalyst system.
- (2) Interactive carriers. This type of alumina is the most widely used. It can react with the active component of the catalyst to disperse the active component of the catalyst into the support, provide an effective specific surface area and a suitable pore structure for the active component to improve the thermal stability of the catalyst And anti-toxic performance.
- (3) Play a synergistic or dual function carrier. In addition to serving as the backbone of the active component, this type of alumina also provides a gain effect for the catalytic effect of the catalyst. [4]