What is activated alumina and its applications?
一、What is activated alumina?
Activated alumina, also known as activated bauxite, is a porous and highly dispersed solid material with a large surface area. Its microporous surface possesses the characteristics required for catalysis, such as adsorption capacity, surface activity, and excellent thermal stability. Therefore, it is widely used as a catalyst and catalyst carrier in chemical reactions. Spherical activated alumina pressure swing adsorbent is a white spherical porous particle. Activated alumina has uniform particle size, smooth surface, high mechanical strength, strong moisture absorption, and does not expand or crack after absorbing water, maintaining its original shape. It is non-toxic, odorless, insoluble in water and ethanol. Activated alumina is an efficient desiccant for deep drying of trace water and is suitable for use in non-thermal regeneration devices.
Activated alumina falls within the category of chemical alumina and is mainly used as an adsorbent, water purifier, catalyst and catalyst carrier. Activated alumina has the ability to selectively adsorb moisture from gases, water vapor and certain liquids. Once saturated, it can be regenerated by heating at approximately 175 to 315 ℃ to remove the water. This adsorption and regeneration process can be repeated multiple times. Besides being used as a desiccant, it can also adsorb the vapor of lubricating oil from contaminated oxygen, hydrogen, carbon dioxide, natural gas, etc. It can also be used as a catalyst and catalyst carrier, as well as a chromatographic analysis carrier. It can be used as a defluoridation agent for high-fluoride drinking water (with a large defluoridation capacity), a defluoridation agent for recycled alkanes in alkylbenzene production, a deacidification and regeneration agent for transformer oil, and as a gas dryer in the oxygen production industry, textile industry, electronic industry, and for drying instrument air. It is also used as a desiccant and purifier in the fertilizer and petrochemical drying industries (with a dew point of -40 ℃), and in the air separation industry, the dew point can reach -55 ℃ through pressure swing adsorption.
二、Applications of Activated Alumina in 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 extensive applications in adsorbents, catalysts and catalyst carriers.
Alumina used as an adsorbent and catalyst carrier is a fine chemical and a specialty chemical. Different applications have different requirements for physical and chemical properties and structures, which is why it has strong specialization and many varieties and grades. According to statistics, the amount of alumina used as catalysts and carriers is more than the total amount of catalysts and carriers made of molecular sieves, silica gel, activated carbon, diatomite and silica-alumina gel. This shows the significant position of alumina in catalysts and carriers.
Applications of Activated Alumina as an Adsorbent
The main industrial applications of activated alumina as an adsorbent include gas drying, liquid drying, water purification, selective adsorption in the petroleum industry, and chromatographic separation processes.
Due to its strong affinity for water, activated alumina is widely used in gas drying. The gases that can be dried by activated alumina mainly include: acetylene, cracking 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 releases a large amount of heat when adsorbing water, the design should take into account the drying capacity, drying speed, heat exchange and regeneration methods, etc.
The liquids that can be dried by activated alumina mainly include: aromatic hydrocarbons, high-molecular olefins, gasoline, kerosene, cyclohexane, propylene, butene, and many halogenated hydrocarbons, etc. When these liquids come into contact with alumina, no reaction or polymerization occurs between them, and the dried liquids do not contain components that are easily adsorbed on the surface of alumina and difficult to remove during regeneration.
In water purification, activated alumina is mainly used to remove fluoride from drinking water, and it is also very effective in eliminating the color and odor of industrial wastewater. In addition, activated alumina is widely used in the recovery of carbohydrates, selective adsorption, and the maintenance of power system oil.
Applications of Activated Alumina as a Catalyst and Carrier
Alumina used as a catalyst carrier can be classified into the following types based on its physical and chemical properties and the role it plays:
(1) High-temperature alumina carriers. This type of alumina has a very small specific surface area, but it has high-temperature resistance, chemical resistance, and high mechanical strength, so it can withstand harsh operating conditions. Due to the inertness of alumina, high-temperature alumina carriers will not become a potential source of side reactions and decreased selectivity, nor will they become a potential source of poisoning for the catalyst system.
(2) Interactive carriers. This type of alumina is the most widely used. It can react with the active components of the catalyst, allowing the active components to disperse into the carrier, providing an effective specific surface area and appropriate pore structure for the active components, thereby enhancing the thermal stability and anti-poisoning performance of the catalyst. (3) Synergistic or bifunctional carrier. In addition to serving as the framework for the active components, this type of alumina also provides an enhancing effect for the catalytic performance of the catalyst.
