Membrane PSA: [Weekly Topic] {June 27, 2011} Let’s discuss issues related to adsorbents

2. Introduction to adsorbents ① Types of adsorbents: Commonly used adsorbents in industry include silica gel, activated alumina, activated carbon, molecular sieves, etc.; in addition, there are also adsorption materials developed for the selective adsorption of specific components. A. Silica gel: Silica gel adsorbents are a type of synthetic amorphous silica; they consist of a rigid, continuous network of spherical particles of colloidal silica. They are generally prepared by mixing sodium silicate solution with inorganic acids. Silica gel not only has a strong affinity for water but also exhibits a high adsorption capacity for hydrocarbons and components such as CO2. B. Activated alumina: Activated alumina is a type of solid with a strong affinity for water; it is produced by heating and dehydrating aluminum hydrates. Its properties depend on the structural state of the initial hydroxide, and it is generally not pure Al2O3, but rather a partially hydrated, amorphous porous material that contains both amorphous gels and crystals of hydroxides. Due to the high activity of its pore channel surface, it is also known as activated alumina. It is mainly used for drying gases. C. Activated carbon: It is produced by carbonizing and activating carbon-containing materials such as charcoal, fruit shells, and coal. Activation methods can be divided into two main categories: chemical activation and gas activation. The chemical activation method involves adding chemicals such as zinc chloride and potassium sulfide to the raw material, followed by heating in a non-reactive atmosphere to carry out carbonization and activation. The gas activation method involves heating the activated carbon precursor in an inert atmosphere; after removing volatile components, usually at temperatures below 700°C, water vapor, carbon dioxide, flue gas, air, etc., are introduced, and a reaction is carried out at temperatures ranging from 700 to 1200°C to activate it. Activated carbon adsorbents are characterized by the oxide groups and inorganic impurities on their surface, which give their surface properties a weakly polar or non-polar nature. Coupled with its extremely large internal surface area, activated carbon becomes a broad-spectrum, water-resistant adsorbent capable of absorbing large quantities of various weakly polar and non-polar organic molecules. Its applications span various fields such as water treatment, decolorization, and gas adsorption. D. Zeolite molecular sieves: Also known as synthetic zeolites or molecular sieves, they are crystalline metasilicate aluminates containing alkaline earth elements. They are highly polar adsorbents; their characteristic is that they exhibit molecular sieve behavior, featuring a very consistent pore structure and strong adsorption selectivity. They have a high adsorption capacity for substances such as CO, CH4, N2, Ar, and O2. It is widely used in gas adsorption separation, gas and liquid drying, as well as the separation of n- and isopentane. E. Carbon molecular sieve: It is actually a type of activated carbon as well; it is a specialized adsorbent made from carbon through a special carbon deposition process, designed for purifying nitrogen from air. Its pore size distribution is very concentrated, being only slightly larger than the diameter of oxygen molecules, which makes it highly effective for separating nitrogen from oxygen in air. F. Cu-loaded adsorbents: These adsorbents generally involve loading copper salts onto solids such as molecular sieves, activated carbon, or alumina, and utilize the chemisorption of carbon monoxide by copper to selectively adsorb carbon monoxide, thereby enhancing its adsorption capacity. Currently, among the chemical adsorption methods used in small and medium-sized devices for the recovery and purification of carbon monoxide, the CO-PSA technology developed by Chiyoda Chemical Engineering Co., Ltd. in Japan, which uses CuAlCl4/Al2O3 as an adsorbent, is quite effective. Many institutions in our country, such as Peking University, Dalian University of Technology, and the Southwest Research Institute of Chemical Engineering, have also developed specialized adsorbents for CO-PSA, such as the PU-1 adsorbent developed by Peking University Pioneer. With this adsorbent, the selectivity and horizontal adsorption capacity for carbon monoxide have been significantly improved; it is now being used on an industrial scale.

Reply to 1# Air separation main cooler: As far as I know, this is related to oxygen production. Common adsorbents include activated alumina, silica gel, 5A, 13X, PU8, etc., all of which are widely used at present

Based on their origin, adsorbents can be divided into natural adsorbents and synthetic adsorbents. Natural adsorbents mainly include diatomite, kaolin, natural zeolites, etc. White clay is used in the decolorization and desulfurization of lubricating oils and heavy petroleum fractions. Synthetic adsorbents are mainly classified into: 1. Activated carbon, which is primarily used for the recovery of organic compounds from gas and liquid mixtures. 2. Silica gel is a polar adsorbent; water, alcohols, phenols, amines, and unsaturated hydrocarbons can be adsorbed preferentially. 3. Activated alumina, with good hydrothermal stability. 4. Molecular sieves, which exhibit high selectivity and are widely used in adsorption, catalytic reactions, and ion exchange applications.

The selection of an adsorbent should be based on the separation system; an appropriate adsorbent must be chosen according to its properties. It is a comprehensive field, and you can consult me via QQ if needed

We produce both nitrogen and oxygen, as well as medical oxygen; all we need are molecular sieves and activated carbon

Reply to 2# Broadband user: I’ve learned about it. It seems that there might be relevant materials on the 2nd floor; could I borrow them? Thank you. cumtlijin@163.com

Reply to 2# Broadband User: There must be some materials related to PSA on the second floor; could you please take a look? We have encountered issues with hydrogen production recently and are trying to identify the problems. Email: wuyushijun1106@163.com