Seek basic knowledge of pressure swing adsorption

The basic principle behind this is as follows: it relies on the fact that different gases are adsorbed by the adsorbent to varying degrees depending on the pressure

Pressure Swing Adsorption (PSA for short) is a new type of gas adsorption and separation technology, which has the following advantages: (1) High product purity. ⑵It can generally operate at room temperature and under low pressure; no heating is required during bed regeneration, making it energy-efficient and cost-effective. ⑶The equipment is simple, with easy operation and maintenance. ⑷Through continuous cyclic operation, full automation can be achieved. Therefore, when this new technology emerged, it attracted the attention of industrial sectors around the world, which competed to develop and research it; as a result, it developed rapidly and became increasingly mature. In 1960, Skarstrom filed a patent for PSA; using 5A zeolite molecular sieves as adsorbents and a two-bed PSA unit, he employed pressure swing adsorption to produce nitrogen and separate oxygen-enriched gas from air. This process was improved and put into industrial use in the 1960s. In the 1980s, significant progress was made in the industrial application of pressure swing adsorption technology, which was mainly used for oxygen-nitrogen separation, air drying and purification, as well as hydrogen purification. Among these, progress in oxygen-nitrogen separation technology involves combining new adsorbents such as carbon molecular sieves with pressure swing adsorption to separate O2 and N2 from air, thereby obtaining nitrogen. 　　As the performance and quality of molecular sieves improve, along with ongoing advancements in pressure swing adsorption technology, the purity and recovery rate of the products increase, which in turn facilitates the economic viability and industrialization of pressure swing adsorption. Principle: For any type of adsorption involving the same gas to be adsorbed (adsorbate), at adsorption equilibrium, the lower the temperature and the higher the pressure, the greater the amount of adsorption that occurs. Conversely, the higher the temperature and the lower the pressure, the smaller the adsorption amount. Therefore, gas adsorption separation methods typically employ two cyclic processes: temperature swing adsorption or pressure swing adsorption. Constant pressure: If the pressure remains constant, and adsorption occurs at normal or low temperatures while desorption is carried out at high temperatures, this is known as temperature-swapped adsorption (abbreviated as TSA). Obviously, temperature swing adsorption involves adsorption and desorption by changing the temperature. Temperature-programmed adsorption is carried out along a line perpendicular to both the adsorption isotherm at low temperatures (room temperature) and the adsorption isotherm at high temperatures. Due to the high specific heat capacity and low thermal conductivity of the adsorbent, it takes a long time to heat or cool it, which makes the process rather complicated; as a result, temperature-programmed adsorption is mainly used for the purification of gases that contain low amounts of adsorbate. Constant temperature: If the temperature remains constant, and adsorption occurs under pressure, then desorption is achieved by reducing the pressure (by creating a vacuum) or by maintaining normal pressure; this process is known as pressure swing adsorption. It can be seen that pressure swing adsorption involves adsorption and desorption by changing pressure. 　　In pressure swing adsorption operations, due to the low thermal conductivity of the adsorbent, the temperature changes in the adsorbent bed caused by the adsorption heat and desorption heat are minimal; therefore, it can be considered an isothermal process. Its operating conditions follow approximately the isotherm of normal-temperature adsorption, with adsorption occurring at higher pressures (P2) and desorption at lower pressures (P1). Since pressure swing adsorption proceeds along an adsorption isotherm, from the perspective of static adsorption equilibrium, the slope of this isotherm has a significant impact on it. At a constant temperature, the relationship between pressure and the amount of adsorption is shown in the graph; here, PH represents the adsorption pressure while PL represents the desorption pressure (after pressure reduction). The difference between the amounts of adsorption corresponding to PH and PL is essentially the effective amount of adsorption, denoted as Ve. Obviously, the effective adsorption capacity of the linear adsorption isotherm is greater than that of the curved (Langmuir-type) isotherm. 　　Adsorption is often carried out under pressure conditions, and pressure swing adsorption introduces a method that combines pressurization and depressurization; it typically consists of an adsorption-desorption system that involves pressurized adsorption followed by depressurization. Under isothermal conditions, a adsorption operation cycle is formed by combining pressure-driven adsorption and pressure-reduced desorption. The amount of adsorbate absorbed by the adsorbent increases as pressure rises and decreases as pressure falls. Meanwhile, during depressurization (to atmospheric pressure or under vacuum), the adsorbed gas is released, regenerating the adsorbent; no external heat supply is required for this regeneration process. Therefore, pressure swing adsorption is also known as isothermal adsorption as well as heat-free regeneration adsorption. Pressure swing adsorption, adsorption, PSA. Pressure swing adsorption, adsorption, PSA. The compressed air from the air compressor first passes through a cold dryer to have its moisture removed, and then enters a PSA nitrogen production unit consisting of two adsorption towers. The specialized carbon molecular sieve adsorbents installed in these towers are used to selectively absorb impurity gases such as O2 and CO2, while the N2 gas, as the product, is discharged from the top of the towers with a purity of 99%. Pressure reduction: During pressure reduction, the oxygen adsorbed by the adsorbent is desorbed and discharged through the bottom of the tower; after washing, the adsorbent is regenerated. After regeneration, the adsorbent can be put back into adsorption after pressure equalization and product pressure increase. The two towers are used alternately to achieve continuous air separation for nitrogen production. 　　Nitrogen production using carbon molecular sieves is based on the different diffusion rates of oxygen and nitrogen within these sieves. At pressures of 0.7–1.0 Mpa, oxygen diffuses more rapidly across the surface of the carbon molecular sieves than nitrogen does; as a result, the carbon molecular sieves preferentially adsorb oxygen, while most of the nitrogen remains in the unadsorbed phase. Carbon molecular sieves inherently have the property that their oxygen adsorption capacity increases under pressure and decreases under reduced pressure. This property is utilized to perform oxygen and nitrogen separation using pressure swing adsorption. Thereby obtaining 99.99% nitrogen.

History of Pressure Swing Adsorption Pressure swing adsorption for oxygen production was first developed in the early 1960s (Skarstrom, 1960; Guerin de Montgarenil & Domine, 1964), and industrial production began in the 1970s. Prior to this, traditional industrial air separation units mostly used the deep cryogenic distillation method. Since the 1980s, the successive development and application of zeolite molecular sieves with high adsorption and separation capabilities such as CaX and LiX, along with improvements in process designs, have led to rapid progress in pressure swing adsorption air separation technology. Compared to deep cryogenic air separation units, the PSA process offers advantages such as shorter startup times and easier operation during start-up and shutdown, lower energy consumption and operational costs, a higher degree of automation and simpler maintenance, as well as smaller footprints and reduced civil engineering costs. It is more competitive than the cryogenic method in small and medium-scale oxygen production (less than 100 tons/day, equivalent to 3000 Nm3/h) where high-purity oxygen is not required. It is widely used in various fields such as electric arc furnace steelmaking, non-ferrous metal smelting, glass processing, methanol production, carbon black production, fertilizer gas production, chemical oxidation processes, pulp bleaching, wastewater treatment, biological fermentation, aquaculture, medicine, and more (Yang, 1991; Kumar, 1996; Jee, Park, Haam & Lee, 2002). 　　The research progress in pressure swing adsorption air separation oxygen production technology over the past forty years has mainly manifested in two aspects: one is the research on adsorbents for air separation oxygen production and their adsorption theories, and the other is the research on the process cycles of air separation oxygen production (Sircar, 1994; Ruthven.Farooq & Knaebel, 1994). Although research on this technology in China began early, its development was relatively slow for a long period of time. It was not until the 1990s that the advantages of pressure swing adsorption oxygen generation equipment were gradually recognized by people in China. In recent years, equipment using various processes has been put into operation, bringing significant economic benefits to various industries.

Are there any books or materials on pressure swing adsorption? I want to learn about it systematically! ~