# Performance Optimization of the Low-Capacity Adsorption Oxygen Generator
## 2 Adsorption Based Oxygen Separation Method  
The method of separating oxygen from the air with the use of adsorption is based on the selection of such sorbents for which the maximum capacity of individual components of the air mixture is different. This way, it is possible to select the operating parameters in such a way that when forcing a portion of the air mixture through the adsorption bed, one of the components is wholly adsorbed. In this way, the remaining air components are concentrated in the stream of non-adsorbed gas [10; 11; 12]. In the case of using a nitrogen-selective sorbent for air separation, the result is the stream of adsorbed gas with a composition of about 85-90% nitrogen and 10-15% oxygen, and the stream of non-adsorbed gas with a composition of about 95% oxygen and 5% argon [5; 13]. The research also indicates the possibility of obtaining oxygen with a purity of 99% with the use of silver-based nitrogen-selective adsorbents [14]. When an oxygen-selective sorbent is used for air separation, a stream of adsorbed gas is obtained with the composition of about 65-75% of oxygen and 25-35% nitrogen, and a stream of non-adsorbed gas with the composition of about 98% nitrogen and 2% argon [15; 16]. Due to the obtained gas stream compositions, nitrogen-selective adsorption beds are usually used to separate oxygen from the air. The adsorption process is a non-equilibrium process. It takes place until the bed is saturated with the adsorbed substance. After the adsorption stage, the adsorption bed needs to be regenerated to be able to be used for the next gas mixture separation cycle. To achieve the relative continuity of the process, paired adsorption tanks are used. The air separation process is carried out in such a way that the adsorption stage takes place in only one of the adsorption tanks at a given time. Simultaneously, the regeneration of the bed is carried out in the second tank. This method is called Swing Adsorption (SA) [10; 11]. The adsorption method allows the use of various energy sources in the oxygen separation process [1; 17; 18]. Most common oxygen generators use the PSA (Pressure Swing Adsorption) or VPSA (Vacuum-Pressure Swing Adsorption) process, which uses an electrically powered gas compressor. These methods are based on the use of the adsorbency difference of the adsorption bed at different pressures. The VPSA process is mostly used in high-yield oxygen generators. The PSA process is mainly used in portable generators with a lower yield. The adsorption method of oxygen separation is characterized by low investment costs. The efficiency of the process and operating costs strongly depend on the compaction rate of the bed, its homogeneity [19; 20], and the optimization quality of the applied oxygen separation procedure. The most frequently used adsorbents for the separation of oxygen with a purity of up to 95% are 5A and 13X zeolites. Studies showed that both adsorbents behave stably over a wide pressure range and allow for predictable operation of the oxygen separator. The literature indicates that devices using zeolite 5A are characterized by the higher efficiency of oxygen separation compared to devices using zeolite 13X under the same process conditions [21]. This paper focuses on the most popular commercially available low-capacity oxygen generator PSA type using 5A zeolite. The schematic diagram of the generator is shown in Figure 1.  
The main part of the oxygen separation system is a pair of adsorbers. In each of them there occurs a phase-shifted pressure cycle. Changes in gas pressure cause changes in the capacity of the adsorption bed. At a given moment, the process of adsorption takes place only in one of the adsorbers. In the second adsorber takes place the regeneration of the bed (desorption). To optimize the operation of the oxygen generator, the adsorption cycle was mapped into individual stages of pressure changes inside the adsorption tanks.